Effect of Pd/Pt decoration on MoSSe monolayer for CH4 signature through surface adsorption mechanism.

Considering the current breakthrough in gas sensor technology, we have examined impact of CH4 in the vicinity of pristine MoSSe and Pd/Pt decorated MoSSe monolayers using first principles approach. The negative formation energies confirm structural stability of considered monolayers. The pristine MoSSe monolayer is semiconductor having 1.52 eV direct band gap. This value decreases in the presence of Pd/Pt adatom. Further, adsorption strength of CH4 to monolayers is validated by sensing parameters such as adsorption energy, recovery time, charge transfer and work function. Though we found maximum adsorption energies of - 0.674 and - 0.636 eV for adsorption on Se site of Pd/Pt decorated MoSSe monolayers, the overall sensing response also reveals high sensitivity for Se surface. However, both sites S and Se are favorable for CH4 adsorption. When CH4 is activated on Pd/Pt decorated monolayers, band gaps vary with marginal alterations and transform to direct type. Moreover, optical dielectric response alters strongly in the visible region after activation of CH4 on to Pd/Pt decorated MoSSe monolayers. This result identifies sensitivity response in the presence of methane which may detect CH4 gas easily in visible region. Generally, these interesting results of methane sensing study provoke Pd/Pt decorated MoSSe monolayers to be good sensing nano-device.

Two-dimensional CsPbI3/CsPbBr3 vertical heterostructure: a potential photovoltaic absorber.

First-principles methods have been employed here to calculate structural, electronic and optical properties of CsPbI3 and CsPbBr3, in monolayer and heterostructure (HS) (PbI2-CsBr (HS1), CsI-CsBr (HS2), CsI-PbBr2 (HS3) and PbI2-PbBr2 (HS4)) configurations. Imaginary frequencies are absent in phonon dispersion curves of CsPbI3 and CsPbBr3 monolayers which depicts their dynamical stability. Values of interfacial binding energies signifies stability of our simulated heterostructures. The CsPbI3 monolayer, CsPbBr3 monolayer, HS1, HS2, HS3 and HS4 possess direct bandgap of 2.19 eV, 2.73 eV, 2.41 eV, 2.11 eV, 1.88 eV and 2.07 eV, respectively. In the HS3, interface interactions between its constituent monolayers causes substantial decrease in its resultant bandgap which suggests its solar cell applications. Static dielectric constants of all simulated heterostructures are higher when compared to those of pristine monolayers which demonstrates that these heterostructures possess low charge carrier recombination rate. In optical absorption plots of materials, the plot of HS3 displayed a red shift and depicted absorption of a substantial part of visible spectrum. Later on, via Shockley-Queisser limit we have calculated solar cell parameters of all the reported structures. The calculations showed that HS2, HS3 and HS4 showcased enhanced power conversion efficiency compared to CsPbI3 and CsPbBr3 monolayers when utilized as an absorber layer in solar cells.

Detection of H2S, HF and H2 pollutant gases on the surface of penta-PdAs2 monolayer using DFT approach.

In this research, the adsorption of targeted noxious gases like H2S, HF and H2 on penta-PdAs2 monolayer are deeply studied by means of the density functional theory (DFT). After the capturing of three kind of pollutant gases (H2S, HF and H2), it is observed that, the electronic properties are slightly affected from the pristine one. In all cases, the physisorption interaction found with adsorption energy of - 0.49, - 0.39 and - 0.16 eV for H2S, HF and H2 gases, respectively. Which is exposed that H2S gas strongly absorbed on penta-PdAs2 nanosheet. In case of HF (H2) gas adsorbed systems, the obtained charge transfer is + 0.111 e (+ 0.037 e), revealed that the electrons are going to PdAs2 nanosheet from the HF (H2) molecules. Further, under the non-equilibrium Green's function (NEGF) theory, the IV response and sensitivity of absorbed H2S, HF and H2 have been discussed. The results demonstrate that the H2S molecules on PdAs2 has suitable adsorption strength and explicit charge transfer compared with other targeted molecules. Hence, our novel findings of H2S, HF and H2 targeted gas sensing on penta-PdAs2 nanosheet might provide reference-line to design modern gas sensor device at the nano-scale.

Selective and sensitive toxic gas-sensing mechanism in a 2D Janus MoSSe monolayer.

With an inspiration of sensing toxic gases, this study is aimed at exploring the potential of a Janus MoSSe monolayer as a gas sensor. Here, we focused on the adsorption mechanism after the exposure to NH3, NO2, NO, HCN, CO2, CO, H2, H2S and SO2 on both the S and Se sites of MoSSe. We investigated the structural geometries and electronic, sensing and electron-transport properties before and after adsorption of the aforementioned gases by applying DFT calculations. The results revealed the higher binding strength of NO2/SO2 and NO on Se and S sites, respectively, among all the gas adsorptions on the MoSSe monolayer. Moreover, DOS revealed strong orbital contributions at EF, which confirmed the n/p-type semiconducting character for the NO/NO2 adsorbed MoSSe monolayer. Further, the specific work function alteration after the adsorption of NO2, SO2 and NO indicated that the MoSSe monolayer could be a potential candidate for Φ-type gas sensor at 300 K. Additionally, the higher electron transmission and prominent electrical response values of 76.4/56 µA and 82 µA suggested a maximum sensitivity of 98%/89% and 93% at a particular voltage for NO2/SO2 and NO on Se and S sites, respectively. Thus, our results promote surface selectivity, i.e. S or Se site, and better sensitivity with recycling potential could enable sensing application of the Janus MoSSe monolayer for toxic gases detection.

Strain modulating electronic band gaps and SQ efficiencies of semiconductor 2D PdQ2 (Q = S, Se) monolayer.

We studied the physical, electronic transport and optical properties of a unique pentagonal PdQ2 (Q = S, Se) monolayers. The dynamic stability of 2Dwrinkle like-PdQ2 is proven by positive phonon frequencies in the phonon dispersion curve. The optimized structural parameters of wrinkled pentagonal PdQ2 are in good agreement with the available experimental results. The ultimate tensile strength (UTHS) was calculated and found that, penta-PdS2 monolayer can withstand up to 16% (18%) strain along x (y) direction with 3.44 GPa (3.43 GPa). While, penta-PdSe2 monolayer can withstand up to 17% (19%) strain along x (y) dirrection with 3.46 GPa (3.40 GPa). It is found that, the penta-PdQ2 monolayers has the semiconducting behavior with indirect band gap of 0.94 and 1.26 eV for 2D-PdS2 and 2D-PdSe2, respectively. More interestingly, at room temperacture, the hole mobilty (electron mobility) obtained for 2D-PdS2 and PdSe2 are 67.43 (258.06) cm2 V-1 s-1 and 1518.81 (442.49) cm2 V-1 s-1, respectively. In addition, I-V characteristics of PdSe2 monolayer show strong negative differential conductance (NDC) region near the 3.57 V. The Shockly-Queisser (SQ) effeciency prameters of PdQ2 monolayers are also explored and the highest SQ efficeinciy obtained for PdS2 is 33.93% at -5% strain and for PdSe2 is 33.94% at -2% strain. The penta-PdQ2 exhibits high optical absorption intensity in the UV region, up to 4.04 × 105 (for PdS2) and 5.28 × 105 (for PdSe2), which is suitable for applications in optoelectronic devices. Thus, the ultrathin PdQ2 monolayers could be potential material for next-generation solar-cell applications and high performance nanodevices.

Synthesis of exfoliated multilayer graphene and its putative interactions with SARS-CoV-2 virus investigated through computational studies.

Our work investigates the interaction of synthesized graphene with the SARS-CoV-2 virus using molecular docking and molecular dynamics (MD) simulation method. The layer dependent inhibitory effect of graphene nanosheets on spike receptor-binding domain of 6LZG, complexed with host receptor i.e. angiotensin-converting enzyme 2 (ACE2) of SARS-CoV-2 was investigated through computational study. Graphene sample was synthesized using mechanical exfoliation with shear stress and its mechanism of inhibition towards the SARS-CoV-2 virus was explored by molecular docking and molecular dynamics (MD) simulation method. The thermodynamics study for the free binding energy of graphene towards the SARS-CoV-2 virus was analyzed. The binding energy of graphene towards the virus increased with an increasing number of layers. It shows the highest affinity of -17.5 Kcal/mol in molecular docking while ΔGbinding is in the order of -28.01 ± 0.04 5 Kcal/mol for the seven-layers structure. The increase in carbon layers is associated with an increasing number of edge sp3 -type carbon, providing greater curvature, further increase the surface reactivity responsible for high binding efficiency. The MD simulation data reveals the high inhibition efficiency of the synthesized graphene towards SARS-CoV-2 virus which would help to design future in-vitro studies. The graphene system could find potential applications in personal protective equipment and diagnostic kits.Communicated by Ramaswamy H. Sarma.

Enhanced thermoelectric properties in Sb/Ge core/shell nanowires through vacancy modulation.

In the present work, we have modified the physical and electronic structure of Sb/Ge core/shell nanowires via vacancy creation and doping with foreign atoms with the aim to improve their thermoelectric energy conversion efficiency. Sb/Ge-NWs having a diameter of 1.5 Å show metallicity with 2Go quantum conductance. The stability of the nanowires is assessed through the calculation of their formation energy. The formation of one vacancy at either the Sb- and Ge-site modifies substantially the electronic properties. From the comparison of the thermoelectric properties of the nanowires with and without the vacancy, we have found that the figure of merit for the Sb/Ge NW with one Sb vacancy increases of 0.18 compared to the pristine NW. The NW doping with different transition metals: Fe, Co, Ni and Cu have been found to also enhance the conversion efficiency. Thus, our calculations show that the thermoelectric performance of metal-semiconductor core-shell NWs can be in principle improved as much as 80% by vacancy formation and doping.

First-Principles Study of Mn-Doped and Nb-Doped CsPbCl3 Monolayers as an Absorber Layer in Solar Cells.

The density functional theory (DFT) based analysis of cubic phase cesium lead chloride (CsPbCl3) perovskite is reported. Here the absence of imaginary frequencies in the phonon dispersion curves of unit cell of bulk and monolayer CsPbCl3 showed that both the structures are dynamically stable. The pristine CsPbCl3 monolayer is a wide bandgap semiconductor with an energy gap of 3.24 eV; therefore, an approach to alter its properties was adopted by doping Mn at the Pb-site and Nb at the Cs-site, respectively. In these Mn- and Nb-doped CsPbCl3 monolayers, intermediate states were generated in both the cases due to Mn-3d and Nb-4d orbitals, respectively, which makes the transfer of excited photoelectrons easier from the valence band to the conduction band. The absorption coefficient plots of Mn-doped and Nb-doped CsPbCl3 monolayers indicated that their absorption edges get shifted toward low photon energy, i.e. red shifted compared to the pristine CsPbCl3 monolayer. As both the impurity atoms considered are transition metals, we have also taken into account the effect of spin polarization on electronic and optical properties of doped monolayers. Solar cell parameters of all of these monolayers have been calculated using the Shockley-Queisser (SQ) limit. The short-circuit current density (Jsc) of the Nb-doped CsPbCl3 monolayer was obtained around 655.45 A/m2, and the efficiency of this material came out to be around 15.68%. For the Mn-doped CsPbCl3 monolayer the value of Jsc came to be around 525.68 A/m2 and showed strikingly high efficiency of 26.88% thus being a suitable candidate for its application as an absorber layer in solar cells.

Metallic one-dimensional heterostructure for gas molecule sensing.

We have investigated a new metallic core-shell nanowire (NW) geometry of that could be obtained experimentally, that is silicon (Si) and germanium (Ge) NWs with cores constituted by group-10 elements palladium (Pd) and platinum (Pt). These NWs are optimized with two different diameters of 1.5 Å and 2.5 Å. The nanowires having diameter of 1.5 Å show semi-metallic nature with GGA-PBE calculation and metallic nature while spin orbit interaction (SOC) is included. The quantum conductance of the NWs increases with the diameter of the nanowire. We have investigated current-voltage (IV) characteristics for the considered NWs. It has been found that current values in accordance with applied voltage show strong dependence on the diameter of the NWs. The optical study of the NWs shows that absorption co-efficient peak moves to lower energies; due to quantum confinement effect. Furthermore, we have extensively studied optical response of Pd and Pt based core-shell NWs in O2 and CO2 environment. Our study on Si and Ge based metallic core/shell NW show a comprehensive picture as possible electron connector in future nano-electronic devices as well as nano gas detector for detecting O2 gas.

Carbon nanotubes for rapid capturing of SARS-COV-2 virus: revealing a mechanistic aspect of binding based on computational studies.

We investigate the binding interactions of synthesized multi-walled carbon nanotubes (MWCNTs) with SARS-CoV-2 virus. Two essential components of the SARS-CoV-2 structure i.e.6LU7 (main protease of SARS-CoV-2) and 6LZG (spike receptor-binding domain complexed with its receptor ACE2) were used for computational studies. MWCNTs of different morphologies (zigzag, armchair and chiral) were synthesized through a thermal chemical vapour deposition process as a function of pyrolysis temperature. A direct correlation between radius to volume ratio of the synthesized MWCNTs and the binding energies for all three (zigzag, armchair and chiral) conformations were observed in our computational studies. Our result suggests that MWCNTs interact with the active sites of the main protease along with the host angiotensin-converting enzyme2 (ACE2) receptors. Furthermore, it is also observed that MWCNTs have significant binding affinities towards SARS-CoV-2. However, the highest free binding energy of -87.09 kcal mol-1 with 6LZG were shown by the armchair MWCNTs with SARS-CoV-2 through the simulated molecular dynamic trajectories, which could alter the SARS-CoV-2 structure with higher accuracy. The radial distribution function also confirms the density variation as a function of distance from a reference particle of MWCNTs for the study of interparticle interactions of the MWCNT and SARS-CoV-2. Due to these interesting attributes, such MWCNTs could find potential application in personal protective equipment (PPE) and diagnostic kits.

2D BeP2 monolayer: investigation of electronic and optical properties by driven modulated strain.

Recently, the two-dimensional (2D) material beryllium diphosphide (BeP2) has attracted significant attention for potential device applications due to its Dirac semimetal state, dynamic and thermal stability, and high carrier mobility. In this work, we investigated its electronic and optical properties under biaxial Lagrangian strain using density functional theory (DFT). Electronic band gaps and effective charge carrier mass were highly sensitive to the Lagrangian strain of BeP2 monolayer. The bandgaps of BeP2 varied from 0 eV to 0.30 eV for 2% to 8% strain, where the strain range is based on the final stable condition of the system. The absorption spectra for the dielectric properties show the highest absorption peaks in the infrared (IR) region. These abundant strain-dependent studies of the BeP2 monolayer provide guidelines for its application in infrared sensors and devices.

Si and Ge based metallic core/shell nanowires for nano-electronic device applications.

One dimensional heterostructure nanowires (NWs) have attracted a large attention due to the possibility of easily tuning their energy gap, a useful property for application to next generation electronic devices. In this work, we propose new core/shell NW systems where Ge and Si shells are built around very thin As and Sb cores. The modification in the electronic properties arises due to the induced compressive strain experienced by the metal core region which is attributed to the lattice-mismatch with the shell region. As/Ge and As/Si nanowires undergo a semiconducting-to-metal transition on increasing the diameter of the shell. The current-voltage (I-V) characteristics of the nanowires show a negative differential conductance (NDC) effect for small diameters that could lead to their application in atomic scale device(s) for fast switching. In addition, an ohmic behavior and upto 300% increment of the current value is achieved on just doubling the shell region. The resistivity of nanowires decreases with the increase in diameter. These characteristics make these NWs suitable candidates for application as electron connectors in nanoelectronic devices.

Highly infrared sensitive VO2 nanowires for a nano-optical device.

Recent studies on the electronic, magnetic and optical properties of VO2 (vanadium dioxide) materials have motivated the exploration of one dimensional VO2 nanowires. First principles calculations were performed to investigate the structural, electronic, magnetic and optical properties of the monoclinic (M) and rutile (R) phases of VO2 nanowires. The monoclinic phase shows semiconducting behaviour with a band gap of 1.17 eV, whereas the rutile phase of VO2 nanowires behaves as a spin gapless semiconducting material, as band lines cross the Fermi level due only to up spin contribution. The monoclinic structure of VO2 nanowires is found to be paramagnetic and the rutile structure shows ferromagnetic half metal behavior. The conductivity calculation for VO2 nanowires shows the metal-insulator transition (MIT) temperature to be 250 K. The possible mechanism of VO2 nanowires to be used as smart windows has been discussed, as the nanowires are highly sensitive in the infrared (IR) region. Interestingly, at low temperature, the VO2 monoclinic structure allows infrared light to be transmitted, while VO2 with the rutile phase blocks light in the IR region. Furthermore, we adsorbed CO2, N2 and SO2 gas molecules on 1D VO2 monoclinic nanowire to investigate their interaction behaviour. It was observed that the absorption and transmission properties of VO2 dramatically change upon the adsorption of CO2 and SO2 gas molecules, which is likely to open up its application as an optical gas sensor.