Nanoscale

Published by Royal Society of Chemistry
Online ISSN: 2040-3372
Publications
Article
Porous Co(3)O(4) nanowires with large aspect ratio have been obtained by annealing long Co(CO(3))(0.5)(OH)·0.11H(2)O precursor nanowires synthesized by a facile hydrothermal method. The results show that the amount of the additive (urea) has an important impact on the morphology of the as-synthesized cobalt-carbonate-hydroxide intermediate, where the uniformity and the overall structure can be controlled by changing the urea concentration. After the heat treatment, the as-obtained phase-pure Co(3)O(4) nanowires with a well retained structure are applied as the electrode material for supercapacitors, and the sample exhibits excellent performance with a high specific capacitance of 240 F g(-1) after 2000 charge/discharge cycles, corresponding to a retention of 98% of the initial capacitance.
 
Article
Visible light photocatalytic H(2) production from water splitting using solar light is of great importance from the viewpoint of solar energy conversion and storage. In this study, a novel visible-light-driven photocatalyst multiwalled carbon nanotube modified Cd(0.1)Zn(0.9)S solid solution (CNT/Cd(0.1)Zn(0.9)S) was prepared by a simple hydrothermal method. The prepared samples exhibited enhanced photocatalytic H(2)-production activity under visible light. CNT content had a great influence on photocatalytic activity and an optimum amount of CNT was determined to be ca. 0.25 wt%, at which the CNT/Cd(0.1)Zn(0.9)S displayed the highest photocatalytic activity under visible light, giving an H(2)-production rate of 78.2 μmol h(-1) with an apparent quantum efficiency (QE) of 7.9% at 420 nm, even without any noble metal cocatalysts, exceeding that of pure Cd(0.1)Zn(0.9)S by more than 3.3 times. The enhanced photocatalytic activity was due to CNT as an excellent electron acceptor and transporter, thus reducing the recombination of charge carriers and enhancing the photocatalytic activity. Furthermore, the prepared sample was photostable and no photocorrosion was observed after photocatalytic recycling. Our findings demonstrated that CNT/Cd(0.1)Zn(0.9)S composites were a promising candidate for the development of high-performance photocatalysts in photocatalytic H(2) production. This work not only shows a possibility for the utilization of low cost CNT as a substitute for noble metals (such as Pt) in the photocatalytic H(2)-production but also for the first time shows a significant enhancement in the H(2)-production activity by using metal-free carbon materials as effective co-catalysts.
 
Article
Here, we show that GaN nanowires (diameter <30 nm) can be used as strain relaxing substrates for the heteroepitaxial growth of stable In(x)Ga(1-x)N alloys of controlled composition and thickness. Thinner nanowires with their smaller interfacial area reduce the heteroepitaxial stress. Also, the limited adatom diffusion length scales on the thinner nanowires aid in reducing the kinetic segregation effects. In addition to being single crystal templates for heteroepitaxial growth, these thick single crystal overlayers on nanowire substrates can provide suitable architectures for photoelectrochemical applications. The stability and crystallinity of the In(x)Ga(1-x)N layers are preserved by the nanowires acting as compliant substrates. Photoelectrochemical water splitting requires In(x)Ga(1-x)N alloys with a 2.2-1.6 eV band gap (i.e. 0.45 < x < 0.65) and 150-200 nm film thickness for efficient light absorption and carrier generation. At such compositions, the In(x)Ga(1-x)N alloys are inherently unstable, the thickness-dependent stress builds up during the commonly employed heteroepitaxial growth methods, and adds to the instability causing phase segregation and property degradation. A dependence of the growth morphology on the GaN nanowire growth orientation was observed and a growth mechanism is presented for the observed orientation dependent growth on a-plane and c-plane GaN nanowires. Photoactivity of GaN and In(x)Ga(1-x)N films on GaN nanowires is also investigated which shows a distinct difference attributable to GaN and In(x)Ga(1-x)N, demonstrating the advantages of using nanowires as strain relaxing substrates.
 
Article
A photocatalyst Sr(0.4)H(1.2)Nb(2)O(6)·H(2)O (HSN) nanopolyhedra with high surface area has been successfully prepared by a simple hydrothermal method. The as-prepared samples were characterized by XRD, BET, SEM, TEM and XPS. The electronic structure of HSN determined by DFT calculations and electrochemical measurement revealed that HSN is an indirect-bandgap and n-type semiconductor, respectively. HSN samples showed high photocatalytic activities for both pure water splitting and the decomposition of benzene. The rate of H(2) evolution over HSN was 15 times higher than that of P25 and the conversion ratio of benzene exceeded twice that of P25. The photocatalytic activities for water splitting can be greatly improved by loading various co-catalysts on HSN, such as Au, Pt, and Pd. The photocatalytic mechanisms were proposed based on the band structure and characterization results of the photocatalyst.
 
Article
Novel hierarchical heteronanostructures of ZnO nanorods/ZnS·(HDA)0.5 (HDA = 1,6-hexanediamine) hybrid nanoplates on a zinc substrate are successfully synthesized on a large scale by combining hydrothermal growth (for ZnO nanorods) and liquid chemical conversion (for ZnS·(HDA)0.5 nanoplates) techniques. The formation of ZnS·(HDA)0.5 hybrid nanoplates branches takes advantage of the preferential binding of 1,6-hexanediamine on specific facets of ZnS, which makes the thickening rate much lower than the lateral growth rate. The ZnS·(HDA)0.5 hybrid nanoplates have a layered structure with 1,6-hexanediamine inserted into interlayers of wurtzite ZnS through the bonding of nitrogen. The number density and thickness of the secondary ZnS·(HDA)0.5 nanoplates can be conveniently engineered by variation of the sulfur source and straightforward adjustment of reactant concentrations such as 1,6-hexanediamine and the sulfur source. The fabricated ZnO/ZnS·(HDA)0.5 heteronanostructures show improved electrochemical catalytic properties for hydrazine compared with the primary ZnO nanorods. Due to its simplicity and efficiency, this approach could be similarly used to fabricate varieties of hybrid heterostructures made of materials with an intrinsic large lattice mismatch.
 
Article
Kinetic and mechanistic studies of the oxygen reduction reaction (ORR) in oxygen saturated 0.5 M sulfuric acid at 298 K at a gold macroelectrode and at an electrodeposited gold nanoparticle-modified glassy carbon electrode are reported. The conditions of electrodeposition are optimized to obtain small nanoparticles of diameter from 17 nm to 40 nm. The mechanism and kinetics of ORR on the gold macroelectrode are investigated and compared with those obtained for nanoparticle-modified electrodes. The mechanism for this system includes two electron and two proton transfers and hydrogen peroxide as the final product. The first electron transfer step corresponding to the reduction of O2 to O2(-)˙ is defined as the rate determining step. No significant changes are found for the nanoparticles here employed: electron transfer rate constant (k0) is k0,bulk = 0.30 cm s(-1) on the bulk material and k0,nano = 0.21 cm s(-1) on nanoparticles; transfer coefficient (α) changes from αbulk = 0.45 on macro-scale to αnano = 0.37 at the nano-scale.
 
Article
We have demonstrated unique CdS0.5Se0.5 and CdSe quantum dot-glass nanosystems with quantum confinement effect. The stable, monodispersed CdS0.5Se0.5 and CdSe quantum dots (QDs) of size 2 to 12 nm have been grown in a germanate glass matrix by a simple melt quench technique at moderate temperature. XRD and Raman studies show formation of hexagonal CdS0.5Se0.5 and CdSe in the glass matrix. The quantum confinement of CdS0.5Se0.5 and CdSe was studied using TEM and UV-Vis spectroscopy. The band gap of the glass nanosystem was tuned from 3.6 to 1.8 eV by controlling the CdS0.5Se0.5 quantum dot size in the glass matrix. It can be further tuned to 1.68 eV using growth of CdSe quantum dots in the glass matrix. Considering the tuneable band gap of the CdS0.5Se0.5 and CdSe quantum dot-glass nanosystem for the visible light absorption, a study of size tuneable photocatalytic activity for hydrogen generation from hydrogen sulfide splitting was performed under visible light irradiation for the first time. The utmost hydrogen evolution, i.e. 8164.53 and 7257.36 μmol h(-1) g(-1) was obtained for the CdS0.5Se0.5 and CdSe quantum dot-glass nanosystems, respectively. The apparent quantum yield (AQY) was observed to be 26% and 21% for the CdS0.5Se0.5 and CdSe quantum dot-glass nanosystems, respectively. It is noteworthy that the present glass nanosystem as a photocatalyst was found to be very stable as compared to naked powder photocatalysts.
 
Article
A peony-like Ag/Ag0.68V2O5 hybrid assembled from nanosheets with the thickness of 40 nm was synthesized through a one-pot hydrothermal approach from vanadium pentoxide (V2O5), oxalic acid (H2C2O4), and silver nitrate (AgNO3) at 180 °C for 24 h. The hybrid exhibits high performance as both anode and cathode materials for rechargeable lithium batteries. Electrochemical measurements revealed that the as-prepared Ag/Ag0.68V2O5 hybrid displayed excellent cycling stability, especially as an anode material. The resulting anode retains 100% of the initial capacity after 1000 cycles under a current density of 400 mA g(-1). This phenomenon may be attributed to electron conductivity improvement by the existence of metallic silver in the hybrid in addition to the convenient access to lithium ion ingress/egress because of its unique structure.
 
Article
The interaction of graphene with metal is of critical importance for further optimization of the growth and transfer processes to achieve productive graphene. Here we report first-principles calculations with van der Waals corrections to address in-plane orientation effects on the geometric structure and electronic properties of monolayer and bilayer graphene on a Ru(0001) surface. We find that the recently measured slight rotation between monolayer graphene and Ru lattices minorly affects the characteristic geometric and electronic structures simulated to date for strict alignment. For epitaxial bilayer graphene, we unveil that a 25°-twisted bilayer graphene commensurate with Ru reproduces at best the hallmarks of free-standing electron-doped monolayer graphene as measured experimentally. At variance the classical Bernal stacking manifests the strongest interlayer coupling by destroying the Dirac point and exhibiting a graphite-like STM appearance. Our theoretical findings question the definite nature of the interfacial coupling of successive graphene layers grown on a strongly interacting metal substrate.
 
Article
Manipulation of graphene-based systems is a formidable challenge, since it requires the control of atomic interactions over long timescales. Although the effectiveness of a certain number of processes has been experimentally demonstrated, the underlying atomic mechanisms are often not understood. An import class of techniques relies on the interaction between hydrogen and graphene, which is the focus of this research. In particular, the growth of epitaxial graphene on SiC(0001) is subject to a single-atom-thick interface carbon layer strongly bound to the substrate, which can be detached through hydrogen intercalation. Here we report that a nucleation phenomenon induces the transformation of this buffer layer into graphene. We study the graphenization dynamics by an ab initio based method that permits the simulation of large systems with an atomic resolution, spanning the time scales from nanoseconds to hours. The early evolution stage (∼ms time scale) is characterised by the formation of a metastable H layer deposited on the C surface. H penetration in the interface between the C monolayer and the SiC(0001) surface is a rare event due to the large penetration barrier, which is ∼2 eV. However, at high H densities, energetically favoured Si-H bonding appears on the substrate's surface. The local increase of the H density at the interface due to statistical transitions leads to the graphenization of the overlying C atoms. Thermally activated density fluctuations promote the formation of these graphene-like islands on the buffer layer: this nucleation phenomenon is evidenced by our simulations at a later evolution stage (>10(2) s at 700 °C for ∼3.6 × 10(15) at. cm(-2) s(-1) H flux). Such nuclei grow and quasi-freestanding graphene forms if the exposition to the H flux continues for a sufficiently long time (∼30 min for the same conditions). We have systematically explored this phenomenon by varying the substrate temperature and the H flux, demonstrating that the surface morphology during graphenization and post-graphenization anneals significantly depends on these variables. The computational findings are consistent with the experimental analyses reported so far and could serve as guidelines for future experimental works on graphene manipulation.
 
Article
A straightforward method of synthesising Au@Pd core-shell particles on a well characterised γ-Fe2O3 (0001) substrate has been developed which will enable fundamental studies into the surface chemistry of these catalytically interesting systems. Au and Pd were sequentially deposited onto a γ-Fe2O3 (0001) substrate in ultra high vacuum by metal vapour deposition and probed by LEIS and STM. Deposition of Au followed by heating at 573 K formed nanoparticles of 5 to 10 nm in diameter whereas subsequent deposition of Pd produced smaller nanoparticles of 2 to 4 nm diameter. At this stage, LEIS shows both metals to be present but heating the combined system to 573 K resulted in the loss of the Au signal in the LEIS and disappearance of the smaller particles from the STM images indicating the formation of Au@Pd core-shell structures.
 
Water trapped-layer in between graphene and MoS 2 . AFM images of graphene – MoS 2 (a) 5 m m  5 m m and (b) 2 m m  2 m m. The line pro fi le taken along the red line is also shown in (b). The area labeled 0WL does not contain trapped water whereas those labeled 1WL and 2WL indicate 
High resolution STM images of graphene on MoS 2. STM images with I t ¼ 33 nA and bias voltages of (a) V bias ¼ À50 mV and (b) V bias ¼ À1 mV. The graphene honeycomb lattice is seen in both images. The faint moirémoir´moiré structure in (a) is more pronounced in (b). In these images the graphene lattice is rotated by $12 relative to the underlying hexagonal lattice of MoS 2 , which gives rise to the pseudo-periodic moirémoir´moiré surperstructure as schematically illustrated in (c). The line scans shown in (d) are along the color-coded lines indicated in (b). The line scans illustrate the atomic corrugation and show that the corrugation of the moirémoir´moiré structure is only $0.3 ˚ A.
Photoemission studies of band lineup and charge doping at the graphene – MoS 2 interface. (a) Core level spectra C-1s. The peak is shifted by $ 0.09 eV to lower binding energy, indicating a downward shift of the Fermi level below the Dirac point. The relationship between the Fermi-level position and the C-1s core level and the work function is schematically illustrated in the inset of (a). (b) Band bending in MoS 2 as evaluated from Mo-3d core level shifts for MoS 2 and G – MoS 2 . He II-UPS measurements of G – MoS 2 and MoS 2 are shown in (c) – (e). (c) depicts the shift in the secondary electron cut-o ff for determining the sample's work function. The shift in the valence band maximum is shown in (d). Apparently the shift 
Article
Heterostructures of dissimilar 2D materials are potential building blocks for novel materials and may enable the formation of new (photo)electronic device architectures. Previous work mainly focused on supporting graphene on insulating wide-band gap materials, such as hex-BN and mica. Here we investigate the interface between zero-band gap semiconductor graphene and band-gap semiconductor MoS2 as a potential building block for entirely 2D-material based semiconducting devices. We show that solution transfer results in water trapping at the interface which may be removed by annealing to ∼300 °C in a vacuum. After removal of the water, by high temperature annealing, ultraflat graphene is obtained on MoS2 with only a very weak moiré pattern observable in scanning tunneling microscopy images due to lattice mismatch and random alignment of graphene with respect to the MoS2 substrate. Photoemission spectroscopy indicates interface dipole formation, p-type doping of graphene by ∼0.09 eV downward shift of the Fermi-level below the Dirac point, and a negative space charge region in bulk MoS2. Interestingly, valence band spectra of the graphene covered MoS2 surface indicate a band gap narrowing of the MoS2 surface by ∼0.1 eV. This band gap reduction at the surface is further evidence that interlayer van der Waals interactions critically influence the band structure of 2D-layered dichalcogenides and suggest that interfacing with dissimilar van der Waals materials allows tuning of their electronic properties.
 
Article
The synthesis and clarifications in structure-property relationship for anatase TiO(2) crystals exposing (001) facets have attracted much attention. In this paper, a novel titania microsphere with nearly all-(001) surface was synthesized by hydrothermal treatment of a thermal sprayed TiN/Ti coating with HF aqueous solution containing chromium powders. Unlike the conventional (001)-facet exposed anatase crystals, which are highly truncated bipyramids, the crystal achieved in the current investigation is drum-like with a round cross section. The formation of the drum-like crystals was contributed to a balance between the erosion and precipitation of anatase single crystallites. The Cr-doping in anatase was believed to increase the surface deficiency which enhanced the erosion procedure, leading to the drum-like crystals. The XPS analysis confirmed the incorporations of N, F and Cr in the microsized anatase crystals through the one-pot reaction, which led to a significantly enhanced solar absorption. The UV-Vis diffuse reflectance revealed a band-to-band red-shift of the band gap of the anatase crystals to 1.60 eV, which is contributed mainly to the homogeneous Cr-doping.
 
(a) TEM image, (b) HRTEM image, (c) SAED pattern of the as- prepared Bi 3 O 4 Cl nanosheets. (d) Schematic illustration of the crystal orientation of the nanosheet. (e) Schematic illustration of the liquid- 
(a) The variation of apparent reaction rate constants of Bi 3 O 4 Cl nanosheets on photocatalytic degradation of salicylic acid under visible-light irradiation along with changing percentages of {001} facets. (b) Photoluminescence spectra, (c) electrochemical impedance spectroscopy and (d) transient photocurrent responses of Bi 3 O 4 Cl nanosheets with different percentages of exposed {001} facets under visible light (l > 420 nm).
(a) Crystal structure of Bi 3 O 4 Cl nanosheets; (b) charge density contour plots viewed from {110} and { 110} facets of Bi 3 O 4 Cl 
Variation of the IEF magnitude, the efficiency of charge separation and transfer, and the photoreactivity versus the percentages of {001} facets of Bi 3 O 4 Cl nanosheets. All the IEF magnitude, the efficiency of charge separation and transfer and photoreactivity values of BOC-86 were set as "1".
Article
We prepared Bi3O4Cl single-crystalline nanosheets with high {001} facet exposure percentages and demonstrated that their photoreactivity strongly depended on the magnitude of the internal electric field (IEF), which was correlated with the {001} facet exposure percentage. More {001} facet exposure could induce the generation of stronger IEF, which favored the photogenerated charge separation and transfer, and thus enhancing the photoreactivity.
 
SEM images and XRD patterns of the seed layers made by (a and c1) spincoating and (b and c2) rubbing methods after calcination in air at 500 C for 2 h. 
(a) Top-view and (b) cross-sectional SEM images and (c) XRD pattern of the as-synthesized WO 3 film by the rubbing seed layer assisted by a hydrothermal method at 180 C for 24 h using 0.1 mol citric acid as a capping agent. (d) Photocurrent of the film after calcination in air at 500 C for 2 h. The inset is a magnified curve from À0.2 to 0.2 V. 
SEM images and XRD patterns of WO 3 films synthesized by the spincoating seed layer assisted by a hydrothermal method at 180 C for 12 h using 0.1 mol citric acid as a capping agent at different pH values. (a and d1) Initial pH 1.9, (b and d2) pH 2.3, and (c and d3) pH 2.5 (Low magnification images are shown in Fig. S2 †). 
(a) Top-view and (b) cross-sectional SEM images and (c) XRD pattern of the WO 3 film synthesized by the spin-coating seed layer assisted by a hydrothermal method at 180 C for 24 h using 0.1 mol oxalic acid as the capping agent. (d) Photocurrent of the film after calcination in air at 500 C for 2 h. 
Article
(001)-oriented monoclinic nanorod and microplate WO3 films are fabricated on commercial FTO-coated glass substrates by a rubbing seed layer and a spin-coating seed layer assisted by hydrothermal reactions. The nanorod film obtained by the rubbing seed layer assisted by hydrothermal reactions is more regular and perpendicular to the substrate.
 
(a, b) FE-SEM images of the flower-like TiO 2 nanostructures at low and high magnifications, respectively. (c) XRD pattern of the flowerlike TiO 2 nanostructures. Vertical bars indicate peak position and intensity of anatase TiO 2 (JCPDS No. 21-1272).
The variation of MB concentration by photoelectrocatalytic reaction with P25 TiO 2 powders and flower-like TiO 2 nanostructures. The inset shows the pseudo-first-order kinetic rate plots for the photochemical degradation of MB.
Article
Flower-like TiO(2) nanostructures with exposed {001} facets were synthesized by a low-temperature hydrothermal process from Ti powders for the first time, and they exhibited enhanced photocatalytic degradation of methylene blue dye under ultraviolet light irradiation.
 
AFM images of SMPs of (a) p 550 600 and (b) p 350 400 , after 50 nm Si buffer growth, the height profiles across the center of SMPs of (c) p 550 600 and (d) p 350 400 , before and after Si buffer growth. The white dashed lines in (a) and (b) denote the position of the height profiles in (c) and (d) respectively.
AFM images of the surface morphologies after 10 ML Ge deposition on SMPs of p 550 600 at (a) 500 C, (b) 540 C, and (C) 580 C. The arrow in (a) indicates a small QD.  
AFM images of the surface morphologies of SMPs of (a) p 450 600  
The surface chemical potential with different thicknesses of the Ge layer denoted by Z s À Z 0 and the corresponding height profile across the center of a SMP of p 550 600 .  
3D AFM images of a SMP of (a) p 550 600 , (b) p 450 600 , and (c) p 350 450 , after 10 ML Ge growth at 500 C, (d)–(f) are the corresponding 2D surface chemical potentials. The black dashed line contours indicate the regions of local chemical potential minima. The yellow dashed line contours in (b) and (c) denote the regions of {113} facets. The fitting parameter (Z s À Z 0 ) is 0.5 nm.  
Article
Self-assembled GeSi nanostructures on periodic Si (001) sub-micro pillars (SMPs) are systematically studied. Different GeSi nanostructures, including circularly arranged quantum dots, quantum rings and quantum dot molecules can be readily obtained at the edge of the pillars by controlling the growth temperatures and the diameter of the pillar. These phenomena are explained by taking into account the surface chemical potential around the top terrace of SMPs, which is considerably affected by the formation of {113} facets. Our results demonstrate a feasible route to obtain novel periodic Si pillars embedded with the desired GeSi nanostructures, which have promising applications in optoelectronic devices.
 
Article
In this work, we report a novel approach to fabricate hierarchical TiO2 microspheres (HTMS) assembled by ultrathin nanoribbons where an anatase/TiO2(B) heterojunction and high energy facet coexist. The as-adopted approach involves (1) nonaqueous solvothermal treatment of a mixture of tetrabutyl titanate and acetic acid and (2) topotactical transformation into HTMS via thermal annealing. By this approach, the TiO2(B) phase usually synthesized from an alkaline treatment route could be initially formed. Subsequently, phase transition from TiO2(B) to anatase TiO2 occurs upon thermal treatment. It is demonstrated that such phase transition is accompanied by crystallographic orientation along the c-axis of anatase and TiO2(B) crystals, resulting in not only a coherent interface between two phases but also oriented attachment of anatase mesocrystals along the [001] direction, and finally high-energy (001) facet exposure. Interestingly, this work provides an alternative fluorine-free route for the synthesis of TiO2 crystals with high-energy (001) facet exposure. The structural analysis reveals that lattice-match induced topotactic transformation from TiO2(B) to anatase is the sole reason for the (001) facet exposure of anatase TiO2. The photocatalytic test for acetaldehyde decomposition shows that HTMS with anatase/TiO2(B) heterojunction and high-energy (001) facet exhibits superior photocatalytic efficiency compared with the relevant commercial product P25, which can be ascribed to the synergistic effect of large surface area, anatase/TiO2(B) heterojunction as well as high-energy facet exposure.
 
Article
Titanium dioxide (TiO2) is one of the most widely investigated metal oxides due to its extraordinary surface, electronic and catalytic properties. However, the large band gap of TiO2 and massive recombination of photogenerated electron-hole pairs limit its photocatalytic and photovoltaic efficiency. Therefore, increasing research attention is now being directed towards engineering the surface structure of TiO2 at the most fundamental and atomic level namely morphological control of {001} facets in the range of microscale and nanoscale to fine-tune its physicochemical properties, which could ultimately lead to the optimization of its selectivity and reactivity. The synthesis of {001}-faceted TiO2 is currently one of the most active interdisciplinary research areas and demonstrations of catalytic enhancement are abundant. Modifications such as metal and non-metal doping have also been extensively studied to extend its band gap to the visible light region. This steady progress has demonstrated that TiO2-based composites with {001} facets are playing and will continue to play an indispensable role in the environmental remediation and in the search for clean and renewable energy technologies. This review encompasses the state-of-the-art research activities and latest advancements in the design of highly reactive {001} facet-dominated TiO2via various strategies, including hydrothermal/solvothermal, high temperature gas phase reactions and non-hydrolytic alcoholysis methods. The stabilization of {001} facets using fluorine-containing species and fluorine-free capping agents is also critically discussed in this review. To overcome the large band gap of TiO2 and rapid recombination of photogenerated charge carriers, modifications are carried out to manipulate its electronic band structure, including transition metal doping, noble metal doping, non-metal doping and incorporating graphene as a two-dimensional (2D) catalyst support. The advancements made in these aspects are thoroughly examined, with additional insights related to the charge transfer events for each strategy of the modified-TiO2 composites. Finally, we offer a summary and some invigorating perspectives on the major challenges and new research directions for future exploitation in this emerging frontier, which we hope will advance us to rationally harness the outstanding structural and electronic properties of {001} facets for various environmental and energy-related applications.
 
Article
In recent years, considerable effort has been devoted to finding novel enzyme mimetics with improved catalytic activities. However, the insightful understanding of such catalytic process is still elusive. In this paper, we report for the first time a typical photoactive layer-structured BiOBr as a novel biomimetic catalyst possessing highly efficient intrinsic peroxidase-like activity. Moreover, we have experimentally achieved high dark peroxidase-like catalytic activity in BiOBr microspheres and provided some new insights into the light-enhanced peroxidase-like catalytic property. On the basis of a typical color reaction derived from catalytic oxidation of peroxidase substrates over BiOBr microspheres with H2O2, the simple and sensitive colorimetric assays for detection of H2O2, glucose and ascorbic acid were successfully established. More interestingly, the BiOBr microspheres showed strong ability towards activation of H2O2, displaying excellent dark catalytic activity for the degradation of organic dye. It is therefore believed that our findings in this study could open up the possibility of utilizing BiOBr as enzymatic mimics in biotechnology and environmental remediation.
 
Article
Dye-sensitized solar cells (DSSCs) are fabricated based on anatase TiO(2) nanosheets (TiO(2)-NSs) with exposed {001} facets, which were obtained by a simple one-pot hydrothermal route using HF as a morphology controlling agent and Ti(OC(4)H(9))(4) as precursor. The prepared samples were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis absorption spectroscopy and N(2) adsorption-desorption isotherms. The photoelectric conversion performances of TiO(2)-NSs solar cells are also compared with TiO(2) nanoparticles (TiO(2)-NPs) and commercial-grade Degussa P25 TiO(2) nanoparticle (P25) solar cells at the same film thickness, and their photoelectric conversion efficiencies (η) are 4.56, 4.24 and 3.64%, respectively. The enhanced performance of the TiO(2)-NS solar cell is due to their good crystallization, high pore volume, large particle size and enhanced light scattering. The prepared TiO(2) nanosheet film electrode should also find wide-ranging potential applications in various fields including photocatalysis, catalysis, electrochemistry, separation, purification and so on.
 
AFM images (0.5 × 0.5 μm 2 ) of the surface morphologies after 5.4 ML Ge deposition at 515 °C on Si (001)/[100] θ with (a) θ = 0°, (b) θ = 3°, (c) θ = 5°, (d) θ = 7°, (e) θ = 9°, (f ) θ = 11°, respectively. The miscut direction of [100] is denoted by the arrow. The unit of color bar is nm.
Article
We demonstrate laterally aligned and catalyst-free GeSi nanowires (NWs) via self-assembly of Ge on miscut Si (001) substrates toward the [100] direction by an angle θ (θ < 11°). The NWs are bordered by (001) and (105) facets, which are thermodynamically stable. By tuning the miscut angle θ, the NW height can be easily modulated with a nearly constant width. The thickness of the wetting layer beneath the NWs also shows a peculiar behavior with a minimum at around 6°. An analytical model, considering the variation of both the surface energy and the strain energy of the epilayer on vicinal surfaces with the miscut angle and layer thickness, shows good overall agreement with the experimental results. It discloses that both the surface energy and stain energy of the epilayer on vicinal surfaces can be considerably affected in the same trend by the surface steps. Our results not only shed new light on the growth mechanism during heteroepitaxial growth, but also pave a prominent way to fabricate and meanwhile modulate laterally aligned and dislocation-free NWs.
 
Article
Porous BiOCl micro-flowers constructed from ultrathin nanosheets with nearly 100% {001} facets exposed were selectively prepared. The exposed {001} facets terminated with a high density of oxygen atoms and are not only favorable for the adsorption of the cationic dye RhB but also can accumulate the photogenerated electrons injected from excited RhB. These electrons can be captured by O(2) and transformed to reactive oxygen species, which possess a strong photooxidative ability to degrade the dye pollutants directly and easily. Therefore, the resultant BiOCl photocatalysts exhibit superior activity for indirect dye photosensitization degradation under visible light, with a rapid degradation rate and high photostability.
 
Article
[111]- and {010}-faceted anatase nanocrystals with controllable crystal size and morphology were synthesized from tri-titanate H2Ti3O7 nanosheets by hydrothermal reaction. The nanostructures and the formation reaction mechanism of the obtained TiO2 nanocrystals were investigated using XRD, FE-SEM, and TEM. Furthermore, the photocatalytic and dye-sensitized solar cell (DSSC) performances of the synthesized anatase nanocrystals were also characterized. Two types of reactions occur in the formation process of the anatase nanocrystals. One is an in situ topochemical conversion reaction of the layered titanate structure to an anatase structure, and another is the dissolution-deposition reaction on the particle surface, which splits the formed nanosheet-like particles into small TiO2 nanocrystals. The surface photocatalytic activity and the DSSC performance of the anatase nanocrystals are dependent on the crystal facet exposed on the particle surface, which increases in the order of non-facet < [111]-facet < {010}-facet. The increasing order corresponds to the increasing order of the bandgap and energy level of the lowest valence band of the anatase nanocrystals. Furthermore, the facet of the anatase also affects the DSSC performance, which is enhanced in the order of non-facet < [111]-facet < {010}-facet.
 
Article
Well shaped single crystalline Mn3O4 nano-octahedra with exposed highly active {011} facets at different particle sizes have been synthesized and used as anode materials for lithium ion batteries. The electrochemical results show that the smallest sized Mn3O4 nano-octahedra show the best cycling performance with a high initial charge capacity of 907 mA h g(-1) and a 50th charge capacity of 500 mA h g(-1) at a current density of 50 mA g(-1) and the best rate capability with a charge capacity of 350 mA h g(-1) when cycled at 500 mA g(-1). In particular, the nano-octahedra samples demonstrate a much better electrochemical performance in comparison with irregular shaped Mn3O4 nanoparticles. The best electrochemical properties of the smallest Mn3O4 nano-octahedra are ascribed to the lower charge transfer resistance due to the exposed highly active {011} facets, which can facilitate the conversion reaction of Mn3O4 and Li owing to the alternating Mn and O atom layers, resulting in easy formation and decomposition of the amorphous Li2O and the multi-electron reaction. On the other hand, the best electrochemical properties of the smallest Mn3O4 nano-octahedra can also be attributed to the smallest size resulting in the highest specific surface area, which provides maximum contact with the electrolyte and facilitates the rapid Li-ion diffusion at the electrode/electrolyte interface and fast lithium-ion transportation within the particles. The synergy of the exposed {011} facets and the smallest size (and/or the highest surface area) led to the best performance for the Mn3O4 nano-octahedra. Furthermore, HRTEM observations verify the oxidation of MnO to Mn3O4 during the charging process and confirm that the Mn3O4 octahedral structure can still be partly maintained after 50 discharge-charge cycles. The high Li-ion storage capacity and excellent cycling performance suggest that Mn3O4 nano-octahedra with exposed highly active {011} facets could be excellent anode materials for high-performance lithium-ion batteries.
 
Article
Monodisperse 10-nm V(2)O(3) pseudocubes enclosed by {012} facets were successfully synthesized for the first time via a novel and facile solvothermal method, offering the first opportunity to elucidate the effect of finite-size and facet on the temperature-induced reversible metal-insulator transition (MIT) behavior of V(2)O(3). Very excitingly, the transition temperature of these V(2)O(3) pseudocubes drastically depressed from 133 K to 36 K and their corresponding hysteresis width highly narrowed from 17 K to 5 K, compared to the MIT behaviors of other irregular V(2)O(3) particles with average sizes of 10 nm, 20 nm, 40 nm, 170 nm and 2 μm. Notably, the size-related surface energy, grain boundary connectivity and volume expansion could be used to account for their strong size-dependent transition temperature and hysteresis width. Moreover, the improved grain boundary connectivity associated with well-defined {012} facets enabled these 10-nm V(2)O(3) pseudocubes to display a 10 times higher resistivity jump (at the order of 10(5)) and by nearly one-half smaller hysteresis width of 5 K than the irregular 10-nm V(2)O(3) particles with randomly exposed facets, directly evidencing the pronounced influence of facets on the MIT behavior. Briefly, the present work not only develops an effective strategy for synthesizing high-quality nanocrystals but also provides an excellent platform to investigate the size- and facet-dependent temperature-induced MIT behavior, enabling to design smart electrical switching nano-devices in the rapidly developing ultra-low temperature field.
 
(a) Topographic STM image (+1.0 V, 50 pA; size: 10.1 × 18.5 nm 2 ) of a linear GB, consisting of individual (1,0) dislocations. The image is obtained by stitching two images with different scanning areas to show the whole length of the GB. (b) The line profile along the GB [the dashed blue line in (a)], showing a period of about 2.1 nm. (c) and (d) High resolution empty-state and filled-state images of the (1,0) dislocation from experiments (upper panel, ±1.0 V and 50 pA) and from simulations (lower panel), respectively; size: 2.1 × 2.3 nm 2 . The structural model of the (1,0) dislocation is superposed. (e) Magnified topographic STM image (3.6 × 5.1 nm 2 ) of the area marked by the rectangle in (a). A Burgers circuit is plotted around a (1,0) dislocation. (f ) An optimized structural model of two neighboring (1,0) dislocations, where the (1,0) dislocations are marked by the symbol ⊥. The notation of the GB is shown. (g) 3D image of the (1,0) dislocation (−1.0 V, 50 pA). (h) Side view of the optimized structural model of the (1,0) dislocation, showing an out-of-plane buckling height of 2.8 Å.  
(a) STM topographic image (−1 V, 50 pA; size: 3.6 × 5.1 nm 2 ), and (b) dI/dV map (+0.6 V, 50 pA), acquired within the same area. (c) and (d) The I–V curves and the dI/dV curves (+1.0 V, 50 pA), respectively, correspondingly acquired at the marked sites 1–11 in (a). The experimental data are shifted vertically for clarity in (c) and (d). The dashed lines in (d) are guides for the eyes only.  
The optimized structural model of GBs consisting of (1,0) dislocations . The simulation supercell and its size are indicated.  
Article
We present an investigation of the structural and electronic properties of an ordered grain boundary (GB) formed by separated pentagon-heptagon pairs in single-layer graphene/SiO2 using scanning tunneling microscopy/spectroscopy (STM/STS), coupled with density functional theory (DFT) calculations. It is observed that the pentagon-heptagon pairs, i.e., (1,0) dislocations, form a periodic quasi-one-dimensional chain. The (1,0) dislocations are separated by 8 transverse rows of carbon rings, with a period of ∼2.1 nm. The protruded feature of each dislocation shown in the STM images reflects its out-of-plane buckling structure, which is supported by the DFT simulations. The STS spectra recorded along the small-angle GB show obvious differential-conductance peaks, the positions of which qualitatively accord with the van Hove singularities from the DFT calculations.
 
Article
Redox behavior of endohedral metallofullerenes, in particular their oxidation process, can be classified as a fullerene-based or endohedral species-based process according to the mechanism of the electron transfer. Here we report on the phenomenon of the strain-driven electrochemical behavior achieved by encapsulating the cerium-containing clusters into a series of carbon cages ranging from C78 to C88. The Ce-based mixed metal nitride clusterfullerenes CexM3-xN@C2n (x = 1, 2; M = Sc or Y; 2n = 78-88) were synthesized and characterized. The magnitude of the inherent strain caused by the limited inner space of the carbon cage for the relatively large nitride clusters can be varied by choosing different scaffold metals (Sc, Lu, or Y) to tailor the size of the encaged CexM3-xN cluster and by matching the nitride cluster with different fullerene cages in the size range from C78 to C88. The redox properties of CexM3-xN@C2n were investigated by cyclic and square wave voltammetry. The mechanism of the electrochemical oxidation of Ce-based mixed metal nitride clusterfullerenes, in particular whether the fullerene-based oxidation or the Ce(III) → Ce(IV) process is observed, is found to be dependent on the scaffold metal and the size of the fullerene cage. The endohedral oxidation of Ce(III) to Ce(IV) was observed for a number of compounds as revealed by the negative shift of their oxidation potentials with respect to the values measured for the non-Ce analogues. Experimental studies are supported by DFT calculations. We conclude that the prerequisites for the Ce-based endohedral oxidation process are suitable inherent cluster-cage strain and sufficiently high oxidation potential of the fullerene cage.
 
Figure S22c Representative narrow beam ED spectrum reveals emission lines for Cu and stronger lines for Zn. Peak integration and background subtraction reveals the actual approximate Cu:Zn ratio for this region to be 0.26  
Figure S12c Representative narrow beam ED spectrum
Figure S18c Representative narrow beam ED spectrum
Article
An array of copper and copper-zinc based nanoparticles (NPs) have been fabricated employing a variety of polymeric capping agents. Analysis by TEM, XRPD and XPS suggests that by manipulating reagent, reductant and solvent conditions it is possible to achieve materials that are mono-/narrow disperse with mean particle sizes in the ≤10 nm regime. Oxidative stability in air is achieved for monometallic NPs using poly(methyl methacrylate) (PMMA) anti-agglomerant in conjunction with a variety of reducing conditions. In contrast, those encapsulated by either poly(1-vinylpyrrolidin-2-one) (PVP) or poly(4-vinylpyridine) (PVPy) rapidly show Cu(2)O formation, with all data suggesting progressive oxidation from Cu to Cu@Cu(2)O core-shell structure and finally Cu(2)O. Bimetallic copper-zinc systems, reveal metal segregation and the formation of Cu(2)O and ZnO. Catalysts have been screened in the synthesis of 1,2,3-triazoles through multicomponent azide-alkyne 1,3-dipolar cycloaddition. Whereas PMMA- and PVPy-coating results in reduced catalytic activity, those protected by PVP are highly active, with quantitative triazole syntheses achieved at room temperature and with catalyst loadings of 0.03 mol% metal for Cu and CuZn systems prepared using NaH(2)PO(2), N(2)H(4) or NaBH(4) reductants.
 
Article
Uniform, ultra-small-sized and well-water-dispersible LaF(3) nanoparticles doped with trivalent rare earth (RE) ions (Eu(3+) or Tb(3+)) have been synthesized by a simple, low temperature synthesis route. The nanoparticles, with sizes of about 3.2 nm (for those doped with Eu(3+)) and 3.0 nm (for those doped with Tb(3+)), are roughly spherical and monodisperse. 1,2,4,5-Benzenetetracarboxylic acid (labeled as BA) as sensitizer has been bonded to the surface of the nanoparticles, which can sensitize the emission of RE(3+) in the LaF(3) nanoparticles. The BA-LaF(3):RE(3+) (RE = Eu or Tb) nanoparticles have a broad absorption band in the UV domain, and show enhanced luminescence of RE(3+) based on an energy transfer from BA ligands to RE(3+) ions (i.e. the so-called "antenna effect"). Due to the dual protection of organic ligands (BA) and inorganic matrices (LaF(3)), BA-LaF(3):RE(3+) (RE = Eu or Tb) nanoparticles have longer excited state lifetimes than LaF(3):RE(3+) (RE = Eu or Tb) nanoparticles as well as lanthanide coordination polymers of BA.
 
Article
We calculate inelastic electron tunneling (IET) spectra for 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and tetrathiafulvalene dithiol (TTF-DT) sandwiched between two gold electrodes using non-equilibrium Green's function (NEGF) theory. The calculated peak positions are in reasonable agreement with the experimental data. We also calculate IET spectrum for thiophene dithiol (Th-DT) sandwiched between two gold electrodes and compare it with that for the Au/DMcT/Au junction. Th-DT and DMcT can be distinguished using the IET spectroscopy by the peak of the C-C stretching mode. The peak intensity in the IET spectra is analyzed using vibronic coupling density (VCD) analysis. For the Au/DMcT/Au junction, large distribution of electron-density difference Δρ(HOMO) on the C-N bond is responsible for the intense peak of the C-N stretching mode; on the other hand, for Au/TTF-DT/Au junction, large distribution of Δρ(HOMO) on the central C=C bond is responsible for the intense peak of the C=C stretching modes.
 
Article
The impacts of Au-thiolate bonding on the near infrared (IR) luminescence of Au nanoclusters are studied by designing two types of monolayer reactions. Firstly, 1,4-dithiol durene (durene-DT) is reacted with Au(25) monolayer protected clusters (MPCs) stabilized by phenylethanethiolate (PhC2S) ligands. Upon the addition of durene-DT, the near IR luminescence of Au MPCs intensifies while the well-defined absorbance bands diminish. The optical transition is associated with the ligand exchange process monitored by proton NMR. In the second approach, PhC2S monothiols are reacted with durene-DT stabilized Au nanoclusters (DTCs). The addition of PhC2S to the Au DTCs induces the gradual decrease of the near IR luminescence. Mass spectrometry and NMR analysis reveal similar final products of mixed thiolate Au nanoclusters from both reactions. The results suggest that the 1,4-dithiolate-Au bonding interaction is a promising factor to further enhance the near IR luminescence of Au nanoclusters for biomedical applications.
 
Article
In this study, novel hierarchical rose-like Cu1.8Se microspheres with a porous three-dimensional (3D) framework were successfully synthesized by using a one-pot in situ growth method at low temperature (60 °C). The Cu1.8Se microspheres covered the surface of the 3D porous framework. The formation mechanism was investigated in detail by adjusting the volume ratio of DMF and EDA, as the blend solvents, and the reaction time. Then, the chemical composition of the Cu1.8Se microspheres was altered by Ag(+) exchange without changing their morphology and structure. In this way, the binary Cu1.8Se was efficiently converted into the ternary CuAgSe. Notably, the band gap of materials was tuned continuously from 3.83 eV to 3.03 eV, and CuAgSe was produced continuously by adjusting the replacement time. This work provides a novel concept and a simple method that can serve as a good reference for improving the performance of tunable materials and the preparation of multielement alloy materials.
 
Article
SnO(2) nanorods with specific growth directions, [101] or [001], were fabricated on α-Fe(2)O(3) substrates via a simple hydrothermal method. The growth behavior of SnO(2) nanorods is facet-selective. Both {11 ̅20} and {10 ̅10} facets of α-Fe(2)O(3) are favorable to direct the growth of SnO(2) nanorods. The correlation between the crystallographic orientation of SnO(2) and the facets of α-Fe(2)O(3) is characterized by TEM observations and investigated on the basis of the interfacial lattice compatibility. Furthermore, the distribution and coordination of oxygen atoms at the interface of α-Fe(2)O(3)-SnO(2) heterostructure are analyzed, which reveals that only slight deviations from their original equilibrium positions are allowed for the formation of heterogeneous interface. And this lower energy activated interfacial construction is beneficial to the feasibility and stability of heterostructures.
 
Article
We have studied the electrochemical and thermodynamic stability of Au(25)(SR)(18)(-), Au(38)(SR)(24), and Au(102)(SR)(44), R = CH(3), C(6)H(13), CH(2)CH(2)Ph, Ph, PhF, and PhCOOH, in order to examine ligand effects on the stability of thiol-stabilized gold nanoclusters, Au(m)(SR)(n). Aliphatic thiols, in general, have higher electrochemical and thermodynamic stability than aromatic thiols, and the -SCH(2)CH(2)Ph thiol is particularly appealing because of its high electrochemical and thermodynamic stability. The stabilization of Au(m) by nSR for Au(m)(SR)(n) can be rationalized by the stabilization of an Au atom by an SR for the simple molecule AuSR, regardless of interligand interaction and system size and shape. Thiol moieties play a strong role in the electron oxidation and reduction of Au(m)(SR)(n). Accounting for the characteristics of thiol ligands is essential for understanding the electronic and thermodynamic stability of thiol-stabilized gold nanoclusters.
 
Article
We report a simple synthesis of silver:glutathione (Ag:SG) clusters using a cyclic reduction under oxidative conditions. Two syntheses are described which lead to solutions containing well-defined Ag31(SG)19 and Ag15(SG)11 clusters that have been characterized by mass spectrometry. The optical properties of silver:glutathione (Ag:SG) cluster solutions have been investigated experimentally. In particular, the solution containing Ag15(SG)11 clusters shows a bright and photostable emission. For Ag31(SG)19 and Ag15(SG)11 clusters, the comparison of experimental findings with DFT and TDDFT calculations allowed us to reveal the structural and electronic properties of such low nuclearity liganded silver clusters.
 
Article
Dual-modality imaging, using Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) simultaneously, is a powerful tool to gain valuable information correlating structure with function in biomedicine. The advantage of this dual approach is that the strengths of one modality can balance the weaknesses of the other. However, success of this technique requires developing imaging probes suitable for both. Here, we report on the development of a nanoparticle labeling procedure via covalent bonding with carbon-11 PET isotope. Carbon-11 in the form of [(11)C]methyl iodide was used as a methylation agent to react with carboxylic acid (-COOH) and amine (-NH2) functional groups of ligands bound to the nanoparticles (NPs). The surface coating ligands present on superparamagnetic iron-oxide nanoparticles (SPIO NPs) were radiolabeled to achieve dual-modality PET/MR imaging capabilities. The proof-of-concept dual-modality PET/MR imaging using the radiolabeled SPIO NPs was demonstrated in an in vivo experiment.
 
Article
The catalytic activity of pure Ni (110) and single Rh layer deposited Ni (110) surface for the complete dehydrogenation of methane is theoretically investigated by means of gradient-corrected periodic density functional theory. A detailed kinetic study, based on the analysis of the optimal reaction pathway for the transformation of CH4 to C and H through four elementary steps (CH4 → CH3 + H; CH3 → CH2 + H; CH2 → CH + H; CH →C + H) is presented for pure Ni (110) and Rh/Ni (110) surfaces and compared with pure Rh (110) surface. Through systematic examination of adsorbed geometries and transition states, we show that single layer deposition of Rh on Ni (110) surface has a striking influence on lowering the activation energy barrier of the dehydrogenation reaction. Moreover, it is found that a pure Ni (110) surface has a tendency for carbon deposition on the catalytic surface during the methane dissociation reaction which decreases the stability of the catalyst. However, the deposition of carbon is largely suppressed by the addition of a Rh overlayer on the pure Ni (110) surface. The physical origin of stronger chemisorption of carbon on Ni (110) relative to Rh/Ni (110) has been elucidated by getting insight into the electronic structures and d-band model of the catalytic surfaces. Considering the balance in both the catalytic activity as well as the catalyst stability, we propose that the Rh/Ni (110) surface possesses much improved catalytic property compared to pure Ni (110) and pure Rh (110) surfaces.
 
Article
In this paper, we report on the fabrication of a novel rutile TiO(2) architecture consisting of nanorods with {110} exposed facets through a simple hydrothermal method without using any templates. An outside-in ripening mechanism is proposed to account for the formation of the TiO(2) architectures.The formation of the TiO(2) architectures can be attributed to the Ostwald step rule and highly acidic medium. Significantly, the current method is suitable for high-yield (>98%) production of the TiO(2) architectures with nearly 100% morphological yield. This research provides a facile route to fabricate rutile TiO(2) with three-dimensional microstructures based on nano units. It is easy to realize their industrial-scale synthesis and application because of the simple synthesis method, low cost, and high yield.
 
Article
Understanding molecular switching between different charge states is crucial to further progress in molecule-based nano-electronic devices. Herein we have employed scanning tunnelling microscopy to visualize different charge states of a single C60 molecule within a molecular layer grown on the WO2/W(110) surface. The results obtained demonstrate that individual C60 molecules within the layer switch between neutral and negatively charged states in the temperature range of 220-260 K over the time scale of the experiment. The charging of the C60 causes changes in the local density of electron states and consequently a variation in tunnelling current. Using density functional theory calculations, it was found that the charged state corresponds to the negatively charged C60-, which has accepted an electron. The switching of the molecule into the charged state is triggered continuously by tunnelling electrons when the STM tip is static above an individual C60 molecule with a bias applied. Molecular movement accompanies the molecule's switching between these states.
 
Article
The thermal induced on-surface chemistry of large polycyclic aromatic hydrocarbons (PAHs) deposited on dielectric substrates is very rich and complex. We evidence temperature-assisted (cyclo)dehydrogenation reactions for C60H30 molecules and the subsequent bottom-up formation of assembled nanostructures, such as nanodomes, on the TiO2(110) surface. To this aim we have deposited, under ultra-high vacuum, a submonolayer coverage of C60H30 and studied, by a combination of experimental techniques (STM, XPS and NEXAFS) and theoretical methods, the different chemical on-surface interaction stages induced by the increasing temperature. We show that room temperature adsorbed molecules exhibit a weak interaction and freely diffuse on the surface, as previously reported for other aromatics. Nevertheless, a slight annealing induces a transition from this (meta)stable configuration into chemisorbed molecules. This adsorbate-surface interaction deforms the C60H30 molecular structure and quenches surface diffusion. Higher annealing temperatures lead to partial dehydrogenation, in which the molecule loses some of the hydrogen atoms and LUMO levels spread in the gap inducing a net total energy gain. Further annealing, up to around 750 K, leads to complete dehydrogenation. At these temperatures the fully dehydrogenated molecules link between them in a bottom-up coupling, forming nanodomes or fullerene-like monodisperse species readily on the dielectric surface. This work opens the door to the use of on-surface chemistry to generate new bottom-up tailored structures directly on high-K dielectric surfaces.
 
(a) and (b) STM images of the same titania area after the deposition of 0.05 MLE Ceria with di ff erent tunneling parameters: (a): 1.1 V 0.07 nA, (b): 0.75 V, 0.07 nA. The inset in (b) displays a high-resolution image of the ceria clusters showing a peculiar shadowing on the surrounding titania. (c) and (d) STM pictures of the same region of 0.45 MLE CeO x taken with di ff erent tunneling parameters (c): 1.3 V, (d) 1.5 V. Titania and ceria 
STM images of (a) 0.75 MLE CeO x ; three distinct type of regions can be seen (1.1 V, 0.1 nA); (b) close up on a type III islands (1.1 V, 0.3 nA); (c) large scan area of the surface after the deposition of 0.9 MLE CeO x (1.2 V, 0.1 nA); (d) zoom in on an island showing some troughs aligned along 
1.2 MLE CeO x on titania; (a) large scale image showing the three di ff erent regions; (b) close view of two cerium oxide islands showing the distinctive zig-zag pattern of the domain boundaries; (c) high resolution image (0.8 V, 0.12 nA) of an oxide island; inset shows the resolution of the same area obtained with a di ff erent tip condition and tunneling parameters (1.2 V, 0.7 nA); (c) STM image showing the epitaxial relationship between the oxide island and the titania substrate. The black lines are positioned on bridging oxygen rows of the TiO 2 (110) surface. 
Phase diagram summarizing the different ceria nanostructures that can be grown on TiO 2 (110) as a function of temperature and coverage.
Article
Novel interface-stabilized ceria nanophases have been grown on TiO2(110) by physical vapor deposition. At low coverage, dumbbell nanostructures constituted by reconstructed titania and ceria clusters are formed, while long range ordered nanoxides can be obtained by increasing the ceria dose. Scanning tunneling microscopy and photoemission spectroscopy were used to characterize the electronic properties of the films, showing that the TiO2 substrate can effectively stabilize ceria in reduced form over a wide range of experimental conditions. Epitaxial coupling is a very useful tool for tuning the chemical properties of mixed oxide systems. The special electronic properties of the films have a direct counterpart in the chemical activity, which has been investigated by temperature programmed desorption using methanol as a probe molecule. The experimental results indicate an exceptional activity of the ceria-titania interface in the selective dehydration of methanol to formaldehyde at an unprecedented low temperature (330 K).
 
Article
Benzotriazole (BTAH) has been used as a copper corrosion inhibitor since the 1950s; however, the molecular level detail of how inhibition occurs remains a matter of debate. The onset of BTAH adsorption on a Cu(111) single crystal was investigated via scanning tunnelling microscopy (STM), vibrational spectroscopy (RAIRS) and supporting DFT modelling. BTAH adsorbs as anionic (BTA(-)), CuBTA is a minority species, while Cu(BTA)2, the majority of the adsorbed species, form chains, whose sections appear to diffuse in a concerted manner. The copper surface appears to reconstruct in a (2 × 1) fashion.
 
Article
Single crystalline, thermally stable, Co(3)O(4) (111) holey nano-sheets were prepared by an efficient, template-free, wet chemical synthetic approach. The high energy (111) surfaces formed can be used as highly active heterogeneous catalysts for methanol decomposition.
 
Article
Heptamethinecyanine J-aggregates display sharp, intense fluorescence emission making them attractive candidates for developing a variety of chem-bio-sensing applications. They have been immobilized on planar thiol-covered Au surfaces and thiol-capped Au nanoparticles by weak molecular interactions. In this work the self-assembly of novel thiolated cyanine (CNN) on Au(111) and citrate-capped AuNPs from solutions containing monomers and J-aggregates has been studied by using STM, XPS, PM-IRRAS, electrochemical techniques and Raman spectroscopy. Data show that CNN species adsorb on the Au surfaces by forming thiolate-Au bonds. We found that the J-aggregates are preferentially adsorbed on the Au(111) surface directly from the solution while adsorbed CNN monomers cannot organize into aggregates on the substrate surface. These results indicate that the CNN-Au interaction is not able to disorganize the large J-aggregates stabilized by π-π stacking to optimize the S-Au binding site but it is strong enough to hinder the π-π stacking when CNNs are chemisorbed as monomers. The optical properties of the J-aggregates remain active after adsorption. The possibility of covalently bonding CNN J-aggregates to Au planar surfaces and Au nanoparticles controlling the J-aggregate/Au distance opens a new path regarding their improved stability and the wide range of biological applications of both CNN and AuNP biocompatible systems.
 
Band structures of the clean Cu(111) substrate and the graphene – Cu(111) system around the (a and b) G and (c and d) K points of the fi rst BZ of graphene, which are measured along the blue and red lines as described in the insets, respectively. The inset in (d) indicates the intensity of photoelectrons. 
Article
Copper is considered to be the most promising substrate for the growth of high-quality and large area graphene by chemical vapor deposition (CVD), in particular, on the (111) facet. Because the interactions between graphene and Cu substrates influence the orientation, quality, and properties of the synthesized graphene, we studied the interactions using angle-resolved photoemission spectroscopy. The evolution of both the Shockley surface state of the Cu(111) and the π band of the graphene was measured from the initial stage of CVD growth to the formation of a monolayer. Graphene growth was initiated along the Cu(111) lattice, where the Dirac band crossed the Fermi energy (EF) at the K point without hybridization with the d-band of Cu. Then two rotated domains were additionally grown as the area covered with graphene became wider. The Dirac energy was about -0.4 eV and the energy of the Shockley surface state of Cu(111) shifted toward the EF by ∼0.15 eV upon graphene formation. These results indicate weak interactions between graphene and Cu, and that the electron transfer is limited to that between the Shockley surface state of Cu(111) and the π band of graphene. This weak interaction and slight lattice mismatch between graphene and Cu resulted in the growth of rotated graphene domains (9.6° and 8.4°), which showed no significant differences in the Dirac band with respect to different orientations. These rotated graphene domains resulted in grain boundaries which would hinder a large-sized single monolayer growth on Cu substrates.
 
Article
The controllable fabrication of self-scrolling SiGe/Si/Cr helical nanoribbons on Si(111) substrates is investigated. The initial lateral etching profile of the Si(111) substrates shows a 2-fold rotational symmetry using 4% ammonia solution, which provides guidance for initial scrolling of one-end-fixed nanoribbons to form helical structures. The chirality of the SiGe/Si/Cr helices with isotropic Young's moduli is governed by the anisotropic underetching in the initial stage, which can be precisely judged, as the orientation of the ribbon is predesigned. Furthermore, the helicity angle and radius of the formed helices are investigated by the lateral etching behavior and Cosserat curve theory of the Si(111) substrates, respectively, which are consistent with the experimental data. The present work provides the scrolling rule of nanoribbons with an isotropic Young's modulus and anisotropic underetching in the formation of micro-/nanohelices.
 
Article
The electropolymerization of 3,4-ethylenedioxythiophene (EDOT) to poly(3,4-ethylenedioxythiophene) (PEDOT) was investigated in the air and water-stable ionic liquids 1-hexyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate [HMIm]FAP and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide [EMIm]TFSA. In situ scanning tunnelling microscopy (STM) results show that the electropolymerization of EDOT in the ionic liquid can be probed on the nanoscale. In contrast to present understanding, it was observed that the EDOT can be oxidised in ionic liquids well below its oxidation potential and the under potential growth of polymer was visualized by in situ STM. These results serve as the first study to confirm the under potential growth of conducting polymers in ionic liquids. Furthermore, ex situ microscopy measurements were performed. Quite a high current of 670 nA was observed on the nanoscale by conductive scanning force microscopy (CSFM).
 
Article
A novel approach to construct organized structures and tunable electronic properties of poly(3-hexylthiophene) (P3HT) monolayers on Au(111) surfaces was developed based on a self-assembly process in a liquid phase. On a bare Au(111) surface, P3HT adsorbs as a monolayer with a randomly oriented and curvy-wire morphology. When the gold surface was pre-modified by an iodine adlayer (I-Au(111)), the passivation effect of iodine decreases the substrate-adsorbate interaction. As a result, P3HT adsorbs as linear chains, stacking and folding into regular arrays of a polymer bundle. By controlling the electrode at more negative potentials, it is able to desorb the iodine adlayer from the substrate. The remaining P3HT adsorbs onto the Au(111) surface directly, retaining a linear and regular arrangement. However, a different electronic structure is imaged by scanning tunneling microscopy (STM). The scanning tunneling spectroscopy (STS) analysis reveals that this molecular image is associated with a 0.16 eV shift of the Fermi level toward HOMO position, indicating a stronger p-doping characteristic of the adlayer. The phenomenon is ascribed to an iodine-induced p-doping reaction which occurs during the desorption of iodine. This work demonstrates that electrode potential and pre-adsorbed halide adlayers can be effectively used to regulate the arrangement and electronic properties of adsorbed molecules on metallic substrates.
 
Article
We demonstrate the fabrication of n-GaN:Si/p-GaN:Mg nanowire arrays on (111) silicon substrate by metal organic chemical vapor deposition (MOCVD) method .The nanowires were grown by a newly developed two-step growth process. The diameter of as-grown nanowires ranges from 300-400 nm with a density of 6-7 × 107 cm-2. The p- and n-type doping of the nanowires is achieved with Mg and Si dopant species. Structural characterization by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) indicates that the nanowires are relatively defect-free. The room-temperature photoluminescence emission with a strong peak at 370 nm indicates that the n-GaN:Si/p-GaN:Mg nanowire arrays have potential application in light-emitting nanodevices. The cathodoluminscence (CL) spectrum clearly shows a distinct optical transition of GaN nanodiodes. The nano-n-GaN:Si/p-GaN:Mg diodes were further completed using a sputter coating approach to deposit Au/Ni metal contacts. The polysilazane filler has been etched by a wet chemical etching process. The n-GaN:Si/p-GaN:Mg nanowire diode was fabricated for different Mg source flow rates. The current-voltage (I-V) measurements reveal excellent rectifying properties with an obvious turn-on voltage at 1.6 V for a Mg flow rate of 5 sccm (standard cubic centimeters per minute).
 
Top-cited authors
Nam-Gyu Park
  • Sungkyunkwan University
Jonathan Coleman
  • Trinity College Dublin
Yi-Jun Xu
  • Fujian
Vincenzo Palermo
  • Italian National Research Council
Daniel Jaque
  • Universidad Autónoma de Madrid