Li-Jen Chou

A Hybrid Piezoelectric Structure for Wearable Nanogenerators

A hybrid-fiber nanogenerator comprising a ZnO nanowire array, PVDF polymer and two electrodes is presented. Depending on the bending or spreading action of the human arm, at an angle of ∼90°, the hybrid fiber reaches electrical outputs of ∼0.1 V and ∼10 nA cm(-2) . The unique structure of the hybrid fiber may inspire future research in wearable energy-harvesting technology.

Lead-free NaNbO3 nanowires for a high output piezoelectric nanogenerator.

Perovskite ferroelectric nanowires have rarely been used for the conversion of tiny mechanical vibrations into electricity, in spite of their large piezoelectricity. Here we present a lead-free NaNbO(3) nanowire-based piezoelectric device as a high output and cost-effective flexible nanogenerator. The device consists of a NaNbO(3) nanowire-poly(dimethylsiloxane) (PDMS) polymer composite and Au/Cr-coated polymer films. High-quality NaNbO(3) nanowires can be grown by hydrothermal method at low temperature and can be poled by an electric field at room temperature. The NaNbO(3) nanowire-PDMS polymer composite device shows an output voltage of 3.2 V and output current of 72 nA (current density of 16 nA/cm(2)) under a compressive strain of 0.23%. These results imply that NaNbO(3) nanowires should be quite useful for large-scale lead-free piezoelectric nanogenerator applications.

Near UV LEDs made with in situ doped p-n homojunction ZnO nanowire arrays.

Catalyst-free p-n homojunction ZnO nanowire (NW) arrays in which the phosphorus (P) and zinc (Zn) served as p- and n-type dopants, respectively, have been synthesized for the first time by a controlled in situ doping process for fabricating efficient ultraviolet light-emitting devices. The doping transition region defined as the width for P atoms gradually occupying Zn sites along the growth direction can be narrowed down to sub-50 nm. The cathodoluminescence emission peak at 340 nm emitted from n-type ZnO:Zn NW arrays is likely due to the Burstein-Moss effect in the high electron carrier concentration regime. Further, the electroluminescence spectra from the p-n ZnO NW arrays distinctively exhibit the short-wavelength emission at 342 nm and the blue shift from 342 to 325 nm is observed as the operating voltage further increasing. The ZnO NW p-n homojunctions comprising p-type segment with high electron concentration are promising building blocks for short-wavelength lighting device and photoelectronics.

Oxygen defect and Si nanocrystal dependent white-light and near-infrared electroluminescence of Si-implanted and plasma-enhanced chemical-vapor deposition-grown Si-rich SiO2

The mechanisms for silicon (Si) defect and nanocrystal related white and near-infrared electroluminescences (ELs) of Si-rich SiO2 films synthesized by Si-ion implantation and plasma-enhanced chemical-vapor deposition (PECVD) are investigated. The strong photoluminescence (PL) of Si-ion-implanted SiO2 (SiO2:Si+) at 415–455 nm contributed by weak-oxygen bond and neutral oxygen vacancy defects is observed after 1100 °C annealing for 180 min. The white-light EL of a reverse-biased SiO2:Si+ metal-oxide-semiconductor (MOS) diode with a turn-on voltage of 3.3 V originates from the minority-carrier tunneling and recombination in the defect states of SiO2:Si+, which exhibits maximum EL power of 120 nW at bias of 15 V with a power–current slope of 2.2μW∕A. The precipitation of nanocrystallite silicon (nc-Si) in SiO2:Si+ is less pronounced due to relatively small excess Si density. In contrast, the 4-nm nc-Si contributed to PL and EL at about 760 nm is precipitated in the PECVD-grown Si-rich SiOx film after annealin...

Gallium Nitride Nanowire Based Nanogenerators and Light-Emitting Diodes

Single-crystal n-type GaN nanowires have been grown epitaxially on a Mg-doped p-type GaN substrate. Piezoelectric nanognerators based on GaN nanowires are investigated by conductive AFM, and the results showed an output power density of nearly 12.5 mW/m(2). Luminous LED modules based on n-GaN nanowires/p-GaN substrate have been fabricated. CCD images of the lighted LED and the corresponding electroluminescence spectra are recorded at a forward bias. Moreover, the GaN nanowire LED can be lighted up by the power provided by a ZnO nanowire based nanogenerator, demonstrating a self-powered LED using wurtzite-structured nanomaterials.

Nanophotonic switch: gold-in-Ga2O3 peapod nanowires.

A novel metal-insulator heterostructure made of twinned Ga2O3 nanowires embedding discrete gold particles along the twin boundary was formed through a reaction between gold, gallium, and silica at 800 degrees C during simple thermal annealing. The Au-in-Ga2O3 peapods spontaneously crystallized under phase separation induced by the formation of twin boundaries. The nanostructures were analyzed by field emission scanning (FESEM) and transmission electron microscopes (FETEM), and their photoresponse was investigated using a double-frequency Nd:YAG laser with a wavelength of 532 nm on a designed single-nanowire device. The surface plasmon resonance (SPR) effects of embedded Au nanoparticles are proposed to be responsible for the remarkable photoresponse of these novel structures.

Lead-free KNbO3 ferroelectric nanorod based flexible nanogenerators and capacitors.

In spite of high piezoelectricity, only a few one-dimensional ferroelectric nano-materials with perovskite structure have been used for piezoelectric nanogenerator applications. In this paper, we report high output electrical signals, i.e. an open-circuit voltage of 3.2 V and a closed-circuit current of 67.5 nA (current density 9.3 nA cm(-2)) at 0.38% strain and 15.2% s(-1) strain rate, using randomly aligned lead-free KNbO(3) ferroelectric nanorods (~1 μm length) with piezoelectric coefficient (d(33) ~ 55 pm V (-1)). A flexible piezoelectric nanogenerator is mainly composed of KNbO(3)-poly(dimethylsiloxane) (PDMS) composite sandwiched by Au/Cr-coated polymer substrates. We deposit a thin poly(methyl methacrylate) (PMMA) layer between the KNbO(3)-PDMS composite and the Au/Cr electrode to completely prevent dielectric breakdown during electrical poling and to significantly reduce leakage current during excessive straining. The flexible KNbO(3)-PDMS composite device shows a nearly frequency-independent dielectric constant (~3.2) and low dielectric loss (<0.006) for the frequency range of 10(2)-10(5) Hz. These results imply that short and randomly aligned ferroelectric nanorods can be used for a flexible high output nanogenerator as well as high-k capacitor applications by performing electrical poling and further optimizing the device structure.

Synthesis of taperlike Si nanowires with strong field emission

Taperlike Si nanowires (SiNWs) have been synthesized by annealing of high-density FeSi2 nanodots on (001)Si at 1200°C in a N2 ambient. The tip regions of SiNWs are about 5–10nm in diameter. The average length of the SiNWs is about 6μm with aspect ratios as high as 150–170. A growth model based on oxide-assisted growth is proposed. The taperlike morphology may be caused by the passivation of the SiO2 coating layer, which results in the different levels of absorption of SiO along the length of the nanowires. The SiNWs exhibit a turn-on field of 6.3–7.3V∕μm and a threshold field of 9–10V∕μm. The excellent field emission characteristics are attributed to the taperlike geometry of the crystalline Si nanowires.

Formation and characterization of NixInAs/InAs nanowire heterostructures by solid source reaction.

The formation of crystalline NixInAs and NixInAs/InAs/NixInAs heterostructure nanowires by the solid source reaction of InAs nanowires with Ni is reported for the first time. The fundamental kinetics of the Ni/InAs alloying reaction is explored, with the Ni diffusion reported as the rate determining step. The diffusivity of Ni is independent of the nanowire diameter, with an extracted diffusion activation energy of approximately 1 eV/atom. The metallic NixInAs exhibits a modest resistivity of approximately 167 micro omega x cm for diameters >30 nm, with the resistivity increasing as the nanowire diameter is further reduced due to the enhanced surface scattering. The alloying reaction readily enables the fabrication of NixInAs/InAs/NixInAs heterostructure nanowire transistors for which the length of the InAs segment (i.e., channel length) is controllably reduced through subsequent thermal annealing steps, therefore enabling a systematic study of electrical properties as a function of channel length. From the electrical transport studies, an electron mean free path on the order of a few hundred nm is observed for InAs NWs with a unit length normalized, ON-state resistance of approximately 7.5 k omega/microm. This approach presents a route toward the fabrication for high performance InAs nanowire transistors with ohmic nanoscale contacts and low parasitic capacitances and resistances.

GAXIN1-XAS QUANTUM WIRE HETEROSTRUCTURES FORMED BY STRAIN-INDUCED LATERAL-LAYER ORDERING

GaxIn1−xAs quantum wire (QWR) arrays were grown on (100) on‐axis InP substrates by single‐step molecular‐beam epitaxy. The QWRs were formed in situ in (GaAs)2/(InAs)2.2 short‐period‐superlattice (SPS) layers by the strain‐induced lateral‐layer ordering (SILO) process. An analysis of the cross‐sectional and plan‐view transmission electron microscopy images, photoluminescence peak energies, and polarization anisotropy has confirmed the QWR nature of these heterostructures. The SILO process occurs over a wide growth temperature range near 500 °C. However, both high and low growth temperatures result in a weaker lateral composition modulation. The strength of the lateral composition modulation is proportional to the total thickness of the SPS quantum‐well layers, regardless of the thickness of the individual quantum well. In other words, the magnitude of composition modulation accumulates when growth proceeds. A strain‐driven bulk solid‐state diffusion model has been proven to be part of the driving force of ...