S. K. Khanna

High Tc superconducting NbN films deposited at room temperature

Thin films of niobium nitride with superconducting transition temperature (Tc ) of 15.7 K have been deposited on a variety of amorphous as well as crystalline substrates including glass, glazed ceramic, fused quartz, and sapphire, maintained at room temperature, by dc reactive magnetron sputtering in a mixture of Ar and N2 gases. The effects of the deposition conditions, particularly the carrier gas pressure and composition, on the film crystal structure, orientation, and resistivity have been studied in an effort to maximize the superconducting transition temperature. A study of the variation of nitrogen consumption with nitrogen injection pressures for constant background argon pressures is conducted and found to be an absolute indicator of the NbN formation systematics. Initially, the consumption increases linearly with the injection pressure but beyond a certain threshold, it shows a distinct drop. The desired high Tc  NbN with B1 crystal structure is formed in the vicinity of this turning point of th...

Stability of polyacetylene films

Abstract The oxidative and radiation stability of polyacetylene films have been determined. The radiation stability of the material is found to be quite good but the intrinsic thermal oxidative stability is poor and presents a serious obstacle to widespread terrestrial or space use.

Refractory amorphous metallic (W0.6Re0.4)76B24 coatings on steel substrates

Refractory metallic coatings of (W0.6Re0.4)76B24 (WReB) have been deposited onto glass, quartz, and heat-treated AISI 52100 bearing steel substrates by dc magnetron sputtering. As-deposited WReB films are amorphous, as shown by their diffuse x-ray diffraction patterns; chemically homogeneous, according to secondary ion mass spectrometry (SIMS) analysis; and they exhibit a very high (~1000°C) crystallization temperature. Adhesion strength of these coatings on heat-treated AISI 52100 steel is in excess of ~20, 000 psi and they possess high microhardness (~2400 HV50). Unlubricated wear resistance of such hard and adherent amorphous metallic coatings on AISI 52100 steel is studied using the pin-on-disc method under various loading conditions. Amorphous metallic WReB coatings, about 4 µm thick, exhibit an improvement of more than two and a half orders of magnitude in the unlubricated wear resistance over that of the uncoated AISI 52100 steel.

Influence of preparation techniques on the structure of amorphous metallic alloy (Mo0.6Ru0.4)82B18

Abstract We report X-ray diffraction studies and density measurements on liquid quenched foils and sputter deposited films of the amorphous metallic alloy, (Mo0.6Ru0.4)82B18. The crystallization temperature (Tx) for both the films and the foils is ∼800 ± 10°C. The density of the as-sputtered films is ∼4% less than that of the foils. The annealing of these films at ∼ T x 2 increases the density to within ∼1.7% of the value for the foils. The X-ray diffractionpatterns for both the foils and films are similar and show the amorphous nature of the samples. The reduced radial distribution functions suggest that as-sputtered films have noticably larger second and third nearest neighbor distances, probably due to excess residual stresses and voids in them.

Effects of disorder on the thermoelectric power and electrical conductivity of TTT2I3

(Tetrathiatetracene)2(iodide )3 is a quasi-one-dimensional organic metal consisting of segregated stacks of (TTT) cation radicals and polyiodide chains. we report the results of a study of the thermoelectric power and electrical conductivity measurements on single crystals of TTT2I3 in which the degree of disorder is varied. Effects of disorder on the phase transition and low temperature conductivity are discussed.