dependence of apertureless scanning near-field spectroscopy on nanoscale refractive index changes

We numerically investigate the spectral dependence of the electric field enhancement on a gold tip above pbtio3 on platinum systems by means of a finite element approach. the localized surface plasmon resonance (lspr) is verified to change with the incident angle, the tip radius, and the tip-sample distance as well as with the refractive index of the sample underneath the tip. the refractive index sensitivity reveals detectable variations of the lspr peak’s wavelength and maximum field enhancement, respectively, large enough to discriminate, e.g., between ferroelectric and paraelectric pbtio3 in tip-enhanced raman spectroscopy (ters) configuration.