Preparation of Ba{sub}2CuO{sub}2(CO{sub}3)mACuO{sub}2n(A=Sr,Ca) films by MBE technique

摘要

[Ba{sub}2CuO{sub}2(CO{sub}3)]m[ACuO{sub}2]n(A=Sr) superlattices containing oxycarbonate blocks as charge reservoir have been prepared on SrTiO{sub}3 using the molecular beam epitaxy technique. First, thin films of the oxycarbonate cuprate Ba{sub}2CuO{sub}2(CO{sub}3) have been prepared on SrTiO{sub}3(001) using NO{sub}2 gas as an oxidant and CO{sub}2 gas. The films have been grown at 500°C. At higher substrate temperature or at lower CO{sub}2 pressure Ba{sub}2CuO{sub}3 was formed instead of Ba{sub}2CuO{sub}2(CO{sub}3), and the films becomes amorphous at lower temperature. X-ray diffraction and reflection high-energy electron diffraction observations indicated that (Ba{sub}xSr{sub}(1-x)){sub}2CuO{sub}2(CO{sub}3) grew along the [001] crystal orientation on SrTiO{sub}3(001) with the following epitaxial relationship: Ba{sub}2CuO{sub}2(CO{sub}3)[100]//SrTiO{sub}3[110] and Ba{sub}2CuO{sub}2(CO{sub}3)[110]//SrTiO{sub}3 [100]. Depth profile of secondary ion mass spectrometry signals indicated the incorporation of carbon into the films. Secondly, the oxycarbonate cuprates and infinite layers have been alternately stacked. It was confirmed that Ba{sub}2CuO{sub}2(CO{sub}3)was inserted between several unit cells of SrCuO{sub}2. Electrical measurements show the as grown films to have a semiconducting behavior.