AFM studies of nanoparticle deposition via electrospray ionization.

Electrospray ionization was used to deposit CdSe nanoparticles on graphite and InP substrates. The charge transferred to the substrate via the deposition was correlated to the number of particles found on the substrate by AFM observation. A charge per nanoparticle was determined from depositions of various lengths of time, which is approximately 1 electron per nanoparticle. This value was found to be consistent for concentrations of nanoparticle solutions, which differed by an order of magnitude. Such a value may be used for predicting the density of nanoparticles deposited on a substrate during the deposition. It was found that above a critical concentration, the deposition process produced large clumps of particles rather than individual particles. At lower concentrations, individual particles deposited on the graphite substrates were found to be mobile, arranging themselves on step edges of the graphite.