Venkateswarlu Gaddam

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.

Low temperature VLS growth of ITO nanowires by electron beam evaporation method

Indium tin oxide (ITO) nanowires were grown at a lower substrate temperature of 400 °C via Au-catalyzed vapor–liquid–solid (VLS) growth mechanism by electron beam evaporation method. The grown nanowires had length and diameter of 0.8–1.2 μm and 20–50 nm, respectively for growth duration of 20 min. Transmission electron microscope studies confirm the single crystalline nature of the nanowires, and energy dispersive spectroscopy studies on the individual nanowires also confirm that nanowire growth proceeds via Au-catalyzed VLS growth mechanism. Transition in the growth mechanism from Au-catalyzed VLS growth to self-catalyzed VLS growth was observed as the growth temperature changed from 400 to 200 °C. Self-catalytic VLS growth as well as Au catalyzed VLS growth was observed in a growth temperature window of 350–250 °C. This transition in the growth mechanism is mainly due to differences in the growth kinetics of Au-VLS and self-catalyzed VLS mechanism. These results indicate a good understanding of ITO nanowires growth by e-beam evaporation method. Diameters of the nanowires were tuned in a broad range of 20–90 nm by changing the Au catalyst layer thickness. This catalyst-assisted and low temperature growth method can be implemented for precise diameter controlled synthesis of ITO nanowires with mono dispersed gold catalyst particles instead of Au catalyst film to tune the optical properties of the nanowires.

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.

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.

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.

Low cost, disposable and wearable body warmer using RGO sheets coated on cloth substrate as heating element

Increase in customer demand for durable and functional fabric has been created an opportunity for nanomaterials to be integrated onto the textile substrates. We have fabricated a single step approach for electrically conductive textile for large scale production of reduced graphene oxide (RGO) nanosheets coated cotton cloth based films for heat generation application. It can be used as electro thermal wearable body warmer, in many industrial and laboratory applications. The RGO nanosheets aqueous dispersion was successfully prepared by solution mixing of RGO in N-Methyl-2-Pyrrolidone (NMP) using ultra sonication process. For the fabrication of RGO coated cotton cloth, the heating element film formation is carried out by dip coating method. The thickness of the heating element film is around 200 µm. As-prepared RGO nanosheets and RGO coated textile (cotton) cloth were characterized using XRD, FE-SEM techniques for their structural and surface morphology analysis. The RGO coated cotton cloth based electro thermal film annealed at 80µC temperature showed a good heating performance. Saturated temperature of around 52µC was attained when 40V is applied for 1 min to the fabricated device. It has been observed that, the power drawn by the device at 40 V was 480mW. The nanomaterials offer wide potential applications when integrated with garments that can be used to sense and respond to external parameters like electrical, optical and physiological signals. Importantly, the direct use of the aqueous dispersion of RGO in NMP opens up a new window for the next generation innovative wearable textile electronic devices. However, the field of nanotechnology, by considering the features of the textiles due to light weight, corrosion free, chemical stability for biomedical, automobile, flexible electronics for wearable technology etc. applications.

A novel piezoelectric ZnO nanogenerator on flexible metal alloy substrate

In this paper, we report a novel piezoelectric ZnO nanogenerator on flexible metal alloy substrate (Phynox alloy) for energy harvesting and sensing applications. The vertically aligned ZnO nanowires are sandwiched between Au electrodes. The aligned growth of ZnO nanowires have been successfully synthesized on Au coated metal alloy substrate by hydrothermal method at low temperature (95±1 °C). The as-synthesized vertically aligned ZnO nanowires were characterized using FE-SEM. Further, PMMA is spin coated over the aligned ZnO nanowires for the purpose of their long term stability. The fabricated nanogenerator is of size 30mm × 6mm. From energy harvesting point of view, the response of the nanogenerator due to finger tip impacts ranges from 0.9 V to 1.4V. Also for sensing application, the maximum output voltage response of the nanogenerator is found to be 2.86V due to stainless steel (SS) ball impact and 0.92 V due to plastic ball impact.

Kinetic Analysis of Human Gait using different types of footwear as Design Input for Activity based prosthetic foot

Recent trends emphasize the use of kinetic analysis (GRF, COP) of human gait for prosthetic development. These analysis help in designing and performance quantification of device specifically lower limb prosthetics. Footwear used plays an important role in normal gait. The effect of footwear was a topic of biomechanics research. The paper evaluates the effect of footwear (heeled and cushioned) in normal walking of individuals. The findings are used as a design input parameters for a development of new prosthetic foot and quantification of indigenously developed electronic knee.

Waste to Wealth Concept: Disposable RGO Filter Paper for Flexible Temperature Sensor Applications

We have developed a flexible reduced graphene oxide (RGO) temperature sensor on filter paper based cellulose substrate using vacuum filtration method. One of the most commonly used synthesized methods for RGO thin films is vacuum filtration process. It has several advantages such as simple operation and good controllability. The structural analysis was carried out by FE-SEM, in which the surface morphology images confirm the formation of RGO nanostructures on the filter paper substrate. It was observed that the pores of the filter paper were completely filled with the RGO material during the filtration process, subsequently the formation of continuous RGO thin films. As a results, the RGO films exhibits a piezoresistive property. The resulted RGO based films on the filter paper reveals the semiconducting behavior having sensitivity of 0.278 Omega/degrees C and negative temperature coefficient (NTC) about -0.00254 Omega / Omega /degrees C. Thus, we demonstrate a simplified way for the fabrication of RGO films on filter paper that possesses better and easier measurable macroscopic electrical properties. Our approach is for easy way of electronics, cost-effective and environment friendly fabrication route for flexible conducting graphene films on filter paper. This will enable for the potential applications in flexible electronics in various fields including biomedical, automobile and aerospace engineering.