Faculty Publications
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Item Enhanced photocatalytic efficiency of layered CdS/CdSe heterostructures: Insights from first principles electronic structure calculations(Institute of Physics Publishing helen.craven@iop.org, 2020) Shenoy, S.; Tarafder, K.Metal sulfides are emerging as an important class of materials for photocatalytic applications, because of their high photo responsive nature in the wide visible light range. In this class of materials, CdS with a direct band gap of 2.4 eV, has gained special attention due to the relative position of its conduction band minimum, which is very close to the energies of the reduced protons. However, the photogenerated holes in the valence band of CdS are prone to oxidation and destroy its structure during photocatalysis. Thus constructing a CdS based heterostructure would be an effective strategy for improving the photocatalytic performance. In this work we have done a detail theoretical investigation based on hybrid density functional theory calculation to get insight into the energy band structure, mobility and charge transfer across the CdS/CdSe heterojunction. The results indicate that CdS/CdSe forms type-II heterostructure that has several advantages in improving the photocatalytic efficiency under visible light irradiation. © 2020 IOP Publishing Ltd.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 Graphene Straintronics by Molecular Trapping(American Chemical Society, 2025) Srivastava, P.K.; Khandelwal, V.; Reddy, I.R.; Tarafder, K.; Ghosh, S.Here, we report on controlling strain in graphene by trapping molecules at the graphene–substrate interface and leveraging molecular dipole moments. Spectroscopic and transport measurements reveal that strain correlates with the dipole moments of trapped molecules extending beyond their molecular sizes, where values ranging from 1.5 to 4.9D lead to a 50-fold increase in strain and a significant rise in residual carrier density. This has been possible by charge transfer between graphene and trapped molecules, altering the C?C bond length and causing biaxial strain. First-principles density functional theory calculations confirm a consistent dependence of the bending height on molecular dipole moments. © 2025 American Chemical SocietyItem Thermally-driven conformational twist in organic azobenzene linker activates molecular doping effect in thin films of lanthanide MOFs(Royal Society of Chemistry, 2025) Bhoi, U.; Kalyani, M.; Ananthram, K.S.; Saha, S.; Acharya, A.; Hassan, N.; Raj, M.; Tarafder, K.; Ballav, N.Azobenzene-based photo-switchable molecules have shown significant potential in stimuli-responsive systems, especially when incorporated into metal–organic frameworks (MOFs). This study reports thin films of lanthanide-based metal–organic frameworks (Ln-MOFs) with 4,4?-azobenzene dicarboxylic acid (H2ADA) as the organic linker – Tb-ADA, Eu-ADA, and Gd-ADA – using an electrodeposition method. Upon heating to 400 K, a reversible structural transition was observed via variable temperature grazing-incidence X-ray diffraction (GIXRD) and Raman spectroscopy, not due to trans–cis isomerization but rather a thermally-induced conformational twist of the ADA linker. Density functional theory (DFT) combined with molecular dynamics (MD) simulations supports this interpretation, revealing high-energy atropisomeric states stabilized by MOF confinement. Molecular doping of these films with 7,7,8,8-tetracyanoquinodimethane (TCNQ) significantly enhanced their electrical conductivity, increasing by two orders of magnitude at 400 K. This enhancement is attributed to improved ?–? stacking and charge-transfer interactions facilitated by the conformational twist. Temperature-dependent X-ray photoelectron spectroscopy (XPS) confirmed redox activity in TCNQ@Tb-ADA films, showing reversible conversion between Tb(iii) and Tb(iv), with back electron transfer at 400 K restoring Tb(iii). These findings introduce a new mechanism of thermally-driven conformational switching in MOFs and open avenues for developing responsive electronic materials based on azobenzene linkers. This journal is © The Royal Society of Chemistry, 2025Item Synergistic Photoconductivity and Ultralow Thermal Conductivity upon Stabilizing Iron(III)-tris(2,2?-bipyridine) in a Two-Dimensional Haloargentate Network(American Chemical Society, 2025) Jose, T.M.; Hassan, N.; Ananthram, K.S.; Kalyani, M.; Tarafder, K.; Ballav, N.Crystalline organic–inorganic halometallate hybrids have emerged as promising materials for optoelectronic applications due to their structural diversity and tunable properties. We report a three-dimensional (3D) hybrid organic–inorganic crystal?[Fe(bpy)3]2Ag6Br11·NO3(bpy = 2,2? bipyridine)?consisting of two-dimensional (2D) Ag(I)-based (Ag6Br11)n5n–anionic sheets, zero-dimensional (0D) [Fe(bpy)3]3+complexes (acting as the structure-directing agent), and interlayer disordered NO3–anions. Specifically, the thermodynamically unstable cation [Fe(bpy)3]3+is stabilized under ambient conditions by the two-dimensional (2D) inorganic anionic scaffold. The crystal exhibits strong ligand-supported argentophilic interactions (Ag···Ag bond distance of 2.98 Å), forming an extended (Ag6Br11)n5n–network, and displays broad UV–visible absorption with a band gap of 1.90 eV. Remarkably, this organic–inorganic hybrid shows a ?103-fold increase in photocurrent under 532 nm light illumination. Density functional theory calculations provided the mechanistic insights, and such a remarkable photoconductivity is attributed to an efficient charge delocalization and inorganic-to-organic charge transfer. Additionally, the crystal exhibits an ultralow thermal conductivity over a broad temperature range (?0.3 W/m·K; 300–400 K), making it an excellent candidate for heat management applications. © 2025 American Chemical Society