Nita Dilawar

Faster response of NO2 sensing in graphene?WO3 nanocomposites

Graphene-based nanocomposites have proven to be very promising materials for gas sensing applications. In this paper, we present a general approach for the preparation of graphene-WO(3) nanocomposites. Graphene-WO(3) nanocomposite thin-layer sensors were prepared by drop coating the dispersed solution onto the alumina substrate. These nanocomposites were used for the detection of NO(2) for the first time. TEM micrographs revealed that WO(3) nanoparticles were well distributed on graphene nanosheets. Three different compositions (0.2, 0.5 and 0.1 wt%) of graphene with WO(3) were used for the gas sensing measurements. It was observed that the sensor response to NO(2) increased nearly three times in the case of graphene-WO(3) nanocomposite layer as compared to a pure WO(3) layer at room temperature. The best response of the graphene-WO(3) nanocomposite was obtained at 250 °C.

Phonon dynamics of Zn"Mg,Cd…O alloy nanostructures and their phase segregation

In this paper we report phonon dynamics in chemically synthesized Zn 1�x Mg x O 0x 0.07 and Zn1�yCdyO 0y 0.03 alloy nanostructures of sizes 10 nm using nonresonant Raman and Fourier transformed infrared spectroscopy. Substitution by Mg makes the unit cell compact while Cd substitution leads to unit cell expansion. On alloying, both A1 LO and E1 LO mode of wurtzite ZnO show blueshift for Zn1�xMgxO and redshift for Zn1�yCdyO alloy nanostructures due to mass defect and volume change induced by the impurity atoms. Significant shift has been observed in E 1 LO mode for Zn 1�x Mg x O 73 cm �1 for x = 0.07 and Zn 1�y Cd y O 17 cm �1 for y = 0.03 nanostructures. The variation in ZnMg,Cd–O bond length determined from the blue- red- shift of IR bands on alloying with Mg Cd is consistent with their respective ionic sizes and the structural changes predicted by x-ray diffraction study. However, on progressive alloying one can detect phase segregation due to presence of interstitial Mg and Cd ions in the alloy nanostructures for relatively higher Mg and Cd concentrations. This is confirmed by the gradual absence of the characteristic IR and Raman bands of wurtzite ZnO near 400– 600 cm �1 as well as by x-ray and TEM studies.

Intercomparison of National Hydraulic Pressure Standards up to 500 MPa

In order to provide inputs for improving the quality of measurements, achieving objective evidences of the technical competence and to build-up and maintain mutual confidence of national hydraulic pressure standards, an extensive in-house laboratory intercomparison is carried out in a systematic manner. The present paper describes the summary of the results thus obtained in this in-house laboratory intercomparison exercise of eight numbers of national hydraulic pressure standards, designated as NPL28MPA, NPL100MPN, NPL100MPA, NPL140MPA, NPL200MPN, NPL280MPA, NPL500MPN, NPL500MPA. The intercomparison of these pressure standards is carried out using an internationally accepted method of cross-floating of pressure balances. The uncertainty in area and pressure measurements is computed as per ISO, WECC and EAL guidelines. The compatibility, uniformity and affirmation of results is re-established by comparing the values of zero pressure effective area (A 0) and distortion coefficient (Λ) with the values obtained during bilateral and international key comparisons sponsored by BIPM, CCM, APLAC, LNE (France) and NIST (USA). The metrological characteristics thus obtained establish a very good agreement within the limits of uncertainty budgets of bilateral and international key comparisons.

Probing the correlation between structure, carrier dynamics and defect states of epitaxial GaN film on (110) sapphire grown by rf-molecular beam epitaxy

A systematic study has been performed to correlate structural, optical and electrical properties with defect states in the GaN films grown on a-plane (110) sapphire substrate via rf-plasma molecular beam epitaxy. Morphological analysis reveals the presence of small lateral size (30–70 nm) hexagonally shaped V-pits on the GaN films. These V-defects possibly contribute as the main source of non-radiative decay. High resolution X-ray diffraction reveals highly single crystalline GaN film grown on a-plane sapphire substrate where the threading dislocations are the cause of V-defects in the film. Photoluminescence measurement shows a highly luminescence band to band emission of GaN film at 3.41 eV along with a broad defect band emission centered at 2.2 eV. A detailed optical and electrical analysis has been carried out to study the defect states and related carrier dynamics for determining the efficacy of the film for device fabrication. The variation in the low temperature current voltage measurements confirms the presence of deep level defects in the mid-band gap region while transient spectroscopy shows that non radiative decay is the dominant relaxation mechanism for the photo excited-carriers from these defect states.

SIMS characterization of GaAs MIS devices at the interface

Abstract We report here the improvements in the electrical characteristics of Au/Si x N y /n-GaAs structures with NH 3 plasma treatment of GaAs prior to PECVD of a Si x N y dielectric film followed by annealing at 450 °C. These structures were characterized by secondary ion mass spectrometry (SIMS) depth profiling. The depth profiles of the three samples discussed in the present report show that the unpassivated sample has a broad interface consisting of both Ga–O and As–O species. After passivation, the interface becomes quite sharp, but the presence of both the oxides is still observed. However, after annealing, although the interface thickness increases marginally due to diffusion further into the substrate, it is observed that the interface becomes N-rich, which has also been supported by preliminary FTIR data. Looking at the electrical properties, it is seen that the unpassivated sample gives poor device characteristics which are attributed to the presence of wide oxide layers as shown by the SIMS data and consequently Fermi level pinning due to high interface state density, while the NH 3 passivated samples show better device characteristics. This is attributed to the fact that the interface state density reduces considerably as the interface thickness reduces. Post-deposition annealing showed marked improvement in device characteristics with decrease in frequency dispersion, conductance and hence interface state density as revealed from C – V and G – V measurements.

A low cost laser-Raman spectrometer

A Jobin Yvon-Spex (HR640) monochromator with a notch filter (514·5 nm) and Ar+ ion laser has been used to set up a low cost laser Raman spectrometer. The selection and setup of the various optical components used in the present work has been solely carried out in our laboratory. The calibration of the monochromator was established from the studies of various standard mercury lines and the obtained data fitted with the reported data. Raman signals have been recorded for a number of samples e.g. diamond, ruby, carbon tetrachloride (CCI4), benzene (C6H6) and ethanol (C2H5OH). The obtained results are found to be in excellent agreement with the reported values for these materials in the literature.

Final report on Key Comparison APMP.SIM.M.P-K1c: Bilateral comparison between NIST (USA) and NPLI (India) in the pneumatic pressure region 0.4 MPa to 4.0 MPa

We report the results of a bilateral comparison of pressure measurement between NIST and NPLI using a piston gauge transfer standard (TS), designated as NPLI-4, over the range of nominal applied pressure 0.4 MPa to 4.0 MPa. This TS was cross-floated against the laboratory secondary standard designated as PG13 at NIST, USA and against NPLI-8 at NPLI, India. The nominal pressure points of the bilateral comparison were (0.4, 0.8, 1.2, 1.6, 2.0, 2.4, 2.8, 3.2, 3.6 and 4.0) MPa, respectively. The comparison was performed in both the institutes in identical pressure cycles in increasing pressures. The comparison data were analysed in terms of the effective area [Ap (mm2)] as a function pressure [p (MPa)] of the TS at the above-mentioned pressures. We have also estimated the zero-pressure effective area [A0 (mm2)] and the pressure distortion coefficient [? (MPa-1)] of the transfer standard. The consistency of the results at every pressure in the range indicates that the laboratory standards used in this comparison are compatible, uniform and can be considered traceable to each other. Finally, the degree of equivalence between NPLI and NIST is 11.4 ? 10-6 or better, which is always less than the relative standard uncertainty of the difference (33.6 ? 10-6). Main text. To reach the main text of this?Paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Characterization of a pneumatic differential pressure transfer standard

The paper describes a novel method for the characterization of a pneumatic differential transfer standard in the differential pressure range 0?Pa to 3.5?MPa up to a high line gas pressure of 7.0?MPa. In view of the advances in the field of automated data acquisition systems an effort has been made to incorporate such a system in the conventional pressure measurement, which uses relatively high accuracy piston gauges and the user-friendly digital transducer. The transfer standard used in the present work is a silicon strain gauge transducer, model PMP 4115, made by Druck, with an output voltage range of 0?V to 5?V with a readout unit/power supply DPI?282. The transducer was characterized against the secondary standard, which is a twin pressure balance, Model?5502, made by Desgranges et Huot, France, designated as NPL-8. The characterization was done through an automated data acquisition system using a model 9118HR A/D interface card made by Adlink, as well as the readout unit DPI?282. The uncertainty estimations showed up considerable differences between the two modes of data acquisition. The observed results were further used to generate a regression equation for the estimation of differential pressure at any given line pressure.

Faster response of NO₂ sensing in graphene-WO₃ nanocomposites.

Graphene-based nanocomposites have proven to be very promising materials for gas sensing applications. In this paper, we present a general approach for the preparation of graphene-WO(3) nanocomposites. Graphene-WO(3) nanocomposite thin-layer sensors were prepared by drop coating the dispersed solution onto the alumina substrate. These nanocomposites were used for the detection of NO(2) for the first time. TEM micrographs revealed that WO(3) nanoparticles were well distributed on graphene nanosheets. Three different compositions (0.2, 0.5 and 0.1 wt%) of graphene with WO(3) were used for the gas sensing measurements. It was observed that the sensor response to NO(2) increased nearly three times in the case of graphene-WO(3) nanocomposite layer as compared to a pure WO(3) layer at room temperature. The best response of the graphene-WO(3) nanocomposite was obtained at 250 °C.

Faster response of NO2sensing in graphene–WO3nanocomposites

Graphene-based nanocomposites have proven to be very promising materials for gas sensing applications. In this paper, we present a general approach for the preparation of graphene-WO(3) nanocomposites. Graphene-WO(3) nanocomposite thin-layer sensors were prepared by drop coating the dispersed solution onto the alumina substrate. These nanocomposites were used for the detection of NO(2) for the first time. TEM micrographs revealed that WO(3) nanoparticles were well distributed on graphene nanosheets. Three different compositions (0.2, 0.5 and 0.1 wt%) of graphene with WO(3) were used for the gas sensing measurements. It was observed that the sensor response to NO(2) increased nearly three times in the case of graphene-WO(3) nanocomposite layer as compared to a pure WO(3) layer at room temperature. The best response of the graphene-WO(3) nanocomposite was obtained at 250 °C.