ABSTRACT
2-Dimensional materials (e.g. graphene and its analogs) have triggered worldwide research interest recently due to their fascinating electrical, optical, thermal, and mechanical properties.This talk will discuss the synthesis of large-area, high-quality monolayers of nitrogen- and boron-doped graphene sheets on Cu foils using ambient-pressure chemical vapor deposition (AP-CVD). Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal that the defects in the doped graphene samples arrange in different geometrical configurations exhibiting different electronic properties. Interestingly, these doped layers could be used as efficient molecular sensors and electronic devices.It will also be showed that the physico-chemical properties of these materials vary significantly as the number of layers approach to monolayers. I will review various approaches to synthesize WS2, WSe2, and MoS2 monolayers, using CVD approaches. Depending on the method and substrates,  various morphologies of layered could be obtained and controlled (e.g. triangular, hexagonal, David stars, butterflies, etc.). Intriguingly, these atom-thick 2D clusters exhibit extraordinary room temperature edge photoluminescence (PL) around 25-40 times stronger than the center of the 2D platelets. The structure and composition of these clusters are likely to be the critical parameters explaining this phenomenon. These 2D nanoscale light sources could find application in diverse venues, including flexible/transparent/low-energy optoelectronics.Due to these outstanding PL characteristics of monolayered WS2, MoS2, WSe2 and MoSe2, recent photo-current studies will be reviewed. From the theoretical stand point, I will discuss recent predictions of the effect of alternating individual layers of different metal chalcogenides (e.g. MoS2, WS2, WSe2 and MoSe2) with particular stackings. It is possible to generate direct band gap bi-layers ranging from 0.790 eV to 1.157 eV. Interestingly, in this direct band gap, electrons and holes are physically separated and localized in different layers. I will also review the synthesis of alternating bilayer systems of different metal chalcogenides (e.g. MoS2, WS2, WSe2 and MoSe2) with particular stacking order. I will demonstrate experimentally and theoretically that these hetero-bilayers possess a direct band gap, which is tunable depending on the layer type. Interestingly, in this direct band gap, electrons and holes are physically separated and localized in different layers. We foresee that the alternation of different chalcogenide layers would result in the fabrication of materials with unprecedented optical and physico-chemical properties. Resonant Raman scattering on these systems will also be presented, as well as the synthesis of van der Waals Solids.

报告人简介:
Prof. Mauricio Terrones was born in Mexico City in 1968. He received his PhD degree from University of Sussex (UK) in 1998 with the guidance of Sir Prof. Harold W. Kroto (Nobel Laureate, FRS). He is currently a Professor of Physics, Chemistry and Materials Science & Engineering with tenure at Penn State University (USA), a chair of excellence at Universidad Carlos III de Madrid (Spain) and a Distinguished Professor at Shinshu University (Japan). He is also the Founder Director of the Center for 2-Dimensional and Layered Materials at Penn State. Mauricio is also Associate Editor of Carbon, J. Mater. Res. and Sci. Rep.(Nature Publishing Group).His research now concentrates on the theory, synthesis and characterization of 2-D materials and nanotubes.He has co-authored more than 300 publications in international journals, including Nature, Science, Phys. Rev. Lett., Nano Lett., Nature Nanotechnol., Nature Mater., Nature Communic., Sci. Rep., Small, ACS Nano, etc. His published work has got more than 17,000 citations (His H-index is 69). In 1999, he was awarded the Alexander von Humboldt Fellowship, and carried out research at the Max-Planck Institut für Metallforschung (Stuttgart, Germany). In 2000, he was recipient of the Mexican National Prize for Chemistry. He also received the Javed Husain Prize and the Albert Einstein medal from UNESCO in 2001, for his contributions to Carbon Nanoscience and Nanotechnology. In 2005, he received the TWAS Prize in Engineering Physics for his contributions in the field of carbon-based nanomaterials. This prize is given by the Academy of Sciences of the Developing world, and Mauricio is the youngest scientist ever to receive any TWAS award. He is member of the Mexican Academy of Sciences since 2002. In 2007, Terrones was elected the National Contact Point in Nanotechnology with the European Union. In 2012, he was elected fellow of the American Association for the Advancement of Science (AAAS).