M.M. Nayak

Morphology controlled synthesis of Al doped ZnO nanosheets on Al alloy substrate by low-temperature solution growth method

We report the morphology-controlled synthesis of aluminium (Al) doped zinc oxide (ZnO) nanosheets on Al alloy (AA-6061) substrate by a low-temperature solution growth method without using any external seed layer and doping process. Doped ZnO nanosheets were obtained at low temperatures of 60–90 °C for the growth time of 4 hours. In addition to the synthesis, the effect of growth temperature on the morphological changes of ZnO nanosheets is also reported. As-synthesized nanosheets are characterized by FE-SEM, XRD TEM and XPS for their morphology, crystallinity, microstructure and compositional analysis respectively. The doping of Al in ZnO nanosheets is confirmed with EDXS and XPS. Furthermore, the effect of growth temperature on the morphological changes was studied in the range of 50 to 95 °C. It was found that the thickness and height of the nanosheets varied with respect to the growth temperature. The study has given an important insight into the structural morphology with respect to the growth temperature, which in turn enabled us to determine the growth temperature window for the ZnO nanosheets. These Al doped ZnO nanosheets have potential application possibilities in gas sensors, solar cells and energy harvesting devices like nanogenerators.

A hollow stainless steel microneedle array to deliver insulin to a diabetic rat

A novel fabrication process has been described for the development of a hollow stainless steel microneedle array using femto second laser micromachining. Using this method, a complicated microstructure can be fabricated in a single process step without using masks. The mechanical stability of the fabricated microneedle array was measured for axial and transverse loading. Skin histology was carried out to study the microneedle penetration into the rat skin. Fluid flow through the microneedle array was studied for different inlet pressures. The packaging of the microneedle array, to protect the microneedle bore blockage from dust and other atmospheric contaminations, was also considered. Finally, the microneedle array was tested and studied in vivo for insulin delivery to a diabetic rat. The results obtained were compared with the standard subcutaneous delivery with the same dose rate and were found to be in good agreement.

Hard anodisation of aluminium and its application to sensorics

Abstract Hard anodising is normally carried out with electrolytes at subzero temperatures and with a very high current density. This may sometimes lead to burning and powdered deposits. In this work, a method of hard anodising at a higher temperature (10°C) using a pulsed power supply is investigated. The quality of coating obtained with this process is better than that obtained with the conventional method. Furthermore, it minimises the refrigeration requirements for cooling the electrolyte and eliminates the problem of burning and powdery coatings. The application of hard anodic coating with insulation resistance 1–30 GΩ up to 100 V dc to a pressure sensor as an insulating base layer is explored. The pressure sensor diaphragm is hard anodised, and this is followed by the deposition of a thin platinum–tungsten (92Pt–8W) film as strain sensor. The fabrication, characterisation and calibration of the pressure sensor and its applications are discussed.

Piezoelectric zinc oxide thin film for MEMS application: A comparative study

We report here, the study carried out on piezoelectric thin film for MEMS/Microsensor applications. The study includes characterization of sputtered thin film using indirect methods and comparison of behavior using cantilever technique for the confirmation of piezoelectric property. A suitable experimental setup was designed and fabricated for subjecting the cantilever to vibrate. The data was recorded for piezoelectric thin films deposited with different compositions. It is clearly evident that the direct method is inexpensive and easier for determining the quality of the deposited piezoelectric thin film.

Highly flexible and sensitive graphene-silver nanocomposite strain sensor

We are reporting, a novel reduced graphene oxide (RGO) and silver (Ag) nanocomposite based piezoresistive thin film sensor realized on kapton (polyimide) membrane substrate by drop casting method for strain sensing application. Incorporation of small quantity of (Ag) fillers into RGO, subsequently it can create a novel nanocomposite with improved structural and functional properties. The as-synthesized RGO and nanocomposite were characterized using X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM) for their structural properties and morphology analysis. As fabricated nanocomposite strain sensor undergoes piezoresistive behavior when mechanical strain is applied to the flexible substrate and its output resistance variations have been observed. The electromechanical property of nanocomposite was analyzed with mechanical cantilever bending method and the gauge factor of about 9 to 12 was observed. The change of electrical resistance of the nanocomposite film can be used in sensing mechanism for changes in chemical, biological, vibrational, temperature, pressure, load or force and displacement sensor applications.

A highly efficient iron doped BaTiO3 nanocatalyst for the catalytic reduction of nitrobenzene to azoxybenzene

In the present study, we report an efficient and high yielding catalytic reduction of nitrobenzene in the presence of 2-propanol or molecular H2 over Fe doped BaTiO3 nanocatalysts. This method provides 100% conversion of nitrobenzene with 93% and 95% AOB yield with 2-propanol and molecular H2 under the described experimental conditions, thus leading to efficient synthesis of azoxybenzene from nitrobenzene. The optimum Fe content to obtain high azoxybenzene yields was 2.5% and 10% in the presence of 2-propanol and molecular H2 respectively.

Synthesis of ZnO nanorods on a flexible Phynox alloy substrate: influence of growth temperature on their properties

A novel flexible alloy substrate (Phynox, 50 mm thick) was used for the synthesis of zinc oxide (ZnO) nanorods via a low-temperature solution growth method. The growth of ZnO nanorods was observed over a low temperature range of 60-90 degrees C for a growth duration of 4 hours. The as-synthesized nanorods were characterized using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) for their morphology, crystallinity, microstructure and composition. The as-grown ZnO nanorods were observed to be relatively vertical to the substrate. However, the morphology of the ZnO nanorods in terms of their length, diameter and aspect ratio was found to vary with the growth temperature. The morphological variation was mainly due to the effects of the various relative growth rates observed at the different growth temperatures. The growth temperature influenced ZnO nanorods were also analyzed for their wetting (either hydrophobic or hydrophilic) properties. After carrying out multiple wetting behaviour analyses, it has been found that the as-synthesized ZnO nanorods are hydrophobic in nature. The ZnO nanorods have potential application possibilities in self-cleaning devices, sensors and actuators as well as energy harvesters such as nanogenerators.

Negative temperature coefficient behavior of graphene-silver nanocomposite films for temperature sensor applications

we are reporting the fabrication of reduced graphene oxide (RGO) - silver (Ag) nanocomposite films for temperature sensor application on the basis of negative temperature coefficient (NTC) resistive element. The nanocomposite was successfully prepared by the solution mixing of RGO nanosheets and Ag metal nanoparticles in N-Methyl-2-Pyrrolidone (NMP) using ultrasonication process. It was found that, the as-formed Ag nanoparticles were dispersed homogeneously and uniformly on the surface of the RGO nanosheets within the nanocomposite system. The as-synthesized RGO nanosheets and nanocomposite were characterized by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD) for their surface analysis and structural properties respectively. The fabrication of temperature sensor, the sensing film formation is carried out on the flexible kapton membrane by using drop casting method. The thickness of the sensing film is around 50 μm. It was observed that the resistivity of nanocomposite sensing film decreased with the increase of temperature resulting in NTC behavior. The measured NTC and sensitivity of the sensor were found to be -0.00187 Ω / Ω / K and 0.40472 Ω /K respectively. Therefore, the synthesized graphene- silver nanocomposite film is an attractive material for making temperature sensors. Since the output is linear with respect to temperature variation, the electronic readout circuitry will be simpler. However, the mechanism of electrical resistance change of nanocomposite films can also be used in sensing environmental parameters such as chemical, biological, moisture and mechanical for their gas, glucose, humidity and strain/pressure sensor applications respectively.

Pressure sensor development using hard anodized aluminum diaphragm and sputtered Pt-W thin film strain sensors

Pressure sensors with a metallic diaphragm and bonded strain gauge are by far the most widely used sensors in pressure measurement. In this work, we describe a method to fabricate a low power, light weight and low cost pressure sensor using aluminum diaphragm. The diaphragm is hard anodized to get insulating base over which Pt-W (Pt: 92%, W: 8%) thin film strain sensors are sputter deposited for sensing the pressure. Hence, this technique eliminates the application of adhesive to bond the strain gauges to the metallic diaphragm. The required level of insulation resistance (in the range of giga-ohms) between the metal diaphragm and the sputtered stain gauge is provided by the hard anodic film. The hard anodic coating is obtained by the wet electrochemical method with pulsed power supply arrangement. The details of diaphragm fabrication, hard anodization of aluminum, testing, calibration of sensor and its applications are discussed and compared with sensors fabricated from different aluminum alloys (AA2024, AA6061 and AA7075).

Graphene-Nickel composite films on flexible PCB for temperature monitoring

This paper presents a novel method to fabricate temperature sensor arrays by screen printing Graphene - Nickel (Ni) nanocomposite film on flexible printed circuit board (PCB). Screen printing is a cost effective fabrication technique to get uniform thickness film on a substrate. The fabricated temperature sensor array, each having sensing thickness of around 50 µm is studied for the temperature response. The synthesized RGO nanosheets and RGO-Ni nanocomposite were characterized by XRD and FE-SEM for structural and compositional analysis. Temperature variation is measured in terms of change in resistance. It is observed that resistance decreases with the increase in temperature showing NTC (Negative Temperature Coefficient) behavior. The calculated response of the sensor in terms of sensitivity is around 2.455 Ω / K and temperature coefficient of resistance (TCR) is around − 2.635 × 10−3 Ω / Ω / K. Our approach shows a very simple fabrication process for making mass production of sensors on PCB that can be easily integrated with electronic devices and as a wearable body temperature sensor.