Quantum dot (QD) solids are emerging materials for many optoelectronic applications. To enhance interdot coupling and charge transport, surface ligands can be removed, allowing individual QDs to be attached along specific crystal orientations (termed “oriented attachment”). Optimizing the electronic and optical properties of QD solids demands a comprehensive understanding of the nanoscale energy flow in individual and attached QDs under photoexcitation. In this work, we employed ultrafast electron diffraction to directly measure how oriented attachment along ⟨100⟩ directions affects the nonequilibrium lattice dynamics of lead selenide QDs. The oriented attachment anisotropically alters the ultrafast energy relaxation along specific crystal axes. Along the ⟨100⟩ directions, both the lattice deformation and atomistic random motions are suppressed in comparison with those of individual QDs. Conversely, the effects are enhanced along the unattached ⟨111⟩ directions due to ligand removal. The oriented attachment switches the major lattice thermalization pathways from ⟨100⟩ to ⟨111⟩ directions.

中文翻译：

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光激发下单个和附着的 PbSe 量子点的非平衡晶格动力学


量子点 (QD) 固体是许多光电应用的新兴材料。为了增强点间耦合和电荷传输，可以去除表面配体，从而允许单个量子点沿着特定的晶体方向连接（称为“定向连接”）。优化量子点固体的电子和光学特性需要全面了解光激发下单个和附着的量子点的纳米级能量流。在这项工作中，我们采用超快电子衍射来直接测量沿⟨100⟩方向的定向附着如何影响硒化铅量子点的非平衡晶格动力学。定向附着各向异性地改变沿特定晶轴的超快能量弛豫。沿着⟨100⟩方向，与单个量子点相比，晶格变形和原子随机运动都受到抑制。相反，由于配体的去除，沿未连接的⟨111⟩方向的效果增强。定向附件将主要晶格热化路径从⟨100⟩方向切换到⟨111⟩方向。