Few-layer black phosphorus (BP) with an in-plane puckered crystalline structure has attracted intense interest for strain engineering due to both its significant anisotropy in mechanical and electrical properties and its high intrinsic strain limit. Here, we investigated the phonon response of few layer BP under uniaxial tensile strain (∼7%) with in situ polarized Raman spectroscopy. Together with the first-principles density functional theory (DFT) analysis, the anisotropic Poisson’s ratio in few-layer BP was verified as one of the primary factors that caused the large discrepancy in the trend of reported Raman frequency shift for strained BP, armchair (AC) direction in particular. By carefully including and excluding the anisotropic Poisson’s ratio in the DFT emulations, we rebuilt both trends reported for Raman mode shifts. Furthermore, the angle-resolved Raman spectroscopy was conducted in situ under tensile strain for systematic investigation of the in-plane anisotropy of BP phonon response. The experimentally observed thickness and crystallographic orientation dependence is elaborated using DFT theory as having a strong correlation between the strain-perturbated electronic-band structure and the phonon vibration modes. This study provides insight, both experimentally and theoretically, for the complex electron–phonon interaction behavior in strained BP, which enables diverse possibilities for the strain engineering of electrical and optical properties in BP and similar two-dimensional nanomaterials.

中文翻译：

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应变黑磷的角度分辨拉曼研究中的各向异性电子-声子相互作用

具有平面内褶皱晶体结构的几层黑磷（BP）由于其在机械和电学性质上的显着各向异性以及其固有的高应变极限而引起了应变工程的强烈兴趣。在这里，我们研究了在原位单轴拉伸应变（约7​​％）下几层BP的声子响应。偏振拉曼光谱。结合第一原理密度泛函理论（DFT）分析，证实了几层BP中的各向异性泊松比是导致应变BP，扶手椅（ AC）方向。通过仔细地在DFT仿真中包括和排除各向异性泊松比，我们重建了针对拉曼模式偏移报道的两种趋势。此外，原位进行了角分辨拉曼光谱在拉伸应变作用下，用于系统研究BP声子响应的面内各向异性。使用DFT理论对实验观察到的厚度和晶体学取向依赖性进行了详细阐述，因为它在应变扰动的电子带结构和声子振动模式之间具有很强的相关性。这项研究从实验和理论上为应变BP中复杂的电子-声子相互作用行为提供了见识，这为BP和类似的二维纳米材料中的电学和光学性质的应变工程化提供了多种可能性。