arXiv subjects

Swastik Kar

Publications and source records attributed to Swastik Kar.

22 records · Page 2Linked to original sources

arXiv2015

Direct and Scalable Chemical Vapor Deposition of Ultrathin Low-Noise MoS2 Membranes on Apertures

We show that atomically thin molybdenum disulfide (MoS2) crystals can grow without any underlying substrates into free-standing atomically-thin layers, maintaining their planar 2D form. Using this property, we present a new mechanism for 2D crystal synthesis, i.e. reagent-limited nucleation near an aperture edge followed by reactions that allow crystal growth into the free-space of the aperture. Such an approach enables us, for the first time, the direct and selective growth of freestanding membranes of atomically thin MoS2 layers across micrometer-scale pre-fabricated solid-state apertures in SiNx membranes. Under optimal conditions, MoS2 grows preferentially across apertures, resulting in sealed membranes that are one to a few atomic layers thick. Since our method involves free-space growth and is devoid of either substrates or transfer, it is conceivably the most contamination-free method for obtaining 2D crystals reported so far. The membrane quality was investigated using atomic-resolution transmission electron microscopy, Raman spectroscopy, photoluminescence spectroscopy, and low-noise ion-current recordings through nanopores fabricated in such membranes.

cond-mat.mtrl-sci↗

arXiv2011

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.

cond-mat.mtrl-sci↗

arXiv2004

A set-up for measurement of low frequency conductance fluctuation (noise) using digital signal processing techniques

We describe a set up for measurements of low frequency (1 mHz < f < 20 Hz) conductance fluctuations in a solid conductor. The set-up uses a five probe a.c. measurement technique and extensive digital signal processing to reach a noise floor down to $S_{v}(f) \leq 10^{-20}$ V$^{2}$Hz$^{-1}$. The set up also allows measurement of noise using an a.c. in presence of a superimposed direct current. This feature is desirable in studies of electromigration damage or in systems that show non-linear conductivity. In addition, we describe a scheme which allows us to obtain the probability density function of the conductance fluctuation after subtracting the extraneous noise contributions (background) from the observed noise. The set-up has been used for conductance fluctuation measurement in the temperature range 1.5 K < T < 500 K in the presence of magnetic fields. We present some representative data obtained by this system.

cond-mat.other↗

arXiv2002

Observation of non-gaussian conductance fluctuations at low temperatures in Si:P(B) at the metal-insulator transition

We report investigations of conductance fluctuations (noise) in doped silicon at low temperatures (T$<20$K) as it is tuned through the metal-insulator transition (MIT). The scaled magnitude of noise, $γ_H$, increases with decrease in T following an approximate power law $γ_H \sim T^{-β}$. At low T, $γ_H$ diverges as $n/n_c$ crosses 1 from the metallic side. We find that the distribution function and second spectrum of the fluctuations show strong non-gaussian behavior below 20K as $n/n_c$ decreases through 1. In particular, the observed distribution function which is gaussian for $n/n_c >> 1$, develops a log-normal tail as the transition is approached from the metallic side and eventually it dominates in the critical region.

cond-mat.dis-nn↗