Abstract
The work is focused on the application of the impedance spectroscopy method to provide evidence and study the effects of aging, temperature, and gas adsorption in chalcogenide-based thin films. The experiments are carried out with thin films of glassy quaternary composition As2Te13Ge8S3 in a wide frequency range at different temperatures under different environmental conditions, in particular, either dry or wet air or their mixtures with NO2 or CO2. It is found that aging has a significant effect on the impedance spectra of Pt–As2Te13Ge8S3–Pt functional structures, which make evidence for the presence of substantial spatial and compositional disordering. This effect can be stabilized by the post-preparation annealing of the sample. The effect of temperature on impedance spectra consists in a variation in the both real and imaginary parts of impedance that appear to be extremely sensitive to adsorptive processes. Adsorption of nitrogen dioxide results in a significant frequency-dependent decrease in the impedance parameters, which is attributed to an effective “strong” chemisorption process due to the interaction of "odd" electrons of NO2 molecules with lone pair electrons of chalcogen atoms. The effect of water vapors leads only to an increase in the real part of impedance, while the imaginary part abruptly decreases; this fact is attributed to a “weak” form of chemisorption. The effect of carbon dioxide on the impedance spectra is attributed to the physical adsorption of CO2 molecules. This effect is weak; however, it is reversible and clearly observed even at room temperature.
Highlights
The unique properties of glassy and amorphous chalcogenides, which have determined the wide application of these materials in micro and optoelectronics [1], are attributed to their special chemistry and defect states, caused by structural and compositional disordering
Aging at room temperature leads to an increase in the radius of the arc, so much that, after 8 months, the values of the imaginary part of the impedance exceed the measuring limits of the analyzer device
The impedance spectroscopy is an effective extremely sensible method to reveal the effect of aging, heating, and gas adsorption on disordered chalcogenide films
Summary
The unique properties of glassy and amorphous chalcogenides, which have determined the wide application of these materials in micro and optoelectronics [1], are attributed to their special chemistry and defect states, caused by structural and compositional disordering. The disordering does not allow using the conventional modern methods, in particular, SEM and XRD, to reveal and study the physical and chemical processes that occur under the action of natural or induced factors, such as aging, annealing, irradiation, and adsorption. In this respect, impedance spectroscopy appears to be an indirect, yet extremely sensible method to provide evidence and study the effect of these external factors on disordered materials, in particular, glassy and amorphous films. Due to Marina Ciobanu and Dumitru Tsiulyanu the high disordering of As2S3Ge8–Te films and their possible chronological degradation, the effects of aging and temperature on complex impedance spectra have been studied first
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