Study of the oxygen vacancies changes in SnO_2 polycrystalline thick films using impedance and photoemission spectroscopies

摘要

Changes in the concentration of oxygen vacancies within the grains of polycrystalline SnO_2, due to different atmosphere exposures, were detected using impedance and photoemission spectroscopies. From measured capacitance values, variations of the potential barrier widths could be determined. It is shown that under the presence of an oxygen rich atmosphere, at relatively low temperature, the width of intergranular potential barriers increase to the point that grains become completely depleted of carriers. With subsequent exposure to vacuum, capacitance adopts a higher value, indicative of intergranular barriers and quasi-neutral regions at the center of the grains. X-ray and ultraviolet photoemission spectroscopy measurements showed that SnO_2 samples treated in oxidizing or reducing environments have similar barrier heights and different work functions. Results are especially relevant in the study of mechanisms responsible for metal oxide gas sensing.