Chemical imaging of patterned inorganic thin-film structures by lateral force microscopy

Factors influencing the chemical image formation by lateral force microscopy (LFM, or friction force microscopy, FFM) under normal ambient conditions were studied by applying LFM to patterned specimens of inorganic thin films deposited predominantly by atomic layer epitaxy. The patterned steps on SnO(2)/Si, CaS/Si, CeO(2)/Si, and Pt/Al(2)O(3) samples were formed by chemical etching or lift-off processing. The results of semiquantitative AFM and LFM studies were compared to the static contact angle studies using capillary force evaluation. The chemical contrast in LFM images of the patterned specimens was the highest in cases where silicon was present. This is in accordance with contact angle data, which showed much higher hydrophilicity on Si than on the other materials studied. Further experiments with a patterned SnO(2)/Si specimen indicated that chemical contrast can be significantly affected (i) by whether the surface was pretreated with ethanol, (ii) by the loading force (2-50 nN or 1-10 μN) applied, and (iii) by using SnO(2)-coated AFM probes instead of the conventional Si probes.