| Interfacing metals with semiconductor surfaces at the nanometer scale has received much attention, as a result of the critical importance of these interfaces for applications such as integrated circuits, optoelectronics, and others. An efficient and versatile approach for the synthesis of metallic nanostructures on a variety of semiconductor surfaces, including GaAs, InP, silicon [Si(111), Si(100) and Si nanowires], and germanium, is galvanic displacement---a spontaneous electrochemical reaction that is a member of the electroless deposition family. These hybrid nanostructures have intriguing properties but have not been elucidated and therefore not understood. To better illuminate the nature of these systems we use a number of different analyses such as X-ray diffraction (XRD), nanobeam (∼5 nm) selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES), as well as high resolution transmission electron microscopy (TEM) imaging. In spite of the fact the reaction is carried out in water, the growth of gold on silicon and germanium surfaces is heteroepitaxial. This high degree of alignment (heteroepitaxy) was directly observed by high resolution TEM imaging the interface between gold and single crystal germanium and silicon substrates, revealing a coincident site lattice (CSL) of four gold lattices to three of the semiconductor substrate (low lattice mismatch). In the case of Au/Ge, we were able to tune the texture nature of the gold epilayer by changing the composition of the deposition bath.;Galvanic displacement of Au nanoparticles (NPs) on Si nanowires (NWs) showed very interesting phenomenon---Au NPs exhibit preferential deposition on the Si(110) faces of Si nanowires, grown along growth direction, than on the Si(111) faces. The direction of elemental diffusion across the metalsemiconductor contacts was investigated. Spectroscopic (AES) investigations suggest little diffusion of the metals into the semiconductor lattice. Finally, the intermetallic nature of metal-semiconductor interfaces was substantiated by depth profile X-ray photoelectron spectroscopy (XPS) and nanobeam diffraction analyses. Hence, galvanic displacement offers a very attractive method for wiring in nanostructures to semiconductor chips, allowing for its use in modern technological applications. |
