MATHEMATICAL MODEL OF THE INTERACTION OF LOW-ENERGY INERT GAS IONS WITH POLYPROPYLENE IN RADIO-FREQUENCY PLASMA OF LOW PRESSURE

Results of the molecular dynamic simulation of the interaction of low-energy ions (from 10 to 100 eV) with the surface of polypropylene fibrous materials in low pressure radio-frequency (RF) argon plasma is presented. A full-atomic model using the LAMMPS classical molecular dynamics code was made. As a result of numerical calculations, it was found that argon ion bombardment initiates the breaking both of an intermolecular and intramolecular bond of polypropylene with sputtered particles being the hydrocarbon radicals and single atoms. The depth of implantation of the ion is determined, the change in the kinetic energy of the argon atom and the temperature of the simulated cell is obtained.

Activation of Small Organic Molecules on Ti2+-Rich TiO2 Surfaces: Deoxygenation vs. C–C Coupling

Rutile TiO2 is an important model system for understanding the adsorption and conversion of molecules on transition metal oxide catalysts. In the last decades, point defects, such as oxygen vacancies and Ti3+ interstitials, exhibited an important influence on the reaction of oxygen and oxygen-containing molecules on titania surfaces. In brief, partially reduced TiO2 containing a significant amount of Ti3+ is often more active for the conversion of such molecules. In this study, we investigate an even higher reduced surface prepared by argon ion bombardment of a rutile TiO2 (110) single crystal. By X-ray photoelectron spectroscopy we show that, besides Ti4+, this surface is almost equally dominated by Ti3+ and Ti2+. To probe the reactivity of these highly reduced surfaces, we have adsorbed two different classes of oxygen-containing molecules and utilized temperature programmed reaction spectroscopy to investigate the conversion. While alcohols (in this case methanol) already show a defect-dependent partial conversion in a deoxygenation reaction on the (stochiometric or slightly reduced) rutile TiO2 (110) surface, ketones (e.g. acetone) are usually not converted on the rutile TiO2 (110) surface independent on the bulk defect density. Here, we present a nearly full conversion for both molecules via deoxygenation reactions and reductive C–C coupling, forming different hydrocarbons at different temperatures between 375 K and 640 K on the sputtered Ti2+ rich surface.

Argon Bombardment of 4H Silicon Carbide Substrates for Tailored Schottky Diode Barrier Heights

In this paper, the impact of substrate preconditioning by ion bombardment in-situ in a conventional sputter equipment on n-doped 4H-silicon carbide (SiC) Schottky diodes with molybdenum nitride metallization is studied. By variation of the plasma power during argon ion bombardment, the effective barrier height is adjustable in the range from 0.66 to 0.96 eV, as deduced by current / voltage measurements over a wide temperature range. Therefore, this approach offers a straightforward method to tailor the Schottky barrier height over a significant range by introducing an insitu substrate pretreatment step available in most sputter equipment.

Effects of Air Exposure on Hard and Soft X-ray Photoemission Spectra of Ultrananocrystalline Diamond/Amorphous Carbon Composite Films

Hard X-ray photoemission spectroscopy (HAXPES) was employed for the structural evaluation of ultrananocrystalline diamond/amorphous carbon (UNCD/a-C) composite films deposited on cemented carbide substrates, at substrate temperatures up to 550 °C by coaxial arc plasma deposition. The results were compared with those of soft X-ray photoemission spectroscopy (SXPES). Since nanocrystalline diamond grains are easily destroyed by argon ion bombardment, the structural evaluation of UNCD/a-C films, without the argon ion bombardment, is preferable for precise evaluation. For samples that were preserved in a vacuum box after film preparation, the sp3 fraction estimated from HAXPES is in good agreement with that of SXPES. The substrate temperature dependencies also exhibited good correspondence with that of hardness and Young’s modulus of the films. On the other hand, the sp3 fraction estimated from SXPES for samples that were not preserved in the vacuum box had an apparent deviation from those of HAXPES. Since it is possible for HAXPES to precisely estimate the sp3 fraction without the ion bombardment treatment, HAXPES is a feasible method for UNCD/a-C films, comprising nanocrystalline diamond grains.