光谱特征关联性分析用于研究CVD生长的单层二硫化钨非均匀性机制

Correlative spectroscopic investigations of the mechanisms of inhomogeneity in CVD-grown monolayer WS_(2)

化学气相沉积(CVD)已被证明是生产二维材料(包括二硫化钨(WS_(2)))最有效的方法.然而,CVD生长的WS_(2)单层中存在的应变、掺杂和缺陷的不均匀性会显著影响材料的光学和电子特性,从而影响其器件应用.在本研究中,我们通过CVD方法在蓝宝石衬底上生长了介观尺寸的三角形单层WS_(2),并利用空间分辨的显微拉曼和光致发光(PL)光谱技术系统地表征了单层WS_(2)中的应变、掺杂和非辐射缺陷中心的不均匀性.我们从全域(整个单层WS_(2)三角形)和分区域(如顶点、边缘、中心)两个维度对其拉曼和PL光谱的相关参数(即峰值位置、强度和半峰宽)随位置的变化进行了相关性分析,发现单层WS_(2)三角形的不同区域往往表现出明显不同的应变、掺杂和缺陷状态.这项研究揭示并解释了单层WS_(2)应变、掺杂和缺陷的不均匀性.此外,我们发现当介观尺寸的三角形结构扩展到连续薄膜时,不均匀性大大降低.我们的工作表明,对光谱特征的相关性分析并辅以对物理机制的了解有助于全面理解材料生长带来的不均匀性,并为优化二维材料的生长过程和器件加工提供指导.

Chemical vapor deposition(CVD)has been proved to be the most useful method to produce two-dimensional(2D)materials,including tungsten disulfide(WS_(2)).However,the existence of inhomogeneity of strain,doping,and defects in the CVD-grown WS_(2) monolayers may significantly influence the optical and electronic properties of the materials,thus affecting their device applications.In this work,we systematically characterized the inhomogeneity of strain,doping,and nonradiative defect centers in mesoscopicsize,triangular-shape monolayer WS_(2) grown by CVD on sapphire substrate by using spatially resolved micro-Raman and photoluminescence(PL)spectroscopy.We performed correlative analyses on the variations of the pertinent spectral parameters(i.e.,peak position,intensity,and full width at half maximum)of Raman and PL signatures in two physical scales:(1)the complete-data-set level,including the data of the whole sample,and(2)the sub-data-set level for individual special regions(e.g.,apexes,edges,center)that exhibit distinctly different strain,doping,and defect states.This study reveals and explains the inhomogeneous strain,doping,and defects across the WS_(2) monolayer.Additionally,we find the inhomogeneity substantially diminishes when a mesoscopic-size triangle structure expands into a continuous film.Our work demonstrates that the correlative analyses,supported with physics insights,can offer comprehensive understanding on the underlying mechanisms of the inhomogeneity and guidance for optimizing the growth process and device processing of 2D materials.