Browsing by Author "Upadhyaya, Hari"

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    Graphene-like dispersion and strong optical absorption in two-dimensional RP-type Sr3Ti2S7 perovskite
    (American Chemical Society, 2023-11-15) Liu, Hairui; Gao, Rui; Yang, Jien; Banthia, Rohan Dinesh; Yang, Feng; Wang, Tianxing; Upadhyaya, Hari; Jain, Sagar M.
    Two-dimensional (2D) Ruddlesden–Popper (RP) perovskite alloys have recently become attractive due to many desired physical properties originating from distinct van der Waals-type layered structures. In this work, a novel 2D RP-type Sr3Ti2S7 perovskite material design is proposed by using first-principles calculations. Our results reveal that the 2D Sr3Ti2S7 perovskite possesses dynamically stable structures, direct band structures with a band gap value of 0.86 eV, and a smaller effective mass (0.15/0.25 m0 for electron/hole) than MAPbI3 and phosphorene. More importantly, 2D Sr3Ti2S7 possesses wide optical spectra (from infrared-to ultraviolet-light region) and a higher absorption coefficient (105 cm–1) than MAPbI3, silicon, and MoS2 in the visible-light region. Interestingly, we also find that the ideal Dirac-like linear dispersion can appear near the Fermi level in the electronic band structures when compressive strain is applied. Especially, the Dirac-cone-like band structures can be realized when compressive strain is enhanced to −6%, indicating ultrahigh carrier mobility. These properties make the 2D Sr3Ti2S7 perovskite a promising candidate for future applications in solar cells and optoelectronic devices.
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    Large-scale manufacturing route to metamaterial coatings using thermal spray techniques and their response to solar radiation
    (Springer, 2021-07-04) Faisal, Nadimul Haque; Sellami, Nazmi; Venturi, Federico; Hussain, Tanvir; Mallick, Tapas; Muhammad-Sukki, Firdaus; Bishop, Alex; Upadhyaya, Hari; Katiyar, Nirmal Kumar; Goel, Saurav
    Metamaterials, an artificial periodic two- or three-dimensional configuration can change propagation characteristics of electromagnetic waves (i.e., reflection, transmission, absorption). The current challenges in the field of metamaterial coatings are their manufacturing in large scale and large length scale. There is a clear need to enhance process technologies and scalability of these. Thermal spraying is a method used to deposit small to large scale coatings where the sprayed layer is typically formed by successive impact of fully or partially molten particles of a material exposed to various process conditions. This work aims to investigate the feasibility to manufacture large scale metamaterial coatings using the thermal spray technique and examine their response to solar radiation. Two types of coatings namely, Cr2O3 and TiO2 were deposited onto various substrates (e.g., steel, aluminium, glass, indium tin oxide (ITO) coated glass) with a fine wire mesh (143 µm and 1 mm aperture sizes) as the masking sheet to manipulate the surface pattern using suspension high-velocity oxy-fuel thermal spraying (S-HVOF) and atmospheric plasma-sprayed (APS) methods, respectively. Post deposition, their responses subjected to electromagnetic wave (between 250 nm to 2500 nm or Ultraviolet (UV)-Visible (Vis)-Infrared (IR) region) were characterised. The additional microstructural characterisation was performed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), three-dimensional profilometry and optical spectroscopy. It is demonstrated that through novel application of thermal spray techniques, large scale manufacturing of metamaterial coating is possible, and such material can affect the electromagnetic wave propagation. Comparison between Cr2O3 and TiO2 coatings on aluminium substrates showed reduced three orders of reduced reflectance for Cr2O3 coatings (for 1 mm aperture size) throughout the spectrum. It was concluded that for a similar bandgap, Cr2O3 coatings on aluminium substrate will yield improved optical performance than TiO2 coating, and hence more useful to fabricate opto-electronic devices.