Satyajit Shukla

Study of mechanism of electroless copper coating of fly-ash cenosphere particles

Abstract Electroless Cu coating process involving Sn–Pd catalyst system is successfully utilized to coat Cu on the surface of fly-ash cenosphere particles to impart electrical conductivity to these non-conducting oxide ceramic particles. The low density Cu-coated cenosphere particles may be utilized for manufacturing conducting polymers for EMI shielding applications. This is the first report in the open literature to investigate the electroless Cu coating of fly-ash cenosphere particles in detail. Extensive characterization of coated particles is carried out by scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), focused ion beam spectroscopy (FIB), and X-ray diffraction (XRD) techniques to study the coating process and to show successful deposition of pure Cu. The mechanism of electroless Cu coating is mainly studied with the help of XPS, which shows the reduction of PdCl 2 (activator) catalyst on the surface of cenosphere particles by SnCl 2 (sensitizer) to produce pure Pd 0 clusters, which subsequently act as nucleation sites for Cu deposition. The concept of XPS core-level binding energy (BE) shift due to small cluster size is utilized to predict the size of pure Pd 0 clusters deposited on the fly-ash particle surface after the activation step. For the first time, the use of FIB technique is described and demonstrated to determine directly the Cu coating thickness.

Sol-Gel Synthesis and Phase Evolution Behavior of Sterically Stabilized Nanocrystalline Zirconia

Nanocrystalline as well as submicron sized, non-agglomerated, spherical ZrO2 particles have been successfully synthesized using the sol-gel technique utilizing hydroxypropyl cellulose (HPC) as a polymeric steric stabilizer. The effect of various parameters such as the ratio of molar concentration of water and alkoxide (R), the molar concentration [HPC] and the molecular weight (MWHPC) of HPC polymer as well as the calcination temperature on ZrO2 nanocrystallites size and their phase evolution behavior is systematically studied. The phase evolution behavior of nanocrystalline ZrO2 is explained and correlated with the adsorption behavior of HPC polymer on ZrO2 nanoparticles surface, which is observed to be a function of R, [HPC], MWHPC and the calcination temperature. Optimum synthesis parameters for obtaining 100% tetragonal phase in nanocrystalline ZrO2 are identified for the present sol-gel method of synthesizing nanoparticles.

Effect of ultraviolet radiation exposure on room-temperature hydrogen sensitivity of nanocrystalline doped tin oxide sensor incorporated into microelectromechanical systems device

The effect of ultraviolet (UV) radiation exposure on the room-temperature hydrogen (H2) sensitivity of nanocrystalline indium oxide (In2O3)-doped tin oxide (SnO2) thin-film gas sensor is investigated in this article. The present sensor is incorporated into microelectromechanical systems device using sol-gel dip-coating technique. The present sensor exhibits a very high sensitivity, as high as 65 000–110 000, at room temperature, for 900ppm of H2 under the dynamic test condition without UV exposure. The H2 sensitivity is, however, observed to reduce to 200 under UV radiation, which is contrary to the literature data, where an enhanced room-temperature gas sensitivity has been reported under UV radiation. The observed phenomenon is attributed to the reduced surface coverage by the chemisorbed oxygen ions under UV radiation, which is in consonance with the prediction of the constitutive equation, proposed recently by the authors, for the gas sensitivity of nanocrystalline semiconductor oxide thin-film sensors.

Hydrogen-discriminating nanocrystalline doped-tin-oxide room-temperature microsensor

Highly hydrogen (H2)-selective [relative to carbon monoxide (CO)] sensor, operating at room temperature, has been fabricated using the micronanointegration approach involving the deposition of the nanocrystalline indium oxide (In2O3)-doped tin oxide (SnO2) thin film on microelectromechanical systems device. The present microsensor exhibits high room-temperature sensitivity towards H2 (S=12700); however, it is insensitive to CO at room temperature. In view of the different gas selectivity mechanisms proposed in the literature, it is deduced that the In2O3 doping, the presence of InSn4 phase, the low operating temperature (room temperature), the mesostructure, the small sizes of H2 and H2O molecules, the bulky intermediate and final reaction products for CO, and the electrode placement at the bottom are the critical parameters, which significantly contribute to the high room-temperature H2 selectivity of the present microsensor over CO. The constitutive equation for the gas sensitivity of the semiconductor ...

Synthesis and Characterization of Silver Sulfide Nanoparticles Containing Sol-Gel Derived HPC-Silica Film for Ion-Selective Electrode Application

Silver sulfide nanoparticles dispersed in sol-gel derived hydroxypropyl cellulose (HPC)-silica films have been successfully synthesized using H2S gas diffusion method. This is the first attempt to produce silver sulfide nanoparticles using this technique. Ag2S nanoparticles are generated through reaction of H2S gas with AgNO3 precursor dissolved in the HPC-silica matrix. Transmission electron microscope (TEM) and atomic force microscope (AFM) analysis reveal nanoparticles size distribution from 2.5 nm to 56 nm for H2S gas exposed sample. The surface chemistry of Ag2S nanoparticles and sol-gel derived HPC-silica matrix is confirmed by X-ray photoelectron spectroscopy (XPS). The negative shifts in the core-level XPS Ag (3d) binding energy of Ag2S nanoparticles are attributed to Ag : S surface atomic ratio exhibited by these nanoparticles with varying processing conditions. Following processing and characterization, suitability of the present method to produce silver sulfide ion-selective electrode is demonstrated by depositing Ag2S nanoparticles on a graphite rod. The high reponse function of the electrode is due to the presence of nanoparticles.

A nanoparticle-based microsensor for room temperature hydrogen detection

In this work, we report a novel micromachined hydrogen sensor operating at room temperature. The sensor has been successfully designed and fabricated, based on interdigitated conductometric microelectrodes integrating indium oxide (In/sub 2/O/sub 3/)-doped tin oxide (SnO/sub 2/) semiconductor nanocrystalline particles with platinum (Pt) nanoclusters. Very high H/sub 2/ sensitivity (110/spl times/10/sup 3/) with fast response and recovery has been observed for the presented sensor at room temperature and low hydrogen gas concentration. The nanomaterial/microdevice integration for a highly efficient sensor device with unprecedented functions has been explored and investigated systematically.

Room Temperature Hydrogen Gas Sensitivity of Nanocrystalline-Doped Tin Oxide Sensor Incorporated into MEMS Device

Nanocrystalline indium oxide (In 2 O 3 )-doped tin oxide (SnO 2 ) thin film sensor has been sol-gel dip-coated on a microelectromechanical systems (MEMS) device. The micro-sensor device is successfully utilized to sense ppm level H 2 at room temperature with high sensitivity. The chamber pressure has no pronounce effect on the room temperature H 2 sensitivity.

CTEM, HRTEM and FE-AEM Investigation of the Metastable Tetragonal Phase Stabilization in Undoped, Sol-Gel Derived, Nanocrystalline Zirconia

Stabilizing the metastable t-phase in ZrO2 powders is a major challenge and dopants are usually used [1]. In this paper, the mechanisms underlying stabilization of the t-phase in undoped, sol-gel derived nanocrystalline ZrO2 are studied by conventional and high-resolution transmission electron microscopy (CTEM/HRTEM) combined with field-emission analytical electron microscopy (FEAEM) utilizing parallel electron energy-loss spectroscopy (PEELS). ZrO2 nanopowders were synthesized by hydrolysis of zirconium (IV) n-propoxide in an alcohol solution at two ratios of molar concentrations of water to zirconium n-propoxide, R=5 and 60, in the presence of 1.0 g/L hydroxylpropyl cellulose. The sol was subsequently dried at 80C following calcination of a gel for 2 h at 400C in air. Samples were examined using bright-field (BF) and dark-field (DF) TEM, selected-area electron diffraction (SAED) and HRTEM in a JEOL 4000EX TEM operating at 400 kV and in a JEOL 2010F FE-AEM operating at 200 kV and equipped with a Gatan Model 678 Imaging Filter. The as-precipitated ZrO2 processed with R=5 contained highly aggregated clusters and elongated denser particles 200-500 nm in diameter. HRTEM examination, however, revealed nanocrystals 5-11 nm in size, randomly distributed in the amorphous matrix (Fig. 1a) that could serve as nuclei for growing crystalline phases during calcination. In contrast, calcinated ZrO2 particles 400-600 nm in size, were found to be highly crystalline as indicate distinct Bragg reflections assigned to the t-phase in a SAED pattern (insert in Fig. 1b). DF TEM using the 1 0 1 reflection showed 10-100 nm–sized crystalline regions of various shapes throughout the particles. Multiple lattice fringes with spacings ~0.25-0.64 nm were observed by HRTEM (Fig. 1c). The ZrO2 powder precipitated at R=60 consisted of 4-11 nm-sized particles forming aggregates (~50-100 nm) with an amorphous structure (Fig. 2a). The SAED pattern (insert in Fig. 2a) shows a broad diffuse ring with an intensity maximum corresponding to the most probable interatomic spacing ~ 0.3 nm. BF TEM (Fig. 2b) and HRTEM of the calcinated powder (Fig. 2b) revealed aggregates of randomly oriented 8-100 nm-sized nanocrystals of various shapes with two families of lattice fringes of ~0.3 nm and 0.71-0.99 nm. The SAED pattern (insert in Fig. 2b) displays discrete rings and spot reflections, which were indexed according to both m and t-phase spacings. The net PEEL intensity (Fig. 2c) satisfactorily fits to the expected position of a direct band gap for ZrO2 (solid curve) between 4-5 eV energy loss [2]. For the as-precipitated nanopowder (dash curve), the intensity threshold is clearly less pronounced, probably due to a number of defect states in the gap. The peaks below 30 eV are primarily associated with plasmons and interband transitions, while those above 30 eV are related to the Zr-N2,3 edge with an onset at ~32 eV energy loss. An unresolved peak at ~7.4 eV is likely due to excitation of valence electrons into unoccupied d-states in the conduction band. The bulk plasmon at 13.4 eV for the nanocrystalline material is reduced in intensity and shifted to 14.7 eV for the as-precipitated sample. The broad peak at 25-26 eV is at least partly due to additional unexhausted collective excitation of all (16) valence electrons of O and Zr per ZrO2 unit. Fingerprints of the ZrO2 band structure in the low-loss PEEL spectra allow differentiation between the amorphous-like and nanocrystalline powders. Stabilization of the t-phase with much larger 410 Microsc Microanal 9(Suppl 2), 2003 Copyright 2003 Microscopy Society of America DOI: 10.1017/S1431927603442050

A Room Temperature Hydrogen Sensor With High Sensitivity and Selectivity Using Nanocrystalline Semiconductor Particles

Micro hydrogen sensor with interdigitated electrodes and indium doped nanopolycrystalline SnO2 particles was fabricated and tested. Giant sensitivity as high as 105 with good repeatability and recovery was observed. The sensor showed an excellant selectivity of hydrogen (H2 ) sensing over helium (He).Copyright

A Novel Theoretical Model for Semiconductor Oxide Gas Sensor

A new constitutive equation for the gas sensitivity of n-type semiconductor oxide thin film gas sensor has been proposed here based on a single-crystal model. The derived constitutive equation shows the dependence of the gas sensitivity on various critical parameters such as nanocrystallite size, space-charge-layer thickness, reducing gas concentration, bulk charge-carrier-concentration, surface-density of states, oxygen-ion-vacancy concentration, operating temperature, and film thickness. The present theoretical model is applicable to all n-type semiconductor oxides gas sensors.