層狀二硫化鉬在渦旋光激發下的共振拉曼光譜

Abstract

二硫化鉬是一種典型的過渡金屬二硫化物，具有敏感的光學性質。由一層鉬原子平面夾在兩層硫原子平面之間，形成單層二硫化鉬。藉由二硫化鉬的拉曼光譜，可以觀察到各峰值振動頻率的變化和位移趨勢。在這項研究中，我們使用空間光調制器（SLM），將入射光改變成具有軌道角動量（OAM）的狀態，並觀察633 nm（1.96 eV）的OAM光激發單層二硫化鉬共振拉曼光譜的變化，經由實驗結果發現隨著軌道角動量（ℓ）的增加，共振拉曼峰值會產生藍移的現象。除了對單層樣品進行照射，還測量了不同單層和雙層二硫化鉬樣品下的拉曼光譜變化，實驗結果顯示，僅在單層樣品中增加軌道角動量才會引起藍移現象。此外，也測量了不同光強度和低溫環境下的拉曼光譜，進一步確認拉曼藍移效應不受環境的熱效應影響。總結而言，在本文的後段中，證實了軌道角動量的提高會導致材料受到的壓縮力變大，使粒子的振動頻率增加，進而產生共振拉曼峰值的藍移現象，藉由實驗和理論的相互印證，更加確定光學軌道角動量對單層二硫化鉬拉曼藍移的物理機制。期待在未來能將光學軌道角動量應用於二維材料的檢測和開發中。Molybdenum disulfide (MoS2) is a typical transition metal dichalcogenide with sensitive optical properties. It consists of a layer of molybdenum atoms sandwiched between two layers of sulfur atoms, forming a monolayer of MoS2. By using the Raman spectroscopy of MoS2, variations and shifting trends in the vibrational frequencies of the peaks can be observed. In this study, we employed a spatial light modulator (SLM) to transform the incident light into a state with orbital angular momentum (OAM) and observed the changes in the resonant Raman spectroscopy of monolayer MoS2 excited by OAM light at 633 nm (1.96 eV). Experimental results revealed a blue-shift in the resonant Raman peak as the orbital angular momentum (ℓ) increased.In addition to irradiating monolayer samples, we also measured the Raman spectroscopy variations in different monolayer and bilayer MoS2 samples. The experimental results showed that the blue-shift phenomenon occurs only when OAM is increased in monolayer samples. Furthermore, we conducted Raman spectroscopy measurements at different light intensities and in a low-temperature environment to confirm that the Raman blue-shift effect is not influenced by thermal effects in the environment. In summary, in the latter part of this paper, it was confirmed that the increase in orbital angular momentum leads to increased compressive forces on the material, resulting in higher vibrational frequencies of particles and hence the blue-shift of resonant Raman peaks. Through mutual verification of experiments and theory, the physical mechanism of Raman blue-shift in monolayer MoS2 due to optical orbital angular momentum was further established. We look forward to applying optical orbital angular momentum in the detection and development of two-dimensional materials in the future.