First stages of Pd/Ge reaction

The structure and the chemical composition of Pd germanides formed on Ge(100) were investigated using transmission electron microscopy (TEM), in-situ X-ray diffraction (XRD), and atom probe tomography (APT). An ultrathin Si film used as a marker was deposited on Ge(100) prior to Pd film deposition in order to identify the diffusing species during the Pd2Ge growth. The observations evidenced the formation of a thin interfacial polycrystalline Pd2Ge layer during Pd room-temperature deposition on Ge(100). In-situ XRD thermal treatments ranging from 50 to 400°C revealed that the Si marker had no influence on the sequential formation of Pd2Ge and PdGe. Ex situ APT and TEM characterizations showed that the Si marker layer was located closer to the Pd2Ge/Ge interface than to the Pd2Ge surface, after reaction. This result indicates that Ge and Pd self-diffusion are in the same order of magnitude during Pd2Ge growth.