Graphene-Like Two-Dimensional Materials Mingsheng Xu,* Tao Liang, Minmin Shi, and Hongzheng Chen State Key Laboratory of Silicon Materials, MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China CONTENTS 1. Introduction 3766 2. Hexagonal Boron Nitride Sheets 3767 2.1. Electronic and Magnetic Properties of Pristine h-BN Sheets 3767 2.2. Functionalization of h-BN Sheets 3768 2.3. Synthesis of h-BN Sheets 3769 3. Layered Transition Metal Dichalcogenides 3772 3.1. Electronic and Magnetic Properties of Pristine TMDs 3772 3.2. Strain Effect on the Electronic Properties of TMDs 3773 3.3. Functionalization of TMDs 3774 3.4. Monolayer and Few-Layer TMD FETs 3774 3.5. Synthesis of TMD Sheets 3776 3.6. Analysis of the Existence of Monolayer TMD Sheets 3778 4. Layered Group-IV and Group-III Metal Chalcoge- nides 3779 4.1. Structural and Electronic Properties of Layered Group-IV Metal Chalcogenides 3779 4.2. Synthesis of Layered Group-IV Metal Chal- cogenides 3780 4.3. Structural and Electronic Properties of Layered Group-III Metal Chalcogenides 3781 4.4. Electronic Properties of Single Tetralayer GaSe 3782 4.5. Synthesis of Layered Group-III Metal Chalco- genides 3782 5. Van der Waals Epitaxy of Layered Metal Chalcogenides 3782 6. Silicene and Germanene 3783 6.1. Structural and Electronic Properties of Pristine Silicene and Germanene 3783 6.2. Functionalization of Silicene and Germa- nene 3785 6.3. Synthesis of Silicene Nanosheets 3785 7. Layered Binary Compounds of Group-IV Ele- ments and Group III-V 3788 8. Valley Physics and Spin Effect in Monolayers of 2D Sheets 3788 8.1. Valley Physics in Monolayer TMDs 3788 8.2. Quantum Spin Hall Effect in Silicene and Germanene 3789 9. Concluding Remarks and Outlook 3790 Author Information 3791 Corresponding Author 3791 Notes 3791 Biographies 3791 Acknowledgments 3792 Abbreviations 3792 References 3792 Note Added in Proof 3798 Note Added after ASAP Publication 3798 1. INTRODUCTION Graphene is composed of a single layer of carbon atoms arranged in a two-dimensional (2D) honeycomb lattice. It is a fundamental building block for a range of well-known carbon materials such as three-dimensional (3D) graphite, one- dimensional (1D) carbon nanotubes, and zero-dimensional (0D) fullerene. The identi fication of graphene among mechanically exfoliated graphite sheets and the subsequent discovery of its unusual electronic properties 1 have led to an extraordinary amount of interest from both academia and industry. Many extraordinary properties, such as its 2.3% absorption in the white light spectrum, high surface area, high Young’s modulus, and excellent thermal conductivity, have all been reported. Because of its remarkable properties, 2,3 applications using graphene in a wide range of areas, including high-speed electronic 4 and optical devices, 5 energy generation and storage, 5-7 hybrid materials, 8,9 chemical sensors, 2,11 and even DNA sequencing, 12-14 have all been explored. A variety of proof-of-concept devices have also been demonstrated. 3a,15 However, pristine graphene itself is unlikely to be used for the fabrication of logical circuits operated at room temperature with low standby power dissipation because graphene has no band gap (E g ). The result is a small current on/off ratio in graphene field-effect transistors (FETs). 16 The prerequisite for such applications is the mass production of graphene in a controlled manner because the number of graphene layers as well as the defects in these graphene layers significantly influence the subsequent transport properties. Methods such as mechanical exfoliation, liquid-phase exfoliation, reduction of graphene oxide, chemical vapor deposition (CVD), surface segregation, 17 and molecular beam epitaxy (MBE) 18 have been developed in order to make suitable graphene layers. Despite these efforts, the fine control of the number and structure of graphene sheets over an entire substrate remains a major challenge. 19 Hence the search to optimize the manufacturing process with a view to the realization of distinct properties of graphene layers is ongoing. Another important challenge pertaining to graphene applica- Received: July 1, 2012 Published: January 3, 2013 Review pubs.acs.org/CR © 2013 American Chemical Society 3766 dx.doi.org/10.1021/cr300263a | Chem. Rev. 2013, 113, 3766-3798