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Screening, Defects, and Dangling Bonds Induced Optical Damage Threshold in Monolayer MoS2

机译：单层MoS2中的筛选，缺陷和悬空键引起的光学损伤阈值

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摘要

An optoelectronic device based on the TMDs should be versatile in its applications and be able to endure high optical intensities. In this thesis, I have shown the experimentally-measured damage threshold intensity range of 75 to 100 kW/cm2 of a monolayer MoS2 at room temperature. The corresponding photo-excited carrier density, for the CW photo-excitation, is ∼1.6 x 1010 cm(-2). While the goal has been to find the damage threshold intensity, certain patterns that have emerged from the optical response of the monolayer MoS2 in the vicinity of the optical damage threshold needed to be thoroughly examined. I have quantified the experimental results and have attempted to qualitatively understand the underlying physics. The many-body effects play a crucial role in all these processes such that there is a complicated correlation. While explaining the physics through experimental results, I have attempted to disentangle the screening-related effects and damage and/or defect states related effects from the experimental dependencies, viz., optical power, laser irradiance time, and beam position.;The measurements have been done by collecting the photoluminescence (PL) signals. The parameters such as excitonic peak amplitude, area, FWHM, and the central wavelength have been extracted from the curve fitting of the PL spectrums. In the optical power dependence measurement, I have compared the optical responses of the material by employing two different methods of measurement, viz., the Direct and Indirect PL measurement methods. In both these methods of measurement, I increase the excitation intensity step-wise but the method of collecting the PL signal differs. We will see that this slight difference in methodology provides us with a strikingly different optical response. In the laser irradiance time dependence measurement, I have exposed the sample continuously for 62 minutes in total. With this, the charge accumulation and resultant changes in the optical response of the material have been demonstrated. We will see that my experiments concretely debunk the claim of laser-induced atomic healing of defects. In the beam position dependent measurement, I deliberately create damage and optically scan the sample through pristine, within the damage, and at the damaged edge by collecting the PL signal from these locations. The characteristic enhancement in the PL signal is evidently found to be a real feature.;From these measurements, salient features have been consistently observed such that these can be marked as the signatures of the damage incurrence. Signatures such as 2x to 4x times the increment in the peak amplitude, a similar increment in the area, changes in PL efficiency, 30% to 50% shrinkage in the FWHM, and 4 nm to 15 nm of a spectral blue shift in the A exciton peak in the PL spectrum. In this thesis, I will further demonstrate that all these reversible and irreversible changes are from the contributions of the screening effects such as Bandgap Renormalization (BGR) and Coulomb screening, defects and dangling bonds induced damage threshold in the monolayer MoS2.
机译：基于TMD的光电子器件在其应用中应该是通用的，并且能够承受高光强度。在本文中，我展示了在室温下实验测量的单层MoS2的损伤阈值强度范围为75至100 kW / cm2。对于CW光激发，相应的光激发载流子密度约为1.6 x 1010 cm（-2）。尽管目标是找到损伤阈值强度，但是从单层MoS2在光学损伤阈值附近的光学响应中出现的某些图案需要进行彻底检查。我已经量化了实验结果，并试图定性地理解了基础物理学。多体效应在所有这些过程中都起着至关重要的作用，因此存在复杂的相关性。在通过实验结果解释物理学的同时，我试图从实验依赖性，即光功率，激光辐照时间和光束位置中解开与筛选有关的效应以及与损伤和/或缺陷状态有关的效应。通过收集光致发光（PL）信号完成。已从PL光谱的曲线拟合中提取了激子峰幅度，面积，FWHM和中心波长等参数。在光功率相关性测量中，我通过采用两种不同的测量方法（即直接和间接PL测量方法）比较了材料的光学响应。在这两种测量方法中，我都会逐步增加激发强度，但是收集PL信号的方法却有所不同。我们将看到，这种方法上的细微差别为我们提供了截然不同的光学响应。在激光辐照时间依赖性测量中，我总共连续暴露了样品62分钟。由此，已经证明了电荷累积和材料的光学响应的​​结果变化。我们将看到，我的实验具体揭露了激光诱导的原子缺陷修复的说法。在依赖于光束位置的测量中，我有意造成损坏，并通过从这些位置收集PL信号在损坏范围内以及损坏边缘处通过原始光扫描样品。显然，PL信号的特征增强是一个真实特征。从这些测量结果中，可以始终观察到显着特征，从而可以将这些显着特征标记为损害发生的标志。诸如峰值幅度增量的2倍至4倍，面积的类似增量，PL效率的变化，FWHM的30％至50％的收缩以及A光谱蓝移的4 nm至15 nm之类的签名PL谱中的激子峰。在本文中，我将进一步证明所有这些可逆和不可逆的变化均来自筛选效应的贡献，如带隙重正化（BGR）和库仑筛选，缺陷和悬空键在单层MoS2中引起的损伤阈值。

著录项

  • 作者

    Dave, Arpit.;

  • 作者单位

    The University of Arizona.;

  • 授予单位 The University of Arizona.;
  • 学科 Optics.;Quantum physics.;Condensed matter physics.
  • 学位 M.S.
  • 年度 2018
  • 页码 70 p.
  • 总页数 70
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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