Jeyanthinath Mayandi

A novel synthesis of tin oxide thin films by the sol-gel process for optoelectronic applications

A novel and simple chemical method based on sol-gel processing was proposed to deposit metastable orthorhombic tin oxide (SnOx) thin films on glass substrates at room temperature. The resultant samples are labeled according to the solvents used: ethanol (SnO-EtOH), isopropanol (SnO-IPA) and methanol (SnO-MeOH). The variations in the structural, morphological and optical properties of the thin films deposited using di ff erent solvents were characterized by X-ray diff raction, atomic force microscopy, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy and photoluminescence (PL) analysis. The XRD patterns confirm that all the films, irrespective of the solvents used for preparation, were polycrystalline in nature and contained a mixed phases of tin (II) oxide and tin (IV) oxide in a metastable orthorhombic crystal structure. FTIR spectra confirmed the presence of Sn=O and Sn-O in all of the samples. PL spectra showed a violet emission band centered at 380 nm (3.25 eV) for all of the solvents. The UV-vis spectra indicated a maximum absorption band shown at 332 nm and the highest average transmittance around 97% was observed for the SnO-IPA and SnO-MeOH thin film samples. The AFM results show variations in the grain size with solvent. The structural and optical properties of the SnO thin films indicate that this method of fabricating tin oxide is promising and that future work is warranted to analyze the electrical properties of the films in order to determine the viability of these films for various transparent conducting oxide applications. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4909542]

Effect of ambient combinations of argon, oxygen, and hydrogen on the properties of DC magnetron sputtered indium tin oxide films

Sputtering has been well-developed industrially with singular ambient gases including neutral argon (Ar), oxygen (O2), hydrogen (H2) and nitrogen (N2) to enhance the electrical and optical performances of indium tin oxide (ITO) films. Recent preliminary investigation into the use of combined ambient gases such as an Ar+O2+H2 ambient mixture, which was suitable for producing high-quality (low sheet resistance and high optical transmittance) of ITO films. To build on this promising preliminary work and develop deeper insight into the effect of ambient atmospheres on ITO film growth, this study provides a more detailed investigation of the effects of ambient combinations of Ar, O2, H2 on sputtered ITO films. Thin films of ITO were deposited on glass substrates by DC magnetron sputtering using three different ambient combinations: Ar, Ar+O2 and Ar+O2+H2. The structural, electrical and optical properties of the three ambient sputtered ITO films were systematically characterized by X-ray diffraction (XRD), atom...

Influence of Oxygen Concentration on the Performance of Ultra-Thin RF Magnetron Sputter Deposited Indium Tin Oxide Films as a Top Electrode for Photovoltaic Devices

The opportunity for substantial efficiency enhancements of thin film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells using plasmonic absorbers requires ultra-thin transparent conducting oxide top electrodes with low resistivity and high transmittances in the visible range of the electromagnetic spectrum. Fabricating ultra-thin indium tin oxide (ITO) films (sub-50 nm) using conventional methods has presented a number of challenges; however, a novel method involving chemical shaving of thicker (greater than 80 nm) RF sputter deposited high-quality ITO films has been demonstrated. This study investigates the effect of oxygen concentration on the etch rates of RF sputter deposited ITO films to provide a detailed understanding of the interaction of all critical experimental parameters to help create even thinner layers to allow for more finely tune plasmonic resonances. ITO films were deposited on silicon substrates with a 98-nm, thermally grown oxide using RF magnetron sputtering with oxygen concentrations of 0, 0.4 and 1.0 sccm and annealed at 300 °C air ambient. Then the films were etched using a combination of water and hydrochloric and nitric acids for 1, 3, 5 and 8 min at room temperature. In-between each etching process cycle, the films were characterized by X-ray diffraction, atomic force microscopy, Raman Spectroscopy, 4-point probe (electrical conductivity), and variable angle spectroscopic ellipsometry. All the films were polycrystalline in nature and highly oriented along the (222) reflection. Ultra-thin ITO films with record low resistivity values (as low as 5.83 × 10−4 Ω·cm) were obtained and high optical transparency is exhibited in the 300–1000 nm wavelength region for all the ITO films. The etch rate, preferred crystal lattice growth plane, d-spacing and lattice distortion were also observed to be highly dependent on the nature of growth environment for RF sputter deposited ITO films. The structural, electrical, and optical properties of the ITO films are discussed with respect to the oxygen ambient nature and etching time in detail to provide guidance for plasmonic enhanced a-Si:H solar PV cell fabrication.

Peanut shaped ZnO microstructures: controlled synthesis and nucleation growth toward low-cost dye sensitized solar cells

This paper describes a simple, low-temperature and cost effective chemical precipitation method in aqueous media to synthesis uniformly distributed zinc oxide (ZnO) microstructures for the fabrication of dye-sensitized solar cells (DSSCs). The size and morphology of the ZnO microstructures are systematically controlled by adjusting the concentration of the precursors, zinc acetate dihydrate and ammonium hydroxide. X-ray diffraction (XRD) and scanning electron microscopy are used for the structural characterizations and photoluminescence and Fourier transform infrared spectroscopy are used to characterize the optical properties of the ZnO, respectively. The results reveal that ZnO crystallites exhibit hexagonal wurtzite structure with preferential orientation along c-axis. The effect of ammonia concentration on the crystallinity, morphology and optical properties of ZnO microstructures and the concomitant effect on the efficiency of DSSCs is also quantified. The peanut-shaped ZnO microstructure, which was found to increase DSSCs performance over other microstructure, is studied in detail in order to develop a formation mechanism. A sandwich type eosin yellow sensitized solar cell is prepared using peanut-shaped ZnO microstructures, which showed an efficiency of 0.37%. Ammonia was found to play a crucial role in the evolution of ZnO morphologies. These results are promising and provide a path towards low-cost high-performance DSSCs based on peanut-shaped ZnO microstructures and produced with only relatively simple wet chemistry synthesis.

Biocompatible curcumin loaded PMMA-PEG/ZnO nanocomposite induce apoptosis and cytotoxicity in human gastric cancer cells

Although curcumin is efficient in killing cancer cells, its poor water solubility and assocaited inadequate bioavailability remain major limitations to its therapeutic application. The formulation of curcumin micellar nanoparticles (NPs) encapsulated with a biodegradable polymer promises to significantly improve curcumins solubility, stability, and bioavailability. The past decade has witnessed the development of nanoscale curcumin delivery systems: curcumin-loaded liposomes or nanoparticles, self-microemulsifying drug delivery systems (SMEDDS), cyclodextrin inclusions, solid dispersions, nanodisks, and nanotubes. The intention of the present investigation was to enhance the bioavailability and ultimately the efficacy of curcumin by developing a curcumin loaded PMMA-PEG/ZnO bionanocomposite utilizing insoluble curcumin and poorly soluble ZnO nanoparticles. Here, the drug (curcumin) may be carry and deliver the biomolecule(s) by polymer-encapsulated ZnO NPs. Physical characteristics of these novel nanomaterials have been studied with transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) in conjunction with spectral techniques. Aqueous solubility of curcumin was augmented upon conjugation with the polymer-stabilized ZnO NPs. A narrow nanocomposite particle size distribution with an average value of 40 to 90nm was found via TEM. Most importantly, the pH-responsive release of curcumin from the nano-vehicle ensures safer, more controlled delivery of the drug at physiological pH. Cytotoxic potential and cellular uptake of curcumin loaded ZnO NPs were assessed by) cell viability assay, cell cycle assays along with the cell imaging studies have been done in addition to MTT using AGS cancer cells. Hence, these studies demonstrate that the clinical potential of the Curcumin Loaded PMMA-PEG/ZnO can induce the apoptosis of cancer cells through a cell cycle mediated apoptosis corridor, which raises its probability to cure gastric cancer cells.

Enhancing the anti-gastric cancer activity of curcumin with biocompatible and pH sensitive PMMA-AA/ZnO nanoparticles

Curcumin loaded ZnO nanoparticles were successfully synthesised and encapsulated with co-polymer PMMA-AA (Cur/PMMA-AA/ZnO NPs). The ZnO nanoparticles have been converted as good cargo materials to carry the well-known hydrophobic drug curcumin by surface functionalization. Physical characteristics of these novel nanomaterials have been studied with transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) in conjunction with spectral techniques. A narrow particle size distribution with an average value of 42nm was found via TEM. Most importantly, the pH-responsive release of curcumin from the nano-vehicle ensures safer, more controlled delivery of the drug at physiological pH. The drug entrapment efficiency and loading was evaluated and the in vitro efficacy as anticancer drug delivery vehicle was analyzed. The potential toxicity of Cur/PMMA-AA/ZnO NPs was studied by using AGS gastric cancer cell lines via MTT assay. These results revealed that the proposed nanomaterials induce a remarkable cell death in in-vitro models. The multifunctional properties of Cur/PMMA-AA/ZnO NPs may open up new avenues in cancer therapy through overcoming the limitations of conventional cancer therapy.

Preparation of meta-stable phases of barium titanate by Sol-hydrothermal method

Two low-cost chemical methods of sol–gel and the hydrothermal process have been strategically combined to fabricate barium titanate (BaTiO3) nanopowders. This method was tested for various synthesis temperatures (100 °C to 250 °C) employing barium dichloride (BaCl2) and titanium tetrachloride (TiCl4) as precursors and sodium hydroxide (NaOH) as mineralizer for synthesis of BaTiO3 nanopowders. The as-prepared BaTiO3 powders were investigated for structural characteristics using x-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The overall analysis indicates that the hydrothermal conditions create a gentle environment to promote the formation of crystalline phase directly from amorphous phase at the very low processing temperatures investigated. XRD analysis showed phase transitions from cubic - tetragonal - orthorhombic - rhombohedral with increasing synthesis temperature and calculated grain sizes were 34 – 38 nm (using the Scherrer formula). SEM and TEM analysis verified that the BaTiO3 nanopowders synthesized by this method were spherical in shape and about 114 - 170 nm in size. The particle distribution in both SEM and TEM shows that as the reaction temperature increases from 100 °C to 250 °C, the particles agglomerate. Selective area electron diffraction (SAED) shows that the particles are crystalline in nature. The study shows that choosing suitable precursor and optimizing pressure and temperature; different meta-stable (ferroelectric) phases of undoped BaTiO3 nanopowders can be stabilized by the sol-hydrothermal method.

Chemical Synthesis and Characterization of Nano Alumina, Nano Composite of Carbon-Alumina and Their Comparative Studies

Abstract Aluminium oxide (Al2O3) nano particles were synthesized by using both the sol gel technique and solid state reaction (SSR) method. Different proportion of nano carbon cones from 0.5% to 3.5% is doped with aluminium nitrate nano hydrate and annealed subsequently at 1000°C for 3 h to synthesize the nano composite of carbon–alumina. The synthesized samples were characterized by X-ray diffraction to identify the presence of different phases and transitions during this process. The average crystallite size of the nano alumina is found to be 45 nm by sol gel and 43 nm by SSR method respectively by Debye–Scherrer method. Average crystallite size and lattice strain of nano alumina are also estimated from Williamson Hall (WH) plot analysis. It is found to be 69 nm with the strain of 3.3×10−3 in sol gel, and in SSR method, it is 72 nm with the strain is 3.9×10−3. The interplanar distance of various planes of alumina are estimated and compared with JCPDS values. Similar analysis has also been extended for the nano composite of carbon–alumina. The surface morphology of the samples are analyzed using scanning electron microscopy and rough estimate of the crystallites is also given. From the Raman analysis, the presence of alpha phase of alumina has been confirmed. The presence of carbon in the composite has been established through diffuse reflectance spectroscopy. The FTIR spectra of the composite samples ensured the presence of Al–O–Al, O–H and C=O bonds.

Micro-Raman scattering of nanoscale silicon in amorphous and porous silicon

Abstract: The size effect of nanoscale silicon in both amorphous and porous silicon was investigated with micro-Raman spectroscopy. Silicon nanostructures in amorphous silicon were deposited on quartz substrates by plasma enhanced chemical vapor deposition (PECVD) with deposition powers of 15, 30 and 50 W. Micro-Raman spectra of the nanostructured silicon show the T2g Raman active mode shifting from the 521 cm−1 crystalline Si Raman line to 494, 499 and 504 cm−1 as deposition power increased. Large Raman mode shifts, up to 27 cm−1 and broadening up to 23 cm−1 of the T2g Raman-active mode is attributed to a phonon confinement effect. The analysis of micro-Raman scattering data is useful to understand the role of deposition condition of the silicon sample. In addition, micro-Raman scattering intensity of porous silicon prepared using various current densities such as 10, 50 and 125 mA/cm2 has also been investigated. The effect of phonon confinement on the nanoscale porous silicon has been quantified. The relationship between Raman shift and stress on the porous silicon has been evaluated.

Ambiance-dependent agglomeration and surface-enhanced Raman spectroscopy response of self-assembled silver nanoparticles for plasmonic photovoltaic devices

Abstract. The agglomeration/dewetting process of thin silver films provides a scalable method of obtaining self-assembled nanoparticles (SANPs) for plasmonics-based thin-film solar photovoltaic (PV) devices. We show the effect of annealing ambiance on silver SANP average size, particle/cluster finite shape, substrate area coverage/particle distribution, and how these physical parameters influence optical properties and surface-enhanced Raman scattering (SERS) responses of SANPs. Statistical analysis performed indicates that generally Ag SANPs processed in the presence of a gas (argon and nitrogen) ambiance tend to have smaller average size particles compared to those processed under vacuum. Optical properties are observed to be highly dependent on particle size, separation distance, and finite shape. The greatest SERS enhancement was observed for the argon-processed samples. There is a correlation between simulation and experimental data that indicate argon-processed AgNPs have a great potential to enhance light coupling when integrated to thin-film PV.