ACS Nano Page 2 of 64 1 2 3 Recent Advances in Two-Dimensional Materials Beyond Graphene 4 5 Ganesh R. BhimanapatiϮ, Zhong Linϙ, Vincent Meunier Ҧ, Yeonwoong Jung €, Judy Cha Ӂ, Saptarshi Das 6 Г, Di Xiao Ф, Youngwoo Son£, Michael S. Strano£, Valentino R. Cooper Ѡ, Liangbo Liang Ҧ, Steven G. 7 LouieϪ, Emilie Ringeζ, Wu ZhouѠ, Bobby G. SumpterѠ, Humberto TerronesҦ, Fengnian XiaӁ, Yeliang 8 WangЋ, Jun Zhuϙ, Deji Akinwande‡, Nasim AlemϮ, Jon A. Schuller¥, Raymond E. Schaak¶, Mauricio 9 TerronesϮ,ϙ,¶, Joshua A RobinsonϮ,* 10 11 Ϯ - Department of Materials Science and Engineering, Center for Two-Dimensional and Layered Materials, 12 Pennsylvania State University, University Park, PA 16802, United States. ϙ - Department of Physics, Center for 13 Two-Dimensional and Layered Materials, Pennsylvania State University, University Park, PA 16802, United States. 14 €- Nanoscience Technology Center, Department of Materials Science and Engineering, University of Central 15 Florida, Orlando, Florida 32826, United States, Ӂ –Department of Mechanical Engineering and Material Science, 16 Yale school of Engineering and Applied Sciences, New Haven, CT 06520, United States. Ҧ- Department of 17 Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, United States 18 and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, 19 United States. Г - Birck Nanotechnology Center & Department of ECE, Purdue University, West Lafayette, Indiana 20 47907, United States. Ф - Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, United States. 21 £ - Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, United 22 States. Ѡ - Center for Nanophase Materials Sciences and Computer Science & Mathematics Division, Oak Ridge 23 National Laboratory, Oak Ridge, Tennessee 37831, United States. Ϫ - Department of Physics, University of California at Berkeley, Berkeley, California 94720, United States and Lawrence Berkeley National Lab, Berkeley, 24 25 California 94720, United States. Ћ- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, 26 Chinese Academy of Sciences, Beijing 100190, China, ζ - Department of Materials Science & Nano Engineering, 27 Rice University, Houston 77005, United States. ‡- Microelectronics Research Centre, The University of Texas at 28 Austin, Texas 78758, United States. ¥-Electrical and Computer Engineering Department, University of California 29 Santa Barbara, Santa Barbara, California 93106, United States ¶ - Department of Chemistry and Materials Research 30 Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, United States. 31 32 Abstract 33 The isolation of graphene in 2004 from graphite was a defining moment for the “birth” of a field: Two- 34 dimensional (2D) materials. In recent years, there has been a rapidly increasing number of papers 35 focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because 36 of the new properties and applications that emerge upon 2D confinement. Here we review significant 37 38 recent advances and important new developments in 2D materials “beyond graphene”. We provide 39 insight into the theoretical modeling and understanding of the van der Waals (vdW) forces that hold 40 together the 2D layers in bulk solids, as well as their excitonic properties and growth morphologies. 41 Additionally, we highlight recent breakthroughs in TMD synthesis and characterization and discuss the 42 newest families of 2D materials, including monoelement 2D materials (i.e., silicene, phosphorene, etc.) 43 and transition metal carbide- and carbon nitride-based MXenes. We then discuss the doping and 44 functionalization of 2D materials beyond graphene that enable device applications, followed by advances 45 in electronic, optoelectronic, and magnetic devices and theory. Finally, we provide perspectives on the 46 future of 2D materials beyond graphene. 47 48 Keywords: two-dimensional materials, graphene, heterostructures, transition metal dichalcogenide, 49 phospherene, silicene, germanene, stanene, van der Waals epitaxy, van der Waals solid. 50 51 52 53 54 55 56 57 * 58 [email protected] 59 60 ACS Paragon Plus Environment Page 3 of 64 ACS Nano 1 2 3 Vocabulary: 4 5 (NH4)2MoS4- Ammonia tetra thiomolybdate LED- Light emitting diodes 6 2D – two-dimensional Li- lithium 7 3D- three dimensional LSPR- Localized surface plasmon resonance 8 ADF- annular dark field LSPR- localized surface plasmon resonance 9 Ag- silver MBE- Molecular beam epitaxy 10 AHM, (NH4)6Mo7O24·4H2O- Ammonium Mn- manganese 11 heptamolybdate Mo- Molybdenum 12 13 ALD- Atomic layer deposition MoCl5- Molybdenum chloride 14 ARPES- Angle resolved photoemission MOCVD- Metal organic chemical vapor 15 spectroscopy deposition 16 Au- gold MoO3- Molybdenum (VI) oxide 17 AuCl3- gold chloride MoS2- Molybdenum disulfide 18 BP- Black phosphorous MoSe2- Molybdenum diselenide 19 BV- Benxyl viologen Na- sodium 20 C- Carbon NADH- Nicotinamide adenine dinucleotide 21 CF3- carbon tetrafluoride radical NbS2- niobium disulfide 22 CH3- methyl radical NH2- ammonia radical 23 CL- cathodoluminescence NO2- Nitrogen dioxide 24 Cl- chlorine atom O - Oxygen 25 2 26 Cl2- chlorine OLED- organic light emitting diode 27 Co- Cobalt OTS – Octadecyltrichlorosilane 28 CrI3- chromium iodide PDMS- polydimethyl siloxane 29 CrSiTe3- chromium silicon telluride PEI- Polyethyleneimine 30 Cs2CO3- cesium carbonate PL- Photoluminescence 31 CVD- chemical vapor deposition PMMA- poly methyl methacrylate 32 DCE- 1,2- dichloroethane PTAS- Perylene-3,4,9,10- tetracarboxylic acid 33 DF- density functional tetrapotassium salt 34 DFPT- density functional perturbation theory p-TSA- p-toluene sulfonic acid 35 DFT- Density functional theory PVA- poly vinyl alcohol 36 DMC- Diffusion quantum Monte Carlo QC- Quantum chemical 37 DNA- deoxy ribonucleic acid QFEG- Quasi- free-standing epitaxial graphene 38 39 EELS- Electron energy loss spectroscopy QSHE- Quantum spin hall effect 40 EG- Epitaxial graphene S- Sulfur 41 FET- Field effect transistor SAMs- self-assembled monolayers 42 GaAlAs- Gallium aluminum arsenide SBs- Schottky barriers 43 GaAs- Gallium Arsenide Sc- scandium 44 GaN- Gallium nitride Se- Selenium 45 GaSe- Gallium selenide SERS- Surface enhanced raman spectroscopy 46 Ge- Germanium Si- Silicon 47 GW-BSE- GW plus Bethe Salpeter equation SiC- Silicon carbide 48 H2O- water SiO2- Silicon dioxide 49 H S- Hydrogen sulfide Sn- tin 50 2 hBN- Hexagonal boron nitride SnS - tun sulfide 51 2 52 HF- hydrogen fluoride SnSe2- Tin diselenide 53 HfSe2- Halfnium selenide SO- spin orbit 54 HRTEM- High resolution Transmission electron SPR- surface plasmon resonance 55 microscopy STEM- scanning transmission electron 56 In2Se3- Indium selenide microscopy 57 K- potassium STM- Scanning tunneling microscopy 58 59 60 ACS Paragon Plus Environment ACS Nano Page 4 of 64 1 2 3 STMDs- semiconducting transition metal TOF-SIMS- time of flight- secondary ion mass 4 dichalcogenides spectroscopy 5 STS- Scanning tunneling spectroscopy UHV- ultra high vacuum 6 7 TaSe2- Tantalum diselenide vdW – van der Waals 8 TCNQ- 7,7,8,8- tetracyanoquinodimethane W- tungsten 9 TEM- Transmission electron microscopy WO3 – Tungsten (VI) oxide 10 TFT- thin film transistors WS2- Tungsten disulfide 11 TMDs – Transition metal dichalcogenides WSe2- Tungsten diselenide 12 13 14 15 Layered materials have existed for eons,1 and have been studied scientifically for more than 150 years.2 16 However, only recently3 have we begun to realize the true potential of these systems for advanced 17 technological applications. Each layered material, when thinned to its physical limits, exhibits novel 18 properties different from its bulk counterpart. Therefore, at the physical limit these materials are referred 19 20 to as two-dimensional (2D) materials. The most highly studied 2D material is graphene because of its 21 exceptional electronic, optoelectronic, electrochemical and biomedical applications. Beyond graphene, 22 there is a very wide spectrum of 2D electronic materials that range from insulators to semiconductors to 23 metals and even to superconductors. 2D materials research initially focused on graphene following the 3 24 seminal paper by Novoselev and Geim, but it was also demonstrated very early on that other 2D 25 materials also possess exciting properties.4 Following graphene, 2D hexagonal boron nitride (hBN) was 26 theoretically predicted to induce a bandgap in graphene when graphene was deposited onto it.5 This led to 27 a significant increase in hBN experimental research, and ultimately to an understanding that hBN may be 28 an ideal substrate for graphene electronics.6 Rapidly following graphene and hBN, research on 29 semiconducting 2D layers provided evidence that the band structure of a subset of the 2D materials family 30 changes drastically as they are thinned to monolayer thickness.7 Device fabrication further ignited the 31 interest of many in the electronics community.8 These novel semiconducting 2D materials, known as 32 33 transition-metal dichalcogenides (TMDs), are now a primary focus of many researchers, as clearly 34 evidenced by the publication record devoted to such materials (Figure 1). There are many layered 35 materials that go beyond TMDs, including monochalcogenides (GaSe, etc.), monoelemental 2D 36 semiconductors (silicene, phosphorene, germanene), and MXenes (Figure 1). Finally, the true potential of 37 these