Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene

Abstract

Graphene's success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in field-effect transistors, spin- and valley-tronics, thermoelectrics, and topological insulators, among many other applications.

Ultrahigh, Ultrafast, and Self‐Powered Visible‐Near‐Infrared Optical Position‐Sensitive Detector Based on a CVD‐Prepared Vertically Standing Few‐Layer MoS2/Si Heterojunction

“…An ultrathin polygon flat layer, instead of vertically oriented MoS 2 nanosheets, was observed at the beginning of growth, and the film exhibits two characteristic MoS 2 Raman peaks ($E_{2\mathrm{g}}^1$ mode at 385.9 cm −1 and $A_{1\mathrm{g}}^{}$ mode at 405.7 cm −1 ) with a peak frequency difference of 19.8 cm −1 (as shown in Figure S2a, Supporting Information), which suggests that the MoS 2 film is nearly a monolayer with a very uniform layer thickness 4, 38. With increasing growth time, the area increases and the MoS 2 nanosheets become thicker gradually.…”

“…Since the discovery of graphene in 2004, 2D materials have attracted significant interest due to their unique electronic and optical properties and numerous potential applications in optoelectronic devices 1, 2, 3, 4. Among various 2D materials, MoS 2 has shown excellent properties in optoelectronic applications due to its suitable band gap value,5, 6 relatively high carrier mobility,2, 7 high light absorbance,3, 8 and, more importantly, good stability,9, 10 and brilliant optoelectronic properties 1, 7, 11, 12.…”

Helicity-Resolved Raman Scattering of MoS2, MoSe2, WS2, and WSe2 Atomic Layers

“…[2][3][4][5] A prominent example is the semiconducting transition metal dichalcogenides (TMDCs) that exhibit rich physical phenomena, including indirect to direct bandgap transition, 6, 7 large exciton and trion binding energy, [8][9][10][11] strong photoluminescence and electroluminescence, 7, 12-14 superior transistor performance with large on-off ratio [15][16][17] and reasonably high mobility, 5, 18, 19 and perhaps most strikingly, the capability to address the valley degree of freedom. [20][21][22][23][24] Manipulation of valley polarized carriers excited by circularly polarized light has led to recent observation of the valley Hall effect 25 that opens up potential for applications in 'valleytronics' envisioned before in graphene.…”

High Electrical Conductivity in Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2, a Semiconducting Metal–Organic Graphene Analogue

“…[1][2][3] The most prominent example is graphene, an atomically thin organic 2D material with inplane π-conjugation. 4 Although graphene exhibits exceptional charge mobility and mechanical stability, its use in semiconductor-based devices is limited by its zero bandgap.…”