Abstract:Graphene and hexagonal boron nitride (h-BN) have similar crystal structures with a lattice constant difference of only 2%. However, graphene is a zero bandgap semiconductor with remarkable high carrier mobility at room temperature, whilst an atomically thin layer of h-BN is a dielectric with a wide bandgap of ~5.9 eV. Additionally, single layered molybdenum disulfide with a direct bandgap is a promising two-dimensional material that goes beyond graphene for next generation nanoelectronics. More importantly, if precise two-dimensional domains of graphene, h-BN and MoS2 atomic layers can be seamlessly stitched together, in-plane heterostructures with interesting electronic and other applications could potentially be created. Here, we show that planar graphene/h-BN heterostructures can be formed by growing graphene in lithographically-patterned h-BN atomic layers . Our approach can create periodic arrangements of domains with size that ranging from tens of nanometers to millimeters. The resulting graphene/h-BN atomic layers can be peeled off from their growth substrate and transferred to various platforms including flexible substrate. Also in this talk, we report the controlled vapor phase synthesis of molybdenum disulfide atomic layers and elucidate a fundamental mechanism for the nucleation, growth, and grain boundary formation in its crystalline monolayers . The atomic structure and morphology of the grains and their boundaries in the polycrystalline molybdenum disulfide atomic layers are examined and first-principles calculations are applied to investigate their energy landscape. The electrical properties of the atomic layers are examined and the role of grain boundaries is evaluated.
 Z. Liu, L. Ma, G. Shi, W. Zhou, Y. Gong, S. Lei, X. Yang, J. Zhang, J. Yu, K. P. Hackenberg, A. Babakhani, J. Idrobo, R. Vajtai, J. Lou and P. M. Ajayan: Nature Nanotechnology, Vol. 8 (2013), p. 119.
 S. Najmaei, Z. Liu, W. Zhou, X. Zou, G. Shi, S. Lei, B.I. Yakobson, J. Idrobo, P. M. Ajayan and J. Lou: Nature Materials, Vol. 12 (2013), p. 754.
Brief Biography: Jun Lou obtained B.E. and M.S. degrees in Materials Science and Engineering from Tsinghua University and Ohio State University, respectively, and his Ph.D. degree from the Department of Mechanical and Aerospace Engineering and Princeton Materials Institute at Princeton University. After a brief postdoc at Brown University he joined the Department of Mechanical Engineering and Materials Science at Rice University, and currently is an associate professor in the same department. He is a recipient of the US Air Force Office of Scientific Research Young Investigator Award and the ORAU Ralph E. Powe Junior Faculty Enhancement Award. His research interests include nanomaterial synthesis, nanomechanical characterization and nanodevice fabrication for energy, environmental and biomedical applications.