拉曼光谱毕业论文题目

材料在合成或加工过程中会有意或无意地引入一些结构缺陷，此外由于熵对系统自由能的贡献，缺陷也可在有限温度下自发地出现。不同缺陷可能对材料性能产生有利或有害的影响。如，外来杂质可以增加载流子浓度，但同时引入的额外散射过程又会降低其迁移率。缺陷设计还可开发出新技术，如可用点缺陷作为量子信息领域中的单光子发射器或量子位主机。随着新材料的发现，缺陷对于工程师和科学家而言，仍然是活跃而重要的研究领域。而现在，这似乎与诸如石墨烯和过渡金属二硫化物（TMD）等二维（2D）材料特别相关。由于2D材料比表面积大，因而多数原子暴露在表面并与周围环境接触。2D材料因与反应物存在相互作用，不仅缺陷浓度远大于块体系统，且缺陷调控也更加容易。缺陷类型的确定可以通过拉曼光谱实现，然而缺陷类型或浓度与拉曼特征变化之间的定量关系难以建立，是一个普遍存在的难题。

来自芬兰阿尔托大学应用物理系的Hannu-Pekka Komsa领导的团队，构建了基于经验势和第一性原理计算的组合方法，可用于模拟缺陷材料的拉曼光谱，其中经验势用于评估缺陷系统的振动模式，然后与第一性原理计算得到的拉曼张量进行结合。他们研究了在何种程度上可以区分空穴类型，并提供随缺陷浓度变化时拉曼光谱演化的起源分析。这种方法不仅能可靠地模拟拉曼光谱，还可深入了解缺陷系统中振动模式的物理内涵，以及如何用拉曼光谱对它们进行探测。作者利用该方法研究了单层MoS2中的空位缺陷，捕获了缺陷对突出峰位移和不对称展宽的影响，其结果与实验数据定性一致。此外，他们使用声子局域模型来拟合其模拟的拉曼光谱，以评估该模型在缺陷材料中的适用性。结果发现，当同时考虑完整的声子色散关系和局域类型时，该模型非常有效。通过本研究发现，只要有适当的经验势，就可以有效地评估缺陷系统的拉曼光谱。

该文近期发表于 npj Computational Materials 6 : 59 (2020)，英文标题与摘要如下，点击可以自由获取论文PDF。

Simulating Raman spectra by combining first-principles and empirical potential approaches with application to defective MoS2

Zhennan Kou, Arsalan Hashemi, Martti J. Puska, Arkady V. Krasheninnikov & Hannu-Pekka Komsa

Successful application of two-dimensional transition metal dichalcogenides in optoelectronic, catalytic, or sensing devices heavily relies on the materials’ quality, that is, the thickness uniformity, presence of grain boundaries, and the types and concentrations of point defects. Raman spectroscopy is a powerful and nondestructive tool to probe these factors but the interpretation of the spectra, especially the separation of different contributions, is not straightforward. Comparison to simulated spectra is beneficial, but for defective systems first-principles simulations are often computationally too expensive due to the large sizes of the systems involved. Here, we present a combined first-principles and empirical potential method for simulating Raman spectra of defective materials and apply it to monolayer MoS2 with random distributions of Mo and S vacancies. We study to what extent the types of vacancies can be distinguished and provide insight into the origin of different evolutions of Raman spectra upon increasing defect concentration. We apply our simulated spectra to the phonon confinement model used in previous experiments to assess defect concentrations, and show that the simplest form of the model is insufficient to fully capture peak shapes, but a good match is obtained when the type of phonon confinement and the full phonon dispersion relation are accounted for.