High resolution scanning near field mapping of enhancement on SERS substrates: comparison with photoemission electron microscopy.

The need for a dedicated spectroscopic technique with nanoscale resolution to characterize SERS substrates pushed us to develop a proof of concept of a functionalized tip-surface enhanced Raman scattering (FTERS) technique. We have been able to map hot spots on semi-continuous gold films; in order to validate our approach we compare our results with photoemission electron microscopy (PEEM) data, the complementary electron microscopy tool to map hot spots on random metallic surfaces. Enhanced Raman intensity maps at high spatial resolution reveal the localisation of hotspots at gaps for many neighboring nanostructures. Finally, we compare our findings with theoretical simulations of the enhancement factor distribution, which confirms a dimer effect as the dominant origin of hot spots.

From meandering to faceting, is step flow growth ever stable?

Based on helium atom beam diffraction and scanning tunneling microscopy data, the coexistence of a meandering and a bunching instability during homoepitaxial step flow growth is established in a class of nonreconstructed, metallic vicinal surfaces, Cu (1,1,n), n=5,9,17. Specifically, the meandering instability is shown to act as a precursor to the bunching instability, indicating that a one-dimensional treatment of bunching in step flow growth is not sufficient. Our findings might be generic to step flow growth in kinetically restricted systems.

Interband electronic excitation-assisted atomic-scale restructuring of metal surfaces by nanosecond pulsed laser light

Interaction of high-power laser light with materials often causes irreversible damage of the near-surface region. It is shown that copper single-crystal surfaces can be patterned by laser light. Irradiation with green light produced adatoms and vacancies, which self-organized into nanoscale pyramids. This restructuring can be removed by annealing. In contrast to green light, infrared laser irradiation at equivalent absorbed energy density did not produce any structural change. This, for metallic systems, unforeseen spectral difference in laser light action points to a concerted process as the source for structural modification, which involves long-lived primary excitation of localized d-electrons through interband transition together with phonon excitation.