Kinetics of photostimulated transformations in nanosized bismuth films

Optical spectroscopy, gravimetric analysis, and microscopy studies show that irradiating bismuth films (d = 3–55 nm) with light (λ = 360 nm and I = 1.8 × 10¹⁵–7.0 × 10¹⁵ quantum cm^?2 s^?1) leads to major changes in their absorption and reflectance spectra and in film mass. The kinetic curves of the degree of photochemical transformation of bismuth films are shown to obey linear, inverse logarithmic, cubic, and logarithmic laws. The contact potential difference (CPD) of Bi and Bi₂O₃ films and the photo-electromotive force (emf) of Bi-Bi₂O₃ systems are measured. An energy band diagram of Bi-Bi₂O₃ systems is constructed. A model that includes the stages of generation, recombination, and redistribution of nonequilibrium charge carriers in the contact field of a Bi-Bi₂O₃ system, oxygen adsorption, diffusion of cation vacancies, and Bi₂O₃ formation is proposed.     

Rules governing the formation of photolysis products in the lead azide-copper(I) oxide system

It was found that, along with a decrease in the rate of photolysis and photocurrent in the region of lead azide intrinsic absorption, the addition of copper(I) oxide broadened the range of spectral sensitivity, and preliminary treatment of the PbN₆(Ab)-Cu₂O system with light (λ = 365 nm) increased the rate of photolysis. The rate constants for photolysis were estimated. An analysis of the results of current-voltage characteristic, contact potential difference, and contact photo-electromotive force measurements was used to construct a diagram of energy zones and suggest a model of the photolysis of the PbN₆(Ab)-Cu₂O system including stages of the generation, recombination, and redistribution of nonequilibrium carriers in a contact field, formation of microheterogeneous PbN₆(Ab)-Pb (photolysis product) systems, and formation of final photolysis products.     

Thermal transformations in nanosized tungsten(VI) oxide films

According to optical spectroscopy data, the thermal treatment of WO₃ films with a thickness of 7–160 nm for 1–140 min at 423–573 K led to an increase in the optical density in the range of λ = 400–1100 nm with a maximum at λ = 850 nm along with a decrease in the range of λ = 300–400 nm with a maximum at λ = 350 nm. The conversion of WO₃ films increases with treatment time and temperature and is higher at lower film thicknesses. A mechanism of the thermal conversion of WO₃ films was suggested; it involves the formation of the [(V_a)⁺⁺e] center and the thermal electron transfer from the valence band to the level of the [(V_a)⁺⁺e] center, forming the [(e(V_a)⁺⁺e] center.     

Kinetic laws of thermal transformations in nickel nanofilms

Transformations in nickel nanofilms as a function of thickness (d = 3–60 nm) and temperature of heat treatment (T = 373–873 K) are studied via optical spectroscopy, microscopy, and gravimetry. It is found that, depending on the thickness of nickel films and temperature of heat treatment, the kinetic curves of the degree of transformation are satisfactorily described in terms of the linear, inverse logarithmic, cubic, and logarithmic laws. The contact potential difference for Ni and NiO films and the photovoltage for Ni-NiO systems are measured. An energy band diagram for Ni-NiO systems is constructed. A model of the thermal transformation of Ni films, including the stages of oxygen adsorption, charge carrier redistribution in a Ni-NiO contact field, and the formation of nickel(II) oxide, is proposed.     

Photostimulated transformations in nanosized MoO3 films

Irradiation of MoO₃ films (with a thickness d = 5–54 nm) with light (λ = 320 nm, I = (1.5–7) × 10¹⁵ quantum cm^?2 s^?1) led to the formation of an absorption band at λ = 870 nm along with the shift of the edge of the absorption band to the short-wave region of the spectrum. Further irradiation of the samples with light at λ = 870 nm caused diffusion of the long-wave absorption band. The conversion of MoO₃ films increased when the incident light intensity and irradiation time increased and the film thickness decreased under the atmospheric conditions. A mechanism of the photochemical transformation of MoO₃ films was suggested. It involves the generation of electron-hole pairs, recombination of some nonequilibrium charge carriers, formation of [(e(V _a )⁺⁺ e] centers, and isolation of photolysis products.     

Thermostimulated transformations in nanosized Bi-MoO3 systems

Transformations in Bi-MoO₃ nanosized systems are studied by optical spectroscopy, microscopy, and gravimetry. The contact potential difference for the Bi and MoO₃ films and the photovoltage of the Bi-MoO₃ systems are measured, depending on the thickness of Bi (d = 3–92 nm) and MoO₃ films (d = 5–40 nm) and the temperature (373–673 K) and time of heat treatment. An energy band diagram of the Bi-MoO₃ systems is constructed. A model of the thermal transformation of MoO₃ films in Bi-MoO₃ systems is proposed that involves the redistribution of equilibrium charge carriers on a contact, the formation of a ([(V_a)⁺⁺e]) center during the preparation of a MoO₃ film, the transformation of this center into a ([e(V_a)⁺⁺e]) center during the formation of Bi-MoO₃ systems, and the thermal transition of an electron to the level of a ([(V_a)⁺⁺e]) center to form a ([e(V_a)⁺⁺e]) center.     

Kinetic regularities of thermal transformations in nanosized bismuth films

Transformations in a nanosized bismuth layer are studied by means of optical spectroscopy, microscopy, and gravimetry, depending on the thickness (d = 3–120 nm), thermal treatment temperature (T = 373–673 K) and time (τ] = 0.05–2500 min). It is established that, depending on the initial thickness of the bismuth films and the thermal treatment temperature, the kinetic curves of the degree of transformation are satisfactorily described within linear, inverse logarithmic, cubic, and logarithmic laws. The contact potential difference for the Bi, Bi₂O₃ films and the photo-electromotive force for the Bi-Bi₂O₃ systems is measured. An energy-band diagram for the Bi-Bi₂O₃ systems is constructed. A model for the thermal transformation of Bi films that includes the stage of oxygen adsorption, the redistribution of charge carriers in the Bi-Bi₂O₃ contact field, and the formation of bismuth(III) oxide is proposed.     

Photostimulated changes in WO3 nanosized films

During the irradiation of WO₃ films d = 7–160 nm thick by light at λ = 320 nm (I = (1.5–7) × 10¹⁵ quantum cm⁻² s⁻¹), absorption band at λ = 850 nm appeared along with absorption band edge shift to shorter waves. The subsequent irradiation of samples at λ = 850 nm caused the disappearance of the longwave absorption band. The intrinsic absorption edge of WO₃ films was determined (λ = 320 nm). The degree of transformations of WO₃ films increased under atmospheric conditions as the intensity of incident light and the time of irradiation (1–140 min) grew and as film thickness decreased. A mechanism of photochemical transformations of WO₃ films was suggested. This mechanism included the generation of electron-hole pairs, the recombination of part of nonequilibrium charge carriers, the formation of [eV_a²⁺e] centers, and the isolation of photolysis products.