E. A. Tutov

The interaction of porous silicon with water: A chemographic effect

Based on the results of pH and chemographic measurements, it is shown for the first time that the oxidation of porous silicon in aqueous media is accompanied by the liberation of hydrogen in the ionic and atomic forms.

Influence of water vapor adsorption on the C-V characteristics of heterostructures containing porous silicon

Porous silicon (por-Si) is prepared by the electrochemical etching of single-crystal n-silicon in an aqueous-alcoholic solution of hydrofluoric acid in the presence of hydrogen peroxide oxidizer. The dependence of the high-frequency C-V characteristics of Al/por-Si/Si heterostructures on the relative humidity is studied. A model of capacitor structure is proposed, and a method of analyzing its capacitance as a function of the water vapor partial pressure in terms of the adsorption isotherm is elaborated. Within the framework of this model, the porosity of the material, the effective fraction of silicon dioxide in the por-Si, the fraction of intercommunicating porosity, the micropore-to-mesopore volume ratio, and the mesopore size distribution are determined. The porous silicon prepared in this work seems promising as a sensitive layer in capacitance-type humidity sensors.

Mis structure with polyamide insulator under the conditions of water vapor sorption

A silicon MIS structure with sulfonate-containing aromatic polyamide as a gate insulator is prepared with the aim of using it as a capacitive-type humidity detector. A detector made of this material offers a high sensitivity at an elevated relative humidity and a high speed of response. Measurements of the capacitance of the structure at different frequencies basically make it possible to determine the water distribution in the polymer matrix. The high-frequency (1 MHz) capacitance versus relative humidity dependence (i.e., the calibration curve of the detector) is typical of the isotherms of water vapor sorption by similar polymers.

Adsorption-based porosimetry using capacitance measurements

It is shown that the dependence of capacitance of an Al/por-Si/Si structure on relative humidity is represented as an isothermal curve of physical adsorption. An analysis of this dependence makes it possible to determine the total porosity, the effective fraction of the oxide phase in por-Si, and the ratio between the volumes of micropores (the monomolecular and polymolecular adsorption of water which results in filling of their volume) and mesopores (which are filled according to the mechanism of capillary condensation). The size distribution for mesopores was obtained.

MOS structures with amorphous tungsten trioxide for capacitive humidity sensors

Electrical characteristics of the Al/a-WO3/n-Si structure under conditions of water vapor sorption were studied. The parameters of this structure as a capacitive humidity sensor were determined.

Equilibrium and nonequilibrium electrode processes on porous silicon

The electrode potential of porous silicon (por-Si) in aqueous electrolytes of variable acidity has been measured for the first time. It is shown that por-Si electrode can be a promising pH sensor. The results of the electrode potential measurements show that water condensed in capillaries of capacitive humidity sensors with a thick layer of mesoporous silicon is probably subject to electrolysis.

Optical properties of SnO2−x nanolayers

Specific features in the optical absorption spectra and capacitance-voltage characteristics of SnO2−x nanolayers have been observed. These features are determined by the surface and intergranular states of Sn2+ ions, which appear due to the oxygen deficit and form localized states in the bandgap of SnO2−x. The observed dimensional effect in SnO2−x nanolayers is manifested by an increase in their bandgap width as compared to that in the bulk SnO2.

Detection of nitrogen dioxide by amorphous films of tungsten trioxide

Data are given about the good “sensor” properties of amorphous tungsten trioxide with respect to NO2 adsorption. The resistance of WO3 film varies appreciably due to the binding of semiconductor electrons by NO2 molecules.

Silicon MOS structures with nonstoichiometric metal-oxide semiconductors

MOS structures are formed by oxidative annealing of tin, tungsten, palladium, nickel, and zinc thin films on silicon, and their high-frequency C-V characteristics are measured. The energy spectra of the density of surface states taken of SnO2 − x, WO3 − x and PdOx nonstoichiometric oxides are found to have common features.

Interaction of metal nanoparticles with a semiconductor in surface-doped gas sensors

A capacitance response of semiconductor sensors fabricated on the basis of thin NiO and SnO2 films with noble-metal nanoparticles deposited on their surface was analyzed. This response was shown to appear due to the solid-phase metal-semiconductor reaction accompanied by the formation of a boundary layer with a fairly high density of surface electron states in its band gap. The chemisorption field effect (the change in work function of the metal after inlet of gases) observed in the capacitance gas sensors not only forms the basis for the sensitive and prompt method of analysis but also represents the basic functional phenomenon responsible for their capacitance response.