Papers by Author: Ranjit R. Hawaldar

Abstract: 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.

Abstract: 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.

Abstract: 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).

Abstract: 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.

Abstract: 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.