Localized Strong Electric Field Research Articles

Enhancing Methane Gas Sensing through Defect Engineering in Ag-Ru Co-doped ZnO Nanorods.

Detection of leaks of flammable methane (CH4) gas in a timely manner can mitigate health, safety, and environmental risks. Zinc oxide (ZnO), a polar semiconductor with controllable surface defects, is a promising material for gas sensing. In this study, Ag-Ru co-doped into self-assembled ZnO nanorod arrays (ZnO NRs) was prepared by a one-step hydrothermal method. The Ag-Ru co-doped sample shows a good hydrophobic property as a result of its particular microstructure, which results in high humidity resistance. In addition, oxygen vacancy density significantly increased after Ag-Ru co-doping. Density functional theory (DFT) calculations revealed an exceptionally high charge density accumulated at the Ru sites and the formation of a localized strong electric field, which provides additional energy for the CH4 reaction with •O2- at the surface at room temperature. Optimized AgRu0.025-ZnO demonstrated an outstanding CH4 sensing performance, with a limit of detection (LOD) as low as 2.24 ppm under free-heat and free-light conditions. These findings suggest that introducing defects into the ZnO lattice, such as oxygen vacancies and localized ions, offers a promising approach to improving the gas sensing performance.

Basin-Type Spacer for DC-GIL—Part I: Surface Charging and Discharging Behaviors

In this study, a downsized direct current (dc)-gas-insulated transmission line (GIL) model is applied to investigate the surface charging and discharging characteristics of the basin-type spacer in 0.1-MPa SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and air. Under a low electric field, the surface charge accumulation is dominated by the bulk conduction of the spacer. As the charging voltage increases, gas ionization occurs in the localized strong electric field, taking over the dominant position. In 0.1-MPa SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas, flashovers typically develop along the convex surface of the spacer under both positive and negative voltages because the homo-charge accumulation induced by brush discharges on the concave surface aggravates the electric field distortion at the convex side. In air, the dc flashovers have the polarity effect. Under the negative voltage, the flashover development is similar to that in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas. But for positive polarity, the space charge region of positive polarity intensifies the electric field ahead of the corona region, thus promoting the air-gap breakdown at the concave side of the spacer.

Performance Improvement of Triplet-Triplet Annihilation-Based Upconversion Solid Films through Plasmon-Induced Backward Scattering of Periodic Arrays of Ag and Al.

The performance improvement of solid-state triplet-triplet annihilation-based photon upconversion (TTA-UC) systems is required for the application to various solar devices. The performance can be improved by making use of the local strong electric field generated through the excitation of localized surface plasmon (LSP) resonance of metal nanostructures. However, since the improvement is effective only within the limited nanospace around nanoparticles (i.e., the near-field effect), a methodology for improving the performance over a wider spatial region is desirable. In this study, a significant improvement in the threshold light excitation intensity (Ith) (77% decrease) as the figure of merit and the upconverted emission intensity (6.3 times enhancement) in a solid-state TTA-UC film with a thickness of 3 μm was achieved by stacking the film with periodic Ag half-shell arrays. The highest-enhanced upconverted emission was obtained by tuning the diffuse reflectance peak, which results from the excitation of LSP resonance of the Ag half-shell arrays, to overlap well with the photoexcitation peak of the sensitizer in the TTA-UC film. The intensity of the enhanced upconverted emission was independent of the distance between the lower edge of the TTA-UC film and the surface of half-shell arrays in the nanometer order. These results suggest that the performance improvement was attributed to the photoexcitation enhancement of the sensitizer by elongating the excitation light path length inside the TTA-UC film, which was achieved through a strong backward scattering of the incident light based on the LSP resonance excitation (i.e., the far-field effect). In addition, the upconverted emission was improved using half-shell arrays comprising low-cost Al, although the enhancement factor was 3.5, which was lower than that of Ag half-shell arrays. The lower enhancement may be attributed to a decrease in the backward scattering of the excitation light owing to the intrinsic strong interband transition of Al at long visible wavelengths.

Promoting photocatalytic hydrogen evolution over the perovskite oxide Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3 by plasmon-induced hot electron injection.

Exploration of highly efficient and stable photocatalysts for water splitting has attracted much attention. However, developing a facile and effective approach to enhance the photocatalytic activity for practical applications is still highly challenging. Herein, we report a newly-fabricated perovskite oxide (Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3) decorated with Au ultrafine nanoparticles for photocatalytic water splitting. An exceptionally high hydrogen evolution rate of 1618 μmol g-1 h-1 was achieved (under 2 h illumination) when the Au mass loading was optimized to 9.3 wt%, which is 540 times higher than that of the pristine one. The splendid photocatalytic activity of the sample was attributed to plasmon-excited hot electron injection from Au to Pr0.5(Ba0.5Sr0.5)0.5Co0.8Fe0.2O3 (PBSCF) under illumination. The finite-difference time-domain simulations (FDTD) demonstrated that the localized strong electric field formed at the interface between Au and PBSCF under illumination, enables the hot electrons to be energetic and make the injection possible.

Degradation Model of a-IGZO TFT due to High Drain Bias Stress

In this paper, the TCAD degradation model of IGZO using spatial distribution (X, Y) of physical parameters is proposed for the first time and is confirmed according to various channel length, active thickness, and bias stress conditions that agree with actual measurements. The asymmetric degradation phenomenon according to the source/drain sweep direction occurs when high VDS stress (> 40 V) is applied to a-IGZO TFT due to the local strong electric field in the drain edge region in the active channel. In the double side gate (DSG) structure, the degree of degradation varies according to VTG, which is influenced by the concentration of electrons induced in the channel. Oxygen vacancy in the presence of 2+ ionized states (VO2+) in IGZO is stable. However, when band bending is severe, the electrons are captured, and the structural transition occurs as a neutral VO in the meta-stable state. This process is assumed to be a mechanism of IGZO degradation at high drain bias stress, and the electric field (>0.5M V/cm) and electron concentration (>1 × 1010 cm−3) in the channel are considered as the main factors of degradation and are modeled using the mapping function provided by Silvaco.

Experimental study on uniformity of dielectric barrier discharge generated by nanosecond pulse in atmospheric air

Dielectric barrier discharge (DBD) with better uniformity, excited by nanosecond pulses, is achieved within 8 mm air gap by using a self-designed DBD structure in airflow. The self-designed DBD structure is characterized by adding a metal rod (MR) in discharge gap, which will produce a local strong electric field and induce surface and volume discharge. It is observed from sequential single periodic discharge images that the uniformity of discharge starts from the electrode edge at the airflow inlet and moves gradually toward downstream under the action of airflow. When the uniformity of discharge is transmitted to a nearby of MR, a stable uniform and symmetrical annular discharge configuration is formed. Besides, that uniform area can be expanded by adding many MRs or MR array in the discharge gap. There is an optimum distance between every two MRs to produce a continuous and maximum discharge area with better uniformity. The above phenomena are mainly ascribed to the change of electric field distribution caused by MR and the charged particles redistribution induced by airflow.

Conductive Graphitic Channel in Graphene Oxide‐Based Memristive Devices

Electrically insulating graphene oxide with various oxygen‐functional groups is a novel material as an active layer in resistive switching memories via reduction process. Although many research groups have reported on graphene oxide‐based resistive switching memories, revealing the origin of conducting path in a graphene oxide active layer remains a critical challenge. Here nanoscale conductive graphitic channels within graphene oxide films are reported using a low‐voltage spherical‐aberration‐corrected transmission electron microscopy. Simultaneously, these channels with reduced graphene oxide nanosheets induced by the detachment of oxygen groups are verified by Raman intensity ratio map and conductive atomic force microscopy. It is also clearly revealed that Al metallic protrusions, which are generated in the bottom interface layer, assist the local formation of conductive graphitic channels directly onto graphene oxide films by generating a local strong electric field. This work provides essential information for future carbon‐based nanoelectronic devices.

Enhancement of near-infrared absorption in graphene with metal gratings

Graphene has been demonstrated as a good candidate for ultrafast optoelectronic devices. However, graphene is essentially transparent in the visible and near infrared with an absorptivity of 2.3%, which has largely limited its application in photon detection. This Letter demonstrates that the absorptance in a monatomic graphene layer can be greatly enhanced to nearly 70%, thanks to the localized strong electric field resulting from magnetic resonances in deep metal gratings. Furthermore, the resonance frequency is essentially not affected by the additional graphene layer. The method presented here may benefit the design of next-generation graphene-based optical and optoelectronic devices.

Polar summer mesospheric extreme horizontal drift speeds during interplanetary corotating interaction regions (CIRs) and high‐speed solar wind streams: Coupling between the solar wind and the mesosphere

AbstractWe report the observation of echo extreme horizontal drift speed (EEHS, ≥ 300 m s−1) during polar mesospheric (80–90 km) summer echoes (PMSEs) by the VHF (52 MHz) radar at Esrange, Sweden, in years of 2006 and 2008. The EEHS occur in PMSEs as correlated with high‐speed solar wind streams (HSSs), observed at least once in 12–17% of all hours of observation for the two summers. The EEHS rate peaks occur either during high solar wind speed in the early part of the PMSE season or during the arrival of interplanetary corotating interaction regions (CIRs) followed by peaks in PMSE occurrence rate after 1–4 days, in the latter part of the 2006 summer. The cause of EEHS rate peaks is likely under the competition between the interval of the CIR and HSS passage over the magnetosphere. A candidate process in producing EEHS is suggested to be localized strong electric field, which is caused by solar wind energy transfer from the interaction of CIR and HSS with the magnetosphere in a sequential manner. We suggest that EEHS are created by strong electric field, estimated as &gt; 10–30 V m−1 at 85 km altitude, exceeding the mesospheric breakdown threshold field.

Mechanism of resistive memory effect in Ga doped ZnO thin films

AbstractA hypothesis based on the model which explains the resistance change effect of resistive random access memory (ReRAM) by redox reaction is proposed. This hypothesis leads a conclusion that the relation between the polarity of the applied bias voltage and the caused resistance change in p ‐type semiconductors is opposite to that in n ‐type. Bias polarity dependence of resultant resistance change of ZnO and Ga‐doped ZnO (GZO), which are n ‐type semiconductors, were investigated using conducting atomic force microscope (C‐AFM). It was clarified that the opposite bias polarity is required to make GZO and NiO into the same resistance state, consistent with our hypothesis. In addition, enhancement of the resistance change effect by increasing Joule heating was observed. The present work also suggested that controlling the local carrier concentration of oxide films by application of localized strong electric field is possible. This technology might enable the fabrication of not only memory devices but also new nano‐scale electronic devices (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effects of shadow‐mask voltage on the discharge in shadow‐mask PDPs

Abstract— A new type of ACPDP with a shadow mask (shadow‐mask PDP, SMPDP) has been developed, featuring an effective structure and lower cost. The distinct difference between an SMPDP and a conventional ACPDP is that the dielectric barrier ribs are replaced by a single metal shadow mask. A three‐dimensional self‐consistent fluid model was used to analyze the effects of the shadow‐mask voltage on the discharge for a simplified driving scheme. The simulation results indicate that by selecting the appropriate shadow‐mask voltage, the addressing speed can be improved due to the local strong electric field. The steady discharge in the sustaining period will not be affected by changes in the shadow‐mask voltages in the addressing period. While in the sustaining period, the shadow‐mask‐voltage variation can directly affect the sustaining discharge. The floating shadow mask in the sustaining period is beneficial in achieving a stable sustaining discharge.

Atom probe and field emission electron spectroscopy studies of semiconductor films on metals

The surface morphology and the electronic states of Ge overlayers deposited on Ir-and Mo-tips were investigated by a combined instrument of an atom probe (AP) and a field emission electron spectroscope (FEES). The overlayers were deposited on the tips while observing field emission microscope (FEM) images of the surfaces. The FEM images of thin Ge overlayers on the Ir-tips show layer-like structures. In field emission electron distribution (FEED) of a Ge overlayer on the Ir-tip, about 5 ML thick, an energy gap near the Fermi level was clearly widened by low temperature annealing. After the thickness was reduced to 3 ML by field evaporation, the energy gap still remained wide. The FEEDs of the Ge overlayers on the Mo-tips exhibit several peaks distinct from those on the Ir-tip. This may be attributed to the local strong electric field surrounding the Ge clusters formed on the Mo-tips.

Low‐frequency instability in Q‐machine plasma with localized strong electric field

This paper reports the experimental result on the instability of Q-machine plasma with large ionic Larmor radius. The experimental method and plasma parameters are described. The experimental result is presented. The boundary condition in localized strong electric field is derived with ionic motion taken into account.