Department Of Physics

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Alloyed monolayers of Cu, Ag, Au and Pt in hexagonal phase: A comprehensive first principles study
(Elsevier Ltd, 2018) Kapoor, Pooja; Kumar, Arun; Sharma, Munish; Kumar, Jagdish; Kumar, Ashok; Ahluwalia, P. K.
We present density functional theory (DFT) based comprehensive study of two-dimensional (2D) alloyed monolayers of noble metals (AgCu, AgPt, AgAu, AuCu, AuPt and CuPt) in hexagonal phase within numerical atomic orbitals and plane wave basis sets methods. The monolayers considered exhibit positive phonon frequencies suggesting them to be dynamically stable. The Pt containing alloyed monolayers have superior structural stability (binding energy and tensile strength) and exhibit metallic and ferromagnetic character amongst all the alloyed monolayers. Interestingly, alloying of Au monolayer with Cu and Ag show semiconducting behavior whereas alloyed AgCu monolayer posseses Dirac-cone like features at high symmetry points. These distinct features in electronic structures of alloyed 2D monolayers have been captured in STM like set up. An anisotropic behavior has been observed in dielectric spectra for all the considered structures. Tunneling characteristics show NDR region for Pt containing alloyed monolayers. The considered alloyed monolayers may potentially be useful as a building blocks for the applications in nano- and opto-electronics. ? 2017 Elsevier B.V.
Armchair and zigzag nanoribbons of gold and silver: A DFT study
(American Institute of Physics Inc., 2018) Kapoor, Pooja; Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.
This paper presents the results from a DFT-based computational study of structural and electronic properties of zigzag and armchair edge shaped nanoribbons of gold and silver in hexagonal phase. The cohesive energy of the considered nanoribbons are found to be more than the corresponding 2D counterpart, thereby, suggesting Au and Ag nanoribbons to be more stable in 1D as compared to 2D. All nanoribbons are found to be metallic with a modulation in quantum ballistic conductance with length and edge type of the nanoribbon. Au nanoribbons are found to have higher conductance than Ag nanoribbon. There is increase in conductance with increase in length of nanoribbon. ? 2018 Author(s).
Electron transport and thermoelectric performance of defected monolayer MoS2
(Elsevier, 2019) Sharm, Munish a; Kumar, Ashok; Ahluwalia, P. K.
Electronic and thermoelectric properties of a two-dimensional MoS2 monolayer containing atomic defects are investigated using density functional theory. All the atomic defects have been found to exhibit endothermic nature. Electronic structure of MoS2 shows tuneability of band gap with the atomic defects. The MoS2 vacancy in pristine monolayer makes it magnetic and narrow band gap semiconductor. The spin-polarized character of the monolayer with defects is clearly captured by the tunneling current calculated in the STM-like setup. A relatively low thermal conductivity has been observed in monolayers with defects as compared to pristine form resulting in enhanced room temperature figure of merit as high as 6.24 and 1.30 respectively. The results presented open up a new window for the use of monolayer MoS2 in electronic devices, thermal management and thermoelectric devices
Electronic properties and STM images of vacancy clusters and chains in functionalized silicene and germanene
(Elsevier B.V., 2017) Jamdagni, Pooja; Kumar, Ashok; Sharma, Munish; Thakur, Anil; Ahluwalia, P. K.
Electronic properties and STM topographical images of X (=F, H, O) functionalized silicene and germanene have been investigated by introducing various kind of vacancy clusters and chain patterns in monolayers within density functional theory (DFT) framework. The relative ease of formation of vacancy clusters and chain patterns is found to be energetically most favorable in hydrogenated silicene and germanene. F- and H-functionalized silicene and germanene are direct bandgap semiconducting with bandgap ranging between 0.1?1.9?eV, while O-functionalized monolayers are metallic in nature. By introducing various vacancy clusters and chain patterns in both silicene and germanene, the electronic and magnetic properties get modified in significant manner e.g. F- and H-functionalized silicene and germanene with hexagonal and rectangle vacancy clusters are non-magnetic semiconductors with modified bandgap values while pentagonal and triangle vacancy clusters induce metallicity and magnetic character in monolayers; hexagonal vacancy chain patterns induce direct-to-indirect gap transition while zigzag vacancy chain patterns retain direct bandgap nature of monolayers. Calculated STM topographical images show distinctly different characteristics for various type of vacancy clusters and chain patterns which may be used as electronic fingerprints to identify various vacancy patterns in silicene and germanene created during the process of functionalization. ? 2016 Elsevier B.V.
Electronic properties of ZnPSe3-MoS2 Van der Waals heterostructure
(American Institute of Physics Inc., 2018) Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.
We present a comparative study of electronic properties of ZnPSe3-MoS2 heterostructure using GGA-PBE functional and DFT-D2 method within the framework of density functional theory (DFT). Electronic band structure for the considered heterostructure shows a direct band gap semiconducting character. A decrease in band gap is observed with the heterostructuring as compared to their constituent pristine monolayers. The alignment of valance band maxima and conduction band minima on different layers in heterostructure indicate the physical separation of charge carriers. A work function of 5.31 eV has been calculated for ZnPSe3-MoS2 heterostructure. These results provide a physical basis for the potential applications of these ZnPSe3-MoS2 heterostructure in optoelectronic devices. ? 2018 Author(s).
Electronic, Mechanical, and Dielectric Properties of Two-Dimensional Atomic Layers of Noble Metals
(Springer New York LLC, 2017) Kapoor, Pooja; Kumar, Jagdish; Kumar, Arun; Kumar, Ashok; Ahluwalia, P. K.
We present density functional theory-based electronic, mechanical, and dielectric properties of monolayers and bilayers of noble metals (Au, Ag, Cu, and Pt) taken with graphene-like hexagonal structure. The Au, Ag, and Pt bilayers stabilize in AA-stacked configuration, while the Cu bilayer favors the AB stacking pattern. The quantum ballistic conductance of the noble-metal mono- and bilayers is remarkably increased compared with their bulk counterparts. Among the studied systems, the tensile strength is found to be highest for the Pt monolayer and bilayer. The noble metals in mono- and bilayer form show distinctly different electron energy loss spectra and reflectance spectra due to the quantum confinement effect on going from bulk to the monolayer limit. Such tunability of the electronic and dielectric properties of noble metals by reducing the degrees of freedom of electrons offers promise for their use in nanoelectronics and optoelectronics applications. ? 2016, The Minerals, Metals & Materials Society.
Energetics and Electronic Properties of Pt Wires of Different Topologies on Monolayer MoSe 2
(AIP Publishing, 2016) Jamdagni, Pooja; Kumar, Ashok; Thakur, Anil; Pandey, Ravindra; Ahluwalia, P. K.
The energetics and electronic properties of different of Pt wires including linear, zigzag and ladder structures on MoSe2 have been investigated in the framework of The predicted order of stability of Pt wire on MoSe2 is found to be: linear > ladder > zigzag. Pt wires induce states near the of MoSe2 that results into metallic characteristics of Pt-wire/MoSe2 assembled system. signifies most of the contribution from Pt atoms near the Fermi energy of assembled wire/MoSe2 system. These findings are expected to be important for the of based on MoSe2 layers for flexible nanoelectronics.
First principles study of electronic and thermoelectric performance of Li intercalated MoSe 2 nanotubes
(American Institute of Physics Inc., 2017) Sharma, Munish; Kumar, Ashok; Pandey, Rabindra; Ahluwalia, P. K.
We present a comparative study of pristine and Li intercalated MoSe 2 nanotube of armchair (6, 6) and zigzag (10, 0) chirality within the framework of density functional theory (DFT). Pristine nanotube is found to have band gap which vanishes upon Li intercalation. Additionally, Li intercalation results in reduction of room temperature ZT e for armchair MoSe 2 nanotube and enhancement in ZT e for intercalated zigzag MoSe 2 nanotube as compared to respective pristine nanotubes. Our results suggest that Li intercalation leads to a relatively high Seeback coefficient which may enhance the thermoelectric performance of zigzag MoSe 2 nanotube.
Interactions of Gas Molecules with Monolayer MoSe 2 : A First Principle Study
(AIP Publishing, 2016) Sharma, Munish; Jamdagni, Pooja; Kumar, Ashok; Ahluwalia, P. K.
We present a first principle study of interaction of toxic gas molecules (NO, NO2 and SO2) with MoSe2. The predicted order of sensitivity of gas molecule is NO2 > SO2 > NO. strongly influence the electronic behaviour of MoSe2 by inducing in the vicinity of Fermi energy. NO and SO2 is found to induce p-type effect while to metallic transitions occur on NO2 Our findings may guide the experimentalist for sensor based on MoSe2
Optical fingerprints and electron transport properties of DNA bases adsorbed on monolayer MoS 2
(Royal Society of Chemistry, 2016) Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.
Electronic, optical and transport properties of DNA nucleobase adsorbed on monolayer MoS2 has been investigated using density functional theory. A significant polarization in MoS2 has been observed upon DNA nucleobase adsorption. The nucleobase origin of the modulation in the electronic properties is clearly captured in the simulated STM measurements. The electronic transport through conjugate systems allows the clear distinction of nucleobases from one another. The modulation in electron energy loss spectra and transport properties of pristine MoS2 has been observed on nucleobase adsorption which could serve as a fingerprint for realization of next generation DNA sequencing devices. We believe that these results also bring out the possibility of fabrication of MoS2 based biosensors for selective detection of DNA bases in real long-chain DNA molecules.
Stability, structural and electronic properties of benzene molecule adsorbed on free standing Au layer
(American Institute of Physics Inc., 2016) Katoch, Neha; Kapoor, Pooja; Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.
We report stability and electronic properties of benzene molecule adsorbed on the Au atomic layer within the framework of density function theory (DFT). Horizontal configuration of benzene on the top site of Au monolayer prefers energetically over other studied configurations. On the adsorption of benzene, the ballistic conductance of Au monolayer is found to decrease from 4G0 to 2G0 suggesting its applications for the fabrications of organic sensor devices based on the Au atomic layers. ? 2016 Author(s).
Structural, electronic and magnetic properties of Au-based monolayer derivatives in honeycomb structure
(American Institute of Physics Inc., 2016) Kapoor, Pooja; Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.
We present electronic properties of atomic layer of Au, Au2-N, Au2-O and Au2-F in graphene-like structure within the framework of density functional theory (DFT). The lattice constant of derived monolayers are found to be higher than the pristine Au monolayer. Au monolayer is metallic in nature with quantum ballistic conductance calculated as 4G0. Similarly, Au2-N and Au2-F monolayers show 4G0 and 2G0 quantum conductance respectively while semiconducting nature with calculated band gap of 0.28 eV has been observed for Au2-O monolayer. Most interestingly, half metalicity has been predicted for Au2-N and Au2-F monolayers. Our findings may have importance for the application of these monolayers in nanoelectronic and spintronics. ? 2016 Author(s).
Topological insulator behavior of WS 2 monolayer with square-octagon ring structure
(American Institute of Physics Inc., 2016) Kumar, Ashok; Pandey, Ravindra; Ahluwalia, P. K.; Tankeshwar, K.
We report electronic behavior of an allotrope of monolayer WS 2 with a square octagon ring structure, refereed to as (so-WS 2 ) within state-of-the-art density functional theory (DFT) calculations. The WS 2 monolayer shows semi-metallic characteristics with Dirac-cone like features around Cyrillic capital letter GHE. Unlike p-orbital's Dirac-cone in graphene, the Dirac-cone in the so-WS 2 monolayer originates from the d-electrons of the W atom in the lattice. Most interestingly, the spin-orbit interaction associated with d-electrons induce a finite band-gap that results into the metal-semiconductor transition and topological insulator-like behavior in the so-WS 2 monolayer. These characteristics suggest the so-WS 2 monolayer to be a promising candidate for the next-generation electronic and spintronics devices.
Tunnelling Characteristics of Stone-Wales Defects in Monolayers of Sn and Group- V Elements
(Institute of Physics (IOP), 2017) Jamdagni, Pooja; Kumar, Ashok; Thakur, Anil; Pandey, Ravindra; Ahluwalia, P. K.
Topological defects in ultrathin layers are often formed during synthesis and processing, thereby, strongly influencing the electronic properties of the layered systems. For the monolayers of Sn and group-V elements, we report the results based on density functional theory determining the role of Stone-Wales (SW) defects in modifying their electronic properties. The calculated results find the electronic properties of Sn monolayer to be strongly dependent on the concentration of SW-defects e.g., defective stanene has nearly zero band gap (≈ 0.03 eV) for the defect concentration of 2.2 x 1013 cm-2 which opens up to 0.2 eV for the defect concentration of 3.7 x 1013 cm-2. In contrast, SW-defects appear to induce conduction states in the semiconducting monolayers of group-V elements. These conduction states act as channels for electron tunnelling, and the calculated tunnelling characteristics show the highest differential conductance for the negative bias with the asymmetric current-voltage characteristics. On the other hand, the highest differential conductance was found for the positive bias in stanene. Simulated STM topographical images of stanene and group-V monolayers show distinctly different features in terms of their cross-sectional views and distance-height profiles. These distinctive features can serve as fingerprints to identify the topological defects in experiments for the monolayers of group-IV and group-V elements.
Two dimensional allotropes of arsenene with a wide range of high and anisotropic carrier mobility
(Royal Society of Chemistry, 2018) Jamdagni, Pooja; Thakur, Anil; Kumar, Ashok; Ahluwalia, P. K.; Pandey, Ravindra
Considering the rapid development of experimental techniques for fabricating 2D materials in recent years, various monolayers are expected to be experimentally realized in the near future. Motivated by the recent research activities focused on the honeycomb arsenene monolayers, the stability and carrier mobility of non-honeycomb and porous allotropic arsenene are determined using first principles calculations. In addition to five honeycomb structures of arsenene, a total of eight other structures are considered in this study. An extensive analysis comprising energetics, phonon spectra and mechanical properties confirms that these structures are energetically and dynamically stable. All these structures are semiconductors with a broad range of band gaps varying from ?1 eV to ?2.5 eV. Significantly, these monolayer allotropes possess anisotropic carrier mobilities as high as several hundred cm 2 V -1 s -1 which is comparable with well-known 2D materials such as black phosphorene and monolayer MoS 2 . Combining such broad band gaps and superior carrier mobilities, these monolayer allotropes can be promising candidates for the superior performance of the next generation nanoscale devices. We further explore these monolayer allotropes for photocatalytic water splitting and find that arsenene monolayers have potential for usage in visible light driven photocatalytic water splitting.
Ultra-narrow blue phosphorene nanoribbons for tunable optoelectronics
(Royal Society of Chemistry, 2017) Swaroop, Ram; Ahluwalia, P. K.; Tankeshwar, K.; Kumar, Ashok
We report optoelectronic properties of ultra-narrow blue phosphorene nanoribbons (BPNRs) within the state-of-the-art density functional theory framework. The positive but small value of formation energy (?0.1 eV per atom) indicates the relative ease of the formation of BPNRs from their two-dimensional (2D) counterpart. The oscillatory behaviour of the electronic band gap of bare BPNRs with increasing width is attributed to the reconstruction of edge atoms. The static dielectric constant of BPNRs depends on the width and applied strain which in turn shows consistency with the Penn's model expression for semiconductors. Bare BPNRs exhibit both ? and ? + ? plasmonic structures while passivated ones possess only a ? + ? plasmonic structure that get blue-shifted (as large as ?3 eV) on increasing the width of the BPNRs which makes electron energy loss spectroscopy useful for identifying the width of BPNRs in real experimental situations. The mechanical strain induces a small red shift in, which is attributed to the modification in electronic band dispersion due to a different superposition of atomic orbitals on the application of applied strain. These tunable electronic and dielectric properties of BPNRs mean they may find applications in optoelectronic devices based on blue phosphorene. ? The Royal Society of Chemistry.