Probing of optical near-fields by electron rescattering on the 1 nm   scale
  We present a new method of measuring optical near-fields within ~1 nm of a metal surface, based on rescattering of photoemitted electrons. With this method, we precisely measure the field enhancement factor for tungsten and gold nanotips as a function of tip radius. The agreement with Maxwell simulations is very good. Further simulations yield a field enhancement map for all materials, which shows that optical near-fields at nanotips are governed by a geometric effect under most conditions, while plasmon resonances play only a minor role. Last, we consider the implications of our results on quantum mechanical effects near the surface of nanostructures and discuss features of quantum plasmonics. 
Sebastian Thomas, Michael Kr\"uger, Michael F\"orster, Markus Schenk,   Peter Hommelhoff
physics.optics cond-mat.mes-hall quant-ph