We report the direct observation of intramolecular hydrogen atom transfer reactions (tautomerization) within a single porphycene molecule on a Cu(110) surface by scanning tunneling microscopy. It is found that the tautomerization can be induced via inelastic electron tunneling at 5 K. By measuring the bias-dependent tautomerization rate of isotope-substituted molecules, we can assign the scanning tunneling microscopy-induced tautomerization to the excitation of specific molecular vibrations. Furthermore, these vibrations appear as characteristic features in the $dI/dV$ spectra measured over individual molecules. The vibrational modes that are associated with the tautomerization are identified by density functional theory calculations. At higher temperatures above $\sim 75\mathrm{K}$, tautomerization is induced thermally and an activation barrier of about 168 meV is determined from an Arrhenius plot.

We fabricated a Surface Enhanced Raman Scattering (SERS)-active surface based on photo-etched and Au-coated GaN. The highest enhancement factor (EF) in SERS and high reproducibility of spectra were obtained from surfaces covered with bunched nanopillars which were produced by relatively long defect-selective photo-etching. The surfaces exhibited SERS enhancements of the order of 2.8 × 10⁶ for malachite green isothiocyanate (MGITC) and 2 × 10⁶ for p-mercaptobenzoic acid (PMBA). These SERS enhancement factors were comparable to those of conventional SERS substrates, while the EF for MGITC was two orders of magnitude larger than the corresponding one reported for the SERS platform made on porous GaN. The standard deviation of the relative intensity of the 1180 cm⁻¹ mode of MGITC was less than 5% for 100 randomly distributed locations across a single platform and less than 10% between different platforms. The SERS signal of MGITC at our GaN/Au surface (kept under ambient conditions) was extremely stable. We could not detect any peak shift or appreciable change of intensity even after three months. We used these surfaces to detect biological molecules such as amino acids and bovine serum albumin (BSA) at low concentration and with short detection time. We developed simple and effective cleaning procedures for our substrates. After cleaning, the same substrate could be used multiple times retaining the SERS activity. We are not aware of any other multiply regenerated SERS substrate which provides simultaneously such high stability with high enhancement, good uniformity, and high reproducibility.