Department of Physics

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IIT Jodhpur

In recent years, two-dimensional (2D) atomically thin crystals ranging from insulator to superconductor such as graphene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMDs), etc. have attracted extensive attention due to their exceptional properties and many potential applications in various areas. In this chapter we focus on the experimental characterization of 2D materials and their heterostructures andcover brief introduction and detailed structural, optical, and chemical characterizations of some important 2D materials. © 2020 Elsevier Inc.

World University root node

2D Nanoscale Heterostructured Materials

Characterizations of nanoscale two-dimensional materials and heterostructures

Plenty of strategies focused on covalent interaction have been developed to functionalize graphene's surface in order to employ it in a wide range of applications. Among them, the use of radical species including nitrene, carbene and aryl diazonium salts is regarded as a promising strategy to establish the covalent functionalization of graphene. In this work, we highlight the effect of diazonium chemistry on the electronic properties of graphene on SiC. On the basis of X-ray and synchrotron-based photoemission experiments, we were able to prove that 3,4,5-trimethoxybenzenediazonium (TMeOD) units, reduced and chemisorbed onto graphene using electrochemistry, preserve the electronic structure of the Dirac cone, through inducing a slightly additional n-type doping of graphene, as revealed by a downshift of the Dirac cone probed by angle-resolved photoemission experiments. © 2020 The Royal Society of Chemistry.

Nanoscale

Impact of covalent functionalization by diazonium chemistry on the electronic properties of graphene on SiC

We investigated NiF2 as an energy storage material in asymmetric supercapacitor together with activated carbon (AC) as the counter electrode. Cyclic voltammetry and galvanostatic charge-discharge profile are carried out to investigate the oxidation-reduction process and capacitive behavior of the NiF2 sample. The interfacial electron transport properties of the sample are also explored using Nyquist plots in two and three electrodes configurations of electrochemical impedance spectroscopy. A very high specific capacitance of 751 F/g is achieved at 1 A/g current density in three electrode system. Further, the asymmetric supercapacitor device based on NiF2//AC structure reveals high capacitance of 175 F/g at 1 A/g in the high window potential of 1.8 V. The fabricated device retained 93% of its initial capacitance after 1000 cycles at 3 A/g current density affirms high electrochemical stability of the device. Ragone plot depicts high energy density of 79.65 Wh/kg with power density of 1727.35 W/kg for 1.8 V window potential at 1 A/g current density. High electrochemical stability of NiF2 sample endures the tetragonal phase even after electrochemical measurement which can be more useful in recycling the electrode material for future recycled supercapacitor devices. © 2020 Elsevier B.V.

Journal of Electroanalytical Chemistry

NiF2 as an efficient electrode material with high window potential of 1.8 V for high energy and power density asymmetric supercapacitor

A chemiresistive, 1T-TiS2 nanosheet (TNS) based gas sensor has been developed, and its ultrahigh sensitivity toward hydrogen sulfide (H2S) and oxygen (O2) gas at room temperature has been experimentally demonstrated. The sensor displayed room-temperature detection with a maximum response of 395% to 4 ppm H2S (reducing gas) in dry air and a response of 234% to 100% oxygen (oxidizing gas) in ambient conditions. The H2S and O2 sensing in humid environment (40% and 80%) has also been demonstrated so as to ensure the reliable operation of sensor in real-time applications. The ultrasensitive nature and linear behavior of the sensor enable it to operate reliably in the wide range of 300 ppb to 4 ppm H2S and 1% to 100% oxygen. Density functional theory (DFT) simulations were carried out to study the structural and electronic properties of TNS. Adsorption behavior of these gas molecules on TNS nanosheets was also studied theoretically. A plausible sensing mechanism based on the theoretical model has been detailed, and interestingly, it suggests physisorption phenomena between the adsorbate and adsorbent which enables fast recovery of the sensor without any external stimulation. The rather low lower limit of detection (LLoD) for H2S and O2 reported here, specifically at room temperature, is unique and competes favorably with reported studies. This outstanding sensor performance can be attributed to small adsorption energy and van der Waals interaction between analyte and the receptor. Copyright © 2020 American Chemical Society.

ACS Applied Nano Materials

1T-Phase Titanium Disulfide Nanosheets for Sensing H2S and O2

Ideal sillenite type Bi12FeO20 (BFO) micron sized single crystals have been successfully grown via inexpensive hydrothermal method. The refined single crystal X-ray diffraction data reveals cubic Bi12FeO20 structure with single crystal parameters. Occurrence of rare Fe4+ state is identified via X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The lattice parameter (a) and corresponding molar volume (Vm) of Bi12FeO20 have been measured in the temperature range of 30–700 °C by the X-ray diffraction method. The thermal expansion coefficient (α) 3.93 × 10–5 K−1 was calculated from the measured values of the parameters. Electronic structure and density of states are investigated by first principle calculations. Photoelectrochemical measurements on single crystals with bandgap of 2 eV reveal significant photo response. The photoactivity of as grown crystals were further investigated by degrading organic effluents such as Methylene blue (MB) and Congo red (CR) under natural sunlight. BFO showed photodegradation efficiency about 74.23% and 32.10% for degrading MB and CR respectively. Interesting morphology and microstructure of pointed spearhead like BFO crystals provide a new insight in designing and synthesizing multifunctional single crystals. © 2020, The Author(s).

Fulltext

Scientific Reports

Growth of sillenite Bi12FeO20 single crystals: structural, thermal, optical, photocatalytic features and first principle calculations

We computed structural, electronic, and magnetic properties of pristine and both intrinsic/extrinsic point defects included InN monolayer. The stability of the pristine InN monolayer is confirmed through the phonon band dispersion. InN pristine monolayer exhibits an indirect bandgap, 0.61 eV between M and Γ high symmetry points. InV, NV, (In/N)V vacancies, and antisite defects such as In↔N are considered in InN monolayer, together with light elements, Li, Be, B, C O, and F doping at nitrogen (N) atomic site. We calculated the formation energies for understanding the stability of point defect included and doped InN monolayers. The NV included InN monolayer showed the most stable behaviour among structures. Vacancy defects InV, NV, and (In/N)V included monolayers showed 3.00 μB, 0.00 μB, and 2.00 μB magnetic moment, respectively. However, antisite defects included monolayers showed zero magnetic moment. Further, Be and C doped monolayers showed 0.91 μB and 1.09 μB magnetic moment, respectively, whereas the other dopants showed zero magnetic moment. Thus, the onset of magnetism can be realized in InN monolayer by inducing defects with a maximum of 3.00 μB for InV defects. © 2020 Elsevier Ltd

Vacuum

Defects and light elements (Li, Be, B, C, O and F) driven d0 magnetism in InN monolayer

Molybdenum Trioxide (MoO3) films are grown on Si(100) substrates by reactive RF magnetron sputtering in plasma containing a mixture of Argon and Oxygen, using a pure Molybdenum target. In this paper, we report the deposition of (MoO3) films on Si(100) substrates under varying gas flow (O2 + Ar gas) (20 sccm to 30 sccm with the duration of deposition~ 1hr) by RF reactive magnetron sputtering at room temperature. To get crystalline MoO3 films annealing in O2 environment at 500 °C for 4 h is done. Phase formation and orientation of the film is characterised by Glancing incidence X-ray diffraction (GIXRD). The identification of the orthorhombic MoO3 phase is investigated by XRD and Raman spectroscopy. Raman lines at 819 cm-1 and 995 cm-1 are due to the (A1g, B1g) symmetric stretching (Mo-O-Mo) bond and asymmetric stretching band (Mo=O) respectively. Surface morphology and cross-sectional image of the deposited thin films were investigated by FE-SEM image. UV-Visible reflectance and cross-sectional FE-SEM image confirm the thickness of the MoO3 films with oxygen-rich and oxygen deficient phase formation occur. Reverse leakage current density of 20 sccm 1hr sample is low (1×10-6 mA/cm2) as compared to 30 sccm 1hr sample (1×10-3 mA/cm2). The higher leakage is due to crack formation during the ex-situ annealing of MoO3 films. This MoO3 films can be used in Gas sensing and switching devices. © 2020, DESIDOC.

Defence Science Journal

RF sputtered MoO3thin film on si (100) for gas sensing applications

We designed an experimental set-up and optimized the process parameters for large scale synthesis (250 g) of low density nickel core metal with graphitic carbon shell as functional nanomaterial with highly reproducible physical properties. Structural characterization reveals formation of nano-core FCC Ni metal ~40 nm with ~7 nm thick graphitic shell after annealing at 850 °C. Room temperature field dependent magnetic (M−H) measurement reveals significant saturation magnetization in the sample even with non-magnetic graphite shell. The structural and magnetic properties are compared with small-scale batch synthesis (10 g), reported earlier. The temperature-dependent magnetic measurements suggest that Ni/graphite core-shell samples, annealed at 550 °C, and 700 °C are superparamagnetic, whereas sample annealed at 850 °C is ferromagnetic. The developed synthesis set-up is simple, environment friendly, and cost-effective. Further, to cater the end use applications of such materials for industrial, bio-medical and microwave absorption, the reported method may be further scaled up for large production. © 2020 Elsevier B.V.

Journal of Magnetism and Magnetic Materials

Large scale re-producible synthesis and magnetic properties of Ni/graphite core-shell nanostructured materials

Quantum non-Markovianity modifies the environmental decoherence of a system. This situation is enriched in complex systems owing to interactions among subsystems. We consider the problem of distinguishing the multiple sources of non-Markovianity using a simple power spectrum technique, applied to a qubit interacting with another qubit via a Jaynes-Cummings-type Hamiltonian and simultaneously subjected to some well-known noise channels, such as the random telegraph noise and non-Markovian amplitude damping, which exhibit both Markovian as well as non-Markovian dynamics under different parameter ranges. © 2020 World Scientific Publishing Company.

International Journal of Quantum Information

Distinguishing environment-induced non-Markovianity from subsystem dynamics

The lepton flavor universality violating (LFUV) measurements RK and RK∗ in B meson decays can be accounted for in non-universal Z′ models. We constrain the couplings of these Z′ models by performing a global fit to correlated b→ sℓℓ and b→ dℓℓ processes, and calculate their possible implications for Bs→ K¯ ∗ℓℓ observables. For real new physics (NP) couplings, the 1σ favored parameters allow the corresponding LFUV ratio RK∗(s) in Bs→ K¯ ∗ℓℓ to range between 0.8 and 1.2 at low q2. Complex NP couplings improve the best fit only marginally, however they allow a significant enhancement of the branching ratio, while increasing the range of RK∗(s)at low q2 to 0.8–1.8. We find that NP could cause zero-crossing in the forward–backward asymmetry AFB to shift towards lower q2 values, and enhancement in the magnitude of integrated AFB. The CP asymmetry ACP may be suppressed and even change sign. The simultaneous measurements of integrated RK∗(s)and ACP values to 0.1 and 1% respectively, would help in constraining the effective NP Wilson coefficient C9 in b→ dμμ interactions. © 2020, The Author(s).