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Intricate Resonant Raman Response in Anisotropic ReS2
Nano Letters ( IF 9.6 ) Pub Date : 2017-09-12 00:00:00 , DOI: 10.1021/acs.nanolett.7b01463
Amber McCreary 1, 2 , Jeffrey R. Simpson 2, 3 , Yuanxi Wang , Daniel Rhodes 1, 4 , Kazunori Fujisawa , Luis Balicas 4 , Madan Dubey 1 , Vincent H. Crespi , Mauricio Terrones 5 , Angela R. Hight Walker 2
Affiliation  

The strong in-plane anisotropy of rhenium disulfide (ReS2) offers an additional physical parameter that can be tuned for advanced applications such as logic circuits, thin-film polarizers, and polarization-sensitive photodetectors. ReS2 also presents advantages for optoelectronics, as it is both a direct-gap semiconductor for few-layer thicknesses (unlike MoS2 or WS2) and stable in air (unlike black phosphorus). Raman spectroscopy is one of the most powerful characterization techniques to nondestructively and sensitively probe the fundamental photophysics of a 2D material. Here, we perform a thorough study of the resonant Raman response of the 18 first-order phonons in ReS2 at various layer thicknesses and crystal orientations. Remarkably, we discover that, as opposed to a general increase in intensity of all of the Raman modes at excitonic transitions, each of the 18 modes behave differently relative to each other as a function of laser excitation, layer thickness, and orientation in a manner that highlights the importance of electron–phonon coupling in ReS2. In addition, we correct an unrecognized error in the calculation of the optical interference enhancement of the Raman signal of transition metal dichalcogenides on SiO2/Si substrates that has propagated through various reports. For ReS2, this correction is critical to properly assessing the resonant Raman behavior. We also implemented a perturbation approach to calculate frequency-dependent Raman intensities based on first-principles and demonstrate that, despite the neglect of excitonic effects, useful trends in the Raman intensities of monolayer and bulk ReS2 at different laser energies can be accurately captured. Finally, the phonon dispersion calculated from first-principles is used to address the possible origins of unexplained peaks observed in the Raman spectra, such as infrared-active modes, defects, and second-order processes.

中文翻译:

各向异性ReS 2中的复杂共振拉曼响应

二硫化rh(ReS 2)的强面内各向异性提供了额外的物理参数,可以针对逻辑电路,薄膜偏振器和偏振敏感光电探测器等高级应用进行调整。ReS 2对于光电器件也具有优势,因为它既是厚度很少的直接间隙半导体(不同于MoS 2或WS 2),又是在空气中稳定的(不同于黑磷)。拉曼光谱法是无损和灵敏地探测2D材料的基本光物理特性的最强大的表征技术之一。在这里,我们对ReS 2中18个一阶声子的共振拉曼响应进行了深入研究。在不同的层厚度和晶体取向。值得注意的是,我们发现,与激子跃迁中所有拉曼模的强度普遍增加相反,这18个模中的每一个相对于彼此的行为都不同,它们是激光激发,层厚和取向的函数,其变化方式如下:强调了电子-声子耦合在ReS 2中的重要性。此外,我们还通过各种报道纠正了SiO 2 / Si衬底上过渡金属二卤化物在拉曼信号上的拉曼信号光学干扰增强的计算中出现的无法识别的误差。对于ReS 2,此校正对于正确评估共振拉曼行为至关重要。我们还实现了一种基于第一性原理的扰动方法来计算频率相关的拉曼强度,并证明,尽管忽略了激子效应,但可以准确地捕获在不同激光能量下单层和整体ReS 2的拉曼强度的有用趋势。最后,从第一性原理计算出的声子色散用于解决在拉曼光谱中观察到的无法解释的峰的可能起源,例如红外活性模式,缺陷和二阶过程。
更新日期:2017-09-12
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