Frequency modulation (FM) and amplitude modulation (AM) atomic force microscopy have been used to image
self-organised assemblies of octanethiol-passivated Au nanoparticles adsorbed on SiO2/Si(111) samples (where
the oxide is either 200 nm or ~ 2 nm thick). Imaging at negative frequency shifts - i.e. in the attractive force
regime - in FM mode in ultrahigh vacuum we measure nanoparticle heights which are over 50 % larger than
those measured using conventional ("repulsive mode") tapping mode imaging in air. A similar difference in
nanoparticle height is observed for attractive mode imaging in air. For nanoparticles adsorbed on 200 nm thick
oxide layers, force-distance (F(z)) spectra (measured in FM mode) comprise both a van der Waals component
with the conventional power law (1/z2) dependence and a strong electrostatic force which is best fitted using a
logarithmic function of the form ln(1/z).
Conference Committee Involvement (1)
Nanostructured Thin Films II
5 August 2009 | San Diego, California, United States
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