Removing optical artifacts in near-field scanning optical microscopy by using a three-dimensional scanning mode

We demonstrate a method of acquiring near-field scanning optical microscopy data that allow for the construction of three different types of images fr om one data set: topographic, constantgap, and constant-height. This data s et includes the topographic features of the surface and the optical respons e at various heights above the sample surface. Comparisons are made between the images recorded in this format and both conventional, constant-gap mod e images, and pseudoconstant-height mode images constructed using a single retraction curve. Z-motion artifacts are identified by analyzing the optica l intensity for a given image as a function of the sample topography. Using this procedure it is shown that significant z-motion artifacts exist in th e constant-gap images of gold particles immobilized on a glass slide. These artifacts are avoided by constructing constant-height images. [S0021-8979( 99)07517-9].