V.M. Arakelyan

Investigation of ceramic Fe2O3〈Ta〉 photoelectrodes for solar energy photoelectrochemical converters

Abstract Photocurrent and electrochemical impedance spectroscopy of a polycrystalline semiconductor photoelectrode, Fe 2 O 3 〈Ta〉, was carried out. The analysis of the frequency dispersion of the real and imaginary parts of the complex impedance allowed us to obtain an equivalent circuit for the electrochemical cell. The capacitance of the space-charge layer in the semiconductor electrode was isolated, and the limiting step of the electrode process was determined. Measurements of the temperature dependencies of the electroconductivity were used to determine the activation energy for the mobility of the charge carriers. A pair of simultaneously illuminated n-Fe 2 O 3 〈Ta〉 and p-Cu 2 O photoelectrodes were shown to split water spontaneously.

Investigations of the Fe1.99Ti0.01O3-electrolyte interface

The Fe1.99Ti0.01O3–electrolyte interface is investigated using electrochemical impedance spectroscopy. The analysis of the frequency dispersion of the real and imaginary parts of the complex impedance at various electrode potentials allows us to define the equivalent circuit for the electrochemical cell and calculate its associated parameters. The capacitance of the space-charge layer in the semiconductor electrode is isolated, and the limiting step of the electrode process is determined.

Porous silicon near room temperature nanosensor covered by TiO2 or ZnO thin films

Hydrogen nanosensor working near room temperature made of porous silicon covered by the TiO2-x or ZnO thin film was realized. Porous silicon layer was formed by electrochemical anodization on a p- and n-type silicon surface. Thereafter, n-type TiO2-x and ZnO thin films were deposited onto the porous silicon surface by electron-beam evaporation and magnetron sputtering, respectively. Platinum catalytic layer and gold electric contacts were for further measurements deposited onto obtained structures by ion-beam sputtering. The sensitivity of manufactured structures to 1000-5000 ppm of hydrogen was studied. Results of measurements showed that it is possible to realize a hydrogen nanosensor which has relatively high sensitivity and selectivity to hydrogen, durability, and short recovery and response times. Such a sensor can also be a part of silicon integral circuit and work near room temperatures.

Gas sensor based on nanosize In2O3:Ga2O3 film

Nanosize films of In2O3:Ga2O3 (96:4 weight %) have been deposited on a glassceramic substrate by the method of rf magnetron sputtering. The surfaces of fabricated films were studied with use of a scanning electron microscope; sizes of grains were determined and the thicknesses of films were measured. In order to prepare a gas-sensitive structure, a thin catalytic palladium layer and ohmic comb contacts were deposited on the In2O3:Ga2O3 film surface by the method of ion-plasma sputtering. The sensitivity of sensors based on the glassceramic/In2O3:Ga2O3 (96:4 weight %)/Pd structure to different concentrations of propane and butane gas mixture, as well as to methane was investigated at temperatures of working substance from 250 to 300°C.

Static and noise characteristics of nanocomposite gas sensors

Thin film gas sensors based on nanocomposite In2O3·Ga2O3·SnO2 (70:20:10) have been manufactured by the high-frequency magnetron sputtering method. The technological cycle of sensor fabrication processes is described. Sensitivity of the prepared sensors at the temperature of working body 250°C and low-frequency noises within the 1–300 Hz range were investigated. The response of sensors to vapors of ethanol and acetone was investigated using resistive and noise methods. It is shown that the value of the sensitivity measured by the noise method exceeds the value of sensitivity measured by the resistive method. Sensors show appreciable sensitivity to the ethanol vapors already at working body temperature 150°C. Sensors can be used for the detection of low concentrations of ethanol vapors. The monotonous increase in the sensitivity of these sensors with increase in the ethanol and acetone vapors content allows applying nanosensors also for fast determination of gases concentration in air.

Investigation of gas sensor based on In2O3:Ga2O3 film

We have fabricated a LPG and butane sensor whose sensitive element is a nanosize In2O3:Ga2O3 (96:4 weight %) film covered with a thin palladium catalytic layer. Technology of deposition of these films on a glassceramic substrate by the method of rf magnetron sputtering was elaborated. The surfaces of fabricated films were studied with use of a scanning electron microscope and the thickness of films was measured. The sensitivity of sensors based on the glassceramic/In2O3:Ga2O3 (96:4 weight %)/Pd structure depending on the thickness and sizes of film grains was studied. We revealed technological regimes of sputtering providing fabrication of films with the best parameters.

Semiconductor photoanodes in the system Fe2O3-Nb2O5 for photoelectrochemical water splitting

Ceramic semiconductor photoelectrodes made of the Fe2O3-Nb2O5 solid solutions were synthesized. The spectral and capacitance-voltage characteristics of the photoelectrodes were determined, and the dynamic polarization with chopped light was investigated. The anodic photocurrent onset potential, the flat band potential and the shallow and deep donor density of these materials were determined. The threshold photon energies corresponding to the inter-band optical transitions near the edge of the fundamental absorption of the semiconductor photoelectrode were calculated. Analysis of the frequency dispersion of the real and imaginary parts of the complex impedance of photoelectrochemical cell was carried out. On the basis of this analysis, equivalent circuits describing the structure of the double electrical layer of the semiconductor - electrolyte interface were proposed and their parameters were calculated. The main limiting steps of the electrode processes, which determine the electrode polarization and current, are determined.