Faculty Publications
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Item Performance and analysis of temperature dependent multi-walled carbon nanotubes as global interconnects at different technology nodes(Kluwer Academic Publishers barbara.b.bertram@gsk.com, 2015) Sandha, K.; Raj, B.A temperature dependent performance in terms of power delay product (PDP) of multi-walled carbon nanotube (MWCNT) bundle interconnect has been analyzed for temperature range from 200 to 450 K at three different technology nodes viz. 32, 22 and 16nm. A similar analysis is performed for copper interconnect and results are compared with MWCNT bundle interconnect. Comparative results revealed that delay and PDP is increased with rise in temperature ranging from 200 to 450 K. It has also been observed that the temperature dependent MWCNT bundle interconnect gives better performance in terms of delay, power and PDP as compared to copper interconnect for three technology nodes at global interconnect length. © 2015, Springer Science+Business Media New York.Item Influence of temperature on MWCNT bundle, SWCNT bundle and copper interconnects for nanoscaled technology nodes(Springer New York LLC journals@springer-sbm.com, 2015) Sandha, K.; Raj, B.This paper presents the comparative analysis of temperature dependent performance of Multi-walled carbon nanotubes (MWCNT), Single-walled carbon nanotube (SWCNT) and copper interconnects for nanoscaled technology nodes. The temperature dependent impedance circuit model is proposed for MWCNT bundle interconnects. The proposed model for MWCNT bundle shows the various electron–phonon scattering mechanisms dependency as a function of temperature. The performance in terms of propagation delay, power dissipation and power delay product for MWCNT bundle interconnects is simulated on the basis of temperature dependent electrical parameters for global interconnects at three different technology nodes viz. 32, 22 and 16 nm for temperature range 200 to 450 K. A similar analysis is performed for SWCNT bundle and copper interconnects and results are compared with the MWCNT bundle interconnects. The comparative results revealed that the performance of MWCNT bundle interconnects is better than the performance of SWCNT bundle and copper interconnects at different temperature ranging from 200 to 450 K for 32, 22 and 16 nm technology nodes at global interconnects. © 2015, Springer Science+Business Media New York.Item Optical absorption, mechanical properties and FTIR studies of silver-doped barium phosphate glasses(Society of Glass Technology christine@glass.demon.co.uk, 2016) Narayanan, M.K.; Shashikala, H.D.Silver-doped barium phosphate glasses, of composition 50BaO-50P2O5-4Ag2O-4SnO, were prepared by conventional melt quenching and subsequent heat treatment. Prepared glasses were heat treated for a fixed duration of 10 h at different temperatures 400, 450 and 500°C to develop silver nanoparticles of different sizes. Formation and the size of the silver nanoparticles were evaluated using the surface plasmon resonance (SPR) band of the optical absorption spectrum, which revealed that both of them were temperature dependent. Spectral positions of the SPR peaks of the glass samples heat treated at 450 and 500°C were observed around 3.0 eV. Absence of significant size dependent shift in SPR peaks of these samples from 3.0 eV indicates the formation of spherical silver nanoparticles smaller than 20 nm inside the glass matrix, which falls in the quasi-static regime of Mie theory. The effect of heat treatment on the local network structure of the phosphate glass matrix assessed using FTIR spectra shows that formation and growth of silver nanoclusters do not affect the basic metaphosphate network structure. A slight improvement is observed in density as well as in the mechanical properties of the heat treated samples due to densification of the glass matrix by dispersed silver nanoparticles.Item Possible Room-Temperature Ferromagnetism in Self-Assembled Ensembles of Paramagnetic and Diamagnetic Molecular Semiconductors(American Chemical Society service@acs.org, 2016) Dhara, B.; Tarafder, K.; Jha, P.K.; Panja, S.N.; Nair, S.; Oppeneer, P.M.; Ballav, N.Owing to long spin-relaxation time and chemically customizable physical properties, molecule-based semiconductor materials like metal-phthalocyanines offer promising alternatives to conventional dilute magnetic semiconductors/oxides (DMSs/DMOs) to achieve room-temperature (RT) ferromagnetism. However, air-stable molecule-based materials exhibiting both semiconductivity and magnetic-order at RT have so far remained elusive. We present here the concept of supramolecular arrangement to accomplish possibly RT ferromagnetism. Specifically, we observe a clear hysteresis-loop (Hc ? 120 Oe) at 300 K in the magnetization versus field (M-H) plot of the self-assembled ensembles of diamagnetic Zn-phthalocyanine having peripheral F atoms (ZnFPc; S = 0) and paramagnetic Fe-phthalocyanine having peripehral H atoms (FePc; S = 1). Tauc plot of the self-assembled FePc···ZnFPc ensembles showed an optical band gap of ?1.05 eV and temperature-dependent current-voltage (I-V) studies suggest semiconducting characteristics in the material. Using DFT+U quantum-chemical calculations, we reveal the origin of such unusual ferromagnetic exchange-interaction in the supramolecular FePc···ZnFPc system. © 2016 American Chemical Society.Item Effect of ripples on the finite temperature elastic properties of hexagonal boron nitride using strain-fluctuation method(Academic Press, 2017) Thomas, S.; Ajith, K.M.; Valsakumar, M.C.This work intents to put forth the results of a classical molecular dynamics study to investigate the temperature dependent elastic constants of monolayer hexagonal boron nitride (h-BN) between 100 and 1000 K for the first time using strain fluctuation method. The temperature dependence of out-of-plane fluctuations (ripples) is quantified and is explained using continuum theory of membranes. At low temperatures, negative in-plane thermal expansion is observed and at high temperatures, a transition to positive thermal expansion has been observed due to the presence of thermally excited ripples. The decrease of Young's modulus, bulk modulus, shear modulus and Poisson's ratio with increase in temperature has been analyzed. The thermal rippling in h-BN leads to strong anharmonic behaviour that causes large deviation from the isotropic elasticity. A detailed study shows that the strong thermal rippling in large systems is also responsible for the softening of elastic constants in h-BN. From the determined values of elastic constants and elastic moduli, it has been elucidated that 2D h-BN sheets meet the Born's mechanical stability criterion in the investigated temperature range. The variation of longitudinal and shear velocities with temperature is also calculated from the computed values of elastic constants and elastic moduli. © 2017 Elsevier LtdItem Assessment of the mechanical properties of monolayer graphene using the energy and strain-fluctuation methods(Royal Society of Chemistry, 2018) Thomas, S.; Ajith, K.M.; Lee, S.U.; Valsakumar, M.C.Molecular statics and dynamics simulations were performed to investigate the mechanical properties of a monolayer graphene sheet using an efficient energy method and strain-fluctuation method. Using the energy method, we observed that the mechanical properties of an infinite graphene sheet are isotropic, whereas for a finite sheet, they are anisotropic. This work is the first to report the temperature-dependent elastic constants of graphene between 100 and 1000 K using the strain-fluctuation method. We found that the out-of-plane thermal excursions in a graphene membrane lead to strong anharmonic behavior, which allows large deviations from isotropic elasticity. The computed Young's modulus and Poisson's ratio of a sheet with an infinite spatial extent are 0.939 TPa and 0.223, respectively. We also found that graphene sheets with both finite and infinite spatial extent satisfy the Born elastic stability conditions. We extracted the variation in bending modulus with the system size at zero kelvin (0.83 eV) using a formula derived from the Foppl-von Karman approach. When the temperature increases, the Young's modulus of the sample decreases, which effectively reduces the longitudinal and shear wave velocities. © 2018 The Royal Society of Chemistry.Item Effect of temperature on magnetic and impedance properties of Fe3BO6 of nanotubular structure with a bonded B2O3 surface layer(American Institute of Physics Inc. subs@aip.org, 2018) Kumari, K.; Ram, S.; Kotnala, R.K.In this investigation, we explore a facile synthesis of Fe3BO6 in the form of small crystallites in the specific shape of nanotubes crystallized from a supercooled liquid Fe2O3-B2O3 precursor. This study includes high resolution transmission electron microscopy (HRTEM) images, magnetic, optical, and impedance properties of the sample. HRTEM images reveal small tubes of Fe3BO6 of 20 nm diameter. A well resolved hysteresis loop appears at 5 K in which the magnetization does not saturate even up to as high field as 50 kOe. It means that the Fe3BO6 nanotubes behave as highly antiferromagnetic in nature in which the surface spins do not align along the field so easily. The temperature dependent impedance describes an ionic Fe3BO6 conductor with a reasonably small activation energy Ea ? 0.33 eV. Impedance formalism in terms of a Cole-Cole plot shows a deviation from an ideal Debye-like behavior. We have also reported that electronic absorption spectra are over a spectral range 200-800 nm of wavelengths in order to find out how a bonded surface layer present on the Fe3BO6 crystallites tunes the 3d ? 3d electronic transitions in Fe3+ ions. © 2018 Author(s).Item Sensitivity Study of Nanocrystalline Fe3BO6 Sensor for Methane Gas Detection(Institute of Electrical and Electronics Engineers Inc., 2018) Kumari, K.; Ram, S.The iron borate Fe3BO6 with functionalized properties in a nanostructure is an important material useful for electrodes, gas sensors, and biological probes. In this paper, we studied the X-ray diffraction pattern, field-emission electron microscopy, and methane (CH4) gas sensing properties of synthesized Fe3BO6 nanocrystallites in a shape of nanoplates and nanobars from an iron borate glass 40Fe2O3-60B2O3 by annealing it in microwave for 15 min at 823 and 1023 K, respectively, in air. The temperature dependent sensitivity for CH4 (1000 ppm) illustrates a maximum value of 43% at an operating temperature 525 K for the 1023 K annealed sample. The sensitivity is found to be varied from 9% to 39% when the CH4 gas concentration is increased from 50 to 1000 ppm. Thus, the sample has a reasonably good sensitivity for methane. Furthermore, the sensor exhibits fast response (1 min) and a good recovery time (1.6 min) as compared with other oxide materials. © 2001-2012 IEEE.Item Route to achieving enhanced quantum capacitance in functionalized graphene based supercapacitor electrodes(Institute of Physics Publishing helen.craven@iop.org, 2019) Sruthi, T.; Tarafder, K.We have investigated the quantum capacitance (CQ) in functionalized graphene modified with ad-atoms from different groups in the periodic table. Changes in the electronic band structure of graphene upon functionalization and subsequently the CQ of the modified graphene were systematically analyzed using density functional theory (DFT) calculations. We observed that the CQ can be enhanced significantly by means of controlled doping of N, Cl and P ad-atoms in the pristine graphene surface. These ad-atoms are behaving as magnetic impurities in the system, generating a localized density of states near the Fermi energy which, in turn, increases charge (electron/hole) carrier density in the system. As a result, a very high quantum capacitance was observed. Finally, the temperature dependent study of CQ for Cl and N functionalized graphene shows that the CQ remains very high in a wide range of temperatures near room temperature. © 2019 Institute of Physics Publishing. All rights reserved.Item Investigation on mechanical and temperature dependent electrical properties of potassium hydrogen oxalate oxalic acid dihydrate single crystal(Elsevier B.V., 2020) Mahendra, K.; Udayashankar, N.K.The potassium hydrogen oxalate oxalic acid dihydrate (KHOOD) single crystals were grown using solvent evaporation technique. The mechanical hardness of grown KHOOD single crystal was performed using Vickers microhardness tester and investigated for different loads starting from 10 g to 100 g and it was decided to include under hard material category. The mechanical parameters such as elastic stiffness and yield strength were calculated and discussed in detail. Temperature dependent I-V, dielectric studies were performed and explained in detail. © 2020 Elsevier B.V.