Direct and scalable deposition of atomically thin low-noise MoS2 membranes on apertures

Published in final edited form as: ACS Nano. 2015 July 28; 9(7): 7352–7359. doi:10.1021/acsnano.5b02369.Molybdenum disulfide (MoS2) flakes can grow beyond the edge of an underlying substrate into a planar freestanding crystal. When the substrate edge is in the form of an aperture, reagent-limited nucleation followed by edge growth facilitate direct and selective growth of freestanding MoS2 membranes. We have found conditions under which MoS2 grows preferentially across micrometer-scale prefabricated solid-state apertures in silicon nitride membranes, resulting in sealed membranes that are one to a few atomic layers thick. We have investigated the structure and purity of our membranes by a combination of atomic-resolution transmission electron microscopy, elemental analysis, Raman spectroscopy, photoluminescence spectroscopy, and low-noise ion-current recordings through nanopores fabricated in such membranes. Finally, we demonstrate the utility of fabricated ultrathin nanopores in such membranes for single-stranded DNA translocation detection.R21 HG006873 - NHGRI NIH HHS; R21-HG006873 - NHGRI NIH HHSPublished versio

Effect of Layer-Stacking on the Electronic Structure of Graphene Nanoribbons

The evolution of electronic structure of graphene nanoribbons (GNRs) as a function of the number of layers stacked together is investigated using \textit{ab initio} density functional theory (DFT) including interlayer van der Waals interactions. Multilayer armchair GNRs (AGNRs), similar to single-layer AGNRs, exhibit three classes of band gaps depending on their width. In zigzag GNRs (ZGNRs), the geometry relaxation resulting from interlayer interactions plays a crucial role in determining the magnetic polarization and the band structure. The antiferromagnetic (AF) interlayer coupling is more stable compared to the ferromagnetic (FM) interlayer coupling. ZGNRs with the AF in-layer and AF interlayer coupling have a finite band gap while ZGNRs with the FM in-layer and AF interlayer coupling do not have a band gap. The ground state of the bi-layer ZGNR is non-magnetic with a small but finite band gap. The magnetic ordering is less stable in multilayer ZGNRs compared to single-layer ZGNRs. The quasipartcle GW corrections are smaller for bilayer GNRs compared to single-layer GNRs because of the reduced Coulomb effects in bilayer GNRs compared to single-layer GNRs.Comment: 10 pages, 5 figure

Onset of long-range diffusion and exponent of 1/f \alpha noise in metal films with electromigration damage

Investigations of low-frequency conductance fluctuations have been done on silver films which have been made to undergo electromigration damage. The system shows a clear increase in noise magnitude after electromigration damage. The noise spectral power shows a distinct presence of 1/f^3^/^2 component arising out of long-range diffusion. The temperature dependence of noise (150 K<T<350 K) shows a marked deviation from the Dutta-Horn type behavior with the 1/f^3^/^2 term showing a strong dominance at higher temperatures. We propose that the increase of noise in metal films after electromigration damage arise predominantly from this spectral component