Prabhash Mishra

Silver Nanoparticles in Comparison with Ionic Liquid and rGO as Gate Dopant for Paper–Pencil-Based Flexible Field-Effect Transistors

Nanoparticle-based flexible field-effect transistors (FETs) containing carbon nanotubes (CNTs) and silicon nanowires (SiNWs) have attracted tremendous attention, since their interesting device performance can be utilized for integrated nanoscale electronics. However, use of CNTs and SiNWs on polymer substrates poses serious limitations in terms of their fabrication procedure, repeatability, and biodegradability. In this article, we report for the first time the fabrication and characteristics of solution-processed FETs on a paper substrate doped with easily prepared silver nanoparticles (AgNPs). To compare the FET performance, we fabricated two other FETs on paper containing ionic liquid (IL, 1-butyl-3-methylimidazolium octyl sulfate) and reduced graphene oxide (rGO) as dopants. We observe that the AgNP-based dopant generated good FET characteristics in terms of linear transconductance variations and higher carrier concentration values, showing negligible changes after bending and aging. In comparison with the AgNP-FET, the rGO- and IL-based dopants yielded high carrier mobilities, but the rGO-based FET is more susceptible to aging and bending. The excellent linearity of the IDS–VG curve found for the AgNP-FET ensures its applicability for devices requiring linear transfer characteristics such as linear amplifiers.

Effect of pyrrolidinium based ionic liquid on the channel form of gramicidin in lipid vesicles

The present work is focused on the interaction between membrane bound gramicidin and 1-butyl-1-methyl-2-oxopyrrolidinium bromide (BMOP) ionic liquid. Ionic liquids (ILs) are solvents that are often liquid at room temperature and composed of organic cation and appropriate anion. The gramicidin peptide forms prototypical ion channels for cations, which have been extensively used to study the organization, dynamics, and function of membrane spanning channels. The interaction was studied by circular dichroism, steady state, time-resolved fluorescence spectroscopy in combination with dynamic surface tension and field emission scanning electron microscopic methods (FESEM). The results obtained from circular dichroism shows that the BMOP interacts with the channel form of gramicidin in lipid vesicle without any considerable effect on its conformation. The Red-edge excitation shift (REES) also supported the above findings. In addition, the fluorescence studies suggested that BMOP makes ground state complex with ion channel, which was further supported by time resolved measurements. Furthermore, dynamic surface tension analysis shows the faster adsorption of BMOP with membrane bound gramicidin at the air-water interface. Additionally, FESEM results indicated that BMOP forms a film around the membrane bound gramicidin at higher concentration. These results are potentially useful to analyze the effect of ionic liquids on the behaviour of membrane proteins.

Influence of thermo-mechanical processing on microstructure, mechanical properties and corrosion behavior of a new metastable β-titanium biomedical alloy

This paper presents the results on the influence of different thermo-mechanical processing (TMP) on the mechanical properties and electrochemical behavior of new metastable β-alloy Ti–20.6Nb–13.6Zr–0.5V (TNZV). TMP included hot working in below β-transus, solution heat treatments at same temperature in different cooling rates in addition to aging. Depending upon the TMP conditions, a wide range of microstructures with varying spatial distributions and morphologies of equiaxed/elongated α, β phases were attained, allowing for a wide range of mechanical and electrochemical properties to be achieved. The corrosion behavior of studied alloy was evaluated in Ringer’s solution at 37∘C using open-circuit potential-time and potentiodynamic polarization measurements.

Effect of Growth Temperature on the Diameter Distribution and Yield of Carbon Nanotubes

Growth of carbon nanotubes (CNTs) on iron sputtered Si substrate has been done by using self design Thermal Chemical Vapor Deposition (TCVD) at atmospheric pressure. Parameters of CNTs are highly dependent on the growth temperature. A strong relation between CNT’s diameter, yield and growth temperature was found. The experiments were done in the temperature range of 750–900 °C with an interval of 25 °C. It was found that at 750 °C there was no growth of CNT. However, at 775 °C, the horizontal network of CNTs having diameter range of 8–12 nm with sufficient yield was observed. As we increase the temperature, an increase in CNT’s diameter and decrease in yield was found. These results demonstrate that diameter and yields of CNTs can be controlled with the growth temperature.

Development and standardization of porous silicon for application as a working electrode in electrochemical immunosensor

Electrectrochemical immunosensors have diverse applications in areas like medical diagnostics, food industry, environmental monitoring etc. The conductive materials like Indium Tin oxide coated glass (ITO), glassy carbon, porous silicon (PS) etc. can be useful as working electrode for electrochemical immunosensor applications. But the porous silicon is particularly attractive for this application due to its modified properties like very large surface area to volume ratio, surface dependent properties (electrical and optical), photoluminescence at room temperature and biocompatibility. In this paper porous silicon is investigated for development as working electrode for label free model immunosensor based on Human IgG.

Reduced graphene oxide (rGO) based wideband optical sensor and the role of Temperature, Defect States and Quantum Efficiency

We report a facile and cost-effective approach to develop self-standing reduced Graphene Oxide (rGO) film based optical sensor and its low-temperature performance analysis where midgap defect states play a key role in tuning the crucial sensor parameters. Graphite oxide (GO) is produced by modified Hummers’ method and reduced thermally at 250 °C for 1 h in Argon atmosphere to obtain rGO. Self-standing rGO film is prepared via vacuum filtration. The developed film is characterized by HRTEM, FESEM, Raman, and XRD techniques. The developed sensor exhibits highest sensitivity towards 635 nm illumination wavelength, irrespective of the operating temperature. For a given excitation wavelength, photoresponse study at low temperature (123K–303K) reveals inverse relationship between sensitivity and operating temperature. Highest sensitivity of 49.2% is obtained at 123 K for 635 nm laser at power density of 1.4 mW/mm2. Unlike sensitivity, response- and recovery-time demonstrate directly proportional dependence with operating temperature. Power dependent studies establish linear relation between power-density and sensitivity, and a safe limit beyond which sample heating prolongs the recovery time. Wavelength-dependent studies shows that proposed sensor can efficiently operate from visible to near NIR region. To the best of our knowledge such rGO based optical sensor performance at low temperature had not been reported earlier.

Development of Commercial Trace Moisture Sensor: A Detailed Comparative Study on Microstructural and Impedance Measurements of Two Phases of Alumina

Porous alumina thin film has been investigated in order to find its sensitivity in the trace moisture level. Alumina, with two different phases were obtained using sol-gel process and fired between 400°C to 1000°C. FESEM, BET, AFM and XRD techniques were employed for microstructural characterization of the sintered thin film in two phases. A detailed analysis is done to assess the superiority of gamma (γ) — over alpha (α) phase using impedance spectroscopy. It was observed that gamma phase is more sensitive towards trace level moisture sensing.

Importance of network density of nanotube: Effect on nitrogen dioxide gas sensing by solid state resistive sensor

Dispersion of single-walled carbon nanotubes (SWCNTs) is an established fact, however, its effect on toxic gas sensing for the development of solid state resistive sensor was not well reported. In this report, the dispersion quality of SWCNTs has been investigated and improved, and this well-dispersed SWCNTs network was used for sensor fabrication to monitor nitrogen dioxide gas. Ultraviolet (UV)-visible spectroscopic studies shows the strength of SWNTs dispersion and scanning electron microscopy (SEM) imaging provides the morphological properties of the sensor device. In this gas sensor device, two sets of resistive type sensors were fabricated that consisting of a pair of interdigitated electrodes (IDEs) using dielectrophoresis technique with different SWCNTs network density. With low-density SWCNTs networks, this fabricated sensor exhibits a high response for nitrogen dioxide sensing. The sensing of nitrogen dioxide is mainly due to charge transfer from absorbed molecules to sidewalls of nanotube and t...

Polymer optimization for the development of low-cost moisture sensor based on nanoporous alumina thin film

Sol-gel processed alumina (Al2O3) thin film has been investigated for sensing moisture. The sensor was based on ordered nanoporous Al2O3 thin film, which consisted of gold electrodes on both sides of the film forming parallel plate capacitor. Alumina substrate was used for supporting thin film moisture sensor. Hydrophilicity was achieved by controlling the surface energy of the substrate and polymer (polyvinyl alcohol (PVA)) optimization was done for developing rigid thin film over it. A high change in capacitance was observed as the moisture level increased from 5 ppmV to 500 ppmV. Scanning electron microscopy (SEM) results revealed that pores were distributed uniformly throughout the sample, which enhanced the adsorption of water molecule over the film. X-ray diffraction (XRD) study clearly confirmed the gamma (γ) phase of alumina thin film. It was found that the sensitivity of our sensor was suitable for commercial application.

Signature of growth deposition technique on the properties of PECVD and thermal SiO2

In this article, we report the process induced variation in the characteristics of PECVD deposited and thermally grown silicon dioxide (SiO2) thin film. We find key differences in the porosity, arrangement of the nano-pores, surface roughness, refractive index and electrical resistivity of the SiO2 thin films obtained by the two methods. While the occurrence of the nanoporous structure is an inherent property of the material and independent of the process of film growth or deposition, the arrangements of these nano-pores in the oxide film is process dependent. The distinct arrangements of the nano-pores are signatures of the deposition/growth processes. Morphological analysis has been carried out to demonstrate the difference between oxides either grown by thermal oxidation or through PECVD deposition. The tunable conductive behavior of the metal filled nano-porous oxides is also demonstrated, which has potential to be used as conductive oxides in various applications.In this article, we report the process induced variation in the characteristics of PECVD deposited and thermally grown silicon dioxide (SiO2) thin film. We find key differences in the porosity, arrangement of the nano-pores, surface roughness, refractive index and electrical resistivity of the SiO2 thin films obtained by the two methods. While the occurrence of the nanoporous structure is an inherent property of the material and independent of the process of film growth or deposition, the arrangements of these nano-pores in the oxide film is process dependent. The distinct arrangements of the nano-pores are signatures of the deposition/growth processes. Morphological analysis has been carried out to demonstrate the difference between oxides either grown by thermal oxidation or through PECVD deposition. The tunable conductive behavior of the metal filled nano-porous oxides is also demonstrated, which has potential to be used as conductive oxides in various applications.