Priyanka Yogi

Interfacial redox centers as origin of color switching in organic electrochromic device

Fabrication and operation of simple solid state electrochromic devices using ethyl viologen diperchlorate in a polymer matrix is presented here. In-situ Raman and transmission/absorption studies have been done to establish the origin of bias induced color change, between a transparent and navy blue color, in the electrochromic device. The origin of bias induced color change has been attributed to the bias induced redox switching between its viologen dication and free redicle forms. Fundamental reason behind colour changes of viologen molecule has been established. In-situ UV-Vis spectra reveals that the navy blue color of the device under biased condition is not due to increase in the transparency corresponding to blue wavelength but due to suppression of the transparency corresponding to the complementary colors. Absorption modulation has been reported from the device with good ON/OFF contrast of the device.

Role of metal nanoparticles on porosification of silicon by metal induced etching (MIE)

Abstract Porosification of silicon (Si) by metal induced etching (MIE) process has been studied here to understand the etching mechanism. The etching mechanism has been discussed on the basis of electron transfer from Si to metal ion (Ag + ) and metal to H 2 O 2 . Role of silver nanoparticles (AgNPs) in the etching process has been investigated by studying the effect of AgNPs coverage on surface porosity. A quantitative analysis of SEM images, done using Image J, shows a direct correlation between AgNPs coverage and surface porosity after the porosification. Density of Si nanowires (NWs) also varies as a function of AgNPs fractional coverage which reasserts the fact that AgNPs governs the porosification process during MIE. The Raman and PL spectrum show the presence of Si NSs in the samples.

Ecofriendly gold nanoparticles – Lysozyme interaction: Thermodynamical perspectives

In the featured work interaction between biosynthesized gold nanoparticles (GNP) and lysozyme (Lys) has been studied using multi-spectroscopic approach. A moderate association constant (Kapp) of 2.66×104L/mol has been observed indicative of interactive nature. The binding constant (Kb) was 1.99, 6.30 and 31.6×104L/mol at 291, 298 and 305K respectively and the number of binding sites (n) was found to be approximately one. Estimated values of thermodynamic parameters (Enthalpy change, ΔH=141.99kJ/mol, entropy change, ΔS=570J/mol/K, Gibbs free energy change, ΔG=-27.86kJ/mol at 298K) suggest hydrophobic force as the main responsible factor for the Lys-GNP interaction and also the process of interaction is spontaneous. The average binding distance (r=3.06nm) and the critical energy transfer distance (Ro=1.84nm) between GNP and Lys was also evaluated using Försters non-radiative energy transfer (FRET) theory and results clearly indicate that non-radiative type energy transfer is possible. Moreover, the addition of GNP does not show any significant change in the secondary structure of Lys as confirmed from circular dichroism (CD) spectra. Furthermore, NMR spectroscopy also indicates interaction between Lys and GNP. The resulting insight is important for the better understanding of structural nature and thermodynamic aspects of binding between the Lys and GNP.

Interplay between phonon confinement and Fano effect on Raman line shape for semiconductor nanostructures: Analytical study

Abstract Theoretical Raman line shape functions have been studied to take care of quantum confinement effect and Fano effect individually and jointly. The characteristics of various Raman line shapes have been studied in terms of the broadening and asymmetry of Raman line shapes. It is shown that the asymmetry in the Raman line-shape function caused by these two effects individually does not add linearly to give asymmetry of line-shape generated by considering the combined effect. This indicates existence of interplay between the two effects. The origin of interplay lies in the fact that Fano effect itself depends on quantum confinement effect and in turn provides an asymmetry. This can not be explained by considering the two effects contribution independent of each other.

Fast electrochromic display: tetrathiafulvalene–graphene nanoflake as facilitating materials

A new electrochromic gel (EC-Gel)-based active material has been prepared by using ethyl viologen (EV)–graphene nanoflakes (GNFs)–tetrathiafulvalene (TTF) for a faster and more efficient electrochromism. A prototype flexible electrochromic device has been fabricated by using the above-mentioned EC-Gel as an active layer which shows overall improved coloring efficiency as high as 208 (C cm−2)−1. At the same time, the abovementioned electrochromism shows color switching at a bias of 1.6 V with coloration/bleaching times as low as 0.4 and 0.9 seconds, respectively, which is better in comparison to that of other traditional EC-Gel or non EC-Gel-based electrochromic devices. Redox activity of EV–TTF pair results in such a fast bias induced color switching. Besides acting as an electrolyte, GNFs also facilitate achieving a faster bleaching time by allowing reversing the redox process quickly. The abovementioned facilitation is done by temporarily storing the electrons, which are released by EV during coloring cycle, to be supplied to TTF in the bleaching cycle through ballistic channels in graphene. An in situ UV-Vis spectroscopy establishes a transmission change of ∼45% in its stable state reversibly for more than 2500 cycles when the device is tested under ambient conditions.

Synthesis of Conducting Polypyrrole-Titanium Oxide Nanocomposite: Study of Structural, Optical and Electrical Properties

Optical and electronic properties of hybrid Polypyrrole (Ppy)–Titanium oxide (TiO2) nanocomposite, synthesized using oxidative chemical polymerization method have been investigated here. The synthesized organic–inorganic hybrid materials have been characterized using XRD, FT-IR, FESEM, UV–Vis, Raman, and TGA. Electrical conductance and dielectric behavior of the electrical phenomena of the sample have also been investigated. XRD results demonstrate the amorphous nature of Ppy, however, its composites with TiO2 exhibit crystalline nature. FT-IR spectroscopy reveals the presence of interaction between conducting Ppy and TiO2. UV–Vis study show changes in spectra of Ppy in presence of TiO2 with a slight increase in the band gap. The SEM results reveal encapsulation of TiO2 particles in Ppy matrix and agglomeration of grains have also been observed with evident changes in morphology with increasing percentages of TiO2. TGA data indicates that the composite materials show good thermal stability. Conductance results show that electrical conductivity of Ppy increases upon addition of TiO2. It has also been noticed that the dielectric parameters (dielectric constant, loss tangent) of Ppy vary with addition of TiO2. The resulting insight clearly suggests that by embedding TiO2 in Ppy the electrical properties of the composites can be improved.

Tent-Shaped Surface Morphologies of Silicon: Texturization by Metal Induced Etching

Nano-metal/semiconductor junction dependent porosification of silicon has been studied here. The silicon nanostructures (SiNSs) have been textured on n- and p- type silicon wafers using Ag (silver) and Au (gold) metal nano particles induced chemical etching. The combinations of n-silicon/Ag as well as p-silicon/Au form ohmic contact and result in the same texturization on the silicon surface on porosification, where tent-shaped morphology has been observed consistently in both n- and p-type silicon. Whereas, porosification result in different surface texturization for other two combinations (p-silicon/Ag and n-silicon/Au) where Schottky contacts are formed. Quantitative analysis have been done using ImageJ to process the scanning electron microscopy images of silicon NS, which confirms that the tent like silicon NS are formed when Ohmic junction is built. These easily prepared sharp tent-shaped Si NSs can be used for enhanced field emission applications.

Significant field emission enhancement in ultrathin nano-thorn covered NiO nano-petals

A power efficient and stable field emission (FE) has been reported here from ultrathin nanothorn covered nickel oxide (NiO) nanopetals (NPs) fabricated using a simple hydrothermal technique. Three orders of magnitude improved electron FE, in terms of threshold and turn-on fields, has been observed from these NiO-NPs. Uniform and vertically aligned NiO-NP structures, grown on a very flat conducting surface (FTO coated glass), show sharp needle like structures on the top edges of the flakes. These ultrafine structures play the main role in FE starting at such a low turn on field. A field enhancement factor of approximately five million and threshold field of 3 V mm−1 has been estimated by analyzing the FE data (J–E plot) within the framework of Fowler–Nordheim (FN). Modification in device geometry and surface micro- (nano-) structure has been found to play the key role in addressing the bottlenecks in achieving an efficient FE.

An insight of spirooxindole-annulated thiopyran – DNA interaction: spectroscopic and docking approach of these biological materials

Abstract The interaction of spirooxindole-annulated thiopyran (STP) with calf thymus DNA (CTDNA) has been studied here using spectroscopic and molecular modeling. A static mode of quenching has been observed from the fluorescence quenching mechanism of ethidium bromide (EB)–CTDNA by STP. A moderately strong binding affinity between STP and CTDNA has been observed (3.98, 2.51, 0.79 × 103 L mol−1 at 293, 303 and 313 K) from the fluorimetric data. Thermodynamic parameter, enthalpy change (ΔH) and entropy change (ΔS), suggested van der Walls force and hydrogen bonds played the main role in the binding of STP to CTDNA. Furthermore, circular dichroism (CD) revealed that STP did not disturb native conformation of CTDNA. As observed in the UV absorption and fluorescence spectroscopy the binding mode of STP with DNA was indicative of a non-intercalative binding, which was supposed to be a groove binding. Above mentioned results are found to be in consonance with molecular docking simulations and supports the STP–CTDNA binding with docking binding energy of -11.00 kcal/mol.

Construction of well aligned highly dense Cobalt nanoneedles for efficient device application

Abstract One step morphology transformation has been reported here by the addition of ammonium fluoride. Two different morphologies of the same structure have been reported for Cobalt Oxide nanostructures. Cobalt oxide nanoneedles in which, one is sleazy needles (s-NDs) and other one is erected needles (e-NDs) have been synthesised. Hydrothermal method has been used for the construction of both the nanoneedles structure. Morphological study by SEM attributes conversion of sleazy bowed done shape to well aligned ones, highly dense and sharp nanostructures. Quantitative analysis shows that after addition of ammonium fluoride, randomly distributed network of nanoneedles converts into a surface covered with vertically aligned, sharp and dense nanoneedles.