Pravin Walke

Indium doped tin oxide submicrometre sized wires have been synthesized by thermal evaporation and characterized by field emission (FE) microscopy. The non-linear Fowler–Nordheim plot corresponds to the typical semiconducting behaviour of the emitter. The field enhancement factor has been estimated to be 29 900 cm−1 indicating that electron emission is due to the nanometric features of the emitter. A current density of the order of 6.36 × 103 A cm−2 with an applied electric field of 1 × 104 V µm−1 has been obtained. The long term FE current stability tested at the preset current level of 1 µA exhibits no severe fluctuations.

Branched nanostructures of semiconducting materials are of great interest for their potential applications in optoelectronic, photonic devices and sensors. We herein describe a facile single-step chemical vapor deposition route for the synthesis of Sb–SnO2 hyperbranched nanostructures comprised of elongated nanowires with 30–40 nm diameter and 10–20 m length. The morphology and structure has been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selective area electron diffraction (SAED), and powder X-ray diffraction (XRD). Also, a possible mechanism is proposed for the growth of nanowires into the hyperbranched form on the basis of the substrate effect, the role of Au nanoparticles, and the effect of Sb doping on specific morphology evolution. Interestingly, electrical conductivity measurements as a function of temperature suggest a semiconducting behavior, despite being governed by different electron-transport mechanisms with activation energies of 0.55 and 0.17 eV, which correspond to pure SnO2 and Sb–SnO2 nanowires, respectively. A precise control over the operating parameters not only envisages custom-designed, branched structures by a simple and economical route but also offers an alternative method to the expensive and tedious nanofabrication techniques for industrial applications.

Integrated magnetic sensors based on niobium dc SQUID (Superconducting Quantum Interference Device) for nanoparticle characterizations are presented. The SQUIDs consists of two Dayem bridges of 90 nm × 250 nm and loop area of 4, 1, and 0.55 μm2. The devices are realized by using an e-beam lithography nano-fabrication process which can directly pattern the devices in an electron-positive resist and then transferred to a 20 nm single niobium layer by a lift-off post-process. The SQUIDs were designed to have a hysteretic current–voltage characteristic in order to work as a magnetic flux-current transducer. The presence of an integrated niobium coil, tightly coupled to the SQUID, allows us to easily excite the SQUID and to flux bias the SQUID at its optimal working point. Current–voltage characteristics, critical current as a function of the external magnetic field and switching current distributions were performed at liquid helium temperature. A critical current modulation of about 20% and a current-magnetic flux transfer coefficient (responsivity) of 30 μA/Φ0 have been obtained, resulting in a magnetic flux resolution better than 1 mΦ0. The authors performed preliminary measurements with and without iron oxide nanoparticles on the SQUID loop in order to show the device sensitivity in view of nano-magnetism applications. It was showed that the presence of magnetic nanoparticles can be easily detected and the magnetic relaxation curve measured.

We present the improved Superconducting Quantum Interference Devices (SQUID) for magnetic microscopy and for nanoscale investigations. Low critical Temperature SQUIDs with integrated micro pick-up coils (with inner diameter ranging from 5 to 50 μm) which can be used as magnetic field sensors in magnetic microscopy have been developed. The level of flux noise spectral density, measured in flux locked loop configuration and using a direct coupled scheme, is about 3μΦ0/√Hz in the white region at T = 4.2 K.
A high sensitive dc-SQUID based on niobium Dayem bridges for nanomagnetism is presented. The sensor has a flux capture area as low as 0.04 μm2, allowing the study of nano–object magnetic properties. The authors report the main design rules of the devices, the fabrication processes and their characterization including also the supercurrent decay measurements at T = 4.2 K.

We report well dispersed horizontal growth of ZnO sub-micron structures using simplest technique ever known i.e. chemical bath deposition (CBD). A set of samples were prepared under two different cases A) dumbbell shaped ZnO grown in CBD bath and B) tubular ZnO structures evolved from dumbbell shaped structures by dissolution mechanism. Single phase wurtzite ZnO formation is confirmed using X-ray diffraction (XRD) technique in both cases. From the morphological investigations performed using scanning electron microscopy (SEM), sample prepared under case A indicate formation of hex bit tool (HBT) shaped ZnO crystals, which observed to self-organize to form dumbbell structures. Further these microstructures are then converted into tubular structures as a fragment of post CBD process. The possible mechanism responsible for the self-assembly of HBT units to form dumbbell structures is discussed. Observed free excitonic peak located at 370 nm in photoluminescence (PL) spectra recorded at 18 K indicate that the micro/nanostructures synthesized using CBD are of high optical quality.

The highly crystalline PbWO4 nanorods were synthesized using simple co-precipitation method which has application in field effect transistor. The synthesized PbWO4 nanorods were characterized by XRD, Raman spectroscopy, TEM and HRTEM indicating highly crystalline nature. Field effect transistor was fabricated on pre-patterned 300 nm SiO2/Si substrates using photolithography technique with channel length 1 µm and width 20 µm. Thin film (~100 nm) was made up of PbWO4 nanorods by spin coating on the pre-patterned device used as channel layer. The field effect mobility was observed to be 4.7 cm2 V−1 s−1 and ION/OFF ratio ~103 which is far better than the organic molecules due to single crystalline nature and rod like morphology of the PbWO4 providing direct path for charges to transport towards channel.

In the present work, we have investigated the charge storage capacitive response and field emission behaviour of platinum (Pt) nanoparticles decorated on carbon nano onions (CNOs) and compared them with those of pristine carbon nano onions. The specific capacitance observed for Pt–CNOs is 342.5 F g−1, about six times higher than that of pristine CNOs, at a scan rate of 100 mV s−1. The decoration with Pt nanoparticles, without any binder or polymer separator on the CNO, leading to enhanced supercapacitance is due to easy accessibility of Na2SO4 electrolyte in the active material. The Density Functional Theory (DFT) calculations of these systems reveal enhancement in the Density of States (DOS) near the Fermi energy (EF) on account of platinum decoration on the CNOs. Furthermore, the field emission current density of ∼0.63 mA cm−2 has been achieved from the Pt-CNOs emitter at an applied electric field of ∼4.5 V μm−1 and from the pristine CNOs sample current density of ∼0.4 mA cm−2 has been achieved at an applied electric field of ∼6.6 V μm−1. The observed enhanced field emission behavior has been attributed to the improved electrical conductivity and increased emitting sites of the Pt–CNO emitter. The field emission current stability of the Pt–CNO emitter over a longer duration is found to be good. The observed results imply multifunctional potential of Pt–CNOs, as supercapacitor material in various next generation hybrid energy storage devices, and field emitters for next generation vacuum nano/microelectronic devices.

The results of an investigation of the structure, composition, and topography of the surface of buffer layers of CeO2, LaNiO3, and CeO2 + LaNiO3 on nonmagnetic textured NiCr9.2W2.4 substrates with a cube texture, which were prepared by pulsed laser deposition, are presented. The substrates with a buffer layer of this composition can be of interest for growing thin films and heterostructures of a wide class of oxide compounds, including superconductors of composition YBa2Cu3O7 − δ (123).

High quality amorphous nanolaminates by means of alternate Al2O3 and TiO2 oxide sublayers were grown with atomic scale thickness control by pulsed laser deposition. A giant dielectric constant (>10 000), strongly enhanced compared to the value of either Al2O3 or TiO2 or their solid solution, was observed. The dependence of the dielectric constant and the dielectric loss on the individual layer thickness of each of the constituting materials was investigated between 0.3 nm and 1 nm, in order to understand the prevailing mechanisms and allow for an optimization of the performances. An impedance study confirmed as the key source of the giant dielectric constant a Maxwell–Wagner type dielectric relaxation, caused by space charge polarization in the nanolaminate structure. The current work provides better insight of nanolaminates and their sublayer thickness engineering for potential applications.

In the present paper, performance of nano-superconducting-quantum-interference devices (SQUIDs) has been investigated in view of their employment in the detection of small spin populations. The analysis has been focused on nano-SQUID sensors having a square loop with a side length of 200 nm. We calculate the spin sensitivity and the magnetic response relative to the single Bohr magneton (single spin), as a function of its position within the SQUID hole. The results show that the SQUID response depends strongly on the spin position; the ratio between the spin sensitivity evaluated in the center of the loop and the minimum one is as high as a factor of 3 for a spin at a reasonable distance z' of 10 nm from the SQUID plane. Furthermore, the magnetic flux due to several hundred of spins has been evaluated by considering different random spin distributions within the SQUID hole. Due to the both nonuniform SQUID response and the random distribution process, the results show a statistical uncertainty which has been evaluated as a function of the spin number. The estimated informations are very useful to optimize the sensor performance in view of the most nanomagnetism applications.

In this work, we have presented high sensitive nanoSQUID fabricated into two different types, hysteretic and nonhysteretic (I-V characteristics). Non-hysteretic SQUID is easy/simple to fabricate and reproduce. Hence it is more reliable for practical applications. We have reported the nanoparticle detection via magnetisation measurement using non-hysteretic SQUID. Due to the recent successful efforts devoted to finely arrange the nano-particles within the sensor loop, the information provided here is very useful to optimize the sensor performance in view of most nano-magnetism applications.

Environmental Pollution is a global issue. Over the last decade the demand for accurate and dedicated sensors to provide precise value of species to be monitored and control the environmental pollution have accelerated efforts for the development of new sensing material and technologies. The most important, hazardous and very common pollutant gases are CO and CO2, H2, which are produced partly by natural decays, and more by industries and other man made burning processes. SnO2, is the most extensively studied oxide while Al2O3, BaTiO3. The other oxides like ZnO, ZrO2, TiO2, MoO2, MnO3, Fe2O3, etc are also reviewed in this context. SnO2, Al2O3, and BaTiO3 are sensitive to many gases but their selectivity is poor. Therefore the selectivity (to CO, H2) may be obtained by proper choice of dopants, operating temperature or some such technique like neural network. The present book gives an overview regarding development of gas sensors based on three metal semiconducting oxides SnO2, BaTiO3, Al2O3 as functional materials. This has particular emphasis on the problem of sensitivity, range and remarkable selectivity towards reducing gases mainly CO and H2.