Molecular speciation analysis of oxidized metal surfaces by TOF SIMS

Abstract

Molecular speciation by Time of Flight Secondary Ion Mass Spectrometry (TOF SIMS) was applied to oxidized bismuth, lead, tin, and tellurium. In their pure elemental form, they are basic constituent elements of both topological insulators and topological crystalline insulators, which are very hot topics in the last decade.The range of specific ions masses used to evaluate the valence of investigated oxides has been significantly expanded towards high-mass clusters MexOy (2 ≤ x ≤ 5). The significant enhancement in the secondary high-mass ion yield by using the Bi cluster ion source reflects the valence of primary ion clusters used in molecular speciation of inorganic species. The results show that chemical composition of clusters differs in three 2, 3, and 4 oxidation states studied. This implies that each oxidation state possesses its own set of the high-mass clusters extracted from oxidized metal surfaces during measurement.Such an approach allows for the first time to perform a semi-quantitatively molecular speciation of oxides exploiting the empirical Plog's model. It describes the secondary ion yield as a function of the metal valency in the oxide. We found that the estimated lattice valence state G0 is close to the valence state of the metal in stable oxides.