Anisotropic Transient Disordering of Colloidal, Two-Dimensional CdSe Nanoplatelets upon Optical Excitation
Anisotropic Transient Disordering of Colloidal, Two-Dimensional CdSe Nanoplatelets upon Optical Excitation
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DOI：
10.1021/acs.nanolett.0c03958
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发表时间：
2021-01-19
期刊：
影响因子：
10.8
通讯作者：
Schaller, Richard D.
中科院分区：
文献类型：
--
作者：
Brumberg, Alexandra;Kirschner, Matthew S.;Schaller, Richard D.
纳米片(NPLs)-胶体合成，空间各向异性，二维半导体量子阱-由于异常窄的过渡线宽度，加上溶液可加工性和带隙可调性而引起了人们的强烈兴趣。然而，考虑到大的表面积和facet角和边缘的不协调结合，在足够强度下的激发可能会导致各向异性结构不稳定，从而影响期望的性能。我们利用时间分辨x射线衍射研究了CdSe NPLs在光激发下的晶体结构。光激发在4和5单层（ML）不良分子中引起的面外无序大于面内无序，而3 ML不良分子则表现出相反的行为。恢复动力学表明，面外冷却略超过面内冷却在5 ML的NPLs与再结晶发生在不可区分的时间尺度。相比之下，对于零维CdSe纳米晶体，无序性是各向同性的，恢复速度更快。这些结果有利于NPLs在光电应用中的应用，在这些应用中，它们可能比传统的零维纳米晶体表现出更优越的性能。
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.