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Electrical Transmission

"Momentum-Space Indirect Interlayer Excitons in Transition-Metal Dichalcogenide van der Waals Heterostructures"

Authors: Jens Kunstmann et al; jens.kunstmann@ tu-dresden.de.

Abstract: Monolayers of transition-metal dichalcogenides feature exceptional optical properties that are dominated by tightly bound electron-hole pairs, called excitons. Creating van der Waals heterostructures by deterministically stacking individual monolayers can tune various properties via the choice of materials and the relative orientation of the layers. In these structures, a new type of exciton emerges where the electron and hole are spatially separated into different layers. These interlayer excitons allow exploration of many-body quantum phenomena and are ideally suited for valleytronic applications. A basic model of a fully spatially separated electron and hole stemming from the K valleys of the monolayer Brillouin zones is usually applied to describe such excitons. Here, the authors combine photoluminescence spectroscopy and first-principles calculations to expand the concept of interlayer excitons. The authors identify a partially charge-separated electron-hole pair in Mo[S.sub.2]/W[Se.sub.2] heterostructures, where the hole resides at the T point and the electron is located in a K valley. The authors control the emission energy of this new type of momentum-space indirect, yet strongly bound exciton by variation of the relative orientation of the layers. These findings represent a crucial step toward the understanding and control of excitonic effects in van der Waals heterostructures and devices. In the future, this research could contribute to electronics with more controlled properties. (Nature Physics, April 2018)

"Direct Evidence of Ferromagnetism in a Quantum Anomalous Hall System"

Authors: Wenbo Wang, Weida Wu, et al; wdwu@physics.rutgers.edu.

Abstract: Quantum anomalous Hall (QAH) systems are of great fundamental interest and potential application because of their dissipationless conduction without the need for an external magnetic field. The QAH effect has been realized in magnetically doped topological insulator thin films. However, full quantization requires extremely low temperature (T<50mK) in the earliest works, although it has been significantly improved by modulation doping or co-doping of magnetic elements. Improved ferromagnetism has been shown in these thin films, yet direct evidence of long-range ferromagnetic order is lacking. Herein, the authors present direct visualization of long-range ferromagnetic order in thin films of Cr and V co-doped [(Bi,Sb).sub.2] [Te.sub.3] using low-temperature magnetic force microscopy with in situ transport. The magnetization reversal process reveals typical ferromagnetic domain behavior--that is, domain nucleation and possibly domain wall propagation--in contrast to much weaker magnetic signals observed in the end-members, possibly due to super-paramagnetic behavior. The observed long-range ferromagnetic order resolves one of the major challenges in QAH systems, and paves the way toward high-temperature dissipation-less conduction by exploring magnetic topological insulators. (Nature Physics, May 2018)

Reliability

"Reliability Assessment of Electronic Assemblies under Vibration by Statistical Factorial Analysis Approach"

Author: Mohammad Gharaibeh; mohammada_fa@hu.edu.jo.

Abstract: This paper aims to present a reliability performance assessment of electronic packages subjected to harmonic vibration loadings by using a statistical factorial analysis technique. The effects of various geometric parameters, the size and thickness of the printed circuit board and component and solder interconnect dimensions on the fundamental resonant frequency of the assembly and the axial strain of the most critical solder joint were thoroughly investigated. A previously published analytical solution for the problem of electronic assembly vibration was adopted. This solution was modified and used to generate the natural frequency and solder axial strains data for various package geometries. Statistical factorial analysis was used to analyze these data. The results of the present study showed the reliability of electronic packages under vibration could be significantly enhanced by selecting larger and thicker PCBs and thinner and smaller electrical components. Additionally, taller and thinner solders might also produce better reliability behavior. (Soldering & Surface Mount Technology, vol. 30 no. 3, 2018)

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Title Annotation:	TECHNICAL ABSTRACTS
Publication:	Printed Circuit Design & Fab Circuits Assembly
Date:	Jul 1, 2018
Words:	660
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