High contrast scanning nano‐Raman spectroscopy of silicon

We have demonstrated that scanning nano‐Raman spectroscopy (SNRS), generally known as tip‐enhanced Raman spectroscopy (TERS), with side illumination optics can be effectively used for analysis of silicon‐based structures at the nanoscale. Even though the side illumination optics has disadvantages such as difficulties in optical alignment and shadowing by the tip, it has the critical advantage that it may be used for the analysis of nontransparent samples. A key criterion for making SNRS effective for imaging Si samples is the optimization of the contrast between near‐field and far‐field (background) Raman signals. This has been achieved by optimizing the beam polarization, resulting in an order of magnitude improvement in the contrast. We estimate the lateral resolution of our Raman images to be ∼20 nm.