Nanoplatelets (NPLs)—colloidally synthesized, spatially anisotropic, two-dimensional semiconductor quantum wells—are of intense interest owing to exceptionally narrow transition line widths, coupled with solution processability and bandgap tunability. However, given large surface areas and undercoordinated bonding at facet corners and edges, excitation under sufficient intensities may induce anisotropic structural instabilities that impact desired properties. We employ time-resolved X-ray diffraction to study the crystal structure of CdSe NPLs in response to optical excitation. Photoexcitation induces greater out-of-plane than in-plane disordering in 4 and 5 monolayer (ML) NPLs, while 3 ML NPLs display the opposite behavior. Recovery dynamics suggest that out-of-plane cooling slightly outpaces in-plane cooling in 5 ML NPLs with recrystallization occurring on indistinguishable time scales. In comparison, for zero-dimensional CdSe nanocrystals, disordering is isotropic and recovery is faster. These results favor the use of NPLs in optoelectronic applications, where they are likely to exhibit superior performance over traditional, zero-dimensional nanocrystals.

中文翻译：

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胶态二维CdSe纳米片的光激发各向异性瞬态无序

纳米片（NPL）是胶体合成的，空间各向异性的二维半导体量子阱，由于过渡线的宽度非常窄，加上溶液的可加工性和带隙可调性，因此引起了人们的极大兴趣。但是，给定较大的表面积并在小面的拐角和边缘处结合不充分，在足够强度下激发可能会导致各向异性的结构不稳定性，从而影响所需的性能。我们采用时间分辨的X射线衍射来研究CdSe NPL的晶体结构，以响应光激发。在4个和5个单层（ML）不良贷款中，光激发比面内混乱引起的面外混乱更大，而3 ML不良贷款则表现出相反的行为。恢复动力学表明，在5 ML NPL中，面外冷却略高于面内冷却，并且在无法区分的时间范围内发生了重结晶。相比之下，对于零维CdSe纳米晶体，无序是各向同性的，并且恢复更快。这些结果有利于在光学电子应用中使用NPL，在这些应用中，NPL可能比传统的零维纳米晶体表现出更好的性能。