Interfacial topological states are a key element of interest for topological insulator thin films, and their properties can depend sensitively on the atomic bonding configuration. We employ in situ nonresonant and resonant surface x-ray scattering to study the interfacial and internal structure of a prototypical topological film system: Bi2Te3 grown on Si(111). The results reveal a Te-dominated buffer layer, a large interfacial spacing, and a slightly relaxed and partially strained bottom quintuple layer of an otherwise properly stacked bulklike Bi2Te3 film. The presence of the buffer layer indicates a nontrivial process of interface formation and a mechanism for electronic decoupling between the topological film and the Si(111) substrate.

Different arrays of Ag-nanoparticles grown on anodic alumina nanochannels with precisely tunable gaps (5~25 nm) are exploited for surface-enhanced Raman spectroscopy (SERS). The enhancement becomes significant for gaps below 10 nm and turns dramatically large when gaps reach an unprecedented value of 5 nm. The results are quantitatively consistent with theories based on collectively coupled surface plasmon. Such nanofabricated substrates with consistently uniform and large dynamic range have many chemical/biological sensing applications.