Negligible contribution of inter-dot coherent modes to heat conduction in quantum-dot superlattice
Negligible contribution of inter-dot coherent modes to heat conduction in quantum-dot superlattice
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DOI：
10.1016/j.mtphys.2021.100601
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发表时间：
2021-12
影响因子：
11.5
通讯作者：
Cheng Shao;J. Shiomi
中科院分区：
文献类型：
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作者：
Cheng Shao;J. Shiomi
胶体量子点（QDs）超晶格是一种以无机核为核心，可以自组装成各种晶格结构的超晶格，在光、电、光电子器件等领域有着广阔的应用前景。最近的非弹性中子散射测量[NAT.COMMUN. 10：4236（2019）]表明，量子点间的振动频率可以通过改变量子点的形状和配体类型来调节，这表明量子点超晶格可以成为声子工程的平台。在这项工作中，我们量化的第二周期性的影响，通过全尺度的分子动力学模拟PbS量子点超晶格与现实的量子点大小和配体形态的热输运。振动模式的分析表明，振动可以分为量子点间的相干模式和空间局域模式所产生的几何限制。光谱分析表明，在0.8-5 THz的频率范围内的空间局域模占主导地位的热输运，并导致非晶的温度依赖性之间的200和400 K。另一方面，量子点间的相干模式，虽然具有10 ps的平均弛豫，具有有限的热导率值为0.01 W/mK在室温下，由于缺乏的振动状态。我们证明了在量子点超晶格的热导率工程中，控制配体的形态比调节第二周期性更有效。
Colloidal quantum dots (QDs) superlattice, which is made of inorganic cores and can self-assemble into various types of lattice structures, finds promising applications in optical, electrical, and optoelectronic devices. Recent inelastic neutron scattering measurement [NAT. COMMUN. 10:4236 (2019)] showed that the inter-quantum-dot vibrational frequencies can be tuned by varying the QDs shapes and ligand types, suggesting that the QDs superlattices can be a platform for phonon engineering. In this work, we quantify the impact of the second periodicity on thermal transport through full-scale molecular dynamics simulations of PbS QDs superlattice with realistic QD size and ligand morphology. The vibrational pattern analysis reveals that the vibrations can be classified into the inter-QDs coherent modes and the spatially localized modes arising from the geometry confinement. The spectral analysis indicates that spatially localized modes in the frequency range of 0.8–5 THz dominate the thermal transport and lead to an amorphous-like temperature dependence between 200 and 400 K. On the other hand, the inter-QDs coherent modes, albeit have an averaged relaxation of 10 ps, have a limited thermal conductivity value of 0.01 W/mK at room temperature due to the scarce of the vibrational states. We demonstrate that controlling the ligand morphology is more efficient than tuning the second periodicity in engineering the thermal conductivity of QDs superlattice.