Ranjit R. Hawaldar

Hydrogenated Nanocrystalline Silicon Thin Films Prepared by Hot-Wire Method with Varied Process Pressure

Hydrogenated nanocrystalline silicon films were prepared by hot-wire method at low substrate temperature (200∘C) without hydrogen dilution of silane (SiH4). A variety of techniques, including Raman spectroscopy, low angle X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), and UV-visible (UV-Vis) spectroscopy, were used to characterize these films for structural and optical properties. Films are grown at reasonably high deposition rates (>15 Å/s), which are very much appreciated for the fabrication of cost effective devices. Different crystalline fractions (from 2.5% to 63%) and crystallite size (3.6–6.0 nm) can be achieved by controlling the process pressure. It is observed that with increase in process pressure, the hydrogen bonding in the films shifts from Si–H to Si–H2 and complexes. The band gaps of the films are found in the range 1.83–2.11 eV, whereas the hydrogen content remains <9 at.% over the entire range of process pressure studied. The ease of depositing films with tunable band gap is useful for fabrication of tandem solar cells. A correlation between structural and optical properties has been found and discussed in detail.

Hierarchical CdS nanostructure by Lawesson's reagent and its enhanced photocatalytic hydrogen production

Lawessons reagent (LR) has been effectively exploited for the synthesis of hierarchical architectures of cadmium sulphide (CdS) nanostructures for the first time. The X-ray diffractograms of the as synthesised CdS nanostructures confirm the formation of hexagonal CdS. The broadness of the XRD peaks clearly indicates the nanocrystalline nature of CdS with average crystallite size of 4 nm. A FESEM study revealed the formation of hierarchical nanostructures, whereas a TEM study showed that the hierarchical arrangement is composed of nanosized CdS particles. A band-gap i.e. 2.4 eV was derived from diffuse reflectance spectroscopy. The photoluminescence spectrum showed an emission peak at 535 and 568 nm which can be attributed to band-edge emission and surface emissions or possible metal vacancies, respectively. Considering the band-gap within the visible region, the photocatalytic hydrogen evolution performance of these CdS nanostructures was performed under visible light irradiation from hydrogen sulphide and water, respectively. Utmost hydrogen evolution i.e. 14 136 μmol h−1 g−1 and 2065 μmol h−1 g−1 was observed over a naked CdS nanostructure via H2S and water decomposition, respectively. The amount of hydrogen obtained by H2S splitting is much higher as compared to earlier reports.

In situ preparation of a novel organo-inorganic 6,13-pentacenequinone–TiO2 coupled semiconductor nanosystem: a new visible light active photocatalyst for hydrogen generation

Previous studies related to the synthesis of stable UV-visible light active photocatalysts for hydrogen generation have been limited to inorganic semiconductors and their nano- and hetero-structures. We demonstrate here the use of an organo-inorganic 6,13-pentacenequinone (PQ)–TiO2 coupled semiconductor nanosystem as an efficient photocatalyst active in visible light for the production of hydrogen. Anatase TiO2 nanoparticles (3–5 nm) were uniformly decorated on thin sheets of monoclinic PQ by an in situ solvothermal method. These as-prepared PQ–TiO2 coupled semiconductor nanosystems had a band gap in the range 2.7–2.8 eV. The strong emission at 590 nm can be attributed to the transfer of electrons from the LUMO energy level of TiO2 to combine with the holes present in the HOMO level of PQ. This electron–hole recombination makes availability of electrons and holes in LUMO of PQ and HOMO of TiO2, respectively. This hybrid semiconductor coupled nanosystem resulted in a rate of hydrogen evolution of 36456 μmol h−1 g−1 from H2S under UV-visible light; this is four times higher than the rate obtained with TiO2 in earlier reports of UV-visible light active photocatalysts. These results open up a new path to explore inorganic systems coupled with PQ as new photoactive hybrid catalysts in a number of chemical and physicochemical processes.

Synthesis and Characterization of Polyaniline -Crooked Gold Nanocomposite with Reduced Conductivity

Conducting Polyaniline (Pani)-crooked Gold nanocomposites were synthesized by in situ chemo-oxidative polymerization of aniline with previously made crooked gold nanoparticles by using ammonium per oxidisulphate as oxidizing agent and p-toluene sulphonic acid (p-TSA) as dopant. The formation of nano gold was established by UV-visible spectroscopy with a SPR peak at 512 nm and crooked morphology was confirmed by TEM. Spectroscopic analysis confirmed the formation of the conducting emeraldine salt phase of the polymer. Due to clustering of composite nanoparticles, the polymer composite formed one-dimensional rod-like morphologies. Thermogravimetric analysis revealed a typical three-step decomposition pattern pertaining to polyaniline emeraldine salt. The conductivity of the nanocomposite was found to be lower (2.47 S/cm) than the virgin p-TSA doped polyaniline (5.55 S/cm).

Synthesis of CdS Nanocrystallites in Polymer Matrix: Sui-Generis Approach

We offer sui-generis strategy for synthesis of nanosized chalcogenide semiconductors in polymer matrix by a novel polymer-inorganic solid-state reaction. In our previous report, the rationale of this strategy has been successfully established by the solid-state reaction between CdI2 and an intentionally chosen engineering thermoplastic, namely, polyphenylene sulphide (PPS). In the pursuit of this work, we explored the possibility of using other cadmium salts viz cadmium nitrate, cadmium chloride and cadmium acetate in place of cadmium iodide for the envisaged solidstate reaction with PPS. All the reactions were carried out at the melting temperature of PPS (285oC) in 1:1 and 10:1 molar ratios of polymer to cadmium salt. The resultant products were characterised by XRD, TEM-SAED and DRS. It is observed that only cadmium nitrate yielded CdS nanocrystallites (average size of 15nm) entrapped in modified polymer matrix in a competing behaviour with cadmium iodide when reacted in 10:1 molar ratio while (i) cadmium acetate leads to the formation of only cadmium oxide and (ii) cadmium chloride exhibits grossly incomplete solid state reaction yielding understated quantity of CdS when reacted with PPS.

XPS and AFM investigations on silver-based photoimageable thick film systems

Purpose – The purpose of this paper is to ascertain chemical changes occurring at various stages involved in processing of silver‐based photoimageable thick films; and to determine ensuing topographical features which other wise appeared to be hindered in 2D scanning electron microscopy.Design/methodology/approach – Surface sensitive techniques, viz. X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used.Findings – Interfacial adhesion of silver film with substrate (Al2O3) was specifically looked into with respect to role played by photoimaging (before and after exposure to ultra‐violet light). XPS results revealed occurrence of subtle chemical changes in terms of unsaturation to saturation in C−C bonding and also an interesting C−Al bonding which presumably improves mechanical adhesion of unfired film with the alumina substrate. AFM was carried out to examine the surface roughness, particle size, and microstructure of film which are very important from the standpoint of high‐f...

Concurrent In Situ Formation of Ag / Ag2S Nanoparticles in Polymer Matrix by Facile Polymer-Inorganic Solid State Reaction

We herein report the feasibility of polymer-inorganic solid-state reaction route for simultaneous in situ generation of Ag & Ag2S nanostructures in polymer network wherein an engineering thermoplastic, polyphenylene sulphide (PPS), itself acts as a chalcogen source as well as a stabilizing matrix for the resultant nanoproducts. Typical solid-state reaction was accomplished by simply heating the physical admixture of the two reactants i.e. AgNO3 and PPS by varying molar ratios mainly 1:1, 1:5, 1:15, 1:20, at the crystalline melting temperature (285 °C) of PPS. The synthesized nanoparticles were characterized by various physico-chemical techniques like X-ray Diffractometry, Scanning Electron Microscopy equipped with EDAX, Transmission Electron Microscopy and UV-Visible spectroscopy. The prima facie observations suggest the effective formation and subsequent entrapment of mainly nanocrystalline metallic silver (fcc) in PPS matrix for all the molar ratios chosen for the reaction. Additionally, simultaneous occurrence of nanocrystalline Ag2S (monoclinic phase) is also noticed in case of heated admixture of AgNO3: PPS with equimolar ratio. The TEM analysis reveals nanoscale polydispersity (5nm to 70nm) and prevalence of mainly spherical morphological features in all the cases with occasional indications of triangular and hexagonal morphological features depending upon the reaction molar ratio.

Influence of Argon Flow on Deposition of Hydrogenated Nanocrystalline Silicon (nc-Si:H) Films by Plasma Chemical Vapor Deposition

In this work we report synthesis and characterization of hydrogenated nanocrystalline silicon (nc-Si:H) thin films by plasma chemical vapor deposition (P-CVD) method at 200 0C on glass substrates. Film properties are carefully and systematically investigated as a function of argon (Ar) flow rate. Characterization of these films with Raman spectroscopy revealed that the addition of Ar into SiH4-H2 plasma endorses the growth of crystallinity in the films. The Fourier transform infrared (FTIR) spectroscopic analysis showed that with increasing Ar flow rate the hydrogen bonding in the films shifts from mono-hydride (Si-H) to di-hydride (Si-H2) and (Si-H2)n complexes. The hydrogen content in the films was found < 7 at. % over the entire range of studied Ar flow rate. The band gap of nc-Si:H films was found to be higher than hydrogenated amorphous silicon (a-Si:H) films (> 2 eV). The nc-Si:H films with dark conductivity 1.3x10-7 S/cm having deposition rate as high as 2.5 Å/s and of crystalline fraction 98 % have been obtained.

Nanostructured Thin films of Anthracene by Liquid-Liquid Interface Recrystallization Technique

Herein, we report the fabrication of anthracene nanostructures and, in turn, their thin films at the air-water interface by recrystallization at the liquid-liquid interface. This method is simple, inexpensive and allows the deposition of anthracene nanoparticulate thin films on large and a variety of substrates. The virgin films were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Hot Stage Polarizing Microscopy and UV-Visible spectroscopy. Interestingly, it was found that these thin films are comprised of nanosized bushy clusters of anthracene molecules as revealed by TEM. Also, with increase in the thickness of the films, the formation of irregular microtapes was evinced by SEM. The absorption spectra reveals the presence of 2 excitonic peaks for the lowest dip sample (10 dips) whereas the spectra recorded for higher dip samples (20 dips, 30dips, 40dips) closely match with that of pure anthracene in chloroform solution. The dramatic reduction in the melting point as revealed by hot stage polarizing microscopy is the salient feature of the work.