Dependence of the thickness profile of pulsed laser deposited bismuth films on process parameters

High resolution, two-dimensional thickness profiles of ArF excimer laser deposited Bi films are recorded by a microdensitometer. The azimuthal dependent cross-sectional profiles are consistently fitted by linear combinations of a cos4Θ evaporation-like component and a much more sharply peaked one with exponents ranging from 8 to 61. When keeping the laser spot dimensions fixed, no dependence on laser fluence is obtained. An increase in Ar pressure from 10-6 to 10-1 Torr leads to the sharpening of the angular distribution along both axes: the forward directed component narrows from cos23Θ to cos61Θ along the short, and from cos9Θ to cos17Θ along the long axis, respectively. Further increase in pressure results in a sudden broadening leading to circular symmetry at around 0.5 Torr. Above 10-4 Torr the deposition rate continuously decreases with increasing Ar pressure. In He atmosphere only narrowing is obtained above 10-1 Torr.This work has been carried out in the Instituto de Optica, CSIC, Madrid, Spain. One of the authors (T.S.) would like to say thanks for a NATO fellowship.Peer Reviewe

AMORPHOUS VANADIUM OXIDES BY CVD : PREPARATION, ELECTRICAL AND MAGNETIC PROPERTIES

Chemical vapour deposition of VOCl3 with H2O in controlled atmosphere is a unique method in producing amorphous vanadium oxides that contain only V5+ and V4+ ions with continuously varying valence ratio /c/ between <0.02 and ≈ 1.0. The room temperature d.c. conductivity of as prepared V2O5 films ranges between 10-5 and 10-3 ohm-1m-1 and is strongly dependent on preparation conditions. Increasing the valence ratio the conductivity first increases to ≈ 10-2 ohm-lm-1, then declines to 10-4 ohm-lm-1. EPR spectra indicate that the environment of V4+ ions is not identical in films of different compositions

The role of water in the conductivity of vanadium pentoxide xerogel films

The measurement of DC conductivity of thin films deposited from vanadium pentoxide gels between 200 and 600 K in air, oxygen and a vacuum of 5 x 10 -7 torr has revealed that reversible changes in conductivity are determined by hydration/dehydration phenomena. The removal of weakly bonded water results in a conductivity decrease from ≃ 2 S/m to ≃ 0.3 S/m at room temperature. Heat treatment between 430 and 550 K in oxygen leads to the maximally dehydrated phase in which σ ≃ 9 × 10-3 S/m at 300 K. The essentially unchanged activation energies in all of the phases suggest that hydration affects the charge carrier concentration only.Nous avons mesuré entre 200 et 600 K la conductivité à l'air libre ou sous un vide de 5 x 10-7 torr, de couches minces obtenues à partir de gels de pentoxydes de vanadium. Ces mesures ont montré que les changements réversibles de la conductivité sont liés à des phénomènes d'hydratation et de déshydratation. Le départ de l'eau faiblement absorbée entraîne, à température ambiante, une diminution de la conductivité de ≃ 2 S/m à 0,3 S/m. Un traitement thermique entre 430 et 550 K dans une atmosphère d'oxygène conduit à une phase de déshydratation maximum avec σ ≃ 9 x 10-3 S/m à 300 K. Le fait que les énergies d'activation sont similaires dans les différentes phases suggère que le processus d'hydratation entraîne seulement une modification de la concentration des porteurs de charge