Papers by Author: Plamen Stefanov

Abstract: In the present work, the surface properties of various Al oxide films were investigated. The oxide films were produced on a stainless steel by spray pyrolysis and cathodic deposition methods. The films obtained represent typical layers that can be used as a support in model systems to investigate alumina-based catalysts. Information about the chemical environment of the Al and O ions in the oxide films depending on the preparation conditions has been deduced from the binding energies of the Al 2p and O 1s electron core levels and corresponding Auger parameters.

Abstract: Electrical, thermal and chemical properties of Ti/Al/Ti/Au ohmic contacts with different former Ti-Al ratio are investigated for application in GaN HEMTs. Lowest resistivity of 4.22x10-5 Ω.cm2 has been obtained to the channel of the HEMT structure. It is found out that the initial Ti/Al ratio influences the optimal annealing temperature at which the lowest resistivity is obtained and the element distribution and interface chemistry of the annealed contacts. XPS analysis revealed two compounds contributing to ohmic properties: an intermetal compound AlAu2 in the contact layer and a semimetal TiN at the interface with GaN.

Abstract: We have investigated the deposition of ZrO2 and Al2O3 films on a stainless steel (SS) substrate by spray pyrolysis method. The ZrO2 films were deposited from aqueous solution of zirconium dinitrate oxide. For Al2O3 films, a boehmite sol was used. The specific surface areas of samples were determined by the BET-method and sample surfaces were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The spray pyrolysis method permits the preparation of ZrO2 and Al2O3 thin films on SS with good adhesion. This method enables preparation of oxide layers with relatively high specific surface area, suitable for applications as catalysts supports.