Papers by Author: N. Popović

Abstract: The reactive sputter deposition of TiN thin films onto glass substrate at the ambient temperature using a homemade broad beam argon ion source was investigated in order to deposit the films with nanostructural characteristics. While constant Ar beam energy of 2 keV was used, the N2 partial pressure and the substrate current, adjusted by different accelerator grid potentials (Vacc) were varied. A negative substrate bias voltage (100 V) was additionally applied. The TiN film structure was investigated by XRD and STM methods. All deposited films exhibited (220) preferred orientation, and the change in normalized peak intensity (I220/d), lattice spacing (d220) and full-with at half-maximum (FWHM) were investigated. As a result of higher energy bombardment with 100 V negative substrate bias, compared to the substrate current change with Vacc, nearly constant (220) peak broadening with the increase of N2 partial pressure was obtained. The measured grain diameter (STM and XRD) confirms that the grain size is less than 12 nm, and the (220) preferred orientation was disturbed but not destructed.

Abstract: The investigated nanometric magnetite powders were synthesized electrochemically, and examined by XRD and SEM techniques. Their reduction was conducted through the isothermal heating in hydrogen in the temperature range from 600 to 860 K. Kinetics of the hydrogen recovery process during oxidation of freshly formed Fe powders in a water vapor stream was also studied. It was assumed that the solid-gas reaction is diffusion controlled, and Jander’s model was applied to describe it. The experimental data suggest that the reoxidation process proceeds in two stages, at various activation energies. By changing the conditions of the electrochemical (EC) process we were able to produce the iron oxide powders with optimal particle size and activity, for pure hydrogen production through appropriate reduction/oxidation processes.

Abstract: Structural, magnetic and electrical properties of iron oxide nano-sized powders synthesised electrochemically under various conditions are presented. The influence of the temperature and current density of synthesis on particular powder characteristics is established. Possibilities for co-existence of various phases and their impact on powder properties, as well as feasible paths of phase relaxation and transition during non-isothermal heating are investigated, too. In this way, optimal procedures for the preparation and stabilisation of iron oxides nano-sized powders of different characteristics are evaluated.