Swapan K. Pati

Bio: Swapan K. Pati is an academic researcher from Jawaharlal Nehru Centre for Advanced Scientific Research. The author has contributed to research in topics: Density functional theory & Graphene. The author has an hindex of 48, co-authored 359 publications receiving 10276 citations. Previous affiliations of Swapan K. Pati include Indian Institute of Science & Udai Pratap Autonomous College.

MoS2 and WS2 Analogues of Graphene

Abstract: Inorganic sheets: Graphene-like MoS2 and WS2 were prepared by three different chemical methods. Examination by microscopic techniques revealed that they consist of one or a few layers (see depicted TEM image of WS2 layers), and an atomic-resolution TEM image showed that layered MoS2 has a hexagonal arrangement of Mo and S atoms (see inset).

Novel properties of graphene nanoribbons: a review

Abstract: Low-dimensional materials are of great interest to both theorists and experimentalists, owing to their novel electronic properties which arise mainly because of a host of quantum confinement effects. Recent experimental findings of graphene have provided a new platform to explore the interesting electronic properties in strictly two dimensions. In this feature article, we review the novel properties of an interesting class of quasi one dimensional materials, known as graphene nanoribbons, which can be obtained by finite termination of graphene sheet with smooth edges. Recent experimental sophistications provide various physical and chemical ways to materialize these systems. Two different edge geometries, namely zigzag and armchair, arising from the finite termination of graphene, control the electronic properties of graphene nanoribbons. Here we attempt to give an overview of their interesting electronic, magnetic, optical, conduction properties and explore possible ways of enhancing their device applicability by a number of ways including external perturbations, doping and chemical modifications.

Intrinsic half-metallicity in modified graphene nanoribbons.

Abstract: We perform first-principles calculations based on density functional theory to study quasi-one-dimensional edge-passivated (with hydrogen) zigzag graphene nanoribbons of various widths with chemical dopants, boron and nitrogen, keeping the whole system isoelectronic. The gradual increase in doping concentration takes the system finally to zigzag boron nitride nanoribbons (ZBNNRs). Our study reveals that for all doping concentrations the systems stabilize in antiferromagnetic ground states. Doping concentrations and dopant positions regulate the electronic structure of the nanoribbons, exhibiting both semiconducting and half-metallic behaviors as a response to the external electric field. Interestingly, our results show that ZBNNRs with a terminating polyacene unit exhibit half-metallicity irrespective of the ribbon width as well as applied electric field, opening a huge possibility in spintronics device applications.

Uptake of H2 and CO2 by Graphene

Abstract: Graphene samples prepared by the exfoliation of graphitic oxide and conversion of nanodiamond exhibit good hydrogen uptake at 1 atm, 77 K, the uptake going up to 1.7 wt %. The hydrogen uptake varies linearly with the surface area, and the extrapolated value of hydrogen uptake by single-layer graphene works out to be just above 3 wt %. The H2 uptake at 100 atm and 298 K is found to be 3 wt % or more, suggesting thereby the single-layer graphene would exhibit much higher uptakes. Equally interestingly, the graphene samples prepared by us show high uptake of CO2, the value reaching up to 35 wt % at 1 atm and 195 K. The first-principles calculations show that hydrogen molecules sit alternately in parallel and perpendicular orientation on the six-membered rings of the graphene. Up to 7.7 wt % of hydrogen can be accommodated on single-layered graphene. CO2 molecules sit alternatively in a parallel fashion on the rings, giving use to a maximum uptake of 37.93 wt % in single-layer graphene. The presence of more t...

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

Abstract: Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets

Abstract: Ultrathin two-dimensional nanosheets of layered transition metal dichalcogenides (TMDs) are fundamentally and technologically intriguing. In contrast to the graphene sheet, they are chemically versatile. Mono- or few-layered TMDs - obtained either through exfoliation of bulk materials or bottom-up syntheses - are direct-gap semiconductors whose bandgap energy, as well as carrier type (n- or p-type), varies between compounds depending on their composition, structure and dimensionality. In this Review, we describe how the tunable electronic structure of TMDs makes them attractive for a variety of applications. They have been investigated as chemically active electrocatalysts for hydrogen evolution and hydrosulfurization, as well as electrically active materials in opto-electronics. Their morphologies and properties are also useful for energy storage applications such as electrodes for Li-ion batteries and supercapacitors.

Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials

Abstract: If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS2, WS2, MoSe2, MoTe2, TaSe2, NbSe2, NiTe2, BN, and Bi2Te3 can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS2 and MoS2 effectively reinforce polymers, whereas WS2/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.

Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene

Abstract: Graphene’s success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in...