Analysis of the influence of the tip vibration in the formation of images in apertureless scanning near-field optical microscopy

The theoretical influence of the vertical vibration of the tip is investiga ted to calculate the images of a quartz grating in an apertureless scanning near-field optical microscope configuration, a realistic model is used for the simulation of the lock-in detection. It is shown that the output signa l issued from the lock-in detection cannot be simply approximated by a mere difference between the intensities of the field between the top and bottom positions of the tip oscillation. Several modes of the lock-in detection, amplitude and phase, X and Y channel, at the fundamental frequency or for t he following harmonics, though all leading to images containing high spatia l frequencies of the grating, show significant differences that can induce misinterpretations in specific cases. (C) 2000 Elsevier Science B.V. All ri ghts reserved.