Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
11 results
Search Results
Item Superior Photostability and Photocatalytic Activity of ZnO Nanoparticles Coated with Ultrathin TiO2 Layers through Atomic-Layer Deposition(Wiley-VCH Verlag info@wiley-vch.de, 2015) Sridharan, K.; Jang, E.; Park, Y.M.; Park, T.J.Atomic-layer deposition (ALD) is a thin-film growth technology that allows for conformal growth of thin films with atomic-level control over their thickness. Although ALD is successful in the semiconductor manufacturing industry, its feasibility for nanoparticle coating has been less explored. Herein, the ALD coating of TiO2 layers on ZnO nanoparticles by employing a specialized rotary reactor is demonstrated. The photocatalytic activity and photostability of ZnO nanoparticles coated with TiO2 layers by ALD and chemical methods were examined by the photodegradation of Rhodamine B dye under UV irradiation. Even though the photocatalytic activity of the presynthesized ZnO nanoparticles is higher than that of commercial P25 TiO2 nanoparticles, their activity tends to decline due to severe photocorrosion. The chemically synthesized TiO2 coating layer on ZnO resulted in severely declined photoactivity despite the improved photostability. However, ultrathin and conformal ALD TiO2 coatings (?0.75-1.5 nm) on ZnO improved its photostability without degradation of photocatalytic activity. Surprisingly, the photostability is comparable to that of pure TiO2, and the photocatalytic activity to that of pure ZnO. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.Item Eliminated Phototoxicity of TiO2Particles by an Atomic-Layer-Deposited Al2O3Coating Layer for UV-Protection Applications(Wiley-VCH Verlag, 2016) Jang, E.; Sridharan, K.; Park, Y.M.; Park, T.J.We demonstrate the conformal coating of an ultrathin Al2O3layer on TiO2nanoparticles through atomic layer deposition by using a specifically designed rotary reactor to eliminate the phototoxicity of the particles for cosmetic use. The ALD reactor is modified to improve the coating efficiency as well as the agitation of the particles for conformal coating. Elemental and microstructural analyses show that ultrathin Al2O3layers are conformally deposited on the TiO2nanoparticles with a controlled thickness. Rhodamine B dye molecules on Al2O3-coated TiO2exhibited a long life time under UV irradiation, that is, more than 2 h, compared to that on bare TiO2, that is, 8 min, indicating mitigation of photocatalytic activity by the coated layer. The effect of carbon impurities in the film resulting from various deposition temperatures and thicknesses of the Al2O3layer on the photocatalytic activity are also thoroughly investigated with controlled experimental condition by using dye molecules on the surface. Our results reveal that an increased carbon impurity resulting from a low processing temperature provides a charge conduction path and generates reactive oxygen species causing the degradation of dye molecule. A thin coated layer, that is, less than 3 nm, also induced the tunneling of electrons and holes to the surface, hence oxidizing dye molecules. Furthermore, the introduction of an Al2O3layer on TiO2improves the light trapping thus, enhances the UV absorption. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Semiconducting B13C2 system: Structure search and DFT-based analysis(Institute of Physics, 2019) Pillai, H.G.; Madam, A.K.; Chandra, S.; Cheruvalath, V.M.DFT calculation on Boron Carbide in B13C2 stoichiometry using a 15-atom unit cell necessarily results in metallic ground state regardless of the crystal structure. This is because such a unit cell consists of odd number of electrons, and hence complete filling of the top most band(s) of nonzero occupancy is impossible. This is in contrast to the observed semiconducting nature. If the crystal structure of B13C2 is made of a 30-atom unit cell which cannot be reduced to a 15 atom cell, there is a possibility of obtaining either a metallic or a semiconducting state as such a cell consists of an even number of electrons. In this work the evolutionary algorithm based structure search using 30-atom unit cells has yielded a previously unreported semiconducting system of B13C2 with unique bonding pattern. The mechanical and dynamical stability of the system have been properly established through the computation of elastic constants and phonon spectra. Its bond lengths, elastic moduli, hardness and infrared spectrum are in good agreement with experimental data. ©2019 IOP Publishing Ltd.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 Theoretical investigation of quantum capacitance in the functionalized MoS2-monolayer(IOP Publishing Ltd, 2021) Sruthi, T.; Devaraj, N.; Tarafder, K.In this work, we investigated the electronic structure and the quantum capacitance of a set of functionalized MoS2 monolayers. The functionalizations have been done by using different ad-atom adsorption on MoS2 monolayer. Density functional theory calculations are performed to obtain an accurate electronic structure of ad-atom doped MoS2 monolayer with a varying degree of doping concentration. Subsequently, the quantum capacitance in each functionalized system was estimated. A marked quantum capacitance above 200 ?F cm-2 has been observed. Our calculations show that the quantum capacitance of MoS2 monolayer is significantly enhanced with substitutional doping of Mo with transition metal ad-atoms. The microscopic origin of such enhancement in quantum capacitance in this system has been analyzed. Our DFT-based calculation reveals that the generation of new electronic states at the proximity of the band-edge and the shift of Fermi level caused by the ad-atom adsorption results in a very high quantum capacitance in the system. © 2021 Institute of Physics Publishing. All rights reserved.Item Understanding and tuning of spinterface for chemisorbed Ni-dinuclear quinonoid on Co(001) substrate(IOP Publishing Ltd, 2021) Reddy, I.R.; Tarafder, K.Planar magnetic molecules are of great research interest in the past few years because of their possible application in molecular spintronics. Microscopic understanding of the adsorption and magnetic exchange interaction of these molecules to the metallic/magnetic surfaces may pave the way in developing efficient molecular spin switching devices. Herein, using density functional theory + U calculations, we have studied the structural, electronic, and magnetic properties of a Ni-dinuclear molecule chemically adsorbed on a Co(001) substrate. Switching of the spin and oxidation state of the Ni atom present in the molecule was observed due to the adsorption. We report a strong antiferromagnetic coupling between the spins of the Ni-dinuclear molecule to the ferromagnetic Co(001) substrate. The study reveals an indirect exchange interaction between the magnetic center of the molecule and the substrate Co atoms. The exchange interaction is mediated through the ligands of the molecule that stabilizes the spin moment of the molecule in an antiferromagnetic alignment to the substrate magnetization. Our study also shows that the spin state and strength of MAE of the adsorbed molecule can be tailored through the magneto-chemical method by adding the Cl atom as an axial ligand to the magnetic center of the molecule. © 2021 IOP Publishing Ltd.Item Optimized electronic performance in half-Heusler Ti-doped NbFeSb materials by stoichiometric tuning at the Fe and Sb sites(Elsevier Ltd, 2022) Kahiu, J.N.; Shenoy, U.S.; Kihoi, S.K.; Kim, H.; Yi, S.; Bhat, D.K.; Lee, H.S.Electronic structure is known to be highly influenced by the site occupancy and the stoichiometry of the material which in turn largely effects the thermoelectric properties. Herein, we present electronic calculations using density functional theory (DFT) of non-stoichiometric Ti doped NbFeSb configuration, showing the effect of the anti-site Fe atoms on the electronic properties, and supporting them with experimental results of the prepared Nb0.8Ti0.2Fe1+xSb1−x samples. The electronic structure of the non-stoichiometric sample shows the introduction of two distinct peaks near the Fermi level by the Fe atoms at the Sb sites. These resonance states are known to cause an increase in the density of states effective mass near the Fermi level, which explains the increase in the Seebeck coefficient in the sample x = 0.03 compared to the sample x = 0.00. In addition, a comparatively higher electrical conductivity is reported from sample x = 0.03, which is attributed to the aliovalent substitution of Sb atoms by Fe atoms. The simultaneous increase in the Seebeck coefficient and electrical conductivity culminates in an increased power factor of ∼50.3 µW/cmK2 at 373 K, which is ∼46% higher than that of samples x = 0.00 and x = 0.05, highlighting the possibility of increasing the power density by stoichiometric variation to achieve the high joule-per-dollar performance of NbFeSb-based TE devices, the relevance of which is also currently emphasized in the quest for commercial viability. © 2021 Elsevier B.V.Item An Optimized Question Classification Framework Using Dual-Channel Capsule Generative Adversarial Network and Atomic Orbital Search Algorithm(Institute of Electrical and Electronics Engineers Inc., 2023) Revanesh, M.; Rudra, B.; Guddeti, R.M.R.The advancement in education has emphasized the need to evaluate the quality of the examination questions and the cognitive levels of students. Many educational institutions now acknowledge Bloom's taxonomy-based students' cognitive levels evaluating subject-related learning. Therefore, in this paper, a novel optimized Examination Question Classification framework, referred to as QC-DcCapsGAN-AOSA, is proposed by combining the Dual-channel Capsule generative Adversarial Network (DcCapsGAN) with Atomic Orbital Search Algorithm (AOSA) for preprocessing a real-time online dataset of university examination questions, thus identify the key features from the raw data using Term Frequency Inverse Document Frequency (TF-IDF) and finally classifying the examination questions. Atomic Orbital Search Algorithm is used to fine-tune the parameters' weights of the DcCapsGAN, and then uses these weights to categorize questions as Knowledge Level, Comprehension Level, Application Level, Analysis Level, Synthesis Level, and Evaluation Level. Experimental results demonstrate the superiority of the proposed method (QC-DcCapsGAN-AOSA) when compared to the state-of-the-art methods such as QC-LSTM-CNN and QC-BiGRU-CNN with an accuracy improvement of 23.65% and 29.04%, respectively. © 2013 IEEE.Item Revealing the Microscopic Picture of the Charge Transfer Mechanism between Graphene and Dopant Molecules(American Chemical Society, 2023) Khandelwal, V.; Srivastava, P.K.; Nagaraja, S.; Yadav, P.; Tarafder, K.; Ghosh, S.It is generally recognized that the dipole moment of the adsorbed molecules is a crucial factor in determining the charge-transfer interaction between molecules and graphene. However, the microscopic details of this process have remained elusive. In this study, we experimentally investigate the charge-transfer interaction between adsorbed molecules and graphene, which holds great promise for achieving controllable doping. By trapping various molecules at the graphene-substrate interface, our results emphasize that the doping effect primarily depends on the reactivity of the constituent atoms in the attached molecules rather than just their dipole moment. Observation of (i) the emergence of the Raman D peak exclusively at the edges for trapped molecules without reactive atoms, and throughout the entire basal plane for those with reactive atoms, and (ii) variations in the density of attached molecules (with and without reactive atoms) to graphene with their respective dipole moments provides compelling evidence to support our claim. These findings are well-supported by experimental results and first-principles density functional theory calculations. © 2023 American Chemical Society.Item On the merit of solute segregation and low angle grain boundary for thermal stability and thermal expansion of cold-sprayed CuCrZr(Elsevier Ltd, 2025) Abhijith Vijay; Sreerag, M.P.; Varalakshmi, S.; Santhy, K.; Singh, R.; Kondás, J.; Makineni, S.K.; Rajasekaran, B.The precipitation hardenable CuCrZr alloy is a potential alternative to copper for inner liners in rocket thrust engines. Cold spray manufacturing has been seen as a promising processing route to manufacture bulk additive structure of CuCrZr. This work reveals that the cold-sprayed as-deposited Cu-Cr-Zr alloy, in its inherent non-equilibrium state. It is highly stable up to 950 °C and exhibits lower thermal expansion than the equilibrium Cu-Cr-Zr alloy, deduced using HT-XRD and Thermo-Calc. Atomic-scale compositional and diffraction analysis using Atom Probe Tomography (APT) and Electron Backscatter Diffraction (EBSD) support the Zener pinning effect of Cr segregation near the grain boundaries, along with a large fraction of low-angle grain boundaries (LAGBs), that contribute to the high thermal stability and controlled thermal expansion of the deposit. Cold spray deposition naturally yields microstructural features that are conducive to high thermal stability and controlled thermal expansion, features which are comparable to the self-organized microstructures observed in segregation engineering (SE). © 2025 Elsevier B.V.