α-MnTe中观测到的拉曼峰的起源
The Origin of the Observed Raman Peaks in α-MnTe
- Northeastern University（东北大学）
- Quantum Materials and Sensing Institute, Northeastern University Innovation Campus（东北大学创新校区量子材料与传感研究所）
- University of Notre Dame（圣母大学）
- V. E. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine（乌克兰国家科学院V.E.拉什卡廖夫半导体物理研究所）
- National Institute of Standards and Technology（美国国家标准与技术研究院）
- George Mason University（乔治梅森大学）
- Kostas Advanced Nano-Characterization Facility, Northeastern University Innovation Campus（东北大学创新校区科斯塔斯先进纳米表征设施）
- Howard University（霍华德大学）
- Stavropoulos Center for Quantum Matter, University of Notre Dame（圣母大学斯塔夫罗普洛斯量子物质中心）
- Department of Chemical Engineering, Northeastern University（东北大学化学工程系）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本研究通过实验证明α-MnTe中观测到的异常拉曼峰源于表面暴露空气后形成的元素碲，而非本征声子模式，并揭示了氧化机制及其对含碲材料表征的重要影响。
AI中文摘要：
据报道，室温交替磁体α-MnTe的拉曼光谱中含有未归属的峰，位于120(3) cm⁻¹和140(3) cm⁻¹处，而这些峰在该材料的预测声子谱中并不存在。这在交替磁体领域引发了相当大的争论，亟需解决。本工作确定这些峰以及位于90(5) cm⁻¹处与理论预测模式匹配的峰，均为外在来源，源于表面暴露于空气时形成的元素碲。分子束外延生长的薄膜的拉曼光谱表明，这些峰与元素碲的峰非常匹配，在暴露于空气后很快出现，而在AlOₓ封盖的薄膜中则不存在。X射线光电子能谱显示，暴露于空气会在1分钟内破坏Mn-Te键并氧化Mn。横截面扫描透射电子显微镜结合能量色散X射线光谱揭示，氧化导致Mn向外扩散，在埋藏的富Te区域上方形成几纳米厚的氧化层，这可能是异常拉曼峰的原因。此外，没有样品表现出通常归因于MnTe₂的175 cm⁻¹拉曼峰。MnTe中剧烈的表面氧化和相关的元素Te的形成，对任何涉及哪怕最短暂空气暴露的MnTe（以及其他类似的含Te材料）的表面敏感和光学表征都具有重要意义。
英文摘要：
The Raman spectrum of the room-temperature altermagnet $α$-MnTe is reported to contain unassigned peaks at 120(3) cm$^{-1}$ and 140(3) cm$^{-1}$, absent from the predicted phonon spectrum of the material. This has generated considerable debate within the altermagnet community and necessitates urgent resolution. This work establishes that these peaks, together with the 90(5) cm$^{-1}$ peak that matches a theoretically predicted mode, are all extrinsic, originating from elemental tellurium formed during air exposure of the surface. Raman spectra of MBE-grown thin films show that these peaks closely match those of elemental tellurium, emerge soon after air exposure, and are absent in AlO$_x$-capped films. X-ray photoelectron spectroscopy shows that air exposure breaks Mn--Te bonds and oxidizes Mn within a minute. Cross-sectional scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy reveals that the oxidation leads to Mn out-diffusion, forming a few-nanometer-thick oxide layer above a buried, Te-enriched region, likely responsible for the anomalous Raman peaks. Additionally, no sample exhibited the 175 cm$^{-1}$ Raman peak which is commonly attributed to MnTe$_2$. The aggressive surface oxidation and associated elemental Te formation in MnTe have important implications for any surface-sensitive and optical characterization of MnTe (and other similar Te-containing materials) involving even the briefest air exposure.
