Effect of interfacial structures on phonon transport across atomically precise Si/Al heterojunctions,Physical Review Materials

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Effect of interfacial structures on phonon transport across atomically precise Si/Al heterojunctions
Physical Review Materials ( IF 3.1 ) Pub Date : 2021-08-26 , DOI: 10.1103/physrevmaterials.5.086002
Zexi Lu ₁ , Nathaniel P. Smith ₂ , Micah P. Prange ₁ , Raymond A. Bunker ₂ , John L. Orrell ₂ , Anne M. Chaka ₁

Affiliation

Phonons are important carriers of energy and information in many cryogenic devices used for quantum information science and in fundamental physics experiments such as dark matter detectors. In these systems phonon behaviors can be dominated by interfaces and their atomic structures; hence, there is increasing demand for a more detailed understanding of interfacial phonon transport in relevant material systems. Previous studies have focused on understanding thermal transport over the entire phonon spectrum at and above room temperature. At ultralow temperatures, however, knowledge is missing regarding athermal phonon behavior due to the challenge in modeling the extreme conditions in microscale, heterogeneous cryogenic systems, as well as extracting single-phonon information from a large ensemble. In this paper, we delineate the effects of interfacial atomic structures on phonon transport using a combination of classical molecular dynamics (MD) and phonon wave-packet simulations, to illustrate the consistency and differences between the ensemble- and single-phonon dynamics. We consider three single-crystal Si surface reconstructions—

(1 \times 1), (\sqrt{3} \times \sqrt{3})

and

(7 \times 7)

—and model both experimentally observed

Si (1 \times 1) / Al

interfaces and hypothesized

Si (\sqrt{3} \times \sqrt{3})

/Al and

Si (7 \times 7) / Al

interfaces. The overall interfacial thermal conductance calculated from non-equilibrium MD shows that for the

Si (1 \times 1) / Al

system, the presence of Al twin boundaries can hinder phonon transport and reduce thermal conductance by 2–12% relative to single-crystal Al; whereas the Si

(\sqrt{3} \times \sqrt{3})

and

(7 \times 7)

reconstructions can enhance it by 6–19%. Normal mode decomposition reveals that both the increase and decrease in conductance are related to inelastic phonon scattering. Single-phonon wave-packet simulations predict phonon transport properties consistent with non-equilibrium MD, while further suggesting that phonon polarization conversion is significant even when elastic transmission dominates, and that the interfacial structures have anisotropic impacts on atomic vibrations along different lattice directions. Our findings suggest avenues for achieving selective phonon transport via controlling interfacial structures of materials using atomically precise fabrication techniques, and that the phonon wave-packet formalism is a potentially powerful method for developing a detailed understanding of non-equilibrium phenomena in the low-temperature limit.

中文翻译：

界面结构对穿过原子级精确 Si/Al 异质结的声子传输的影响

在用于量子信息科学和基础物理实验（如暗物质探测器）的许多低温设备中，声子是能量和信息的重要载体。在这些系统中，声子行为可以由界面及其原子结构控制；因此，越来越需要更详细地了解相关材料系统中的界面声子传输。以前的研究侧重于了解在室温及室温以上整个声子光谱上的热传输。然而，在超低温下，由于在模拟微尺度、异质低温系统的极端条件以及从大型集合中提取单声子信息方面存在挑战，因此缺乏关于无热声子行为的知识。在本文中，我们结合经典分子动力学 (MD) 和声子波包模拟来描绘界面原子结构对声子传输的影响，以说明整体声子动力学和单声子动力学之间的一致性和差异。我们考虑三种单晶硅表面重建——

(1 \times 1), (\sqrt{3} \times \sqrt{3})

和

(7 \times 7)

- 并模拟实验观察到的

硅 (1 \times 1) / 铝

接口和假设

硅 (\sqrt{3} \times \sqrt{3})

/一片地

硅 (7 \times 7) / 铝

接口。从非平衡 MD 计算的总界面热导表明，对于

硅 (1 \times 1) / 铝

系统中，铝孪晶界的存在会阻碍声子传输，并使热导率相对于单晶铝降低 2-12%；而Si

(\sqrt{3} \times \sqrt{3})

和

(7 \times 7)

重建可以将其提高 6-19%。正常模式分解表明电导的增加和减少都与非弹性声子散射有关。单声子波包模拟预测与非平衡 MD 一致的声子传输特性，同时进一步表明即使在弹性传输占主导地位时声子极化转换也很重要，并且界面结构对沿不同晶格方向的原子振动具有各向异性影响。我们的研究结果提出了通过使用原子级精确制造技术控制材料的界面结构来实现选择性声子传输的途径，

更新日期：2021-08-26

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