In this work, we synthesize layered two-dimensional (2D) single crystals of CrCl3 by chemical vapor transport method using a three-zone tube furnace and mechanically exfoliated to bilayers under atmospheric conditions. The anomalous photoluminescence (PL) spectra of bulk CrCl3 at 1.75 μm and 2.4μm were observed at varying temperatures for the first time. The temperature-dependent PL spectroscopy from flakes to bilayer CrCl3 represents that the PL linewidth increases proportionally with increasing temperature in the range of 80-300K. Through microscale and nanoscale investigations, we confirm that the broadening of PL spectra of CrCl3 with varying temperatures emphasizes the effect of the exciton-phonon interactions. The narrowing of PL spectra at low temperatures is attributed to a reduced contribution of exciton-phonon coupling. Furthermore, there is a strong dependence of the linewidths broadening on various numbers of layers of 2D CrCl3. The temperature-induced broadening is extensive for the bilayers compared to the 72 layers upon the cooling and heating of 2D CrCl3 layers. In addition, the exciton-phonon coupling strength drastically decreased from the bilayer to the 72 layers, suggesting that the exciton-phonon coupling-induced homogeneous broadening is significant in the bilayer compared to the multilayer. Finally, we explored the effect of exciton-phonon interaction for the first time based on the various layers in the 2D CrCl3 semiconductor.

Abstract i
Acknowledgments ii
List of Tables iii
List of Figure iv
Table of Contents viii
Chapter 1 Introduction 1
1.1 Two Dimensional (2D) Layered Materials 1
1.1.1 Graphene 2
1.1.2 h-BN 3
1.1.3 Transition metal trihalides 3
1.2 Chromium trichloride (CrCl3) 4
1.3 Photoluminescence (PL) 5
1.4 Exciton 7
1.4.1 Free excitons 8
1.4.2 Tightly bound excitons 9
1.4.3 Bound excitons 9
1.5 Motivation 9
Chapter 2 Synthesis and Characterization 11
2.1 Synthesis method - Chemical vapor transport (CVT) 11
2.1.1 Mechanical exfoliation of bulk CrCl3 crystals 13
2.2 Characterization 13
2.2.1 Optical Microscopy 14
2.2.2 Field Emission Scanning Electron Microscopy (FESEM) 15
2.2.3 Energy Dispersive X-ray Spectroscopy (EDS) 16
2.2.4 X-ray photoelectron spectroscopy (XPS) 17
2.2.5 X-Ray Diffraction (XRD) 19
2.2.6 Transmission electron microscopy (TEM). 20
2.2.7 Atomic Force Microscopy (AFM) 22
2.2.8 Photoluminescence (PL) 23
2.2.9 Raman spectroscopy 24
Chapter 3 Results and Discussion 26
3.1 Morphological Surface Studies 26
3.1.1 Optical Microscopy Analysis 26
3.1.2 Field Emission Scanning Electron Microscopy (FESEM) 27
3.2 Chemical Composition Studies 27
3.2.1 Energy Dispersive X-ray Spectroscopy Analysis 27
3.2.2 X-ray Photoelectron Spectroscopy Analysis 28
3.3. Crystallinity Studies 29
3.3.1 X-ray Diffraction analysis 29
3.3.2 Transmission electron microscopy (TEM) analysis 30
3.4 Raman Spectroscopy Analysis 31
3.5 Few layers CrCl3 Optical Microscopy Analysis 32
3.6 Atomic Force Microscopy (AFM) analysis 32
3.7 Photoluminescence Spectroscopy Analysis 35
3.7.1 Photoluminescence of single-crystal CrCl3 at room temperature 35
3.7.2 Temperature-dependent photoluminescence of single-crystal CrCl3 38
Chapter 4 Conclusion 51
Reference 52

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