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The well known surface enhanced Raman scattering (SERS) needs a lot of experimental optimization for its proper implementation. In this report, we demonstrate the efficient SERS using gold nanoparticles (AuNPs) on quartz plate. The AuNPs were prepared by depositing direct current sputtered Au thin film followed by suitable annealing. The parameters varied for getting best SERS effect were 1) Numerical Aperture of Raman objective lens and 2) Sputtering duration of Au film. It was found that AuNPs formed from the Au layer deposited for 40s and Raman objective lens of magnification 50X are the best combination for obtaining efficient SERS effect. © 2018 Author(s).

World University root node

Department of Metallurgical & Materials Engineering

AIP Conference Proceedings

Experimental optimization during SERS application

The CZTS films are made by direct liquid coating of solution precursors. A benign solution of propanol and polyethylene glycol as solvent is used. Films of CZTS are prepared by drop casting and spin coating followed by annealing and sulfurisation. The present synthesis need as low as 350°C to form the kesterite phase CZTS films. The presence of secondary phase in CZTS films are not conclusively detectable using X-ray diffraction and hence the role of Raman spectroscopy for the same is emphasized. © 2017 Elsevier Ltd.

Materials Today: Proceedings

Secondary Phases in CZTS Thin Films Grown Using Direct Liquid Coating Approach

We report hydrogen peroxide (H2O2)sensing using free standing graphene oxide thin films prepared using a cost effective scalable approach. Such sensors may find application in pharmaceutical and food processing industries.

Free standing graphene oxide film for hydrogen peroxide sensing

A low cost, non-explosive process for the synthesis of graphene oxide (GO) is demonstrated. Using suitable choice of reaction parameters including temperature and time, this recipe does not require expensive membranes for filtration of carbonaceous and metallic residues. A pre-cooling protocol is introduced to control the explosive nature of the highly exothermic reactions during the oxidation process. This alleviates the requirement for expensive membranes and completely eliminates the explosive nature of intermediate reaction steps when compared to existing methods. High quality of the synthesized GO is corroborated using a host of characterization techniques including X-ray diffraction, optical spectroscopy, X-ray photoemission spectroscopy and current-voltage characteristics. Simple reduction protocol using ultra-violet light is demonstrated for potential application in the area of photovoltaics. Using different reduction protocols together with the proposed inexpensive method, reduced GO samples with tunable conductance over a wide range of values is demonstrated. Density functional theory is employed to understand the structure of GO. We anticipate that this scalable approach will catalyze large scale applications of GO.

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Scientific Reports

A Low-Cost Non-explosive Synthesis of Graphene Oxide for Scalable Applications

We have synthesized free-standing films of graphene oxide (GO), reduced graphene oxide (rGO) and graphene oxide-manganese oxide composite (GMC) for humidity and hydrogen peroxide sensing applications. Structural and morphological characterizations of these free-standing films were performed using X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The presence of anionic sites in the form of oxygen functional groups (OFGs) at the surface of GO along with its hydrophilic nature makes GO a unique candidate as a suitable material for humidity and hydrogen peroxide sensing. In contrast, rGO has a relatively lower fraction of OFGs, higher electrical conductivity and hydrophobicity compared to GO. We estimate the response time, recovery time and stability of free-standing films over multiple sensing-degassing cycles of the as chemically prepared GO, rGO and GMC films for humidity sensing. We observed a dramatic improvement in both the response and recovery times for rGO and GMC films compared to GO film at relatively low humidity, while at higher humidity percentages, rGO film has the best response and recovery times compared to GMC and GO films. Regarding stability, GO was found to be more stable over multiple sensing cycles compared to rGO and GMC at high humidity values. In addition to this, we observed that the addition of metal oxide to GO makes GMC film more selective for hydrogen peroxide sensing in comparison to GO and rGO film at a lower concentration. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.

Journal of Materials Science: Materials in Electronics

Graphene oxide based free-standing films for humidity and hydrogen peroxide sensing

Erratum to: A Low-Cost Non-explosive Synthesis of Graphene Oxide for Scalable Applications (Scientific Reports, (2018), 8, 1, (12007), 10.1038/s41598-018-30613-4)

We investigate the effect of sputtered gold nanoclusters (AuNCs) on the Raman spectra of graphene. The two prominent Raman peaks of graphene – 2D and G – show drastically different behaviour with AuNC introduction. The Raman 2D peak intensity decreases with gold coverage and finally is quenched for moderate gold nanoparticle coverage, while the G peak shows a AuNC size-dependent enhancement in peak intensity. The quenching of the 2D peak is attributed to the hybridization of graphene's 2pz orbital with the 5d orbitals of Au. The G peak enhancement is due to the surface-enhanced Raman scattering induced by the surface plasmons created in the AuNC by the incident laser beam (He–Ne laser, wavelength = 632.8 nm). The existence of surface plasmons is independently confirmed by UV-visible spectrophotometry measurements. Copyright {\textcopyright} 2017 John Wiley & Sons, Ltd.

Journal of Raman Spectroscopy

Au concentration-dependent quenching of Raman 2D peak in graphene

The well known localized surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) supported on a dielectric substrate depends on the particle shape, size and type of dielectric material. The particle size and shape mainly vary with the method of preparation and the parameters involved there in. In this report, we show preparation of AuNPs supported on quartz substrate by direct current sputtering followed by thermal annealing at an optimized temperature of 400 °C. The samples were characterized using optical absorption spectra, scanning electron microscopy (SEM) and the energy dispersive x-ray spectrum. The LSPR position could be tuned by varying annealing temperature. The LSPR was found to be blue shifted up to 10 nm with annealing temperature varying from 400 °C to 800 °C. The change in LSPR was ascribed to the morphology of AuNPs over quartz. © 2016 Author(s).

Temperature dependent localized surface plasmon resonance properties of supported gold nanoparticles

A new modified technique of synthesizing tin oxide nanoparticles with crystallite size of 2?nm to 6?nm has been developed. Surface area of the nanoparticle has been increased as we approached towards the Debye length. Such a techniques for approaching the Debye length is expected to bring remarkable changes in the properties of resistive based gas sensors. The technique used here is less toxic, economical and has high yield. Phase purity, size, shape and composition has been investigated using x-ray diffraction, micro Raman, scanning electron microscopy and energy dispersive x ray spectroscopy. While surface area has been calculated through Brunaur-Emmett-Teller (BET). © 2016 Author(s).