BITS Faculty Publications
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Item Temperature dependent behavior of sub-monolayer quantum dot based solar cell(Elsevier, 2023-08) Kumar, RahulThis work investigates the temperature dependence of the performance of In(Ga)As-based solar cells made from sub-monolayer (SML) quantum dots (QDs), quantum wells (QWs), and Stranski-Krastanov QDs (SK-QDs). Well-defined sub-bandgap peaks are observed in external quantum efficiency (EQE) spectra for all samples. Apparently, changes in minority carrier lifetime affect both the sub-bandgap and the above bandgap EQE. Lateral confinement of carriers in the SMLs and QDs also affects the temperature dependence of the EQE. Finally, a “U” shaped curve was observed from the temperature dependence of the short-circuit current (ISC) from these nanostructure-based solar cells. This is due to the competition between the decreasing bandgap and the increasing carrier loss to recombination within the nanostructures as the temperature increases. In contrast, the solar cell's open-circuit voltage and power efficiency decrease monotonically with temperature.Item Aluminum as a competitive plasmonic material for the entire electromagnetic spectrum: A review(Elsevier, 2024-11) Arora, PankajWith plasmonics taking the lead in most sensing applications, research has geared towards alternative, cost-effective materials that can strive for large-scale production along with CMOS compatibility. Aluminum (Al) is among those competitive plasmonic metal films that have seen unprecedented research in recent years. The ability to exhibit appreciable plasmonic response in the entire electromagnetic spectrum has been reported along with improved performance sensing parameters. This review article covers different aspects of Al-based nanostructures, nano-films, and nano-particles in different wavelength regimes, displaying efficient plasmonic sensing for myriad purposes. A comprehensive review is conducted to explore the diverse and exciting possibilities emerging from Al-based tunable plasmons at the metal-dielectric interface. Al has already entered many applications, from on-chip plasmonic integration to point-of-care diagnosis. Thus, the application of Al in wide applications (heath, fluorescence, image-filtering techniques, and many more) is discussed here, along with the corresponding limitations and future scope associated with them.Item Growth and characterization of epitaxially stabilized ceria(001) nanostructures on Ru(0001)(RSC, 2016-05) Gangopadhyay, SubhashisWe have studied (001) surface terminated cerium oxide nanoparticles grown on a ruthenium substrate using physical vapor deposition. Their morphology, shape, crystal structure, and chemical state are determined by low-energy electron microscopy and micro-diffraction, scanning probe microscopy, and synchrotron-based X-ray absorption spectroscopy. Square islands are identified as CeO2 nanocrystals exhibiting a (001) oriented top facet of varying size; they have a height of about 7 to 10 nm and a side length between about 50 and 500 nm, and are terminated with a p(2 × 2) surface reconstruction. Micro-illumination electron diffraction reveals the existence of a coincidence lattice at the interface to the ruthenium substrate. The orientation of the side facets of the rod-like particles is identified as (111); the square particles are most likely of cuboidal shape, exhibiting (100) oriented side facets. The square and needle-like islands are predominantly found at step bunches and may be grown exclusively at temperatures exceeding 1000 °C.Item Highly Selective Low-Temperature Acetone Sensor Based on Hierarchical 3-D TiO2 Nanoflowers(IEEE, 2016-05) Manjuladevi, V.; Gupta, Raj KumarThe dimensionality of the nanostructures plays a pivotal role in determining the sensing performance of metal oxide semiconductors. In this paper, 2-D TiO 2 nanosheets were assembled to form hierarchical 3-D nanoflowers by a low-temperature hydrothermal process and tested for volatile organic compound (VOC) sensing. Structural characterization, such as X-ray diffraction, revealed the anatase crystallinity of the TiO 2 nanoflowers. The chemical composition of the nanoflowers was confirmed through energy dispersive spectroscopy and X-ray mapping techniques. Field emission scanning electron microscopy results demonstrated the 3-D nanoflower like structure, consisting of 2-D nanosheets of length 120 nm and a thickness of 12-23 nm. A suitable growth mechanism for hierarchical nanoflowers has been proposed. The nanoflowers were found to offer promising sensing performance toward VOCs, such as acetone, methanol, 2-butanone, toluene, and 2-propanol at relatively low optimum operating temperature of 60 °C, 90 °C, 60 °C, 120 °C, and 60 °C, respectively. The sensor appreciably showed fast response (~6-15 s) and recovery (~15-39 s) characteristics. Furthermore, the sensor offered high selectivity toward acetone. The sensing performance of the nanoflowers has been correlated with a space charge model at the grain boundary.Item ZnO Nanorod Based Ultra Sensitive and Selective Explosive Sensor(IEEE, 2013-02) Rao, V. RamgopalA small scale (20 μm), ultra sensitive (50 ppb) and highly selective sensor based on ZnO nanostructures using Micro-electro-mechanical system (MEMS) platform has been reported here for the detection of explosive and Volatile Organic Compound (VOC) vapors. Flower and rod like architectures of nanorods were used as a sensing layer. The nanorods prepared via chemical synthesis were uniform with diameters of 50-80 nm and lengths about 3-4 μm. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) reveal that the nanostructures are well oriented with the c-axis, perpendicular to the substrate. A relatively higher selectivity for 2, 4, 6-Trinitrotoluene (TNT) vapors compared to other VOCs at room temperature were observed. The intensity of deep level green emission peak associated with point defects decreases after exposure as revealed from Photoluminescence (PL) spectra.Item Mobility enhancement of solution-processed Poly(3-Hexylthiophene) based organic transistor using zinc oxide nanostructures(Elsevier, 2012-04) Rao, V. RamgopalThis work reports the mobility enhancement of p-type organic transistors formed using Poly(3-Hexylthiophene) (P3HT) using the dispersion of ZnO (zinc oxide) nanostructures. The ZnO nanostructures considered here are nanorods that were fabricated via a simple one-step aqueous-based chemical approach. Organic Thin Film Transistors (OTFTs) based on these nanocomposites show a mobility enhancement of more than 60% for the P3HT/ZnO nanorod composite compared to its pristine state polymer devices. The results presented here show a great promise for the mobility enhancement of p-type solution processed OFETs and applications.Item A molecular dynamics based artificial intelligence approach for characterizing thermal transport in nanoscale material(Elsevier, 2014-10) Sangwan, Kuldip SinghA molecular dynamics (MD)-based-artificial intelligence (AI) simulation approach is proposed to investigate thermal transport of carbon nanotubes (CNTs). In this approach, the effect of size, chirality and vacancy defects on the thermal conductivity of CNTs is first analyzed using MD simulation. The data obtained using the MD simulation is then fed into the paradigm of an AI cluster comprising multi-gene genetic programming, which was specifically designed to formulate the explicit relationship of thermal transport of CNT with respect to system size, chirality and vacancy defect concentration. Performance of the proposed model is evaluated against the actual results. We find that our proposed MD-based-AI model is able to model the phenomenon of thermal conductivity of CNTs very well, which can be then used to complement the analytical solution developed by MD simulation. Based on sensitivity and parametric analysis, it was found that length has most dominating influence on thermal conductivity of CNTs.Item Stain free colorimetric sensors using hybrid mode plasmonic microscopy(IEEE, 2016) Arora, PankajWe present colorimetric stain free image based sensing of antibody-antigen binding and refractive index perturbation, using substrates that support hybrid mode surface plasmons and demonstrate their integration with microfluidic channels for real time index sensing.Item Metal and Metal Oxide Nanostructure on Resin Support(Wiley, 2011-07-11) Basu, MrinmoyeeItem A Green Chemistry Approach for the Synthesis of Flower-like Ag-Doped MnO2 Nanostructures Probed by Surface-Enhanced Raman Spectroscopy(ACS, 2009) Basu, MrinmoyeeNovel hierarchical flower-like nanostructures of Ag-doped MnO2 have been obtained by facile wet chemical and photochemical routes. UV−visible absorption spectroscopy measurement reveals that doping of Ag nanoparticles in MnO2 nanostructures leads to a red shift of the absorption edge and reduces the optical band gap energy from 2.68 to 2.51 eV while compared with undoped MnO2. Raman study reveals that the band broadens and shifts toward higher wavenumbers as the MnO6 octahedron is contorted by Ag doping and thus the loss of translational symmetry activates otherwise Raman-forbidden oxygen vibrations. Finally, SERS activity upsurges from Ag-doped MnO2 with Rhodamine 6G and 2-aminothiophenol as probe molecules.