Probing interactions among molecules, substrate, and tip using tip-enhanced Raman spectroscopy.

Tip-Enhanced Raman Spectroscopy (TERS) has shown that spatial resolution <1 nm is possible, but is technically challenging and difficult even in Ultra-High Vacuum at low temperatures with plasmonic substrates. Here we demonstrate that in ambient conditions it is possible to obtain Raman signal from isolated molecules on Au and submonolayer molecular islands on bulk MoS2. Analysis of the relative Raman peak ratio and the Raman peak position shift from the spatial TERS mapping show differences in the adsorbates-adsorbates interaction and the adsorbates-substrates interaction on Au and MoS2. TERS tips can influence the shape and diffusion of surfaces and adsorbates. We show the directional growth of Ag island stripes at room temperature via tip-assisted coarsening of hexagonal islands on Ag(111) using scanning tunneling microscope (STM). Tip-assisted island growth is not directly related to the tunneling current, bias voltage, tip composition or atmospheric O2 content but strongly depends on tip morphology.