Tin Oxides: Insights into Chemical States from a Nanoparticle Study

Tin oxides are semiconductor materials currently attracting close attention in electronics, photovoltaics, gas sensing, and catalysis. Depending on the tin oxidation state—Sn(IV), Sn(II), or intermediate—the corresponding oxide has either n- or p-type natural conductivity, ascribed to oxygen or metal deficiency in the lattice. Such crystalline imperfections severely complicate the task of establishing tin oxidation state, especially at nanoscale. In spite of the striking differences between SnO2 and SnO in their most fundamental properties, there have been enduring problems in identifying the oxide type. These problems were to a great extent caused by the controversy around the characteristic chemical shift, that is, the difference in electron binding energy of a certain core level in an oxide and its parent metal. Using in situ fabricated bare tin oxide nanoparticles, we have been able to resolve the controversy: Our photoelectron spectroscopic study on tin oxide nanoparticles shows that, in contrast to ...