Nanofire and scale effects of heat

Zhiyu Hu,Sebastiaan A. Meijer,Qiuchen Wang,Erzhen Mu,Gang Yang,Zhimao Wu 나노기술연구협의회 2019 Nano Convergence Vol.6 No.5

Combustion is a chemical reaction that emits heat and light. Nanofire is a kind of flameless combustion that occurs on the micro–nano scale. Pt/Al2O3 film with a thickness of 20 nm can be prepared as a catalyst by micro–nano processing. When the methanol-air mixture gas passes through the surface of the catalyst, a chemical reaction begins and a significant temperature rise occurs in the catalyst region. Compared to macroscopic combustion, Nanofire has many special properties, such as large temperature gradients, uniform temperature distribution, and fast temperature response. The large temperature gradient is the most important property of Nanofire, which can reach 1330 K/mm. Combined with thermoelectric materials, it can realize the efficient conversion of chemical energy to electric energy. Nanoscale thickness offers the possibility of establishing thermal gradient. On the other hand, large thermal gradient has an effect on the transport properties of phonons and electrons in film materials. From these we can get the scale effects of heat. This article will provide an overview of the preparation, properties and applications of Nanofire, and then a comprehensive introduction to the thermal scale and thermal scale effects.

A Study on Multi-core Task Scheduling Algorithm based on Artificial Intelligence

Hu Zhiyu,Li Li 보안공학연구지원센터 2016 International Journal of Grid and Distributed Comp Vol.9 No.12

With the rapid development of science technology, the multi-core processor system has been become one of the hottest issues in the high performance computation field at present. At the same time, there are some problems in the application and the process of development. In order to find the more efficient task scheduling algorithm, this paper will research the multi-core processors task scheduling algorithm. With exploring the existing task scheduling algorithm principle, the heterogeneous multi-core processor system task scheduling mathematical model is be built, and based on the genetic algorithm, the paper proposes the heterogeneous multi-core processor system scheduling based on population genetic algorithm. Then, through the feasibility, parameter analysis, verification algorithm, the improved genetic algorithm effectively improves the system performance, and reduces the running time. The model, in a certain extent, increases the application and development of artificial intelligence, and provides a theoretical basis for related research.

Robot Manipulator Visual Servoing via Kalman Filter- Optimized Extreme Learning Machine and Fuzzy Logic

Zhiyu Zhou,Yanjun Hu,Jiangfei Ji,Yaming Wang,Zefei Zhu,Donghe Yang,Ji Chen 한국인터넷정보학회 2022 KSII Transactions on Internet and Information Syst Vol.16 No.8

Visual servoing (VS) based on the Kalman filter (KF) algorithm, as in the case of KF-based image-based visual servoing (IBVS) systems, suffers from three problems in uncalibrated environments: the perturbation noises of the robot system, error of noise statistics, and slow convergence. To solve these three problems, we use an IBVS based on KF, African vultures optimization algorithm enhanced extreme learning machine (AVOA-ELM), and fuzzy logic (FL) in this paper. Firstly, KF online estimation of the Jacobian matrix. We propose an AVOA-ELM error compensation model to compensate for the sub-optimal estimation of the KF to solve the problems of disturbance noises and noise statistics error. Next, an FL controller is designed for gain adaptation. This approach addresses the problem of the slow convergence of the IBVS system with the KF. Then, we propose a visual servoing scheme combining FL and KF-AVOA-ELM (FL-KF-AVOA-ELM). Finally, we verify the algorithm on the 6-DOF robotic manipulator PUMA 560. Compared with the existing methods, our algorithm can solve the three problems mentioned above without camera parameters, robot kinematics model, and target depth information. We also compared the proposed method with other KF-based IBVS methods under different disturbance noise environments. And the proposed method achieves the best results under the three evaluation metrics.

Study on Cybersecurity of Hybrid, Multi-hop, Wireless Network

Li Li,Hu Zhiyu 보안공학연구지원센터 2016 International Journal of Security and Its Applicat Vol.10 No.10

As the frontier of Internet development, hybrid, wireless, multi-hop network has transformed the way we live. Nowadays, this network has been engaged in many areas like economy, war, culture, medical treatment, agriculture, ecology, commerce, etc. The concepts of digital coalmine and digital oil field, in special, promote the development of the study on hybrid, wireless, multi-hop network. The paper establishes cybersecurity mechanism by introducing concepts relevant to this network, and by summarizing its internal and external security threats. By conducting simulation experiment to the security mechanism, the paper concludes that to the influence on security mechanism, the number of nodes is in direct proportion, while the transmission period of node connection in inverse proportion. The paper aims to offer reasonable suggestions and guidance to the development of hybrid, wireless, multi-hop network, to promote the application of the wireless network, and to increase its value, solve security problems and ensure sound operation of hybrid, wireless, multi-hop network.

A comparative experimental study on the cross-plane thermal conductivities of nano-constructed Sb2Te3/(Cu, Ag, Au, Pt) thermoelectric multilayer thin films

Yang Gang,Pan Jiahui,Fu Xuecheng,Hu Zhiyu,Wang Ying,Wu Zhimao,Mu Erzhen,Yan Xue-Jun,Lu Ming-Hui 나노기술연구협의회 2018 Nano Convergence Vol.5 No.22

Thermoelectric multilayer thin films used in nanoscale energy conversion have been receiving increasing attention in both academic research and industrial applications. Thermal transport across multilayer interface plays a key role in improving thermoelectric conversion efficiency. In this study, the cross-plane thermal conductivities of nano-constructed Sb2Te3/(Cu, Ag, Au, Pt) thermoelectric multilayer thin films have been measured using time-domain thermoreflectance method. The interface morphology features of multilayer thin film samples were characterized by using scanning and transmission electron microscopes. The effects of interface microstructure on the cross-plane thermal conductivities of the multilayer thin films have been extensively examined and the thermal transfer mechanism has been explored. The results indicated that electron–phonon coupling occurred at the semiconductor/metal interface that strongly affected the cross-plane thermal conductivity. By appropriately optimizing the period thickness of the metal layer, the cross-plane thermal conductivity can be effectively reduced, thereby improving the thermoelectric conversion efficiency. This work presents both experimental and theoretical understanding of the thermal transport properties of Sb2Te3/metal multilayer thin film junctions with important implications for exploring a novel approach to improving the thermoelectric conversion efficiency. Introduction Thermoelectric multilayer thin films used in nanoscale energy conversion have been receiving increasing attention in both academic research and industrial applications. Thermal transport across multilayer interface plays a key role in improving thermoelectric conversion efficiency. In this study, the cross-plane thermal conductivities of nano-constructed Sb2Te3/(Cu, Ag, Au, Pt) thermoelectric multilayer thin films have been measured using time-domain thermoreflectance method. The interface morphology features of multilayer thin film samples were characterized by using scanning and transmission electron microscopes. The effects of interface microstructure on the cross-plane thermal conductivities of the multilayer thin films have been extensively examined and the thermal transfer mechanism has been explored. The results indicated that electron–phonon coupling occurred at the semiconductor/metal interface that strongly affected the cross-plane thermal conductivity. By appropriately optimizing the period thickness of the metal layer, the cross-plane thermal conductivity can be effectively reduced, thereby improving the thermoelectric conversion efficiency. This work presents both experimental and theoretical understanding of the thermal transport properties of Sb2Te3/metal multilayer thin film junctions with important implications for exploring a novel approach to improving the thermoelectric conversion efficiency. Introduction

Sustained electron tunneling at unbiased metal-insulator-semiconductor triboelectric contacts

Liu, Jun,Miao, Mengmeng,Jiang, Keren,Khan, Faheem,Goswami, Ankur,McGee, Ryan,Li, Zhi,Nguyen, Lan,Hu, Zhiyu,Lee, Jungchul,Cadien, Ken,Thundat, Thomas Elsevier 2018 Nano energy Vol.48 No.-

<P><B>Abstract</B></P> <P>Generating sufficient current density for powering electronic devices remains as one of the critical challenges of mechanical energy harvesting techniques based on piezo and triboelectricity, mainly due to the high impedance of the insulating material systems. Here we report on producing sustainable tunneling current using an unbiased, triboelectrically charged metal-insulator-semiconductor (MIS) point contact system, consisting of p-type silicon, silicon oxide and a metal tip. The native thin oxide (~ 1.6 nm) on the silicon surface provides a natural pathway for quantum mechanical tunneling of the triboelectrically generated electrons into the silicon substrate. Lateral back and forth sliding motion of the tip, irrespective of the direction of motion, generates a constant direct current (d.c.) with very high current density. The measured current shows an exponential decay with the thickness of oxide layer deposited with atomic layer deposition (ALD), confirming the quantum mechanical tunneling mechanism. It is proposed that the contact potential difference enhanced by triboelectric charging provides potential difference between metal point contact and the substrate. With single metallic micro probe sliding on a moderately doped p-type silicon, an open circuit voltage (<I>V</I> <SUB>oc</SUB>) of 300–400 mV and a short-circuit direct current (<I>I</I> <SUB>sc</SUB>) of 3–5 μA (a corresponding high current density, <I>J</I>, in the order of 1–10 A/m<SUP>2</SUP>) have been observed. It is predicted from conductive-atomic force microscopy (C-AFM) experiment that the theoretical <I>J</I> can be as high as 10<SUP>4</SUP> A/m<SUP>2</SUP>. This new concept has the potential as a green energy harvesting technique where a broad range of material candidates and device configurations could be used.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Quantum mechanical tunneling at triboelectrically charged interface through ultrathin oxide layer is demonstrated. </LI> <LI> Tribo-tunneling is found to be a universal phenomenon in MIS frictional contact system. </LI> <LI> High current density <I>J</I> of 5 A/m<SUP>2</SUP> is experimentally measured in doped silicon materials at macroscale. </LI> <LI> Ultrahigh C-AFM <I>J</I> of 10<SUP>4</SUP> A/m<SUP>2</SUP> is observed due to the nano-size probe-induced high electric field. </LI> <LI> This method can be used as cost-effective triboelectric DC current generator, due to easily available silicon wafers with native oxide. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Direct-current triboelectricity generation by a sliding Schottky nanocontact on MoS₂ multilayers

Liu, Jun,Goswami, Ankur,Jiang, Keren,Khan, Faheem,Kim, Seokbeom,McGee, Ryan,Li, Zhi,Hu, Zhiyu,Lee, Jungchul,Thundat, Thomas Nature Publishing Group UK 2018 Nature nanotechnology Vol.13 No.2

<P>The direct conversion of mechanical energy into electricity by nanomaterial-based devices offers potential for green energy harvesting(1-3). A conventional triboelectric nanogenerator converts frictional energy into electricity by producing alternating current (a.c.) triboelectricity. However, this approach is limited by low current density and the need for rectification(2). Here, we show that continuous direct-current (d.c.) with a maximum density of 10(6) A m(-2) can be directly generated by a sliding Schottky nanocontact without the application of an external voltage. We demonstrate this by sliding a conductive-atomic force microscope tip on a thin film of molybdenum disulfide (MoS2). Finite element simulation reveals that the anomalously high current density can be attributed to the non-equilibrium carrier transport phenomenon enhanced by the strong local electrical field (105-106 V m(-2)) at the conductive nanoscale tip(4). We hypothesize that the charge transport may be induced by electronic excitation under friction, and the nanoscale current-voltage spectra analysis indicates that the rectifying Schottky barrier at the tip-sample interface plays a critical role in efficient d.c. energy harvesting. This concept is scalable when combined with microfabricated or contact surface modified electrodes, which makes it promising for efficient d.c. triboelectricity generation.</P>

Ultrathin MEMS thermoelectric generator with Bi2Te3/(Pt, Au) multilayers and Sb2Te3 legs

Liu Yang,Mu Erzhen,Wu Zhenhua,Che Zhanxun,Sun Fangyuan,Fu Xuecheng,Wang Fengdan,Wang Xinwei,Hu Zhiyu 나노기술연구협의회 2020 Nano Convergence Vol.7 No.8

Multilayer structure is one of the research focuses of thermoelectric (TE) material in recent years. In this work, n-type 800 nm ­Bi 2 Te 3 /(Pt, Au) multilayers are designed with p-type ­Sb 2 Te 3 legs to fabricate ultrathin microelectromechanical systems (MEMS) TE devices. The power factor of the annealed ­Bi 2 Te 3 /Pt multilayer reaches 46.5 μW cm −1 K −2 at 303 K, which corresponds to more than a 350% enhancement when compared to pristine ­Bi 2 Te 3 . The annealed ­Bi 2 Te 3 /Au multilayers have a lower power factor than pristine ­Bi 2 Te 3 . The power of the device with ­Sb 2 Te 3 and ­Bi 2 Te 3 /Pt multilayers measures 20.9 nW at 463 K and the calculated maximum output power reaches 10.5 nW, which is 39.5% higher than the device based on ­Sb 2 Te 3 and ­Bi 2 Te 3 , and 96.7% higher than the ­Sb 2 Te 3 and ­Bi 2 Te 3 /Au multilayers one. This work can provide an opportunity to improve TE properties by using multilayer structures and novel ultrathin MEMS TE devices in a wide variety of applications.