Monday, March 27, 2017
Hello all! Welcome to Episode 30 of #MondayMaterials. It’s a little different today as we’re meeting with recent graduate Ella Row to discuss her industrial placement. Ella was introduced to me by former #MondayMaterials participant Patsy Perry. Patsy was particularly excited by this student’s progression because Ella, after a year...
2D electronics: From graphene to transition metal dichalcogenides to layered and tubular group V allotropes
Monday, June 05, 2017
If graphene had a band gap, it would probably be the optimum 2D system for electronics applications. Layered transition metal dichalcogenides (TMDs) with a robust intrinsic band gap appear as the next-best alternative. Only after a long search, however, optimum strategies have been devised to make low-resistance, ohmic contacts to TMDs . In the meantime, a new class of 2D semiconductors has been rapidly gaining attention, namely layered black phosphorus and related phosphorene monolayers . These 2D systems display a tunable, direct fundamental band gap and thus are ideal candidates for optoelectronics applications. Recent Quantum Monte Carlo (QMC) calculations show that the inter-layer bonding, while weak, is not well described by dispersive van der Waals (vdW) interactions . As seen in Fig. 1, QMC results differ qualitatively from vdW-enhanced DFT functionals and the common designation of similar systems as “van der Waals solids” is strictly incorrect. Also other group V systems including monolayers of AsxP1-x , IV-VI compounds such as SiS  with the same average valence, and related 2D phosphorus carbide  share the same nonplanarity of their structure with phosphorene. These systems share another similarity with phosphorene, namely the dependence of the fundamental band gap on the number of layers and in-layer strain. Surprisingly, the story of group V semiconductors does not end with layered 2D systems. A previously unknown 1D structure of coiled phosphorus represents the most stable P allotrope to date. The predicted structure  has recently been synthesized and contained inside carbon nanotubes . In all cases, predictive ab initio calculations provide a useful guidance to experimental studies. * Partly supported by the NSF/AFOSR EFRI 2-DARE grant number #EFMA-1433459. References:  Jie Guan, Hsun-Jen Chuang, Zhixian Zhou, and David Tománek, ACS Nano 11 (2017).  H. Liu et al. ACS Nano 8, 4033 (2014).  L. Shulenburger, A.D. Baczewski, Z. Zhu, J. Guan, and D. Tománek, Nano Lett. 15, 8170 (2015).  Zhen Zhu, Jie Guan, and David Tománek, Nano Lett. 15, 6042 (2015).  Zhen Zhu, Jie Guan, Dan Liu, and David Tománek, ACS Nano 9, 8284 (2015).  Jie Guan, Dan Liu, Zhen Zhu, and David Tománek, Nano Lett. 16, 3247 (2016).  Dan Liu, Jie Guan, Jingwei Jiang, and David Tománek, Nano Lett. 16, 7865 (2016).  Jinying Zhang et al. Angew. Chem. Int. Ed. 56, 1850-1854 (2017) Biography Professor David Tomanek studied Physics in Switzerland and received his Ph.D. from the Free University in Berlin. While holding a position as Assistant Professor of Physics, he pioneered theoretical research in Nanostructures at the AT&T Bell Laboratories and the University of California at Berkeley. He established the field of Computational Nanotechnology at Michigan State University, where he holds a position as Full Professor of Physics. His scientific expertise lies in the development and application of numerical techniques for structural, electronic and optical properties of surfaces, low-dimensional systems and nanostructures.