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1,073 results on '"Shen, Zhijian"'

2. A unified theory of grain growth in polycrystalline materials

Author

Hu, Jianfeng, Wang, Xianhao, Zhang, Junzhan, Shen, Zhijian, Luo, Jun, and Luo, Jian

Subjects
Condensed Matter - Materials Science
Abstract

Grain growth is a ubiquitous and fundamental phenomenon observed in the cellular structures with the grain assembly separated by a network of grain boundaries, including metals and ceramics. However, the underlying mechanism of grain growth has remained ambiguous for more than 60 years. The models for grain growth, based on the classically linear relationship between the grain boundary migration and capillary driving force, generally predict normal grain growth. Quantitative model for abnormal grain growth is lacking despite decades of efforts. Here, we present a unified model to reveal quantitatively how grain growth evolves, which predicts the normal, abnormal and stagnant behaviors of grain growth in polycrystalline materials. Our model indicates that the relationship between grain boundary migration and capillary driving force is generally nonlinear, but will switch to be the classically linear relationship in a specific case. Furthermore, the grain growth experiments observed in polycrystalline SrTiO3 demonstrates the validity of the unified model. Our study provides a unified, quantitative model to understand and predict grain growth in polycrystalline materials, and thus offers helpful guides for the microstructural design to optimize the properties of polycrystalline materials.

Published
2018
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3. The surface-tension-driven Benard conventions and unique sub-grain cellular microstructures in 316L steel selective laser melting

Author

Zhou, Xin, Zhong, Yuan, Shen, Zhijian, and Liu, Wei

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

The unique sub-grain patterns have been found in some particular alloys (316L, Al-Si, Co-Cr-Mo) selective laser melting (SLM), the submicron-scale cellular, elongated cellular or even band structures are always coexisting inside one single macro-solidified grain. Furthermore, the cellular structures are symmetrical with hexagonal, pentagonal and square cellular patterns where the cellular size is only around 1{\mu}m. Single-layer and bulk 316L SLM experiments are presented that reveals the forming mechanism of these sub-grain cellular microstructures. Complex cellular sub-micron patterns were formed by the local convection and B\'enard Instabilities in front of the solid/liquid (S/L) interface (so-called mushy zones) affected by intricate temperature and surface tension gradients. In other words, this nonlinear self-organization phenomenon (B\'enard Instability) occurring at the S/L interface is superimposed on the macro-grain solidification process to form the sub-grain patterns/structures and elemental microsegregations. This simple and unified explanation can be expanded to other eutectic alloys formed by SLM, like the Al-Si system., Comment: 32 pages, 20 figures

Published
2018

23. Laser spectroscopy of gas confined in nanoporous materials

Author

Svensson, Tomas and Shen, Zhijian

Subjects
Physics - Atomic Physics, Physics - Optics
Abstract

We show that high-resolution laser spectroscopy can probe surface interactions of gas confined in nano-cavities of porous materials. We report on strong line broadening and unfamiliar lineshapes due to tight confinement, as well as signal enhancement due to multiple photon scattering. This new domain of laser spectroscopy constitute a challenge for the theory of collisions and spectroscopic lineshapes, and open for new ways of analyzing porous materials and processes taking place therein., Comment: 4 pages, 3 figures, partly presented orally at 7th International Conference on Tunable Diode Laser Spectroscopy (TDLS), July 2009 in Zermatt, Switzerland; Accepted for Applied Physics Letters (December 2009)

Published
2009
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47. High-Speed Mid-Wave Infrared Uni-Traveling Carrier Photodetector With Inductive Peaked Dewar Packaging

Author

Shen, Zhijian, Yao, Jinshan, Huang, Jian, Dai, Zhecheng, Wang, Luyu, Liu, Fengyu, Zou, Xinbo, Peng, Bo, Liu, Weimin, Lu, Hong, and Chen, Baile

Abstract

Recently, there has been a growing demand for high-speed mid-wave infrared (MWIR) photodetectors (PDs) driven by the emergence of new fields, such as free-space communication and frequency comb spectroscopy. In this study, we investigated a high-speed InAs/GaSb type-II superlattice (T2SL) MWIR uni-traveling carrier (UTC) PD with relatively low dark current and high responsivity. We also perform an inductive peaked dewar packaging on the PD to be user-friendly and allow cryogenic operation. The original on-wafer PD shows a dark current density of 54.05 A/cm2 at 300 K, along with a responsivity exceeding 0.36 A/W at 4.5 μm and a 3-dB bandwidth of 3.83 GHz at −5 V bias. The inductive-peaked device in dewar packaging demonstrates a dark current density of 1.65×10−5 A/cm2 at 77 K, and a responsivity of 0.39 A/W at 4 μm, and a 3-dB bandwidth of 5.29 GHz.

Published
2024
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