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Electronic Materials

"Asymmetric 3D Elastic-Plastic Strain Modulated Electron Energy Structure in Monolayer Graphene by Laser Shocking"

Authors: Maithilee Motlag, Prashant Kumar, Kevin Y. Hu, Shengyu Jin, Ji Li, Jiayi Shao, Xuan Yi, Yen Hsiang Lin, Jenna C. Walrath, Lei Tong, Xinyu Huang, Rachel S. Goldman, Lei Ye and Gary J. Cheng;

Abstract: Graphene has a great potential to replace silicon in prospective semiconductor industries due to its outstanding electronic and transport properties; nonetheless, its lack of energy bandgap is a substantial limitation for practical applications. To date, straining graphene to break its lattice symmetry is perhaps the most efficient approach toward realizing bandgap tunability in graphene. However, due to the weak lattice deformation induced by uniaxial or in plane shear strain, most strained graphene studies have yielded bandgaps <1 eV. In this work, a modulated, inhomogeneous local asymmetric elastic-plastic straining is reported that utilizes GPa-level laser shocking at a high strain rate (d[epsilon]/dt) [approximately equal to] 106-107 s-1, with excellent formability, inducing tunable bandgaps in graphene of up to 2.1 eV, as determined by scanning tunneling spectroscopy. High-resolution imaging and Raman spectroscopy reveal strain-induced modifications to the atomic and electronic structure in graphene, and first-principle simulations predict the measured bandgap openings. Laser shock modulation of semi-metallic graphene to a semiconducting material with controllable bandgap has the potential to benefit the electronic and optoelectronic industries. (Advanced Materials, Mar. 29, 2019)

"Flow Equation Approach to Periodically Driven Quantum Systems"

Authors: Michael Vogl, Pontus Laurell, Aaron D. Barr and Gregory A. Fiete

Abstract: The authors present a theoretical method to generate a highly accurate time-independent Hamiltonian governing the finite-time behavior of a time-periodic system. The method exploits infinitesimal unitary transformation steps, from which renormalization-group-like flow equations are derived to produce the effective Hamiltonian. The tractable method has a range of validity reaching into frequency --and drive strength--regimes that are usually inaccessible via high-frequency co expansions in the parameter h/[omega], where h is the upper limit for the strength of local interactions. The authors demonstrate exact properties of the approach on a simple toy model and test an approximate version of it on both interacting and noninteracting many-body Hamiltonians, where it offers an improvement over the more well-known Magnus expansion and other high-frequency expansions. For the interacting models, the approximate results are compared to those found via exact diagonalization. While the approximation generally performs better globally than other high-frequency approximations, the improvement is especially pronounced in the regime of lower frequencies and strong external driving. This regime is of special interest because of its proximity to the resonant regime where the effect of a periodic drive is the most dramatic. The results open a new route toward identifying novel nonequilibrium regimes and behaviors in driven quantum many-particle systems. (Physical Review X 9, May 23, 2019;

Solder Alloys

"Experimental and Numerical Investigations of the Vibration Reliability of BGA and LGA Solder Configurations and SAC 105 and 63Sn37Pb Solder Alloys"

Authors: Mohammad Gharaibeh, Aaron J. Stewart, Quang T. Su and James M. Pitarresi; jmp@

Abstract: This paper aims to investigate and compare the reliability performance of land grid array (LGA) and ball grid array (BGA) solders, as well as the SAC 105 and 63Sn37Pb solder alloys in vibration loading conditions. Reliability tests were conducted using a sine dwell with resonance tracking vibration experiment. Finite element simulations were performed to help understand the observed failure trends. Reliability results showed the SnPb solders outperform Pb-free solders in vibration loading. Additionally, the LGA solder type could provide a better vibration reliability performance than BGA solders. Failure analysis results showed that in LGAs, the crack is initiated at the printed circuit board side and at the component side in BGAs. In both types, the crack is propagated throughout the intermetallic compound layer. (Soldering & Surface Mount Technology, vol. 31, no. 2, 2019)

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Publication:Printed Circuit Design & Fab Circuits Assembly
Date:Jul 1, 2019
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