  A nanoscopy technique that can characterize light-matter interactions with
ever increasing spatial resolution and signal-to-noise ratio (SNR) is desired
for spectroscopy at molecular levels. Photoinduced force microscopy (PiFM) with
Au-coated probe-tips has been demonstrated as an excellent solution for this
purpose. However, its accuracy is limited by the asymmetric shape of the
Au-coated tip resulting in tip-induced anisotropy. To overcome such
deficiencies, we propose a Si tip-Au nanoparticle (NP) combination in PiFM. We
map the near-field distribution of the Au NPs in various arrangements with an
unprecedented SNR of up to 120, a more than 10-fold improvement compared to
conventional optical near-field techniques, and a spatial resolution down to
5.8 nm, smaller than 1/100 of the wavelength, even surpassing the tip-curvature
limitation. We also map the beam profile of an azimuthally polarized beam (APB)
with an excellent symmetry. The proposed approach can lead to the promising
single molecule spectroscopy.
