Controlled Growth of WO Photoanode under Various pH Conditions for Efficient Photoelectrochemical Performance.

Herein, the effects of the precursor solution's acidity level on the crystal structure, morphology, nucleation, and growth of WO·nHO and WO nanostructures are reported. Structural investigations on WO·nHO using X-ray diffraction and Fourier-transform infrared spectroscopy confirm that the quantity of hydrate groups increases due to the interaction between H and water molecules with increasing HCl volume. Surface analysis results support our claim that the evolution of grain size, surface roughness, and growth direction on WO·nHO and WO nanostructures rely on the precursor solution's pH value.

Polarization-insensitive broadband omni-directional anti-reflection in ZnO nanoneedle array for efficient solar energy harvesting.

Broadband omni-directional anti-reflection characteristics have been an important issue because they can maximize the optical absorption in photovoltaic devices. Here, we investigate the optical properties of ZnO nanoneedle arrays to demonstrate broadband anti-reflection, omni-directionality, and polarization insensitivity using optical simulations and experimental approaches. The results of this work clarify that the ZnO nanoneedle array plays an important role as a broadband anti-reflection layer due to its spatially graded refractive index, omni-directionality and polarization insensitivity.

Dynamics of driftless preconcentration using ion concentration polarization leveraged by convection and diffusion.

Over the past several decades, separation and preconcentration methods of (bio)molecules have been actively developed for various biomedical and chemical processes such as disease diagnostics, point of care test and environmental monitoring. Among the great developments of the electrokinetic method in a micro/nanofluidic platform is the ion concentration polarization (ICP) phenomenon, in which a target molecule is accumulated near a permselective nanoporous membrane under an applied electric field. ICP method has been actively studied due to its easy implementation and high preconcentration/separation efficiency.

dCas9-mediated Nanoelectrokinetic Direct Detection of Target Gene for Liquid Biopsy.

The-state-of-the-art bio- and nanotechnology have opened up an avenue to noninvasive liquid biopsy for identifying diseases from biomolecules in bloodstream, especially DNA. In this work, we combined sequence-specific-labeling scheme using mutated clustered regularly interspaced short palindromic repeats associated protein 9 without endonuclease activity (CRISPR/dCas9) and ion concentration polarization (ICP) phenomenon as a mechanism to selectively preconcentrate targeted DNA molecules for rapid and direct detection. Theoretical analysis on ICP phenomenon figured out a critical mobility, elucidating two distinguishable concentrating behaviors near a nanojunction, a stacking and a propagating behavior.

Flexible piezoelectric nanogenerators based on a transferred ZnO nanorod/Si micro-pillar array.

Flexible piezoelectric nanogenerators (PNGs) based on a composite of ZnO nanorods (NRs) and an array of Si micro-pillars (MPs) are demonstrated by a transfer process. The flexible composite structure was fabricated by hydrothermal growth of ZnO NRs on an electrochemically etched Si MP array with various lengths followed by mechanically delaminating the Si MP arrays from the Si substrate after embedding them in a polydimethylsiloxane matrix. Because the Si MP arrays act as a supporter to connect the ZnO NRs electrically and mechanically, verified by capacitance measurement, the output voltage from the flexible PNGs increased systematically with the increased density ZnO NRs depending on the length of the Si MPs.

Periodically Diameter-Modulated Semiconductor Nanowires for Enhanced Optical Absorption.

A diameter-modulated silicon nanowire array to enhance the optical absorption across broad spectral range is presented. Periodic shape engineering is achieved using conventional semiconductor processes and the unique optical properties are analyzed. The periodicity in the diameter of the silicon nanowires enables stronger and more closely spaced optical resonances, leading to broadband absorption enhancement.

Output power enhancement from ZnO nanorods piezoelectric nanogenerators by Si microhole arrays.

We demonstrate the enhancement of output power from a ZnO nanorod (NR)-based piezoelectric nanogenerator by using Si microhole (Si-μH) arrays. The depth-controlled Si-μH arrays were fabricated by using the deep reactive ion etching method. The ZnO NRs were grown along the Si-μH surface, in holes deeper than 20 μm.

Investigation of the surface passivation mechanism through an Ag-doped Al-rich film using a solution process.

Electronic recombination loss is an important issue for photovoltaic (PV) devices. While it can be reduced by using a passivating layer, most of the techniques used to prepare passivating layers are either not cost effective or not applicable for device applications. Previously, it was reported that a low cost sol-gel derived Al-rich zinc oxide (ZnO:Al) film serves as an effective passivating layer for p-type silicon but is not effective for n-type silicon.

Paraboloid Structured Silicon Surface for Enhanced Light Absorption: Experimental and Simulative Investigations.

In this paper, we present an optical model that simulates the light trapping and scattering effects of a paraboloid texture surface first time. This model was experimentally verified by measuring the reflectance values of the periodically textured silicon (Si) surface with the shape of a paraboloid under different conditions. A paraboloid texture surface was obtained by electrochemical etching Si in the solution of hydrofluoric acid, dimethylsulfoxide (DMSO), and deionized (DI) water.

Hierarchical ZnO nanorods on Si micropillar arrays for performance enhancement of piezoelectric nanogenerators.

Enhanced output power from a ZnO nanorod (NR)-based piezoelectric nanogenerator (PNG) is demonstrated by forming a heterojunction with Si micropillar (MP) array. The length of the SiMP array, which was fabricated by electrochemical etching, was increased systematically from 5 to 20 μm by controlling the etching time. Our structural and optical investigations showed that the ZnO NRs were grown hierarchically on the SiMPs, and their crystalline quality was similar regardless of the length of the underlying SiMPs.

A flexible and transparent graphene/ZnO nanorod hybrid structure fabricated by exfoliating a graphite substrate.

We demonstrate the fabrication of a graphene/ZnO nanorod (NR) hybrid structure by mechanical exfoliation of ZnO NRs grown on a graphite substrate. We confirmed the existence of graphene sheets on the hybrid structure by analyzing the Raman spectra and current-voltage (I-V) characteristics. The Raman spectra of the exfoliated graphene/ZnO NR hybrid structure show G and 2D band peaks that are shifted to lower wavenumbers, indicating that the exfoliated graphene layer exists under a significant amount of strain.

Dependence of performance of Si nanowire solar cells on geometry of the nanowires.

The dependence of performance of silicon nanowires (SiNWs) solar cells on the growth condition of the SiNWs has been described. Metal-assisted electroless etching (MAE) technique has been used to grow SiNWs array. Different concentration of aqueous solution containing AgNO3 and HF for Ag deposition is used.

A low temperature process for phosphorous doped ZnO nanorods via a combination of hydrothermal and spin-on dopant methods.

We demonstrate the fabrication of solution based low temperature-processed p-type ZnO NRs doped with phosphorous by using a spin-on-dopant method coupled with a hydrothermal process. We confirmed the incorporation of phosphorous dopants into a ZnO crystal by analyzing SIMS profiles, together with the evolution of the photoluminescence spectra. It is further revealed that the electrical properties of the p-type ZnO/n-type Si heterojunction diode exhibited good rectifying behavior, confirming that p-type ZnO NRs were successfully formed.

Fabrication and characterization of hybrid Si/ZnO subwavelength structures as efficient antireflection layer.

In this study, we fabricated and characterized three dimensional (3D) silicon (Si)/zinc oxide (ZnO) hybrid subwavelength structures to investigate their antireflective properties. Si nanorods (SiNRs) were fabricated by electrochemical etching, and subsequentially we grew ZnO NRs on SiNR as templates by using hydrothermal synthesis. The morphological and optical properties of hybrid Si/ZnO subwavelength structures were investigated by scanning electron microscopy (SEM) and ultra violet-visible-near infrared (UV-VIS-NIR) spectrophotometer, respectively.

Morphological evolution of silver nanoparticles and its effect on metal-induced chemical etching of silicon.

In this report, we have demonstrated the morphological evolution of the silver nanoparticles (AgNPs) by controlling the growth conditions and its effect on morphology of silicon (Si) during metal-induced electroless etching (MICE). Self-organized AgNPs with peculiarly shape were synthesized by an electroless plating method in a conventional aqueous hydrofluoric acid (HF) and silver nitrate (AgNO3) solution. AgNP nuclei were densely created on Si wafer surface, and they had a strong tendency to merge and form continuous metal films with increasing AgNO3 concentrations.

Surface plasmon-enhanced light-emission mechanism of Ag-coated ZnO/Al2O3 core/shell nanorod structures.

Surface plasmon (SP)-enhanced light emission mechanism has been investigated for the Ag-coated ZnO/Al2O3 core/shell nanorods (NRs). Structural characterizations showed that the ZnO NRs were covered by conformal Al2O3 layer and coated by Ag nanoparticles (NPs). The optical studies by photoluminescence (PL) showed abnormal variation of PL intensity with increasing the thickness of Al2O3.

Petroleum hydrocarbon contaminations in the intertidal seawater after the Hebei Spirit oil spill--effect of tidal cycle on the TPH concentrations and the chromatographic characterization of seawater extracts.

In December 2007, the oil tanker Hebei Spirit released approximately 12,547,000 L of crude oil off the west coast of Korea, impacting more than 375 km of coastline. The seawater TPH concentrations immediately after the spill ranged from 1.5 to 7310 μg L⁻¹, with an average of 732 μg L⁻¹.

Characteristics of Al-doped ZnO films grown by atomic layer deposition for silicon nanowire photovoltaic device.

We report the structural, electrical, and optical characteristics of Al-doped ZnO (ZnO:Al) films deposited on glass by atomic layer deposition (ALD) with various Al2O3 film contents for use as transparent electrodes. Unlike films fabricated by a sputtering method, the diffraction peak position of the films deposited by ALD progressively moved to a higher angle with increasing Al2O3 film content. This indicates that Zn sites were effectively replaced by Al, due to layer-by-layer growth mechanism of ALD process which is based on alternate self-limiting surface chemical reactions.

Fabrication and characterization of silicon wire solar cells having ZnO nanorod antireflection coating on Al-doped ZnO seed layer.

In this study, we have fabricated and characterized the silicon [Si] wire solar cells with conformal ZnO nanorod antireflection coating [ARC] grown on a Al-doped ZnO [AZO] seed layer. Vertically aligned Si wire arrays were fabricated by electrochemical etching and, the p-n junction was prepared by spin-on dopant diffusion method. Hydrothermal growth of the ZnO nanorods was followed by AZO film deposition on high aspect ratio Si microwire arrays by atomic layer deposition [ALD].

Visible emission from Ce-doped ZnO nanorods grown by hydrothermal method without a post thermal annealing process.

Visible light-emitting Ce-doped ZnO nanorods [NRs] without a post thermal annealing process were grown by hydrothermal method on a Si (100) substrate at a low temperature of 90°C. The structural investigations of Ce-doped ZnO NRs showed that the Ce3+ ions were successfully incorporated into the ZnO lattice sites without forming unwanted Ce-related compounds or precipitates. The optical investigation by photoluminescence spectra shows that the doped Ce3+ ions in the ZnO NRs act as an efficient luminescence center at 540 nm which corresponds to the optical transition of 5d → 4f orbitals in the Ce3+ ions.