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Solution-synthesized nanocrystalline semiconductor quantum dots with core/shell structure exhibit distinct quantum confinement effects in light emission. For instance the photoluminescence of the CdSe/ZnS dots can be tuned from blue to red by controlling diameter of the core, and internal quantum yield of the photoluminescence is extending to 80%. These findings strongly stimulated interests in fabricating light emitting thin films by using the pre-synthesized quantum dots in liquid solution. It is, however, still a matter of challenge to fabricate the thin films which satisfy with the process conditions for the inorganic light emitting devices. Here we report a new fabrication technique of the organic-free thin films from a solution of the surfactant-capped nanocrystalline dots. Colloidal solutions of CdSe/ZnS nanocrystals with diameters of 2.1-5.1 nm were made into ion beams and deposited on polycrystalline substrates under high-vacuum ambient by the ion beam direct deposition technique employing an electrospray ionizer, a supersonic jet emitter and an energy analyzer. We characterized the deposited films by photoluminescence (PL) spectra, cross-sectional high resolution transmission electron microscopic (TEM) images and secondary ion mass spectrometric (SIMS) semi-quantitative analysis. It was evidenced that the nanocrystalline structure was preserved in the thin films and PL spectra were identical with those obtained for the source solution, notwithstanding the thin films were almost surfactant- and solvent-free. |