Bhavesh Sinha

Monodispersed wurtzite Cu2SnS3 nanocrystals by phosphine and oleylamine free facile heat-up technique

Wurtzite Cu2SnS3 (CTS) nanocrystals with an average size 8.5 nm were prepared for the first time by a phosphine and oleylamine free facile one-step thermolysis method. The as-prepared nanocrystals were investigated for structural, morphological and compositional properties. The advantages of the heat-up technique for a swift synthesis of gram scale, phase pure CTS nanocrystals; applicable for various energy devices like solar cell, batteries etc., are discussed. Nanocrystals were synthesized at different reaction times viz. 10, 20 and 30 minutes. The possible growth mechanism for colloidal CTS nanocrystals has been investigated. Herein we observed that CTS nanocrystals growth starts with the formation of copper sulphide nanoparticles, acting as nuclei for the subsequent growth of CTS nanocrystals. X-ray diffraction analysis revealed the formation of phase pure wurtzite CTS nanocrystals which is further supported by high resolution transmission electron microscopy, selected area electron diffraction and energy dispersive X-ray analysis. To the best of our knowledge colloidal wurtzite CTS nanocrystals synthesis has been reported with the use of strongly co-ordinating, highly toxic oleylamine (OLA) solvent, herein stepping towards a green synthesis we report for the first time on the synthesis of sub 10 nm wurtzite CTS nanocrystals using neutral, less toxic and less expensive octadecene (ODE) solvent.

Facile linker free growth of CdS nanoshell on 1-D ZnO: Solar cell application

One dimensional type-II core/shell heterostructures are widely employed in solar cells because of their adventitious role in both light absorption and charge separation. Here we report a facile two step chemical approach to synthesizing ZnO/CdS core/shell nanorod arrays. ZnO nanorods (ZNR) with a high aspect ratio were grown using a hydrothermal technique where a uniform CdS shell was deposited using a facile, linker free, one pot, Hexamethylenetetramine (HMTA) based reflux technique for the first time. Though the reflux technique is quite similar to the chemical bath deposition technique (CBD), we obtained more uniform CdS coating and improved solar cell performance with the ZnO/CdS heterostructure compared to CBD-grown ZnO/CdS heterostructures. To obtain a conformal coating of CdS, we optimized the CdS deposition time. Formation of pure phase ZnO/CdS core/shell heterostructure was confirmed by high resolution transmission electron microscopy and X-ray photoelectron spectroscopy (XPS) depth analysis. Improved solar cell performance of 1.23% was obtained for ZnO/CdS core/shell structures with ZnS surface treatment.

Sulfur ion concentration dependent morphological evolution of CdS thin films and its subsequent effect on photo-electrochemical performance

The sulfur ion concentration dependent morphological evolution and its subsequent effect on photo-electrochemical properties of chemically synthesized CdS thin films have been systematically investigated. The plausible growth mechanism for the morphological evolution of CdS thin films due to a change in sulfur ion concentration has been proposed. Scanning electron micrographs (SEMs) reveal that the morphology of CdS thin films has been changed from spherical grains to vertically aligned nanoflakes by systematic control of sulfur ion concentration. This article elucidates the astute relationships between precursor concentrations, reaction rate and morphological evolution. The X-ray diffraction (XRD) patterns reveal the formation of hexagonal wurtzite CdS thin films with the preferred (002) orientation for CdS nanoflakes, which is further supported by the analysis of the high resolution transmission electron micrographs (HRTEMs). Optical absorption studies show a red shift in the absorption edge with an increase in sulfur concentration. The beneficial role of nanoflake formation is easily reflected in the photo-electrochemical performance. Improved solar cell performances are observed for CdS nanoflakes grown with a sulfur to cadmium ion concentration ratio of 4 (S : Cd = 4).

Evidence of robust 2D transport and Efros-Shklovskii variable range hopping in disordered topological insulator (Bi 2 Se 3 ) nanowires

We report the experimental observation of variable range hopping conduction in focused-ion-beam (FIB) fabricated ultra-narrow nanowires of topological insulator (Bi2Se3). The value of the exponent (d + 1)−1 in the hopping equation was extracted as

Large magnetic entropy change at cryogenic temperature in rare earth HoN nanoparticles

\sim \frac{1}{2}\,\,

Synthesis, structure and magnetic properties of nanostructured La1−xAxFe0.5Mn0.5O3 (A = Ca, Sr and Pb; x = 0 & 0.25) perovskites

~12for different widths of nanowires, which is the proof of the presence of Efros-Shklovskii hopping transport mechanism in a strongly disordered system. High localization lengths (0.5 nm, 20 nm) were calculated for the devices. A careful analysis of the temperature dependent fluctuations present in the magnetoresistance curves, using the standard Universal Conductance Fluctuation theory, indicates the presence of 2D topological surface states. Also, the surface state contribution to the conductance was found very close to one conductance quantum. We believe that our experimental findings shed light on the understanding of quantum transport in disordered topological insulator based nanostructures.

Boosting the Performance of ZnO/CdS Core-Shell Nanorod Array-based Solar Cells by ZnS Surface Treatment

AbstractCadmium selenide (CdSe) thin films were grown by electrochemical technique on fluorine-doped tin oxide (FTO)-coated conducting glass substrates in the presence of organic surfactants. The influence of organic surfactants like polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) on different physico-chemical properties and its subsequent impact on photoelectrochemical (PEC) performance of CdSe thin films have been investigated. It has observed that the organic surfactants play an important role in modifying the surface morphology of CdSe thin films. The compact grain like morphology of pure CdSe is tuned to interconnected nanofibrous network on addition of PEG and to sprouting nanorods like morphology on addition of PVP. Among these nanostructures, CdSe sprouting nanorods exhibits improved power conversion efficiency of 0.55% as compared to nanofibrous (0.24%) and granular CdSe (0.16%) nanostructures. It reveals the fourfold enhancement in the PEC performance on PVP-mediated growth which can be attributed to conversion of compact dense nanostructure to porous and relatively high surface area nanostructure. This work exemplifies the ability of organic surfactant to modulate the surface morphology of the electrodeposits and pinpoints the organic surfactant that gives rise to the suitable morphology for PEC solar cell application. Graphical abstractTOC: The morphology of CdSe nanostructure has successfully tuned with use of surfactants to enhance the photoelectrochemical solar cell performance.

Solution-processed nanometers thick amorphous carbon-coated boron as an efficient precursor for high-field performance of MgB2

The most extensive cooling techniques based on gases have faced environmental problems. So, tremendous effort has been devoted to developing an alternative cooling technique and the search for solid state materials that show a large magnetocaloric effect (MCE) at cryogenic temperature. In the present work, we report the synthesis of HoN nanoparticles by a plasma arc discharge method with different composition of N2/H2 gases and its effect on magnetocaloric properties. HoN prepared under gas compositions (N2/H2: 40/60, 60/40, 80/20, and 100% N2) were structurally and morphologically characterized. The paramagnetic to ferromagnetic transition temperature TC is observed to be 13.9, 14.2, 14.5 and 14.2 K for all samples, respectively. The magnetic entropy change (−ΔSM) is found to be extended over a wide range of temperatures around TC, and its maximum value at an applied magnetic field of 5 T is obtained to be 27.7, 29.8, 30.2 and 34.2 J kg−1 K−1 for all investigated samples, respectively. It is noted that the relative cooling power improved significantly from 555 to 632 J kg−1 compared to 507 J kg−1 K−1 of bulk HoN. The larger MCE values obtained for HoN nanoparticles will be very useful for its cryogenic application.