Micropattern deposition of colloidal semiconductor nanocrystals by aerodynamic focusing

We report the use of aerodynamic lenses to deposit micropatterns of colloidal semiconductor nanocrystals (or quantum dots). CdSe and CdSe/ZnS core/shell nanocrystals, with core diameters of 3.5-5 nm, were dispersed in hexane and then nebulized to generate agglomerates a few tens of nm in diameter, consisting of hundreds of nanocrystals. These agglomerates were then focused aerodynamically by a lens system. Microscale towers, lines, and patterns were deposited on thin sapphire plates and silicon wafers. The heights and widths of the deposits were adjustable by varying the experimental parameters. Line widths below 10 m at full-width half-maximum are demonstrated. Upon exposure to near-UV illumination, these deposits exhibited robust fluorescence in the visible, with the color depending on the diameter of the individual nanocrystal cores. A red shift of the photoluminescence peaks from the nanocrystal dispersion to the glassy solid deposits was also observed, which confirmed that the deposits consist of closely packed nanocrystals embedded in the organic matrices. This approach, which is not restricted to semiconductor nanocrystals, provides an alternative means for the deposition of microscale patterns of colloidal nanoparticles.