BITS Faculty Publications
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Item Unveiling the dichotomy between cobalt(ii)-exchanged x and y faujasite zeolites via oxidative carboxylation of alkene to cyclic carbonate(ACS, 2025-04) Ray, SaumiCobalt(II)-exchanged X and Y zeolites with varying metal loadings were employed to convert CO2 to cyclic carbonates starting from alkenes. The transformation was carried out using O2 as an oxidant in a mixture of O2 and CO2 under atmospheric pressure, and a maximum yield of 35.7% cyclic carbonate was achieved. Studies revealed a stark difference among both the zeolites, primarily arising from a difference in their ion exchange behaviors. Their catalytic and recyclability properties differed as a result of this variationItem Application of the self-consistent quantum method for simulating the size quantization effect in the channel of a nano-scale dual gate MOSFET(AIP, 2015-06) Sarkar, NiladriSelf-Consistent Quantum Method using Schrodinger-Poisson equations have been used for determining the Channel electron density of Nano-Scale MOSFETs for 6nm and 9nm thick channels. The 6nm thick MOSFET show the peak of the electron density at the middle where as the 9nm thick MOSFET shows the accumulation of the electrons at the oxide/semiconductor interface. The electron density in the channel is obtained from the diagonal elements of the density matrix; [ρ]=[1/(1+exp(β(H − μ)))] A Tridiagonal Hamiltonian Matrix [H] is constructed for the oxide/channel/oxide 1D structure for the dual gate MOSFET. This structure is discretized and Finite-Difference method is used for constructing the matrix equation. The comparison of these results which are obtained by Quantum methods are done with Semi-Classical methods.Item Ultrathin Films of TiO2 Nanoparticles at Interfaces(ACS, 2015-01) Gupta, Raj Kumar; Manjuladevi, V.; Hazra, ArnabThe properties of a material change remarkably as a result of the scaling dimensions. The Langmuir–Blodgett (LB) film deposition technique is known to offer precise control over the film thickness and the interparticle separation. To form a well-ordered LB film, it is essential to form a stable Langmuir film at the air–water interface. Here, we report our studies on ultrathin films of TiO2 nanoparticles at air–water and air–solid interfaces. The Langmuir film of TiO2 nanoparticles at the air–water interface was found to be very stable, and it exhibits loose-packing and close-packing phases. The LB films were transferred onto solid substrates for characterization and application. The surface morphology of the LB film was obtained by a field emission scanning electron microscope. The optical and electronic properties of the LB films of TiO2 nanoparticles were studied using UV–vis spectroscopy and current–voltage measurements, respectively. The LB film of TiO2 nanoparticles was employed for ethanol gas sensing, and the sensing performance was compared to that of bulk material. Because of the enormous gain in the surface to volume ratio and the increase in crystalline defect density in the ultrathin LB film of TiO2 nanoparticles, the LB film is found to be a potential functional layer for ethanol sensing as compared to the bulk material.Item Li2SO4-Li2O-P2O5 Ionic glass dispersed with [Bmim] [PF6] ionic liquid: Electrical transport and thermal stability investigations(AIP, 2014-04) Dalvi, AnshumanA fast ionic composite is prepared by dispersion of Ionic liquid [Bmim][PF6] in glass matrix by mixing and through grinding. Amorphous/glassy nature of the samples is confirmed by X-Ray diffraction (XRD). Surprisingly, the electrical conductivity of the samples is found to be increasing by ∼ 2 orders of magnitude and exhibits typical Arrhenius behavior with low activation energy. DC polarization and impedance spectroscopy measurements suggest that samples are essentially ionic in nature. The conductivity isotherms were also obtained at different temperatures (T < 100 °C) and found to be appreciably stable at least for ∼ 10 days.Item High Field Stressing Effects in JVD Nitride Capacitors(SPIE, 2001) Rao, V. RamgopalThe performance of Jet Vapour Deposited (JVD) Silicon Nitride devices under high field stressing is reported in this paper. Border traps were generated when n-substrate capacitors were stressed with negative gate voltages. Also, an increase in bulk positive charges as well as interface trap density was observed. These results indicate that stressing under negative gate voltages may cause long term reliability problems in Metal-Nitride-Semiconductor (MNS) devices'. Stressing with positive gate voltage, however, does not show any significant degradation.Item NEXT Fabrication of Unipolar Graphene Field-Effect Transistors by Modifying Source and Drain Electrode Interfaces with Zinc Porphyrin(ACS, 2012) Rao, V. RamgopalWe report a unipolar operation in reduced graphene oxide (RGO) field-effect transistors (FETs) via modification of the source/drain (S/D) electrode interfaces with self-assembled monolayers (SAMs) of 5-(4-hydroxyphenyl)-10,15,20-tri-(p-tolyl) zinc(II) porphyrin (Zn(II)TTPOH) molecules. The dipolar Zn(II)TTPOH molecules at the RGO/platinum (Pt) S/D interface results in an increase of the electron injection barrier and a reduction of the hole-injection barrier. Using dipole measurements from Kelvin probe force microscopy and highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) calculations from cyclic voltammetry, the electron and hole injection barriers were calculated to be 2.2 and 0.11 eV, respectively, indicating a higher barrier for electrons, compared to that of holes. A reduced gate modulation in the electron accumulation regime in RGO devices with SAM shows that unipolar RGO FETs can be attained using a low-cost, solution-processable fabrication technique.Item Sequential Energy and Electron Transfer in Polynuclear Complex Sensitized TiO2 Nanoparticles(ACS, 2012-05-19) Banerjee, TanmayPolynuclear–polypyridyl complexes exhibit a directional energy-transfer property that can improve their photosensitization activity. In the present work, the energy-transfer process is explored in a trinuclear Ru2∧Os1 complex using transient absorption spectroscopy. This study reveals an efficient excitation energy transfer from the terminal (RuII complex) to the core (OsII complex) region in the ultrafast time domain (400 fs–40 ps). The excitation energy funnel is useful in improving the functionalized core activity. This is evidenced in an interfacial electron-transfer study of Ru2∧Os1, Ru2∧Ru1, and Os1 complex sensitized TiO2 nanoparticle (TiO2 NP) systems. The intramolecular energy transfer causes sequential excitation of the core part of the Ru2∧Os1 complex, which leads to multiexponential electron injection into TiO2 NP. Besides this, the electronic coupling between the metal ion centers stabilizes the positive charge within the trinuclear complex, which results in a slow charge recombination reaction. This study shows that polynuclear complexes can be very useful for their panchromatic effects, unidirectional energy- and electron-transfer properties.Item Newly Designed Resorcinolate Binding for Ru(II)– and Re(I)–Polypyridyl Complexes on Oleic Acid Capped TiO2 in Nonaqueous Solvent: Prolonged Charge Separation and Substantial Thermalized 3MLCT Injection(ACS, 2013-01-23) Banerjee, TanmayFemtosecond pump–probe spectroscopic studies on a series of newly synthesized resorcinol-based Ru(II) and Re(I) complexes on oleic acid capped TiO2 nanoparticles have been carried out in chloroform, and the results are compared with those of the catechol analogues. The ruthenium complex shows biexponential injection; the second component arises due to injection from the thermally equilibrated 3MLCT states as a result of a weaker strength of the resorcinolate binding. Also, in comparison with catechol binding, as a result of a greater diffusion of the injected electrons into TiO2, the back electron transfer (BET) is slowed down significantly for the ruthenium complex. These are distinctive observations for any mononuclear ruthenium–polypyridyl–enediol complex reported thus far. However, the rhenium complex educes single exponential ultrafast injection (<120 fs) because of apparent injection in a high density of states and shows the most prominent results with ∼50% slowdown in the charge recombination rate as compared to the analogous catechol bound system. These results exemplify the probable development of highly capable sensitizer dyes with resorcinol as the anchoring group for the development of efficient dye-sensitized solar cells.Item Synthesis, Steady-State, and Femtosecond Transient Absorption Studies of Resorcinol Bound Ruthenium(II)- and Osmium(II)-polypyridyl Complexes on Nano-TiO2 Surface in Water(ACS, 2013-04-05) Banerjee, TanmayThe synthesis of two new ruthenium(II)- and osmium(II)-polypyridyl complexes 3 and 4, respectively, with resorcinol as the enediol anchoring moiety, is described. Steady-state photochemical and electrochemical studies of the two sensitizer dyes confirm strong binding of the dyes to TiO2 in water. Femtosecond transient absorption studies have been carried out on the dye–TiO2 systems in water to reveal <120 fs and 1.5 ps electron injection times along with 30% slower back electron transfer time for the ruthenium complex 3. However, the corresponding osmium complex 4 shows strikingly different behavior for which only a <120 fs ultrafast injection is observed. Most remarkably, the back electron transfer is faster as compared to the corresponding catechol analogue of the dye. The origin and the consequences of such profound effects on the ultrafast interfacial dynamics are discussed. This Article on the electron transfer dynamics of the aforesaid systems reinforces the possibility of resorcinol being explored and developed as an extremely efficient binding moiety for use in dye-sensitized solar cells.Item Photon Upconversion and Photocurrent Generation via Self-Assembly at Organic–Inorganic Interfaces(ACS, 2015-10-22) Banerjee, TanmayMolecular photon upconversion via triplet–triplet annihilation (TTA-UC), combining two or more low energy photons to generate a higher energy excited state, is an intriguing strategy to surpass the maximum efficiency for a single junction solar cell (<34%). Here, we introduce self-assembled bilayers on metal oxide surfaces as a strategy to facilitate TTA-UC emission and demonstrate direct charge separation of the upconverted state. A 3-fold enhancement in transient photocurrent is achieved at light intensities as low as two equivalent suns. This strategy is simple, modular and offers unprecedented geometric and spatial control of the donor–acceptor interactions at an interface. These results are a key stepping stone toward the realization of an efficient TTA-UC solar cell that can circumvent the Shockley–Queisser limit.