Scientists and engineers have dreamed for decades of fast, low-cost, reliable, and multi-component nanopatterning techniques for printing functional colloidal nanoparticles. Although countless efforts have been devoted, it is still a daunting challenge to organize different nanocomponents into a predefined structure with nanometer precision over millimeter scale without forming defects. We have developed a nanoprinting technique, which utilizes a tip-based high-voltage writing process to generate nanoscale charged patterns on the substrates (Fig. 1a). This process not only enables electrostatic trapping but also creates a high local surface potential in contrast to the uncharged area, both favoring highly efficient site-specific NP assembly (Fig. 1b).
Print nanoparticles into defined patterns with a 200 nm pitch (~125,000 DPI), 30 nm (or larger) pixel size, 10 nm position accuracy in millimeter scale, with minimum error (error ratio < 2×10-6)
With our developed method, we can accurately assemble perovskite quantum dots (QDs) in an area of 100×800 μm2, as shown in the photoluminescence (PL) image of “Nanjing University” Logo, composed of 9481 pixels, approximately 4.7×105 10-nm CsPbBr3 NPs (Fig. 2a,b). No nonspecific adsorption was found in the uncharged area. In other words, the error ratio (i.e., the ratio of the number between nonspecific adsorbed and correctly printed NPs) is lower than 2×10-6. Moreover, the printing technique enjoys a very high resolution and accuracy. The pitch size can reach 200 nm (125, 000 DPI), or even a smaller value, as supported by the Kelvin probe force microscope (KPFM) potential maps and the corresponding AFM height maps of the printed structure (Fig. 2c). This has exceeded the diffraction limit of light and can potentially allow direct printing of metasurface-like structures in the optical regime.
Print multiple functional nanoparticles
The combinational patterning of different nanoparticles can be achieved by repeating the writing/deposition cycles. We printed a pseudo-color image with four different NPs, with 15-nm Fe2O3 NPs being used for creating the white color, and NaYF4:Yb,Er, CsPbBr3, and CdSe@ZnS NPs for magenta, green and red colors in the image captured by the dark-field microscopy (Fig. 3). No cross-contamination is observed in each pixel, further confirming the robustness of the method for printing multiple functional NPs. To the best of our knowledge, this is the first time that true color nanoprinting is achieved.
We believe this technique provides a powerful yet straightforward construction tool for large-scale positioning and integration of multiple functional nanoparticles toward next-generation photonics, optoelectronic, and biomedical devices.
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