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Efficient colloidal route to pure phase kesterite Cu2ZnSnS4 (CZTS) nanocrystals with controlled shape and structure
No full textThis work reports the synthesis of varied shaped Cu2ZnSnS4 (CZTS) nano inks in a most stable kesterite phase via a hot injection colloidal route. CZTS nanoparticles of varied shape were synthesized by using various capping ligands with the introduction of butylamine as a new capping ligand and two different sulfur precursors respectively. The shape of the as synthesized kesterite CZTS nanocrystals can be well controlled in the form of nanofibers, spherical nanoparticles, nano hexagons, nanotriangles, and nanodiscs. A detailed analysis of the effects of various capping ligand and sulfur source on reaction conditions to obtain pure phase kesterite CZTS nanocrystals for different shapes is explained using LaMer's diagram. It has been found that the choice of sulfur precursor also plays an important role in determining the symmetry and orientation of the plane of the CZTS nanocrystals. Due to different morphology and capping ligands present on the surface, diverse surface properties were obtained which was confirmed by contact angle measurements. The variation in the band gap was also found with changes in morphology of kesterite phased CZTS nanoparticles. Due to variations obtained in band gap, changes in I-V characteristics were also observed which may leads different CZTS nanoparticles to have their potential applications in different regime other than photovoltaics like sensors, photocatalysis etc
Engineering novel synthetic strategy to develop mesocarbon microbeads for multi-functional applications
No full textTo assess the challenge of affordable technology, present synthetic strategies can be extended to new low-cost synthesis and processing methods that have potential to tailor the properties of the materials. Here we report, a novel method for the synthesis of mesocarbon microbeads (MCMB) through a preprocessing involved pyrolysis technique. The resulting MCMB is compressed into a product and effects of heat treatment temperature on different properties of MCMB is studied. The use of MCMB for the electromagnetic interference (EMI) shielding is new and hence, the effect of heat treatment temperature on EMI shielding effectiveness is studied in X-band. It is observed that EMI shielding effectiveness increases to -39.6 dB on increasing the heat treatment temperature. The high conductivity of MCMB plate heat treated up to 2500 degrees C contributes to highly conducting networks. Additionally, to investigate the electrochemical performance of MCMB as an anode material for lithium ion batteries, 2500 degrees C heat treated MCMB powder is used to fabricate the electrode. The MCMB electrode exhibits high discharge capacity of 345 mAh g(-1) with a stable capacity for over 50 cycles and good rate capability. Thus, MCMB synthesized by this novel approach can be used for the development of high performance anode materials for Li-ion batteries
D-pi-A-pi-D Structured Diketopyrrolopyrrole-Based Electron Donors for Solution-Processed Organic Solar Cells
No full textSolution-processable D-pi-A-pi-D structured two organic small molecules bearing thienyl diketopyrrolopyrrole (TDPP) and furanyl diketopyrrolopyrrole (FDPP) as central acceptor units and cyano on the pi-bridge and phenothiazine as the terminal donor units, coded as TDPP-PTCN and FDPP-PTCN, are designed and synthesized. The CH arylation and Suzuki coupling protocols have been adopted for synthesizing the molecules. Solution-processed organic solar cells (OSCs) were constructed with these molecules as the donors and phenyl-C-71-butyric acid methyl ester as the acceptor yielding power conversion efficiencies (PCE) of 4.0% for FDPP-PTCN and 5.2% for TDPP-PTCN, which is the highest PCE reported so far from the small molecular DPP-phenothiazine-based architecture for solution-based OSCs. The effect of heteroatom substitution on thermal stability and optoelectronic and photovoltaic performances is also systematically investigated herein. This work demonstrates that replacement of oxygen with sulfur in these kinds of small molecules remarkably improves the photovoltaic performance of OSCs
Evaluation of Humidity Sensor Based on PVP-RGO Nanocomposites
No full textThis paper describes the humidity sensing properties of one step in situ synthesized poly (N-vinyl pyrrolidone)- reduced graphene oxide (PVP-RGO) nanocomposites. Different PVP-RGO nanocomposites were obtained by varying PVP/GO weight %ratio as x/50 mg, wherein x = 25, 50, and 75 mg, respectively. The real-time adsorption kinetics of the water molecules during the humidity sensing were also discussed using Elovich model, pseudo first and second order equations. The increase in humidity response of 1.5 PVP-RGO nanocomposite is attributed to the presence of large amount of oxygen functionalities. The above observation was corroborated using spectroscopic analysis. The optimized PVP-RGO nanocomposite showed faster response kinetics with response and recovery times of 10 and 20 s, respectively. The present humidity sensor shows remarkable linearity over the range of 20-90%RH. More specifically, sensitivity was correlated with oxygen functionalities created due to variation of PVP during the functionalization of RGO nanosheets
Study of enhancement in the dielectric and electrical properties of WO3-doped LiF nano-composite
No full textWe report the dielectric and electrical behavior of thermally evaporated lithium fluoride (LiF)-tungsten trioxide (WO3) (x wt% WO3-doped LiF; x = 0, 1, 3, 5, 7, 10) nano-composite thin films at room temperature over a wide range of frequencies from 0.1 Hz to 1 MHz. Among the various doping concentrations of WO3, the 5 wt% WO3-doped LiF nano-composite thin film reaches to the maximum dielectric constant similar to 25, compared with those of pure LiF similar to 9 thin film. The electrical studies of the films have been done by complex impedance spectroscopy and show the presence of grain and grain boundaries contribution in the films for all doping concentrations. The relaxation behavior in the nano-composite films has been observed in the dielectric curve at low frequencies which is superimposed by electrode polarization. The non-Debye type of relaxation in the films has been observed in the impedance and modulus curve. The peaks appearing at low frequencies for each doping concentration in loss tangent spectrum show the presence of relaxing dipoles in the films. An increment in the ac conductivity has been observed with doping concentration up to 5%. The ac conductivity curves obey the jump relaxation power law where an electrode polarization effect can be seen at low-frequency region
Nitrogen doped high quality CVD grown graphene as a fast responding NO2 gas sensor
No full textNitrogen doped graphene (NGr) has been synthesized using a chemical vapor deposition (CVD) method for the fast detection of NO2 gas at room temperature. The quality of these NGr nanosheets has been confirmed using FESEM, XPS and Raman spectroscopy. Different nitrogen doping concentrations in the Gr lattice have been investigated by varying the growth time for the diffusion of nitrogen in the Gr lattice sites. The design and fabrication of the gas sensor device have been optimized using a SiO2 substrate and patterned gold electrodes. This nitrogen doped graphene honeycomb lattice improves the adsorption sites for gas molecules, which could improve the sensitivity of the gas sensor compared to CVD grown pristine graphene (Gr) nanosheets. Thus, the NGr nanosheet NO2 gas sensor reported here presents a better alternative for next generation ultrathin lightweight portable devices
Precursor ratio optimizations for the synthesis of colloidal CZTS nanoparticles for photocatalytic degradation of malachite green
No full textCu2ZnSnS4 (CZTS) is a foremost applicant material for photovoltaics application constituting environmentally friendly elements in Zn-rich Cu-poor configuration (Zn/Sn > 1, Cu/(Zn + Sn) 1, for Znrich) varied keeping other conditions and precursor ratios (Cu/(Zn + Sn), S/Metal = 1) constant. Different nanorods obtained were characterized by X-Ray Diffraction (XRD), Photoluminescence (PL) spectra and UV-Vis absorption spectroscopy and Transmission Electron Microscopy (TEM) respectively. The quality of different CZTS samples obtained was analyzed by XPS depth profiling analysis. Zn incorporation in both cases was optimized with respect to tin (Sn), phosphorus (P) and copper (Cu) for photocatalysis application. It was found that addition of more Zn into CZTS samples in precursors during synthesis may lead to lower incorporation of zinc amount, which results in varied properties advantageous for different photoactive applications. On the basis of different characterizations, CZTS nanorods synthesized with precursor ratio Zn: Sn = 2:1 was found to exhibits excellent photocatalytic activity as compared to other CZTS nanoparticles with precursor ratio Zn:Sn = 1.2:1 and 4:1 respectively, toward degradation of Malachite Green dye under sunlight
Magnetism by embedding 3d transition metal atoms into germanene
No full textWe have performed a series of first-principles calculations within the framework of density functional theory for germanene including mono vacancy (MV) and double vacancy (DV). Perdew-Burke-Ernzerhof generalized gradient approximation (GGA) in the form of exchange-correlation potential was used. Ten transition metals (TMs) i.e. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn, have been embedded at MV and DV site for the purpose to introduce magnetism into germanene. We find TM embedded germanene is stable and the value of magnetic moment can be tune with the TM impurities. Further, carbon (C) or nitrogen (N) in the vicinity of MV has been considered to find its influence on stability and total magnetic moment. Present predictions indicate Mn impurity shows largest magnetic moment among considered ten TMs. The Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional based calculations have been also carried out for Mn system only for shake of comparison standpoint. The GGA/HSE06 calculations show better stability of TM embedded germanene after doping of C or N in vicinity of TM. Our calculations may provide a promising approach to design germanene based spintronic devices
Microwave assisted scalable synthesis of titanium ferrite nanomaterials
No full textTitanium ferrite magnetic nanomaterials are synthesized by one-step, one pot, and scalable method assisted by microwave radiation. Effects of titanium content and microwave exposure time on size, shape, morphology, yield, bonding nature, crystalline structure, and magnetic properties of titanium ferrite nanomaterials are studied. As-synthesized nanomaterials are characterized by X-ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UV-Vis), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, transmission electron microscopy (TEM), and vibrating sample magnetometer measurements. XRD measurements depict the presence of two phases of titanium ferrite into the same sample, where crystallite size increases from similar to 33 nm to 37 nm with the increase in titanium concentration. UV-Vis measurement showed broad spectrum in the spectral range of 250-600 nm which reveals that its characteristic peaks lie between ultraviolet and visible region; ATR-FTIR and Raman measurements predict iron-titanium oxide structures that are consistent with XRD results. The micrographs of TEM and selected area electron diffraction patterns show formation of hexagonal shaped particles with a high degree of crystallinity and presence of multi-phase. Energy dispersive spectroscopy measurements confirm that Ti:Fe compositional mass ratio can be controlled by tuning synthesis conditions. Increase of Ti defects into titanium ferrite lattice, either by increasing titanium precursor or by increasing exposure time, enhances its magnetic properties
Investigation on sub nano-crystalline silicon thin films grown using pulsed PECVD process
No full textPresent work discusses the structural modifications in intrinsic layer of hydrogenated amorphous silicon (a-Si: H) deposited using Pulsed Wave Plasma Enhanced Chemical Vapor Deposition (PW-PECVD) technique which highlights the crystallite formation within the boundaries of nano crystallite silicon thin films. These investigations were carried out for the films deposited under the variation of applied pulsed power from 10W to 60 W. The resultant film phases were generalized as sub-nano crystalline silicon phases. The evolution of such phases has been effectively probed using various spectroscopic and structural characterization techniques including Raman spectroscopy, Fourier Transform Infrared spectroscopy (FTIR), and Field Emission Scanning Electron Microscopy (FESEM). The observed sub-nano crystalline volume fraction varies from similar to 28-46%. This marks the modification in crystallite growth from the partial nucleation to coalescence phase. From this the importance of pulsed wave PECVD (PW-PECVD) has been discussed in terms of high growth rates as well as the extended transition zones with the formation of sub-nano crystallite structures. The study found to be specific for understanding the sub-nano crystalline phases in the film silicon having high photo-stability and photo-response like in mu c/nc-Si: H (micro/nano crystalline silicon) and a-Si: H respectively