Papers by Author: Ts. Marinova

Abstract: Electrical, morphological and chemical properties of nanolayered Au/Ti/Al ohmic contacts with different Ti:Al ratio are investigated. Contact resistivities of 1.42×10-5 ⋅cm2 and 1.21×10-5 ⋅cm2 are achieved for Au/Ti(70)/Al(30) and Au/Ti(30)/Al(70) contacts, respectively. It is found that the Ti:Al ratio does not affect the lowest resistivity value but influences on the optimal annealing temperature at which it is obtained. The different optimal annealing temperature provokes different element distributions and interface chemistry of the annealed contacts. An increase of the Al concentration in the contact composition causes essentially the surface morphology leading to an increase in surface roughness of the as-deposited and annealed contacts.

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.

Abstract: X-ray photoelectron spectroscopy is used to study the effect of the metal composition on the electrical and thermal properties of Au/Pd/Ti/Pd contacts to SiC. No reactions and interdiffusion between the contact components and SiC are found for the as-deposited contact layer. The steep metal/SiC interface corresponds to the Schottky behaviour observed before the annealing. Annealing at 900 oC causes Pd2Si formation at the SiC interface and ohmic properties appearance. Due to the addition of Ti to the contact composition the carbon resulting from the SiC dissociation during annealing is completely consumed, which leads to improvement of the thermal stability.