Jyoti Prakash Kar

ZnO single nanowire-based UV detectors

In this report, ZnO single nanowire (NW)-based devices were fabricated on the same nanowire by e-beam lithography so that both sides had Ohmic contact and one side had Schottky contact. Information about the mechanism for low-power UV detection by these devices was unambiguously provided by I-V measurements. Adsorption and desorption of oxygen molecules at the NW surface are responsible for the UV detection by the device with Ohmic contacts on both sides. Barrier height modulations and interface states are responsible for UV detection by the device with Schottky contact on one side.

Biomimetic hierarchical ZnO structure with superhydrophobic and antireflective properties

A two step method, with a combination of top-down and bottom-up approaches, was developed for the fabrication of ZnO based hierarchical structures with nanorods on microcraters. A layer of well c-axis aligned, transparent, conductive ZnO thin film was deposited by pulsed DC sputtering on a Corning glass substrate. The microcraters were created with anisotropic etching on the as-deposited ZnO thin film. ZnO nanorods were then synthesized onto the etched film by means of metal organic chemical vapor deposition. The resulting hierarchical film exhibits a high water contact angle (>160 degrees) with a low contact angle hysteresis (2 degrees) and low reflection over a wide spectral range. This biomimetic material may find potential applications in many industrial fields, e.g., self-cleaning, solar cells, displays.

Junction properties of Au/ZnO single nanowire Schottky diode

In this study, we have analyzed the Au/ZnO single nanowire based Schottky diode by investigating temperature dependent current voltage and x-ray photoelectron spectroscopy (XPS) measurements. The calculated barrier height of the Schottky diodes by using the thermionic emission model is in good agreement with the value obtained from the XPS measurements but lower than the theoretically predicted value. The ionization of interface states has been considered for explaining this discrepancy.

Programmable Direct-Printing Nanowire Electronic Components

In order for recently developed advanced nanowire (NW) devices(1-5) to be produced on a large scale, high integration of the separately fabricated nanoscale devices into intentionally organized systems is indispensible. We suggest a unique fabrication route for semiconductor NW electronics. This route provides a high yield and a large degree of freedom positioning the device on the substrate. Hence, we can achieve not only a uniform performance of Si NW devices with high fabrication yields, suppressing device-to-device variation, but also programmable integration of the NWs. Here, keeping pace with recent progress of direct-writing circuitry,(6-8) we show the flexibility of our approach through the individual integrating, along with the three predesigned N-shaped sites. On each predesigned site, nine bottom gate p-type Si NW field-effect transistors classified according to their on-current level are programmably integrated.

Influence of surface morphology on the optical property of vertically aligned ZnO nanorods

In this letter we have studied an influence of surface morphology on the optical property of vertically aligned ZnO nanorods. At low temperature the near band edge excitonic emission shows a strong dependence on surface morphology. A prominent and well resolved near band edge photoluminescence (PL) peak was obtained for nanowires with decreasing diameter and thus assigned due to the contributions to the optical properties of individual nanorods. Depending on surface morphology, the difference in low temperature PL property is attributed to the tailing of the density of states due to the potential fluctuations in randomly distributed intrinsic defects.

Electrical Contact Tunable Direct Printing Route for a ZnO Nanowire Schottky Diode

Although writing was the first human process for communication, it may now become the main process in the electronics industry, because in the industry the programmability as an inherent property is a necessary requirement for next-generation electronics. As an effort to open the era of writing electronics, here we show the feasibility of the direct printing of a high-performance inorganic single crystalline semiconductor nanowire (NW) Schottky diode (SD), including Schottky and Ohmic contacts in series, using premetallization and wrapping with metallic nanofoil. To verify the feasibility of our process, SDs made of Al-premetalized ZnO NWs and plain ZnO NWs were compared with each other. Even with cold direct printing, the Al-premetalized ZnO NW SD showed higher performance, specifically 1.52 in the ideality factor and 1.58 x 10(5) in its rectification ratio.

One-Dimensional Semiconductor Nanostructure Based Thin-Film Partial Composite Formed by Transfer Implantation for High-Performance Flexible and Printable Electronics at Low Temperature

Having high bending stability and effective gate coupling, the one-dimensional semiconductor nanostructures (ODSNs)-based thin-film partial composite was demonstrated, and its feasibility was confirmed through fabricating the Si NW thin-film partial composite on the poly(4-vinylphenol) (PVP) layer, obtaining uniform and high-performance flexible field-effect transistors (FETs). With the thin-film partial composite optimized by controlling the key steps consisting of the two-dimensional random dispersion on the hydrophilic substrate of ODSNs and the pressure-induced transfer implantation of them into the uncured thin dielectric polymer layer, the multinanowire (NW) FET devices were simply fabricated. As the NW density increases, the on-current of NW FETs increases linearly, implying that uniform NW distribution can be obtained with random directions over the entire region of the substrate despite the simplicity of the drop-casting method. The implantation of NWs by mechanical transfer printing onto the PVP layer enhanced the gate coupling and bending stability. As a result, the enhancements of the field-effect mobility and subthreshold swing and the stable device operation up to a 2.5 mm radius bending situation were achieved without an additional top passivation.

Morphological investigation of aluminium nitride films on various substrates for MEMS applications

Abstract Piezoelectric films, such as aluminium nitride (AlN), are of great interest for the fabrication of thin film bulk/surface acoustic resonators, where the growth parameters and the substrate material influence the morphological properties. Herein, AlN films were deposited using RF reactive sputtering on Si, SiO2, metal (Al, Cu, Cr and Au) coated silicon, GaAs and InP substrates. C-axis (002) oriented AlN films were observed on most of the substrates, where the surface morphologies of the films grown on the 1·5 μm thick SiO2 layer and GaAs substrate were found to be non-uniform. Moreover, AlN films deposited on the Cr electrode exhibit well textured film with fairly uniform grains, while the films deposited on other metal electrodes exhibit a granular type of structure with mixed small and large grains. After optimisation of growth parameters, silicon micromachining was performed by the wet chemical etching method. Suspended Cr–AlN–Cr–SiO2 cantilevers of 20 μm in width were fabricated for futuristic microelectromechanical systems (MEMS) applications.

SURFACE MODIFICATION OF HYDROTHERMALLY GROWN ZnO NANOSTRUCTURES WITH PROCESS PARAMETERS

ZnO nanorods (NRs) were hydrothermally synthesized by using equimolar zinc nitrate hydrate (Zn(NO3)2 ⋅ 6H2O) and hexamethylenetetramine (C6H12N4) solutions. The shape of the nanostructures, obtained by aqueous method, was greatly influenced by the growth temperature and the molar concentrations. NRs grown at higher temperature (90°C) have rounded tips, whereas nanostructures of hexagonal flat-end shape were obtained at 75°C. Hardly any nanostructures were observed by further reducing the temperature to 60°C. In addition, solutions with higher molarity favored the appearance of nanoflowers. Scattered ZnO NRs were observed on silicon substrate, whereas aligned ZnO nanowires (NWs) 50–70 nm in diameter were obtained at 75°C by introducing sputtered ZnO film as a seed layer. High-resolution transmission electron microscopy (HRTEM) confirmed the growth of ZnO nanowires along [001] direction. A band-edge luminescence along with a broad visible spectrum was observed for the ZnO nanowires.

Self-regulating pseudo-monolayer printing of percolating networks of ZnO nanostructures for macroelectronics

A patterned dry transfer printing technique that can generate monolayer-like percolating networks of ZnO nanorods (NRs) has been developed. The method relies on the relative adhesion strength between NR–NR and NR–substrate, as well as soft and elastomeric nature of polydimethylsiloxane (PDMS) stamp material. When the NR–substrate adhesion is stronger than the rod–rod interaction, which is the usual case due to a large difference in the contact area, the printing leads to a monolayer-like percolating network of NRs on substrate. The method exploits the contact area difference between NR–NR and NR–substrate, which is inherent in the systems involving high aspect ratio nanostructures on a soft stamp, without considering the complex and elaborate tailoring of the surface chemistry or energetics. When the stamp has multilayer stacks of nanostructures, the monolayer-like printing can be repeated many times, possibly on a large area substrate, due to the self-regulating printing characteristics. The printed percolating network of semiconductor nanostructures have been used as active channels in thin film transistors, where the better gate coupling due to the pseudo-monolayer leads to higher-performance devices compared to other configurations of nanostructures. This self-regulating, patterned dry transfer printing method may enable high-performance macroelectronics with various functional nanostructured materials that have high aspect ratios.