arXiv subjects

Arkamita Bandyopadhyay

Publications and source records attributed to Arkamita Bandyopadhyay.

4 recordsLinked to original sources

arXiv2021

Direct Opto-Electronic Imaging of 2D Semiconductor - 3D Metal Buried Interfaces

The semiconductor-metal junction is one of the most critical factors for high performance electronic devices. In two-dimensional (2D) semiconductor devices, minimizing the voltage drop at this junction is particularly challenging and important. Despite numerous studies concerning contact resistance in 2D semiconductors, the exact nature of the buried interface under a three-dimensional (3D) metal remains unclear. Herein, we report the direct measurement of electrical and optical responses of 2D semiconductor-metal buried interfaces using a recently developed metal-assisted transfer technique to expose the buried interface which is then directly investigated using scanning probe techniques. We characterize the spatially varying electronic and optical properties of this buried interface with < 20 nm resolution. To be specific, potential, conductance and photoluminescence at the buried metal/MoS$_2$ interface are correlated as a function of a variety of metal deposition conditions as well as the type of metal contacts. We observe that direct evaporation of Au on MoS$_2$ induces a large strain of ~5% in the MoS$_2$ which, coupled with charge transfer, leads to degenerate doping of the MoS$_2$ underneath the contact. These factors lead to improvement of contact resistance to record values of 138 kohm-um, as measured using local conductance probes. This approach was adopted to characterize MoS$_2$-In/Au alloy interfaces, demonstrating contact resistance as low as 63 kohm-um. Our results highlight that the MoS$_2$/Metal interface is sensitive to device fabrication methods, and provides a universal strategy to characterize buried contact interfaces involving 2D semiconductors.

cond-mat.mes-hall↗

arXiv2014

Nitrogen Doped Graphene Quantum Dots as Possible Substrates to Stabilize Planar Conformer of Au 20 Over its Tetrahedral Conformer: A Systematic DFT Study

Utilizing the strengths of nitrogen doped graphene quantum dot (N-GQD) as a substrate, here in, we have shown that one can stabilize the catalytically more active planar Au 20 (P-Au 20 ) compared to the thermodynamically more stable tetrahedral structure (T-Au 20 ) on an N-GQD. Clearly, this simple route avoids the usage of traditional transition metal oxide substrates which have been suggested and used for stabilizing the planar structure for a long time. Considering the experimental success in the synthesis of N-GQDs and in the stabilization of Au nanoparticles on N-doped graphene, we expect our proposed method to stabilize planar structure will be realized experimentally and will be useful for industrial level applications.

cond-mat.mtrl-sci↗

arXiv2013

Structural Stability, Electronic, Magnetic and Optical Properties of Rectangular Graphene and Boron-Nitride Quantum Dots: Effects of Size, Substitution and Electric Field

Using density functional theory calculations, we have examined the structural stability, electronic, magnetic and optical properties of rectangular shaped quantum dots (QDs) of graphene (G), Boron Nitride (BN) and their hybrids. Different hybrid QDs have been considered by substituting a GQD (BNQD) with BN-pairs (carbon atoms) at different positions. Several parameters like size, amount of substitution etc. have been varied for all these QDs (GQDs, BNQDs, hybrid-QDs) to monitor the corresponding changes in their properties. Among the considered parameters, we find that substitution can act as a powerful tool to attain interesting properties with these QDs, for example, broad range of absorption (~2000 nm) in the near infrared (NIR) region, spin-polarized HOMO-LUMO gaps without the application of any external-bias etc., which are highly required in the preparation of opto-electronic, electronic/spintronic devices etc. Explanations have been given in details by varying different factors, like, changing the position and amount of substitution, application of external electric-field etc., to ensure the reliability of our results.

cond-mat.mtrl-sci↗

arXiv2013

Tuning the Electronic and Optical properties of Graphene and Boron-Nitride Quantum Dots through Molecular Charge-transfer Interactions

Spin-polarized first-principles calculations have been performed to tune the electronic and optical properties of graphene (G) and boron-nitride (BN) quantum dots (QDs) through molecular charge-transfer using Tetracyanoquinodimethane (TCNQ) and Tetrathiafulvalene (TTF) as dopants. From our calculations, we find that the nature of interaction between the dopants and QDs is similar to the interaction between the dopants and their two-dimensional counter parts of the QDs, namely, graphene and hexagonal boron-nitride sheets. Based on the values of formation energy and distance between QDs and dopants, we find that both the dopants are physisorbed on the QDs. Also, we find that GQDs interact strongly with the dopants compared to the BNQDS. Interestingly, though the dopants are physisorbed on QDs, their interaction lead to a decrement in the HOMO-LUMO gap of QDs by more than half of their original value. We have also observed a spin-polarized HOMO-LUMO gap in certain QD-dopant complexes. Mulliken population analysis, Density of states (DOS), projected DOS (pDOS) plots and optical conductivity calculations have been performed to support and understand the reasons behind the above mentioned findings.

cond-mat.mtrl-sci↗