Pan Jia-Ahn, Wu Haoqi, Gomez Anthony, Ondry Justin C, Portner Joshua, Cho Wooje, Hinkle Alex, Wang Di, Talapin Dmitri V
Department of Chemistry, James Franck Institute, and Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States.
Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, United States.
ACS Nano. 2022 Oct 25;16(10):16067-16076. doi: 10.1021/acsnano.2c04189. Epub 2022 Sep 19.
Microscale patterning of colloidal nanocrystal (NC) films is important for their integration in devices. Here, we introduce the direct optical patterning of all-inorganic NCs without the use of additional photosensitive ligands or additives. We determined that photoexposure of ligand-stripped, "bare" NCs in air significantly reduces their solubility in polar solvents due to photo-oxidation of surface ions. Doses as low as 20 mJ/cm could be used; the only obvious criterion for material selection is that the NCs need to have significant absorption at the irradiation wavelength. However, transparent NCs can still be patterned by mixing them with suitably absorbing NCs. This approach enabled the patterning of bare ZnSe, CdSe, ZnS, InP, CeO, CdSe/CdS, and CdSe/ZnS NCs as well as mixtures of ZrO or HfO NCs with ZnSe NCs. Optical, X-ray photoelectron, and infrared spectroscopies show that solubility loss results from desorption of bound solvent due to photo-oxidation of surface ions. We also demonstrate two approaches, compatible with our patterning method, for modulating the porosity and refractive index of NC films. Block copolymer templating decreases the film density, and thus the refractive index, by introducing mesoporosity. Alternatively, hot isostatic pressing increases the packing density and refractive index of NC layers. For example, the packing fraction of a ZnS NC film can be increased from 0.51 to 0.87 upon hot isostatic pressing at 450 °C and 15 000 psi. Our findings demonstrate that direct lithography by photo-oxidation of bare NC surfaces is an accessible patterning method for facilitating the exploration of more complex NC device architectures while eliminating the influence of bulky or insulating surfactants.
胶体纳米晶体（NC）薄膜的微尺度图案化对于其在器件中的集成至关重要。在此，我们介绍了全无机NCs的直接光学图案化方法，无需使用额外的光敏配体或添加剂。我们确定，在空气中对去除配体的“裸”NCs进行光曝光会由于表面离子的光氧化而显著降低它们在极性溶剂中的溶解度。低至20 mJ/cm²的剂量即可使用；材料选择的唯一明显标准是NCs需要在照射波长处有显著吸收。然而，透明NCs仍可通过与适当吸收的NCs混合来进行图案化。这种方法能够对裸ZnSe、CdSe、ZnS、InP、CeO、CdSe/CdS和CdSe/ZnS NCs以及ZrO或HfO NCs与ZnSe NCs的混合物进行图案化。光学、X射线光电子能谱和红外光谱表明，溶解度损失是由于表面离子的光氧化导致结合溶剂的解吸。我们还展示了两种与我们的图案化方法兼容的方法，用于调节NC薄膜的孔隙率和折射率。嵌段共聚物模板法通过引入介孔来降低薄膜密度，从而降低折射率。或者，热等静压提高了NC层的堆积密度和折射率。例如，在450°C和15000 psi下进行热等静压后，ZnS NC薄膜的堆积分数可从0.51提高到0.87。我们的研究结果表明，通过对裸NC表面进行光氧化的直接光刻是一种可行的图案化方法，有助于探索更复杂的NC器件架构，同时消除庞大或绝缘表面活性剂的影响。
