Cj. Hill et al., Scanning apertureless microscopy below the diffraction limit: Comparisons between theory and experiment, APPL PHYS L, 75(25), 1999, pp. 4022-4024
The exact nature of the signal in scanning apertureless microscopy techniqu
es is the subject of much debate. We have sought to resolve this controvers
y by carrying out simulations and experiments on the same structures. Simul
ations of a model of tip-sample coupling are shown to exhibit features that
are in agreement with experimental observations at dimensions below the di
ffraction limit. The simulation of the optical imaging process is carried o
ut using atomic force microscope data as a topographical template and a tip
-sample dipole coupling model as the source of optical signal. The simulati
ons show a number of key fingerprints including a dependence on the polariz
ation of the external laser source, the size of the tip, and index of refra
ction of the sample being imaged. The experimental results are found to be
in agreement with many of the features of the simulations. We conclude that
the results of the dipole coupling theory agree qualitatively with experim
ental data and that apertureless microscopy measures optical properties, no
t just topography. (C) 1999 American Institute of Physics. [S0003-6951(99)0
2451-1].