XPS study of the Y/SiO_x interface at room temperature

Abstract

The reducing reaction of vapour-deposited yttrium layers on silicon oxide was measured by XPS at room temperature. The redox reaction was confined essentially to the deposition period. The thickness of the insulating SiO, layer decreiases by -0.203 om. No further reaction during the 8 h following deposition could be observed. INTRODUCTIO VThis paper deals with yttrium metal/silicon oxide/Si structures used as solar cells.' Yttrium is a very reactive metal and forms Y,O, in the presence of oxygen.' In air, yttrium fornis a passivation layer, which was already investigated in a previous work.3 Further favourable properties, such as good electric conductivity, low work function and good optical transparency, are of great importance for its use as a barrier metal in MIS solar cells. The determination of the thickness of this metal layer is of immediate practical importance. A further important parameter is the thickness of the thin layer of silicon oxide. Any chemical reactions occurring between the barrim metal yttrium and the silicon oxide strongly influence the characteristics of the MIS solar cells. Gurvitch et d4 have already investigated the reaction of yttrium films with SiO, by transmission electron microscopy and IRutherford back-scattering and have proved that an intermediate layer of Y-Si oxide is formed. The samples, however, were heated up to several hundred degrees centigrade in dry oxygen for 1 h. Corresponding investigations at room temperature do not exist so far. The way that a thin yttrium metal film reacts with i.he clean Si substrate at room temperature has already been studied by XPS,5,6 while our interest has focused on the chemical reaction of Y/SiO, layers. Accordingly, in this work, XPS measurements were performed 011 the yttrium/silicon oxide interface at room temperature.Corresponding investigations of metal/thin SiO, layers at room temperature with other metals (e.g. A1 (Ref. 7) or Ti (Ref. 8)) showed that SiO, may be reduced by the evaporated metal, while in other cases (e.g. Pt (Ref. 8) and Ni (Ref. 9)) the formation of silicides was observed. A comparison of the heats of formation of Y,O, (455 kcal jmol-') ' and SiO, shows that Y,O, is the compound that is thermodynamically favoured at the Y/SiO, interface. Therefore, a redox reaction at this interface seems possible. As we are dealing with very thin layers, the use of XPS is favourable as a non-destructive analysing method.

Synthesis of Carbon‐Supported Pt–YOx and PtY Nanoparticles with High Catalytic Activity for the Oxygen Reduction Reaction Using a Microwave‐based Polyol Method

“…Chemical shifts of the Y component are apparent at 157.2 eV for both Pt–YO x /C(A):6:2 and Pt–YO x /C(A):5:5. Based on these findings, most of the Y component exists as a strongly oxidized Y 2 O 3 layer, and there is little component attributable to Pt 3 Y. The Pt/Y atomic ratio of the surface was estimated as 86:14 for Pt–YO x /C(A):6:2 and 66:34 for Pt–YO x /C(A):5:5.…”

Thickness dependence of thermally induced changes in surface and bulk properties of Nafion® nanofilms

“…The binding energy scale was further calibrated by setting the F 1s peak to 690.0 eV. This results in a Si 2p peak at 103.2 eV when present, well within the range for SiO 2 and silicon‐supported SiO 2 films . The carbon peak is not used directly because the multiple contributions of the Nafion ® film produce slight shifts in this peak.…”

Characteristics of Self-Assembled Ultrathin Nafion Films

“…To prevent excessive charging, a charge neutralizer was used. The binding energy scale was further calibrated by setting the Si 2p peak to 103.4 eV. , This value is well within the range for SiO 2 and silicon-supported SiO 2 films [103–104 eV from ref ] and results in an adventitious carbon peak at ∼284.8 eV. The carbon peak is not used directly because the multiple contributions of the Nafion film produce slight shifts in this peak.…”