Preface

Two-dimensional (2D) materials have attracted a great deal of attention in recent years due to their potential applications in gas/chemical sensors, healthcare monitoring, biomedicine, electronic skin, wearable sensing technology, flat panel displays, optoelectronics, photodetectors, catalysis, electrochemical sensing, bio sensing, water/air purification, batteries, fuel cells and advanced electronic devices. One of the most popular 2D nanomaterials in this era is graphene, which has unique properties such as large specific surface area, high electrical conductivity, excellent electron transfer rate and high mechanical strength. However, it is not only 2D graphene that has been widely applied in a large variety of potential applications but also other 2D materials such as boron nitrides, molybdenum disulfide, black phosphorus and metal oxide nanosheets, all of which open up new opportunities for future devices.

This book focuses on models and theoretical backgrounds, important properties, characterizations and applications of current, popular 2D materials such as graphene, silicon nitride, aluminum nitride, ZnO thin films, phosphorene and molybdenum disulfide. Chapter 1 presents an overview, synthesis methods and applications of popular 2D materials. Chapter 2 focuses on properties and characterizations of graphene, graphite and graphene nanoplatelets via Raman spectroscopy. Chapter 3 provides an insight into the properties of undoped and doped ZnO thin films. Chapter 4 describes structures, kinetics and thermodynamics of 2D silicon nitride and aluminum nitride. Chapter 5 focuses on structure, electronic properties, polarizability and dielectric function of 2D phosphorene based on theoretical approaches via the tight-binding model. Chapter 6 demonstrates synthesis, characterizations, and mechanical and electrical properties of molybdenum disulfide as well as its photovoltaic applications.

We would like to express our deep appreciation to all contributors who are experts in their respective research fields. It should be emphasized that all chapters have been submitted to re-review and revision in order to improve their presentation with several interactions between editors, authors and publisher. We hope this book will be a useful tool and provide inspiration and motivation to interested readers for further developments in the field.

> **Asst. Prof. Dr. Chatchawal Wongchoosuk and Dr. Yotsarayuth Seekaew** Department of Physics, Faculty of Science, Kasetsart University, Thailand

**1**

**Figure 1.**

*"carbon nanotube," and "graphene" on March 18, 2019).*

**Chapter 1**

**1. Overview**

2D Materials

Introductory Chapter:

*Yotsarayuth Seekaew and Chatchawal Wongchoosuk*

Two-dimensional (2D) materials are a class of nanomaterials that have two dimensions (XY plane) outside of the nanometric size range and atomic-scale thicknesses (Z dimension). The first well-known 2D material is graphene consisting of a single layer of carbon atoms arranged in a hexagonal lattice. To compare with 0D material (fullerene) and 1D material (carbon nanotube), the researches related to 2D material (graphene) have grown up quickly over other carbon allotropes as shown in **Figure 1**. Based on Scopus database (search by keyword "graphene" on March 18, 2019), publications on graphene increased from 3772 papers in 2010 to 21,439 papers in 2018. The total number of graphene-related publications is 132,628 documents. However, it is not only 2D graphene that has been widely applied in a large variety of potential applications but also other 2D materials such as tungsten disulfide, molybdenum disulfide, and silicon nitride open up new opportunities for the future devices. In this chapter, synthesis and

applications of these 2D materials have been introduced and presented in brief.

*Number of publications versus publication years based on Scopus database (search by keyword "fullerene,"* 

## **Chapter 1**
