Substrates For Device Applications Research Articles

Performance of SnO2 Thin Film Prepared by CWD Technique on Different Substrates for Device Applications: An Innovative Approach

Performance of SnO2 Thin Film Prepared by CWD Technique on Different Substrates for Device Applications: An Innovative Approach

Comprehensive study of graphene grown by chemical vapor deposition

Graphene was grown on Cu foil by chemical vapor deposition with CH4 as carbon source, and then was transferred onto various substrates for device applications. The structural and optical properties of graphene were investigated, comprehensively. Raman spectra indicate as-grown and transferred graphene films are homogenous monolayer graphene. Optical microscopy and scanning electron microscopy images reveal wrinkle-free and smooth surface of transferred graphene, confirming the high quality of graphene. In addition, the transferred graphene on glass exhibits excellent transmittances in the visible region (89.3 % at ~500 nm). Therefore, the results present the controllable approaches to achieve as-grown and transferred high quality graphene for the fabrication of multiple nanoelectronic devices.

Experimental and simulated study of electrical behaviour of ZnO film deposited on Al substrate for device applications

In this paper, zinc oxide (ZnO) film has been deposited on Al substrate by chemical wet and dry technique which is just a simple modified version of the dip coating method. In this method, it is possible to precisely control the immersion and withdrawal speed, with drying as well as annealing at the same time. The polycrystalline nature of ZnO has been confirmed by X-ray diffraction (XRD) analysis. The XRD analysis clearly indicates that some percentage of Al diffuses into the ZnO matrix at its interface region; hence it affects mobility of the sample. Hall measurement indicates the ZnO semiconductor as n-type. I–V characteristic of the sample shows that the contact is Ohmic and it can be used as a sensor at low potential value. The mobility decreases with increase in temperature. The simulation study carried out for I–V and mobility through simulation using ATLAS (SILVACO) software confirms that the experimental and simulation results are in close agreement with respect to the I–V characteristic and the mobility.

Near room-temperature synthesis of transfer-free graphene films

Large-area graphene films are best synthesized via chemical vapour and/or solid deposition methods at elevated temperatures (~1,000 °C) on polycrystalline metal surfaces and later transferred onto other substrates for device applications. Here we report a new method for the synthesis of graphene films directly on SiO(2)/Si substrates, even plastics and glass at close to room temperature (25-160 °C). In contrast to other approaches, where graphene is deposited on top of a metal substrate, our method invokes diffusion of carbon through a diffusion couple made up of carbon-nickel/substrate to form graphene underneath the nickel film at the nickel-substrate interface. The resulting graphene layers exhibit tunable structural and optoelectronic properties by nickel grain boundary engineering and show micrometre-sized grains on SiO(2) surfaces and nanometre-sized grains on plastic and glass surfaces. The ability to synthesize graphene directly on non-conducting substrates at low temperatures opens up new possibilities for the fabrication of multiple nanoelectronic devices.

An Electrochemical Route to Graphene Oxide

Large-scale graphene oxide (GO) with adjustable resistivity was synthesized from graphite via an electrochemical method using KCl solution as an effective electrolyte. During the exfoliation process, electrostatic force intercalates chloride ions between the expanded graphite layers on the anode. These chloride ions form small gas bubbles between the graphite layers in the electrochemical reaction. It is believed that the gas bubbles expand the gap between graphite sheets and produce a separating force between adjacent graphene layers. This separating force overcomes the Van der Waals force between adjacent sheets and exfoliates graphene layers from the starting graphite. Because the graphene is electrochemically oxidized by chorine during the exfoliation, the exfoliated GO sheets are hydrophilic and easily dispersed in the electrolyte solution. The GO solution prepared by the electrochemical exfoliation can be simply sprayed or spin-coated onto any substrate for device applications. The measured average thicknesses of a monolayer, bilayer, and trilayer exfoliated GO on SiO2 substrate were 1.9, 2.8, and 3.9 nm, respectively. It was observed that the measured resistance of the exfoliated GO sheets increases due to electrochemical oxidation in the solution. This electrochemical approach offers a low-cost and efficient route to the fabrication of graphene based devices.

Highly luminescent columnar ZnO films grown directly on n-Si and p-Si substrates by low-temperature electrochemical deposition

In this study, nanocolumnar zinc oxide thin films were catalyst-free electrodeposited directly on n-Si and p-Si substrates, what makes an important junction for optoelectronic devices. We demonstrate that ZnO thin films can be grown on Si at low cathodic potential by electrochemical synthesis. The scanning electron microscopy SEM showed that the ZnO thin films consist of nanocolumns with radius of about 150 nm on n-Si and 200 nm on p-Si substrates, possess uniform size distribution and fully covers surfaces. X-ray diffraction (XRD) measurements show that the films are crystalline material and are preferably grown along (0 0 2) direction. The impact of thermal annealing in the temperature range of 150–800 °C on ZnO film properties has been carried out. Low-temperature photoluminescence (PL) spectra of the as-prepared ZnO/Si samples show the extremely high intensity of the near bandgap luminescence along with the absence of visible emission. The optical quality of ZnO thin films was improved after post-deposition thermal treatment at 150 °C and 400 °C in our experiments, however, the luminescence intensity was found to decrease at higher annealing temperatures (800 °C). The obtained results indicate that electrodeposition is an efficient low-temperature technique for the growth of high-quality and crystallographically oriented ZnO thin films on n-Si and p-Si substrates for device applications.

Surface preparation of substrates from bulk GaN crystals

Large gallium nitride (GaN) crystals were grown using a hydride vapor phase epitaxy (HVPE) technique and were processed into substrates for device applications. Polishing procedures were developed for GaN substrates to produce surfaces prepared for epitaxial growth. Surface preparation of (0 0 0 1) and (0 0 0 1¯) substrates was examined, along with preparation of (1 1 2¯ 0) and (1 1¯ 0 0) non-polar surfaces. For all surfaces, chemical mechanical polishing (CMP) resulted in an average root mean square (RMS) surface roughness on a 5 μm×5 μm scanning probe microscope (SPM) image of <0.2 nm. Characterization of the surfaces of polished substrates by cross-sectional transmission electron microscope (TEM) showed no sub-surface damage and no epitaxial defects generated at the substrate/epi interface during homoepitaxial growth. Cathodoluminescence (CL) imaging was used to verify the defect density and that no defects related to polishing were present. The average dislocation density of the substrates was <5×10 6 cm −2.

Combinational template-assisted fabrication of hierarchically ordered nanowire arrays on substrates for device applications

By combining two self-organized templates, the authors fabricate hierarchically ordered nanowire arrays on substrates. The nanowire arrays consist of periodic voids at the microscale and hexagonally packed nanowires at the nanoscale. The nanowires are created by selective electrodeposition using nanoporous anodic alumina as a template and a porous gold film as a working electrode that is patterned by microsphere monolayers. In addition to in-plane hierarchical structure, they have sequentially varied the vertical structure of the nanowires. This approach is simple, inexpensive, and high throughput to fabricate nanostructures on substrates.

Pendeo Epitaxy Of 3C-SiC on Si Substrates

ABSTRACTPendeo Epitaxy is a type of Lateral Epitaxial Overgrowth (LEO) that instead of using a dielectric buffer layer, uses an etched substrate to grow laterally without an interface layer. We report the first successful growth of 3C-SiC on Si using Pendeo epitaxy. Rectangular stripes of 3C-SiC on (100) Si substrates were fabricated, along both the [110] and [100] directions. Pendeo epi was only observed for columns parallel to [001], indicating a preferred growth facet for Pendeo epi of 3C-SiC on Si. SEM and TEM investigations were performed to assess the material quality of the Pendeo 3C-SiC material. Films were grown for 60 min at 1310°C and film coalescence was achieved without evidence of voids where the growth fronts joined. TEM data indicate not only the growth of vertical and lateral 3C-SiC on the 3C-SiC seed layer but direct nucleation of 3C-SiC on the exposed Si columns side wall and trench bottom, despite the lack of a carbonization procedure. The quality of the Pendeo 3C-SiC film appears to be of high quality indicating that Pendeo epi of 3C-SiC on low-cost, large-diameter Si substrates may prove to be a cost effective way to grow device-grade SiC layers on Si substrates for device applications.

Oriented Silicon Films on Glass Substrates for Device Applications

Oriented Silicon Films on Glass Substrates for Device Applications

In situ grown superconducting YBCO films on buffered silicon substrates for device applications

Thin films of YBa2Cu3O7−δ (YBCO) have been grownin situ on silicon single-crystal (100) substrate by using SrTiO3 as a buffer layer. The deposition has been carried out by on-axis rf magnetron sputtering method. The deposition condition have been optimized by studying the plasma characteristics and correlating them with the superconducting performance of the film. Films deposited at substrate temperature in the range of 680–700°C from stoichiometric YBCO targets in an argon + oxygen mixture (3∶1) are superconducting and showc-axis epitaxy. Compositional confirmation has been carried out using Rutherford backscattering. Scanning tunneling microscopy of the films reveal formation of well-defined layered structure with some defects in the initial stages ofin situ growth of the films. Films grown on SrTiO3 substrates have excellent crystalline quality (XRD), transition temperatureTc0=81 K and the critical current densityJc>2×105 A/cm2 for unpatterned films at 77 K. On silicon substrates using buffer layers thein situ deposited YBCO films shows a higher transition width andTc0 is also slightly less (71 K).