Low-bandgap, highly <i>c</i>-axis-oriented Al-doped ZnO thin films

Wen, Long,Kumar, Manish,Cho, Hyung Jun,Leksakul, Komgrit,Han, Jeon Geon IOP 2017 Journal of physics. D, applied physics Vol.50 No.18

<P>Low-bandgap transparent conductive oxides will be of interest to researchers who wish to address the health hazards of blue radiation emission from electronic displays. Here, we present a single-step, low-temperature fast enough (throughput  >  60 nm min<SUP>−1</SUP>) process to grow highly <I>c</I>-axis-oriented crystalline Al-doped ZnO thin films via advanced plasma processing. Dual-power DC-magnetron sputtering plasma was employed for the synthesis of thin films. The addition of top power to a pre-existing rectangular power pushed additional ions to a confined plasma and increased the plasma density and electron temperature. The effect of this additional-ion pushing was systematically studied using the microstructure, surface properties, and electronic properties. As a result, bandgap reduction from 3.35 eV to 3.10 eV and tailoring of electrical resistivity (4.89  ×  10<SUP>−4</SUP>–8.32  ×  10<SUP>−3</SUP> Ω cm) and Seebeck coefficients (21–48 <I>µ</I>V K<SUP>−1</SUP>) were achieved in addition to excellent transparency. Given their properties, the obtained films show promise for multifunctional applications, such as in UV and near-blue radiation shielding, transparent conductive electrodes and low-temperature thermoelectrics.</P>

Development and utility of a new 3-D magnetron source for high rate deposition of highly conductive ITO thin films near room temperature

Wen, Long,Sahu, Bibhuti Bhusan,Han, Jeon Geon The Royal Society of Chemistry 2018 Physical chemistry chemical physics Vol.20 No.7

<P>As transparent conductive films, indium tin oxide (ITO) materials are being extensively used as electrodes in various technological and optoelectronic applications. The demand for ITO films is firmly increasing because of the widespread market growth in these industries, but the available solutions only partly fulfill the prerequisites of high transmittance, low resistivity, large area process, cost-effective manufacturing, high growth rate and low-temperature process. The present work demonstrates a possible framework for the detailed study of ITO coatings in addition to the development of a novel highly confined 3-D magnetron source (3DMS) that can be simply used for tailored products. In this work, the deposition conditions are optimized through plasma chemistry by utilizing various <I>in situ</I> plasma diagnostics. The emphasis is given to studying the effects of different deposition conditions such as power density and oxygen (O2) flow. Measurements show that the 3DMS can efficiently produce very high-density plasmas at a low-discharge voltage. The combined effect of high electron density and energy flux favors high growth rate deposition up to ∼1.75 nm s<SUP>−1</SUP>. By controlling the plasma parameters, energy flux on the substrate, In<SUP>3+</SUP>, Sn<SUP>4+</SUP>, oxygen vacancies, and mobility, highly transparent ITO film with a very low resistivity of ∼4.2 × 10<SUP>−4</SUP> Ω cm is fabricated at low-temperature using a 3DMS process with the incorporation of O2 flow.</P>

Advantage of dual-confined plasmas over conventional and facing-target plasmas for improving transparent-conductive properties in Al doped ZnO thin films

Wen, Long,Kumar, Manish,Sahu, B.B.,Jin, S.B.,Sawangrat, C.,Leksakul, K.,Han, J.G. Elsevier 2015 Surface & coatings technology Vol.284 No.-

<P><B>Abstract</B></P> <P>Al doped ZnO films are prepared in dual-confined plasmas (rectangular side-ways and one top-side) in DC magnetron sputtering system without intentional substrate-heating. Present confinement shows improved transparent-conductive properties in Al doped ZnO thin films, when compared to those of deposited by conventional and facing-target confinement. As a function of working pressure and power density, plasma diagnostics is carried out at substrate location using optical emission spectroscopy, thermal energy transfer and net current density measurements. The optical, and electrical properties of the synthesis AZO films were studied and correlated to plasma conditions. It is found that high electron temperature, higher plasma density and highly ionization of oxygen play a key role in enhancing the deposition rate and transmittance ~90% along with minimizing resistivity in the order of 10<SUP>−4</SUP> Ωcm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Developed advanced DC magnetron sputtering system to deposit highly conductive and transparent Al doped ZnO thin films. </LI> <LI> Presented plasma diagnostics using OES, net current density and thermal energy transfer at substrate location. </LI> <LI> Presented the effects of partial pressure and power density on transparent-conductive performances. </LI> <LI> Shown the advantage of present process over conventional DC magnetron sputtering systems. </LI> </UL> </P>

Probabilistic Risk Assessment of RCC Dam Considering Grey-Stochastic-Fuzzy Uncertainty

Wenlong Chen,Xiaoling Wang,Minghui Liu,Yushan Zhu,Shaohui Deng 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.11

Greyness, randomness and fuzziness are three inseparable uncertainty factors influencing the safety of a roller compacted concrete dam (RCC dam), which can be regarded as a system reliability problem associated with multiple failure modes. Aiming at the current probabilistic risk analysis of RCC dams, most of the studies limited to single failure mode and single uncertainty. A probabilistic risk assessment method for dam under Grey-Stochastic-Fuzzy (GSF) uncertainty is proposed to consider the randomness and greyness of parameters and the fuzziness of the failure criteria. First, the fault tree model of an RCC dam is established based on Fault Tree Analysis (FTA). Then, bootstrap repeated sampling is embedded into grey system theory to quantify the grey properties of stochastic variables. The Latin Hypercube Sampling (LHS) function is improved to compensate for the inability of describing the fuzzy failure criteria. Finally, considering the correlated multiple failure modes, the proposed method is applied to analyze the parameter sensitivity and failure probability of the LDL dam in China. The results show that the proposed method is a high-efficiency, fastconvergence and more scientific method with reasonable outputs compared to common uncertainty probability analysis methods. The proposed method also provides an effective basis for the structural design and safety analysis of a concrete dam.

Effect of Particle Size of Cellulose Nanofibril on the Structure and Property of Polyacrylonitrile (PAN) Membrane by Electrospinning

Wenlong Xu,Xue Yang,Binjie Xin 한국섬유공학회 2020 Fibers and polymers Vol.21 No.1

Polyacrylonitrile (PAN)/cellulose nanofibril (CNF) nanofiber membranes were successfully prepared by anelectrospinning method, in which the amount of CNF kept 1 wt%. The effects of CNF sizes on the morphology and propertyof spinning solutions and PAN electrospun nanofiber membrane were systematically investigated by rheological propertytest, conductivity test, SEM, TG, DSC, contact angle test and mechanical test. The results showed that the viscosity andconductivity of the spinning solution was improved with the increasing of CNF sizes, as the formation of the strong polarinteractions of nitrile groups and the hydroxyl groups between PAN and CNF. All the morphology of the PAN/CNF nanofibermembrane exhibited a uniform diameter with no visible beads or beads to the string structure, and the average diameter of thePAN/CNF nanofiber was decreased with the increasing of the CNF size. Moreover, the addition of CNF could improve thethermal stability, mechanical property, and hydrophilicity of the PAN membrane. And the PAN/CNF-10 nanofiber membraneexhibited the optimal properties.

Factors Affecting Switching Intention through Trust and Distrust: Focusing an ofo Shared Bike Platform

( Wenlong Lu ),( Yung-ho Suh ) 한국품질경영학회 2019 한국품질경영학회 학술대회 Vol.2019 No.-

With the rapid development of sharing economy, consumer/user trust has become a major factor in its development. Studying the factors affecting the trust of consumers and users will be of great benefit to the development of sharing economy. As a former leader in the bike-sharing field, Ofo has gone from being ubiquitous in the streets to losing consumer trust in the past two years. There have been internal management problems, and the decline of user and consumer trust is leading to the current near-bankruptcy situation. This paper takes ofo as a case to analyze the factors affecting consumer trust/distrust in this bike-sharing market. First, this paper sums up the theory of the consumer trust, combining with China's present situation of sharing economy and the characteristic of the ofo's shared bike(problems), Secondly, four aspects such as personal factors (propensity to trust, propensity to distrust, price sensitivity), product factors (product quality, product availability), platform factors (perceived privacy protection, perceived payment security, reputation), social factors (social norms, government regulation) are considered as the independent variables. Since December 2018, the problem of ofo's 'difficult to refund' has been continuously growing. This study takes this event as a serious factor and from this perspective, focuses on the influencing factors that affect trust/distrust, which in turn leads to switching intention.

Design, test and numerical simulation of a low-speed horizontal axis hydrokinetic turbine

Wenlong Tian,Zhaoyong Mao,Hao Ding 대한조선학회 2018 International Journal of Naval Architecture and Oc Vol.10 No.6

A small-scale horizontal axis hydrokinetic turbine is designed, manufactured and studied both experimentally and numerically in this study. The turbine is expected to work in most of China's sea areas where the ocean current velocity is low and to supply electricity for remote islands. To improve the efficiency of the turbine at low flow velocities, a magnetic coupling is used for the non-contacting transmission of the rotor torque. A prototype is manufactured and tested in a towing tank. The experimental results show that the turbine is characterized by a cut-in velocity of 0.25 m/s and a maximum power coefficient of 0.33, proving the feasibility of using magnetic couplings to reduce the resistive torque in the transmission parts. Three dimensional Computational Fluid Dynamics (CFD) simulations, which are based on the Reynolds Averaged NaviereStokes (RANS) equations, are then performed to evaluate the performance of the rotor both at transient and steady state.

Numerical simulations of a horizontal axis water turbine designed for underwater mooring platforms

Wenlong Tian,Baowei Song,James H. VanZwieten,Parakram Pyakurel,Yanjun Li 대한조선학회 2016 International Journal of Naval Architecture and Oc Vol.8 No.1

In order to extend the operational life of Underwater Moored Platforms (UMPs), a horizontal axis water turbine is designed to supply energy for the UMPs. The turbine, equipped with controllable blades, can be opened to generate power and charge the UMPs in moored state. Threedimensional Computational Fluid Dynamics (CFD) simulations are performed to study the characteristics of power, thrust and the wake of the turbine. Particularly, the effect of the installation position of the turbine is considered. Simulations are based on the Reynolds Averaged Navier- Stokes (RANS) equations and the shear stress transport k-u turbulent model is utilized. The numerical method is validated using existing experimental data. The simulation results show that this turbine has a maximum power coefficient of 0.327 when the turbine is installed near the tail of the UMP. The flow structure near the blade and in the wake are also discussed.

Modified Preview Control for a Wireless Tracking Control System With Packet Loss

Wenlong Zhang,Joonbum Bae,Tomizuka, Masayoshi IEEE 2015 IEEE/ASME transactions on mechatronics Vol.20 No.1

<P>In this paper, a modified preview control technique is proposed to compensate packet loss in a wireless tracking control system, where future reference signals over a finite horizon can be previewed. In order to utilize future reference information for the controller design, the system model is augmented with a reference generator whose states are the future reference signals. As a response to the packet loss that occurs in the wireless network, the preview control technique is modified by employing Bernoulli variables to represent packet loss in both controller-actuator and sensor-controller channels. The Bernoulli packet loss model, along with tracking errors and control inputs, is included in a quadratic cost function, and the optimal controller gain that minimizes the cost function is obtained by dynamic programming. A modified Kalman filter considering packet loss is utilized for full-state estimation and state feedback control. The choice of preview horizon is discussed and the performance of the proposed controller is verified by simulation and experimental results.</P>

Conceptual design and numerical simulations of a vertical axis water turbine used for underwater mooring platforms

Wenlong, Tian,Baowei, Song,Zhaoyong, Mao The Society of Naval Architects of Korea 2013 International Journal of Naval Architecture and Oc Vol.5 No.4

Energy is a direct restriction to the working life of an underwater mooring platform (UMP). In this paper, a vertical axis water turbine (VAWT) is designed to supply energy for UMPs. The VAWT has several controlled blades, which can be opened or closed by inside plunger pumps. Two-dimensional transient numerical studies are presented to determine the operating performance and power output of the turbine under low ocean current velocity. A standard k-${\varepsilon}$ turbulence model is used to perform the transient simulations. The influence of structural parameters, including foil section profile, foil chord length and rotor diameter, on the turbine performance are investigated over a range of tip-speed-ratios (TSRs). It was found that turbine with three unit length NACA0015 foils generated a maximum averaged coefficient of power, 0.1, at TSR = 2.