Browsing by Author "Nair, Sindhu S."

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Enhanced performance characteristics of electropolymerized poly (3, 4 ethylenedioxythiophene) films on ITO by one step cyclic voltammetry
(Springer, 2013-01) Nair, Sindhu S.
Thin films of Poly (3, 4 ethylenedioxythiophene) (PEDOT) was electropolymerized onto indium tin oxide (ITO) coated glass substrate by simple one step cyclic voltammetry technique in an aqueous potassium nitrate medium. PEDOT films deposited on ITO/glass substrates were characterized for its, electrical, optical and structural properties. The redox properties of PEDOT thin films were carried out using cyclic voltammetry. The diffusion coefficient of the polymer films was calculated from cyclic voltammogram, which showed a less value when compared to the previous reports. The FTIR spectrum revealed the presence of PEDOT polymer on the substrate and SEM result showed flower–like structures of PEDOT thin film on ITO/glass with particle size of ~150 nm.
Enhancement of electrochemical reversibility in Poly 3-hexylthiophene layers for flexible dynamic glass windows applications
(Elsevier, 2024-06) Nair, Sindhu S.
Thin films of Poly 3-hexylthiophene (P3HT) were deposited onto Indium Tin Oxide (ITO) coated glass substrates using a spin coating method and the films were vacuum annealed at different temperatures to study the effect of annealing on the electrochemical reversibility. From the absorption spectra, the variation of the optical band gap with annealing temperature was studied for different annealing temperatures. The optical band gap obtained for P3HT film deposited at room temperature (RT) was around 1.94 eV and 1.92 eV for the sample annealed at 100 °C. A cyclic voltammetry (CV) analysis showed that at certain applied redox potentials, P3HT thin films changed the colour from magenta to transparent and then back to magenta in the reverse potential. P3HT films annealed at 100 °C showed the best electrochemical reversibility among all the annealed samples. These electrically switchable electrochromic P3HT thin films can be used in flexible dynamic windows (FDWs) as smart windows for controlling the temperature and light in buildings, displays and mirror light modulators.
Fabrication of fast switching electrochromic window based on poly(3,4-(2,2-dimethylpropylenedioxy)thiophene) thin film
(Springer, 2016-02) Nair, Sindhu S.
An electroactive poly(3,4-(2,2-dimethylpropylenedioxy)thiophene) (PProDOT-Me2) thin film was electropolymerized by cyclic voltammetry technique, and its electrochemical and electrochromic properties were systematically studied. The prepared PProDOT-Me2 thin film was electrochemically reversible, and it showed a linear relation between peak current with scan rates. The electrochemical impedance spectrum also indicated the diffusion limitation of the film during charge/discharge process. The film showed a good color contrast (60 %) with a low applying potential of 1.2 V. The electrochromic window (ECW) based on PProDOT-Me2 film was fabricated and studied for its electrochromic performance. The color contrast of the device was achieved as 36 % at λmax of 560 nm. The switching speed of fabricated ECW for coloring and bleaching were almost 0.7 s in a range of +1.5 to −1.5 V. The fabricated device showed better cyclic current response and remarkable switching stability over 100 cycles. The novelty of the electrochromic window based on PProDOT-Me2 is the maximum absorbance at photopic wavelength that would be highly sensitive to human eyes.
Fabrication of novel thin film capacitor based on PVA/ZnO nanocomposites as dielectric material
(Springer, 2020-11) Nair, Sindhu S.
A three-layer thin film capacitor was designed and fabricated with PVA/ZnO nanocomposite as dielectric material. Addition of ZnO nanoparticles showed change in dielectric constant, which varied with frequency and weight percentage. ZnO nanoparticles of weight percentage of 0.5% is chosen for the synthesis of nanoparticles with a grain size of 54 nm, using cost-effective and simple co-precipitation method. It is a low-cost method for large-scale production without impurities. The agglomeration was reduced by adding the starch molecules so that the O–H functional groups could hold together to the nanoparticles at the earlier nucleation stage and can be removed when purification by centrifugation is done. Fourier-transform infrared spectroscopy analysis showed peaks due to the O–H groups in the polymer backbone, CH2 asymmetric and symmetric stretching, C–C stretching and Zn–O stretching, respectively, indicating formation of the proper film. From the profilometer, the thickness was calculated as 195.73 nm for the dielectric film. The fabricated device showed capacitance of 210 nF m−2 in par with the theoretical value (254.451 nF m−2) at 298 K.
Fourth order nonlinear elastic coefficients of hexagonal close packed lattice
(Elsevier, 1996-09) Nair, Sindhu S.
The expressions for the fourth-order elastic constants of a hexagonal close packed lattice is derived using the sublattice displacements to the second order in strains. These expressions together with the expressions for the second- and third-order elastic constants have been used to obtain the higher order nonlinear elastic coefficients in some hexagonal metals. These expressions are used to find the second-order, third-order and fourth-order elastic constants of cadmium. The pressure derivatives of their elastic constants are also obtained. The results obtained are compared with the available experimental results.
Generalized Grüneisen parameters and low temperature limit of lattice thermal expansion of cadmium and zirconium
(Springer, 2006-09) Nair, Sindhu S.
The generalized Grüneisen parameters (γ′ j ) and (γ″ j ) for cadmium and zirconium were calculated from the second- and third-order elastic constants to determine the low temperature limit of the volume thermal expansion of these metals of hexagonal symmetry. The low temperature limit of cadmium and zirconium was calculated to be positive values indicating a positive volume expansion down to 0 K even though many Grüneisen gammas were found to be negative.
Gray to transmissive electrochromic switching based on electropolymerized PEDOT-ionic liquid functionalized graphene films
(Springer, 2015-01) Nair, Sindhu S.
A supporting electrolyte based on lithium perchlorate has been functionalized with graphene (ionic liquid functionalized graphene (IFGR)) by facile electrochemical exfoliation of graphite rods in aq. LiClO4 solution. Poly(3,4-ethylenedioxythiophene) (PEDOT)-IFGR films were prepared by electropolymerization of EDOT monomer with IFGR as supporting electrolyte in ethanol at static potential of 1.5 V. The Raman, SEM, and XPS analysis of PEDOT-IFGR film confirmed the presence of functionalized graphene in the film. The PEDOT-IFGR films showed good electrochemical properties, better ionic and electrical conductivity, significant band gap, and excellent spectroelectrochemical and electrochromic properties. The electrical conductivity of PEDOT-IFGR film was measured as about 3968 S cm−1. PEDOT-IFGR films at reduced state showed strong and broad absorption in the whole visible region and remarkable absorption at near-IR region. PEDOT-IFGR film showed electrochromic response between transmissive blue and darkish gray at redox potential. The color contrast (%T) between fully reduced and oxidized states of PEDOT-IFGR film is 25 % at λ max of 485 nm. The optical switching stability of PEDOT-IFGR film has retained 80 % of its electroactivity even after 500 cycles.
Growth mechanism and angle-resolved photoemission spectra of cobalt oxide (CoO) thin films on Ag(1 0 0)
(Elsevier, 2004-09) Nair, Sindhu S.
Using Auger electron spectroscopy we have studied the growth of cobalt oxide on Ag(1 0 0) substrate at different substrate temperatures (25, 170 and 250 °C). The films grown at 170 °C substrate temperature were found to grow closest to a layer-by-layer growth mode. In order to experimentally investigate the electronic structure of the CoO films angle-resolved UV photoelectron spectra were recorded for a 10 ML CoO film that are discussed and compared with available experimental results.
Higher order elastic constants and generalised gruneisen parameters of elastic waves and low temperature thermal expansion of dysprosium
(Elsevier, 1997-12) Nair, Sindhu S.
The expressions for the 19 fourth order elastic constants, 10 third order elastic constants and six second order elastic constants are derived using the method of homogenous deformation with interactions extending up to second neighbours using the sublattice displacements to the second degree in strains. These expressions are used to obtain the higher order elastic constants and their pressure derivatives in dysprosium. Dysprosium belongs to the hexagonal class of crystals. The higher order elastic constants are used to find out the generalised Gruneisen parameters of the elastic waves propagating in different directions in dysprosium. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with the available reported values.
Higher order elastic constants and generalized Gruneisen parameters of elastic waves and low temperature thermal expansion of gadolinium
(Springer, 1996-12) Nair, Sindhu S.
Expressions for the higher order elastic constants are derived using the sublattice displacements to the second degree in strains. These expressions are used to obtain the higher order elastic constants and their pressure derivatives in gadolinium. The higher order elastic constants are used to find out the generalized Gruneisen parameters of the elastic waves propagating in different directions in gadolinium. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with the available reported values.
Higher Order Elastic Constants and Generalized Gruneisen Parameters of Elastic Waves and Low Temperature Thermal Expansion of Titanium
(Elsevier, 1997-02) Nair, Sindhu S.
The expressions for the 19 fourth order elastic constants, 10 third order elastic constants, and 6 second order elastic constants of a solid are derived using the method of homogenous deformation with interactions extending up to second neighbors using the sublattice displacements to the second degree in strains. These expressions are used to obtain the higher order elastic constants and their pressure derivatives in titanium. Titanium belongs to the hexagonal class of crystals. The higher order elastic constants are used to find the generalized Gruneisen parameters of the elastic waves propagating in different directions in titanium. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with the available reported values.
Higher order elastic constants and second pressure derivatives of zirconium
(IAEA, 1997) Nair, Sindhu S.
Expressions for the higher order elastic constants are derived using the sublattice displacements to the second degree in strains. These expressions together with the expressions for the second and third order elastic constants have been used to obtain the higher order elastic constants and the pressure derivatives to second order elastic constants of hexagonal zirconium. The results obtained are compared with the reported values. The second pressure derivatives of zirconium are also reported
An investigation on the performance of Di-isopropyl benzyl derivative of Poly (3, 4-propylene dioxythiophene) thin film based electrochromic pixels displays
(IOP, 2019-08) Nair, Sindhu S.
Electrochromic (EC) smart pixel display was designed and fabricated using a novel monomer di-4-isopropyl benzyl substituted (3, 4-propylene dioxythiophene) (ProDOT-IPBz2). The polymer thin film showed absorption between 450 and 650 nm at a fully reduced state. The absorption peak narrowed down slightly towards longer wavelength region (850–900 nm) at the oxidation states. Siju et al has reported the coloration efficiency (CE) of the thin film as ∼305 cm2C−1. The ProDot-IPBZ2 thin film was used to fabricate EC pixel display of 2 × 2 pixel array on a patterned ITO coated glass. The optical color contrast of the EC pixel display is 40% at 600 nm, with a switching time of about 2 s and 2.5 s respectively. The CE of EC pixel was found to be 555 cm2C−1 at 600 nm in the fully doped state. This EC pixel switched for more than 1000 cycles with good color contrast (<5% T). EC pixel displays showed transmissive, magenta and violet colored states at applied potentials of 1.5, −1.0 and −2.0 V respectively. This EC pixel display is efficient with faster response time and better color contrast.
Micromagnetic simulations of the domain structure and the magnetization reversal of Co50Ni50/Pt multilayer dots
(Elsevier, 2002-01) Nair, Sindhu S.
The domain structure and the switching field of Co50Ni50/Pt multilayer dots, prepared by laser interference lithography, were micromagnetically simulated. The simulations were carried out with a three-dimensional simulation package, optimized for large-scale problems. The single-domain state is the lowest energy state for dots with a diameter below 75 nm. The switching field was computed by using suitable minimization techniques, and was used to analyze the effect of size, dot shape and edge defects.
Novel high contrast electrochromic polymer materials based on 3,4-propylenedioxythiophene
(Elsevier, 2007-09) Nair, Sindhu S.
Mono and di allyl and napthyl substituted 3,4-propylenedioxythiophenes were synthesized and polymerized electrochemically. All the monomers were characterized for their molecular structures, and the polymers were characterized for their electrochemical properties. The disubstituted derivatives showed higher contrast than the corresponding mono substituted derivatives. The allyl substituted polymers showed higher contrast and faster switching time than corresponding napthyl substituted derivatives. The presence of the allyl group as the pendant can be used for further functionalization of the polymer.
Optical, electrochemical and morphological investigations of poly (3,4-propylenedioxythiophene)–sultone (PProDOT–S) thin films
(Springer, 2012-09) Nair, Sindhu S.
In this paper, we have carried out thin film characterization of poly(3,4-propylenedioxythiophene)–sultone (PProDOT–S), a derivative of electrochromic poly(3,4-propylenedioxythiophene) (PProDOT). PProDOT–S was deposited onto transparent conducting oxide coated glass substrates by solution casting method. Single wavelength spectrophotometry is used to monitor the switching speed and contrast ratio at maximum wavelength (λ max). The percentage transmittance at the λ max of the neutral polymer is monitored as a function of time when the polymer film is repeatedly switched. This experiment gives a quantitative measure of the speed with which a film is able to switch between the two states i.e. the coloured and the bleached states. PProDOT–S films were switched at a voltage of 1·9 V with a switching speed of 2 s at λ max of 565 nm and showed a contrast of ∼37%. Cyclic voltammetry performed at different scan rates have shown the characteristic anodic and cathodic peaks. The structural investigations of PProDOT–S films by IR spectra were in good agreement with previously reported results. Raman spectra of PProDOT–S showed a strong Raman peak at 1509 cm − 1 and a weak peak at 1410 cm − 1 due to the C = C asymmetric and symmetric stretching vibrations of thiophene rings. The morphological investigations carried out by using scanning electron microscope (SEM) of polymer films have shown that these polymers are found to be arranged in dense packed clusters with non-uniform distribution having an average width and length of 95 nm and 160 nm, respectively.
Optical, Electrochemical, and Structural Properties of Spray Coated Dihexyl Substituted Poly (3,4 Propylene Dioxythiophene) Film for Optoelectronics Devices
(Taylor & Francis, 2014-02) Nair, Sindhu S.
The dihexyl substituted poly (3,4-propylenedioxythiophene) (PProDOT-Hx2) thin films uniformly deposited by cost effective spray coating technique on transparent conducting oxide coated substrates. The electro-optical properties of PProDOT-Hx2 films were studied by UV-Vis spectroscopy that shows the color contrast about 45% with coloration efficiency of ∼ 185 cm2/C. The electrochemical properties of PProDOT-Hx2 films were studied by cyclic voltammetry and AC impedance techniques. The cyclic voltammogram shows that redox reaction of films are diffusion controlled and ions transportation will be faster on the polymer film at higher scan rate. Impedance spectra indicate that polymer films are showing interface charge transfer process as well as capacitive behavior between the electrode and electrolyte. The XRD of the PProDOT-Hx2 thin films revealed that the films are in amorphous nature, which accelerates the transportation of ions during redox process.
Orange Fluorescent Ru(III) Complexes Based on 4′-Aryl Substituted 2,2′:6′,2″-Terpyridine for OLEDs Application
(Springer, 2017-09) Nair, Sindhu S.
A series of ruthenium (III) complexes of the formulae [Ru(4-Mephtpy)2]Cl3(1) [Ru(L 1 )], [Ru(3,4,5-tmphtpy)2]Cl3(2) [Ru(L 2 )], and [Ru(4-thptpy)2]Cl3(3) [Ru(L 3 )], (where L = terpy = 2.2′:6′2″ terpyridine ligands) are synthesized. The complexes were characterized by elemental analyses, spectroscopic and electrochemical data. The density functional theory (DFT) outlines the geometric optimisation and electronic charge transition of these complexes. Photophysical studies describe that the luminescence of Ru(III) complexes is due to electronic transition between the energy levels of singly unoccupied molecular orbitals (SUMO) and singly occupied molecular orbitals (SOMO). It also exhibits the potential charge transfer to π–π* and n–π* states due to MLCT and ILCT processes of the complexes. The observed bands centered at 591 and 620 nm demonstrate that these emissions originated from the transition of SUMO to SOMO energy levels, that is, from the radiative decay from the doublet exciton. Due to the heavy metal effect of Ru(III) ions the photophysical behaviour depends on the MLCT process. In conclusion, that the all three Ru(L 1 -L 3 ) complexes are fallen orange emission.
A Photoemission study of CoO films on Au (111) Surface Science
(Elsevier, 2003-09) Nair, Sindhu S.
Angle-resolved ultraviolet photoemission spectroscopy has been used to study thin layers of Co and CoO on an Au(1 1 1) substrate. A bulk-like CoO layer was obtained for a nominal coverage of 7 ML Co, with Co evaporated in an oxygen atmosphere of 10−4 Pa and the Au(1 1 1) substrate at 350 K. Low-energy electron diffraction of this layer exhibits a (1 × 1) structure, indicating an unreconstructed CoO(1 1 1) surface. Considering the instability of a bulk-like terminated CoO surface, we assume stabilization by OH termination. At low coverage, the CoO layer is oxygen deficient and exhibits metallic character. For the bulk-like CoO layers we found band-like oxygen states and no detectable dispersion for the states near the Fermi edge, which is in agreement with previous investigations of single-crystalline CoO.
Specroelectrochemical, switching kinetics, and chronoamperometric studies of dibenzyl derivative of poly(3,4-propylenedioxythiophene) thin-film-based electrochromic device
(Wiley, 2014-04) Nair, Sindhu S.
The dibenzyl derivative of poly(3,4-propylenedioxythiophene) (PProDOT-Bz2) thin film is deposited onto ITO-coated glass substrate by electropolymerization technique. The electropolymerization of ProDOT-Bz2 is carried out by a three-electrode electrochemical cell. The cyclic voltammogram shows the redox properties of electrochemically prepared films deposited at different scan rates. The thin films prepared were characterized for its morphological properties to study the homogeniety. Classic six-layer structure of PProDOT-Bz2 electrochromic device using this material was fabricated and reported for the first and its characterizations such as spectroelectrochemical, switching kinetics, and chronoamperometric studies are performed. The color contrast of the thin film and the device achieved are 64 and 40%, respectively, at λmax (628 nm). The switching time is recorded and the observed values are 5 s from the coloring state to the bleaching state and vice versa. The chronoamperometry shows that the device performed up to 400 cycles, and it is capable of working up to 35 cycles without any degradation.