Interface contact and modulated electronic properties by external vertical strains and electric fields in graphene/MoS2 heterostructure

Shi Jiakuo,Chen Li,Yang Maoyou,Mi Zhishan,Zhang Mingjian,Gao Kefu,Zhang Duo,Su Shuo,Hou Weimin 한국물리학회 2022 Current Applied Physics Vol.39 No.-

Based to the first-principles calculations, we study the electronic properties of graphene/MoS2 heterostructure by modulating the vertical strains and applying external electric field. Graphene/MoS2 heterostructure is a van der Waals heterostructure (vdWH) with the interlayer spacing is 3.2 Å for the equilibrium state, and the contact property of the interface is n-type Schottky contact. The Schottky barrier height (SBH) changes with vertical strains which induces a change of charge transfer between graphene and MoS2 layer. In addition, with strain or without strain, the applied positive electric field can effectively promote the charge transfer from graphene to MoS2, while the negative electric field has the opposite effect. These findings support for the design of field effect transistors based on graphene vdWHs.

Texture characteristics of a warm rolled 0.085 wt%-P interstitial free (IF) steel with and without lubrication

Weimin Guo,Zuocheng Wang,Na Xu,Ning Ding,Junbo Shi 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.7

A 0.085 wt% P micro - alloyed and Ti-stabilized high strength IF (interstitial free) steel was warm rolled under two conditions: One with lubrication and the other without. The results show that lubrication has a significant effect on texture evolution during warm rolling and the subsequent annealing process. Without lubrication, severe shear deformation occurs in the surface layer, which results in recrystallization and the formation of a <110>//ND (normal direction) texture, while the central layer undergoes plane strain deformation and forms a weak <111>//ND deformation texture (typical of bcc iron). With good lubrication, both the surface and central layer experience plane strain deformation and a strong <111>//ND texture is normally formed. The warm rolling texture (which contains both recrystallized and deformed grains) has a profound effect on the subsequent annealing texture. The final textures influence the draw - ability of the plates, i.e. the r - value (r-value: The ratio of the true width strain to the true thickness strain in a sheet tensile test) and |Dr|-value (planar anisotropy coefficient). After annealing, the lubricated plates are characterized by a higher r - value (1.27) and a much lower |Dr|-value (0.075) than those rolled without lubrication (i.e. 0.96 for the r - value and 0.465 for the |Dr|-value).

Fracture analysis of a welded front axle tube structure from a mini-truck

Weimin Guo,Ning Ding,Na Xu,Long Liu,Nan Li,Junbo Shi,Chi-Man Lawrence Wu 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.1

The failure (fracture) mechanism of a welded front axle tube structure made of C45E4 steel from a mini truck was analyzed. The fracture occurred on the right side of the right support frame with the fracture surface perpendicular to the tube axis. SEM examination showed that the fracture surface could be divided into three areas: intergranular area, cleavage area and dimple area. Crack initiation site of the failed front axle tube was at the front weld joint fixing the right support frame on the axle tube. The crack propagated in two opposite directions along the circumference of the tube and converged at the dimple area. Intergranular fracture was found to be in heat affected zone (HAZ). With higher magnification, fine dimples, intergranular and trans-granular fracture characteristics were observed in the crack initiation site. By metallurgical examination, Widmanstätten ferrites, which could decrease the toughness and strength of the weld joint, were observed in the columnar grains. The hardness of HAZ coarse grain area (623 VHN) was far higher than HAZ fine grain area (310 VHN) and base metal (225 VHN). As the weld process indicates, neither pre-weld nor post-weld treatment was carried out. A non-uniform temperature distribution around the weld joint could generate large thermal residual tensile stress in HAZ; thus, the material was very unstable. It could fracture for very small or even no external stress. Hydrogen atoms would be released during welding and microstructures with the highest hardness are the most susceptible of hydrogen assisted cracking. It is concluded that the fracture was caused by hydrogen assisted brittleness under the induction of weld residual stress. Post-weld aging treatment (PWAT) is recommended to release the residual stress generated during welding process. In this case, PWAT was carried out on the failed weld joint and Vickers hardness of HAZ coarse grain area, HAZ fine grain area and base metal decreased to 232 VHN, 205 VHN and 125 VHN, respectively. That indicates that the PWAT procedure could effectively soften the material and relieve residual stress.

Coaxial Solution Blown Core-Shell Structure Nanofibers for Drug Delivery

Xupin Zhuang,Lei Shi,Bo Zhang,Bo-wen Cheng,Weimin Kang 한국고분자학회 2013 Macromolecular Research Vol.21 No.4

Bombyx mori used as a fast detection model of liver melanization after a clinical drug – Acetaminophen exposure

Yue He,Xu Xu,Jianfeng Qiu,Weimin Yin,Yang-Hu Sima,Shi-Qing Xu 한국응용곤충학회 2020 Journal of Asia-Pacific Entomology Vol.23 No.1

Acetaminophen (APAP) is an effective and widely used analgesic. However, APAP overdose is the principal cause of acute liver failure (ALF) in many countries. Here, we report the phenomenon of liver melanization which occurred before APAP-induced ALF in mice. A melanic surface induced by APAP which was time- and dosedependent in the silkworm invertebrate model was observed. In addition, an APAP-induced acute tissue failure model (ATF) was established using a metabolic detoxification tissue fat body which simulated mouse liver. An investigation of the anabolic mechanism of melanin in experimental animals showed that dopaquinone and dopamine which were synthesized from tyrosine via dopa in silkworms were further metabolized to melanin, while in mice, epinephrine was synthesized via the dopamine branch and melanin was only synthesized via the dopaquinone branch. On this basis, it is proposed that melanin-metabolic levels in plasma could be used as an early diagnostic marker of APAP overdose and the black spots on insect epidermis could be used as a fast detection model of toxicity.

Extraction of density-of-states in amorphous InGaZnO thin-film transistors from temperature stress studies

Xing-Wei Ding,Jianhua Zhang,Weimin Shi,Hao Zhang,Chuanxin Huang,Jun Li,Xueyin Jiang,Zhilin Zhang 한국물리학회 2014 Current Applied Physics Vol.14 No.12

The instability of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) with different active layer thicknesses under temperature stress has been investigated through using the density-of-states (DOS). Interestingly, the a-IGZO TFT with 22 nm active layer thickness showed a better stability than the others, which was observed from the decrease of interfacial and semiconductor bulk trap densities. The DOS was calculated based on the experimentally-obtained activation energy (EA), which can explain the experimental observations. We developed the high-performance Al2O3 TFT with 22 nm IGZO channel layer (a high mobility of 7.4 cm2/V, a small threshold voltage of 2.8 V, a high Ion/Ioff 1.8 107, and a small SS of 0.16 V/dec), which can be used as driving devices in the next-generation flat panel displays.

Contact Stiffness Determination of High-Speed Double- Locking Toolholder-Spindle Joint based on a Macro- Micro Scale Hybrid Method

Yongsheng Zhao,Jingjing Xu,Ligang Cai,Weimin Shi,Zhifeng Liu,Qiang Cheng 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.6

The stiffness of toolholder-spindle joint at high speeds plays an important role in the cutting efficiency and the machining accuracy. A double-locking toolholder (BTF type) is designed to improve the stiffness of joint. This paper presents a macro-micro scale hybrid method to determine the stiffness of double-locking toolholder-spindle joint at high speeds. In this method the finite element method and the three-dimensional fractal method are combined. It is assumed flat in macro-scale for the contact surfaces of joint. The finite element method is introduced to obtain the pressure distribution with the influence of centrifugal force at high speeds. In micro-scale, the contact surfaces are fractal featured and the three-dimensional fractal method is used to compute the stiffness based on the pressure. Experiments with BTF40-type toolholder are conducted to verify the efficiency of the proposed model in zero-speed case. The relationship between the stiffness and the technological parameters of the system can be derived based on the presented model. The upper limit of speed, the optimized range of each technological parameter are determined for obtaining the higher stiffness of joint. The results can provide theoretical basis for improving the cutting efficiency and the machining accuracy of high-speed machine tool.

Effect of Au film and absorption groups on minority carrier life of porous silicon

Yue Zhao,Linjun Wang,Jiahua Min,Weimin Shi 한국물리학회 2010 Current Applied Physics Vol.10 No.3

In this paper, the samples were prepared with or without metal assistance in different time. The effect of Au film and absorption groups on minority carrier life of porous silicon was studied by using l-PCD measurements,and the result was further proved by FTIR spectra and SEM images. The results were showed that the existed hydrogen-related groups on the surface of porous silicon would decrease the minority carrier life and the grid Au film also can decrease the minority carrier life. The minority carrier life may be controlled by the more effective factor, metal elements or absorption groups.

Mechanical Behavior of PMMA/SiO2 Multilayer Nanocomposites: Experiments and Molecular Dynamics Simulation

Xiangshi Zhen,Liyan Zhang,Meinong Shi,Li Li,Lisheng Cheng,Zhiwei Jiao,Weimin Yang,Yumei Ding 한국고분자학회 2020 Macromolecular Research Vol.28 No.3

Poly(methyl methacrylate) (PMMA)/nano-silica (nano-SiO2) nanocomposite film with 256 layers containing different amounts of nano-SiO2 was manufactured by a new type of micro-nano multilayer co-extrusion technology. The structure, morphology and mechanical properties of PMMA/nano-SiO2 nanocomposite films were investigated through Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and tensile test. Besides, molecular dynamics simulation was adopted to study the dispersion and content effect on mechanical properties of PMMA/nano-SiO2 nanocomposite film. It is demonstrated that the tensile strength and the elongation at break of the composites improved with increasing nano-SiO2 content from 0 to 5 wt%, which was in good agreement with the Molecular Dynamics simulation. And the nanofiller dispersion in the multilayer nanocomposite film was better than that in the single-layer film with equivalent thickness under the effect of torsion lamination. Overall, the best performance was found for the nanocomposites of PMMA with nano-SiO2 content of 3.5 wt%.