High-Resolution Raman Nano-Imaging with an Imperfect Probe

Tip-enhanced Raman (TER) spectral images of functionalized plasmonic metal nanoparticles contain a wealth of information about molecules and the nanoscopic local optical fields that are used to interrogate them. Akin to tip convolution effects in atomic force microscopy, the shape of the probe inevitably affects TER spectral images in ways that are not fully appreciated. Herein, we examine high-resolution TER spectral images of silver nanocubes functionalized with 4-bromothiophenol (BTP), which we record using an imperfect probe. We highlight artifacts that are encountered in both topographic atomic force and TER nanoimages. We also derive the orientation of BTP molecules on the surface from the recorded enhanced spectra both with and without the plasmonic tip. We find that the role of the probe, an imperfect one, in particular, is not trivial to dissect in the context of gauging molecular orientation via TER spectral imaging.