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Structure and bonding in amorphous iron carbide thin films
Abstract
We investigate the amorphous structure, chemical bonding, and electrical properties of magnetron sputtered Fe 1−x C x (0.21 x 0.72) thin films. X-ray, electron diffraction and transmission electron microscopy show that the Fe 1−x C x films are amorphous nanocomposites, consisting of a two-phase domain structure with Fe-rich carbidic FeC y , and a carbon-rich matrix. Pair distribution function analysis indicates a close-range order similar to those of crystalline Fe 3 C carbides in all films with additional graphene-like structures at high carbon content (71.8 at% C). From x-ray photoelectron spectroscopy measurements, we find that the amorphous carbidic phase has a composition of 15–25 at% carbon that slightly increases with total carbon content. X-ray absorption spectra exhibit an increasing number of unoccupied 3d states and a decreasing number of C 2p states as a function of carbon content. These changes signify a systematic redistribution in orbital occupation due to charge-transfer effects at the domain-size-dependent carbide/matrix interfaces. The four-point probe resistivity of the Fe 1−x C x films increases exponentially with carbon content from ∼200 µµ cm (x = 0.21) to ∼1200 µµcm (x = 0.72), and is found to depend on the total carbon content rather than the composition of the carbide. Our findings open new possibilities for modifying the resistivity of amorphous thin film coatings based on transition metal carbides through the control of amorphous domain structures.
... Utilization of compound target may not be useful to control the composition of Fe-C films and using gases like CH 4 and C 2 H 2 may also result in formation of undesired C-H bonds. On the other hand, co-sputtering of Fe and C from two different sources is a clean method providing a wide range of option to control the composition by changing the flux of each source as demonstrated recently by Furlan et al. [34]. A survey of available literature suggests that most of the Fe-C thin films reported hitherto are either amorphous or nanocrystalline. ...
... Similarly, Mi et al. [29] deposited Fe-C thin films by sputtering of a compound target (at room temperature) and also found amorphous Fe-C phases. More recently, Furlan et al. [34] deposited Fe-C thin films by co-sputtering of Fe and C from two separate targets (at 300 K) and varied C concentration from 20.8 to 71.8 at.%. It was observed that the resulting Fe-C films were amorphous, irrespective of the amount of C in Fe. ...
... Beyond this limit, the presence of C produces a disordered crystal structure due to immiscibility of C with Fe. This results in formation of an amorphous phase in our sample and show agreement with previous reports [34]. Increasing substrate temperature pushes C at the interstitial position of the orthorhombic crystal lattice of Fe, this results in growth of θ -Fe 3 C phase. ...
We studied the structural and magnetic properties of Fe0.8C0.2 thin films deposited by co-sputtering of Fe and C targets in a direct current magnetron sputtering (dcMS) process at a substrate temperature (Ts) of 300, 523, and 773 K. The structure and morphology were measured using x-ray diffraction (XRD), x-ray absorption near-edge spectroscopy (XANES) at Fe L and C K edges and atomic/magnetic force microscopy (AFM, MFM). An ultrathin (3-nm) Fe0.857C0.2 layer, placed between relatively thick Fe0.8C0.2 layers was used to estimate Fe self-diffusion taking place during growth at different Ts using depth profiling measurements. Such Fe0.857C0.2 layer was also used for Fe57 conversion electron Mössbauer spectroscopy (CEMS) and nuclear resonance scattering (NRS) measurements, yielding the magnetic structure of this ultrathin layer. We found from XRD measurements that the structure formed at low Ts (300 K) is analogous to Fe-based amorphous alloy and at high Ts (773 K), predominantly a Fe3C phase has been formed. Interestingly, at an intermediate Ts (523 K), a clear presence of Fe4C (along with Fe3C and Fe) can be seen from the NRS spectra. The microstructure obtained from AFM images was found to be in agreement with XRD results. MFM results also agree well with NRS as the presence of multi-magnetic components can be clearly seen in the sample grown at Ts = 523 K. The information about the hybridization between Fe and C, obtained from Fe L- and C K-edge XANES also supports the results obtained from other measurements. In essence, from this work, a possibility for experimental realization of Fe4C has been demonstrated. It can be anticipated that by further fine-tuning of the deposition conditions, even single-phase Fe4C can be realized which hitherto remains an experimental challenge.
... With pristine Low-Rate network the intensity of peak ~709 eV is higher in comparison to High-Rate which indicated that the former contains slightly more oxidized phases of iron, presumably, Fe 3 O 4 and Fe 2 O 4 [29][30][31]. These oxides have considerably higher intensity than the metallic iron at 707.36 eV [27,32]. However, the relative intensities of the two peaks around 720-723 eV indicate that there could also be some contribution from lower iron oxides (FeO) in this case [31,33]. ...
... We suggest that Fe 2p spectrum for the EC treated arise from phases of metallic Fe, Fe 3 O 4 and Fe 2 O 3 . Additionally, it is very likely that some carbon is dissolved into the iron as well [32,36]. In the double peak region (around 722 eV) one can now observe that the intensities of the two peaks are different when compared to pristine sample, which indicates less contribution from oxygen poor oxides relative to the oxygen rich oxides [31,33]. ...
... For MSCN, the binding energy peak at 286.6 eV shifts to 286.3 eV due to a significant change in the electron distribution of O-containing functional groups on the surface of the nanocatalyst [47]. A new peak also appeared at ~283.3 eV in C1s spectra of MSCN corresponding to Fe-C bond formed as a result of co-precipitation of iron salts on MSCN, thus validating the interaction of Fe 3 O 4 nanoparticles with carbon nanotubes, consistent with the findings of FTIR study [42,75,76]. Yin [77]. ...
... The increase in the adsorption efficiency of MSCN till pH 7 highlights the fact that electrostatic attractions are not solely responsible for the adsorption process. The deprotonation of C 1 -C 3 and C 10 -C 12 in TC -1 could lead to strong binding towards metal active sites of adsorbent by the process of complexation, thus, facilitating the adsorption efficiency of the MSCN adsorbent [75,76]. Beyond pH 7.68, tetracycline adsorption decreased sharply due to the increase in electrostatic repulsion between tetracycline and MSCN as tetracycline attained the TC -2 form. ...
Recurrent waves of novel COVID-19 and its variants have resulted in the usage of antimicrobials to hitherto
unprecedented levels, aggravating the threat of antibiotic-resistant pathogens. We devised a facile yet robust
nano-bio-engineering strategy for the detection, mitigation, and degradation of tetracycline and erythromycin
antibiotics in water bodies. The strategy includes magnetic single-walled carbon nanotubes (MSCN) based
adsorption and degradation of these antibiotics. Antibiotics were detected and their degradation was monitored
using bioengineered biosensors showing high specificity and sensitivity (1.33 and 51.24 ppb for tetracycline and
erythromycin, respectively). The MSCN followed pseudo-second-order kinetics with >75% adsorption of antibiotics. The degradation efficiency of >93% in 4 h at pH 7 and 313 K was attained by adding H2O2, activating the
heterogeneous Fenton-like reaction-based degradation system. The universality of this approach was proven by
showing the degradation of other xenobiotics. This strategy manifests a novel approach for mitigating xenobiotics and their detrimental environmental effects.
... Previous work on disordered binary metal carbide systems has shown that their properties are tuneable. In the amorphous phase, the relative bond content determines hardness, resistivity and elasticity [45][46][47]. Amorphicity may lower cleavage fracture susceptibility and grain boundary decohesion [28], which lowers corrosion through a reduced ability of oxygen to diffuse through grain boundaries. This can also be related to the flattening of the DOS as a function of energy that we calculated in the amorphous case and which can be attributed to the increased disorder in bond energy, as observed in a previous work on amorphous transition metal carbides [29]. ...
... However, in these experiments, amorphicity is obtained by adding silicon to the system, which may be a further source of the raised resistivity, in addition to the inhibition of band formation by disorder. Nevertheless, it is not strictly necessary to introduce additional elements, such as Si [27,48] or B [47], to drive the amorphization in metal carbides, since amorphized yet metalloid-free ternary metal carbides have been reported previously [46,[49][50][51]. In the specific case of transition metal carbide films, TEM-amorphous CrC [50] and WC-based films [49] have been synthesized and their electronic structure has been characterized experimentally. ...
High entropy materials (HEMs) are of great interest for their mechanical, chemical and electronic properties. In this paper we analyse (TaNbHfTiZr)C, a carbide type of HEM, both in crystalline and amorphous phases, using density functional theory (DFT). We find that the relaxed lattice volume of the amorphous phase is larger, while its bulk modulus is lower, than that of its crystalline counterpart. Both phases are metallic with all the transition metals contributing similarly to the density of states close to the Fermi level, with Ti and Nb giving the proportionally largest contribution of states. We confirm that despite its great structural complexity, 2 × 2 × 2 supercells are large enough for reliable simulation of the presented mechanical and electronic properties by DFT.
... Previous work on disordered binary metal carbide systems has shown that their properties are tuneable. In the amorphous phase, the relative bond content determines hardness, resistivity and elasticity [45][46][47]. Amorphicity may lower cleavage fracture susceptibility and grain boundary decohesion [28], which lowers corrosion through a reduced ability of oxygen to diffuse through grain boundaries. This can also be related to the flattening of the DOS as a function of energy that we calculated in the amorphous case and which can be attributed to the increased disorder in bond energy, as observed in a previous work on amorphous transition metal carbides [29]. ...
... However, in these experiments, amorphicity is obtained by adding silicon to the system, which may be a further source of the raised resistivity, in addition to the inhibition of band formation by disorder. Nevertheless, it is not strictly necessary to introduce additional elements, such as Si [27,48] or B [47], to drive the amorphization in metal carbides, since amorphized yet metalloid-free ternary metal carbides have been reported previously [46,[49][50][51]. In the specific case of transition metal carbide films, TEM-amorphous CrC [50] and WC-based films [49] have been synthesized and their electronic structure has been characterized experimentally. ...
High entropy materials (HEMs) are of great interest for their mechanical, chemical and electronic properties. In this paper we analyse (TaNbHfTiZr)C, a carbide type of HEM, both in crystalline and amorphous phases, using density functional theory (DFT). We find that the relaxed lattice volume of the amorphous phase is larger, while its bulk modulus is lower, than that of its crystalline counterpart. Both phases are metallic with all the transition metals contributing similarly to the density of states (DOS) close to the Fermi level, with Ti and Nb giving the proportionally largest contribution of states. We confirm that despite its great structural complexity, 2x2x2 supercells are large enough for reliable simulation of the presented mechanical and electronic properties by DFT.
... 64 A component at a similar BE was also found in the amorphous Fe 1−x C x films. 63 We also note that at the excitation energy of 435 eV, the C− O bond component is almost suppressed at −1 V vs Ag/AgCl, which suggests that the part of the chemisorbed CO species contributing to the C5 component were quantitatively converted at this potential into reduced C species. ...
... The predominant effect we observe at a more negative potential, when CO 2 reduction occurs, is a reduction of the CO chemisorbed on the metal species (part of the O3 component in Figure 6c), which is accompanied by the increase in the amount of the component assigned to the Fe− C species of interstitial or weakly bound atomic C in the Fe phase in the most surface-sensitive experiment (Figures 5b and 6a). [63][64][65]73 The amounts of other more electron-deficient CO species (part of the higher BE species in Figure 6c) increase as the potential decreases but are related to chemisorbed species due to capacitive processes on larger particles. The NEXAFS data show changes in the symmetry of the Fe sites (Fe L-edge NEXAFS in Supplementary Figure S16) induced by the hydrolysis of Fe−O and Fe−N bonds with the formation of NO x moieties (Supplementary Figure S17). ...
Surface-sensitive ambient pressure X-ray photo-electron spectroscopy and near-edge X-ray absorption fine structure spectroscopy combined with an electrocatalytic reactivity study, multilength-scale electron microscopy, and theoretical modeling provide insights into the gas-phase selective reduction of carbon dioxide to isopropanol on a nitrogen-doped carbon-supported iron oxyhydroxide electrocatalyst. Dissolved atomic carbon forms at relevant potentials for carbon dioxide reduction from the reduction of carbon monoxide chemisorbed on the surface of the ferrihydrite-like phase. Theoretical modeling reveals that the ferrihydrite structure allows vicinal chemisorbed carbon monoxide in the appropriate geometrical arrangement for coupling. Based on our observations, we suggest a mechanism of three-carbon-atom product formation, which involves the intermediate formation of atomic carbon that undergoes hydrogenation in the presence of hydrogen cations upon cathodic polarization. This mechanism is effective only in the case of thin ferrihydrite-like nanostructures coordinated at the edge planes of the graphitic support, where nitrogen edge sites stabilize these species and lower the overpotential for the reaction. Larger ferrihydrite-like nanoparticles are ineffective for electron transport.
... With High-Rate SWCNT network only one peak is observed at the L 3 -edge. This feature arises from metallic Fe [31,48], although a relatively similar shape is seen for FeO in the work of Regan et al. [31]. However, based on the Fe-O phase diagram, the thermodynamically most feasible structure below 570°C with low oxygen loading is metallic Fe. ...
... However, based on the Fe-O phase diagram, the thermodynamically most feasible structure below 570°C with low oxygen loading is metallic Fe. In case of Low-Rate SWCNTs, a smalls houlder-like feature is observed at the higher energy in the L 3 -edge due to carbide and/or oxidized phase of iron [31,48,49]. For oxidized phases of iron, Fe 3 O 4 and Fe 2 O 4 , intensity of the oxide peak at L 3 -edge is considerably higher than the metallic peak [49][50][51]. ...
Carbon nanotubes (CNT) have been extensively investigated for various electroanalytical applications. As the properties of CNTs heavily depend on the fabrication conditions, it is expected that the electrochemical performance will also vary between CNTs from different processes. However, it is still not well known how the different synthesis conditions affect the electrochemical properties of CNTs. Thus, here we investigate the effect of synthesis rate on the physicochemical properties of CNT networks. Through extensive structural and chemical analysis, we show that the widely different synthesis rates, fast and slow, produced CNT networks with surprisingly similar properties. The only distinct differences were seen in the TEM tomography 3D reconstructions, where the faster synthesis produced a less dense network with larger bundle size. Moreover, minor changes were seen in the composition of Fe catalyst particles where the faster rate network mainly exhibited metallic Fe, whereas carbide and oxidized Fe phases were observed in the slower rate network. Although no changes were seen in the electron transfer kinetics with outer-sphere probes, it was clear that even these small changes in physicochemical properties affected the surface sensitive inner-sphere analytes. With slower synthesis rate i) sensitivity towards all analgesics, especially oxycodone, was enhanced and ii) oxidation potential of all analytes shifted to cathodic direction in comparison to higher synthesis rate. In the wider context, we propose that good quality CNTs can be fabricated rapidly in industrial scale for biosensing purposes. However, in electroanalytical applications properties of CNTs should be optimized for the analyte of interest.
... Table 1. The core-level XPS C1s spectra in Fig. 4 show peaks at 283.1 eV for the samples with added carbon, a binding energy typical for a carbidic environment in amorphous Me-C films of similar composition [46][47][48]. Little to no contribution from free carbon is found, as seen by some diffuse intensity around 285 eV [49]. ...
... 282.9-283.5 eV for Cr 7 C 3 [50][51][52]) than between carbides of the different metals (e.g. 283.3 eV for amorphous Fe-C [48]). A separate study will be published in the near future on the local environment of the carbon, using Hard X-ray Photoelectron Spectroscopy (HAXPES) and Near Edge X-ray Absorption Spectroscopy (NEXAFS). ...
This study explores carbon addition as a materials design approach for simultaneously improving the hardness, crack resistance, and corrosion resistance of high entropy thin films. CoCrFeMnNi was selected as a starting point, due to its high concentration of weak carbide formers. The suppression of carbides is crucial to the approach, as carbide formation can decrease both ductility and corrosion resistance. Films with 0, 6, and 11 at.% C were deposited by magnetron co-sputtering, using a graphite target and a sintered compound target. The samples with 0 at.% C crystallized with a mixture of a cubic closed packed (ccp) phase and the intermetallic χ-phase. With 6 and 11 at.% C, the films were amorphous and homogenous down to the nm-scale. The hardness of the films increased from 8 GPa in the carbon-free film to 16 GPa in the film with 11 at.% C. Furthermore, the carbon significantly improved the crack resistance as shown in fragmentation tests, where the crack density was strongly reduced. The changes in mechanical properties were primarily attributed to the shift from crystalline to amorphous. Lastly, the carbon improved the corrosion resistance by a progressive lowering of the corrosion current and the passive current with increasing carbon concentration.
... The peak at 284.6 eV is attribution to the C-C/ C--C group of g-C 3 N 4 or sp 2 C-N, and the peak at 288.2 eV can be assigned to sp 2 -hybridized carbon in the triazine rings (N-C--N) (Zhu et al., 2015;Chuang et al., 2016;Yang et al., 2016b;Wang et al., 2019). The peak at 282.4 eV may be the binding energy of C-O-Fe (Mao and Jiang, 2019;Furlan et al., 2015;Hinnen et al., 1994), yet, needs to be further analyzed. In Fig. 4C, the spectra of N 1s contains two peaks at 296.5 and 298.0 eV, which the peak at 298.0 eV is identified as the sp 2 -bonded N (C-N--C) in the triazine rings of g-C 3 N 4 (Mao and Jiang, 2019;Zhu et al., 2015;Chuang et al., 2016;Yang et al., 2016b;Wang et al., 2019;Furlan et al., 2015;Hinnen et al., 1994), and the peak at 296.5 eV may be the binding energy of N-Fe (Mao and Jiang, 2019;Hinnen et al., 1994). ...
... The peak at 282.4 eV may be the binding energy of C-O-Fe (Mao and Jiang, 2019;Furlan et al., 2015;Hinnen et al., 1994), yet, needs to be further analyzed. In Fig. 4C, the spectra of N 1s contains two peaks at 296.5 and 298.0 eV, which the peak at 298.0 eV is identified as the sp 2 -bonded N (C-N--C) in the triazine rings of g-C 3 N 4 (Mao and Jiang, 2019;Zhu et al., 2015;Chuang et al., 2016;Yang et al., 2016b;Wang et al., 2019;Furlan et al., 2015;Hinnen et al., 1994), and the peak at 296.5 eV may be the binding energy of N-Fe (Mao and Jiang, 2019;Hinnen et al., 1994). The two peaks at 527.0 and 529.5 eV of O 1s (Fig. 4D) are the binding energy of Fe-O band. ...
Mesoporous magnetic Fe3O4/g-C3N4 nanocomposites were synthesized by a facile precipitation method using deionized water as solution. And the prepared magnetic materials were characterized by mean of various detection methods. At the same time, the photocatalytic activity of the synthetic material as photocatalyst under visible light was tested by taking the degradation of rhodamine B in water as a mark. Results show that as-synthesized Fe3O4/g-C3N4 nanocomposites have high specific surface areas of about 5–10.5 times that of pure g-C3N4 and high saturation magnetizations, which can ensure the smooth recovery of used nanomaterials under the action of external magnetic field. The addition of Fe3O4 greatly extents the response range of g-C3N4 nanomaterials to visible light and reduces the recombination rate of photoinduced electron-hole pairs. Meanwhile, the photocatalytic activity of the synthetic materials increases so that the degradation ratio of rhodamine B in water reached 97.6% after 4 h visible light irradiation. Furthermore, prepared magnetic Fe3O4/g-C3N4 nanocomposites have also excellent stability so that the degradation ratio of rhodamine B was almost not reduce after 5 times of continuous reuse of photocatalyst. Free radical scavenging experiments shows that hydroxyl groups are the main free radicals of photocatalytic reaction, peroxyradicals and holes play the secondary role. Therefore, it can be predicted that the synthesized mesoporous magnetic Fe3O4/g-C3N4 nanomaterials will have a broad application prospect in environmental remediation.
... The dominant component A moved to 283.7 eV, and the other is positioned in the range between 284.9 eV (for S 1 ) to 285.6 eV (for S 2 ). A component probably originates from sp 2 hybridized carbon [38], although it could also originate from carbides (Fe x -C compounds) which are positioned at somewhat lower energies (283.2-283.3 eV) [38,39]. ...
... A component probably originates from sp 2 hybridized carbon [38], although it could also originate from carbides (Fe x -C compounds) which are positioned at somewhat lower energies (283.2-283.3 eV) [38,39]. However, it is known that our samples contain a small fraction of iron, especially in the area few nanometers from the very surface [31], so that this peak cannot be ascribed to carbides. ...
In the presented paper, changes of high-density polyethylene’s (HDPE) surface properties along with the changes of chemical composition, as a consequence of Fe ion implantation with different fluences, were investigated. Applied implantation fluences were as follows: 5×1016, 1×1017, 2×1017 and 5×1017 ions cm-2, while the implantation energy was 95 keV. The samples were analyzed by X-ray photoelectron spectroscopy (XPS), Atomic Force Microscopy (AFM), Four point contact probe, Fourier transform infrared spectroscopy (FTIR) and contact angle measurements. Significant changes in the chemical composition were found by XPS and FTIR, which were followed by changes in surface morphology, increase of roughness, and decrease of sheet resistance that has a percolation threshold that starts for the fluence of 1×1017 ions cm-2. Surface free energy increases as a consequence of implantation, up to the fluence of 1×1017 ions cm-2, and then decreases for the 2 higher fluences.
... It follows from the shape and energy position of the Fe2p, Cr2p and Ni2p lines that metals on the steel surface are oxidized and partly belongs to metal carbides. This also follows from the fact that in C1s XPS spectra (Figs. 2 and 4), peak A corresponds to an energy of around 283 eV, which is attribute to the metal carbides [20]. ...
... In Fig. 5 the component A with an energy of 529.7e530.0 eV is attributed to the metal oxides of the steel surface [20,23,24] under the GO-BScB lubrication. Components B and B / with energies from 531.4 to 532.1 eV corresponds to OH functional groups between graphene layers. ...
Ionic liquid bis(salicylato)borate (BScB) functionalized graphene oxide (GO) was prepared by γ-irradiation for tribological application. Dose dependent friction behavior of ionic liquid functionalized GO and dynamic changes of chemical phases of tribofilm was investigated by depth resolved X-ray photoelectron spectroscopy. Few layers of graphene oxide tribofilm was observed and it was found to be stable in the sliding interfaces. This was the main reason for the improvement of friction behavior of metallic sliding interfaces.
... Only sample 5%NaFe 3 O 4 _WI_a shows a component at 288.6 eV, due to COOH species. If we look at the lower binding energies side, we can infer the appearance of two components: one due to FeC x bond at 283.1 eV and another one at 284.5 eV, which can be due to C-C sp 2 arrangement or to C-Fe* charge transfer effects (Furlan et al., 2015) which appears when charge is transferred from the metal surface atoms to the more electronegative carbon atoms in the a-C matrix, which, in our case, can be represented by the outer C amorphous shell, as shown in TEM analysis previously. The last region we have analyzed is the one related to Na1s peak, Fig. 11 (c, f). ...
... In the XRD pattern of GO/Fe-micron talc hybrid additive given in Fig. 4(a), there was a low intense peak at 2θ = 43.8° belonging to Fe-C bonding [33]. The same trend was also monitored in XRD patterns of fine talc-based hybrid additives after direct carbonization and catalytic heat treatment process in Fig. 4b. ...
It is challenging to produce high value-added carbon nanomaterials using a rich hydrocarbon source in thermoplastics with conventional recycling processing techniques which limit their usage. This study demonstrated the growth of sheet-like and spherical graphene oxide structures on talc substrates by providing dissociation of carbon atoms from waste polypropylene (PP) and applying a new upcycling approach by mimicking chemical vapor deposition and supporting with life cycle assessment (LCA) protocols. In the developed process, waste polypropylene was mixed with neat and iron-treated talc templates and then exposed to thermal treatment to provide the deposition of carbon atoms coming from polypropylene waste on the lamellar structure of talc. A selective method to obtain 2D and 3D graphene oxide structures was developed with a suitable talc size and by activating the talc surface, producing different PP blends with talc, and defining suitable pyrolysis and carbonization techniques. Regarding the characterization results, talc size of 12 μm enhanced the growth of graphene oxide nanoplatelets whereas talc size less than 2 μm led to the formation of spherical graphene oxide structures. In addition, a benchmarking study was carried out by this new graphene oxide/talc hybrid additive as a reinforcing agent in PP to develop sustainable and lightweight automotive composites. The incorporation of 5 wt% new hybrid additive into PP enhanced flexural modulus by 88% compared to unfilled PP, and 6 wt% enhancement in flexural modulus and 12% reduction in density are achieved with the new hybrid additive inclusion into PP compared to commercial PP having 15 wt% of talc. LCA study showed 28% CO2 reduction with the new upcycled graphene oxide structures compared to one produced by chemical exfoliation.
... [65]. With the increased etching depth, another peak at 282.2 eV appeared, which may be assigned to the peak of carbide [66,67], indicating that the depth reached the substrate. ...
This paper studied a fully formulated oil (FFO) in the hydraulic piston pump, containing mainly zinc dialkyldithiophosphate (ZDDP), detergents, and dispersants. The results of tribo-tests show that the antiwear characteristics are different when using FFO compared to using a single additive oil such as base oil + ZDDP. A two-phase temperature-dependent wear trend was found when FFO is used. Phase (I) is in the low-temperature range, where wear increases with increasing tribofilm thickness and temperature. Phase (II) is in the high-temperature range where the tribofilm thickness increases but wear decreases as the temperature increases. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis of the tribofilm show that the most temperature-dependent compositions are phosphate and iron sulphides, where the signal intensity of phosphates increases, but that of sulphides decreases when the temperature increases. It indicates that the participation of detergent and ZDDP in the tribofilm formation increases at low and high temperatures, respectively. However, no signal shows the dispersant participating in the tribofilm formation. A hypothesis of mechanisms of reaction priority or enhanced competition among different additives at different temperatures is proposed from the iron loss perspective to explain the two-phase temperature-dependent wear mechanism. This study also provides the experimental basis for the wear modelling involving the tribochemistry of FFO in Part (II) of the research series.
... The C 1s spectra at low temperature are quite weak, with a minuscule presence of the chemisorbed carbidic carbon signal at 283.3 eV and the adventitious sp 2 carbon around 284.6 eV. 45 Upon increase of the temperature, the signal at 530.1 eV and around 710.0 eV is reduced, while the Fe 0 multiplet turns into a single component at approximately 706.9 eV, indicating carburization of iron. 5,46−48 The C 1s region at the same time develops, at first, a peak at 283.3 eV, followed by an increase of the signal at 283.6 eV and a broad feature spanning the interval between approximately 283.8 and 285.8 eV. ...
Carbide formation on iron-based catalysts is an integral and, arguably, the most important part of the Fischer–Tropsch synthesis process, converting CO and H2 into synthetic fuels and numerous valuable chemicals. Here, we report an in situ surface-sensitive study of the effect of pressure, temperature, time, and gas feed composition on the growth dynamics of two distinct iron–carbon phases with the octahedral and trigonal prismatic coordination of carbon sites on an Fe(110) single crystal acting as a model catalyst. Using a combination of state-of-the-art X-ray photoelectron spectroscopy at an unprecedentedly high pressure, high-energy surface X-ray diffraction, mass spectrometry, and theoretical calculations, we reveal the details of iron surface carburization and product formation under semirealistic conditions. We provide a detailed insight into the state of the catalyst’s surface in relation to the reaction.
... Although carbidic carbon is commonly expected at binding energies below 283 eV, [44] according to literature, a binding energy range of 283-284 eV is reported for Fe 3 C [45][46][47] or Fe x C-like carbon. [48,49] The carbonization process at 800°C may allow for formation of similar Fe 3 C or Fe-rich Fe x C species. Tian et al. [50] similarly reported on the formation of crystalline Fe 3 C nanoparticles encapsulated with graphitic-shells through a pyrolysis process at 800°C, where the corresponding BE contribution in the C 1s spectrum is fitted at 284 eV. ...
Lithium‐ion capacitors (LICs), potentially bring together the advantages of batteries and supercapacitors. For the faradaic anodes, nanostructured carbonaceous materials hold immense potential, in contrast to graphite where limitations in Li‐ion diffusivity exist. Herein, onion‐like carbons (OLCs), synthesized from Fe‐BTC metal‐organic framework (MOF), is implemented as the LIC anode, owing to its high charge storage capacity and rate capability as compared to graphite. The enhanced charge storage and Li‐ion transference in OLCs was understood to be due to hierarchical porosity with accessible inner voids along with high defect concentration. Therefore, full‐LIC cells with OLC anodes exhibited a markedly higher specific capacitance and an enhanced rate capability than graphite‐LIC. The OLC‐LIC achieved an outstanding maximum energy density of 224 Wh kg−1 at 122 W kg−1 and maximum power density of 14436 W kg−1 at 80 Wh kg−1. Thus, MOF‐derived OLC with distinctive morphology is presented as a highly attractive anode for practical LIC systems. Towards high‐performance Li‐ion capacitor: The metal organic framework (MOF)‐derived onion‐like carbon (OLC) material, although already reported, is a promising carbonaceous anode for hybrid Li‐ion capacitor (LIC), with high surface area and porosity, along with accessible inner void, facilitating better charge storage. Herein, LICs with MOF‐derived OLCs as anode demonstrate significantly higher energy and power density in comparison to LICs with conventional graphite anodes.
... For the coke briquette shown in Fig. 17(a-j), the binding state of C 1 s is deconvoluted into three peaks. The peak at 283.18 eV corresponds to the Fe 3 C phase present in the compound [40,41]. The other peak at 286.07 eV corresponds to the C-O-C bond connecting two aromatic rings of the starch molecule. ...
In the present investigation, a novel composite binder which aids in forming coke briquettes from industrial waste coke dust were synthesized in one pot setup. The composite binder enables efficient utilization of the coke fines by their reformulation into coke briquettes. The novel binder has been characterized by scanning electron microscopy, Fourier transform infrared spectrophotometry, X-ray diffraction, X-ray photonic spectroscopy and nuclear magnetic resonance spectrometry to understand the grafting efficiency and bentonite as filler incorporation. The composite binder with a secondary filler (bentonite) and a secondary binder (ordinary Portland cement) was mixed in definite proportion to obtain the compound binder. The coke briquette was made from coke fines and compound binder in a fixed ratio confers to high thermal stability with improved cold compressive strength. The high-temperature study indicates that the characteristics of coke briquette resemble that of coke used in submerged arc furnaces for ferroalloy production.
... The same we assume about the effect of iron atoms upon the lower layer. According to the Fe 2p absorption spectrum (Figure 4b), the relative content of carbon atoms chemically bound to the iron atoms is C C−Fe = 0.5%, 33 which correlates with XPS data (C C−Fe = 0.7%). In addition, in our opinion, the intensity of the peak c does not only correspond to such an insignificant amount of C−O bonds. ...
... Besides, a new peak (283.6 eV) appeared in the C 1s spectra for the catalyst after CO treatment. According to the literature, 58 this peak can be associated with charge-transfer C−Fe* bonds or sp 2 C−C bonds. The former has a slightly higher binding energy than the typical C−Fe (281.8 eV), which is caused by the damage of the metal carbide grains during sample preparation and charge transfer effects, 59,60 while the latter is generally regarded as the precursor of coke. ...
Novel K-promoted bimetallic Fe- and In-based catalysts on a Ce–ZrO2 support were prepared and tested for higher alcohol synthesis from CO2 and hydrogen. The FeIn/Ce–ZrO2 precursors with different Fe contents were characterized in detail, and well-dispersed Fe2O3 and In2O3 phases with oxygen vacancies were observed. The catalysts were tested in a continuous setup at extended times on stream (up to 100 h) at 300 °C, 10 MPa, a gas hourly space velocity of 4500 mL g–1 h–1, and a H2/CO2 ratio of 3. The effect of K loading, the pretreatment atmosphere, Fe/(Fe + In) molar ratios, and calcination temperature on CO2 conversion and product selectivity were studied. Best performance with a CO2 conversion of 29.6% and a higher alcohol selectivity of 28.7%, together with good stability, was obtained over a K-0.82-FeIn/Ce–ZrO2_900 catalyst after activation under a CO atmosphere. These findings were rationalized by considering the effects of the individual catalyst components (K, Fe, and In) on catalyst performance. Surprisingly, the presence of calcined SiC, used as a diluent in the packed bed reactor, was shown to have a positive effect on catalyst performance and as such also is catalytically active. The best performance in terms of higher alcohol yield (8.5%) obtained in this work ranks in the top three of reports on CO2 hydrogenation to higher alcohols in a continuous setup. Moreover, light olefins with 20.3% selectivity (6.0% yield) were coproduced over the optimized catalyst, which has a positive effect on the economic potential of the catalysts.
... With the 1.3 V oxidized sample, the intensity of this feature decreases, which could be attributed to the increase in Fe 3+ states, making Fe2O3 the more dominant phase, consistent with the increase in the amount of oxygen in the solution phase. Additionally, it is very likely that some carbon is dissolved into the iron as well [30,31] unambiguously identified, we can predict the most feasible structure using simple thermodynamic arguments. If we assume that some of the iron remains non-oxidized, we can deduce, based on the assumption that local equilibria is established at the interfaces, the thermodynamically most feasible structure of these particles simply based on the corresponding Fe-O binary phase diagram. ...
Metal catalysts are necessary for fabricating carbon nanotubes, but are often considered impurities in the end products, and arduous steps are used to remove catalyst residues from the nanotube structure. However, as metals can be electrocatalytic, instead of removing them we can utilize their role in detection of analgesics. Herein, we study the physicochemical properties of Fe‐containing single‐walled carbon nanotubes (SWCNTs), and the effect of simple oxidative pretreatment on them. We show that a gentle anodic pretreatment i) increased the amount of oxidized Fe nanoparticles, most likely exhibiting phases Fe3O4 and Fe2O3 and ii) effectively removed disordered carbonaceous material from SWCNT bundles surfaces. Pretreatment had only a marginal effect on sensitivity towards analgesics. However, interestingly, selectivity of Fe‐SWCNTs towards paracetamol and morphine could be modified with pretreatment. Through this kind of in‐depth investigation, we can, to a certain extent, correlate various material properties of SWCNTs with the observed electrochemical performance. This approach allows us to evaluate what factors in SWCNTs truly affect the electrochemical detection of biomolecules.
... This is attributed to sp 2 hybridized carbon. 34,36,40,41 The broad peaks are overlapping features from the C─Fe at 283.3 eV and the C─B bond. The same gradual shift of the C 1s signal was observed in boron carbide films by Ronning et al. 42 B 4 C-related C 1s features are expected at 282.7 and 284.0 eV, but the latter peak does not show up in our scans. ...
Multilayer (ML) thin film coatings have shown promise in achieving hard x-ray nanofocusing with high reflectivity and high resolution. The chemical, structural, and long-term stability of Ir/B4C MLs, which are of great interest to the synchrotron and astrophysics communities, are not yet fully understood. The evolution of the x-ray performance of Ir/B4C ML mirrors was monitored over 5 years, and the chemical and structural properties were investigated in depth. Reflectivity scans reveal significant alteration in the energy range of 3.4 to 10 keV over this period. Furthermore, thickness and density degradation of B4C layers were observed in scanning electron transmission microscopy results. The oxidation of B4C occurs only for the top layers, whereas the buried B4C layers go through various complex chemical modifications. The x-ray reflectivity model of Ir/B4C structure was modified, based on the experimental findings, and resulted in good understanding of the long-term reflectivity performance of the x-ray mirror coatings.
... The peak (b) at 285.4 eV corresponds to C 2p-Fe 3d hybridized states from carbon in the solid solution in the ferrite matrix and empty * orbitals, viz. sp 2 and sp 1 hybridized C states in carbon from surface contamination [33] . The peaks (c) 287.7 and (d) 288.6 eV correspond to C 2p-Fe 3d hybridized states and C-O bond contributions in the surface oxidation layer [34] , respectively. ...
To understand the formation mechanism of carbon clusters in low-carbon steel, the dynamic behavior of carbon in solid solutions subjected to aging at low temperatures was investigated by X-ray absorption spectroscopy. While it is hypothesized that the C-Fe bond distance and lattice strain induced by the carbon in solid solution affect the formation and strengthening mechanism of carbon clusters in low-carbon steels, currently, there is no information on the local structure of carbon in ferritic steels. Therefore, in this study, the relationship between the correlation coefficient derived from C K near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and mechanical properties, in terms of Vickers hardness, was elucidated. The changes occurring in the spectral shape in the initial stages of aging were found to be clearly associated with the diffusion of carbon in the solid solution. The presence of the carbon-cluster precursor state suggested that the correlation coefficient calculated from the C K NEXAFS spectra experienced variations in spite of a constant Vickers hardness. Furthermore, we proposed a method to analyze the local structure of carbon in solid solution in steels using C K NEXAFS. Finally, our observations illustrate that the local structure of carbon is dependent on age-hardening during low-temperature aging.
... The metallic iron nanoparticle or surface, which can form iron carbides and allow diffusion of carbon atoms to sustain the CNT growth, may be the main reason for the formation of highly crystalline MWCNTs from the CO/CH4 dry mixture. However, the characteristic XPS peaks of iron carbides (Fe1−xCx) around 285-295 and 710-722 eV overlap with the strong peaks of carbonaceous compounds in C 1s and Fe 2p3/2 spectra, respectively [36]. Hence, the iron carbides would not be distinguishable due to the expected minimal mass amount, even if they existed. ...
A nanocrystalline chromium-doped ferrite (FeCr) catalyst was shown to coproduce H2 and multiwalled carbon nanotubes (MWCNTs) during water gas shift (WGS) reaction in a H2-permselective zeolite membrane reactor (MR) at reaction pressures of ~20 bar. The FeCr catalyst was further demonstrated in the synthesis of highly crystalline and dimensionally uniform MWCNTs from a dry gas mixture of CO and CH4, which were the apparent sources for MWCNT growth in the WGS MR. In both the WGS MR and dry gas reactions, the operating temperature was 500 °C, which is significantly lower than those commonly used in MWCNT production by chemical vapor deposition (CVD) method from CO, CH4, or any other precursor gases. Extensive ex situ characterizations of the reaction products revealed that the FeCr catalyst remained in partially reduced states of Fe3+/Fe2+ and Cr6+/Cr3+ in WGS membrane reaction while further reduction of Fe2+ to Fe0 occurred in the CO/CH4 dry gas environments. The formation of the metallic Fe nanoparticles or catalyst surface dramatically improved the crystallinity and dimensional uniformity of the MWCNTs from dry gas reaction as compared to that from WGS reaction in the MR. Reaction of the CO/CH4 mixture containing 500 ppmv H2S also resulted in high-quality MWCNTs similar to those from the H2S-free feed gas, demonstrating excellent sulfur tolerance of the FeCr catalyst that is practically meaningful for utilization of biogas and cheap coal-derived syngas.
... Furthermore, the difference between the binding energy of Fe 2p 1/2 and Fe 2p 3/2 for the two samples is found to be 13.7 eV which obviously falls within the well known acceptable standard value (13.0-14.0 eV) [47]. The correlated and good chemical property shown by these samples prove the efficacy of the synthesis approach used for the samples preparation. ...
In this paper, the effect of Zn incorporation into the lattice of Fe3C, CoCx and Ni3C is investigated. It is discovered that the oxygen reduction reaction (ORR) of Fe3C, CoCx and Ni3C can be enhanced through Zn incorporation into their lattices. This results in the formation of Co3ZnC, Fe3ZnC and Ni3ZnC electrocatalysts. The catalysts show appreciable ORR performances in O2-saturated 0.1 M KOH, with Fe3ZnC and Co3ZnC exhibit the most positive onset potential (0.92 V) and half-wave potential (0.8 V). The Fe3ZnC electrocatalyst exhibits the highest current density (5.3 mA cm⁻²) at low electrode potential (0.2-0.6 V); comparable to that of commercial Pt/C. Both Fe3ZnC and Co3ZnC show activity retention of 99.9 % for ∼15 h, and offer good methanol tolerance. It indicates their superior performance. This work shows a rather interesting and rather simple chemical strategy to enhance the ORR activity of binary metal carbides for fuel applications.
... Nevertheless, the spectrum suggests the presence of aldehyde, ketone, and carboxyl functional groups on the SWCNT, as seen in ref 17. The Fe 2p spectrum shown in Figure 2E also closely matches that of previous work, where the iron is expected to be bonded to carbon and oxygen (indicating the presence of a mix of iron carbide 34 and iron oxide seen as the higher energy peaks of the Fe 2p LII and LIII spectra) and metallic iron (as the lower energy peaks of the Fe 2p LII and LIII spectra). The results of the characterization from the previous and this work are summarized in Table 1. ...
Oxycodone is a strong opioid frequently used as an analgesic. Although proven efficacious in the management of moderate to severe acute pain and cancer pain, the use of oxycodone imposes a risk of adverse effects such as addiction, overdose, and death. Fast and accurate determination of oxycodone blood concentration would enable personalized dosing and monitoring of the analgesic as well as quick diagnostics of possible overdose in emergency care. However, in addition to the parent drug, several metabolites are always present in the blood after a dose of oxycodone and, as of today, there is no electrochemical data available on any of these metabolites. In this paper, a single-walled carbon nanotube (SWCNT) electrode and a Nafion-coated SWCNT electrode were used, for the first time, to study the electrochemical behavior of oxycodone and its two main metabolites, noroxycodone and oxymorphone. Both electrode types could selectively detect oxycodone in the presence of noroxycodone and oxymorphone. However, we have previously shown that the addition of Nafion coating on top of the SWCNT electrode is essential for direct measurements in complex biological matrices. Thus, the Nafion/SWCNT electrode was further characterized and used for measuring clinically relevant concentrations of oxycodone in buffer solution. The limit of detection for oxycodone with the Nafion/SWCNT sensor was 85 nM and the linear range 0.5 - 10 µM in buffer solution. This study shows that the fabricated Nafion/SWCNT sensor has potential to be applied in clinical concentration measurements.
... Moreover, the Fe 2p XAS spectrum very closely matches those previously observed for iron carbides. 45 These results are further supported by the TEM analysis, showing the presence of iron carbides. Nevertheless, it should be noted that the spectrum could also arise from a mixture of metallic and oxidized iron species. ...
We prepare disposable single-walled carbon nanotube network electrodes for the detection of the potent opioid fentanyl, currently a leading cause for opioid overdose deaths in the USA. We show repeatable dry transfer of single-walled carbon nanotube (SWCNT) networks to produce robust electrodes. This process directly produces highly conductive SWCNT electrodes without the need for any further modifications required for conventional carbon electrodes. The realized electrode showed low background currents combined with spontaneous enrichment of fentanyl resulting in high signal-to-noise ratio. With this electrode, a detection limit of 11 nM and a linear range of 0.1 to 1 μM were found for fentanyl. In addition, selectivity is demonstrated in the presence of several common interferents.
... Article energy in the metal carbide should be slightly lower than that of a sp 3 -hybridized carbon (C−C-sp 3 ) in the C 1s region and lower than that of M 0 in the Mn 2p region. 44,45 However, there is no noticeable manganese carbide peaks to be identified in the C 1s or Mn 2p regions (in Figures 4 and S5 To determine the effect of the G/C ratio on the capacitance, electrodes made with different G/C ratios, that is, Spec. #: G 10 C 0 -M 25 -P 10 , G 9 C 1 -M 25 -P 10 , G 8 C 2 -M 25 -P 10 , G 7 C 3 -M 25 -P 10 , G 5 C 5 -M 25 -P 10 , G 2 C 8 -M 25 -P 10 , and G 0 C 10 -M 25 -P 10 , were examined with chronopotentiometric (CP) measurements under a current density of 1 A/g, as shown in Figure 8a. ...
Herein, we describe the preparation and characterization of graphene/carbon nanotube (CNT)/MnO
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composites and the effects of chemical composition and phase transformation on the properties of the corresponding electrode film. In general, the effect of graphene-to-CNT ratio (G/C ratio) and the manganese (Mn) content on the morphology, chemical state, crystallization properties, and microstructure of the composite material was examined by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and selected area electron diffraction. The bonding mechanism between MnO
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and graphite-based materials, that is, graphene and CNTs, is discussed. The influence of the composition of the composites on the performance of the electrode was investigated using charge-discharge curves. The faradically active MnO
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also functioned as a considerable cobinder and allowed for a reduced amount of polymeric binder, which enhanced the conductivity and capacitance of the electrode. The optimized electrode composition was obtained based on our present graphene and CNT specifications. In summary, the results discussed in this article provide significant background information for future applications of graphene/CNT/MnO
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composite electrodes.
... From the plots shown in Fig. 3(b), two main peaks are observed, which can be related to the spin orbit splitting peaks of Fe 2p at binding energies of 707.0 and 720.0 eV. These binding energy values are consistent with previous report [39]. High-resolution C 1s core level spectra display a single peak centered at 283.2 eV, corresponding to the carbon in iron carbides. ...
Fabrication of iron carbide by plasma-enhanced atomic layer deposition - Xu Tian, Xiangyu Zhang, Yulian Hu, Bowen Liu, Yuxia Yuan, Lizhen Yang, Qiang Chen, Zhongwei Liu
... Moreover, the amount of h-Ni 3 C appears to decrease along with increasing Fe content in the measurement series, whereas the amount of Fe x C y goes to the opposite direction. It is worth mentioning that XPS analysis for the sample under study, Ni 80 Fe 20 (NiFe@UTG) also show oxidized metals ( Fig. 1 d and e) to which both carbides and oxides can contribute, as also reported previously [41][42][43][44]. ...
Core-shell nanoparticles represent a class of materials that exhibit a variety of properties. By rationally tuning the cores and the shells in such nanoparticles (NPs), a range of materials with tailorable properties can be produced which are of interest for a wide variety of applications. Herein, experimental and theoretical approaches have been combined to show the structural transformation of NPs resulting to the formation of either NiFexCy encapsulated in ultra-thin graphene layer (NiFe@UTG) or Ni3C/FexCy@FeOx NPs with the universal one-step pulse laser ablation in liquid (PLAL) method. Analysis suggests that carbon in Ni3C is the source for the carbon shell formation, whereas the final carbon-shell thickness in the NPs originates from the difference between Ni3C and FexCy phases stability at room temperature. The ternary Ni-Fe-C phase diagram calculations reveal the competition between carbon solubility in the studied metals (Ni and Fe) and their tendency toward oxidation as the key properties to produce controlled core-shell NP materials. As an application example, the electrocatalytic hydrogen evolution current on the different NPs is measured. The electrochemical analysis of the NPs reveals that NiFe@UTG has the best performance amongst the NPs in this study in both alkaline and acidic media.
Earth‐abundant commercial conductive carbon materials are ideal electrocatalyst supports but cannot be directly utilized for single‐atom catalysts owing to the lack of anchoring sites. Therefore, we employed crosslink polymerization to modify the conductive carbon surface with Fe−Co dual‐site electrocatalysts for oxygen reduction reaction (ORR). First, metal‐coordinated polyurea (PU) aerogels were prepared using via crosslinked polymerization at ambient temperature. Then, carbon‐supported, atomically dispersed Fe−Co dual‐atom sites (FeCoNC/BP) were formed by high‐temperatures pyrolysis with a nitrogen source. FTIR and ¹³ C NMR measurements showed PU linkages, while ¹⁵ N NMR revealed metal–nitrogen coordination in the PU gels. Asymmetric, N‐coordinated, and isolated Fe−Co active structures were found after pyrolysis using XAS and STEM. In alkaline media, FeCoNC/BP exhibited excellent ORR activity, with a E 1/2 of 0.93 V vs. RHE, higher than that of Pt/C (20 %) (0.90 V), FeNC/BP (0.88 V), and CoNC/BP (0.85 V). An accelerated durability test (ADT) on FeCoNC/BP indicated good durability over 35000 cycles. FeCoNC/BP also showed moderate ORR and ADT performance in acidic media. The macro/mesoporous N‐doped carbon structures enhanced the mass transport properties of the dual Fe−Co active‐sites. Therefore, modifying carbon supports with nonprecious metal catalysts may be a cost‐effective‐strategy for sustained electrochemical energy conversion.
Electrodeposition from an environmentally friendly iron‐sulfate electrolyte with citric acid as carbon source has gained attention recently, because of excellent mechanical properties of the resulting Fe‐C coatings with intentionally co‐deposited high carbon concentrations. While being very attractive as protective coatings and sustainable alternatives for hard chrome coatings, comprehensive understanding of the coatings’ chemical constitution including the type and location of carbon‐containing phases is still lacking. The amount of co‐deposited carbon of up to about 0.8 wt.% significantly exceeds the solubility of carbon in ferrite, although carbon‐free ferrite is the only unambiguously reported phase in as‐deposited Fe‐C coatings so far. In the present work, time‐of‐flight secondary ion mass spectrometry, X‐ray photoelectron spectroscopy and soft X‐ray emission spectroscopy have been applied to identify the carbon‐containing phases, which are present as minor secondary phases in the coatings, but are known to have an important influence on the coatings’ properties. Three carbon‐containing phases could be distinguished, homogeneously distributed in the nanocrystalline ferrite base material. Iron acetates, amorphous carbon and carbides were found in both as‐deposited and annealed Fe‐C coatings up to 300 °C, but their fraction changes during post‐deposition annealing.
A one-step approach to synthesize ultrafine transition metal particles (size < 5 nm) in carbon substrates is highly desirable for fabricating electrodes for energy devices. Herein, cobalt ion implantation into amorphous carbon films (a:C) and hydrogenated amorphous carbon films (a:CH) was explored, with the aim of synthesizing ultrafine metallic cobalt nanoparticles at room temperature. Co ions of 30 keV energy were implanted into the carbon films to achieve a Co areal density of 1.0 ± 0.1 × 1017 atoms cm-2. Rutherford backscattering measurements revealed that hydrogenated amorphous carbon films gave a broader Co depth distribution compared to the amorphous carbon films. Further, cross-sectional TEM analysis revealed that hydrogenated carbon films suppressed metallic Co nanoparticle aggregation, leading to the creation of ultrafine Co nanoparticles (size < 5 nm). Co L-edge X-ray absorption spectroscopy measurements confirmed the formation of predominantly metallic Co nanoparticles by ion implantation. Results conclusively demonstrate that the presence of hydrogen (~ 28 at.%) in the carbon matrix facilitates the synthesis of ultrafine metallic Co nanoparticles during Co ion implantation.
The development of wear-resistant steels requires an understanding of deformation behavior and chemical evolution in cementite (Fe3C) under tribological loading. Previous investigations of chemical changes in steels during wear provided limited knowledge of the cementite stability and its transformations as the single phase is conventionally embedded in a metal matrix. This study examines elemental and phase distributions in bulk polycrystalline cementite with minor fractions of graphite, iron, and wüstite after single-pass sliding wear. We employ energy-dispersive X-ray spectroscopy in scanning transmission electron microscope, Auger electron spectroscopy, and X-ray photoelectron spectroscopy to characterize cementite composition before and after wear. Our results demonstrate that severe plastic deformation via contact shear leads to the partial decomposition and mechanical mixing of the non-cementite inclusions into the cementite matrix and the partial elemental homogenization in the outermost deformed region. In addition, we relate the dissolution of the graphite, which is present in the initial microstructure, to the formation of the Hägg carbides (Fe5C2).
The (Mo-Ta-W)-C and (Nb-Ta-W)-C carbide thin films were prepared by non-reactive magnetron co-sputtering. The (Mo-Ta-W)-C thin films exhibited the simple BCC structure with the strip-like surface morphologies and a double-layer structure for cross sections with a columnar upper layer and an featureless lower layer. In the (Mo-Ta-W)-C thin films, the metal-metal and metal-oxygen bonds were observed with no metal-carbon bonds. The carbon-carbon bonds were observed, indicating free carbon phases existed in the (Mo-Ta-W)-C thin films. The surface roughness of (Mo-Ta-W)-C thin films was small with Ra value of 3.11-3.74 nm. The hardness of (Mo-Ta-W)-C thin films was 32.6-33.5 GPa. The (Nb-Ta-W)-C thin films formed the amorphous structure. Different from (Mo-Ta-W)-C thin films, the metal-carbon bonds existed in the (Nb-Ta-W)-C thin films, except the metal-metal and metal-oxygen bonds. The C-C bonds were also observed, indicating free carbon phases existed in the (Nb-Ta-W)-C thin films. The surfaces of (Nb-Ta-W)-C thin films displayed a granular structure with Ra of 0.86-1.00 nm, and the cross sections exhibited a fine fibrous structure. The hardness values of (Nb-Ta-W)-C thin films ranged from 34.5 to 36.1 GPa with elastic modulus of 319.6 to 349.5 GPa. The corrosion current density and polarization resistance of (Nb-Ta-W)-C thin films were better than 304 stainless steel, indicating good anti-corrosive performance of (Nb-Ta-W)-C thin films. The (Nb23Ta21W23)C33 thin film had low reflectivity in the visible light band (300-800 nm), and high reflectivity in the near-infrared band (800-2500 nm), with the solar absorption ratio αs of 0.4577 and the infrared emissivity εH of 0.178.
The microstructure that governs the nature of carbon steel is determined by the combination of iron and carbon. Ferrite and austenite differ in their arrangements of iron atoms, and they differ from cementite with respect to iron and carbon bonding. In this work, we combine structural studies (X-ray diffraction, scanning electron microscopy, and atomic force microscopy) and synchrotron-based in-situ X-ray photoelectron spectroscopy (XPS) to demonstrate the behavior of the carbon in carbon steel using a thermal annealing process conducted from room temperature to 900 °C in an ultrahigh-vacuum chamber. In situ XPS experiments revealed not only that the chemical states varied depending on depth from the surface but also that the carbide changed into the C-solute phase at temperatures between than 300 – 600 °C. Our findings provide important insights into the subtle balance of interactions involving the properties of steel that differ between the surface and bulk phases, offering new opportunities to engineer the properties of carbon steel.
Electrocatalytic nitrogen reduction reaction (eNRR) is a sustainable alternative to the traditional Haber–Bosch process due to its eco‐friendly nature and capability of utilizing renewable energy. However, its low Faradic efficiency (FE), caused by the excessive adsorption and reduction of protons, has been regarded as the main challenge, which leads to low ammonia yield as well. Herein, a carbon‐supported iron electrocatalyst is reported, which is fabricated by low‐temperature (300 °C) potassium vapor reduction of FeF3‐intercalated graphite fluoride, for efficient electrochemical nitrogen reduction. The strategy enables the unique formation of exposed Fe nanoparticles uniformly anchored on graphene and in situ doped with fluorine heteroatoms. These specific features can alter the electronic configuration of the Fe nanoparticles, leading to strong surface polarization that boosts nitrogen absorption capability for eNRR, resulting in high FE (41.6%) and ammonia yield rate (53.3 μg h‐1 mg‐1) simultaneously. First‐principle calculation attributes this enhanced eNRR capability to more empty orbitals carried by the Fe atoms through the electron transfer with F dopant and substrate. As a versatile strategy for synthesizing various ultrafine and highly dispersed metal nanoparticles on the carbon support, this work might shed light on rational designing essential electrocatalysts with effective electronic structure manipulation. Exposed Fe nanoparticles are uniformly anchored on graphene and in situ doped with fluorine heteroatoms. These unique features can alter the electronic configuration of the Fe nanoparticles, leading to strong surface polarization that boosts nitrogen absorption capability for electrocatalytic nitrogen reduction reaction, resulting in high Faradaic efficiency (41.6%) and ammonia yield rate (53.3 μg h−1 mg−1) simultaneously.
Fe-based catalysts are efficient systems for CO2 conversion via reverse water-gas shift (rWGS) reaction. Nevertheless, the nature of the active phase, namely metallic iron, iron oxide or iron carbide remains a subject of debate which our paper is meant to close. Fe⁰ is a much better catalyst for the rWGS than Fe3C. The activity of Fe⁰ can be promoted by the addition of Cs and Cu whose presence hinders iron carburisation while favouring both higher conversion and enhanced selectivity. When the samples are aged in the rWGS reaction mixture during stability test a new phase appear: Fe5C2, resulting in a more active but less selective catalysts than Fe⁰ for the rWGS reaction. Hence our results indicate that we could potentially achieve an optimal activity/selective balance upon finely tuning the proportion Fe/Fe5C2. Beyond the fundamental information concerning active phase we have observed the presence of advanced Fischer-Tropsch-like products at ambient pressure opening new opportunities for the design of hybrid rWGS/Fischer-Tropsch systems.
The tribological performance of six low viscosity, hydrophobic, halogen- sulfur-, and phosphorous free trioctylammonium-based protic ionic liquids with 2-naphthoate, 4-tert-butylbenzoate, 2-hexyldecanoate, 4-phenylbutanoate, 3,4-dimethylbenzoate, and salicylate anions were studied as lubricants for steel-steel interfaces using a four-ball tribo-tester. The results showed a significant friction reduction up-to 28 ̶ 65% compared to polyalphaolefin lube base oil. Where the salicylate protic ionic liquid showed the lowest coefficient of friction. In terms of wear, the 2-naphthoate and salicylate protic ionic liquids exhibited wear scar diameter values lower than polyalphaolefin by 4.7 and 0.42%, respectively. The scanning electron microscopy and X-ray photoelectron spectrometer analysis outcomes of the wear scar surfaces indicated that tribo-chemical reactions were involved among the protic ionic liquid molecules and the steel surfaces during the tribo-test, developing a protective boundary film, which contributed significantly to the lubrication performance of the protic ionic liquids’ lubricants. No corrosion was observed for the copper strip corrosion test carried out to examine the corrosion characteristics of the studied protic ionic liquids. The overall results confirm the high capability of applying this group of protic ionic liquids as lubricants.
Electrochemical water splitting provides a promising approach to storing renewable electricity in the form of hydrogen on a grand scale. However, the current techniques for large‐scale electrochemical hydrogen production rely on the use of noble‐metal catalysts making it uncompetitive to traditional methods using fossil fuels, due to the high cost and scarcity of noble‐metal catalysts. Thus, replacing noble‐metal electrocatalysts with cheap materials made of abundant elements holds the key to achieve cost‐effectiveness. Recently, amorphous electrocatalysts emerged as promising candidates due to their unique physical and chemical properties compared to their crystalline counterparts leading to superior catalytic performance. Given the rapid advances made in the design, synthesis and development of amorphous catalysts, namely monometallic and multimetallic borides, sulfides, phosphides, oxides, and hydroxides based on transition metals, this review aims to summarize the recent progress on compositional designs, microstructure, morphology, electronic properties, and interaction with host materials. Special attention is paid to uncover the main strategies adopted in each material category and the underlying structure–property relationship that improves hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances. As a result, this review provides guidance for the design and synthesis of novel amorphous electrocatalysts with high performance for large‐scale electrochemical water splitting application.
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Using our proposed structure prediction algorithm coupled with first-principle calculations, we performed the crystal structure prediction on a series of iron-rich iron carbide phases (FexCy, 1 ≤ y ≤ x ≤ 7, 0 < y/x ≤ 1) with not more than 32 total number of atoms per cell at T = 0 K and P = 0 GPa. The experimentally well-known structures in the region (0 < y/x ≤ 0.5 and y/x = 1) for η-Fe2C(Pnnm), θ-Fe3C(Pnma), χ-Fe5C2(C2/c) and h-Fe7C3(P63mc) have been successfully reproduced, and more stable phases of Fe4C(Fdd2) and FeC(Pnnm) are found. For the unknown region (0.5 < y/x < 1), we have predicted the lowest-enthalpy structures for Fe7C5(C2), Fe4C3(Cmcm), Fe5C4(C2/m), Fe6C5(Imm2) and Fe7C6(P63/m). We have examined the structural, thermodynamic and mechanical stability for all predicted structures. The local structure of the new region is quite different from that of the known region. The atomic magnetic moments and magnetic hyperfine field parameters are drastically reduced in the new region, which is unexpected magnetic properties for the iron carbides so far. We qualitatively analyze the relationship between the local atomic structure and magnetic moment, and further quantitatively establish a high accuracy model by using machine learning method with a small root mean square errors for training set (0.079μB) and validation set (0.083μB). Our work can not only help us to enrich the understanding of iron carbide phases, and provide a new method for the correlation of local structure and magnetism, but also provide a new way for the discovery and design of novel iron-based materials.
In this study, iron carbide nanoparticles (NPs) were prepared by the plasma‐based method using a gas aggregation source of NPs. In‐flight plasma treatment of the NPs was performed to improve their temporal stability. The auxiliary radiofrequency plasma used for the in‐flight treatment resulted in trapping of the NPs in the plasma for several 10s of seconds. Scanning electron microscopy and small‐angle X‐ray scattering analyses showed a decrease in the size of NPs due to the plasma treatment, whereas the X‐ray diffraction analysis showed that the structure of the NPs changed from amorphous iron carbide to the crystalline Fe3C (cementite). In situ and ex situ X‐ray photoelectron spectroscopy measurement confirmed better temporal stability of plasma‐treated NPs against oxidation.
This work reports the synthesis of novel cross-linked and functional porous carbon nanosheets (CNSs). The polyvinylpyrrolidone/transition metal acetates/N–N-dimethylformamide precursors are first woven into networks by electrospinning. The resultant precursor networks are transformed into the three-dimensional (3D) hierarchically porous material consisting of cross-linked and meso/macroporous CNSs (i.e., [email protected]) after pyrolysis. Characterization results prove that abundant ultrafine [email protected] units, N–C bonds, metal-nitrogen doped carbon (M-N-C) species and oxygen-containing functional groups disperse along the surfaces of the [email protected], which act as electrocatalytic active sites for Oxygen reduction reaction (ORR) and Oxygen evolution reaction (OER). Due to the synergistic effect of the hierarchically porous structures and high-density active sites, the optimal [email protected] exhibits more positive onset potential (0.98 V relative to a reversible hydrogen electrode (vs. RHE)) and half-wave potential (0.827 V vs. RHE) than Pt/C (0.97 V vs. RHE and 0.819 vs. RHE) for ORR. Meanwhile, the OER potential at 10 mA cm⁻² of the [email protected] (1.597 V vs. RHE) is more negative than RuO2 (1.631). Furthermore, the oxygen electrode activity (ΔE = E10,OER - E1/2,ORR) of the [email protected] is as low as 0.772 V, which surpasses the state-of-the-art Pt/C(ORR)-RuO2(OER) catalyst combination (ΔE = 0.812 V). Experimental results prove that the [email protected] is among the best non-precious metal based bifunctional electrocatalyst for ORR and OER.
Graphene-based vertical spin valves (SVs) are expected to offer a large magnetoresistance effect without impairing the electrical conductivity, which can pave the way for the next generation of high-speed and low-power-consumption storage and memory technologies. However, the graphene-based vertical SV has failed to prove its competence due to the lack of a graphene/ferromagnet heterostructure, which can provide highly efficient spin transport. Herein, the synthesis and spin-dependent electronic properties of a novel heterostructure consisting of single-layer graphene (SLG) and a half-metallic Co2 Fe(Ge0.5 Ga0.5 ) (CFGG) Heusler alloy ferromagnet are reported. The growth of high-quality SLG with complete coverage by ultrahigh-vacuum chemical vapor deposition on a magnetron-sputtered single-crystalline CFGG thin film is demonstrated. The quasi-free-standing nature of SLG and robust magnetism of CFGG at the SLG/CFGG interface are revealed through depth-resolved X-ray magnetic circular dichroism spectroscopy. Density functional theory (DFT) calculation results indicate that the inherent electronic properties of SLG and CFGG such as the linear Dirac band and half-metallic band structure are preserved in the vicinity of the interface. These exciting findings suggest that the SLG/CFGG heterostructure possesses distinctive advantages over other reported graphene/ferromagnet heterostructures, for realizing effective transport of highly spin-polarized electrons in graphene-based vertical SV and other advanced spintronic devices.
Through calculation and analysis of electronic structure and lattice dynamics in 3d transition metal carbides, we identify MnC as a novel compound displaying unconventional superconductivity. Though unstable in the absence of applied pressure at 0 K, MnC may be stabilized above 300 K or 13 GPa due to enhanced t2g orbital overlap or phonon-phonon interactions respectively. In the resulting structure, which adopts a ferromagnetic configuration with magnetization of 1.55 μB/Mn, we predict superconductivity occurring below a critical temperature of 16.2 K. Further investigation reveals this unconventional superconductivity derives from phonon-mediated minority-spin-triplet Cooper pairs, for which competing magnetic order is also suggested to play a role. Consideration of all 3d transition metal carbides yields a holistic explanation of trends in stability and superconductivity. Two unique cases are highlighted: (i) FeC, with a critical temperature of 4.0 K, may be stabilized by temperature or pressure, whereas (ii) ZnC, with a high critical temperature of 27.8 K, remains stable at 0 K owing to complete filling and strong localization of its 3d shell. The findings here contribute to the understanding of factors influencing superconductivity, hence forming a basis on which a materials-by-design approach may be utilized for next-generation applications such as spintronic devices.
The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni 1−x C x (0.05 x 0.62) thin films have been investigated by high-resolution x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and soft x-ray absorption spectroscopy. By using x-ray as well as electron diffraction, we found carbon-containing hcp-Ni (hcp-NiC y phase), instead of the expected rhombohedral-Ni 3 C. At low carbon content (4.9 at%), the thin film consists of hcp-NiC y nanocrystallites mixed with a smaller amount of fcc-NiC x . The average grain size is about 10–20 nm. With the increase of carbon content to 16.3 at%, the film contains single-phase hcp-NiC y nanocrystallites with expanded lattice parameters. With a further increase of carbon content to 38 at%, and 62 at%, the films transform to x-ray amorphous materials with hcp-NiC y and fcc-NiC x nanodomain structures in an amorphous carbon-rich matrix. Raman spectra of carbon indicate dominant sp 2 hybridization, consistent with photoelectron spectra that show a decreasing amount of C–Ni phase with increasing carbon content. The Ni 3d–C 2p hybridization in the hexagonal structure gives rise to the salient double-peak structure in Ni 2p soft x-ray absorption spectra at 16.3 at% that changes with carbon content. We also show that the resistivity is not only governed by the amount of carbon, but increases by more than a factor of two when the samples transform from crystalline to amorphous.
The same method used to determine {sigma}{sup *} excitations in the x-ray-absorption spectra of organic molecules is applied to analyze the structure of the {sigma}{sup *} band in the x-ray absorption spectra of amorphous carbon (a-C) films. The analysis assumes that only a {sigma} bond interaction to first neighbors is relevant to explain the structure of the {sigma}{sup *} band in a-C films. This is justified by the local character of the x-ray absorption probe and the short- range order existing in these films. The identification of the different {sigma}{sup *} components is based on the dependence of the {sigma}{sup *} binding energy with bond distance. The {sigma}{sup *} band is built up by summing the components resulting from the possible different types of {sigma} bonds in a-C. This method serves to separate the {pi}{sup *} states from the {sigma}{sup *} states and to identify the kind of chemical bonds existing between carbon atoms. This analysis yields a proportion of sp{sup 3}-bonded atoms of 60% in a film with a density of about 2.9 g/cm{sup 3}, which is a value closer to what is expected from theoretical calculations. The analysis identifies a component at about 288.5 eV which is associated to strained {sigma} bonds of the type of the existing in sp{sup 3} bonded rings like cyclopropene. Raman and photoemission spectroscopies help in the interpretation of the x-ray absorption spectra and the assignment of the {sigma}{sup *} components.
First-principles’ calculations of GGA and GGA+U type have been performed for γ-Fe23C6, a complex iron carbide with 116 atom in the unit cell. GGA results were found to be in better agreement with experimental data than GGA+U results. Various occupancies for Wyckoff positions and corresponding magnetic orderings have been explored. Our calculations reveal that the crystal structure is composed of a framework of strongly linked Fe atoms, and additional stabilizing Fe and C atoms positioned in cavities. The local electronic and magnetic properties vary strongly among the non-equivalent Fe sites in γ-Fe23C6. The lattice parameters of γ-Fe23C6 match those of austenite well. Surprisingly, pure γ-Fe23C6 is found to be more stable than commonly occurring θ-Fe3C cementite. Moreover, the calculations show low vacancy energy (about 0.37eV) for Fe at 4a sites in γ-Fe23C6. Conditions of formation and factors hampering the formation of γ-Fe23C6 in steel manufacturing processes are discussed.
We propose two methods for obtaining the atomic-like background
for the x-ray absorption fine structure (XAFS): the methods of smoothing
spline and of Bayesian smoothing. Both are capable of using the prior
information, calculated or experimental, about the background. The XAFS
signals obtained by these techniques are shown to be significantly
corrected in comparison with standard methods. The method of Bayesian
smoothing is the only method that gives the errors of approximation of the
atomic-like background by an artificial smooth function. These errors are
shown to be the main source of the uncertainty of the XAFS function.
The origin and interpretation of the Raman features of amorphous (hydrogenated) carbon films deposited at room temperature in the region of 1000–1700 cm<sup>-1</sup> is discussed in this paper. Possible interpretations of the linewidths, positions of the ‘‘G’’ graphite peak and ‘‘D’’ disordered peak, and their intensity ratios are examined using results obtained from magnetron sputtered and magnetic field enhanced plasma deposited films. It is shown that even small ‘‘clusters’’ of condensed benzene rings (cluster size below 20 Å) in carbon films can explain the observed Raman scattering. Besides the care that should be taken in the correct interpretation of Raman results, the utility of Raman scattering in obtaining an estimate of cluster sizes in amorphous (hydrogenated) carbon films is discussed. Carbon films prepared by magnetron sputtering show two additional Raman features at 1180 and 1490 cm<sup>-1</sup> in addition to the G and D peaks. It is shown that a correlation exists between the 1180 cm<sup>-1</sup> peak and the sp<sup>3</sup> content in the films. © 1996 American Institute of Physics.
Controlling the performance of structures and components of all sizes and shapes through the use of engineered coatings has long been a key strategy in materials processing and technological design. The ever-increasing sophistication of en- neered coatings and the rapid trend toward producing increasingly smaller devices with greater demands on their fabrication, properties and performance have led to signi?cant progress in the science and technology of coatings, particularly in the last decade or two. Nanostructured coatings constitute a major area of sci- ti?c exploration and technological pursuit in this development. Withcharacteristic structural length scales on the order of a few nanometers to tens of nanometers, nanostructured coatings provide potential opportunities to enhance dramatically performance by offering, in many situations, extraordinary strength and hardness, unprecedented resistance to damage from tribological contact, and improvements in a number of functional properties. At the same time, there are critical issues and challenges in optimizing these properties with ?aw tolerance, interfacial adhesion and other nonmechanical considerations, depending on the coating systems and applications. Nanostructured coatings demand study in a highly interdisciplinary research arena which encompasses: surface and interface science study of defects modern characterization methodologies cutting-edge experimental developments to deposit,synthesize, conso- date, observe as well as chemically and mechanically probe materials at the atomic and molecular length scales state-of-the-art computational simulation techniques for developing - sightsintomaterialbehaviourattheatomicscalewhichcannotbeobtained in some cases from experiments alone The interdisclipinary nature of the subject has made it a rich playing ?eld for scienti?c innovation and technological progress.
Local structures of diamond-like carbon (DLC) films formed by various methods were studied by near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy. The DLC films are characterized by the sp2/sp 3 ratio, which influences the mechanical and electronic properties. NEXAFS spectroscopy is sensitive to the sp2/sp3 ratio, because the isolated peak corresponding to the 1s→π* resonance transition can be observed. Carbon K-edge NEXAFS spectra for DLC thin films, which were synthesized by various methods, were measured using the total electron yield mode in the range of 275eV-320eV. A peak due to the coupling of carbon with oxygen was observed in the spectra of some DLC films, whereas it was not observed in the spectra of hydrogenated carbon films formed by RF sputtering. The obtained relative sp2 contents of the DLC films were distributed in the range of ≈20%. The minimum sp2/sp3 ratio was obtained from DLC films formed by vacuum arc deposition from graphite, and large sp2/sp3 ratios were obtained from DLC films formed by plasma chemical vapor deposition from hydrocarbons. The local structure of a DLC film was concluded to depend on the synthesis method, and in particular, the carbon source material.
The crystallization mechanisms of sputtered Fe1-xCx amorphous thin films for three values of atomic carbon content x = 0.28, 0.30 and 0.32 are directly observed using hot stage transmission electron microscopy. Images recorded sequentially are used to track the change caused by heating. Observations concern the nucleation and the growth of iron carbides and their structural identification. Information is also given about their crystallochemistry. They belong to the family of interstitial carbides with carbon atoms located inside iron Triangular Prisms (TP). They are built either from TP Sheets (TPS) stacks deriving from the cementite θ-Fe3C or from TP Chains (TPC) arrangements deriving from the Eckström-Adcock Fe7C3 carbide. The sharp transition between dominant TPS and dominant TPC carbides formations is illustrated. Nucleation and growth processes of both types of carbides are discussed and focus is put on the TPC crystals. They are the first to be formed whatever carbon content of the specimen and really correspond to the dominant phase for the richest-carbon film. When they are less numerous, they can act as nucleation sites for TPS carbides and it is in situ illustrated during the crystallization of the poorest-carbon film where orientation relationships can be found between the TPC-Fe7C3 carbide and a TPS carbide close to the Hägg carbide χ-Fe5C2 The crystallization of Fe0.70C0.30 film corresponds to a particular case where TPC carbides and TPS carbides can coexist with the same composition.
Thin films of M—C (M = Cr, Mn, Fe) have been deposited on silicon substrates by magnetron sputtering. It was found that interdiffusion between carbide films and silicon substrates occurred for Mn—C/Si and Fe—C/Si samples. The hardness and elastic modulus of the Cr—C films were around 16 ± 1 GPa and 210 ± 21 GPa, respectively. Mn—C and Fe—C films were not so hard as Cr—C films. The resistivity of these films at room temperature was between 0.267 and 3.40 mΩ cm. The resistivity of Cr—C and Mn—C films changed a little with time at 673 K in air.
Every surface scientist knows about the importance of carbon spectroscopy: the signals of C 1 s and C KLL usually are indicating the surface cleanness, whereas C 1 s peak is often used as a reference for the calibration of energy scale. Carbon spectroscopy becomes even more important in the case of the studies dedicated to new carbon‐based materials, such as nanotubes, graphene, diamond‐like carbon (DLC), carbon nitride, carbides, etc. It is well‐known that the carbon atoms can be arranged in a great variety of crystalline and disordered structures, because their electrons can hybridize in sp3, sp2 and even in linear sp configurations. Namely, the hybridization of carbon electrons defines the mechanical, electrical and optical properties of these materials. Indeed, between the pure diamond (sp3) and graphite (sp2), there are many phases of amorphous material characterized by different sp2/sp3 ratios and generally named DLC. Electron spectroscopies (X‐ray photoelectron spectroscopy, Auger electron spectroscopy and electron energy loss spectroscopy) are widely recognized as analytical techniques, able to identify the bonds of diamond, graphite and amorphous phases of carbon. The binding energy of C 1 s spectrum together with its plasmon losses, the shape of Auger peak and valence band spectra can be used to characterize the structure of carbon‐based materials. In this study, an overview is reported on carbon spectroscopy, comparing different experimental methods. Their application for the characterization of DLC and carbon nitride films, including the determination of carbon's sp2/sp3 ratio is discussed and illustrated by experimental results obtained for a series of thin films of these materials. Copyright © 2012 John Wiley & Sons, Ltd.
The structure of metallic glasses (MGs) has been a long-standing mystery. On the one hand, MGs are amorphous materials with no long-range structural order; on the other hand, topological and chemical short-to-medium range order is expected to be pronounced in these alloys, due to their high atomic packing density and the varying chemical affinity between the constituent elements. The unique internal structure of MGs underlies their interesting properties, which render MGs potentially useful for various applications. While more and more glass-forming alloys have been developed in recent years, fundamental knowledge on the structural aspect of MGs remains seriously lacking. For example, how atoms pack on the short-to-medium range, how the structure differs in different MGs and changes with composition, temperature, and processing history, and more importantly, how the structure influences the properties of MGs, are still unresolved questions. In this paper, we review the tremendous efforts over the past 50 years devoted to unraveling the atomic-level structure of MGs and the structural origin of their unique behaviors. Emphasis will be placed on the progress made in recent years, including advances in structural characterization and analysis of prototypical MGs, general structural models and fundamental principles, and the correlations of thermodynamic, kinetic, and mechanical properties with the MG structures. Some widely observed property–property correlations in MGs are also examined from the structural perspective. The insights summarized are shown to shed light on many intriguing behaviors of the MG-forming alloys and expected to impact the development of MGs. Outstanding questions in this important research area will also be outlined.
Thin films in the Cr–C system with carbon content of 25–85 at.% have been deposited using non-reactive DC magnetron sputtering from elemental targets. Analyses with X-ray diffraction and transmission electron microscopy confirm that the films are completely amorphous. Also, annealing experiment show that the films had not crystallized at 500 °C. Furthermore, X-ray spectroscopy and Raman spectroscopy show that the films consist of two phases, an amorphous CrCx phase and an amorphous carbon (a-C) phase. The presence of two amorphous phases is also supported by the electrochemical analysis, which shows that oxidation of both chromium and carbon contributes to the total current in the passive region. The relative amounts of these amorphous phases influence the film properties. Typically, lower carbon content with less a-C phase leads to harder films with higher Young’s modulus and lower resistivity. The results also show that both films have lower currents in the passive region compared to the uncoated 316L steel substrate. Finally, our results were compared with literature data from both reactively and non-reactively sputtered chromium carbide films. The comparison reveals that non-reactive sputtering tend to favour the formation of amorphous films and also influence e.g. the sp2/sp3 ratio of the a-C phase.
Thin films based on transition-metal carbides exhibit many interesting physical and chemical properties making them attractive for a variety of applications. The most widely used method to produce metal carbide films with specific properties at reduced deposition temperatures is sputter deposition. A large number of papers in this field have been published during the last decades, showing that large variations in structure and properties can be obtained. This review will summarise the literature on sputter-deposited carbide films based on chemical aspects of the various elements in the films. By considering the chemical affinities (primarily towards carbon) and structural preferences of different elements, it is possible to understand trends in structure of binary transition-metal carbides and the ternary materials based on these carbides. These trends in chemical affinity and structure will also directly affect the growth process during sputter deposition. A fundamental chemical perspective of the transition-metal carbides and their alloying elements is essential to obtain control of the material structure (from the atomic level), and thereby its properties and performance. This review covers a wide range of materials: binary transition-metal carbides and their nanocomposites with amorphous carbon; the effect of alloying carbide-based materials with a third element (mainly elements from groups 3 through 14); as well as the amorphous binary and ternary materials from these elements deposited under specific conditions or at certain compositional ranges. Furthermore, the review will also emphasise important aspects regarding materials characterisation which may affect the interpretation of data such as beam-induced crystallisation and sputter-damage during surface analysis.
During the last years, several binary transition metals (TM)–Carbon systems have been explored with the aim of, first obtaining amorphous alloys in a wide range of composition, especially towards the carbon-rich concentrations and second, studying the thermal stability and the crystallization of these new materials. Sputtering has been chosen as means of elaboration to obtain the films and electron probe microanalysis was used to determine the composition. The as-sputtered amorphous state was detected by electron diffraction and/or X-ray. For each amorphous film, the thermal stability was studied by differential scanning calorimetry and the crystallization was followed by hot-stage transmission electron microscopy. The products of crystallization were identified by electron diffraction. In this paper, we present a comparison of the main results we have got on amorphous and then crystallized films belonging to the well-known Fe–C, Mn–C and Cr–C systems. The thermal stability increases from Fe–C to Cr–C systems. Depending both on the carbon content and the nature of the transition metal, various unknown carbides form from the amorphous films. We find that they are often isomorphous with interstitial compounds already existing among borides, nitrides, carbonitrides and other carbides. The emphasis is put in their structural description. It is thus demonstrated that the new structures can offer either prismatic, octahedral or both sites to the C atoms. This suggests that more than one type of local orders may exist in the amorphous state for these TM–C systems.
Mössbauer, magnetic and crystallization studies were performed in amorphous Fe1−xCx films for 0.19 ≤ × ≤ 0.49. All results revealed the existence of a characteristic carbon content xr ≅ 0.32. They are explained by assuming the existence of a two-phase domain in the amorphous state for x >xr with an amorphous FeC phase with a carbon content x ≅ xr and an amorphous carbon phase with a negligible iron content.
The crystallisation of amorphous iron-carbon alloys of atomic composition Fe75C25 and Fe70C30 has been studied using electron microscopy and the in situ formation of the iron carbide Fe-C3 has been observed. The electron diffraction patterns show spots of diffracted intensity which are indicative of a hexagonal unit cell of the type Ru7B3 (a = 6.88 A ̊) and C = 4.54 A ̊ and layers of diffuse intensity along (00.1). with 1 # 0. In each of these layers some of the diffuse intensity is localised on the hexagons, centred on the nodes of the basic structure and arranged in hexagons the sides of which lie along the 〈11.0〉 directions. These experimental results lead us to propose a structural model containing two types of ordered microdomains: one is described by the orthorhombic cell (Fruchart et al) with a volume double that of the unit cell, and the other by a hexagonal of three times this volume. This second structure can originate from the orthorhombic structure of Fe7C3 by invoking structural defects such as the antiphase {11.0}. To conform with the experimentally observed hexagonal symmetry in the reciprocal lattice, the existence of the twins {10.0} and {11.0} is also envisaged.
Density functional theory calculations have been performed on the structure and stability of Fe4C bulk and the corresponding low-index surfaces. It is found that the structure with octahedral interstitial carbon (Fe4C/oct) is more stable than that with tetrahedral interstitial carbon (Fe4C/tet). For Fe4C/oct, the most stable surface termination is the (100) surface with mixed carbon and iron (TFe/C). For Fe4C/tet, the most stable surface termination is the dramatically reconstructed (110) surface with the newly formed TFe/C surface layer.
A survey of investigations concerning 3d TM1−xCx films obtained in a large atomic carbon content x in several binary TM–C systems is presented. Sputtering was chosen as means of elaboration and electron probe microanalysis was used to determine the composition of the films. Their structural states were analyzed by X-ray and transmission electron microscopy. The glass-forming range and the glass thermal stability are described and compared. Adding carbon to the structure of TM-based films for Cr, Mn, Fe and Co causes a fully amorphization coming from the destabilization of the solid solution and extended in a large x range whereas for V and Ni, only a partly amorphization is detected in a narrow x range shifted towards higher x values. The thermal stability of the fully or partly amorphous films increases when TM moves from Ni to V. The role of the carbon–metal interaction is highlighted.
Cubic FeC nanoparticles were observed in amorphous iron carbon matrix produced by pulsed laser deposition directly onto electron microscopy grids. The observed lattice constant is close to a theoretically predicted value.
The model and theoretical understanding of the Raman spectra in disordered and amorphous carbon are given. The nature of the G and D vibration modes in graphite is analyzed in terms of the resonant excitation of π states and the long-range polarizability of π bonding. Visible Raman data on disordered, amorphous, and diamondlike carbon are classified in a three-stage model to show the factors that control the position, intensity, and widths of the G and D peaks. It is shown that the visible Raman spectra depend formally on the configuration of the sp2 sites in sp2-bonded clusters. In cases where the sp2 clustering is controlled by the sp3 fraction, such as in as-deposited tetrahedral amorphous carbon (ta-C) or hydrogenated amorphous carbon (a-C:H) films, the visible Raman parameters can be used to derive the sp3 fraction.
The electronic structure of the nanolaminated transition metal carbide Ti2AlC has been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured Ti L, C K, and Al L emission spectra are compared with calculated spectra using ab initio density-functional theory including dipole matrix elements. The detailed investigation of the electronic structure and chemical bonding provides increased understanding of the physical properties of this type of nanolaminates. Three different types of bond regions are identified: The relatively weak Ti 3d–Al 3p bond 1 eV below the Fermi level and the Ti 3d–C 2p and Ti 3d–C 2s bonds which are stronger and deeper in energy are observed around 2.5 and 10 eV below the Fermi level, respectively. A strongly modified spectral shape of the 3s final states in comparison to pure Al is detected for the intercalated Al monolayers indirectly reflecting the Ti 3d–Al 3p hybridization. The differences between the electronic and crystal structures of Ti2AlC, Ti3AlC2, and TiC are discussed in relation to the number of Al layers per Ti layer in the two former systems and the corresponding change of the unusual materials properties.
The anisotropy of the electronic structure of ternary nanolaminate V2GeC is investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependent emission spectra of V L2,3, C K, Ge M1, and Ge M2,3 in V2GeC are compared with those from monocarbide VC and pure Ge. The experimental emission spectra are interpreted with calculated spectra using ab initio density-functional theory including dipole transition matrix elements. Different types of covalent chemical bond regions are revealed: V 3d-C 2p bonding at −3.8 eV, Ge 4p-C 2p bonding at −6 eV, and Ge 4p-C 2s interaction mediated via the V 3d orbitals at −11 eV below the Fermi level. We find that the anisotropic effects are high for the 4p valence states and the shallow 3d core levels of Ge, while relatively small anisotropy is detected for the V 3d states. The macroscopic properties of the V2GeC nanolaminate result from the chemical bonds with the anisotropic pattern as shown in this work.
In this paper, the total resistivity of a thin metal film is calculated from a model in which three types of electron scattering mechanisms are simultaneously operative: an isotropic background scattering (due to the combined effects of phonons and point defects), scattering due to a distribution of planar potentials (grain boundaries), and scattering due to the external surfaces. The intrinsic or bulk resistivity is obtained by solving a Boltzmann equation in which both grain-boundary and background scattering are accounted for. The total resistivity is obtained by imposing boundary conditions due to the external surfaces (as in the Fuchs theory) on this Boltzmann equation. Interpretation of published data on grain-boundary scattering in bulk materials in terms of the calculated intrinsic resistivity, and of thin-film data in terms of the calculated total resistivity suggests that (i) the grain-boundary reflection coefficient in Al is ≈ 0.15, while it is somewhat higher in Cu; (ii) the observed thickness dependence of the resistivity in thin films is due to grain-boundary scattering as well as to the Fuchs size effect; and (iii) the common observation that single-crystal films possess lower resistivities than polycrystalline films may be accounted for by grain-boundary effects rather than by differences in the nature of surface scattering.
In this work we calculate the x-ray absorption spectra at the L2,3 edges of the early 3d elements by solving the Bethe-Salpeter equation. We focus our discussion on the origin of the observed deviation of the branching ratio between L2 and L3 edges from its statistical value. Using the absorption edge of Ca in CaF2 we show that the deviation is related to the mixing between the excitations from 2p1/2 and 2p3/2 core levels. Furthermore we find that the mixing is triggered by the exchange term of the electron-hole Hamiltonian. This term does not depend on the dielectric function, therefore such coupling is also present in metals explaining the high values of the branching ratios observed in the metals Ca and Ti. The calculated Ti L2,3 spectra of SrTiO3 and the anatase and rutile phases of TiO2 reproduce even all fine details of the experimental spectra.
Sputtered amorphous Fe1-x Cx films with 0˙19 ≤ x ≤ 0˙49 have been studied. The mean magnetic moment per iron atom and the mean Fe hyperfine field decrease, while the mean Fe isomer shift increases, with increasing x up to a carbon content xr ≈ 0˙32, while they remain almost constant above xr. The crystallization mechanisms also change dramatically at xr; only the Fe7C3 carbide is observed above xr. All the experimental results are explained by assuming the existence of a two-phase domain in the amorphous state for x ≈xr, one phase being amorphous Fe-C with a constant carbon content x≈ xr, and the second an amorphous C phase with a negligible Fe content. The carbon content xr, is close to the maximum amount of carbon one can combine with iron to form a carbide: x = 0˙33, in Fe2C.
Fe1–x
C
x
coatings were synthesized by triode magnetron sputtering of an iron target in a methane/argon atmosphere with a large range of composition (x = 0.3 to 0.6 ± 0.06). Film surfaces were characterized by grazing incidence x-ray diffraction, scanning and transmission electron microscopies, and electron energy loss spectroscopy, to study effects of the variation of the methane gas flow rate on their structural properties. The coatings were constituted of the ε-Fe3C carbide (x = 0.3 and 0.36), in which carbon atoms are in octahedral sites, and of nanocomposite structure constituted of disordered and crystalline carbide nanograins embedded in a carbon matrix made of an amorphous and poorly crystallized graphenelike material (x = 0.55 and 0.60). In situ annealing of the nanocomposite Fe0.45C0.55 coating led to the formation of carbides θ-Fe3C and Fe7C3 (with carbon atoms in prismatic sites) and C-rich cubic carbide possibly related to the τ2-Fe2C7 compound.
The microstructure, electronic structure and chemical bonding of chromium carbide thin films with different carbon contents have been investigated with high-resolution transmission electron microscopy, electron energy loss spectroscopy and soft x-ray absorption-emission spectroscopies. Most of the films can be described as amorphous nanocomposites with non-crystalline CrC(x) in an amorphous carbon matrix. At high carbon contents, graphene-like structures are formed in the amorphous carbon matrix. At 47 at.% carbon content, randomly oriented nanocrystallites are formed creating a complex microstructure of three components. The soft x-ray absorption-emission study shows additional peak structures exhibiting non-octahedral coordination and bonding.
The resistance R f of Pt and Ni films has been measured during deposition (by ion‐beam sputtering) for different deposition rates r and substrate temperatures T S (300≤T S ≤575 K). At the onset of deposition (the nucleation stage) R f varies only slowly with deposition time T and oscillations occur in R f vs T which are damped at the larger values of r,T S . Over the second stage, during which the metallic nuclei grow in size, R f decreases over many orders of magnitude and the R f versus fractional coverage x behavior is described by percolation‐type equations around a critical thickness t c . The film thickness t min (=rT min ) at which the film becomes continuous (x=1) is identified with the minimum in the Rt<sup>2</sup> vs t graph. For t≳t min the R f vs t behavior is described by surface and grain‐boundary scattering equations, the derived values of grain size are related to T S , r, and compared with transmission electron microscope observations. Postdeposition temperature cycling measurements on films deposited at T S =300 K show predominantly thermally activated conduction for t≪t 0 (t c ≪t 0 ≪t min ). R f is decreased by annealing, except in the case of Pt (t≪1 nm) and Ni (t≤1.5 nm), due to agglomeration and the formation of conducting links which also change the temperature coefficient of resistance.
A comparison among XPS and XAES spectra features of graphite (sp2 bonding), diamond (sp3 bonding), amorphous carbon (i-C) and several hydrogenated amorphous carbon samples (i-C:H) has been carried out. XAES derivative spectra of graphite, i-C and i-C:H samples show a fine structure (275–280 eV) which is assigned to KVV transitions involving pπ electrons. An estimate of the sp2/sp3 ratio on the basis of the presence of such structures in the spectra has been attempted. Values of the sp2/sp3 ratio between 0.5 and 1.5 have been found for hydrogenated samples, whereas for amorphous carbon a value of 3 has been obtained.
The L2,3 X-ray emission of Cu metal has been measured using monochromatic
synchrotron radiation. The self-absorption effect in the spectra is shown to be
very small in our experimental geometry. From the quantitative analysis of
spectra recorded at different excitation energies, the L3/L2 emission intensity
ratio and the partial Auger-width are extracted. High-energy satellite features
on the L3 emission line are separated by a subtraction procedure. The satellite
intensity is found to be slowly increasing for excitation energies between the
L3, L2 and L1 core-level thresholds due to shake-up and shake-off transitions.
As the excitation energy passes the L2 threshold, a step of rapidly increasing
satellite intensity of the L3 emission is found due to additional Coster-Kronig
processes.
The spin transition in LaCoO3 is investigated by temperature-dependent
resonant soft X-ray emission spectroscopy near the Co 2p absorption edges. This
element-specific technique is more bulk sensitive with respect to the
temperature induced spin-state of the Co3+ ions in LaCoO3 than other
high-energy spectroscopic methods. The spin transition is interpreted and
discussed with ab-initio density-functional theory within the fixed-spin moment
method, which is found to yield consistent spectral functions to the
experimental data. The spectral changes for LaCoO3 as a function of temperature
suggest a change in spin-state as the temperature is raised from 85 to 300 K
while the system remains in the same spin state as the temperature is further
increased to 510 K.
A software package for computing radial distribution functions and other pair correlation functions from electron diffraction patterns of disordered solids is presented. The package, called RDFTools, is freely available via the internet and allows rapid in situ measurements of such quantities as interatomic nearest neighbor distances, average bond angles and coordination numbers. The software runs under DigitalMicrograph™ (Pleasanton, California, Gatan), a very widely used program in transmission electron microscopy. All implemented algorithms have been designed to compute diffraction integrals and data-processing averages in a fast and efficient manner to enable quick processing of publication ready, quantitative pair distribution function information. In the development of RDFTools, significant attention was paid to provide a robust and intuitive user-interface for deriving reliable semiquantitative information. For example, RDFTools enables accurate pair separation distances to be revealed upon immediate interrogation at the microscope; even for potentially thick specimens and/or regions of unknown elemental composition.
The electronic structure of nanocrystalline (nc-) TiC/amorphous C nanocomposites has been investigated bysoft x-ray absorption and emission spectroscopy. The measured spectra at the Ti 2p and C 1s thresholds of thenanocomposites are compared to those of Ti metal and amorphous C. The corresponding intensities of theelectronic states for the valence and conduction bands in the nanocomposites are shown to strongly depend onthe TiC carbide grain size. An increased charge transfer between the Ti 3d-eg states and the C 2p states hasbeen identified as the grain size decreases, causing an increased ionicity of the TiC nanocrystallites. It issuggested that the charge transfer occurs at the interface between the nanocrystalline-TiC and the amorphous-Cmatrix and represents an interface bonding which may be essential for the understanding of the properties ofnc-TiC/amorphous C and similar nanocomposites.
The L3- to L2-intensity ratios of the valence-band x-ray-emission spectra of 3d transition metals are corrected for effects of Coster-Kronig transitions. A quantity RE is obtained which is the x-ray-emission analog of the ``white-line'' L3- to L2-intensity ratio measured in x-ray absorption. The values of RE so obtained do not show evidence for a dependence on magnetic moment that is observed in the corresponding intensity ratios in x-ray absorption. A comparison is made between the values of RE obtained here, and those of a related quantity determined with use of appearance-potential spectroscopy. We find evidence supporting a spin-orbit-splitting model for the L3- to L2-intensity ratio of Ni metal in x-ray absorption.
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