TiC Surface Research Articles

Effects of W segregation on oxidation of TiC(001) studied by low-energy ion scattering and Auger electron spectroscopy

The segregation of W impurities at the TiC(001) surface has been investigated by using impact collision ion scattering spectroscopy and Auger electron spectroscopy. The topmost layer of TiC(001) is strongly enriched with W accompanied by carbon vacancies (20–25%) in their nearest neighbors, while no marked enrichment of W occurs in the deeper layers. The oxygen is incorporated by the (001) surface irrespective of the existence of W segregants, whereas its uptake rate is moderately enhanced by W, due probably to oxygen diffusion into the bulk mediated by the carbon vacancies.

Electronic structure of monolayer graphite on a TiC(111) surface.

Electronic structure of monolayer graphite on a TiC(111) surface.

Surface segregation in titanium carbide studied by low-energy Li + ion scattering

Low-energy Li + ion scattering is employed to study surface segregation of dilute transition-metal impurities (0.6 wt% of W, Ta, Zr, Nb and Mo) in TiC by applying two scattering angles so as to perform the layer-by-layer analysis of the atomic concentration. A marked face dependence of the impurity distribution is observed in the first five layers. At the close-packed (100) surface, the first layer is strongly enriched with the segregants substituted for the Ti atoms with the concentration of as large as 90 at%, though the deeper layers exhibit no marked enrichment of the segregants. At the TiC(111) surface, on the other hand, the segregants distribute not only at the topmost layer but also in the deeper layers at least up to the fifth layer with almost the same concentration of about 6 at%.

Microstructure and fracture behavior of hot-pressed [formula omitted] composites

Silicon nitride containing various compositions of TiC were hot-pressed at 1800°C for 1 h in a nitrogen atmosphere. The grain growth was inhibited and the aspect ratio was slightly decreased with the addition of TiC. Cracks were often observed cleavaging along preferred orientations inside TiC with large deflected angles. Typical secondary brittle fracture patterns were observed inside TiC with fracture initiated near the TiC surface. Fracture toughness was enhanced by 30% with the addition of 20% vol TiC.

Surface-shifted N 1s and C 1s levels on the (100) surface of TiN and TiC.

A high-resolution core-level-photoemission investigation of the (100) surface of TiN and TiC is reported. A surface-shifted component is revealed in both the N 1s level on TiN and in the C 1s level on TiC. Using a curve-fitting procedure a surface shift of -0.57 eV is extracted for the N 1s component on TiN and a shift of -0.26 eV for the C 1s component on TiC. No surface-shifted Ti 2p level could be revealed on either TiN or TiC. These results do not agree with earlier calculated results for TiC which predicted no surface shift in the C 1s level but a small positive shift in the Ti s levels. Using a thermochemical model and accounting only for the loss of coordination at the surface, a shift of -0.07 eV is estimated both for the N 1s level in TiN and for the C 1s level in TiC.

Electronic states of monolayer graphite formed on TiC(111) surface

Electronic states of a monolayer graphite formed on TiC(111) surface have been investigated by means of XPS, UPS, and work-function measurement. The chemical shift of C1s peaks in XPS spectra has inhibited a large electron transfer from the substrate to the monolayer graphite. On the other hand, the band structure of the graphite overlayer has altered from that of bulk graphite. The work-function measurement has suggested an electron redistribution in the graphite layer. These results indicate that the electronic states of the graphite monolayer are modified not by the charge transfer, but mainly by the orbital hybridization between the graphite monolayer and the substrate, which differs from graphite intercalation compounds.

Electronic states of monolayer graphite formed on TiC(111) surface

Electronic states of monolayer graphite formed on TiC(111) surface

Chemisorption state of atomic oxygen on TiC(100) surface: angle-resolved photoemission study

Angle-resolved photoemission spectroscopy with synchrotron radiation has been used to study oxygen adsorption on a TiC(100) surface at room temperature. Oxygen is adsorbed dissociatively, and the O 2p-derived states of atomic oxygen are found at 4.1 and 5.9 eV at the Γ̄gG point. From polarization-dependent measurements, these states are assigned to the 2p x,y - and 2p z -derived states, respectively. Two-dimensional band dispersions of these states in the Γ̄gGM̄ direction are mapped from the off-normal-emission measurements. The measured band structure suggests that the 2p z orbital is relatively more stabilized through the chemisorption bonding. The cross section of the O 2p-derived states does not show a resonance at the energy region of the Ti3p-3d transition threshold, indicating that a hybridization of the Ti3d and O 2p orbitals contributes little to the chemisorption bonding. These results are compatible with the C on-top site adsorption model.

Chemisorption state of atomic oxygen on TiC(100) surface: angle-resolved photoemission study

Chemisorption state of atomic oxygen on TiC(100) surface: angle-resolved photoemission study

A Pseudolipoma on the Diaphragmatic Surface of the Liver in a Female B6C3F1 Mouse

A Pseudolipoma on the Diaphragmatic Surface of the Liver in a Female B6C3F1 Mouse

Effects by Coating with Titanium Carbide of Carburized Gear Steel on Fatigue Strength.

The purpose of this study is to investigate the fatigue strength of carburized gear steel chemically vapor deposited with titanium carbide, and to clarify the main effect of carburized gear steel coated with titanium carbide on fatigue strength, including comparison with noncoated steel. Case depth of carburized gear deff is 1.3 mm. Quenching and tempering heat treatment after coating was also introduced. Smooth specimen, that is, flat plates and spur gear, module 4 with number of teeth 55, were supplied to fatigue test. Residual stress in TiC surface layer and substrate was detected by X-ray diffraction method. It is concluded that main effect on fatigue strength of chemically coated steel on carburized steel is substrate hardness near surface layer, and residual stress in titanium carbide layer doesn't effect prominently on fatigue strength. And finally it is found that the residual stress in both TiC layer and substrate near interface indicates possibility of a micro crack initiation at the interface between titanium carbide and substrate.

Electronic structure of the (1 x 1) oxygen overlayer on TiC(111): Angle-resolved photoemission study.

Angle-resolved photoemission spectroscopy with synchrotron radiation has been used to study the electronic state of oxygen adsorbed on a TiC(111) surface at room temperature. Oxygen is adsorbed dissociatively forming a (1×1) overlayer on the TiC(111) surface at saturation coverage. The band structure of the (1×1)-O overlayer is measured in the two symmetry directions; (Γ M) and (Γ K)of the TiC(111) surface

Two-dimensional plasmons in monolayer graphite

Two-dimensional (2D) plasmons in the monolayer graphite formed on TiC(111) surface have been detected by using electron energy loss spectroscopy. The plasmon due to the intraband transition has shown a peculir dispersion proportional to a sqare root of the wave vector parallel to the surface in the energy region of 0 – 3 eV. In addition, the other branch appearing at high energies above 5.4 eV presumably originates from the longitudinal 2D plasmon due to the interband transition.

Hydrogen adsorption on a TiC(111) surface: angle-resolved photoemission study

Angle-resolved photoemission spectroscopy (ARPES) utilizing synchrotron radiation has been used to study the adsorption of hydrogen on a TiC(111) surface at 300 K. This system was studied by Bradshaw et al. [Solid State Commun. 37 (1980) 37] using ARPES and their results are well reproduced in this study. Furthermore, the two-dimensional band structure of the H 1s-induced state (which is found at 6.5 eV at the Γ point) along the ΓM and ΓK directions is directions is fully determined. The result shows that the bandwidth of this state is 1.1 eV. This band-width correlates well with those of metal-H adsorption systems. An H-induced surface state is also found at just below EF in off-normal-emission spectra.

Electron energy loss study of TiC [111

The electron energy loss (EEL) spectra of TiC (111) were measured over a wide range of electron primary energies. The electron energy losses below 16 eV were analyzed using the theoretical band calculations of Price and Cooper [11]. The volume and surface plasma excitations were identified from their electron primary energy dependence. Energy losses due to core electrons autoinization effects were identified above 35 eV. We observed a difference in the electronic structure of the surface vs the bulk of TiC. The temperature dependence of the EEL spectra was studied between 300 to 1250 K. The reaction of the TiC surface with ethylene and oxygen was also investigated. The ethylene bonding to the TiC surface was found to be very weak. There is evidence of the formation of surface defects on the TiC (111) surface at high temperatures.

Monolayer Graphite on TiC(111) Studied by Using Angle-Resolved Electron Spectroscopies

Electronic states of monolayer graphite formed on TiC (111) surface have been investigated by means of LEED, XPS and UPS. The chemical shift of XPS Cls peak has indicated that a small amout of charge (10_-2 electrons per carbon atom) transfers from the substrate to the monolayer graphite, which is in consistent with the work function change. In addition, UPS spectra has shown a large change in the energy band structure of the graphite layer. From those data, it has been concluded that the change in the electronic states originates mainly from the interaction between the overlayer and substrate.

Theory of STM images of monolayer graphite on transition-metal surface

A first-principles band calculation is performed on monolayer graphite on a TiC(111) surface. Occupied π bands of the monolayer graphite are similar to those of a bulk graphite and are lowered by 2 eV. Unoccupied π * bands are largely affected and split into bonding and antibonding bands due to a hybridization effect with d-bands of top-layer Ti. A calculated local density of states shows a 2 × 2 superstructure of graphite lattice, which explains the shorter period of the moirépattern observed in scanning tunneling microscopy.

Hydrogen ion interaction behaviour of plasma-sprayed TiC coatings

Abstract The high melting point, low atomic number, and resistance to thermal fatigue and erosion are desirable attributes of TiC coatings for fusion reactor containment vessels and components. However, such coatings are subjected to hydrogen ion bombardment from circulating plasma. This can result in the formation and adsorption of various molecular complexes. Conventional characterization techniques involving low energy electron beams cause desorption of these complexes. The unenhanced surface Raman scattering technique was used to investigate the possibility of the formation of C-H and Ti-H complexes on the plasma-sprayed TiC surface.

Oxygen chemisorption on transition-metal carbide (100) surfaces studied by X-ray photoelectron spectroscopy and low-energy He + scattering

The mechanism for oxidation of the (100) surfaces of TiC, VC, ZrC, and TaC has been studied using X-ray photoemission and low-energy He + ion scattering. The oxidation of TiC(100) is found to proceed into the bulk even at room temperature by replacing a part of the surface carbon atoms with oxygen and subsequent diffusion of oxygen into the bulk via carbon vacancies suggesting that the preferential bonding of oxygen with carbon exists at the surface. In case of the (100) surfaces of VC and TaC oxidation into the bulk is prevented by formation of an additional metal-oxygen bond at the surface. These significant differences will be elucidated on the basis of the electronic band structures characteristic of the transition-metal carbides.

Scanning tunneling microscopy of monolayer graphite epitaxially grown on a TiC(111) surface

The two-dimensional (2D) electronic and atomic structures of monolayer graphite epitaxially grown on a TiC(111) clean surface have been investigated by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The atomic structure of the monolayer graphite observed by LEED consists of double superlattices, 2 × 2 and 7 × 7, with respect to the unit meshes of the graphite and the Ti-lattice at the top of the substrate, respectively. These superlattices are rotated 30° with respect to each other. The structure of the monolayer graphite is commensurate with that of the Ti-layer. The electronic structure observed by STM is also modulated by the same superlattices as those of the LEED pattern. The local charge transfer from the Ti-layer to the π ∗- bond of the monolayer graphite across the interface has been observed directly by STM with atomic resolution. The surface band structure of the monolayer graphite on TiC(111) is discussed based on the voltage dependence of the constant current image.