Field enhancement of optical radiation in the nearfield of scanning probe microscope tips

A brief outline of the methods and approaches in the theory for field enhancement of laser radiation in the nearfield of a scanning probe microscope tips is given. The simple analytical "small spheroid model" (mainly used in Surface Enhanced Raman Spectroscopy) as well as a more realistic numerical model based on the boundary element method are used for field enhancement calculations on the tip apex. The small spheroid model gives a rough estimation from below for tips with spheroid geometry, whereas the numerical model can take into account arbitrary tip geometry and include the effect of substrate surface. Tremendous field concentration with nanometer localization for certain tip and substrate materials is used for applications in surface nano modification with laser radiation. Experimental data supporting the surface modification due to the enhanced field mechanism are presented.