Analytical evaluation of tapping mode atomic force microscopy for chemical imaging of surfaces

Scanning probe methods like atomic force microscopy (AFM) and related techniques are promising candidates for morphological, physical, and chemical characterization of surfaces on the sub-micrometer scale. In order to evaluate the analytical potential of tapping mode AFM for obtaining material specific information on surface structures along with topography, we have studied the influence of various experimental parameters on height and phase contrast using self-assembled monolayers (SAMs) as well defined model systems. The organic films were deposited onto silicon substrates starting from alkyltrichlorosilanes with methyl-, ester-, and hydroxyl-end groups, respectively. As a result it was found that reproducibility suffers from the fact that even small changes in parameters determining the force interaction between tip and sample can lead to pronounced changes in image contrast. Nevertheless it has been possible to identify comparatively stable regions for the imaging parameters allowing to distinguish different sample systems by their specific pattern of height and phase contrasts, which can be seen as a valuable analytical contribution towards sub-micrometer chemical imaging with scanning probe microscopy. (C) 2001 Elsevier Science B.V. All rights reserved.