A laser-assisted spray process was developed to deposit surfactant-free PbSe quantum dot (QD) films directly on a substrate. These QDs are in close contacts with each other, forming a percolation path for charge transport. Absorption spectroscopy confirmed the quantum confinement of the deposited particles. Room temperature current-voltage measurements across a 2 μm tunnel junction formed by the QDs produced a power-law dependence of the form I∝V2.25, which describes a percolation path of dimensionality slightly above two dimensions. Temperature dependent conductance studies showed thermally activated transport at high temperatures and temperature independent tunneling, followed by previously unobserved metallic conduction at low temperatures.
We present a laser-assisted spray pyrolysis method to fabricate nanoparticle coatings of metal oxides. In this process, 1.5-μm size droplets of a titanium- or iron-containing organometallic precursor were injected into a vacuum chamber with SF6 carrier gas. The strong absorption of a 3W CO2 laser beam focused onto the injector tip in the presence of SF6 increased the temperature of the gas and the droplets to about 300 °C. Films deposited on heated substrates with and without the CO2 laser heating were studied by atomic force microscopy. The laser heating of the droplets caused the solvent to evaporate before depositing on the substrate, leading to grain sizes that are about a factor of 3 smaller than those deposited without laser heating. By controlling the concentration of the precursor in the solvent, the average particle sizes have been tuned from 80 to 50 nm.
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