Investigation of copper(I) oxide quantum dots by near edge X-ray absorption fine structure spectroscopy

Copper(I) oxide quantum dots (OQDs) were grown in various thicknesses on different SrTiO3(001) surfaces and were investigated by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The experimental growth conditions for the OQDs were optimized to obtain Cu2O as the major phase. The OQDs grown on clean SrTiO3(001) surfaces at 825 K and higher with p(O-2) of 9.0 x 10(-7) Torr or greater contain mostly CuO, contrasting to OQDs grown at 800 K with p(O-2) of similar to 7.0 x10(-7) Torr that contain primarily Cu2O. Furthermore, there is a strong interaction between the SrTiO3(001) surface and the first few monolayers of the OQDs, which induces the formation of Cu(II). However, this interaction is mitigated with increasing thickness of OQDs, resulting in the exclusive formation of Cu2O in the top most layers. The influence of the SrTiO3(001) substrate on the formation of OQDs can be minimized by modifying the substrate surface using chemical treatment and/or energetic Au2+ ion-beam irradiation. Examination of the photochemical properties of these OQDs shows that prolonged soft X-ray irradiation under vacuum reduces Cu(II), which is present as a minor impurity in the Cu(I)OQDs