An Update from Flatland.

For more than a decade after the discovery of the unique physical properties of graphene, two-dimensional (2D) materials have been attracting the attention of the nanoscale research community and beyond. This continuing interest is fueled by frequent reports of the discovery of new 2D materials, with silicene, germanene, and phosphorene already being intensely researched. More than 20 carbides and nitrides of transition metals have also been added to the materials flatland in the past 5 years, and 2D GaN grown under the cover of graphene has recently been reported. However, 2D boron (borophene) has attracted the most attention this year (Figure 1), where the experimental synthesis followed theoretical predictions. This case has thus demonstrated the ability of modeling to guide the synthesis of new materials, which is one of the primary goals of the Materials Genome Initiative. Borophene has been shown experimentally and theoretically to possess metallic properties, potentially offering the thinnest metal sheets for applications such as interconnects, electromagnetic shielding, and transparent conductors, where 2D metals can outperform all other materials. Realization of these applications in addition to fundamental studies of other charge transport phenomena such as superconductivity will require the development of borophene transfer and processing methods that minimize chemical and structural degradation. Two-dimensional materials offer additional opportunities for self-assembly and integration compared to zero-dimensional or one-dimensional structures, such as nanocrystals or nanotubes. Specifically, 2D heterostructures are attracting increasing attention because they enable researchers to combine the properties of individual 2D sheets and create layered assemblies with unique hybrid properties, including property gradients. The race is now on to find practical applications afforded by these 2D systems. Recent conferences on 2D materials have offered an excellent overview of ongoing efforts in the field and show that the 2D world stretches far beyond graphene. Even at Graphene 2016 in Genoa, Italy, about half of the talks were dedicated to materials other than graphene. In recent years, there have been growing numbers of 2D materials “beyond graphene” conferences, reflecting the widespread interest in this field. One such recent event was the International Conference on Electronic Materials (IUMRS-ICEM 2016) held in Singapore in early July, 2016. At a symposium on 2D materials and devices beyond graphene, many speakers spoke about their recent work on 2D materials including monolayer transition metal dichalcogenides (TMDs), phosphorene, and borophene, and their potential applications in electronics or optoelectronics. Mark Hersam (Northwestern University) presented his collaborative work with Nathan Guisinger at Argonne National Laboratory on the synthesis of borophenes, and Lan Chen (Chinese Academy of Sciences) showed that two types of 2D boron sheets can be grown epitaxially on Ag(111) substrates. Wei Chen (National University of Singapore) talked about interface engineering of 2D black phosphorus and its photoreactivity to oxygen and water. Lain-Jong Li (KAUST) presented impressive electron microscopy images on chemical vapor deposition (CVD) grown vertical and lateral heterostructures, which was the theme of several other speakers. Electronic screening effects between organic monolayers and 2D TMDs were also discussed.