Length- and Thickness-Dependent Optical Response of Liquid-Exfoliated Transition Metal Dichalcogenides
Length- and Thickness-Dependent Optical Response of Liquid-Exfoliated Transition Metal Dichalcogenides
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DOI：
10.1021/acs.chemmater.9b02905
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发表时间：
2019-12-24
影响因子：
8.6
通讯作者：
Backes, Claudia
中科院分区：
文献类型：
--
作者：
Synnatschke, Kevin;Cieslik, Patrick Arthur;Backes, Claudia
由于维度降低，二维材料表现出有趣的光学特性和强烈的光与物质相互作用。特别是，VI族过渡金属二硫属化物已得到广泛研究，并已论证光学应用的原理验证。迄今为止，大多数研究都集中在单个单层或双层微机械剥离样品上，这些样品通常显示出薄片之间的显着差异。在这项工作中，我们研究了四种 VI 族 TMD 材料的尺寸依赖性光学特性：WS2、MoS2、WSe2 和 MoSe2，每种材料均由悬浮在液体环境中的纳米片集合组成。样品通过液相剥离产生，并使用级联离心选择尺寸，并通过统计原子力显微镜量化尺寸和层数分布。横向尺寸和层数的差异反映在消光和吸收光谱的系统变化中，我们利用这些变化来建立定量光谱指标，以方便测量四种材料中每种材料的纳米片尺寸。对最低能量共振（称为 A 激子）进行了更详细的分析。在所有情况下，随着层数的增加，观察到指数红移。我们的实验数据以第一原理计算为基础，表明偏移的幅度取决于中心金属原子（W、Mo）的分子质量，而峰值从单层转移到块体的速率取决于半导体的带隙。
Because of their reduced dimensionality, two-dimensional materials show intriguing optical properties and strong light-matter interaction. In particular, group VI transition metal dichalcogenides have been extensively studied and proof-of-principle optical applications have been demonstrated. Most studies to date focus on individual mono- or bilayered micromechanically exfoliated samples, which often display significant variations between flakes. In this work, we study size-dependent optical properties of four group VI TMD materials: WS2, MoS2, WSe2, and MoSe2, each consisting of ensembles of nanosheets suspended in the liquid environment. Samples were produced by liquid-phase exfoliation and size-selected using cascade centrifugation with size and layer number distributions quantified by statistical atomic force microscopy. Differences in lateral size and layer number are reflected in systematic changes in the optical extinction and absorbance spectra, which we exploit to establish quantitative spectroscopic metrics to facilitate the measurement of nanosheet dimensions for each of the four materials. The lowest energy resonance, referred to as A-exciton, is analyzed in more detail. In all cases, an exponential red shift with increasing layer number is observed. Our experimental data, backed up with first-principle calculations, reveal that the magnitude of the shift is dependent on the molecular mass of the central metal atom (W, Mo), while the rate at which the peak shifts from monolayer to bulk depends on the band gap of the semiconductor.