Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

We have discovered a carbonized polymer film to be a reliable and durable carbon-based substrate for carbon enhanced Raman scattering (CERS). Commercially available SU8 was spin coated and carbonized (c-SU8) to yield a film optimized to have a favorable Fermi level position for efficient charge transfer, which results in a significant Raman scattering enhancement under mild measurement conditions. A highly sensitive CERS (detection limit of 10-8 M) that was uniform over a large area was achieved on a patterned c-SU8 film and the Raman signal intensity has remained constant for 2 years. This approach works not only for the CMOS-compatible c-SU8 film but for any carbonized film with the correct composition and Fermi level, as demonstrated with carbonized-PVA (poly(vinyl alcohol)) and carbonized-PVP (polyvinylpyrollidone) films. Our study certainly expands the rather narrow range of Raman-active material platforms to include robust carbon-based films readily obtained from polymer precursors. As it uses broadly applicable and cheap polymers, it could offer great advantages in the development of practical devices for chemical/bio analysis and sensors. © 2017 American Chemical Society.

World University root node

Department of Micro and Nanoelectronics

School of Electronics Engineering

Vellore Campus

ACS Applied Materials and Interfaces

Highly Enhanced Raman Scattering on Carbonized Polymer Films

We present a facile yet efficient single-step pyrolysis method to prepare bulk-scale high-performance N-doped 3D-graphitic foams with various length-scale pores. The iron precursors act as catalysts for the conversion of organic substances to a graphitic structure while simultaneously providing a rigid template that prevents the aggregation of organic components, and soluble polymers act as a carbon source for the formation of N-doped multilayer graphene under high-temperature and inert conditions. The 3D-graphitic foams possess highly interconnected networks composed of micro-, meso-, and macropores with a specific surface area of up to 1509 m2 g-1 and a high conductivity of 10 S m-1. The resulting 3D-graphitic foams exhibited specific capacitance values of 330 and 242 F g-1 with outstanding cycling stability (a 23% loss after 100 000 cycles for a symmetric cell) in a three-electrode system and in a symmetric cell, respectively, when used as active materials in a supercapacitor. This study suggests the great potential of bulk-scale fabricated N-doped 3D-graphitic foams with a large surface area and excellent conductivity, as well as controlled porosity, for applications in various fields. © 2017 American Chemical Society.

ACS Sustainable Chemistry and Engineering

Single-Step Synthesis of N-Doped Three-Dimensional Graphitic Foams for High-Performance Supercapacitors

Graphene-enhanced Raman spectroscopy (GERS) is a technique to increase the Raman scattering of adsorbed probe molecules on graphene. Here we systematically explore the effect of the method used to transfer the CVD-grown graphene onto another substrate on Raman scattering. We have found that graphene transferred using poly methyl methacrylate (PMMA) produces 6 times the Raman scattering signal increase of that produced by graphene transferred using thermal release tape. The reason for this is that PMMA-assisted graphene contains a larger amount of defects such as carboxyl and hydroxyl groups that help the attachment of probe molecules to the graphene surface, leading to improved π-π∗ interactions and thus easier charge transfer between the probe molecules and graphene. Our results indicate the need for a much closer look at the functional groups of graphene which are different for the two transfer methods. © 2015 The Royal Society of Chemistry.

RSC Advances

A case study: Effect of defects in CVD-grown graphene on graphene enhanced Raman spectroscopy

This work investigates the thermoelectric properties of a three dimensional nanofoam of few layer graphene (3D-NFG) decorated with holes having diameter of several tens of nanometer. The nanoporous 3D graphene structures were fabricated by a chemical vapor deposition method to ensure high electrical conductivity required for potential applications as thermoelectric materials. The thermal conductivity of the suspended 3D-NFG samples was measured by an optothermal method and found to be 10.8 W m-1 K-1. The substantially reduced values of thermal conductivity were attributed to the small diameter of the pores and their inhomogeneous distribution. Suppression of heat conduction with preserved electrical conductivity is beneficial for the proposed thermoelectric applications. © 2015 The Royal Society of Chemistry.

Thermal conductivity reduction in three dimensional graphene-based nanofoam

By creating a p-n heterojunction of molybdenum sulfide (MoSx)/Ti-doped Fe2O3 (Ti-Fe2O3), we successfully addressed electron-hole transfer problems of hematite and thus achieved the enhanced photoelectrochemical (PEC) performance. MoSx/Ti-Fe2O3 with a thin MoSx layer on the surface of Ti-Fe2O3 fabricated a p-n junction that provided facile charge transfer pathways due to an internal electric field between Ti-Fe2O3 and MoSx, and achieved suppressed charge recombination. The optimized MoSx/Ti-Fe2O3 sample showed a 240% increased photocurrent density (3.03 mA cm-2) over pristine Fe2O3 at RHE 1.50 V. All our data including IPCE, PL, and EIS clearly confirmed the improved PEC performance of MoSx/Ti-Fe2O3 achieved by the formation of a p-n junction with a facile electron-hole transport pathway. © The Royal Society of Chemistry.

Journal of Materials Chemistry A

MoSx supported hematite with enhanced photoelectrochemical performance

Advanced Optical Materials

Graphene Quantum Dot-Protected Cadmium Selenide Quantum Dot-Sensitized Photoanode for Efficient Photoelectrochemical Cells with Enhanced Stability and Performance

In this letter, we report a facile approach to improve the capacitor properties of nickel hydroxide (Ni(OH)2) by simply coating gold nanoparticles (Au NPs) on the surface of Ni(OH)2. Au NP-deposited Ni(OH)2 (Au/Ni(OH)2) has been prepared by application of a conventional colloidal coating of Au NPs on the surface of 3D-Ni(OH)2 synthesized via a hydrothermal method. Compared with pristine Ni(OH)2, Au/Ni(OH)2 shows a 41% enhanced capacitance value, excellent rate capacitance behavior at high current density conditions, and greatly improved cycling stability for supercapacitor applications. The specific capacitance of Au/Ni(OH)2 reached 1927 F g-1 at 1 A g-1, which is close to the theoretical capacitance and retained 66% and 80% of the maximum value at a high current density of 20 A g-1 and 5000 cycles while that of pristine Ni(OH)2 was 1363 F g-1 and significantly decreased to 48% and 30%, respectively, under the same conditions. The outstanding performance of Au/Ni(OH)2 as a supercapacitor is attributed to the presence of metal Au NPs on the surface of semiconductor Ni(OH)2; this permits the creation of virtual 3D conducting networks via metal/semiconductor contact, which induces fast electron and ion transport by acting as a bridge between Ni(OH)2 nanostructures, thus eventually leading to significantly improved electrochemical capacitive behaviors, as confirmed by the EIS and I-V characteristic data. © 2014 the Partner Organisations 2014.

Nanoscale

Great improvement in pseudocapacitor properties of nickel hydroxide via simple gold deposition

We propose three dimensional-graphene nanonetworks (3D-GN) with pores in the range of 10 ∼ 20 nm as a potential candidate for thermoelectric materials. The 3D-GN has a low thermal conductivity of 0.90 W/mK @773 K and a maximum electrical conductivity of 6660 S/m @ 773 K. Our results suggest a straightforward way to individually control two interdependent parameters, σ and κ, in the nanoporous graphene structures to ultimately improve the figure of merit value. © 2014 AIP Publishing LLC.

Fulltext

Applied Physics Letters

Thermoelectric properties of nanoporous three-dimensional graphene networks

A hierarchically patterned metal/semiconductor (gold nanoparticles/ZnO nanowires) nanostructure with maximized photon trapping effects is fabricated via interference lithography (IL) for plasmon enhanced photo-electrochemical water splitting in the visible region of light. Compared with unpatterned (plain) gold nanoparticles-coated ZnO NWs (Au NPs/ZnO NWs), the hierarchically patterned Au NPs/ZnO NWs hybrid structures demonstrate higher and wider absorption bands of light leading to increased surface enhanced Raman scattering due to the light trapping effects achieved by the combination of two different nanostructure dimensions; furthermore, pronounced plasmonic enhancement of water splitting is verified in the hierarchically patterned Au NPs/ZnO NWs structures in the visible region. The excellent performance of the hierarchically patterned Au NPs/ZnO NWs indicates that the combination of pre-determined two different dimensions has great potential for application in solar energy conversion, light emitting diodes, as well as SERS substrates and photoelectrodes for water splitting. A hierarchically patterned metal/semiconductor nanostructure is fabricated via interference lithography for plasmon-enhanced photoelectrochemical water splitting in the visible region of light. Compared with unpatterned Au NPs/ZnO NWs, the hierarchically patterned structures demonstrate higher and wider absorption bands leading to increased surface enhanced Raman scattering and surface plasmon-enhanced water splitting. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Small

Hierarchical metal/semiconductor nanostructure for efficient water splitting

Dual-scale diamond-shaped gold nanostructures (d-DGNs) with larger scale diamond-shaped gold nanoposts (DGNs) coupled to smaller scale gold nanoparticles have been fabricated via interference lithography as a highly reliable and efficient substrate for surface enhanced Raman scattering (SERS). The inter- and intra-particle plasmonic fields of d-DGNs are varied by changing the periodicity of the DGNs and the density of gold nanoparticles. Because of the two different length scales in the nanostructures, d-DGNs show multipole plasmonic peaks as well as dipolar plasmonic peaks, leading to a SERS enhancement factor of greater than 109. Simulations are carried out by finite-difference time-domain (FDTD) methods to evaluate the dependence of the inter- and intra-particle plasmonic field and the results are in good agreement with the experimentally obtained data. Our studies reveal that the combination of two different length scales is a straightforward approach for achieving reproducible and great SERS enhancement by light trapping in the diamond-shaped larger scale structures as well as efficient collective plasmon oscillation in the small size particles. © 2013 The Royal Society of Chemistry.

An optimal substrate design for SERS: Dual-scale diamond-shaped gold nano-structures fabricated via interference lithography

A gold nanoparticle-coated and surface-textured TiO2 inverse opal (Au/st-TIO) structure that provides a dramatic improvement of photoelectrochemical hydrogen generation has been fabricated by nano-patterning of TiO2 precursors on TiO2 inverse opal (TIO) and subsequent deposition of gold NPs. The surface-textured TiO2 inverse opal (st-TIO) maximizes the photon trapping effects triggered by the large dimensions of the structure while maintaining the adequate surface area achieved by the small dimensions of the structure. Au NPs are incorporated to further improve photoconversion efficiency in the visible region via surface plasmon resonance. st-TIO and Au/st-TIO exhibit a maximum photocurrent density of ∼0.58 mA cm-2 and ∼0.8 mA cm-2, which is 2.07 and 2.86 times higher than that of bare TIO, respectively, at an applied bias of +0.5 V versus an Ag/AgCl electrode under AM 1.5 G simulated sunlight illumination via a photocatalytic hydrogen generation reaction. The excellent performance of the surface plasmon-enhanced mesoporous st-TIO structure suggests that tailoring the nanostructure to proper dimensions, and thereby obtaining excellent light absorption, can maximize the efficiency of a variety of photoconversion devices. © 2013 The Royal Society of Chemistry.

Optimization for visible light photocatalytic water splitting: Gold-coated and surface-textured TiO2 inverse opal nano-networks

Graphene oxide-terminated partially fluorinated poly(arylene ether sulfone) (GO-PAES) was synthesized via step growth polymerization with graphene oxide. A small amount of graphene oxide was incorporated into the polymer matrix to enhance the properties of the polymer/GO composites. The chemical structures of the synthesized copolymers containing graphene oxide were confirmed by 1HNMR and FT-IR spectra. The thermal properties of GO-PAES analyzed by TGA and DSC were significantly improved due to the thermal stability of graphene oxide. © 2012 The Chemical Society of Japan.

Chemistry Letters

Graphene oxide-terminated partially fluorinated poly(arylene ether sulfone)

A simple chemical route has been used to synthesize highly sinterable strontium titanate (SrTiO3) powders using titanium isopropoxide, strontium nitrate and ethylene glycol. This method utilizes complexation- polymerization using ethylene glycol as an organic carrier, which leads to compositional homogeneity and fine particle sizes. The calcined SrTiO 3 powder showing a porous nature was fully crystallized to a cubic phase at 1,300 °C for 1 hour. Through ball-milling the porous SrTiO3 powders with particle sizes of 200-300 nm were easily obtained, which was sintered to a bulk density of 4.8 g/cm3 at 1,400 °C for 1 h with a grain size of approximately 6.0 mm. The relative dielectric constant and loss tangent of SrTiO3 sintered at 1,400 °C for 1 hour were 2078 and 0.022, respectively.