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G-C₃N₄ has a bright application prospect as an electrode material of supercapacitors, which makes it a concern. In order to increase the specific capacitance of g-C₃N₄, we consider to combine it with a metal oxide with high theoretical specific capacitance and utilize the synergistic effect. As a common metal oxide, CuO has the characteristics of high theoretical capacitance, high chemical stability, simple preparation and environmental friendliness. A composite containing CuO nanobelts and graphitic C₃N₄ (g-C₃N₄) was successfully synthesized by a chemical precipitation method. Various testing methods were used to explore its composition, microstructure and electrochemical properties to discuss whether CuO is suitable for improving the electrochemical properties of g-C₃N₄.

A porous biomorphic woodceramic was prepared from bagasse powders infiltrated with the epoxy resin followed by sintering in vacuum. The microstructures and chemical structures of the woodceramics were studied by SEM and FTIR, respectively. The effect of the sintering temperature and content of bagasse on the carbon yield ratio, volume shrinkage ratio, and volume electrical resistivity of the woodceramics were studied. Experimental results show that the pores in woodceramics present the irregular distribution but the main structural features of the tracheidal cell structures are retained. The woodceramic is a carbon material containing C–O–C, C=C, C=O and C–H bonds. The carbon yield ratio of the woodceramics decreases with the increase of the content of bagasse. While the volume shrinkage ratio and volume electrical resistivity increase with the increase of the content of bagasse.

Much more is known about material failure, such as fracture and crack propagation, than the reverse effect of material formation, i.e., how bulk materials form or consolidate during material processing or crack healing. Using the Surface Forces Apparatus, optical interferometry, optical and scanning probe microscopy, and x-ray diffraction, we have studied how gold and platinum films sinter or cold-weld at the nano-scale to form continuous bulk films when two initially rough surfaces composed of nanometer-scale asperities are pressed together. We find that coalescence of these ductile materials occurs abruptly, like a first order phase transition, once a critical local pressure or interparticle separation is reached. Simple thermodynamic and kinetic considerations suggest that it may be a more general phenomenon for ductile materials interacting at the nano-scale. We also make some qualitative comparisons with the very different behavior observed with hard, brittle materials.

The interface between an oxide substrate and a metal overlayer may crucially influence the macroscopic behavior of technological devices such as sensors, catalysts, ceramics, and semiconductor chips. Hence investigations of adsorption, nucleation and growth of ultrathin metal films on metal oxide surfaces have attracted increasing interest during recent years. Experimental results on the growth of metal overlayers on a model oxide, TiO 2 (110), are reviewed. The emphasis is on the very initial stages of overlayer growth and on extracting general trends on metal/metal-oxide interaction by comparing results from different metal overlayers. The electronic and geometric structure, growth mode, interface formation, and thermal stability of metal films are discussed. The strength of the oxidation/reduction reaction at the interface, the wetting ability and the tendency to form a disordered layer are all related to the reactivity of the overlayer metal towards oxygen. We propose that ‘reactive adsorption’ accounts for the observed trends.

A study of ultrathin Cr films on TiO2(110) surfaces is reported. The combination of low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS) enables us to study quantitatively the growth of reactive metal films on metal oxides, and the chemical interactions at the interface. Ultrathin Cr films grow initially in a quasi-two-dimensional fashion at room temperature. Changes in oxidation states of both Ti and Cr during film formation suggest that strong chemical interactions at the interface are of great importance in the growth of reactive metal films. Cr “wets” the surface more effectively at 300 K than ultrathin films of less reactive metals, Fe and Cu. This suggests that a relation exists between the metal reactivity with oxygen and the wetting of metal films on oxides: The more reactive the metal towards oxygen, the better is the wetting ability. The chemical interaction is accompanied by charge transfer at the interface, causing a reduction of the surface work function. The interfacial interaction also causes the interfacial Cr layer to behave differently from the top metallic Cr atoms upon thermal annealing. The top layers of metallic Cr show a strong clustering tendency at 500°C, while the interfacial Cr seems to have less surface mobility and slow bulk diffusion.

As part of a systematic study of metals on oxides, we report here a study of the growth of Fe films on TiO2(110) surfaces using low‐energy ion scattering and x‐ray photoelectron spectroscopy (XPS). Our studies reveal that Fe grows initially in an island growth mode, and completely covers the TiO2 substrate for thicknesses of a few monolayers. XPS shows evidence for a strong interaction between Fe films and the oxide substrate, i.e., oxidation of Fe overlayers and reduction of the oxide substrate, at submonolayer thickness. Comparing the wetting ability of Fe with that of Cu, a less reactive metal, and with that of Cr, a more reactive metal, we observe a relation between the wetting ability of the metal films and the reactivity of metal with oxygen. Complete coverage of the TiO2 substrate can be obtained for a 1 monolayer Fe film following oxidation of the film. Studies of Fe film growth on sputtered TiO2 surfaces indicate that surface roughness also plays an important role in the morphology of the metal f...

A structural study of ultrathin Cr, Fe and Cu metal films on stoichiometric and Ar+ sputtered TiO2(110) surfaces has been carried out using low energy electron diffraction (LEED), angle-resolved XPS (ARXPS) and two-dimensional medium energy backscattered electron diffraction (MEED). Although LEED results indicate only weak long range order for all three metal films (Cr, Fe and Cu) on TiO2(110), clear evidence for a locally ordered structure can be observed using ARXPS and MEED. Both Cr and Fe films grow with bcc(100) structures on stoichiometric TiO2(110) yielding pronounced forward scattering features in ARXPS and MEED data. Cu overlayers grow with fcc(111) structures exhibiting two equivalent domain orientations on TiO2(110) that yield less pronounced features in ARXPS. However, MEED measurements of Cu films with different electron surface incidence angles show clear fcc(111) patterns for different domains. Both bcc(100) and fcc(111) MEED patterns are simulated by single scattering cluster (SSC) calculations, and the results are qualitatively consistent with experimental data. A bcc(100) short range ordering is also observed for ultrathin Cr and Fe films on long range disordered Ar+ sputtered TiO2(110) surfaces.

We have studied the growth of ultrathin (< 50 A) Cu overlayers on stoichiometric TiO2(110) surfaces. Using low energy ion scattering, the growth mode of Cu was determined to be Volmer-Weber type (three-dimensional islands) at room temperature; evidence for cluster growth is observed even at 160 K. A comparison with Fe and Cr metal films shows that the spreading of the films correlates with the heat of formation of the metal oxide of the overlayer. Fe and Cr cause a reduction of the Ti4+ surface cations at the metal/metal oxide interface as observed with X-ray photoelectron spectroscopy. No reduction of the TiO2 cations takes place upon contact with a Cu overlayer.

Copper overlayers with thicknesses up to several tens of angstroms have been vapor deposited at various substrate temperatures onto rutile ${\mathrm{TiO}}_{2}$(110) surfaces that have different defect concentrations. The metal films have been studied by means of ${\mathrm{He}}^{+}$ low-energy ion scattering, x-ray photoelectron spectroscopy, and LEED (low-energy electron diffraction). Our measurements clearly show that Volmer-Weber growth (formation of three-dimensional crystallites) occurs even at sample temperatures as low as 160 K. Defects created by sputtering the substrate prior to Cu deposition do not influence the subsequent growth of the Cu films. The clusters are oriented with their (111) orientation parallel to the surface as confirmed by LEED. During low-temperature annealing, a coarsening of the crystallites takes place. The size of the clusters and the coverage have been modeled using simple assumptions about their shape. An average thickness of approximately 10 \AA{} is needed to cover half of the sample with Cu. The growth mode can be attributed to a very weak interaction between Cu and the substrate.

We report evidence in this letter for the encapsulation of Fe clusters supported by single crystal TiO2. After thermal annealing in ultrahigh vacuum (UHV) at 500–700 ° C for several hours, Fe clusters are almost completely covered by Ti suboxides TiOx while Fe remains mainly in the metallic state. The phenomenon can be clearly measured using LETS (low energy ion scattering) and XPS (X-ray photoelectron spectroscopy).

We have studied the stoichiometric (annealed in oxygen), the slightly oxygen‐deficient (annealed in vacuum), and the highly defective (sputtered with Ar+) TiO2(110) surfaces and their reactivities to molecular oxygen, molecular water, and 50‐eV hydrogen ions using x‐ray photoelectron spectroscopy (XPS) and low‐energy ion scattering spectroscopy (LEIS). The use of isotopically labeled 18O enables us to distinguish adsorbed oxygen from lattice oxygen, and the concentration of surface oxygen vacancies is titrated by 18O2 adsorption. LEIS (1‐keV He+) is used to analyze the chemical composition of the outermost surface layer before and after 18O2 and H218O exposure. Water adsorbs on both stoichiometric and slightly O‐deficient surfaces [with oxygen vacancies ∼0 and 0.08 monolayer (ML), respectively] at room temperature. There is little or no dependence of saturation water coverage (lower limit of ∼0.07 ML for both surfaces) on the concentration of surface oxygen vacancies. On the highly defective surfaces, the...

We have studied the growth kinetics and structure of 3d transition metals (Cr, Fe, Cu) evaporated onto TiO2(110), a model oxide substrate. Using Low Energy Ion Scattering (LEIS) and X-ray Photoelectron Spectroscopy (XPS), we find that Cu grows in the Volmer-Weber (3-D island) mode. The mobility of Cu atoms is very high, and 3-dimensional clusters are formed even at 160 K for Cu thicknesses < 30 A. In contrast, the Cr and Fe films completely cover the TiO2 substrate for thicknesses of a few ML, indicating that Cr and Fe “wet” the surface better than Cu. The ability of the metal film to cover (wet) the oxide substrate correlates directly with the reactivity of the metal toward oxygen. There is no XPS evidence for a strong chemical interaction between the Cu film and the oxide substrate. However, for the Cr and Fe films, we observe a strong interaction between the films and the oxide substrate, i.e., oxidation of the metal overlayers and reduction of the substrate, at submonolayer thickness. A bcc(100) structure is observed for Cr and Fe films with thickness ≥ 10 A, on both stoichiometric and sputtered substrates using Angle-Resolved XPS (ARXPS), Medium Energy backscattered Electron Diffraction (MEED) and LEED. The overlayer structure orientation is related to the substrate local structure.

Low energy He+ ion scattering (LEIS) studies have been performed on TiO2(110), polycrystalline Ti, and Ti with oxide and water overlayers. It is found that the energy dependence of the O/Ti LEIS intensity ratio for TiO2 is due to ion neutralization and/or reionization and is not the result of shadowing effects. The studies of water covered surfaces indicate attenuation of LEIS intensities due to the presence of hydrogen atoms.

Medium-energy backscattered electron diffraction (MEED) studies are reported for the rutile TiO 2 (110) surface. Two-dimensional diffraction images are obtained using a retarding field analyzer with a microchannel plate-intensified detector. Background removal is accomplished using digital image processing techniques. We find that the backscattered pattern for 750 eV incident electrons is predominantly due to diffraction of the outgoing electrons (subsequent to backscattering from subsurface atoms) by overlying lattice atoms. We also find effects related to the orientation of the incident beam relative to the surface. These effects are ascribed to diffraction of the incoming electrons (prior to backscattering) and possibly the focusing of electron intensity on second-layer atoms. Single-scattering cluster (SSC) calculations are used to model the outgoing diffraction process. The results are qualitatively consistent with a bulk-like termination of the TiO 2 (110) surface.