S. A. Gangal

ZnO-nanowires modified polypyrrole films as highly selective and sensitive chlorine sensors

Room temperature sensing characteristics of the polypyrrole (PPy) films modified with different weight percentages of ZnO nanowires (ZnO-NWs) have been studied for various oxidizing (NO2 and Cl2) as well as reducing (H2S, NH3, CH4, and CO) gases. We demonstrate that ZnO-NW (50 wt %):PPy composite films are highly selective to Cl2 along with high-sensitivity (40 at 10 ppm), fast-response (55 s), and highly reproducible response curves. It has been shown that negatively charged O2− surfaces of ZnO-NW transfer electrons to PPy, making it in a highly reduced form. A strong localization of charge carriers in the reduced PPy makes composite film highly resistive (>1010 Ω cm) as well insensitive to interaction with most of the gases except Cl2. Cl2 being highly oxidizing gas interacts with composite films and causes a sharp reduction in its resistivity.

Characterization of SnO2-based H2 gas sensors fabricated by different deposition techniques

Thick and thin films of SnO2 are extensively used for resistive gas sensors. Characteristics are compared for films produced by four different techniques – chemical vapour deposition (CVD), spray pyrolysis, vacuum evaporation and screen printing. The films are characterized for H2 sensing only, using a static measurement system to investigate their temperature selectivity. The samples are tested at a concentration of 300 p.p.m. H2 gas, a typical value for comparison. No selective peak is observed for CVD and spray deposited samples, and the selective peak for vacuum evaporated samples has a low sensitivity. But the selective peak for screen printed samples has a sensitivity of 55% (δR/Rair). And what is more, the screen printed samples have a repeatable response.

Electrochemical polymerization of poly(o-anisidine) thin films: effect of synthesis temperature studied by cyclic voltammetry

The effect of temperature on the electrochemical synthesis of poly(o-anisidine) (POA) thin films has been investigated. The POA films were synthesized electrochemically under cyclic voltammetric conditions in aqueous solutions of H2SO4 at various temperatures between -6°C and 40°C. These films were characterized by cyclic voltammetry (CV), UV–visible spectroscopy and scanning electron microscopy (SEM). It has been found that the rate of polymer formation depends on the synthesis temperature and is highest at 15°C. The optical absorption spectra indicate a major peak at about 800nm and a shoulder at about 440nm independent of the synthesis temperature. The peak at about 800nm corresponds to the presence of the emeraldine salt phase of POA, while the latter may be attributed to the formation of radical cations. The absorbance and width of the peak at about 800nm is observed to increase at low synthesis temperatures. The POA film synthesized at 15°C shows predominant formation of the emeraldine salt phase of POA. The surface morphology as revealed by SEM, is observed to depend on the synthesis temperature, and is caused by different rates of polymer formation at different temperatures.

Microwave ring resonator as a novel bio-material moisture sensor

Abstract A novel miniature microwave microstrip sensor for the study of moisture in bio-materials (paper and leaves) is suggested. The leaf-drying process (time-variation) exhibits the leaf-specific nature. The paper-moisture estimation using f r and Q r variations are the two complementary moisture sensing methods. The Q r variations are useful to sense low moisture level, less than 10% M ww , with sensitivity of the order of 300% M ww −1 , with an error of 1.57% M ww in the estimated moisture. The f r variations are useful to sense moisture in the wider range 0–40% M ww , with sensitivity of the order of 25 MHz % M ww −1 , with an error of 2.2% M ww in the estimated moisture. The trend of f r variations with percentage M ww for both types of bio-materials, could be divided broadly in two regions with an additional region shown by the high moisture containing leaves. A preliminary explanation of the related dominant phenomena is attempted.

Characterization of silicon films deposited in presence of nitrogen plasma

Abstract Silicon films are deposited in presence of nitrogen plasma with the technique known as ‘activated reactive evaporation (ARE)’ with a view to deposit silicon nitride films on silicon substrate at room temperature. The in-house fabricated ARE system consists of a high vacuum chamber (e-beam gun housing) and a low vacuum chamber (reaction chamber) separated by a plate with an opening at the center. Silicon was evaporated by an electron beam (e-beam) gun in the presence of nitrogen plasma and films were deposited on a silicon substrate at room temperature. A number of experiments were carried out for testing the system and for checking the repeatability of the deposition of the films. The characterization of the films deposited on silicon substrates was done using X-Ray Diffraction, X-ray Photoelectron Spectroscopy and Energy Dispersive Analysis of X-ray (EDAX). Refractive index of 1.97 obtained from ellipsometric measurements is in good agreement with that of the standard value of silicon nitride. Observation under SEM showed particulates of silicon on the surface of the film. The same was confirmed from spot EDAX analysis. These results indicate that the deposited films are non-stoichiometric and contain both silicon nitride and a phase of silicon oxynitride.

Deposition of silicon films in presence of nitrogen plasma—A feasibility study

A design, development and validation work of plasma based ‘activated reactive evaporation (ARE) system’ is implemented for the deposition of the silicon films in presence of nitrogen plasma on substrate maintained at room temperature. This plasma based deposition system involves evaporation of pure silicon by e-beam gun in presence of nitrogen plasma, excited by inductively coupled RF source (13.56 MHz). The activated silicon reacts with the ionized nitrogen and the films get deposited on silicon substrate. Different physical and process related parameters are changed. The grown films are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and ellipsometry. The results indicate that the film contains silicon nitride and a phase of silicon oxy nitride deposited even at room temperature. This shows the feasibility of using the ARE technique for the deposition of silicon films in nitrogen plasma.

STUDY OF BI-COLOURED LEAVES BY MICROWAVE MICROSTRIP MOISTURE SENSOR

Abstract The manuscript reports for the first time, the study of bi-coloured leaves using Microstrip Moisture Sensor. The sensor gives different trends of fr and BW variations for complete green leaves, complete yellow leaves and those with patchy combination of the two colours. The colour dependent trends are related to the chlorophyll concentration. This study brings out the basic differences in the yellow and green leaves like high porosity and hence, low ϵeff of yellow leaves compared to green leaves. The possibility to use it as a moisture sensor with different calibration equations depending on colour and two moisture ranges (which are related to dominant phenomena) makes it more versatile. The maximum sensitivity of the sensor is obtained in the high moisture range for fr variations and is 22 MHz/%Mww for green leaves and 39 MHz/%Mww for yellow leaves. Thus, the most important application of the sensor will be to check the leaf moisture for water scheduling of cash crops.

Comparative Study of Irradiated And Annealed ZnO Thin Films For Room Temperature Ammonia Gas Sensing

Ceramic based thin film sensors are well known for gas sensing applications. These sensors are operated at elevated temperature for good sensitivity. ZnO thin film sensors operated at high temperature are used in ammonia sensing application. But to the best of authors knowledge no room temperature ZnO (Zinc Oxide) thin film sensors are reported. The deposited ZnO films are found to be highly unstable with respect to resistance of the films at room temperature. To increase the stability two different techniques viz annealing and irradiation are tried. Comparative study of annealed and irradiated ZnO films for stability in resistance is done. Further the performance of these films as ammonia (NH3) gas sensor at room temperature has been studied. The results obtained are reported in this paper and analyzed.

Characterization of indium nitride films deposited by activated reactive evaporation process

Indium nitride films are deposited in the presence of nitrogen plasma by ‘activated reactive evaporation (ARE)’ process on silicon substrate maintained at room temperature. Indium powder was evaporated by resistive heating in the presence of nitrogen plasma excited by a radio frequency (RF) power source (13.56 MHz). The refractive index of 2.91 obtained by ellipsometry, was in good agreement with that of the standard value of indium nitride (η=2.9). Observation of the films by scanning electron microscope shows a smooth and pinhole-free surface and the diffraction pattern reveals the polycrystalline nature with characteristics of hexagonal structure. In3d5/2, In3d3/2 and N1s levels X-ray photoelectron spectra are observed at binding energies of 443.4 eV, 451.8 eV and 396.5 eV, respectively, indicating the formation of indium nitride. Fourier transform infrared spectrum of the deposited film shows the presence of InN bond. These results indicate the feasibility of the ARE process for the deposition of indium nitride on silicon 〈100〉 substrate maintained at room temperature.

Nadi Parikshan Yantra and analysis of radial pulse

Diagnosis according to Ayurveda is to find the root cause of a disease. Out of the eight different kinds of examinations Nadi-Pariksha (pulse examination) is important. Nadi-pariksha is done at the root of the thumb by examining the radial artery using three fingers. The features associated with the pulse pressure signals are important from diagnostic point of view. Ancient Ayurveda identifies the health status by observing the wrist pulses in terms of ‘Vata’, ‘Pitta’ and ‘Kapha’, collectively called as tridosha, as the basic elements of human body and in their combinations.