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BB5.04 - Pseudopotential-Based Study of Electron Transport in Low-Dimensionality Nanostructures 
April 23, 2014   11:00am - 11:30am

Scaling electronic devices to (and beyond) the 10 nm gate-length will likely require intrinsically two-dimensional (2D) materials. This stems from the necessity of confining electrons within the thickness requires by conventional scaling laws, avoiding the intolerable gate leakage currents that result from the shift of the ground-state subband induced by quantum confinement. Pseudopotentials- empirical and ab initio - are now being more commonly used to study not only the atomic and electronic structure of these 2D materials (, graphene, silicene, transition-metal dichalcogenides -TMDs), but also their electronic transport properties. Here we shall give a bird’s-eye view of the use of density functional theory (DFT) to calibrate empirical pseudopotentials (EPs), of EPs to calculate efficiently the electronic structure of low-dimensionality systems, the most significant electronic scattering processes, and to study semiclassical electronic transport. Low-dimensionality systems considered here include thin semiconductor layers, graphene, graphene- and silicane-nanoribbons, silicon nanowires, TMDs and single-layer Sn (“stannanane”). Regarding graphene, the high electron mobility measured in suspended graphene sheets (~200,000 cm/Vs) is the result of a relatively weak carrier-phonon coupling and the strong dielectric-screening property. However, in practical applications graphene is likely to be supported by an insulating substrate, top-gated, and possibly used in the form of narrow armchair-edge nanoribbons (AGNRs) in order to open a gap. We will discuss several scattering processes that may affect electron transport in these situations. First, we shall present results of the calculation of the intrinsic electron-phonon scattering rates in suspended graphene and AGNRs using empirical pseudopotentials and the rigid-ion approximation or DFT calculated deformation potentials, resulting in an electron mobility consistent with the experimental results. We shall then discuss the role of interfacial coupled substrate optical-phonon/graphene-plasmons (i.e., remote phonons) in depressing the electron mobility in graphene supported by SiO, HfO, AlO, and h-BN. We shall also review the strong effect of line edge roughness (LER) on electron transport and localization in narrow AGNRs resulting from the `claromatic’ width dependence of the band-gap of the sp2-coordinated AGNRs. This will lead us to consider sp3-coordinate ribbons (silicane) and Si nanowires as possible alternative structures -- less affected by LER scattering -- of interest in nano-electronics application. Finally, we shall discuss the effect of high-κ gate dielectrics to boost the mobility of MoS single layers and DFT calculations of the properties of halogen-terminated stannanane as a 2D topological insulator.Work supported by NRI/SWAN2.0

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Keynote Address
Panel Discussion - Different Approaches to Commercializing Materials Research
Business Challenges to Starting a Materials-Based Company
Fred Kavli Distinguished Lectureship in Nanoscience
Application of In-situ X-ray Absorption, Emission and Powder Diffraction Studies in Nanomaterials Research - From the Design of an In-situ Experiment to Data Analysis