Fabrication and characterization of thermally oxidized TiO2 thin films on Si(100) substrates

Mixed phase TiO2 is known to have better photocatalytic property as the resulting grain boundaries and interfaces between substrate, anatase and rutile phases play a crucial role in transferring/trapping photogenerated electrons. Here we have grown three different thicknesses (10 nm, 30 nm and 50 nm) of Ti thin films on Si(100) substrate in a sputter coater. Thermal oxidation in air at 600 °C for 1 h leads to the formation of mixed phase TiO2 thin films. Surface morphology and crystalline quality of thin film are discussed using XRD, SEM and TEM results. Moiré fringes resulting from interfacial strain have been discussed using lattice resolved HRTEM images

Facile growth of perovskite nanoparticles confined on dimension-controlled Si nanorod arrays for various promising photophysical applications

In this study, a facile growth of hybrid perovskite nanoparticles (NPs) has been demonstrated on mesoporous, high-aspect ratio, morphology-controlled Si nanorod (NR) arrays. A generic method of directly confining perovskite nanocrystallites (average size <7 nm) on a mesoporous substrate without the use of colloidal stabilization was introduced. The perovskite NPs coated on dimension-and position-controlled Si NR arrays were systematically investigated by their various photophysical properties such as optical reflectance, cathodoluminescence (CL), and photoluminescence (PL) behaviors at both room temperature and low temperature. The dimension and position of the Si NR arrays were controlled by e-beam lithography followed by selective metal-assisted chemical etching (MACE). Organic-inorganic perovskite NPs were synthesized on the surface of Si NR array by spin coating of perovskite precursor solution and followed by annealing. The porous and rough sites on the surface of the NR arrays acted as nucleation centers for the formation of perovskite NPs. Due to the excitonic recombination of CH3NH3PbBr3, the NPs confined on the various NR templates exhibited strong PL emission in the 505–510 nm region. Furthermore, due to greater radiative recombination and lesser carrier trapping in the NPs, the PL and CL emission intensities of the perovskite NPs localized on the surface of the NR array were dramatically increased (PL enhancement factor ∼ 7.7, when NR aspect ratio ∼ 17.2) as compared to the bulk perovskite microcrystals. The low-temperature PL study revealed higher exciton binding energy of the NPs as compared to the bulk microcrystalline film. A systematic investigation revealed that the optical absorption, as well as the emission color of the perovskite NPs, can be tuned by the aspect ratio of the Si NR arrays. The results of our studies indicate the application of bandgap engineering of perovskite nanocrystals through confinement in a mesoporous, well-organized, regularly-ordered template as a powerful tool for tuning the emission wavelength in next-generation photonic sources. Furthermore, the important findings on the periodic array of photoactive nanoscale materials introduced in this manuscript may open up huge opportunities in numerous cutting-edge applications such as light emitting diode arrays, photodetector arrays, individually addressable devices, display devices with controlled pixel size and pixel density, etc

Individually addressable and flexible pressure sensor matrixes with ZnO nanotube arrays on graphene

We report the fabrication of individually addressable, high-density, vertical zinc oxide (ZnO) nanotube pressure sensor arrays. High-sensitivity and flexible piezoelectric sensors were fabricated using dimension- and position-controlled, vertical, and free-standing ZnO nanotubes on a graphene substrate. Significant pressure/force responses were achieved from small devices composed of only single, 3 × 3, 5 × 5, and 250 × 250 ZnO nanotube arrays on graphene. An individually addressable pixel matrix was fabricated by arranging the top and bottom electrodes of the sensors in a crossbar configuration. We investigated the uniformity and robustness of pressure/force spatial mapping by considering the pixel size, the number of ZnO nanotubes in each pixel, and the lateral dimensions of individual ZnO nanotubes. A spatial resolution as high as 1058 dpi was achieved for a Schottky diode-based force/pressure sensor composed of ZnO nanotubes on a flexible substrate. Additionally, we confirmed the excellent flexibility and electrical robustness of the free-standing sensor arrays for high-resolution tactile imaging. We believe that this work opens important opportunities for 1D piezoelectric pressure/force sensor arrays with enormous applications in human-electronics interfaces, smart skin, and micro- and nanoelectromechanical systems

Fabrication and characterization of thermally oxidized TiO2 thin films on Si(100) substrates

732-736Mixed phase TiO2 is known to have better photocatalytic property as the resulting grain boundaries and interfaces between substrate, anatase and rutile phases play a crucial role in transferring/trapping photogenerated electrons. Here we have grown three different thicknesses (10 nm, 30 nm and 50 nm) of Ti thin films on Si(100) substrate in a sputter coater. Thermal oxidation in air at 600 °C for 1 h leads to the formation of mixed phase TiO2 thin films. Surface morphology and crystalline quality of thin film are discussed using XRD, SEM and TEM results. Moiré fringes resulting from interfacial strain have been discussed using lattice resolved HRTEM images

Low-energy ion beam synthesis of ag endotaxial nanostructures in silicon

Coherently, embedded metal nanostructures (endotaxial) are known to have potential applications concerning the areas of plasmonics, optoelectronics and thermoelectronics. Incorporating appropriate concentrations of metal atoms into crystalline silicon is critical for these applications. Therefore, choosing proper dose of low-energy ions, instead of depositing thin film as a source of metal atoms, helps in avoiding surplus concentration of metal atoms that diffuses into the silicon crystal. In this work, 30 keV silver negative ions are implanted into a SiO (x) /Si(100) at two different fluences: 1 x 10(15) and 2.5 x 10(15) Ag- ions/cm(2). Later, the samples are annealed at 700 A degrees C for 1 h in Ar atmosphere. Embedded silver nanostructures have been characterized using planar and cross-sectional TEM (XTEM) analysis. Planar TEM analysis shows the formation of mostly rectangular silver nanostructures following the fourfold symmetry of the substrate. XTEM analysis confirms the formation of prism-shaped silver nanostructures embedded inside crystalline silicon. Endotaxial nature of the embedded crystals has been discussed using selected area electron diffraction analysis.UGC-DAE CSR, KC Collaborative Research Project UGC-DAE-CSR-KC/CRS/15/IOP/MS/01/0669/0670/075

Confinement-Induced Growth of Gold Nanocrystals in Hybrid Hierarchical Polymer Nanowire

The growth of metal nanocrystals within polymer nanowiresdeviates from the conventional nucleation-growth process asmovements of nucleated metal nanocrystals are hindered due tosimultaneous growth of the polymer. We have carried out systematic insitu small-angle and diffraction measurements simultaneously duringgrowth of gold-polypyrrole composite nanowire within membranes anddeveloped a method to extract the shape and size of gold nanocrystals tounderstand the growth mechanism. Our results give unique informationregarding the early growth processes of nanocrystals as a function of thepore diameter of membranes and concentration of HAuCl4 solution usedfor the polymerization reaction. We have shown that gold nanocrystalsfirst grow along the [111] direction through contact epitaxy as acylindrically shaped nanocrystal and then get transformed into nearsphericalnanocrystals. The synchrotron X-ray scattering techniquepresented here can be used to study similar growth processes

Capping Layer (CL) Induced Antidamping in CL/Py/β‑W System (CL: Al, β‑Ta, Cu, β‑W)

For achieving ultrafast switching speed and minimizing dissipation losses, the spin-based data storage device requires a control on effective damping (α_eff) of nanomagnetic bits. Incorporation of interfacial antidamping spin orbit torque (SOT) in spintronic devices therefore has high prospects for enhancing their performance efficiency. Clear evidence of such an interfacial antidamping is found in Al capped Py­(15 nm)/β-W­(<i>t</i>_W)/Si (Py = Ni₈₁Fe₁₉ and <i>t</i>_W = thickness of β-W), which is in contrast to the increase of α_eff (i.e., damping) usually associated with spin pumping as seen in Py­(15 nm)/β-W­(<i>t</i>_W)/Si system. Because of spin pumping, the interfacial spin mixing conductance (<i>g</i>^↑↓) at Py/β-W interface and spin diffusion length (λ_SD) of β-W are found to be 1.63(±0.02) × 10¹⁸ m^–2 (1.44(±0.02) × 10¹⁸ m^–2) and 1.42(±0.19) nm (1.00(±0.10) nm) for Py­(15 nm)/β-W­(<i>t</i>_W)/Si (β-W­(<i>t</i>_W)/Py­(15 nm)/Si) bilayer systems. Other different nonmagnetic capping layers (CL), namely, β-W­(2 nm), Cu­(2 nm), and β-Ta­(2,3,4 nm) were also grown over the same Py­(15 nm)/β-W­(<i>t</i>_W). However, antidamping is seen only in β-Ta­(2,3 nm)/Py­(15 nm)/β-W­(<i>t</i>_W)/Si. This decrease in α_eff is attributed to the interfacial Rashba like SOT generated by nonequilibrium spin accumulation subsequent to the spin pumping. Contrary to this, when interlayer positions of Py­(15 nm) and β-W­(<i>t</i>_W) is interchanged irrespective of the fixed top nonmagnetic layer, an increase of α_eff is observed, which is ascribed to spin pumping from Py to β-W layer

Dimension- and position-controlled growth of GaN microstructure arrays on graphene films for flexible device applications

This paper describes the fabrication process and characteristics of dimension- and position-controlled gallium nitride (GaN) microstructure arrays grown on graphene films and their quantum structures for use in flexible light-emitting device applications. The characteristics of dimension- and position-controlled growth, which is crucial to fabricate high-performance electronic and optoelectronic devices, were investigated using scanning and transmission electron microscopes and power-dependent photoluminescence spectroscopy measurements. Among the GaN microstructures, GaN microrods exhibited excellent photoluminescence characteristics including room-temperature stimulated emission, which is especially useful for optoelectronic device applications. As one of the device applications of the position-controlled GaN microrod arrays, we fabricated light-emitting diodes (LEDs) by heteroepitaxially growing InxGa1-xN/GaN multiple quantum wells (MQWs) and a p-type GaN layer on the surfaces of GaN microrods and by depositing Ti/Au and Ni/Au metal layers to prepare n-type and p-type ohmic contacts, respectively. Furthermore, the GaN microrod LED arrays were transferred onto Cu foil by using the chemical lift-off method. Even after being transferred onto the flexible Cu foil substrate, the microrod LEDs exhibited strong emission of visible blue light. The proposed method to enable the dimension- and position-controlled growth of GaN microstructures on graphene films can likely be used to fabricate other high-quality flexible inorganic semiconductor devices such as micro-LED displays with an ultrahigh resolution