Ti based composites containing Si3N4 and TiN were produced by spark plasma sintering to develop wear resistant Ti based materials. Sliding tests were conducted by sliding the composite disk against a Si3N4 ball in dry atmospheres and in the liquids of n-hexane, water and ethanol. The wear of the composite was much smaller than that of Ti metal in the tests. Observations and elemental analyses of the worn surfaces revealed that water and ethanol prevented the adhesion while adhesive wear occurred in dry atmospheres and in n-hexane. The experimental results indicated the wear mechanism of the composite might be strongly dependent on the tribochemical reactions between the composite and species in the surroundings.
Hydrogen-terminated diamond surface shows p-type conduction even if it is not intentionally doped. Metal-semiconductor (MES) and metal-insulator-semiconductor (MIS) field-effect transistors have been fabricated on hydrogen-terminated diamond surface conductive layers, and their high-frequency performance is demonstrated. Nano-fabrication on a hydrogen-terminated diamond surface is performed by controlling surface adsorbates, using an atomic force microscope (AFM) technique. Insulated areas are successfully obtained by changing hydrogen termination to oxygen termination. Single hole transistors are also fabricated by AFM oxidation, and are operated at liquid nitrogen temperature (77 K). Polycrystalline diamond FET is operated in electrolyte solution. A perfect pinch-off and saturated current-voltage characteristics have been obtained for bias voltages within the potential window. The threshold voltages are almost constant in the electrolytes with different pH values of 7−13. Using this pH insensitive surface, ion selective regions can be fabricated to form transistor-based biosensors.
Solid carbon forms two kinds of local structures, i.e., diamond-like and two-dimensional graphite structures. In contrast, silicon carbide tends to prefer only diamond structure that is composed of sp3 bonds. In order to clarify whether or not two-dimensional graphitic SixC layer exists, we investigate the local structures of SixC layer produced by Si+-ion implantation into highly oriented pyrolitic graphite (HOPG) by means of near-edge X-ray absorption fine structure (NEXAFS). The energy of the resonance peak in the Si K-edge NEXAFS spectra for Si+-implanted HOPG is lower than those for any other Si-containing materials. The intensity of the resonance peak showed a strong polarization dependence. These results suggest that the final state orbitals around Si atoms have π*-like character and the direction of this orbital is perpendicular to the graphite plane. It is elucidated that the Si-C bonds produced by the Si+-ion implantation are nearly parallel to the graphite plane, and SixC phase forms a two-dimensionally spread graphite-like layer with sp2 bonds.
We studied the adsorption state of dimethyl disulfide (DMDS), methylthiolate (MeS), ethylthiolate (EtS), and butylthiolate (BuS) molecules on Au(111) surfaces by means of the density functional theory (DFT) within a generalized gradient approximation (GGA). It turns out that the MeS adsorption is more stable than the DMDS adsorption and that the most stable adsorption site for MeS is the bridge site slightly off-centered towards the fcc-hollow site with its S-C bond tilted from the surface normal by 53o. The fcc-hollow site adsorption is less stable than that of the bridge configuration. The bridge configuration excellently reproduces experimental HREELS as well as core level shift results. The energy difference between the bridge and the fcc-hollow configurations depends on the coverage, indicating that there is a rather strong adsorbate-adsorbate interaction, while its dependence on the alkyl chain length is small. Vacancy formation upon alkanethiolate adsorption on Au(111) is suggested from our GGA calculations.
Adatom diffusion process during decay of a 2D island formed on Si(100)-2×1 surface is analyzed using a kinetic Monte Carlo simulation based on a solid-on-solid model. The diffusion is basically a mass transport on the surface; both a source and a drain of adatoms are needed. The experimental results of the decay process of a 2D island at the substrate temperature around 800 K are reproduced when a boundary condition with proper drains is adopted in the system of simulation. The decay rate depends on the boundary condition. The decay is governed by adatom diffusion process, but the process is not so simple. An adatom does not move long distance on a flat terrace. It is trapped by a vacancy created by hopping of another atom from the terrace, and the latter atom moves on the terrace instead of the former in the next step. This vacancy mediated diffusion of adatom is a key issue for understanding diffusion process on surface, especially at high temperature.
Today, over 70,000 synthetic organic chemicals are in general use. Some of the chemicals causes hormone imbalance. Those chemicals were called endocrine disruptors, for example bisphenol. In this study, the interaction between the surface of activated carbons and bisphenol A was estimated from the relation of the Freundlich constants and surface properties of activated carbons. The polarity groups of the activated carbon inhibited the adsorption of bisphenol A onto the pore of activated carbons the radius of which was from 7.5 to 20 Å. Adsorption of bisphenol A onto the activated carbons depended upon both the polarity and pore structure of activated carbon. The reduced activated carbon was utilized for the removal of bisphenol A in water.
Controlled dehydrogenation of individual trans-2-butene molecules adsorbed on the Pd(110) surface is achieved with inelastically tunneled electrons from the tip of a scanning tunneling microscope (STM). The reaction product is identified as 1,3-butadiene molecule by inelastic tunneling spectroscopy (IETS) using the STM. The reaction yield increases significantly above a threshold bias voltage of ∼366 mV for trans-2-butene and ∼275 mV for fully deuterated trans-2-butene. These coincide with the excitation of C-H and C-D vibrational stretching modes, respectively. The strong isotope effect and the power-law dependence of the reaction rate on the tunneling current explain of the microscopic mechanism for the reaction as vibrational heating via resonant inelastic electron tunneling process.
The scanning Auger microprobe can be widely used for the analysis of sub-micron area of industrial products; e.g. semiconductors, metals, inorganic materials etc. In high-resolution AES analysis the current density of primary electron is very high. It is, then, very important to estimate the electron beam damage of the specimen quantitatively, especially for oxides. Much work has been done for the evaluation of electron irradiation damage of SiO2 by AES. However, it is very complicated or tedious task to determine the critical dose of electrons from intensity of the Si LVV Auger spectra vs. irradiation time quantitatively. Then, we propose a simple measurement method using the effective decomposition cross section (ECS) of SiO2/Si sample due to electron irradiation (instead of the critical dose) from the intensity measurement of metallic Si LVV peak. The critical electron dose of SiO2 could be calculated from the values of decomposition cross sections of SiO2 and SiO.
The contact potential differences on various substrates were measured as a function of organic layers thickness. Two different types of structures: traditional ITO/TPD/Alq3/Al structure LiF/Al cathode device. It was found that the introduction of LiF in Alq3/Al interface declined the electron injection barrier, which is supported by I-V characteristics and, in addition, contact potential changed abruptly in 10∼20 Å deposition. A gap state model enables us to explain the shifts of electronic level in organic interface layers.