53 results on '"Pratibha, Dev"'
Search Results
2. Site-Dependent Properties of Quantum Emitters in Nanostructured Silicon Carbide
- Author
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Tamanna Joshi and Pratibha Dev
- Subjects
Physics ,QC1-999 ,Computer software ,QA76.75-76.765 - Abstract
Deep defects in silicon carbide (SiC) possess atomlike electronic, spin, and optical properties, making them ideal for quantum computing and sensing applications. In these applications, deep defects are often placed within fabricated nanostructures that modify defect properties due to surface and quantum confinement effects. Thus far, theoretical studies exploring deep defects in SiC have ignored these effects. Using density-functional theory, this work demonstrates site dependence of properties of bright negatively charged silicon monovacancies within a SiC nanowire. It is shown that the optical properties of defects depend strongly on the hybridization of the defect states with the surface states and on the structural changes allowed by proximity to the surfaces. Additionally, analysis of the first-principles results indicates that the charge-state conversion and/or migration to thermodynamically favorable undercoordinated surface sites can deteriorate deep-defect properties. These results illustrate the importance of considering how finite-size effects tune defect properties and of creating mitigating protocols to ensure the charge-state stability of a defect within nanostructured hosts. more...
- Published
- 2022
- Full Text
- View/download PDF
Catalog
3. Substrate-Induced Modulation of Quantum Emitter Properties in 2D Hexagonal Boron Nitride: Implications for Defect-Based Single Photon Sources in 2D Layers
- Author
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Sai Krishna Narayanan and Pratibha Dev
- Subjects
General Materials Science - Published
- 2023
- Full Text
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4. Charge Transport through Superexchange in Phenothiazine–7,7,8,8-Tetracyanoquinodimethane (PTZ–TCNQ) Cocrystal Microribbon FETs Grown Using Evaporative Alignment
- Author
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Scott Melis, Samantha Hung, Chaitali Bagade, Yuri Chung, Eleni Hughes, Xinran Zhang, Paola Barbara, Peize Han, Tingting Li, Daniel McCusker, Robert Hartsmith, Jeffery Bertke, Pratibha Dev, Iris Stone, Jaydeep Joshi, Patrick Vora, and Edward Van Keuren more...
- Subjects
Materials Chemistry ,Electrochemistry ,Electronic, Optical and Magnetic Materials - Published
- 2022
- Full Text
- View/download PDF
5. Healing Se Vacancies in Bi2Se3 by Ambient Gases
- Author
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Sharmila N. Shirodkar, Gregory M. Stephen, Aubrey T. Hanbicki, Adam L. Friedman, and Pratibha Dev
- Subjects
General Energy ,Physical and Theoretical Chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2022
- Full Text
- View/download PDF
6. Fingerprinting quantum emitters in hexagonal boron nitride using strain
- Author
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Pratibha Dev
- Subjects
Physics ,QC1-999 - Abstract
Two-dimensional van der Waals crystals and their heterostructures provide an exciting alternative to bulk wide-band-gap semiconductors as hosts of single-photon emitters. Among different layered materials, bright and robust defect-based single-photon emitters have been observed within hexagonal boron nitride, a layered wide-band-gap semiconductor. Despite research efforts to date, the identities of the deep defects responsible for quantum emissions in hexagonal boron nitride remain unknown. In this theoretical work, I demonstrate that the strain-induced changes in emission frequencies depend on (i) the detailed nature of the defect states involved in the optical excitations, and (ii) the rich boron chemistry that results in complex interactions between boron atoms. As each defect shows a distinct response to the strain, it can be used not only to tune emission frequencies but also to identify the quantum emitters in hexagonal boron nitride. more...
- Published
- 2020
- Full Text
- View/download PDF
7. Quantum materials interfaces: Graphene/bismuth (111) heterostructures
- Author
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Ivan I. Naumov and Pratibha Dev
- Subjects
Physics ,QC1-999 - Abstract
Heterostructures involving graphene and bismuth, with their ability to absorb light over a very wide energy range, are of interest for engineering next-generation optoelectronics. Critical to the technological application of such heterostructures is an understanding of the underlying physics governing their properties. Here, using first-principles calculations, we study the interfacial interactions between graphene and bismuth thin films. Our study reveals nonintuitive phenomena associated with the moiré physics of these superlattices. We show a preservation of graphene-derived Dirac cones in spite of proximity to a substrate with large spin-orbit coupling, a greater influence of graphene on the electronic structure properties of bismuth, and the surprising presence of a magnetic solution, only slightly higher in energy (by several meV) than the nonmagnetic structure, possibly validating experiments. Such subtle and unanticipated phenomena associated with the moiré physics are expected to play key roles in the practical applications of heterogeneous assemblies of two-dimensional quantum systems. more...
- Published
- 2020
- Full Text
- View/download PDF
8. One-dimensional magnetism and Rashba-like effects in zigzag bismuth nanoribbons
- Author
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Ivan I. Naumov and Pratibha Dev
- Subjects
Physics and Astronomy (miscellaneous) ,General Materials Science - Published
- 2023
- Full Text
- View/download PDF
9. Magnetotransport in Graphene/Pb
- Author
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Gregory M, Stephen, Ivan, Naumov, Nicholas A, Blumenschein, Y-J, Leo Sun, Jennifer E, DeMell, Sharmila N, Shirodkar, Pratibha, Dev, Patrick J, Taylor, Jeremy T, Robinson, Paul M, Campbell, Aubrey T, Hanbicki, and Adam L, Friedman more...
- Abstract
While heterostructures are ubiquitous tools enabling new physics and device functionalities, the palette of available materials has never been richer. Combinations of two emerging material classes, two-dimensional materials and topological materials, are particularly promising because of the wide range of possible permutations that are easily accessible. Individually, both graphene and Pb more...
- Published
- 2022
10. Predicting phase preferences of two-dimensional transition metal dichalcogenides using machine learning
- Author
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Pankaj Kumar, Vinit Sharma, Sharmila N. Shirodkar, and Pratibha Dev
- Subjects
Condensed Matter - Materials Science ,Physics and Astronomy (miscellaneous) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Materials Science - Abstract
Two-dimensional transition metal dichalcogenides (TMDs) can adopt one of several possible structures, with the most common being the trigonal prismatic and octahedral symmetry phases. Since the structure determines the electronic properties, being able to predict phase-preferences of TMDs from just the knowledge of the constituent atoms is highly desired, but has remained a long-standing problem. In this study, we applied high-throughput quantum mechanical computations with machine learning algorithms to solve this old problem. Our analysis provides insights into determining physiochemical factors that dictate the phase-preference of a TMD, identifying and going beyond the attributes considered by earlier researchers in predicting crystal structures. A knowledge of these underlying physiochemical factors not only helps us to rationalize, but also to accurately predict structural preferences. We show that machine learning algorithms are powerful tools that can be used not only to find new materials with targeted properties, but also to find connections between elemental attributes and the target property/properties that were not previously obvious. more...
- Published
- 2022
- Full Text
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11. Quantum transport in functionalized epitaxial graphene without electrostatic gating
- Author
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M. S. Osofsky, Joseph Prestigiacomo, R. L. Myers-Ward, Anindya Nath, D. K. Gaskill, Pratibha Dev, Thomas L. Reinecke, and Evgeniya H. Lock
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Materials science ,Graphene ,Dirac (software) ,Doping ,Physics::Optics ,Fermi energy ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Nanocrystal ,Hall effect ,Chemical physics ,law ,Phase (matter) ,Surface modification ,General Materials Science ,Physics::Chemical Physics ,0210 nano-technology - Abstract
Graphene, the first isolated two-dimensional material, has captivated researchers for the last decade due to its unique structure that leads to novel electronic, chemical, mechanical, and thermal properties. The most intriguing properties are the large electronic mobilities that are achievable for low carrier concentrations and the large tunability of graphene’s electrical properties via electrostatic gating, in which the Fermi energy is shifted relative to the charge neutrality, or Dirac, point and the high electronic mobilities obtained when the Fermi energy is close to that point. In this report, we show that both covalent and non-covalent functionalization of graphene leads to adsorbate-induced doping. This results in a three-fold increase in the graphene systems’ mobilities and the observation of quantum transport phenomena (Hall effect plateaus, Shubnikov-de Haas oscillations, and Berry’s phase) which were not observed in the unfunctionalized graphene. This ability to control the electronic properties without electrostatic gating is critical for chemical and biological sensing, optical, and electronic applications, which require both low carrier concentrations and the attachment of nanocrystals, biomolecules, increased adhesion and wettability of graphene layers, and enable strong cohesion between graphene layers in stacked graphene structures. more...
- Published
- 2021
- Full Text
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12. Magnetotransport in graphene/Pb0.24Sn0.76Te heterostructures: finding a way to avoid catastrophe
- Author
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Gregory M. Stephen, Ivan Naumov, Nicholas A. Blumenschein, Y.-J. Leo Sun, Jennifer E. DeMell, Sharmila N. Shirodkar, Pratibha Dev, Patrick J. Taylor, Jeremy T. Robinson, Paul M. Campbell, Aubrey T. Hanbicki, and Adam L. Friedman more...
- Subjects
Condensed Matter - Materials Science ,General Engineering ,General Physics and Astronomy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Materials Science - Abstract
While heterostructures are ubiquitous tools enabling new physics and device functionalities, the palette of available materials has never been richer. Combinations of two emerging material classes, two-dimensional materials and topological materials, are particularly promising because of the wide range of possible permutations that are easily accessible. Individually, both graphene and Pb0.24Sn0.76Te (PST) are widely investigated for spintronic applications because graphene's high carrier mobility and PST's topologically protected surface states are attractive platforms for spin transport. Here, we combine monolayer graphene with PST and demonstrate a hybrid system with properties enhanced relative to the constituent parts. Using magnetotransport measurements, we find carrier mobilities up to 20,000 cm2/Vs and a magnetoresistance approaching 100 percent, greater than either material prior to stacking. We also establish that there are two distinct transport channels and determine a lower bound on the spin relaxation time of 4.5 ps. The results can be explained using the polar catastrophe model, whereby a high mobility interface state results from a reconfiguration of charge due to a polar/non-polar interface interaction. Our results suggest that proximity induced interface states with hybrid properties can be added to the still growing list of remarkable behaviors in these novel materials. more...
- Published
- 2022
13. Organic Dyes Containing Coplanar Dihexyl-Substituted Dithienosilole Groups for Efficient Dye-Sensitised Solar Cells
- Author
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Ciaran Lyons, Neelima Rathi, Pratibha Dev, Owen Byrne, Praveen K. Surolia, Pathik Maji, J. M. D. MacElroy, Aswani Yella, Michael Grätzel, Edmond Magner, Niall J. English, and K. Ravindranathan Thampi
- Subjects
Renewable energy sources ,TJ807-830 - Abstract
A chromophore containing a coplanar dihexyl-substituted dithienosilole (CL1) synthesised for use in dye-sensitised solar cells displayed an energy conversion efficiency of 6.90% under AM 1.5 sunlight irradiation. The new sensitiser showed a similar fill factor and open-circuit voltage when compared with N719. Impedance measurements showed that, in the dark, the charge-transfer resistance of a cell using CL1 in the intermediate-frequency region was higher compared to N719 (69.8 versus 41.3 Ω). Under illumination at AM 1.5G-simulated conditions, the charge-transfer resistances were comparable, indicative of similar recombination rates by the oxidised form of the redox couple. The dye showed instability in ethanol solution, but excellent stability when attached to TiO2. Classical molecular dynamics indicated that interactions between ethanol and the dye are likely to reduce the stability of CL1 in solution form. Time-dependent density functional theory studies were performed to ascertain the absorption spectrum of the dye and assess the contribution of various transitions to optical excitation, which showed good agreement with experimental results. more...
- Published
- 2017
- Full Text
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14. Effect of Sn Doping on Surface States of Bi2Se3 Thin Films
- Author
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Gregory M. Stephen, Ivan Naumov, Aubrey T. Hanbicki, Pratibha Dev, Jennifer DeMell, Adam L. Friedman, Isaak D. Mayergoyz, Patrick J. Taylor, Michael Dreyer, Siddharth Tyagi, Owen Vail, and R. E. Butera more...
- Subjects
Materials science ,business.industry ,Doping ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,Topological insulator ,Optoelectronics ,Condensed Matter::Strongly Correlated Electrons ,Electronics ,Physical and Theoretical Chemistry ,Thin film ,business ,Quantum computer ,Surface states - Abstract
Bi2Se3, widely studied as a topological insulator, has great potential for applications in low-power electronics and quantum computing. Intrinsic doping, however, presents a persistent challenge, l... more...
- Published
- 2020
- Full Text
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15. Non-linear hybrid surface-defect states in defective Bi$_2$Se$_3$
- Author
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Sharmila N Shirodkar and Pratibha Dev
- Subjects
Condensed Matter - Materials Science ,General Energy ,Condensed Matter - Mesoscale and Nanoscale Physics ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Physical and Theoretical Chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
Surface-states of topological insulators are assumed to be robust against non-magnetic defects in the crystal. However, recent theoretical models and experiments indicate that even non-magnetic defects can perturb these states. Our first-principles calculations demonstrate that the presence of Se vacancies in Bi$_2$Se$_3$, has a greater impact than a mere n-doping of the structure, which would just shift the Fermi level relative to the Dirac point. We observe the emergence of a non-linear band pinned near the Fermi level, while the Dirac cone shifts deeper into the valence band. We attribute these features in the bandstructure to the interaction between the surface and defect states, with the resulting hybridization between these states itself depending on the position and symmetry of the Se vacancy relative to the surfaces. Our results bring us a step closer to understanding the exotic physics emerging from defects in Bi$_2$Se$_3$ that remained unexplored in prior studies. more...
- Published
- 2022
16. Peripheral chiral spin textures and topological Hall effect in CoSi nanomagnets
- Author
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Rabindra Pahari, Balamurugan Balasubramanian, Ahsan Ullah, Priyanka Manchanda, Hiroaki Komuro, Robert Streubel, Christoph Klewe, Shah R. Valloppilly, Padraic Shafer, Pratibha Dev, Ralph Skomski, and David J. Sellmyer more...
- Subjects
Physics and Astronomy (miscellaneous) ,0103 physical sciences ,General Materials Science ,02 engineering and technology ,021001 nanoscience & nanotechnology ,010306 general physics ,0210 nano-technology ,01 natural sciences - Published
- 2021
- Full Text
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17. Site-dependent properties of quantum emitters in nanostructured silicon carbide
- Author
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Tamanna Joshi and Pratibha Dev
- Subjects
Condensed Matter - Materials Science ,General Engineering ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Earth and Planetary Sciences ,General Environmental Science - Abstract
Deep defects in silicon carbide (SiC) possess atom-like electronic, spin and optical properties, making them ideal for quantum-computing and -sensing applications. In these applications, deep defects are often placed within fabricated nanostructures that modify defect properties due to surface and quantum confinement effects. Thus far, theoretical studies exploring deep defects in SiC have ignored these effects. Using density functional theory, this work demonstrates site-dependence of properties of bright, negatively-charged silicon monovacancies within a SiC nanowire. It is shown that the optical properties of defects depend strongly on the hybridization of the defect states with the surface states and on the structural changes allowed by proximity to the surfaces. Additionally, the analysis of the first principles results indicates that the charge-state conversion and/or migration to thermodynamically-favorable undercoordinated surface sites can deteriorate deep-defect properties. These results illustrate the importance of considering how finite-size effects tune defect properties, and of creating mitigating protocols to ensure a defect's charge-state stability within nanostructured hosts. more...
- Published
- 2021
18. Doping-limitations of cubic boron nitride: effects of unintentional defects on shallow doping
- Author
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Tamanna Joshi, Pankaj Kumar, Bipul Poudyal, Sean Paul Russell, Priyanka Manchanda, and Pratibha Dev
- Subjects
Condensed Matter - Materials Science ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
Cubic boron nitride (cBN) is an ultra-wide bandgap, super-hard material with potential for extreme-temperature and -pressure applications. A proof-of-principle p-n junction using cBN was demonstrated almost three decades ago. However, to date, there remain two unresolved challenges that prevent its practical use in technologies: (i) it is difficult to produce high-quality cBN films and (ii) it is difficult to controllably n- and p-dope its matrix. In this theoretical work, we study the reasons for doping-limitations, which is an acute issue in realizing cBN-based electronics. In particular, we find that different unintentionally-present intrinsic and extrinsic defects act as compensating defects and/or introduce trap states. In turn, the presence of these defects and their complexes affect the incorporation, as well as the electronic structure properties, of shallow dopants [silicon and beryllium], which are introduced intentionally to n- and p-dope cBN. Our analysis of doping-limitations provides a path towards finding solutions for controllably n- and p-doping cBN. more...
- Published
- 2021
19. Thickness dependence of hydrogen-induced phase transition in MoTe2
- Author
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P. Manchanda, Pankaj Kumar, and Pratibha Dev
- Subjects
Condensed Matter - Materials Science ,Phase transition ,Materials science ,Hydrogen ,Condensed matter physics ,business.industry ,Bilayer ,Kinetics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Semiconductor ,chemistry ,Transition metal ,Ab initio quantum chemistry methods ,0103 physical sciences ,Monolayer ,010306 general physics ,0210 nano-technology ,business - Abstract
Two-dimensional (2D) transition metal dichalcogenides (TMDs) usually exist in two or more structural phases with different physical properties, and can be repeatedly switched between these phases via different stimuli, making them potentially useful for memory devices. An understanding of the physics of interfaces between the TMDs and conventional semiconductors, or other 2D crystals forming heterogenous or homogeneous assemblies, is central to their successful application in technologies. However, to date, most theoretical works have explored phase-change properties of isolated TMD monolayers in vacuum. Using ab initio calculations, we show how interfacial effects modify the thermodynamics and kinetics of the phase transition by studying hydrogen-induced transitions in monolayers and bilayers of ${\mathrm{MoTe}}_{2}$. The phase-change properties of ${\mathrm{MoTe}}_{2}$ show substantial thickness dependence, with the timescale for a transition in the hydrogenated bilayer being about ${10}^{7}$ times longer than that in a monolayer at room temperature. Our study highlights the importance of taking effects of immediate environment into account when predicting properties of 2D crystals. more...
- Published
- 2020
- Full Text
- View/download PDF
20. Silicon-bridged triphenylamine-based organic dyes for efficient dye-sensitised solar cells
- Author
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Xinxin Xiao, J. M. D. MacElroy, Pathik Maji, Edmond Magner, K. Ravindranathan Thampi, Pratibha Dev, Ciaran Lyons, Praveen K. Surolia, Owen Byrne, Niall J. English, and Neelima Rathi
- Subjects
chemistry.chemical_classification ,Materials science ,Absorption spectroscopy ,Renewable Energy, Sustainability and the Environment ,Electron donor ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,Triphenylamine ,01 natural sciences ,0104 chemical sciences ,Absorbance ,chemistry.chemical_compound ,Dye-sensitized solar cell ,Aniline ,chemistry ,Moiety ,General Materials Science ,0210 nano-technology ,Alkyl - Abstract
Three dyes based on a triphenylamine (TPA) moiety using a silicon bridge have been synthesised, namely CL-1D, CL-OMe and CL-SiMe. Structural benefits of long alkyl chains and electron donor group on photo conversion efficiency (PCE) of dye sensitized solar cells is discussed. A previously synthesised dye, denoted CL-1, which contained long alkyl chains and exhibited an efficiency of 6.90%, was compared with CL-SiMe, which contained shorter alkyl chains and showed and efficiency of 3.41%. A large drop in Jsc and Voc was found to be the reason for the appreciable decline in efficiency for CL-SiMe vis-a-vis CL-1. Electron donor group studies were performed using CL-1D and CL-OMe. CL-1D, which contained bulky aniline electron donor groups, showed an efficiency of 4.20%, whilst CL-OMe, featuring smaller methoxy donor groups had an efficiency of 5.50%. Theoretical UV–Vis absorption spectra were obtained for the CL-1D dye by time-dependent density functional theory (TD-DFT); the experimental and calculated values of the energy for maximum absorbance were in good agreement with experimental data. more...
- Published
- 2018
- Full Text
- View/download PDF
21. Quantum materials interfaces: graphene/Bismuth (111) heterostructures
- Author
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Pratibha Dev and Ivan Naumov
- Subjects
Materials science ,Superlattice ,Dirac (software) ,FOS: Physical sciences ,chemistry.chemical_element ,02 engineering and technology ,Substrate (electronics) ,7. Clean energy ,01 natural sciences ,Bismuth ,law.invention ,law ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,010306 general physics ,Quantum ,Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics ,business.industry ,Graphene ,Materials Science (cond-mat.mtrl-sci) ,Heterojunction ,021001 nanoscience & nanotechnology ,Coupling (physics) ,chemistry ,Optoelectronics ,0210 nano-technology ,business - Abstract
Heterostructures involving graphene and bismuth, with their ability to absorb light over a very wide energy range, are of interest for engineering next-generation opto-electronics. Critical to the technological application of such heterostructures is an understanding of the underlying physics governing their properties. Here, using first-principles calculations, we study the interfacial interactions between graphene and bismuth thin-films. Our study reveals non-intuitive phenomena associated with the moir\'e-physics of these superlattices. We show a preservation of graphene-derived Dirac cones in spite of proximity to a substrate with large spin-orbit coupling, a greater influence of graphene on the electronic structure properties of bismuth, and the surprising presence of a magnetic solution, only slightly higher in energy (by several meV) than the non-magnetic structure, possibly validating experiments. Such subtle and unanticipated phenomena associated with the moir\'e-physics are expected to play key roles in the practical applications of heterogeneous assemblies of two-dimensional quantum systems. more...
- Published
- 2020
22. Defect-induced $4p$-magnetism in layered platinum diselenide
- Author
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Pratibha Dev, Pankaj Kumar, and P. Manchanda
- Subjects
Condensed Matter - Materials Science ,Materials science ,Condensed matter physics ,Magnetism ,Strong interaction ,chemistry.chemical_element ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Substrate (electronics) ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Diselenide ,chemistry ,Magnet ,0103 physical sciences ,Thin film ,010306 general physics ,0210 nano-technology ,Platinum - Abstract
Platinum diselenide (${\mathrm{PtSe}}_{2}$) is a recently-discovered extrinsic magnet, with its magnetism attributed to the presence of Pt vacancies. The host material to these defects itself displays interesting structural and electronic properties, some of which stem from an unusually strong interaction between its layers. To date, it is not clear how the unique intrinsic properties of ${\mathrm{PtSe}}_{2}$ will affect its induced magnetism. In this theoretical work, we show that the defect-induced magnetism in ${\mathrm{PtSe}}_{2}$ thin films is highly sensitive to: (i) defect density, (ii) strain, (iii) layer thickness, and (iv) substrate choice. These different factors dramatically modify all magnetic properties, including the magnitude of local moments, strength of the coupling, and even nature of the coupling between the moments. We further show that the strong interlayer interactions are key to understanding these effects. A better understanding of the various influences on magnetism can enable controllable tuning of the magnetic properties in Pt-based dichalcogenides, which can be used to design novel devices for magnetoelectric and magneto-optic applications. more...
- Published
- 2020
- Full Text
- View/download PDF
23. A multiconfigurational study of the negatively charged nitrogen-vacancy center in diamond
- Author
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Churna Bhandari, Pratibha Dev, Aleksander L. Wysocki, Kyungwha Park, and Sophia E. Economou
- Subjects
Physics ,Quantum Physics ,Condensed Matter - Materials Science ,Quantum sensor ,Center (category theory) ,Diamond ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,Coupling (probability) ,01 natural sciences ,Qubit ,Excited state ,0103 physical sciences ,engineering ,Atomic physics ,Quantum information ,010306 general physics ,0210 nano-technology ,Nitrogen-vacancy center ,Quantum Physics (quant-ph) - Abstract
Deep defects in wide band gap semiconductors have emerged as leading qubit candidates for realizing quantum sensing and information applications. Due to the spatial localization of the defect states, these deep defects can be considered as artificial atoms/molecules in a solid state matrix. Here we show that unlike single-particle treatments, the multiconfigurational quantum chemistry methods, traditionally reserved for atoms/molecules, accurately describe the many-body characteristics of the electronic states of these defect centers and correctly predict properties that single-particle treatments fail to obtain. We choose the negatively charged nitrogen-vacancy (NV$^-$) center in diamond as the prototype defect to study with these techniques due to its importance for quantum information applications and because its properties are well-known, which makes it an ideal benchmark system. By properly accounting for electron correlations and including spin-orbit coupling and dipolar spin-spin coupling in the quantum chemistry calculations, for the NV$^-$ center in diamond clusters, we are able to: (i) show the correct splitting of the ground (first-excited) triplet state into two levels (four levels), (ii) calculate zero-field splitting values of the ground and excited triplet states, in good agreement with experiment, and (iii) calculate the energy differences between ground and exited spin-triplet and spin-singlet states, as well as their ordering, which are also found to be in good agreement with recent experimental data. The numerical procedure we have developed is general and it can screen other color centers whose properties are not well known but promising for applications., Comment: 14 pages and 5 figures more...
- Published
- 2020
- Full Text
- View/download PDF
24. Controlling the Infrared Dielectric Function through Atomic-Scale Heterostructures
- Author
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Christopher J. Winta, Rhonda M. Stroud, Pratibha Dev, Alexander J. Giles, Thomas L. Reinecke, D. Scott Katzer, Ilya Razdolski, Jonathan P. Winterstein, Joshua R. Nolen, Nikolai Christian Passler, Igor Vurgaftman, Alexander Paarmann, Martin Wolf, Joseph G. Tischler, Neeraj Nepal, Joseph R. Matson, Juan Carlos Idrobo, Nabil Bassim, Ioannis Chatzakis, Daniel Ratchford, Jordan A. Hachtel, Michael B. Katz, Joshua D. Caldwell, Matthew T. Hardy, and Chase T. Ellis more...
- Subjects
Materials science ,Phonon ,Infrared ,Superlattice ,General Physics and Astronomy ,FOS: Physical sciences ,Physics::Optics ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Atomic units ,Article ,Condensed Matter::Materials Science ,interface phonon ,Condensed Matter::Superconductivity ,Polariton ,General Materials Science ,Condensed Matter - Materials Science ,business.industry ,Scattering ,second harmonic generation ,optic phonons ,General Engineering ,Materials Science (cond-mat.mtrl-sci) ,superlattice ,Surface phonon ,polar semiconductor ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Surface plasmon polariton ,surface phonon polaritons ,0104 chemical sciences ,infrared ,Optoelectronics ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,business - Abstract
Surface phonon polaritons (SPhPs), the surface-bound electromagnetic modes of a polar material resulting from the coupling of light with optic phonons, offer immense technological opportunities for nanophotonics in the infrared (IR) spectral region. However, once a particular material is chosen, the SPhP characteristics are fixed by the spectral positions of the optic phonon frequencies. Here, we provide a demonstration of how the frequency of these optic phonons can be altered by employing atomic-scale superlattices (SLs) of polar semiconductors using AlN/GaN SLs as an example. Using second harmonic generation (SHG) spectroscopy, we show that the optic phonon frequencies of the SLs exhibit a strong dependence on the layer thicknesses of the constituent materials. Furthermore, new vibrational modes emerge that are confined to the layers, while others are centered at the AlN/GaN interfaces. As the IR dielectric function is governed by the optic phonon behavior in polar materials, controlling the optic phonons provides a means to induce and potentially design a dielectric function distinct from the constituent materials and from the effective-medium approximation of the SL. We show that atomic-scale AlN/GaN SLs instead have multiple Reststrahlen bands featuring spectral regions that exhibit either normal or extreme hyperbolic dispersion with both positive and negative permittivities dispersing rapidly with frequency. Apart from the ability to engineer the SPhP properties, SL structures may also lead to multifunctional devices that combine the mechanical, electrical, thermal, or optoelectronic functionality of the constituent layers. We propose that this effort is another step toward realizing user-defined, actively tunable IR optics and sources. more...
- Published
- 2019
25. Chiral Magnetism and High-Temperature Skyrmions in B20-Ordered Co-Si
- Author
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David J. Sellmyer, Wenyong Zhang, Shah R. Valloppilly, Zhen Chen, Ahsan Ullah, Ralph Skomski, George C. Hadjipanayis, Lanping Yue, Balamurugan Balasubramanian, Pratibha Dev, Xingzhong Li, Priyanka Manchanda, Anandakumar Sarella, David A. Muller, and Rabindra Pahari more...
- Subjects
Quantum phase transition ,Materials science ,Condensed matter physics ,Spins ,Magnetism ,Skyrmion ,General Physics and Astronomy ,Order (ring theory) ,Crystal structure ,01 natural sciences ,0103 physical sciences ,Content (measure theory) ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,Spin-½ - Abstract
Magnets with chiral crystal structures and helical spin structures have recently attracted much attention as potential spin-electronics materials, but their relatively low magnetic-ordering temperatures are a disadvantage. While cobalt has long been recognized as an element that promotes high-temperature magnetic ordering, most Co-rich alloys are achiral and exhibit collinear rather than helimagnetic order. Crystallographically, the B20-ordered compound CoSi is an exception due to its chiral structure, but it does not exhibit any kind of magnetic order. Here, we use nonequilibrium processing to produce B20-ordered ${\mathrm{Co}}_{1+x}{\mathrm{Si}}_{1\ensuremath{-}x}$ with a maximum Co solubility of $x=0.043$. Above a critical excess-Co content (${x}_{c}=0.028$), the alloys are magnetically ordered, and for $x=0.043$, a critical temperature ${T}_{c}=328\text{ }\text{ }\mathrm{K}$ is obtained, the highest among all B20-type magnets. The crystal structure of the alloy supports spin spirals caused by Dzyaloshinskii-Moriya interactions, and from magnetic measurements we estimate that the spirals have a periodicity of about 17 nm. Our density-functional calculations explain the combination of high magnetic-ordering temperature and short periodicity in terms of a quantum phase transition where excess-cobalt spins are coupled through the host matrix. more...
- Published
- 2019
26. Nitrogen-Doped Graphene and Twisted Bilayer Graphene via Hyperthermal Ion Implantation with Depth Control
- Author
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Pratibha Dev, Cory D. Cress, James C. Culbertson, Jeremy T. Robinson, Scott W. Schmucker, Adam L. Friedman, and Joseph W. Lyding
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Materials science ,Graphene ,Doping ,General Engineering ,General Physics and Astronomy ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,law.invention ,symbols.namesake ,Molecular dynamics ,Ion implantation ,law ,0103 physical sciences ,Monolayer ,symbols ,General Materials Science ,Scanning tunneling microscope ,010306 general physics ,0210 nano-technology ,Bilayer graphene ,Raman spectroscopy - Abstract
We investigate hyperthermal ion implantation (HyTII) as a means for substitutionally doping layered materials such as graphene. In particular, this systematic study characterizes the efficacy of substitutional N-doping of graphene using HyTII over an N(+) energy range of 25-100 eV. Scanning tunneling microscopy results establish the incorporation of N substituents into the graphene lattice during HyTII processing. We illustrate the differences in evolution of the characteristic Raman peaks following incremental doses of N(+). We use the ratios of the integrated D and D' peaks, I(D)/I(D') to assess the N(+) energy-dependent doping efficacy, which shows a strong correlation with previously reported molecular dynamics (MD) simulation results and a peak doping efficiency regime ranging between approximately 30 and 50 eV. We also demonstrate the inherent monolayer depth control of the HyTII process, thereby establishing a unique advantage over other less-specific methods for doping. We achieve this by implementing twisted bilayer graphene (TBG), with one layer of isotopically enriched (13)C and one layer of natural (12)C graphene, and modify only the top layer of the TBG sample. By assessing the effects of N-HyTII processing, we uncover dose-dependent shifts in the transfer characteristics consistent with electron doping and we find dose-dependent electronic localization that manifests in low-temperature magnetotransport measurements. more...
- Published
- 2016
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27. Machine learning substitutional defect formation energies in ABO3 perovskites
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Pratibha Dev, Pankaj Kumar, Ghanshyam Pilania, and Vinit Sharma
- Subjects
010302 applied physics ,Materials science ,Ionic radius ,Dopant ,business.industry ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Machine learning ,computer.software_genre ,01 natural sciences ,Standard enthalpy of formation ,Oxidation state ,Lattice (order) ,0103 physical sciences ,Artificial intelligence ,Electronics ,0210 nano-technology ,business ,computer ,Quantum ,Perovskite (structure) - Abstract
Perovskite oxides are a promising material platform for use in a wide range of technological applications including electronics, sensors, fuel cells, and catalysis. This is owing to the extraordinary tunability of their physical and chemical properties via defect engineering. The feasibility and the stability of a defect, such as a substitutional dopant, in the host lattice is usually obtained via experiments and/or through detailed quantum mechanical calculations. Both of these conventional routes are expensive and time consuming. An alternative is a data-driven machine learning (ML)-based approach. In this work, we have applied ML techniques to identify the factors that influence defect formation energy, which is an important measure of the stability of the defects, in perovskite oxides. Using 13 elemental properties as features and random forest regression, we demonstrate a systematic approach to down-selecting from the larger set of features to those that are important, establishing a framework for accurate predictions of the defect formation energy. We quantitatively show that the most important factors that control the dopant stability are the dopant ionic size, heat of formation, effective tolerance factor, and oxidation state. Our work reveals previously unknown correlations, chemical trends, and the interplay between stability and underlying chemistries. Hence, these results showcase the efficacy of ML tools in identifying and quantifying different feature-dependencies and provide a promising route toward dopant selection in the perovskites. We have developed a framework that itself is general and can be potentially applied to other material classes. more...
- Published
- 2020
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28. Surface engineering with Chemically Modified Graphene
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Thomas L. Reinecke, Scott G. Walton, Pratibha Dev, Keith E. Whitener, Stanislav Tsoi, Sandra C. Hernández, Paul E. Sheehan, David R. Boris, Jeremy T. Robinson, Woo-Kyung Lee, and Shawn P. Mulvaney
- Subjects
Materials science ,Graphene ,law ,Nanotechnology ,Surface engineering ,law.invention - Published
- 2018
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29. van der Waals Screening by Single-Layer Graphene and Molybdenum Disulfide
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Jeremy T. Robinson, Stanislav Tsoi, Pratibha Dev, Thomas L. Reinecke, Adam L. Friedman, Paul E. Sheehan, and Rory Stine
- Subjects
inorganic chemicals ,Materials science ,Graphene ,Doping ,General Engineering ,General Physics and Astronomy ,Self-assembled monolayer ,Nanotechnology ,Substrate (electronics) ,law.invention ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,law ,Chemical physics ,symbols ,General Materials Science ,van der Waals force ,Silicon oxide ,Molybdenum disulfide ,Layer (electronics) - Abstract
A sharp tip of atomic force microscope is employed to probe van der Waals forces of a silicon oxide substrate with adhered graphene. Experimental results obtained in the range of distances from 3 to 20 nm indicate that single-, double-, and triple-layer graphenes screen the van der Waals forces of the substrate. Fluorination of graphene, which makes it electrically insulating, lifts the screening in the single-layer graphene. The van der Waals force from graphene determined per layer decreases with the number of layers. In addition, increased hole doping of graphene increases the force. Finally, we also demonstrate screening of the van der Waals forces of the silicon oxide substrate by single- and double-layer molybdenum disulfide. more...
- Published
- 2014
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30. Organic dyes containing coplanar dihexyl-substituted dithienosilole groups for efficient dye-sensitised solar cells
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K. Ravindranathan Thampi, Neelima Rathi, Michael Grätzel, Ciaran Lyons, Aswani Yella, Pratibha Dev, Edmond Magner, Praveen K. Surolia, Pathik Maji, Owen Byrne, Niall J. English, J. M. D. MacElroy, SFI, ERC, IRC, and HEA more...
- Subjects
Absorption spectroscopy ,Article Subject ,lcsh:TJ807-830 ,molecular-dynamics ,lcsh:Renewable energy sources ,02 engineering and technology ,010402 general chemistry ,Photochemistry ,7. Clean energy ,01 natural sciences ,Redox ,Molecular dynamics ,General Materials Science ,impedance spectroscopy ,Renewable Energy, Sustainability and the Environment ,Chemistry ,Energy conversion efficiency ,General Chemistry ,Chromophore ,021001 nanoscience & nanotechnology ,Electron transport chain ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Dielectric spectroscopy ,electron-transport ,charge-transfer ,Density functional theory ,0210 nano-technology - Abstract
peer-reviewed A chromophore containing a coplanar dihexyl-substituted dithienosilole (CL1) synthesised for use in dye-sensitised solar cells displayed an energy conversion efficiency of 6.90% under AM 1.5 sunlight irradiation. The new sensitiser showed a similar fill factor and open-circuit voltage when compared with N719. Impedance measurements showed that, in the dark, the charge-transfer resistance of a cell using CL1 in the intermediate-frequency region was higher compared to N719 (69.8 versus 41.3 Omega). Under illumination at AM 1.5G-simulated conditions, the charge-transfer resistances were comparable, indicative of similar recombination rates by the oxidised form of the redox couple. The dye showed instability in ethanol solution, but excellent stability when attached to TiO2. Classical molecular dynamics indicated that interactions between ethanol and the dye are likely to reduce the stability of CL1 in solution form. Time-dependent density functional theory studies were performed to ascertain the absorption spectrum of the dye and assess the contribution of various transitions to optical excitation, which showed good agreement with experimental results. PUBLISHED peer-reviewed more...
- Published
- 2017
31. Spin-photon entanglement interfaces in silicon carbide defect centers
- Author
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Sophia E. Economou and Pratibha Dev
- Subjects
Materials science ,Photon ,Silicon ,chemistry.chemical_element ,FOS: Physical sciences ,Bioengineering ,02 engineering and technology ,Quantum channel ,Quantum entanglement ,Quantum key distribution ,01 natural sciences ,Photon entanglement ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,General Materials Science ,Electrical and Electronic Engineering ,010306 general physics ,Spin-½ ,Quantum computer ,Quantum Physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,business.industry ,Mechanical Engineering ,General Chemistry ,021001 nanoscience & nanotechnology ,chemistry ,Mechanics of Materials ,Optoelectronics ,0210 nano-technology ,business ,Quantum Physics (quant-ph) - Abstract
Optically active spins in solid-state systems can be engineered to emit photons that are entangled with the spin in the solid. This allows for applications such as quantum communications, quantum key distribution, and distributed quantum computing. Recently, there has been a strong interest in silicon carbide defects, as they emit very close to the telecommunication wavelength, making them excellent candidates for long range quantum communications. In this work we develop explicit schemes for spin-photon entanglement in several SiC defects: the silicon monovacancy, the silicon divacancy, and the NV center in SiC. Distinct approaches are given for (i) single-photon and spin entanglement and (ii) the generation of long strings of entangled photons. The latter are known as cluster states and comprise a resource for measurement-based quantum information processing., Comment: Published version more...
- Published
- 2016
32. A TD-DFT study of the effects of structural variations on the photochemistry of polyenedyes
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J. M. D. MacElroy, Pratibha Dev, K. Ravindranathan Thampi, Saurabh Agrawal, and Niall J. English
- Subjects
Photochemistry ,General Chemistry ,Dye-sensitized solar cells ,Polyene ,Polyenes--Absorption and adsorption ,Improved performance ,chemistry.chemical_compound ,Donor group ,Charge transfer ,Adsorption ,chemistry ,Group (periodic table) ,Titanium dioxide ,Moiety ,Absorption (chemistry) ,TD-DFT ,Linker ,Polyene dyes ,Density functionals - Abstract
We report a TD-DFT study of three polyene dyes namely: NKX-2553, NKX-2554 and NKX-2569 in isolation as well as upon their adsorption on TiO2 nanoparticles. By choosing closely related dyes we wish to focus on the effects of structural variations on the absorption and charge-transfer properties of these systems. These three dyes show a non-intuitive trend in their respective efficiencies and therefore, were chosen to shed light on the structural components that contribute to this behaviour. Although, NKX-2554 has an additional donor group, it is less efficient compared to the simpler NKX-2553 dye that contains only one donor group. When NKX-2554 structure is slightly modified by lengthening the linker-group, one obtains the most efficient dye among this set, namely, NKX-2569. In this work, we show that the changes in the donor moiety has very little or no effect on the efficiency of these dyes as can be seen in the case of NKX-2553 and NKX-2554. On the other hand, the improved performance of NKX-2569-titania complex can be understood to be a result of the longer linker group. A better understanding of these properties within different dye-titania complexes is important for the continual improvement of DSSCs. In this regards, this study will serve to provide guidelines to improve efficiencies of novel organic dyes. Science Foundation Ireland Irish Research Council for Science, Engineering and Technology 12M embargo - release after 6/10/2012 - AV 7/10/2011 au, ke, - kpw22/12/11 more...
- Published
- 2012
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33. Molecular dynamics study of water in contact with the TiO2rutile-110, 100, 101, 001 and anatase-101, 001 surface
- Author
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Pratibha Dev, J. M. D. MacElroy, Niall J. English, and Ritwik S. Kavathekar
- Subjects
Anatase ,Chemistry ,Biophysics ,Molecular dynamics ,Oxides--Surfaces ,Condensed Matter Physics ,Oxide-water interface ,TiO2 surface ,Bond length ,Rutile ,Dipole ,Molecular geometry ,Chemical physics ,Computational chemistry ,Monolayer ,Titanium dioxide ,Molecule ,Physical and Theoretical Chemistry ,Molecular Biology - Abstract
We have carried out classical molecular dynamics of various surfaces of TiO2 with its interface with water. We report the geometrical features of the first and second monolayers of water using a Matsui Akaogi (MA) force field for the TiO2 surface and a flexible single point charge model for the water molecules. We show that the MA force field can be applied to surfaces other than Rutile-(110). It was found that water OH bond lengths, H-O-H bond angles and dipole moments do not vary due to the nature of the surface. However, their orientation within the first and second monolayers suggest that planar Rutile-(001) and Anatase-(001) surfaces may play an important role in not hindering removal of the products formed on these surfaces. Also, we discuss the effect of surface termination in order to explain the layering of water molecules throughout the simulation box. Science Foundation Ireland Irish Research Council for Science, Engineering and Technology Other funder Irish Centre for High End Computing 12M embargo: release in May 2012 - AV 24/05/2011 Duplicate item withdrawn - OR 17/08/2012 more...
- Published
- 2011
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34. Electron–phonon renormalization and phonon anharmonicity in metals
- Author
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Yu Xue, Pratibha Dev, and Peihong Zhang
- Subjects
Condensed matter physics ,Phonon ,Chemistry ,Anharmonicity ,Doping ,Diamond ,General Chemistry ,Electron ,Electronic structure ,engineering.material ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Renormalization ,Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,Materials Chemistry ,engineering ,Condensed Matter::Strongly Correlated Electrons ,Density functional theory - Abstract
Electron–phonon renormalization and phonon anharmonicity in metals are investigated by employing density functional theory based first-principles electronic structure methods. Using doped silicon, diamond, and MgB2 as examples, it is shown that phonon anharmonicity may be significantly renormalized by electron–phonon interactions, especially for phonon modes that couple strongly with electrons. The unusually large third-order anharmonic potential of the E 2 g phonon in MgB2 is largely due to the electron–phonon renormalization effect. more...
- Published
- 2008
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35. Stabilizing graphene-based organometallic sandwich structures through defect engineering
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Thomas L. Reinecke and Pratibha Dev
- Subjects
Materials science ,Spintronics ,Spin polarization ,business.industry ,Graphene ,Nanotechnology ,Condensed Matter Physics ,Nanomagnet ,Electronic, Optical and Magnetic Materials ,law.invention ,Hydrogen storage ,Semiconductor ,Transition metal ,Nanoelectronics ,law ,business - Abstract
In this theoretical work, we propose a chemical route to creating stable benzene-transition metal-graphene sandwich structures. The binding energy of the transition metal to graphene is enhanced through adsorption at appropriate defects, immobilizing the metal onto the graphene web. Capping the metal with a benzene ring further stabilizes the structure. The stability and the magnetic properties of these composite structures vary for different defects such as vacancies and nitrogen substitutionals in graphene. The proposed complexes have high cohesive energies and are either metallic or are small-band-gap semiconductors. Several of the proposed structures also have large spin polarization energies that make them suitable for use as nanomagnets in ambient conditions. This work also sheds light on the experimental results in the field where the sandwich structures may have been successfully created. We show that defect engineering is a viable option for creating designer, graphene-based structures that may play an important role in fields as diverse as spintronics, nanoelectronics, hydrogen storage, and catalysis. more...
- Published
- 2015
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36. Silicon vacancy center in 4H-SiC: Electronic structure and spin-photon interfaces
- Author
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Öney O. Soykal, Pratibha Dev, and Sophia E. Economou
- Subjects
Photon ,Materials science ,Silicon ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Center (category theory) ,chemistry.chemical_element ,FOS: Physical sciences ,Nanotechnology ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,chemistry.chemical_compound ,chemistry ,Vacancy defect ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Quantum metrology ,Silicon carbide ,010306 general physics ,0210 nano-technology ,Spin-½ - Abstract
Defects in silicon carbide are of intense and increasing interest for quantum-based applications due to this material's properties and technological maturity. We calculate the multi-particle symmetry adapted wave functions of the negatively charged silicon vacancy defect in hexagonal silicon carbide via use of group theory and density functional theory and find the effects of spin-orbit and spin-spin interactions on these states. Although we focused on $\textrm{V}_{\textrm{Si}}^-$ in 4H-SiC, because of its unique fine structure due to odd number of active electrons, our methods can be easily applied to other defect centers of different polytpes, especially to the 6H-SiC. Based on these results we identify the mechanism that polarizes the spin under optical drive, obtain the ordering of its dark doublet states, point out a path for electric field or strain sensing, and find the theoretical value of its ground-state zero field splitting to be 68 MHz, in good agreement with experiment. Moreover, we present two distinct protocols of a spin-photon interface based on this defect. Our results pave the way toward novel quantum information and quantum metrology applications with silicon carbide., Comment: 6 pages, 4 figures, 1 Table, Supplementary more...
- Published
- 2015
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37. RESPIRATORY FUNCTIONS IN TEXTILE MILL WORKERS: ROLE OF PEAK EXPIRATORY FLOW RATE
- Author
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Pratibha Dev, Seema Gupta, Varun Malhotra, and Yogesh Tripathi
- Subjects
Pharmacology ,Vital capacity ,business.industry ,Pharmaceutical Science ,respiratory tract diseases ,law.invention ,Toxicology ,FEV1/FVC ratio ,law ,measurement_unit.measuring_instrument ,Breathing ,Medicine ,Pharmacology (medical) ,Respiratory system ,business ,Peak flow meter ,Textile mill ,Body mass index ,Spirometer ,measurement_unit - Abstract
Background: Textile industries play a significant role in economical growth of the country. Health concern of these textile mill workers is the biggest challenge. Respiratory alterations were found in these workers with long term exposure of cotton dust. Effect of cotton dust on peak expiratory flow rate is not very well documented in the past.Aim/objective: The main objective of this study was the assessment of respiratory functions in textile mill workers along with the effect on peak expiratory flow rate in these workers.Material & Methods: 130 male textile mill workers were recruited for this study from the different sections of a textile mill. In which, 80 workers were present from exposed and remaining 50 were from non exposed area of a textile mill. 30 to 40 year of age workers with the working history of not more than 5 years, were included for the part of the study. Their Body mass index and respiratory functions were evaluated. Body mass index was calculated by using weight and height of an individual. Respiratory functions including Forced vital capacity and forced expiratory volume in 1 second was estimated by using spirometer and peak expiratory flow rate was measured by means of Wright’s peak flow meter.Results: the mean values of FVC, FEV1 and PEFR were found to be significantly (25kg/m2 were found with lower mean values of FVC, FEV1 and PEFR when compared with workers with BMI more...
- Published
- 2017
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38. Substrate effects: Disappearance of adsorbate-induced magnetism in graphene
- Author
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Pratibha Dev and Thomas L. Reinecke
- Subjects
Work (thermodynamics) ,Copper substrate ,Materials science ,Condensed matter physics ,Magnetic moment ,Magnetism ,Graphene ,Doping ,Substrate (electronics) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,Impurity ,law ,Physics::Chemical Physics - Abstract
In this theoretical work, we show that substrates play key roles in the properties of layered systems such as graphene by focusing on magnetic properties associated with adsorbates. Local magnetic moments formed in fluorinated and hydrogenated graphene layers are quenched when they are deposited on a copper substrate due to several interconnected effects: doping by the substrate, increased structural distortion, and broadening of the defect states. We find that these effects contribute in different degrees to the changes in the structural, electronic and magnetic properties of the system and that they vary between adsorbates. The most important factor in the disappearance of magnetism in the functionalized graphene is shown to be the formation of metal-carbide bonds and the subsequent broadening of the impurity states that erases their spin splitting. We show that interactions with the substrate and the formation of local magnetic moments can be modified using multiple layers of graphene. more...
- Published
- 2014
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39. Blood pressure variations in textile mill middle-aged male workers exposed to noise
- Author
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Pratibha Dev, Seema Gupta, Yogesh Tripathi, and Varun Malhotra
- Subjects
010302 applied physics ,Mean arterial pressure ,medicine.medical_specialty ,Physiology ,business.industry ,Diastole ,Sphygmomanometer ,01 natural sciences ,Pulse pressure ,Blood pressure ,Internal medicine ,0103 physical sciences ,Heart rate ,Cardiology ,Medicine ,Population study ,General Pharmacology, Toxicology and Pharmaceutics ,business ,010301 acoustics ,Body mass index - Abstract
Backgr ound: Continuous exposure to occupational noise may create physiological derangements of parameters pertaining to stress and anxiety of an individuals life. Controversial outcomes over the years from different studies made this a topic of debate. Aims and Objective: The aim of this study was to investigate the effect of noise exposure on blood pressure of textile mill workers depending on the intensity of noise. Materials and Methods: A total of 120 male textile mill workers were enrolled for the study. 30 workers from each section including weaving, spinning, packaging and administration section, of the textile mill on the basis of noise level, were selected. They were categorized into groups on the basis of high noise exposure and low noise exposure. The age group criteria for this study were 35-55 years. Blood pressure of this study population was estimated using sphygmomanometer using auscultatory method. Body mass index and heart rate were also noted. Results: Significant results were obtained in this study. 22.5% workers were found to be hypertensive in this study population. The maximum numbers of hypertensive were found in weaving section. 5.8% workers of the total study population were having isolated systolic hypertensive and isolated diastolic hypertensive. Systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and pulse pressure (PP) were found be significantly higher in high noise group ( more...
- Published
- 2017
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40. Graphene Chemical Modification
- Author
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Sandra Catalina Hernandez, Chad Junkermeier, Pratibha Dev, Woo Lee, Jeremy Robinson, Paul Sheehan, Thomas Reinecke, and Scott Walton
- Abstract
Graphene has been a research focus due to its numerous unique properties which have motivated vast interdisciplinary research in the search of materials for next-generation technologies. With its unique atomically thin nature, graphene has enabled a closer look at material surface interactions and highlighted the importance of surface interfaces, defects and adsorbates. Purposeful and native defects have demonstrated to have advantageous or adverse influences on the chemical, electrical, optical, mechanical and even magnetic properties of graphene. On the other hand, control of the localization of defects and their arrangement onto ordered and extended structures has enabled new graphene-based materials with novel properties. It is clear that fundamental understanding of the modification of graphene relies on the understanding of the chemical functionalization dynamics, kinetic barriers, chemical transitions, and diffusion energies experienced by the added adsorbates with the graphene surface as well as the influence of the substrate on each. Plasmas provide both ease and versatility by enabling a single tool process on a wide range of background gases. In particular, electron-beam generated plasmas can introduce different functional groups over a large coverage range with atomic layer precision, allowing for global or local surface chemistry modulation with a large range of functional group types. Here in we demonstrate the effect of functional group type and quantity on chemical and structural changes. In particular, the degree of graphene lattice distortion as they originate for -oxygen, -fluorine, -hydrogen and -nitrogen functionalities with increasing surface coverage, demonstrating chemical and structural dependence on functional group types (F, O, H, N) and substrate interactions. more...
- Published
- 2016
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41. Functional Assessment for Predicting Charge-Transfer Excitations of Dyes in Complexed State: A Study of Triphenylamine-Donor Dyes on Titania for Dye-Sensitized Solar Cells
- Author
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Niall J. English, Saurabh Agrawal, and Pratibha Dev
- Subjects
Chemistry ,Nanoparticle ,Charge (physics) ,Vis spectra ,Photochemistry ,Triphenylamine ,Dye-sensitized solar cells ,Triphenylamine dyes ,Dye-sensitized solar cell ,chemistry.chemical_compound ,Time-dependent density functional theory ,Molecule ,Density functional theory ,Physical and Theoretical Chemistry ,Excitation - Abstract
Time-dependent density functional theory (TD-DFT) was employed to calculate the UV/vis spectra for three of the triphenylamine (TPA)-donor dyes, TC1, L1, and LJ1, in isolation as well as when complexed with a titania nanoparticle. TPA-donor dyes are a class of promising organic dyes for use in dye-sensitized solar cells (DSSCs). The three dyes studied here are among the smallest of these molecules and provide important insight into the entire series of TPA dyes that are being explored as possible sensitizers in titania-based DSSCs. An attempt to calculate the optical spectra for these dyes within the B3LYP approximation to the exchange correlation functional produces erroneous results. However, Coulomb attenuated approximation (CAM-B3LYP) captures the correct photophysics of the dyes and produces more accurate charge-transfer excitation energies of their complexes with titania. This work shows that the extent to which a given approximation fails or succeeds to correctly predict the charge-transfer excitation energies in the isolated dyes is propagated in that it fails (or succeeds) to correctly predict the values of the excitation energies for the complexes. It is, therefore, important to determine the most appropriate functional for a dye before considering it in more complicated structures such as dye-titania complexes. SFI Solar Energy Conversion SRC [07/B1160/SRC]. Irish Research Council. AMS more...
- Published
- 2012
42. Dynamic Jahn-Teller Effect in theNV−Center in Diamond
- Author
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Bi-Ching Shih, Shengbai Zhang, Tesfaye A. Abtew, Yi-Yang Sun, Pratibha Dev, and Peihong Zhang
- Subjects
Physics ,Phonon ,Ab initio quantum chemistry methods ,Jahn–Teller effect ,Dephasing ,Excited state ,Center (category theory) ,engineering ,General Physics and Astronomy ,Diamond ,Quantum information ,engineering.material ,Atomic physics - Abstract
The negatively charged nitrogen-vacancy (${\mathrm{NV}}^{\ensuremath{-}}$) center in diamond is considered to be one of the most promising solid state systems for quantum information applications. Excited states of the ${\mathrm{NV}}^{\ensuremath{-}}$ center play a center role in the proposed applications. Using a combination of first-principles calculations and vibronic interaction model analysis, we establish the presence of a dynamic Jahn-Teller effect in the $^{3}E$ excited state. The calculated temperature-dependent dephasing rate for the zero phonon line as well as the splitting of the first two vibronic states are in good agreement with experiment. more...
- Published
- 2011
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43. Defect-induced magnetism in nitride and oxide nanowires: Surface effects and quantum confinement
- Author
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Pratibha Dev, Peihong Zhang, and Hao Zeng
- Subjects
Condensed Matter::Materials Science ,Materials science ,Condensed matter physics ,Magnetism ,Quantum dot ,Quantum wire ,Nanowire ,Density functional theory ,Magnetic semiconductor ,Nitride ,Thin film ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Abstract
Defect-induced local moment formation in GaN and ZnO nanowires is investigated using density functional theory-based first-principles electronic-structure methods. We find that quantum confinement and surface effects, coupled with strong structural relaxations in nanowires, significantly enhance the spin-polarization energy and reduce the defect formation energy. These results are consistent with the fact that unconventional magnetism is often found in nanostructures and thin films. more...
- Published
- 2010
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44. Unconventional magnetism in semiconductors: Role of localized acceptor states
- Author
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Peihong Zhang, Shengbai Zhang, and Pratibha Dev
- Subjects
Materials science ,Condensed matter physics ,Magnetic moment ,Condensed Matter::Other ,Magnetism ,Heisenberg model ,Magnetic semiconductor ,Condensed Matter Physics ,Acceptor ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,Ferromagnetism ,Vacancy defect ,Physics::Atomic and Molecular Clusters ,Antiferromagnetism ,Physics::Chemical Physics - Abstract
Magnetism induced by the localized defect states in the otherwise ``nonmagnetic'' $sp$ semiconductors---GaN and ZnO---is investigated using ab initio methods. The defects studied include the cation vacancy in ZnO, a potassium substitutional in GaN, and an acceptor like defect complex (gallium vacancy along with oxygen as an anion substitutional). In all three cases, spontaneous spin-polarized ground states are obtained within density-functional theory (DFT). Magnetic coupling between defect-induced local moments is also studied by mapping the DFT total energy to a nearest-neighbor Heisenberg model. The coupling between magnetic moments is found to be ferromagnetic for the case of cation vacancies in ZnO. This is also found to be the case for the potassium substitutional in GaN. However, the magnetic coupling is antiferromagnetic for the acceptorlike defect complex. A kinetic exchange model is used to explain this diverse magnetic behavior shown by the different systems. more...
- Published
- 2010
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45. Deterioration of lung functions in type II diabetic subjects from Northern India
- Author
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Vinay, Agarwal, Bhavyesh, Gupta, Pratibha, Dev, Yogesh, Kumar, Nisar, Ahmad, and K K, Gupta
- Subjects
Adult ,Blood Glucose ,Male ,Vital Capacity ,India ,Maximal Voluntary Ventilation ,Peak Expiratory Flow Rate ,Middle Aged ,Diabetes Mellitus, Type 2 ,Spirometry ,Case-Control Studies ,Forced Expiratory Volume ,Humans ,Female ,Lung - Published
- 2010
46. Prediction Of A Multi-Center Bonded Solid Boron Hydride for Hydrogen Storage
- Author
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Peihong Zhang, Tesfaye A. Abtew, Bi Ching Shih, Vincent H. Crespi, and Pratibha Dev
- Subjects
Phase transition ,Phase boundary ,Condensed Matter - Materials Science ,Materials science ,Hydrogen ,Hydride ,Cryo-adsorption ,chemistry.chemical_element ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,7. Clean energy ,3. Good health ,Electronic, Optical and Magnetic Materials ,Hydrogen storage ,chemistry ,Chemical physics ,0103 physical sciences ,Dehydrogenation ,010306 general physics ,0210 nano-technology ,Boron - Abstract
An ideal material for on-board hydrogen storage must release hydrogen at practical temperature and pressure and also regenerate efficiently under similarly gentle conditions. Therefore, thermodynamically, the hydride material must lie within a narrow range near the hydrogenation/dehydrogenation phase boundary. Materials involving only conventional bonding mechanisms are unlikely to meet these requirements. In contrast, materials containing certain frustrated bonding are designed to be on the verge of frustration-induced phase transition, and they may be better suited for hydrogen storage. Here we propose a novel layered solid boron hydride and show its potential for hydrogen storage. The absence of soft phonon modes confirms the dynamical stability of the structure. Charging the structure significantly softens hydrogen-related phonon modes. Boron-related phonons, in contrast, are either hardened or not significantly affected by electron doping. These results suggest that electrochemical charging may facilitate hydrogen release while the underlying boron network remains intact for subsequent rehydrogenation., Comment: 6 pages, 6 Figures submitted more...
- Published
- 2010
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47. Defect-Induced intrinsic magnetism in wide-gap III nitrides
- Author
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Peihong Zhang, Yu Xue, and Pratibha Dev
- Subjects
Physics ,Condensed Matter::Materials Science ,Spin polarization ,Condensed matter physics ,Magnetism ,Vacancy defect ,General Physics and Astronomy ,Electronic structure ,Magnetic semiconductor ,Nitride ,Wave function ,Duality (electricity and magnetism) - Abstract
Cation-vacancy induced intrinsic magnetism in GaN and BN is investigated by employing density-functional theory based electronic structure methods. The strong localization of defect states favors spontaneous spin polarization and local moment formation. A neutral cation vacancy in GaN or BN leads to the formation of a net moment of 3 muB with a spin-polarization energy of about 0.5 eV at the low density limit. The extended tails of defect wave functions, on the other hand, mediate surprisingly long-range magnetic interactions between the defect-induced moments. This duality of defect states suggests the existence of defect-induced or mediated collective magnetism in these otherwise nonmagnetic sp systems. more...
- Published
- 2007
48. Engineering Chemical Functionality in Graphene
- Author
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Sandra Catalina Hernandez, Paul Sheehan, Stanislav Tsoi, Pratibha Dev, Jeremy Robinson, Chad Junkermeier, Keith Whitener, Woo Lee, Thomas Reinecke, and Scott Walton
- Abstract
Graphene has attracted enormous attention due to its unique properties. Equally important is the ability to further tailor these properties through modification of select attributes such as surface chemistry, number of layers, sheet width, and edge structures. Manipulating the surface chemistry of graphene is important since the chemical composition strongly impacts the electronic properties as well as chemical reactivity both globally and locally. Precise control of the surface chemistry of graphene can also allow for subsequent surface procedures focused on band gap engineering, device fabrication and sensor applications. Given the strong impact of adsorbates, global chemical modification provides opportunities towards greater control over the properties of graphene films. Control over the spatial distribution of these groups provides an even greater functionality in that the local graphene reactivity can be manipulated, opening up a wealth of opportunities in biosensing, plasmonics, catalysis, smart surfaces, and heterojunction devices. This work demonstrates the ability to manipulate the chemistry of graphene while regulating the spatial distribution of various functional groups on the surface. Spatial control over structural and chemical changes is characterized through micro (m-Raman and high-resolution x-ray photoelectron spectroscopy (XPS) mapping and electrical measurements are used to determine how local changes in chemistry influence the electronic properties. Lastly, we show that the resulting chemical moieties can be used to manipulate the local surface reactivity of graphene, enabling programmable, site-specific electrochemical deposition. These findings demonstrate the ability to tailor the locality of the surface chemistry on graphene surfaces opening up a wide range of reactivity studies and synthesis capabilities, such as programmable material deposition. more...
- Published
- 2015
- Full Text
- View/download PDF
49. Determining the appropriate exchange-correlation functional for time-dependent density functional theory studies of charge-transfer excitations in organic dyes
- Author
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Niall J. English, Pratibha Dev, and Saurabh Agrawal
- Subjects
chemistry.chemical_compound ,Benzonitrile ,Work (thermodynamics) ,Field (physics) ,Chemistry ,Computational chemistry ,Excited state ,General Physics and Astronomy ,Charge (physics) ,Density functional theory ,Time-dependent density functional theory ,Physical and Theoretical Chemistry ,Alizarin - Abstract
UV-Vis spectra are calculated using time-dependent density functional theory for several organic dyes – 4-(N, N-dimethylamino) benzonitrile, alizarin, squaraine, polyene-linker dyes, oligothiophene-containing coumarin dyes (NKX series) and triphenylamine-donor dyes. Most of these dyes (except, for the first two) or their derivatives are considered to be promising organic dyes for dye-sensitized solar cells. An accurate description of the photophysics of such dyes is imperative for understanding and creating better dyes. To this end, we studied the dyes within several approximations to the exchange-correlation functional. The chosen functionals – PBE, M06L, B3LYP, M06, CAM-B3LYP, and wB97 – represent the various classes of approximations that are currently being used to study material properties. From amongst the six approximations studied here, CAM-B3LYP outperformed the others in its description of charge-transfer excitations in most (though, not all) of the dyes. This study shows why it is difficult to choose a particular functional a priori, especially when starting out with a new dye for solar cell application. A possible way to judge the fitness of an approximation is used in this work and it is shown to provide a good quantitative guideline for subsequent research in this field. more...
- Published
- 2012
- Full Text
- View/download PDF
50. First-principles study of the excited-state properties of coumarin-derived dyes in dye-sensitized solar cells
- Author
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K. Ravindranathan Thampi, J. M. D. MacElroy, Pratibha Dev, Saurabh Agrawal, and Niall J. English
- Subjects
Absorption spectroscopy ,Chemistry ,Coumarin derived dye ,General Chemistry ,Photochemistry ,Coumarin ,Dye-sensitized solar cells--Optical properties ,Dye-sensitized solar cell ,chemistry.chemical_compound ,Adsorption ,Deprotonation ,Coumarins ,Excited state ,Materials Chemistry ,TiO2 ,Titanium dioxide ,Density functional theory ,DSSC ,TD-DFT ,Linker ,Density functionals - Abstract
Using Time-Dependent Density Functional Theory (TD-DFT), we have investigated the optical properties of dye-sensitized solar cells (DSSCs) comprised of TiO2 nanoparticle sensitized with two coumarins, namely, NKX-2311 and NKX-2593. The two sensitizers (dyes) differ only in their linker moieties and are shown to have different absorption spectra when adsorbed on to the TiO2 surface. Knowledge of different light absorption and charge transfer (CT) behavior within these complexes is useful for further improving the photo-dynamics of newer organic dyes presently being designed and investigated worldwide. Moreover, we have also investigated the effect of deprotonation of the sensitizers' carboxylic groups during adsorption on the titania surface and the excited state electronic properties of the resulting species. Science Foundation Ireland Irish Research Council for Science, Engineering and Technology 12M embargo until June 2012 - AV 30/06/2011 au, ke - AS 08/07/2011 more...
- Published
- 2011
- Full Text
- View/download PDF
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