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Electrochemical deposition regimes and critical influence of organic additives on the structure of Bifilms
... The efficiency of electrochemical deposition significantly depends on the chemical composition of the electrolyte. A large number of studies have been devoted to the electrodeposition of Bi films from silicate, pyrophosphate, nitrate, citric, stearic, sulfate, lactate, and other electrolytes [29][30][31][32][33]. Besides, for a specific electrolyte composition, organic additives provide additional control over the film structure [34,35]. ...
... A well-known nitrate electrolyte can allow the electrodeposition of uniform coatings in specific conditions, but the deposition is limited in speed down to 12 µm/h [30,39]. In this work, we used a recently developed [36,40] perchlorate electrolyte, which is more suitable for practical applications due to a higher growth speed (up to 200 µm/h) and comparable quality of deposits [34]. ...
... The change in dominating texture of Bi film synthesized under j = 70.0 mA/cm 2 probably is attributed to different adsorption of atomic hydrogen and beginning of electrochemical reaction of hydrogen ions reduction: such a high cathode current density causes the reduction of Bi 3+ in the diffusion-limited mode [34]. ...
The study is devoted to the electronic properties and structure of bismuth films obtained by electrodeposition from high-speed perchlorate electrolyte. Polycrystalline samples were synthesized in acidic perchlorate electrolyte under the (0.18 – 70.0) mA/cm² cathode current density and annealed at 265 oC in the He gas atmosphere. The structure, microstructure and electron properties of Bi films were characterized using X-Ray diffraction analysis, scanning electron microscopy, and electron backscattered diffraction. Electrical resistance, magnetoresistance, and Hall coefficient were studied at the 5 – 300 K temperature range under magnetic field up to 8 T. A specific and unexpected behavior has been found concerning the average size and shape of Bi grains with increasing of the current density: the increase in deposition current density up to 70.0 mA/cm² contributes to Bi films formation with more isotropic and reduced average grains size. Samples synthesized under 0.18 mA/cm² current density after annealing showed electronic properties, including magnetoresistance, similar to those of flawless single-crystals. The differences in the electronic characteristics of Bi films electrodeposited under different currents and electrolyte composition were explained by changes in electronic mobility due to scattering on grain boundaries.
... The cheapest and fastest technique is melt spinning [39], but the film properties can change with time [43]. Therefore, electrodeposition combines both low cost and the ability to cover surfaces of complex shapes with a high deposition rate [44][45][46][47]. ...
... A well-known and widely used nitrate electrolyte contributes to uniform films deposition but with a low deposition rate (0.012 mm/h) [49,53,54]. In the present research, we used the perchlorate electrolyte developed in our previous work [45], which is more appropriate for practical applications because of its high speed of growth up to 0.2 mm/h and good deposit quality. The microstructure of samples can be engineered by the possibility of adjusting the synthesis conditions, i.e., composition, temperature, pH of the electrolyte, electrodeposition regimes (galvano-or potentiostatic, pulse, reverse, etc.), or their combinations. ...
... The semiconducting photocatalyst has appeared as useful automation because of diverse favors counting modest, low energy depletion, non-toxicity, and the ability to efficiently use UV and/or visible light productively [6][7][8]. Among the abundant and various multifunctional semiconductor photocatalysts [9,10], ZnO sticks out as the most encouraging matter due to its high photosensitivity, non-toxic/stable nature, low cost, competing for photocatalytic performance, and ability to handle amply accessible sunlight as well as extraordinary physical/chemical properties [11]. ...
... The interspace between the lamp and the glass beaker was kept at 10 cm for all cases. The pH of the mixture was regulated by NaOH to 10. In prior to the irradiation, the total mixture containing MB solution and photocatalysts was thoroughly mixed by a magnetic stirrer and maintained in dark conditions for 30 min, to get adsorption-desorption equilibrium. ...
Herein, to investigate the photodegradation of methylene blue (MB) under UV light irradiation and the photocatalytic activity of chemically derived ZnO, ZnO: Co 5% nano rod-like thin films and ZnO/ZnO: Co 5% homojunction, the role of grain size and microstrain on their structural, optical, electrical and photocatalytic properties were studied. Hexagonal wurtzite structure, the doping of Co²⁺ into ZnO host lattice, reduced crystallite/grain size, and enhanced microstrain have been confirmed by structural and morphological analysis. The presence and the atomic content of Zn/Zn²⁺, Co/Co²⁺, O/O²⁻ elements, and ions have been confirmed by EDS and XPS measurements. The n/p-type conductivity in nano rod-like film and p-n bilayers have been verified by Hall and I-V characterizations. The PL analysis showed that the decreased luminescence intensity and the formation of defect/trapping centers by Co²⁺ doping and formation of p-n homojunction as crystallite/grain size decreased while microstrain increased. With 5% Co-doping and the emergence of p-n homojunction, the photocatalytic efficiency (ղ %) was reduced compared with parent ZnO photocatalyst, while the crystallite/grain size decreases and microstrain enhances. The decreased ղ % was attributed to the reduced crystallite/grain size, increment of microstrain, and the generation of defects/trapping centers via 5% Co-doing and formation of ZnO/ZnO:Co 5% nano rod-like homojunction. These results demonstrate that the fabrication of p-n homojunction will not always result in an enhanced ղ % even if it puts down the recombination of light-induced charge transporters.
... Following neutralization, the fibers are washed again with distilled water and left to air-dry at room temperature for 2 days. Fig. 2 represents the alkaline chemical treatment of the palm fruit fiber to reduce impurities [28]. ...
The study focuses on Palm fruit Fibers (PF) extracted from the palmyra palm tree (Borassus flabellifer) treated with 5 % alkali solution (NaOH). This treatment eliminates impurities from the fiber surface and enhances bonding with the epoxy matrix. Epoxy composites, reinforced with PF/nanofillers (h-BN, Al2O3 and MWCNT), are developed by using the box Behnken method (BBD) and dielectric constant is investigated under high-frequency and electrical field conditions. Dielectric constants (K) of the nanocomposites are determined using various capacitor terminal setups. The electrical properties of the Epoxy/PF nanocomposite, based on fiber content (Wt. %), fiber mesh size (μm) and nanofillers are evaluated using response surface methodology (RSM). Models, predicting nanocomposite dielectric constants, are established, fitting experimental values closely with R² nearing 1 and residuals adhering to a normal probability plot. The optimized dielectric constant of 1.05 is achieved at 3 wt% palm fiber content, 150 μm fiber mesh size and 1 wt% nano h-BN.
... Among them, doping of EMD electrodes with BaCO 3 [12], Ag 4 Bi 2 O 5 [13], BaBiO 3 [14], NaBiO 3 [15], Bi 2 O 3 [16][17][18], PbO [19], CeO [20], MgO [21], TiB 2 [22], CuSO 4 [23], TiS 2 [24], Al(NO 3 ) 3 [25], Ni(OH) 2 [26], Ti(OC 4 H 9 ) 4 [27,28] and others had been shown to be effective in improving the discharging performance of manganese dioxide electrodes. Many studies had also shown that Bi ions had good electrochemical performance [29][30][31], and doping Bi ions in EMD electrodes could cause a twoelectron discharge, thus greatly improving the discharge specific capacity of the EMD electrodes. ...
To improve the rechargeability and conductivity of electrolytic manganese dioxide (EMD) electrodes in rechargeable alkaline manganese batteries. In this work, ultrafine Ag3BiO3 powders were prepared by a novel hydrothermal in situ dispersion method and doped into EMD electrodes by physical grinding. The effects of hydrothermal time, hydrothermal temperature and cetyltriethylammnonium bromide (CTAB) in-situ dispersant on the phase composition and micromorphology of the prepared powders were investigated, and the synthesis process of ultrafine Ag3BiO3 was recommended. Then, the effect of Ag3BiO3 doping amounts on the electrochemical performance of EMD electrodes was further investigated, and the modification mechanism was deeply discussed. The results showed that well-dispersed spherical Ag3BiO3 of about 100 nm could be synthesized at a molar ratio of AgNO3:Bi(NO3)3 of 2:1, with 3 wt% CTAB as in situ dispersant, and a hydrothermal time of 12 h and a hydrothermal temperature of 120 °C. The discharge specific capacities of the EMD electrode doped with 10 wt% Ag3BiO3 were reached 519.9 mAh/g and 98.3 mAh/g after initial and 50 cycles, respectively, which were 323.5%, 72.15% and 108.8%, 18.3% higher than those of the pure EMD electrode and the EMD electrode doped with 10 wt% Bi2O3, respectively. The doping of Ag3BiO3 could increase the discharge voltage of the EMD electrode and improve its redox process. Besides, the Bi³⁺ ions could form complexes with Mn²⁺ and Mn³⁺, inhibit the disproportionation reaction, reduce the production of electrochemically inert products Mn3O4, and also stimulate the second electron discharge of the EMD electrode, which played an important role in lattice stabilisation. Furthermore, the reduction of Ag⁺ to Ag during charging and discharging could increase the conductivity of the EMD electrode and enhance the modification effect of Bi³⁺. Therefore, the doping of Ag3BiO3 in the EMD electrode could significantly increase the discharge specific capacity and rechargeability. This is an important contribution to the modification mechanism of Ag3BiO3 doped EMD cathode for rechargeable alkaline manganese batteries.
... μm thick, while the Zn-10ZnO-10MgO coating was 223.5 μm thick. Although the thicknesses of Zn-10ZnO-10MgO-2UPP and Zn-10ZnO-10MgO-4UPP coatings are comparatively lower; however, these coating thicknesses were still observed to be comparable to most coating thicknesses in the literature [31]. While the thickness of coatings could sometimes affect their thermal stability, mechanical properties, and interfacial structure, the most stable coating might not be the thickest coating [32]. ...
The numerous industrial application of mild steel despite its susceptibility to degradation on exposure to the environment has called for the continuous search for materials that can protect its surface from contaminants which could affect its inherent properties. This paper therefore examined the corrosion-resistance, hardness, and microstructure properties of unripe plantain peel (UPP) nanoparticle-reinforced Zn–ZnO–MgO composite coatings deposited on the surface of mild steel (AISI 1015 Carbon Steel). The corrosion properties of the coated steel samples were investigated using the potentiodynamic polarization technique, utilizing simulated seawater (3.65% NaCl solution) as the test medium. The hardness of the coated steel samples was studied using the Brinell hardness method, while the microstructure properties were investigated using XRD and SEM/EDS. The as-received mild steel sample was observed to exhibit a hardness value and corrosion rate of 136.8 kgf/mm2 and 8.6272 mm/year, respectively, while the Zn–10ZnO–10MgO-coated mild steel sample exhibited a hardness value and corrosion rate of 246.53 and 1.7698 mm/year, respectively. Relative to the other samples, the Zn–10ZnO–10MgO–6UPP-coated mild steel (sample coated with 10 g/L of ZnO, 10 g/L of MgO and 6 g/L of UPP) exhibited a highest hardness value and lowest corrosion rate of 254.77 kgf/mm2 and 0.6645 mm/year, respectively. These corrosion rate and hardness values of the Zn–10ZnO–10MgO–6UPP-coated mild steel sample showed that the unripe plantain peel nanoparticles further enhanced the strengthening and passivating ability of Zn–ZnO–MgO–UPP coating. The SEM micrographs revealed that the Zn–ZnO–MgO–UPP coating possessed a more refined microstructure relative to the Zn–ZnO–MgO coating, signifying the grain refining ability of the unripe plantain peel nanoparticles. The EDS additionally indicated the occurrence of crucial and dispersion strengthening elements in the coatings. The XRD profile of the coatings exhibited high intensities, which signified that the coatings have high stability and good texture with microstructural and chemical homogeneity.
... The polar hydroxyl groups of the polymer chain form intermolecular and intramolecular hydrogen bonds with transition metal ions. Therefore, PVA-added Tellurium electrolyte might produce microstructures with uniform crystal grain [47]. Fig. 5 shows the morphology results of Tellurium films with PVA additives. ...
Thin film technologies in terms of preparation and fabrication are of great importance in various fields, such as integrated circuits (IC), LCD monitors, photovoltaics, solar cells and sensors. Tellurium, as a narrow bandgap semiconductor, has attracted much attention due to its rich optical and electrical properties. Taking advantage of these properties, its films have been explored in recent years as saturable absorbers, gas sensors, and thermoelectric materials. However, it is challenging to control the growth of the specific morphology of tellurium films. In this work, based on the electrodeposition challenge, we systematically investigated the electrodeposition process of tellurium films. It was found that the CV curves of electrodeposited tellurium shift in the positive direction with increasing deposition time. In addition, the stabilized potential was determined based on the stable deposition peak potential after a certain deposition time. Moreover, three different additives, namely polyvinyl alcohol (PVA), tartaric acid (TA) and sodium lignosulfonate (SLS), were adopted to manipulate the morphology of as-deposited tellurium films. A rational route to deposit tellurium films with various morphologies have been established.
... A spray jet tends to work mainly with crack arresters, thus improving coating toughness [148]. The Effect on Energy Efficiency of Yttria-Stabilized Zirconia non Brass, Copper and Hardened Steel Nozzle in Additive Manufacturing was analyzed, which is the recent advancement of the application of TBCs in additive manufacturing [149][150][151][152]. Other methods can also be used, such as electrochemical deposition regimes, to develop thin films [153,154]. ...
Thermal barrier coating is critical for thermal insulation technology, making the underlying base metal capable of operating at a melting temperature of 1150 °C. By increasing the temperature of incoming gases, engineers can improve the thermal and mechanical performance of gas turbine blades and the piston cylinder arrangement. Recent developments in the field of thermal barrier coatings (TBCs) have made this material suitable for use in a variety of fields, including the aerospace and diesel engine industries. Changes in the turbine blade microstructure brought on by its operating environment determine how long and reliable it will be. In addition, the effectiveness of multi-layer, composite and functionally graded coatings depends heavily on the deposition procedures used to create them. This research aims to clarify the connection between workplace conditions, coating morphology and application methods. This article presents a high-level overview of the many coating processes and design procedures employed for TBCs to enhance the coating’s surface quality. To that end, this review is primarily concerned with the cultivation, processing and characteristics of engineered TBCs that have aided in the creation of specialized coatings for use in industrial settings.
... In this case the following can be noted: sufficiently high mechanical strength and thermal conductivity [45], high electrochemical resistance [13], resistant to the high temperatures [46]. Moreover, as already mentioned, its geometric characteristics can be easily adjusted by synthesis conditions' changing [47,48]. Such templates are considered as the most relevant for integration into microelectronic technologies [1,[49][50][51]. ...
The results of studies on the wettability properties and preparation of porous anodic alumina (PAA) membranes with a 3.3 ± 0.2 μm thickness and a variety of pore sizes are presented in this article. The wettability feature results, as well as the fabrication processing characteristics and morphology, are presented. The microstructure effect of these surfaces on wettability properties is analyzed in comparison to outer PAA surfaces. The interfacial contact angle was measured for amorphous PAA membranes as-fabricated and after a modification technique (pore widening), with pore sizes ranging from 20 to 130 nm. Different surface morphologies of such alumina can be obtained by adjusting synthesis conditions, which allows the surface properties to change from hydrophilic (contact angle is approximately 13°) to hydrophobic (contact angle is 100°). This research could propose a new method for designing functional surfaces with tunable wettability. The potential applications of ordinary alumina as multifunctional films are demonstrated.
... Single crystals, especially from metal oxides, received enormous attention worldwide in the past few decades due to their distinguished optoelectronic and gas sensing properties over a large scale [1][2][3][4]. Single crystals of zinc oxide, a wide and direct bandgap (~3.37 eV) semiconductor, gained extra interest among other counterparts due to its unique luminescence feature at 378 nm wavelength and large exciton binding energy (60 meV) [5][6][7]. The intense near band edge emission and the large exciton binding energy make ZnO a promising candidate for optoelectronic devices such as laser diodes [8], light-emitting diodes [9], and photodetectors [10]. ...
Temperature-, excitation wavelength-, and excitation power-dependent photoluminescence (PL) spectroscopy have been utilized to investigate the orientation-modulated near band edge emission (NBE) and deep level emission (DLE) of ZnO single crystals (SCs). The near-band-edge emission of ZnO SC with <0001> orientation exhibits strong and sharp emission intensity with suppressed deep level defects (mostly caused by oxygen vacancies Vo). Furthermore, Raman analysis reveals that <0001> orientation has dominant E2 (high) and E2 (low) modes, indicating that this direction has better crystallinity. At low temperature, the neutral donor-to-bound exciton (DoX) transition dominates, regardless of the orientation, according to the temperature-dependent PL spectra. Moreover, free-exciton (FX) transition emerges at higher temperatures in all orientations. The PL intensity dependence on the excitation power has been described in terms of power-law (I~Lα). Our results demonstrate that the α for <0001>, <1120>, and <1010> is (1.148), (1.180), and (1.184) respectively. In short, the comprehensive PL analysis suggests that DoX transitions are dominant in the NBE region, whereas oxygen vacancies (Vo) are the dominant deep levels in ZnO. In addition, the <0001> orientation contains fewer Vo-related defects with intense excitonic emission in the near band edge region than other counterparts, even at high temperature (~543 K). These results indicate that <0001> growth direction is favorable for fabricating ZnO-based highly efficient optoelectronic devices.
... While Zn-10ZnO-10MgO-6UPP coating was observed to be 224 µm thick, Zn-10ZnO-10MgO coating was 223.5 µm thick. Although the thicknesses of Zn-10ZnO-10MgO-2UPP and Zn-10ZnO-10MgO-4UPP coatings are comparatively lower, however, these coating thicknesses were still observed to be comparable to most coating thicknesses in literature [31]. While the thickness of coatings could sometimes affect its thermal stability, mechanical properties and interfacial structure the most stable coating might not be the thickest coating [32]. ...
The numerous industrial application of mild steel despite its susceptibility to degradation on exposure to the environment has called for the continuous search for materials that can protect its surface from contaminants which could affect its inherent properties. This paper therefore examined the corrosion-resistance, hardness and microstructure properties of unripe plantain peel (UPP) nanoparticles reinforced Zn-ZnO-MgO composite coatings deposited on the surface of mild steel. The corrosion properties of the coated steel samples were investigated using the potentiodynamic polarization technique, utilizing simulated seawater (3.65% NaCl solution) as the test medium. The hardness of the coated steel samples was studied using the Brinell hardness method, while the microstructure properties were investigated using XRD and SEM/EDS. The as-received mild steel sample was observed to exhibit a hardness value and corrosion rate of 136.8 kgf/mm ² and 8.6272 mm/year, respectively, while the Zn-10ZnO-10MgO coated mild steel sample exhibited a hardness value and corrosion rate of 246.5 and 1.7698 mm/year, respectively. Relative to the other samples, the Zn-10ZnO-10MgO-6UPP coated mild steel (sample coated with 10 g/L of ZnO, 10 g/L of MgO and 6 g/L of UPP) exhibited a highest hardness value and lowest corrosion rate of 254.8 kgf/mm ² and 0.6645 mm/year, respectively. These corrosion rate and hardness values of the Zn-10ZnO-10MgO-6UPP coated mild steel sample showed that the unripe plantain peel nanoparticles further enhanced the strengthening and passivating ability of Zn-ZnO-MgO-UPP coating. The SEM micrographs revealed that the Zn-ZnO-MgO-UPP coating possessed a more refined microstructure relative to the Zn-ZnO-MgO coating, signifying the grain refining ability of the unripe plantain peel nanoparticles. The EDS additionally indicated the occurrence of crucial and dispersion strengthening elements in the coatings. The XRD profile of the coatings exhibited high intensities, which signified that the coatings have high stability, good texture with microstructural and chemical homogeneity.
... For example, Nb-doped SnO 2 thin films possess stable cycling life of 200 cycles at 0.5C with a discharge specific capacity about 982.7 mA h g -1 [38]; Fe-doped Li 0.5 La 0.5 TiO 3 with a nano-sphere structure is a novel n-type H 2 S sensing material, which has ultra-fast response/recovery properties [39]. Numerous techniques for fabricating thin films of metal-containing materials are successfully developed so far [40][41][42][43]. Single-layer MoS 2 , which can be easily fabricated by means of the exfoliation technique [44][45][46][47][48][49], is a typical promising film material possessing many extraordinary properties such as high electrical conductivity [50][51][52], superior mechanical strength [53,54], and excellent thermal stability [55,56], that lead to important applications as field-effect transistors [57][58][59][60], sensors [61][62][63], and phototransistors [64,65]. ...
The transport property of a four-terminal MoS2NR/V7(Bz)8 device is computed within the framework of density functional theory combined with the nonequilibrium Green’s function (NEGF) technique. This device is constructed by a MoS2 nanoribbon (MoS2NR) as the source-to-drain channel and a spin-polarized V7(Bz)8 nanowire grafted on the MoS2NR surface as the double gate channel, where the four terminals are all connected to a semi-infinite one-dimensional (1D) Au lead. The transport characteristic is explored by investigating the conductance, currents, local density of states (LDOS), and scattering states. The currents of different leads are dissimilar due to the complex interplay between the four terminals that is otherwise not present in a two-terminal setup. The most interesting feature we articulate is that the induced promising properties including negative differential resistance (NDR) behavior, input/output current switching, as well as spin-polarized lead currents can be fine-tuned by the magnitude of either source bias or gate bias. These features can be utilized in designing multi-terminal nanoelectronic devices.
Graphical abstract
... As the VO content increases in the growth solutions of the SILAR process, the energy of nucleus formation decreases. Therefore, the nucleus density increases, and the crystallite size of the ZnO samples decreases [48]. ...
In the present study, nanostructured zinc oxide (ZnO) films have been successfully synthesized using fruit extract of Viburnum opulus L. (VO) on glass slides by successive ionic layer adsorption and reaction (SILAR) procedure. The impact of VO concentrations on the structural, morphological, optical, electrical, and antibacterial attributes of ZnO films has been investigated in detail. The samples' XRD patterns present a hexagonal crystal structure with a preferential orientation along the (002) plane. The crystallite size values of ZnO samples were found to be in the ranges from 14.88 to 9.23 nm. The supplementation of VO to the synthesis solution remarkably affected the surface morphological features of the ZnO films. The optical results demonstrated that band gap energy values of the ZnO films at room temperature were decreased from 3.20 to 3.07 eV as a function of VO content in the bath solution. The films' electrical properties were determined by impedance analysis in the frequency range of 20Hz -1 MHz. Impedance-frequency measurements showed VO insertion to ZnO thin films cause an increase in impedance value at the low frequencies. Cole-Cole plots with a single semi-circle confirmed the contribution of grain and grain boundary for the electrical conduction process. The agar disk diffusion method was used to test the antibacterial properties of ZnO/VO inserted ZnO and inhibition zones were measured. VO inserted ZnO showed a stronger inhibitory effect on gram-positive bacteria Staphylococcus aureus (ATCC 25923) and gram-negative bacteria Escherichia coli (ATCC 35218) than ampicillin antibiotic used as a control group. In line with the promising bactericidal results of a new generation, VO inserted ZnO, the nanostructured product with this study, it can also be applied in multidrug-resistant clinical isolates obtained from patients.
... Various materials including graphene family, transition metal dichalcogenides, metal selenides and sulfides, metal carbides, metal halides, oxide compounds have been synthesized or revisited as 2D layers, continuously expanding 2D materials library [3][4][5][6][7][8][9][10][11][12][13][14]. There are many methods to fabricate monolayer 2D atomic crystal materials, including mechanical stripping, electrochemical deposition, chemical vapor deposition and molecular beam epitaxy (MBE) [15][16][17][18][19][20]. Comparing with other methods, MBE method is more competitive because of its advantages in epitaxial thickness and doping control at single atom level [21][22][23][24][25][26][27][28][29][30]. ...
CuSe monolayer possesses intrinsically patterned triangular nanopores with uniform
size and can serve as a template for selective adsorptions for molecules and nanoclusters.
Here, we prepare the CuSe monolayer on Cu(111) substrate by molecular beam epitaxy
method and characterize CuSe monolayer in detail by bond-resolved scanning
tunneling microscopy and non-contact atomic force microscopy. The results further
confirm the honeycomb feature and triangular nanopores existence of CuSe monolayer.
In addition, scanning tunneling spectroscopy measurements reveal the semiconducting
features of CuSe monolayer with a band gap of 2.40 eV. This work helps to understand
the structure and electronic properties of those intrinsically patterned two-dimensional
materials.
The present work consists of the simulation of the interaction of a beam of Kr+ ions with a solid iron target by the software SRIM (Stopping and Range of Ions In Matter). Our goal is to calculate different parameters related to sputtering and ion implantation in a target, such as the spatial distribution of implanted ions, the distributions of electronic and nuclear energy losses as a function of penetration depth and sputtering efficiency, as well as the damage created inside the target. The sputter induced photon spectroscopy technique was used to study the luminescence spectra of the species sputtered from Iron powder, during 5 keV Kr+ ions bombardment in vacuum better than 107 torr. The optical spectra recorded between 350 and 470 nm exhibit discrete lines which are attributed to neutral excited atoms of Iron (Fe). The experiments are also performed under 105 torr ultra-pure oxygen partial pressure. To ensure the maximum efficiency of molecular modification process, energy of irradiation was decided by using of SRIM software. Based on SRIM simulation of Iron ions interaction with Krypton, the areas on which effect of high energy ions will maximum were predicted. A comparative analysis of molecular before and after irradiation was carried out by scanning electron microscopy. The maximum change in Krypton morphology, in the form of destruction of walls, was appeared at a distance of about μm from the start point of Fe+ ions track inside the molecular. A substantiation of reason of wall degradation in this area was proposed.
Spinel Li4Ti5O12 (LTO) is a potential anode material for innovative high-power lithium-ion batteries (LIBs) because of its ''zero strain'' features during quick charging/discharging, extended cycle life, and elevated rate capability. However, LTO has limited application due to its poor ionic/electronic conductivity and slow ionic diffusion coefficient. In this work, LTO/polyether sulfone (PES) composite is synthesized via pulsed laser ablation in liquid media technique based on an infrared Nd:YAG nanosecond laser. The influences of laser ablation power were used to vary the particle sizes of the generated LTO nanoparticles on the formation of the LTO/PES structure, followed by the electrochemical performances of LTO. Various methods were used to investigate the composite's structural, optical, and morphological properties. The interactions between the polymer and nanoparticles, as well as the fine dispersion of NPs, were evident in the optical tests, which showed that the absorbance greatly improved and the energy band gap decreased. Also, the morphological images display the cubic shape of pure LTO NPs with varying particle sizes between 5 and 26 nm as the laser power changes. Furthermore, from XRD characterization, the intensity of this crystalline peak of PES decreases as a function of LTO wt. % increase without appearing of any other impurities. After that, the electrochemical performances were tested for all prepared samples, which showed that the as-prepared composite structure with a lower particle size exhibits excellent electrochemical performances. This result demonstrates that providing surface defects by forming Ti3+/Ti4+ pairs and oxygen vacancies in LTO is a successful method for increasing ion/electron mobility. This method can be applied to improve the battery efficiency of other substances with low ionic conductivities in the developed batteries.
In the present study, Eu ³⁺ -doped zinc fluoro-telluroborate transparent glasses were prepared by the conventional melt−quench technique. Their density and refractive index values were measured, and using these values, different physical parameters (number density, oxygen packing density, no. of bonds/vol, etc.) were calculated and analysed. The XRD pattern displayed a disordered atomic arrangement in the glass network. The EDS spectra proved the purity of the samples exhibiting only those elements used during the synthesis. The good solubility of Eu ³⁺ ions in zinc fluoro-telluroborate glasses was analysed through fine absorption peaks in the UV−Vis−NIR range. The absorption intensities increased in all samples up to 3.0 mol% of Eu ³⁺ -doping concentration. The stabilities of the samples, such as ∆ T ~ (144–156) °C and H r ~ 2.33–4.00, calculated using characteristic temperatures ( T g , T x , T c , T m ) from DSC studies exhibited their promising candidature in a high-temperature environment. The Eu7 (Eu ³⁺ with 3.0 mol%) glass confirmed better attenuation properties (LAC, Z eff , HVL, MFP) compared to other composition (0–2.5 mol%) glasses.
This article deals with the effects of current modes on saccharin adsorption during NiFe electrodeposition, and, as a consequence, its effect on chemical composition, crystal structure, and microstructure of deposited films. For this purpose, we obtained NiFe films using direct, pulse, and pulse-reverse electrodeposition modes. The deposit composition, crystal structure, and surface microstructure are studied. Direct current (DC) and pulse current (PC) films have a smooth surface, while a pulse-reverse current (PRC) film surface is covered by a volumetric cauliflower-like microstructure. The mechanism of the film surface development was considered from the point of view of saccharin adsorption and its action as an inhibitor of vertical grain growth during different current modes. During the DC and PC modes, saccharin is freely adsorbed on the growth centers and restrains their vertical growth. Whereas in the case of the PRC electrodeposition, saccharin adsorbs during cathodic pulses and desorbs during anodic pulses. Therefore, its inhibiting action decreases, vertical grain growth rises, and a rougher surface develops.
Polymer composite (PC) films comprising polyvinyl alcohol (PVA) and poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with manganese dioxide (MnO2) as filler were prepared by simple solution casting method. The structural confirmation of PCs was investigated by Fourier transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. The morphological and thermal properties were analyzed using scanning electron microscope (SEM) and thermogravimetric analysis (TGA). Under the frequency range, 50 Hz to 20 MHz, and temperature from 40 to 150 °C, the dielectric properties and Q-factor values for the as-synthesized PC films were investigated by an impedance analyzer. PVA/PEDOT:PSS/MnO2 having wt% 50:35:15 revealed high dielectric constant (ε) at 1949 and low dielectric loss(tanδ) at 8.13. The obtained results suggest that the titled PC films are effective materials for energy storage applications.
Reasonable construction of multi-pore heterogeneous structures and enhancement of synergistic interaction between metal ions are important means to improve the performance of supercapacitors. This work selected metal organic frameworks (MOF) as the sacrificial template, and Se-doped needle-like nanosphere heterostructures Se-CoSe2@ZnSe were successfully prepared by in situ growth and selenization treatment. The specific capacity of the Se-CoSe2@ZnSe-5 (CZS-5) electrode is up to 2469.12 F g⁻¹ at 1 A g⁻¹, and the capacity retention rate of 3000 cycles at a current density of 10 A g⁻¹ is 85.39%. The CZS-5//AC hybrid supercapacitor has a high power density of 1280.00 W kg⁻¹ at an energy density of 68.88 Wh kg⁻¹. The excellent electrochemical properties are attributed to the construction of Se-CoSe2@ZnSe heterostructure of needle-shaped nanospheres enhances the synergy between Zn and Co ions; the doping of selenium effectively improves the conductivity of the electrode material; selenium vacancies produced during selenization increase the activity of the active site. In addition, the density functional theory (DFT) calculation shows that Se-CoSe2@ZnSe-5 has higher density of states (DOS) near the Fermi energy level, which provides additional theoretical support for the improvement of electrochemical performance.
The heterostructure of bismuth (Bi) and Bi2Sr2CaCu2O8+δ (Bi2212) is considered as a potential type of quantum material. The strain-engineering controls the band structure in the composite films, which is applied in the high-temperature quantum spin Hall materials. In this work, Bi/Bi2212 composite film is synthesized using a two-step method to reduce the fabrication cost. The microstructure and transport properties of the composite films are characterized and analyzed. Experimental results demonstrate that the Bi/Bi2212 composite film obtains the high-quality crystallinity and excellent connectivity. The transport property measurement results show that the band structure changes due to the coupled effects of the strain and electric field. The origin is the compensation between the electron and hole charge carriers. The above band gap change leads to a shift in the metal-semiconductor transition temperature. Functionally coupled composite films exhibit new properties in magnetoresistance devices.
A comprehensive study of the present work aimed to investigate the radiation shielding features for W–Cu composites materials with high density. Isostatic hot pressing technique was applied to obtain W85 wt%Cu15 wt% and W75 wt%Cu25 wt% composites with various thickness (0.6, 0.9, 1.2, 1.5 and 2.7 cm). Composites were the pollycristalline samples with well packed microstructure. The statistical grain size distribution performed that the size of an agrolemerated copper grains increases with the Cu content rising. X-ray diffraction (XRD) analysis showed that the main spectrum lines of the composites are corresponded to the bcc phase of tungsten and fcc phase of copper. The linear attenuation coefficient (LAC) was detected experimentally using a NaI detector at various incoming photon energy. The highest values of LAC are found 2.11 and 4.33 cm⁻¹ for W75 wt%Cu25 wt% and W85 wt%Cu15 wt%, respectively, at low energy 0.266 MeV while the lowest values (0.44 and 0.48 cm⁻¹ for W75 wt%Cu25 wt% and W85 wt%Cu15 wt%, respectively) are observed at high energy 1.25 MeV. From the obtained results, it can deduce the discussed W–Cu composites are suitable to be used in several applications of radiation protection.
Active metals, such as platinum and palladium, were doped in TiZrHfMoNb high-entropy alloy to tune its electronic structure. The electronic structure, activation, and kinetic properties were experimentally investigated. The results indicate that electron transfer occurred between the active metal atoms and other metal atoms after platinum or palladium doping, and that the oxide on the surface was destabilized by active metal doping due to improved activation performance. Therefore, TiZrHfMoNbPt0.0025 could reach a maximum hydrogen storage capacity of 1.749 wt% (1.80 H/M) at around 100 s on the first absorption curve. The electron transfer process is believed to aid in optimizing the electron density of interstitial sites, allowing additional interstitial sites to accommodate additional hydrogen atoms. The presented results provide new insights into the hydrogen storage properties of high-entropy alloys, and it is expected that hydrogen storage capacity can be increased by tuning the concentration and type of doping elements.
In this work, pre-lithiated VO2(B) nanobelts are synthesized by a two-step hydrothermal method. After pre-lithiation, the VO2(B) nanobelts exhibit a uniformly dispersed morphology with a large specific surface area. Compared to pure VO2(B) nanobelts, the pre-lithiated VO2(B) nanobelts show much better electrochemical performance in terms of cycling stability and high-rate capability. The lithium-ion diffusivity in the pre-lithiated VO2(B) nanobelts is enhanced due to enlargement of the crystal lattice after pre-lithiation. The pre-lithiated VO2(B) nanobelt cathode delivers an initial specific capacity of 264 mAh g–1 at 0.1 A g–1 with a capacity retention of 81.6% after 100 cycles, which is superior to that obtained for pure VO2(B) under the same conditions (initial capacity of 221.5 mAh g–1 and capacity retention of 63.3%). Moreover, the pre-lithiated VO2(B) nanobelt electrode exhibits outstanding long-term cycling stability (capacity retention of 87.2% after 800 cycles at 1000 mA g–1). These results indicate that pre-lithiated VO2(B) nanobelts have great potential to be applied as an advanced cathode material for next-generation lithium-ion batteries.
Hierarchical ZnO/CuO nanorods were grown on RF sputtered ZnO seed layer via the hydrothermal method and their characteristics are analyzed by high resolution scanning electron microscope (HRSEM) and X-ray diffraction (XRD) techniques to confirm the elemental composition, crystal structure, and morphology of the sensing material. The sensing performance of the carbon dioxide sensor was evaluated at room temperature under the various concentration of carbon dioxide gas from 150 ppm to 1000 ppm. The result obtained shows that the sensor yields a high response of 9.7% for 1000 ppm of carbon dioxide gas with fast response and recovery time varied in the range of 1 min to 4 min. The above results indicate the accomplishment of room temperature sensing with good reversibility and repeatability compared to conventional previously reported high temperature carbon dioxide sensors.
In this work, a two-nearest-neighbor structure model, named the 3-1 model, of the face-centered cubic (FCC) solid solution alloy is found based on the Cowley short-range order parameter and the Friedel’s periodic spherical oscillated (FPSO) model. The proposed 3-1 model has high symmetry, high density, and large separation. The model error between the 3-1 model and the standard spherical periodic model is only 0.004 nm. Besides, the chemical composition formula of the present model is applied to analyze the common grade compositions of various alloys. This work shows that the 3-1 model has universality in mature industrial grades of Au–Ag and Au–Cu alloys, and provides a simplified method to design the composition of alloys.
Arylazopyrazoles (AAPs) show significant potential as a new family of molecular photoswitches owing to their efficient reversible trans -to- cis photoisomerization behavior and the high thermal stability of their metastable cis -isomer. In this study, AAPs have been used for the fabrication of solid-state photoswitchable polydimethylsiloxane (PDMS) based composite thin films. The thin films were prepared by using PDMS as a polymer matrix and different concentrations of AAPs as chromophores at 150 °C via spin-coating. The photoswitching behavior of the AAPPDMS composite films and the pristine AAP samples induced by irradiation with specific wavelength of light were investigated. We found that the as prepared AAPPDMS composite films showed rapid and near-quantitative (>98%) reversible trans -to- cis isomerization upon alternating irradiation with UV (λ = 365 nm) and green (λ = 525 nm) light which is comparable to the isomerization behavior of the pristine AAP chromophores in solution. This indicates that the excellent photoswitching property of the AAPs is preserved in the solid-state of the AAP-PDMS composite films. The results also show that the optical properties of the AAP-PDMS composite films can be tuned by using different ratios of the AAP chromophores and exposure to UV-light irradiation. Additionally, the thin films were tested for their photo-actuation behavior by UV–vis spectroscopy. Irradiation of the thin film with alternating 365 nm UV and 525 nm green light lead to a slight reversible bending behavior. This is presumably caused by the light-induced conformational change of the AAP moiety embedded within the PDMS matrix and the soft nature of the PDMS. This methodology provides a new approach for exploring the fabrication of polymers with enhanced mechanical behavior and solidstate photoswitching properties. Arylazopyrazoles (AAPs) show significant potential as a new family of molecular photoswitches owing to their efficient reversible trans -tocis photoisomerization behavior and the high thermal stability of their metastable cis - isomer. In this study, AAPs have been used for the fabrication of solid-state photoswitchable polydimethylsiloxane (PDMS) based composite thin films. The thin films were prepared by using PDMS as a polymer matrix and different concentrations of AAPs as chromophores at 150 °C via spin-coating. The photoswitching behavior of the AAP-PDMS composite films and the pristine AAP samples induced by irradiation with specific wavelength of light were investigated. We found that the as prepared AAP-PDMS composite films showed rapid and near-quantitative (>98%) reversible trans -to- cis isomerization upon alternating irradiation with UV (λ = 365 nm) and green (λ= 525 nm) light which is comparable to the isomerization behavior of the pristine AAP chromophores in solution. This indicates that the excellent photoswitching property of the AAPs is preserved in the solid-state of the AAP-PDMS composite films. The results also show that the optical properties of the AAP-PDMS composite films can be tuned by using different ratios of the AAP chromophores and exposure to UV-light irradiation. Additionally, the thin films were tested for their photo-actuation behavior by UV–vis spectroscopy. Irradiation of the thin film with alternating 365 nm UV and 525 nm green light lead to a slight reversible bending behavior. This is presumably caused by the light-induced conformational change of the AAP moiety embedded within the PDMS matrix and the soft nature of the PDMS. This methodology provides a new approach for exploring the fabrication of polymers with enhanced mechanical behavior and solid-state photoswitching properties.
Commercial AA-7075-T6 material was subjected to thermal exposure for 60 min in the temperature range 100–300 °C with an interval of 20 °C. There was no noticeable effect of exposure temperature on the yield stress, ultimate tensile stress, fracture stress, and surface hardness in the temperature range 100–200 °C. However, each strength parameter decreased rapidly with the increase in exposure temperature from 200 to 300 °C. This behavior was accounted for in terms of dislocation glide by Orowan mechanism in an atmosphere of semi-coherent ή precipitates (MgZn2) in the main matrix. Stress relaxation at a fixed strain for 1000 s was recorded at various stress levels over the entire stress – strain curve of a given AA-7075-T6 specimen. The stress relaxation rate s increased linearly with the strain εo at which initial stress σo was allowed to relax in the specimen. The stress relaxation parameter (ds/dεo) varied with exposure temperature in a manner similar to that of the strength parameters. The rate process of stress relaxation in the low-strain region was precipitate – dislocation interaction whereas that in the high-strain region was recovery by cross-slip mechanism.
Transparent conductive tin-doped zinc oxide (ZTO) thin films were deposited on glass substrate by using radio frequency (RF) magnetron sputtering method. The effect of sputtering power on crystalline structure, morphology, optical and electrical properties of the ZTO film was systematically studied. XRD results showed that the as-deposited ZTO thin films had a hexagonal wurtzite structure, with (002) orientation. Combining with SEM images, it was found that the grain size was increased with increasing sputtering power. The AFM images revealed that low sputtering powers of <210 W should be used to have ZTO films with small roughness (Rq). The optimized sample exhibited an average transmittance of 93.4% in the wavelength range of 400-900 nm, while the band gap had a significant red shift relative to that of the intrinsic ZnO. Carrier concentration and mobility of the ZTO films were decreased, whereas the resistivity was increased, with increasing sputtering power. The sample sputtered at 120 W had the maximized figure of merit (ФTC) of 11.87 × 10⁻⁴ Ω⁻¹·sq, with the variation trend to nearly mirror-symmetrical with that of surface roughness of the films.
Five kinds of phenolic acid-chitosan composite films including p-coumaric acid-chitosan, ferulic acid-chitosan, gallic acid-chitosan, vanillic acid-chitosan and salicylic acid-chitosan composite films with same content of phenolic acids were prepared, respectively. Their physical, mechanical and biological properties were investigated. Further, the preservative effect of ferulic acid-chitosan composite films and p-coumaric acid-chitosan composite films on Penaeus vannamei was evaluated. The results indicated that phenolic acids changed physical properties, decreased the mechanical properties, and increased biological properties of chitosan film. Among the phenolic acid-chitosan composite films, gallic acid-chitosan composite films possessed the best physical properties, mechanical properties, antioxidant and antimicrobial activities, which may be related to three phenolic hydroxyl groups in its molecule. In the shrimp preservation experiment, ferulic acid-chitosan composite films showed better preservative effect on shrimps in terms of weight loss, pH value, total volatile basic nitrogen, thiobarbituric acid value, total bacterial count and sensory score of shrimps during storage. The results may be related to the methoxy group in ferulic acid. The work revealed that the properties and preservative effect on shrimp of chitosan film were influenced by structures of phenolic acids.
In this work, a new Ultraviolet Optically Controlled Graphene Field-Effect Transistor (UV-OC-GFET) based on Graded Band-Gap (GBG) ZnMgO photosensitive-gate is proposed. The device drain current model is numerically developed by self-consistently solving the Schrödinger/Poisson equations based on non-equilibrium Green's function (NEGF) formalism. The influence of GBG strategy with different profiles on the device sensing performances is analyzed. Our investigation reveals that the use of both GBG ZnMgO photo-gate and graphene nanoribbon channel offers the dual-benefit of improved electric field distribution in the photosensitive layer and enhanced drain current. This leads to outperforming the device Figure of Merits (FoMs). In this context, it is found that the proposed UV sensor with optimized band-gap profile exhibits giant responsivity exceeding 1.5 × 10⁶ A/W with superb detectivity of 7 × 10¹⁴ Jones, far surpassing that of the conventional Si-channel based phototransistors. Therefore, this innovative strategy based on graphene nanoribbon channel combined with GBG sensitive-gate pinpoints a new path towards achieving high-performance visible-blind UV-phototransistor, making it a potential alternative photoreceiver for chip-level optical communication and optoelectronic applications.
Hydrogen storage alloys of La2-xYxMg16Ni (x = 0, 0.1, 0.2, 0.3, 0.4) were smelted by vacuum induction melting furnace. The microstructure of the cast alloys were observed by scanning electron microscope, and the alloys structure were analyzed by X-ray Diffractometer (XRD) before and after hydrogen absorption. The electrochemical capacity, cyclic stability, high-rate discharge, potentiodynamic polarization curves, and constant potential crossing curves were tested. Besides, the limited current density and diffusion coefficient were calculated. The results show that the main phase of the as-cast alloy is La2Mg17, and a little amount of the second phase Mg2Ni exist. In addition, LaH3 and MgH2 and a small amount of Mg2NiH4 phases were formed in the alloy after saturated hydrogen absorption. With the increasing of La element substituted by Y element in La2Mg16Ni alloy, the discharge specific capacity of alloy shows a decreasing tendency, it’s unconspicuous, though. The cyclic stability and high rate discharge of hydrogen storage alloys increase first and then decrease with the increasing of La element substituted by Y element in La2Mg16Ni alloy. When S50 is 34.01%, the cyclic stability of La1.8Y0.2Mg16Ni alloy is best. Both the limited discharge current density and hydrogen diffusion coefficient of the alloy increase first and then decrease with the increasing of the La element of La2Mg16Ni alloy replaced by Y element. The maximum current density of La1.8Y0.2Mg16Ni alloy is IL = 325.11 mA/g, and the maximum diffusion coefficient is D = 1.849 × 10⁻⁸ cm²/s.
Addition of D-Asp in the electrochemical deposition process of Bismuth film resulted the generation of a new diffraction peak in X-ray diffraction (XRD) spectrum. This phenomenon was not observed in the situation of L-Asp. The new diffraction peak might suggest D-Asp could result in the generation of a specific Bismuth structure. Enantioselective recognition of D- and L-Asp can be realized based on this new XRD peak. The limit of detection was determined to be 3.5 × 10⁻⁸ and 1.7 × 10⁻⁸ mol L⁻¹ for D- and L-Asp, respectively. The XRD spectra of electrodeposited Copper films fabricated in the presence of D- or L-Asp showed different lattice plane diffraction peak intensity ratios. The reason was believed to be chirality induced different binding capabilities of Asp enantiomers that influenced Copper film growth. Therefore, the combination of electrochemical deposition using Copper as metal source and XRD technology can be used to achieve enantioselective recognition of Asp. The limit of detection for D- and L-Asp were determined to be 1.5 × 10⁻¹⁰ and 1.2 × 10⁻¹¹ mol L⁻¹, respectively.
The two conventional aluminate precursor preparation methods are liquid-state co-precipitation and mechanical mixture, needing high temperature to fabricate thermionic cathodes for vacuum devices. Herein, we introduce the room temperature solid states (RTSS) approach to fabricate the precursors of barium calcium aluminates (BCA). For this, crystalline hydrates are used to prepare the precursor through mechanical grinding. The resulting product comprises of crystallized α-(Ba,Ca)CO3 solid solution and Al³⁺-contained amorphous precipitants. After sintering at 1200 °C, the active phases of Ba3CaAl2O7 and Ba3Al2O6 were obtained. The direct current (dc) emission measurements in a close-space diode configuration revealed that the divergent current density (Jdiv) of the test cathode reaches 7.2 A/cm² at 1130 °CB, which is comparable to that of the co-precipitation liquid phase method. Considering the virtue of an environmentally-friendly and low-temperature preparation approach, the preparation of aluminates using the RTSS technique has great potential for the fabrication of dispenser cathodes for vacuum devices.
The thermal stability of Cu/W nano-multilayers deposited on a Si substrate using ion beam deposition was analyzed in situ by GISAXS and transmission EDX—a combination of methods permitting the observation of diffusion processes within buried layers. Further supporting techniques such as XRR, TEM, WAXS, and AFM were employed to develop an extensive microstructural understanding of the multilayer before and during heating. It was found that the pronounced in-plane compressive residual stress and defect population induced by ion beam deposition result in low thermal stability driven by thermally activated self-interstitial and vacancy diffusion, ultimately leading to complete degradation of the layered structure at moderate temperatures. The formation of Cu protrusions was observed, and a model was formulated for stress-assisted Cu diffusion driven by Coble creep along W grain boundaries, along with the interaction with Si substrate, which showed excellent agreement with the observed experimental data. The model provided the explanation for the experimentally observed strong correlation between thin film deposition conditions, microstructural properties, and low thermal stability that can be applied to other multilayer systems.
We report the effect of Co2N impurity on the superconducting properties of δ-MoN thin films grown by polymer-assisted deposition on c-cut sapphire (Al2O3). The films show a superconducting transition temperature of 10.4 K and an upper critical field Hc2(0) perpendicular to the film surface around 3 T. The latter corresponds to a relatively large coherence length ξ, which enhances the two-dimensional limit when the magnetic field is applied parallel to the film surface. In comparison with pure δ-MoN films, the inclusion of Co2N impurity in the δ-MoN films could significantly modify the critical current density at the vortex-free state. The ability to tune the superconducting properties of metal-nitride superconductors by introducing chemically and structurally compatible impurity may find potential applications for superconducting single-photon detectors.
The defect creation on the surface of the metal oxide structure by infrared laser irradiation played a vital role in enhancing its optical properties. Herein, Zn/ZnO thin film was synthesized by pulsed laser deposition of Zn metal, followed by creating oxygen vacant by infrared laser irradiation, then the Ag layer was used to coat the irradiated ZnO thin film by pulsed laser deposition of Ag metal to produce Ag/ir-Zn/ZnO nanocomposite structure. The effect of creating vacancies on the thin films of ZnO has appeared on the optical and structural properties of Ag/ir-Zn/ZnO thin film was studied by X-ray diffraction, X-ray photoelectron spectrometer, and energy dispersive X-ray diffraction. The response of nonlinearity of Ag/ir-Zn/ZnO thin film was enhanced in compared with that of thin films of a single layer of CdO, single layer Ag, or CdO/Ag thin film.
Graphic abstract
Valley polarization of multi-valleyed materials is of significant interest for potential applications in electronic devices. The main challenge is removing the valley degeneracy in some controllable way. The unique properties of bismuth, including its anisotropic electronic structure and Dirac valley degeneracy, make this material an excellent system for valleytronics. It is demonstrated theoretically that the direction of an externally applied magnetic field in the binary-bisectrix plane has a profound effect not only on the charge, but also on the thermal transport along the trigonal direction. The rotating field probes the electronic mass anisotropy and tunes the contribution from a particular Dirac valley in the electrical resistivity, Seebeck coefficient, and thermal conductivity at moderate temperatures and field strengths. It is further shown that the field polarization of the transport properties is accompanied by selective filtering of the carriers type providing further opportunities for thermoelectric transport control.
We have observed a large increase in the magnetoresistance (MR) of polycrystalline and epitaxial thin Bi films, which were subjected to a post-annealing procedure at 3°C below the Bi melting point. We have achieved an increase in the MR by a factor of 2560 at 5K as compared with 343 for an as-grown epitaxial film due to enhanced carrier mobilities.
Polycrystalline Bi films were deposited onto p-GaAs(100) by electrochemical deposition. Annealing resulted in the formation of large grains with a preferred [012] orientation. The p-GaAs/Bi junctions were rectifying and the barrier height and ideality factor decreased with increasing film thickness. For films greater than 0.5 μm in thickness, the barrier height was about 0.56 eV and the ideality factor was between 1.1–1.2 for both as-deposited and annealed films. The resistance of the as-deposited films exhibited a negative temperature coefficient whereas the annealed films exhibited a positive temperature coefficient due to the limiting carrier mean free path. The magnetoresistance (MR) exhibited a quasilinear field dependence with an MR effect as large as 5600 (560 000%) at 5 K and 2.2 (220%) at room temperature. © 2000 American Institute of Physics.
The electrochemical deposition of bismuth on n-GaAs(100),
and p-GaAs(100) from
solution is characterized by cyclic voltammetry and impedance measurements. Electron capture at the conduction band forms
the rate-determining step in the reduction of
at n-type GaAs. The morphology of the bismuth films is related to the deposition kinetics. The rectifying n-GaAs/Bi Schottky
barrier formed on low-doped substrates prevents oxidation of bismuth, whereas tunneling through the space-charge layer allows
anodic stripping of Bi on highly doped substrates. Under illumination, electroless deposition of Bi is observed on n-GaAs.
Surface-state mediated hole injection is responsible for the slow deposition of Bi on p-GaAs in the dark. Photoassisted nucleation
and subsequent growth in the dark results in the formation of continuous thin Bi films on p-GaAs. © 2001 The Electrochemical
Society. All rights reserved.
Bismuth thin films are formed electrochemically on n- Ga As (110). Bismuth films up to a few hundred nanometers in thickness exhibit a strong (018) texture, while thicker films are polycrystalline. The barrier height of the n- Ga As / Bi Schottky contacts is 0.62 eV , about 0.2 eV lower than for electrodeposited bismuth films on GaAs (100).
Single-crystal bismuth thin films 1 to 20 micrometers thick were fabricated by electrodeposition and suitable annealing. Magnetoresistance
up to 250 percent at 300 kelvin and 380,000 percent at 5 kelvin as well as clean Shubnikov–de Haas oscillations were observed,
indicative of the high quality of these films. A hybrid structure was also made that showed a large magnetoresistive effect
of 30 percent at 200 oersted and a field sensitivity of 0.2 percent magnetoresistance per oersted at room temperature.
Multilayered Ni80Fe20/Cu film shields were obtained via electrochemistry method with different thickness and number of partial magnetic layers. Magnetic properties and shielding characteristics were investigated as well as function of thickness and number of layers. Difference in magnetic properties for Ni80Fe20 films with different thickness is due to formation of defect layers on the top and bottom film surfaces during electrodeposition processes. These layers can be characterized as layers with high density defects (as a result poor iron content). Main deviation in magnetic properties is typical for thinner films. It was measured DC and AC shielding and results discussed. Maximal value of DC-shielding effectiveness was observed for multilayered samples with small number magnetic layers with large thickness (80–400 μm). The minimal value of DC-shielding effectiveness was observed for the multilayered sample with the minimum thickness of the magnetic layer (5 μm) and maximal number of the layers (80 layers). It is in good agreement with shunting mechanism. In low frequency range maximal values of AC-shielding effectiveness were observed like in case of DC-shielding for samples with small number magnetic layers with large thickness. With frequency increasing the situation was radically changed and AC- shielding effectiveness was higher for samples with maximal number of layers. In the frequency range above 40 kHz AC- shielding effectiveness was sharply decreased due to sharply decreasing of permeability value. As a result it leads to decrease of absorption loses (SEabs.). It was discussed the main shielding mechanisms for multilayered Ni80Fe20/Cu film samples under different external influences. Main contribution in electromagnetic shielding in the range 300 Hz – 20 kHz is absorption and reflection processes. In the range 20 kHz – 50 kHz main shielding mechanisms are reflection and re-reflection. For 300 Hz – 50 kHz frequency range most appropriate to use multilayered structures with large number of thin layers with cardinally different values of magnetic permeability and electrical conductivity.
The BaFe12-xGaxO19 (x = 0.1-1.2) solid solutions of the barium hexagonal ferrite of M-type were synthesized and attested by the powder X-ray diffraction method at 300 K. The unit cell parameters were refined. With increase of substitution level the parameters of unit cell monotonically decrease. These samples were investigated by the vibration magnetometry method. With increase of substitution level the magnetic parameters monotonically decrease. The concentration dependence of the TC Curie temperature as well as the MS spontaneous specific magnetization and the HC coercive force at 300 K is constructed. The microwave properties of the considered samples in the external magnetic bias field were also investigated at 300 K. It is shown that with increase of Ga³⁺ concentration from x = 0.1 to x = 0.6 the frequency value of the natural ferromagnetic resonance decreases in the beginning, and at further increase in concentration up to x = 1.2 it increases again. With increase in Ga³⁺ concentration the line width of the natural ferromagnetic resonance increases that indicates the increase of frequency range where there is an intensive absorption of electromagnetic radiation. At the same time the peak amplitude of the resonant curve changes slightly. The frequency shift of the natural ferromagnetic resonance in the external magnetic bias field takes place more intensively for the samples with small Ga³⁺ concentration. It is shown the prospects of use of the Ga-substituted barium hexagonal ferrite as the material effectively absorbing the high-frequency electromagnetic radiation.
The lightly doped BaFe12-xDxO19 (D = Al³⁺, In³⁺; x = 0.1 and 0.3) polycrystalline hexaferrite samples have been investigated by powder neutron diffractometry as well as by vibration sample magnetometry in a wide temperature range from 4 K up to 740 K and in magnetic field up to 14 T to establish the nature of Fe³⁺(Al³⁺, In³⁺) – O²⁻ - Fe³⁺(Al³⁺, In³⁺) indirect exchange interactions. The crystal structure features such as the ionic coordinates and lattice parameters have been defined and Rietveld refined. The Invar effect has been observed in low temperature range below 150 K. It was explained by the thermal oscillation anharmonicity of ions. It is established that the ferrimagnet-paramagnet phase transition is a standard second-order one. From the macroscopic magnetization measurement the Curie temperature and ordered magnetic moment per nominal iron ion are obtained. From the microscopic diffraction measurement the magnetic moments at all the nonequivalent ionic positions and total magnetic moment per iron ion have been obtained at different temperatures down to 4 K. The light diamagnetic doping mechanism and magnetic structure model are proposed. The effect of light diamagnetic doping on nature of Fe³⁺(Al³⁺, In³⁺) – O²⁻ - Fe³⁺(Al³⁺, In³⁺) indirect exchange interactions with temperature increase is discussed.
M-type BaFe11.9Al0.1O19 hexaferrite was successfully synthesized by solid state reactions. Precision investigations of crystal and magnetic structures of BaFe11.9Al0.1O19 powder by neutron diffraction in the temperature range 4.2 – 730 К have been performed. Magnetic and electrical properties investigations were carried out in the wide temperature range. Neutron powder diffraction data were successfully refined in approximation for both space groups (SG): centrosymmetric #194 (standard non-polar phase) and non-centrosymmetric #186 (polar phase). It has been shown that at low temperatures (below room temperature) better fitting results (value χ²) were for the polar phase (SG: #186) or for the two phases coexistence (SG: #186 and SG: #194). At high temperatures (400–730 K) better fitting results were for SG: #194. It was established coexistence of the dual ferroic properties (specific magnetization and spontaneous polarization) at room temperature. Strong correlation between magnetic and electrical subsystems was demonstrated (magnetoelectrical effect). Temperature dependences of the spontaneous polarization, specific magnetization and magnetoelectrical effect were investigated.
Electroanalysis with bismuth film electrodes and other Bi electrodes is reviewed. The review offers a retrospective insight into a short history, reminding of all the important milestones in the field and the basic characteristics of all hitherto known types of Bi electrodes and including inevitable comparison with related mercury electrodes. Furthermore, special attention has been paid to discussion on specific features of bismuth-based electrodes in electrochemical stripping analysis. The text is illustrated by numerous examples mostly based on author's results and includes also tables summarising the individual studies and methods mentioned in the review. Last but not least, the most important achievements are critically evaluated and future prospects outlined. A review with 100 references.
Well dispersed RuCu nanoparticles (NPs) supported on graphene were in situ synthesized by a one-step co-reduction of aqueous solution of ruthenium (III) chloride, cupric (II) chloride, and graphite oxide (GO) with ammonia borane (AB) under ambient condition. The nature of the NPs was fully characterized by TEM, HRTEM, XRD, energy dispersive spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The as-synthesized NPs exhibit much higher catalytic activity for hydrolytic dehydrogenation of AB than the monometallic Ru and Cu, bimetallic RuCu/graphene reduced by NaBH4, and graphene free RuCu counterparts. Additionally, the as-synthesized NPs supported on graphene exhibit higher catalytic activity than the catalysts with other conventional supports, such as SiO2, γ-Al2O3, and carbon black. The activity of Ru1Cu7.5/graphene NPs in terms of turnover frequency (TOF) is 135 mol H2 min−1 (mol Ru)−1, which is higher than Ru/graphene, and most reported Ru-based or other noble metal-based NPs for the catalytic hydrolysis of AB. The activation energy for hydrolysis of AB in the presence of Ru1Cu7.5/graphene NPs was determined as 30.59 kJ mol−1, which is lower than most of the reported catalysts. Furthermore, the as-prepared NPs exert satisfied durable stability for the hydrolytic dehydrogenation of AB.
Reversible electrodeposition of metallic bismuth onto transparent conducting substrates was studied with interest in the electrochromic phenomena produced by plating and stripping a thin metallic film. Different bismuth films were prepared potentiostatically by applying potential steps of different amplitude (whilst maintaining the electric charge at a constant value), and the change in transmittance was followed in situ simultaneously during the electrodeposition process. A large change of transmittance was observed for constant charge films prepared at different deposition potentials. As the absorbance is related to the deposition charge (amount of metallic bismuth electrodeposited), changes in optical properties of equivalent films must be related to large changes in film morphology; this was corroborated by scanning electron microscopy. The effect of copper additives was also analyzed: this produced changes in film morphology, leading to bidimensional deposition being predominant over the tridimensional process.
The effect of controlled amounts of irreversibly adsorbed bismuth on a Pt (111) oriented electrode surface on the electrocatalytic oxidation of formic acid has been studied in the whole range of coverage. The experimental method used in this work enables us to maintain a constant surface coverage in heteroatoms while the electrode is cycled in the whole range of potential of oxidation of the organics. For a coverage range from 0 up to 0.8 the electroactivity of the surface for the direct oxidation of formic acid is enhanced by a factor of 40, while in the whole range of coverage the accumulation of the blocking intermediate is lowered to an undetectable level.
The effect of adsorbing submonolayers of bismuth and tin onto single-crystal, polycrystalline and dispersed platinum electrodes on the oxidation of formic acid and methanol was investigated. While the oxidation of formic acid on Pt(111) was found to be enhanced by adsorbed sub-monolayers of bismuth, the oxidation of methanol was inhibited by all adsorbed coverages of both tin and bismuth on all electrodes. The adsorbed tin was found to be more stable on the dispersed Pt electrodes than on the smooth electrodes.
The status of electrochromic devices based upon the reversible electrodeposition of thin bismuth–copper films is reported. The electrochemistry and interface chemistry of the system relevant to information display applications are briefly described. Low information content displays are currently being produced in small quantities with saturated black and white contrast ratio of 25:1 and lifetimes of greater than ten million cycles. Electrochemical scanning tunneling microscopy (ECSTM) studies on highly ordered pyrolytic graphite (HOPG) substrates were undertaken as a first step in the unraveling of the detailed nucleation and growth behavior of the Bi–Cu system at the atomic level. The results obtained support previous studies using scanning electron microscopy and surface spectroscopy. Preliminary results on the plating current efficiency of the system using a quartz crystal microbalance (QCM) are reported.
Bismuth films (200-1400 Å) were grown epitaxially on freshly cleaved mica substrates. These films consisted of a mosaic of equally oriented crystallites averaging several microns in diameter. The plane of the films coincided with the trigonal plane of Bi. We have studied the thickness dependence of the resistivity, the Hall coefficient, and the transverse magneto-resistance, by gradually varying the thickness of a single film which was kept under high vacuum during the entire experiment. The resistivity at 360 and 77 °K is a smooth monotonic function of the thickness. At 12 °K, we observed small oscillations in the resistivity and in the magnetoresistance. These oscillations are regarded as probable manifestations of the quantum size effect (QSE). The thickness dependence of the Hall coefficient is in striking disagreement with the predictions of the infinite-potential-well model. Better agreement between the theory and experimental results is obtained when we assume a less rigid boundary condition. Also for several films we have investigated the temperature dependence of these three transport coefficients and found it to be quite different from that of bulk bismuth. We have attempted to explain these results in terms of the behavior of the carrier concentration and of the different scattering mechanisms that can come into play in these films.
The voltammetric profile in sulfuric acid electrolytes of high coverage bismuth monolayers on Pt(111) having a fractional coverage (θ) of 0.39 exhibits two pairs of peaks located positive and negative, respectively, of the redox peak associated with the 0.33 coverage Bi/Pt(111) adlayer. The ΔEfwhm (full width at half-maximum) values for these peaks are 10 and 20 mV, respectively, suggesting that the redox events involve significant near-neighbor interactions and may correspond to phase transitions within the bismuth adlayer. The formal potentials of these redox peaks shift by 65 mV per pH unit, suggesting that two protons are involved in the two-electron redox reaction of the bismuth adatoms. This provides evidence that the two pairs of redox peaks could correspond to the abrupt formation of [Bi(OH)2]ad and [BiO]ad from Biad. Upon continuous potential scanning in sulfuric acid electrolyte, these peaks decay while two new peaks grow in, with an isopotential point forming between the two anodic peaks. The new, latter peak corresponds to that found for the 0.33 coverage Bi/Pt(111) adlayer. The peaks that grow in upon potential scanning could arise from the interconversion of the hydroxide and oxide network to a stable, long-range hydrogen-bonded (bi)sulfate network upon bismuth oxidation. The peak associated with the 0.33 coverage Bi/Pt(111) adlayer could then be ascribed to the abrupt formation of this (bi)sulfate network upon bismuth oxidation. In perchloric acid electrolytes the two pairs of high coverage bismuth redox peaks are also present, but one increases monotonically while the other decreases upon potential scanning, without the appearance of any new peaks. The high coverage peaks are thus associated with the formation of a long-range hydroxide and oxide network upon bismuth oxidation. The presence of halide anions (Cl-, Br-, I-) dramatically affects the voltammetric profile of Bi/Pt(111). Initially, chloride appears to form a complex with the bismuth adlayer. Upon potential scanning, the redox peak ascribed to the chloride complex decays while that associated with the stable bismuth adlayer reemerges. Bromide and iodide anions both cause the complete desorption of the bismuth adlayer, suggesting that they have significantly stronger bonding interactions to Pt(111) than does bismuth.
This paper reports an investigation of the large magnetoresistance (MR) of 0.3–1.5 µm thick polycrystalline Bi films deposited in vacuum on non-crystalline substrates and annealed at critical temperatures. The occurrence of critical temperatures is associated with intensive growth of crystallites. It is demonstrated that such films consist of large 50–200 µm high-quality crystallites and exhibit a large transverse MR. At temperatures higher than 77 K the magnitude of the MR can exceed that of epitaxial Bi films. The experimental results are interpreted on the basis of a polycrystalline Bi thin-film model. The data suggest that in Te-doped Bi films the MR can be larger than that in pure Bi films. It is found that the grain-boundary scattering is weak. However, there exist rather isotropic extra carrier scattering channels which reduce the anisotropy of electrical conductivity and MR. The relative importance of this extra scattering changes with temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
In this article, the decade of electroanalysis with bismuth-based electrodes is reviewed (with 222 refs.). Emphasis is put on the environmentally friendly (“green”) character of bismuth electrodes, their versatility and variability in use, as well as the actual classification of the individual types of electrodes, sensors, and detectors that utilize the unique properties of metallic bismuth. Of particular interest is the genesis of the field, when the respective activities and achievements are monitored year by year over the whole period of 2000–2009, including the circumstances of the introduction of bismuth-coated electrodes into electrochemical stripping analysis. The review highlights all the significant milestones and break-points that had directed the experimental work around the globe, outlining the present day's position of this lively, inspiring, and still highly prospective area. Finally, it provides a special insight into electroanalysis with bismuth electrodes through numerous surveys, summaries, and detailed statistical data obtained by analyzing the accessible literature database.
The underpotential deposition (UPD) and overpotential deposition (OPD) of bismuth on Au(1 1 1) have been studied with in situ scanning tunneling microscopy (STM). Large area STM images obtained in the UPD region indicate that adsorbed bismuth lifts the reconstruction of the Au(1 1 1) surface. This results in the formation of gold islands at potentials less than 0.170 VSCE. In situ STM images of the Bi OPD process reveal needle growth across the gold surface, beginning at step edges and proceeding to form relatively uniform films. This growth behavior is observed at −0.070 VSCE, after stepping the potential to −0.120 VSCE for 4 s. Atomic resolution images of the OPD bismuth layer indicate that the unit cell is nearly rectangular with dimensions of 3.9±0.2 and 4.3±0.2 Å. This corresponds to having the shorter side of the Bi unit cell along the long edge of the bismuth needles. The reduced spacing hinders the incorporation of atoms diffusing along these edges. Instead, diffusing atoms become incorporated at the needle end where the structure is more open, resulting in the observed Bi growth anisotropy.
Metal bismuth with various morphologies, with particle size from nanometer to micrometer, has been successfully prepared by electrodeposition onto Pt, Au, Al and ITO electrodes at room temperature. The size and morphology of the deposits are strongly dependent on preparation conditions, such as deposition potential, current density, electrode and electrolyte. As observed by scanning and transmission electron microscopes, the deposited Bi particles exhibit plentiful appearances, such as prickly rod, banch, skeleton and strip-like shapes. A significant positive magnetoresistence effect is observed even at room temperature.
Single crystalline bismuth nanowire arrays in anodic alumina membrane have been fabricated by pulsed electro-deposition. The nanowires of different diameters were obtained by changing the electrical parameter of the pulsed electrodeposition using anodic alumina membrane as template with the same pore size. X-ray diffraction and TEM analysis show that the bismuth nanowires are single crystalline with highly preferential orientation, and the diameter of nanowires increases with increasing the relaxation time of pulse. The growth mechanism of nanowires was discussed.
For many years mercury electrodes were the transducer of choice in stripping voltammetry of trace metals owing to their high sensitivity, reproducibility, and renewability. However, because of the toxicity of mercury, alternative (‘environmentally friendly’) electrode materials are highly desired for both centralized and field applications. Recently introduced bismuth electrodes offer a very attractive alternative to commonly used mercury electrodes. Such electrodes display well-defined, undistorted and highly reproducible response, favorable resolution of neighboring peaks, high hydrogen evolution, with good signal-to-background characteristics comparable to those of common mercury electrodes. The attractive stripping behavior of bismuth electrodes reflects the ability of bismuth to form ‘fused’ multicomponent alloys with heavy metals. Bismuth stripping electrodes thus hold great promise for decentralized metal testing, with applications ranging from continuous remote sensing to single-use measurements. Fundamental studies aimed at understanding the behavior of bismuth film electrodes should lead to rational preparation and operation of reliable alternative (‘non–mercury’) stripping electrodes that would have a major impact upon electroanalysis of trace metals. This article reviews the development, behavior, scope and prospects of bismuth electrodes for stripping-based electrochemical measurements of trace metals.
The electrocatalytic effect of underpotential deposition (UPD) of bismuth on the cathodic reduction of oxygen and hydrogen peroxide has been investigated on poly- and mono-crystalline (111) and (100) gold electrodes in 0.5 M HClO4 solution. On the bare gold substrates an incomplete 2-electron reduction of O2 to H2O2 predominates, which in the presence of Bi3+ in the solution is positively catalysed indicated by a decrease of the overvoltage and an increase of the rate of H2O2 reduction. The catalytic effects can be correlated with the degree of Bi adsorbate coverage and the structural arrangement of Bi adatoms depending on the crystallographic orientation of the substrate. The effect of a mixed anion (Cl−) and cation (Bi3+) adsorption on the reduction process was also studied.
The electrodeposition of bismuth on glassy carbon electrodes (GCEs) from nitrate solutions was studied by cyclic voltammetry, chronoamperometry, and scanning electron microscopy. Cyclic voltammograms exhibit a crossover between the cathodic and anodic branches, characteristic of the formation of bismuth nuclei on GCEs. The bismuth electrodeposition on GCEs is a diffusion-controlled reaction. The current transients for bismuth electrodeposition were analyzed according to the Scharifker–Hills models, the Scharifker’s general equation and the Heerman–Tarallo equation. For 1 and 5 mM Bi3+, the nucleation and growth mechanism is independent of deposition potential and follows the three-dimensional (3D) progressive nucleation and growth model. However, a deposition potential dependence of nucleation and growth mechanism can be found in the cases of 10 and 20 mM Bi3+. The quantitative analysis by the two equations shows that A and N0 exponentially grow with the increase of deposition potential, while D decays in an exponential mode. It should be noted that the two equations produced the very close N0 and D values and the distinct A values (especially at −300 and −350 mV). However, the critical size of the nuclei (Nc) estimated by using the two equations was all zero. Both of the equations can be used for describing the electrodeposition of bismuth on GCEs in this work. SEM images show that high deposition potential as well as high concentration can enhance the nuclei density of bismuth on GCEs and favors the formation of small crystallites with a less defined structure.
The properties of the bismuth film electrode designed for adsorptive stripping voltammetry were examined by electrochemical and microscopic techniques. The various bismuth plating solutions containing bromide ions were tested in bismuth film generation on glassy carbon. The composition of the plating solution, the influence of accumulation potential, and the stability of bismuth coating as well as the memory effect is discussed. The analytical usefulness of the BiFEs obtained by the proposal procedure was estimated for adsorptive stripping measurement of cobalt traces in a solution of 1 × 10−4 M DMG and 0.1 M ammonia buffer. It has been found that the plating solution of 0.02 M Bi(NO3)3, 1 M HCl and 0.5 M LiBr as well as −0.28 V plating potential and 20 s plating time ensure the finest quality bismuth film deposited on the glassy carbon support for analytical purposes. The electrode-to-electrode reproducibility of the described plating procedure was characterized by the relative standard deviation (RSD) equal to 12%. The repeatability of the cobalt response for 30 subsequent adsorptive stripping measurements of the same BiFE amounted RSD=6%.
Dissociative adsorption of formic acid and methanol on adatom-modified Pt(111) electrodes has been carried out as a way of studying poison formation reactions on these surfaces. The electrodes were prepared using irreversible adsorption of Bi and As. A modification of the dissociative adsorption technique used for poison formation studies has been employed. For clean Pt(111) surfaces the behaviour of the poison formation reaction of the two organic molecules is almost the same, but on adatom-modified Pt(111) electrodes different results are found. Bi and As show an important long-range electronic effect which inhibits poison formation from the dissociative adsorption of formic acid at very low adatom coverage. However, for methanol, the inhibition due to the presence of Bi adatoms on the surface can be explained by a simple third-body effect. A computer simulation of the dissociative adsorption of formic acid on Bi-modified Pt(111) electrodes has been carried out in order to calculate the width of the domains affected by the presence of Bi adatoms.
We report an investigation of the low-temperature electrical transport properties of bismuth films under applied hydrostatic pressure. Films with their trigonal axis perpendicular to the film plane and thicknesses of 30, 50, and 500 nm were grown by molecular-beam epitaxy on BaF2 substrates. At 500 nm thickness the behavior resembles that of bulk Bi. From the observed Shubnikov-de Haas oscillations we find a pressure-induced decrease in extremal Fermi cross section. For the 30-nm film, we obtain the low-temperature carrier densities for electrons and holes together with the corresponding mobilities from magnetoconductance data at pressures up to 20 kbar. We find that pressure strongly reduces the surface-induced excess hole concentration, clearly revealing a finite electron concentration at high pressures. We discuss our results within the context of a possible semimetal-semiconductor transition in thin Bi films.
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