What makes something a crystal? A transparent and glittery gemstone? Not necessarily, in the microscopic world. When all of its atoms are arranged in accordance with specific mathematical rules, we call the material a single crystal. As the natural world has its unique symmetry, e.g., snowflakes or honeycombs, the atomic world of crystals is designed by its own rules of structure and symmetry. This material structure has a profound effect on its physical properties as well. Specifically, single crystals play an important role in inducing a material's intrinsic properties to its full extent. Faced with the coming end of the miniaturization process that the silicon-based integrated circuit has allowed up to this point, major efforts have been dedicated to find a single crystalline replacement for silicon.
In the search for the transistor of the future, two-dimensional (2-D) materials, especially graphene, have been the subject of intense research around the world. Being thin and flexible as a result of being only a single layer of atoms, this 2-D version of carbon even features unprecedented electricity and heat conductivity. However, the last decade's efforts for graphene transistors have been held up by physical restraints—graphene allows no control over electricity flow due to the lack of band gap. So then, what about other 2-D materials? A number of interesting 2-D materials have been reported to have similar or even superior properties. Still, the lack of understanding in creating ideal experimental conditions for large-area 2-D materials has limited their maximum size to just a few millimeters.
Scientists at the Center for Multidimensional Carbon Material (CMCM) within the Institute for Basic Science (IBS) have presented a novel approach to synthesize on a large scale, silicon-wafer-size, single crystalline 2-D materials. Prof. Feng Ding and Ms. Leining Zhang in collaboration with their colleagues at Peking University, China and other institutions have found a substrate with a lower order of symmetry than that of a 2-D material that facilitates the synthesis of single crystalline 2-D materials in a large area. "It was critical to find the right balance of rotational symmetries between a substrate and a 2-D material," notes Prof. Feng Ding, one of corresponding authors of this study. The researchers successfully synthesized hBN single crystals of 10 x 10 cm2 by using a new substrate: a surface near Cu(110) that has a lower symmetry of (1) than hBN with (3).
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