The phonon confinement effect in two-dimensional nanocrystals of black phosphorus with anisotropic phonon dispersions
The phonon confinement effect in two-dimensional nanocrystals of black phosphorus with anisotropic phonon dispersions
复制标题
各向异性声子色散二维黑磷纳米晶中的声子限域效应
DOI：
10.1039/c8nr01531g
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发表时间：
2018
期刊：
影响因子：
6.7
通讯作者：
Ping-Heng Tan
中科院分区：
文献类型：
--
作者：
Tong Lin;Xin Cong;Miao-Ling Lin;Xue-Lu Liu;Ping-Heng Tan
研究发现，RWL模型对纳米晶体声子限制效应的描述存在一定的偏差和局限性，对具有明显各向异性声子色散的纳米晶体，提出了修正模型以克服这些缺陷。在这里，我们研究这个问题在黑磷（BP），一个典型的各向异性的二维晶体表现出明显的各向异性声子色散。对离子注入法制备的BP纳米碳的拉曼光谱进行了详细的研究。随着NC尺寸的减小，三个特征拉曼模式，Ag 1，B2 g和Ag 2模式的峰位置几乎保持不变，而Ag 1和Ag 2模式显示出显着的不对称加宽的尾巴向高，低频率侧，分别。研究发现，基于布里渊区（BZ）内沿着Γ-Y和Γ-X轴一维声子色散的RWL模型不能解释这三种模式异常的频率不变性和不均匀的线形展宽。然而，在考虑了整个BZ的二维各向异性声子色散的贡献后，可以很好地再现Ag 1和Ag 2模的频率和不对称展宽。这项研究表明，只要适当考虑整个二维或三维BZ中的声子，RWL模型就可以适用于具有各向异性声子色散的晶体，并为理解各向异性系统的声子限制效应提供了物理上合理的途径。
The RWL model for the phonon confinement effect in nanocrystals (NCs) had been found to result in deviations and limitations for crystals exhibiting obvious anisotropic phonon dispersions and modified models have been proposed to overcome these deficiencies. Here, we examine this issue in black phosphorus (BP), a typical anisotropic two-dimensional crystal exhibiting pronounced anisotropy in phonon dispersions. A detailed study is performed on the Raman spectra of BP NCs prepared by the ion implantation technique. With decreasing NC size, the peak positions of the three characteristic Raman modes, Ag1, B2g and Ag2 modes, remain almost unchanged, while the Ag1 and Ag2 modes show significant asymmetrical broadening tails towards higher- and lower-frequency sides, respectively. It is found that the RWL model based on one-dimensional phonon dispersion along Γ–Y and Γ–X axes in the Brillouin zone (BZ) cannot interpret the unusual frequency invariance and inhomogeneous line shape broadening of these three modes. However, after considering the contribution of two-dimensional anisotropic phonon dispersions from the whole BZ, the frequency and asymmetrical broadening of the Ag1 and Ag2 modes can be well reproduced. This study demonstrates that the RWL model can be applicable for crystals with anisotropic phonon dispersions once the phonons in the whole two-dimensional or three-dimensional BZ are properly taken into account, and provides a physically sound route into understanding the phonon confinement effect for anisotropic systems.