Investigation of thin films of mixed oxides for gas‐sensing applications

Abstract

Recently, the thin films of some mixed metal oxides (Mo, Ti, Sn, W, etc.) have been indicated as very promising materials for gas-sensing applications. Nevertheless, there is still a significant lack of experimental information on these compounds, where the surface properties can be defined not only by their chemical composition but also by the nanosized morphology of the films.In this study we report the results of XPS investigations of Mo-Ti, Mo-Sn and Mo-W oxides. The films of mixed oxides with different composition ratios were prepared by sol-gel and magnetron sputtering techniques. The gas sensitivity of the films at different temperatures was studied by measuring the electrical response to typical gases.Selected-area XPS depth profiling of the samples was carried out by using cyclic Ar + sputtering. The separation of different chemical species of the same element and quantitative analysis of experimental depth profiles enabled us to reveal completely the chemical composition of the films investigated. In such a way, the samples of mixed oxides, prepared by two different techniques and annealed at different temperatures (450-700• C), were characterized and compared.

Depth profiling of thin films of binary metal oxides

“…tin was found to be in stable Sn(IV) state, like in other oxides. 5,6 A very similar Mo(VI) reduction to Mo(IV) and Mo(0), dependent on the sputtering depth, was observed in the Mo-Ti and Mo-Sn oxides. 6 When the same Mo-Ti sample has been profiled at two different energies (E Ar D 1.0 and 2.0 keV), the identical Mo 3d and Ti 2p spectra were registered, as is shown in Fig.…”

“…magnetron sputtering, 4,6 while the samples of Mo-Ti oxides have been prepared by means of the sol-gel technique. 2,6 All these samples have been analysed by using XPS depth profiling, carried out in an Escalab MkII (Thermo VG Scientific), equipped with a 5-channeltron detection system and a standard Al K˛excitation source. The samples were positioned with respect to the analyser at the electron takeoff angle normal to the surface, and the analyser was set to a constant pass energy of 50 eV.…”

“…9 Even if in the most experimental cases the existence of reduced species seems to be resulting mostly from the film deposition, the contribution of ion sputtering cannot be fully neglected, particularly when the compounds with Mo, Ti and W are analysed. 4,6,10,11 In order to clarify the role of this contribution and to reveal the real chemical composition of mixed oxides, a thorough investigation by using XPS depth profiling at different ion energies and photoelectron collection angles was carried out in the present work.…”

Processing and Characterization of Nanostructured Metal Oxides for Gas Sensing Applications

“…This is a room or slightly elevated temperature process. The process involves the hydrolysis of a metal organic compound such as a metal alkoxide (23) (24) (usually, or can be hexachlorides as well), or inorganic salts such as chlorides (25) (26) to produce a colloidal sol.…”

Gas Sensing Studies of an n-n Hetero-Junction Array Based on SnO2 and ZnO Composites

“…The use of such composite material systems in gas sensing has been reported in a number of papers in the literature [2,7,[9][10][11][12], suggesting that enhanced gas response behaviour is promoted as a result of synergistic effects between the two different composite components. Zakrzewska [12] pursued a theoretical approach and reported that the formation of such composite oxides modifies the system's electronic structure through changes in its associated bulk and surface components.…”