Parag V. Adhyapak

Removal of OH impurities from GeS2 by reactive atmosphere and its glass preparation

Abstract The transparency of the chalcogenide glasses depends upon the purity of the raw materials used for the glass preparation. Especially, the glasses used for optical fiber systems are generally prepared using high purity raw materials. In optical fiber glasses, the OH radicals are critical since they quench the fluorescence. In the present investigation, we have prepared germanium sulfide-based chalcogenide glasses. The sulfide usually contains significantly large amount of hydroxyl impurities which act as high energy phonons in the glass structure. These high energy phonons are known to quench fluorescence. Hence OH impurity removal is essential for optical fiber systems. Considering the criticality of OH impurity in optical fiber system, the efforts have been made to purify raw materials of germanium sulfide glasses. The present investigation focuses research on decreasing impurities content in the raw materials used for glass preparation. The GeS2, Ga2S3 powders were purified by reactive atmosphere of HCl and hydrogen. The glasses using these powders were melted and thermal and spectroscopic studies have been made.

Synthesis, characterization and optical properties of silver and gold nanowires embedded in mesoporous MCM-41

Uniform nanowires of silver and gold inside the channels of MCM-41 were prepared by controlled reduction of their respective metal salts with sodium borohydride (NaBH4). Presence of nanowires of silver and gold in MCM-41 were confirmed by high angle X-ray diffraction (XRD) data (peaks between 2ϑ = 30 − 60°) and transmission electron microscopy (TEM) confirmed the diameter of the nanowires. Diameter of nanowires is found to be ∼ 2.8 nm which is coincident with channel diameter of MCM-41. Optical properties of these heterostructured materials Ag-MCM-41 and Au-MCM-41 reveals the presence of surface plasmon absorption peaks of silver and gold respectively, and the shift in the absorption bands are associated to agglomeration of clusters inside the channels. Room temperature photoluminescence spectra exhibits interesting optical properties as observed for direct band gap semiconductors. Non-linear optical properties (NLO) corresponding to second harmonic generation (SHG) values were also recorded for self supported films of these heterostructured materials. Enhanced optical non-linearity was found to be arising from a corresponding increase of local field near the surface plasmon resonance. Further enhancement in SHG was found with poling due to an induction of orientation order.

Thickness-dependent humidity sensing by poly(vinyl alcohol) stabilized Au–Ag and Ag–Au core–shell bimetallic nanomorph resistors

We herein report a simple chemical route to prepare Au–Ag and Ag–Au core–shell bimetallic nanostructures by reduction of two kinds of noble metal ions in the presence of a water-soluble polymer such as poly(vinyl alcohol) (PVA). PVA was intentionally chosen as it can play a dual role of a supporting matrix as well as stabilizer. The simultaneous reduction of metal ions leads to an alloy type of structure. Ag(c)–Au(s) core–shell structures display tendency to form prismatic nanostructures in conjunction with nanocubes while Au(c)–Ag(s) core–shell structures show formation of merely nanocubes. Although UV–visible spectroscopy and X-ray photoelectron spectroscopy analyses of the samples typically suggest the formation of both Ag(c)–Au(s) and Au(c)–Ag(s) bimetallic nanostructures, the definitive evidence comes from high-resolution transmission electron microscopy–high-angle annular dark field elemental mapping in the case of Au(c)–Ag(s) nanomorphs only. The resultant nanocomposite materials are used to fabricate resistors on ceramic rods having two electrodes by drop casting technique. These resistors are examined for their relative humidity (RH) response in the range (2–93% RH) and both the bimetallic nanocomposite materials offer optimized sensitivity of about 20 Kohm/% RH and 300 ohm/% RH at low and higher humidity conditions, respectively, which is better than that of individual nanoparticles.

Single-Stroke Synthesis of Tin Sulphide/Oxide Nanocomposites Within Engineering Thermoplastic and Their Humidity Response

SnS nanostructured materials have attracted enormous interest due to their important properties and potential application in low cost solar energy conversion systems and optical devices. From the perspective of SnS based device fabrication, we offer single-stroke in-situ technique for the generation of Sn based sulphide and oxide nanostructures inside the polymer network via polymer-inorganic solid state reaction route. In this method, polyphenylene sulphide (PPS)-an engineering thermoplastic-acts as chalcogen source as well as stabilizing matrix for the resultant nano products. Typical solid state reaction was accomplished by simply heating the physical admixtures of the tin salts (viz. tin acetate/tin chloride) with PPS at the crystalline melting temperature (285 °C) of PPS in inert atmosphere. The synthesized products were characterized by using various physicochemical characterization techniques. The prima facie observations suggest the concurrent formation of nanocrystalline SnS with extraneous oxide phase. The TEM analysis revealed formation of nanosized particles of assorted morphological features with polydispersity confined to 5 to 50 nm. However, agglomerated particles of nano to submicron size were also observed. The humidity sensing characterization of these nanocomposites was also performed. The resistivity response with the level of humidity (20 to 85% RH) was compared for these nanocomposites. The linear response was obtained for both the products. Nevertheless, the nanocomposite product obtained from acetate precursor showed higher sensitivity towards the humidity than that of one prepared from chloride precursor.

Fabrication of WO 3 /PANI nanocomposites for ammonia gas sensing application

Herein present study, organic-inorganic hybrids based on WO3/PANI nanocomposites have been synthesized at room temperature, by using oxidative polymerization. The as-synthesized products have been studied by using X-ray diffraction analysis, FE-SEM and optical characterization. The XRD analysis depicts peak broadening and the shift in peak position from standard values, which can be attributed to the formation of WO3 in the polyaniline matrix. Study of FE-SEM micrograph revealed that the cube-like WO3 particles get well dispersed in PANI matrix. WO3/PANI composite shows enhanced response and recovery time towards ammonia gas at room temperature.

α-Fe 2 O 3 nanorods: Low temperature synthesis, characterization and humidity response properties

α-Fe2O3 nanorods have been prepared at low temperature by a facile surfactant free chemical route. The advantage of this method is good composition control and homogeneity. The products were characterized using various physicochemical characterization techniques such as X-ray Diffractometry, Raman spectroscopy, UV-Visible spectroscopy and Field Emission Scanning Electron Microscopy. These powders were further studied for their humidity sensing performance. The sensors exhibited quick responses for change in the humidity. The resistance systematically varies by four orders of magnitude on exposure to humidity from 20 to 90 % RH.

Size dependent relative humidity sensing of Ag/PVP nanocomposites by direct optical transmission method

Ag particles having different sizes (A1 A2 A3 A4 and A5) were in situ synthesized by using chemical route in 0.01M PVP. Size dependent humidity sensing was studied by direct optical transmission method. Structural characterization and elemental analysis of the synthesized materials is carried out using UV-Visible, DLS and Impedance spectra. Change in impedance spectra with reaction time gave explanation about structural changes in polymer nanocomposite. Samples taken out after reaction time of 30 min show more sensitivity during wide humidity sensing range (2–94 % RH) i.e. 5.37 (78–94), 2.31 (77–59) and 0.32 (2–58) mv/% RH. A1samples have low hysteresis with response and recovery time of about 24 and 33 sec respectively. They have shown good repeatability over 7 cycles and reproducibility for two samples.