Screening effect of ultrathin gold films on excitons in monolayer WS2
Screening effect of ultrathin gold films on excitons in monolayer WS2
复制标题
超薄金膜对单层WS2激子的屏蔽作用
DOI：
10.1007/s11468-018-00894-6
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发表时间：
2019
期刊：
影响因子：
3
通讯作者：
Yanpeng Cao
中科院分区：
文献类型：
--
作者：
Guangyi Jia;Yan Zhou;Yongzheng Niu;Shubin Huang;Yanpeng Cao
筛选在确定二维半导体中激子的能级和结合能方面起着重要作用。然而，沉积在金属薄膜上的二维材料的光电性能通常被认为不受屏蔽效应的影响。本文采用传递矩阵法推导了单层WS2在不同厚度超薄金膜上的反射率对比光谱，并研究了超薄金膜对单层WS2中激子的屏蔽作用。我们发现，随着金膜厚度的增加，由于屏蔽效应的增强，基态的激子结合能逐渐降低。然而，这可能是由于自由电子散射对金膜介电常数的影响：基态和第一激发态的激子共振能量随着金膜厚度的增加而逐渐增加，这与之前报道的激子能级随二维材料筛选介质厚度的变化趋势不同。结果表明，随着金膜厚度从0.0 nm增加到40 nm，激子的电子带隙仅呈现小于4 meV的变化范围。这些发现有助于理解金薄膜的筛选效应在多大程度上影响二维材料中的激子。
Screening plays an important role in determining the energy levels and binding energies of excitons in two-dimensional (2D) semiconductors. However, the photoelectric properties of 2D materials deposited upon metal films are often assumed to remain unaffected by the screening effect. Herein, we derive the reflectance contrast spectra of monolayer WS2 on different thicknesses of ultrathin gold films by using the transfer matrix method, and investigate the screening effect of ultrathin gold films on excitons in monolayer WS2. We show that the exciton binding energy of the ground state gradually decreases as the gold film thickness increases due to the enhanced screening effect. Nevertheless, it may be due to the impact of free-electron scattering on the permittivities of gold films: exciton resonance energies of the ground state and the first excited state gradually increase as the gold film thickness increases, which are different from previously reported variation trend of exciton energy levels with the thickness of screening media of 2D materials. As a consequence, the electronic bandgap of the exciton only presents a small variation range of less than 4 meV with thickening of the gold film from 0.0 to 40 nm. These findings shed light on understanding to what extent the screening effect of gold films affects the excitons in 2D materials.