IMAGING OF DROPLETS OF AQUEOUS-SOLUTIONS BY TAPPING-MODE SCANNING FORCE MICROSCOPY

Droplets of aqueous solutions of CaCl2 and P2O5 have been imaged with a scanning force microscope operated in tapping mode. We found two dis tinctly different modes of imaging, as revealed by both the obtained t opography and the resonance curves of the cantilever under imaging con ditions. One mode seems to comprise the formation of a liquid bridge b etween the tip and the sample and thus leads to distortions of the ima ged droplets. The other mode seems to circumvent the formation of a br idge and yields droplet-profiles which are in perfect agreement with t heoretical predictions. The phase lag between the cantilever motion an d the piezo voltage was monitored simultaneously with the topography s ignal, providing a strong material contrast between the liquid and the substrate. PACS: 07.79.-v; 68.45.Gd.