Optical Properties Of Two Dimemsional Van Der Waals Crystals

Van der Waals (vdW) materials are layered structures bonded by the weak vdW force. As such, stable single atomic layers can be isolated either by mechanical exfoliation or chemical methods as chemical vapor deposition. Atomically thin vdW materials have emerged as new types of two-dimensional (2D) systems with unique electronic and optical properties that are distinct from that of their bulk counterparts. Studies of this new class of material are not only interesting fundamentally; they can potentially also lead to applications in next-generation electronics and optoelectronics devices. In this thesis, we investigate two prototypes of 2D vdW materials, graphene (a semimetal) and semiconducting transition metal dichalcogenides (TMD) based on optical spectroscopy. Electro-magnetic radiation ranging from the far-infrared (or terahertz (THz)) to the visible has been utilized to investigate two questions: (1) the excitonic effects in Mo/W dichalcogenides; and, (2) the free carrier response in graphene. For the first topic, exciton series in monolayer WSe2 and the effect of electric field on the excitons is studied. A exciton series of WSe2 is observed by a complimentary measurement of linear absorption and two-photon photoluminescense excitation (2PPLE). Strong exciton binding energy ($\sim$ 0.4 eV) and non-Rydberg series are observed arising from 2D screening of Coulomb interactions. Using field-effect transistor structures we apply electrostatic doping and/or perpendicular electric field to WSe2 monolayer through the gates. Trion peak is observed under doping, which further splits under high electric fields. This phenomenon can be explained by Rashba spin-orbit interaction induced spin sub-bands hybridization. For the second topic, the free carrier response in monolayer graphene is investigated using the Fourier transform infrared (FTIR) spectroscopy in steady state conditions and the optical pump-THz probe spectroscopy under non-equilibrium conditions. We observe the Drude response under both conditions. For the steady states study, we find the Drude scattering rate strongly dependent on the doping density, revealing different scattering mechanisms. Under low power photo excitation, we observe that mobilities remain in relatively high values and carrier multiplication is achievable.

2D Materials for Photonic and Optoelectronic Applications introduces readers to two-dimensional materials and their properties (optical, electronic, spin and plasmonic), various methods of synthesis, and possible applications, with a strong focus on novel findings and technological challenges. The two-dimensional materials reviewed include hexagonal boron nitride, silicene, germanene, topological insulators, transition metal dichalcogenides, black phosphorous and other novel materials. This book will be ideal for students and researchers in materials science, photonics, electronics, nanotechnology and condensed matter physics and chemistry, providing background for both junior investigators and timely reviews for seasoned researchers. Provides an in-depth look at boron nitride, silicene, germanene, topological insulators, transition metal dichalcogenides, and more Reviews key applications for photonics and optoelectronics, including photodetectors, optical signal processing, light-emitting diodes and photovoltaics Addresses key technological challenges for the realization of optoelectronic applications and comments on future solutions

Learn about the most recent advances in 2D materials with this comprehensive and accessible text. Providing all the necessary materials science and physics background, leading experts discuss the fundamental properties of a wide range of 2D materials, and their potential applications in electronic, optoelectronic and photonic devices. Several important classes of materials are covered, from more established ones such as graphene, hexagonal boron nitride, and transition metal dichalcogenides, to new and emerging materials such as black phosphorus, silicene, and germanene. Readers will gain an in-depth understanding of the electronic structure and optical, thermal, mechanical, vibrational, spin and plasmonic properties of each material, as well as the different techniques that can be used for their synthesis. Presenting a unified perspective on 2D materials, this is an excellent resource for graduate students, researchers and practitioners working in nanotechnology, nanoelectronics, nanophotonics, condensed matter physics, and chemistry.

Ultrafast photonics has become an interdisciplinary topic of high international research interest because of the spectacular development of compact and efficient lasers producing optical pulses with durations in the femtosecond time domain. Present day long-haul telecommunications systems are almost entirely based on the transmission of short burst

The advent of graphene and, more recently, two-dimensional materials has opened new perspectives in electronics, optoelectronics, energy harvesting, and sensing applications. This book, based on a Special Issue published in Nanomaterials – MDPI covers experimental, simulation, and theoretical research on 2D materials and their van der Waals heterojunctions. The emphasis is the physical properties and the applications of 2D materials in state-of-the-art sensors and electronic or optoelectronic devices.

2D Materials for Nanophotonics presents a detailed overview of the applications of 2D materials for nanophotonics, covering the photonic properties of a range of 2D materials including graphene, 2D phosphorene and MXenes, and discussing applications in lighting and energy storage. This comprehensive reference is ideal for readers seeking a detailed and critical analysis of how 2D materials are being used for a range of photonic and optical applications. Outlines the major photonic properties in a variety of 2D materials Demonstrates major applications in lighting and energy storage Explores the challenges of using 2D materials in photonics

This thesis provides the first comprehensive theoretical overview of the electronic and optical properties of two dimensional (2D) Indium Selenide: atomically thin films of InSe ranging from monolayers to few layers in thickness. The thesis shows how the electronic propertes of 2D InSe vary significantly with film thickness, changing from a weakly indirect semiconductor for the monolayer to a direct gap material in the bulk form, with a strong band gap variation with film thickness predicted and recently observed in optical experiments. The proposed theory is based on a specially designed hybrid k.p tight-binding model approach (HkpTB), which uses an intralayer k.p Hamiltonian to describe the InSe monolayer, and tight-binding-like interlayer hopping. Electronic and optical absorption spectra are determined, and a detailed description of subbands of electrons in few-layer films and the influence of spin-orbit coupling is provided. The author shows that the principal optical excitations of InSe films with the thickness from 1 to 15 layers broadly cover the visible spectrum, with the possibility of extending optical functionality into the infrared and THz range using intersubband transitions.

The investigation on novel optical materials with unprecedented optical properties is of paramount importance for the development of advanced applications in many fields having a strong impact on our everyday lives such as biomedicine, food and agriculture security, optical communication and information technology, etc. Moreover, the interaction of light with matter in the past decades has allowed the quick growth of new disciplines such as biophotonics, covering all aspects of this interaction with biological materials; nanophotonics, investigating the optical behavior of nanostructures; opto-mechanics, going from optical manipulation of small objects to optical control of micro- and nano-robots.This book comprises timely contributions from active research groups covering several classes of materials and processes including nano-structured plasmonic and photonic materials, 2-D materials, photo-polymers, liquid crystals, photo-sensitive and opto-thermal, and other specially engineered materials.Novel Optical Materials will serve as a useful reference for researchers, engineers, and optical and materials scientists in both industry and academia. It is also an excellent supplement and reference for graduate courses in materials science, physics, and optical engineering.

This book represents a significant advance in our understanding of the synthesis and properties of two-dimensional (2D) materials. The author’s work breaks new ground in the understanding of a number of 2D crystals, including atomically thin transition metal dichalcogenides, graphene, and their heterostructures, that are technologically important to next-generation electronics. In addition to critical new results on the direct growth of 2D heterostructures, it also details growth mechanisms, surface science, and device applications of “epi-grade” 2D semiconductors, which are essential to low-power electronics, as well as for extending Moore’s law. Most importantly, it provides an effective alternative to mechanically exfoliate 2D layers for practical applications.