A study has just been carried out on hot electron effects in GaAs/Al0.3Ga0.7As potential well barrier(PWB)diodes using both Monte Carlo(MC)and drift-diffusion(DD)models of charge transport.We show the operation and be...A study has just been carried out on hot electron effects in GaAs/Al0.3Ga0.7As potential well barrier(PWB)diodes using both Monte Carlo(MC)and drift-diffusion(DD)models of charge transport.We show the operation and behaviour of the diode in terms of electric field,mean electron velocity and potential,mean energy of electrons andΓ-valley population.The MC model predicts lower currents flowing through the diode due to back scattering at anode(collector)and carrier heating at higher bias.At a bias of 1.0 V,the current density obtained from experimental result,MC and DD simulation models are 1.35,1.12 and1.77μA/μm^2 respectively.The reduction in current over conventional model,is compensated to a certain extent because less charge settles in the potential well and so the barrier is slightly reduced.The DD model results in higher currents under the same bias and conditions.However,at very low bias specifically,up to 0.3 V without any carrier heating effects,the DD and MC models look pretty similar as experimental results.The significant differences observed in the I-V characteristics of the DD and MC models at higher biases confirm the importance of energy transport when considering these devices.展开更多
Mg-13.1 Gd-1.6 Ag-0.4 Zr(wt%)alloy was either iso-thermally extruded at 350℃ or differentialthermally extruded with respectively pre-heated billet at 500℃ and die at 350℃.The iso-thermal extrusion leads to a near f...Mg-13.1 Gd-1.6 Ag-0.4 Zr(wt%)alloy was either iso-thermally extruded at 350℃ or differentialthermally extruded with respectively pre-heated billet at 500℃ and die at 350℃.The iso-thermal extrusion leads to a near fully recrystallized structure and a[0001]//ED(extrusion direction)texture.In contrast,the differential-thermally extruded alloy develops a bimodal-grained structure composed of fine equiaxed recrystallized grains and coarse elongated unrecrystallized grains with a0110//ED texture.The differential-thermally extruded alloy has a higher number density of precipitates after postextrusion ageing than that of the iso-thermally extruded counterpart.Moreover,precipitation in the differential-thermally extruded alloy is further enhanced with cold rolling before ageing.Finally,the alloy obtains room temperature tensile yield strength of 421 MPa and ultimate tensile strength of 515 MPa via differential-thermal extrusion,cold rolling and ageing,mainly ascribed to the coupled strengthening from the bimodal-grained structure and enhanced precipitation.Strength of the alloy is noticeably higher than those of Mg-Gd(-Y)-Ag extruded alloys with similar compositions reported previously and is comparable to those of other high-strength Mg wrought alloys.The findings suggest that differentialthermal extrusion plus strain ageing is a suitable approach for achieving high strength in age-hardenable Mg alloys.展开更多
In this paper, the texture and microstructure evolution of drawn-torsion and drawn-annealing-torsion ferrite wires are studied by electron back scattering diffraction （EBSD） in order to investigate the special torsi...In this paper, the texture and microstructure evolution of drawn-torsion and drawn-annealing-torsion ferrite wires are studied by electron back scattering diffraction （EBSD） in order to investigate the special torsion texture evolution. Compared to the simulation results, the stable texture components {110}〈 110 〉 and {110}〈112〉 in both drawn-torsion and drawn-annealing-torsion wires display different evolution processes. The texture of the drawn-annealing-torsion wire fits to the Taylor model. A special texture evolution is found in drawn-torsion wires, related to the grain shape, and the heterogeneous deformation. A new plastic deformation viewpoint is suggested based on the special microstructure of drawn ferrite wire.展开更多
基金supported by the College of Physical Sciences, University of Aberdeen, UK
文摘A study has just been carried out on hot electron effects in GaAs/Al0.3Ga0.7As potential well barrier(PWB)diodes using both Monte Carlo(MC)and drift-diffusion(DD)models of charge transport.We show the operation and behaviour of the diode in terms of electric field,mean electron velocity and potential,mean energy of electrons andΓ-valley population.The MC model predicts lower currents flowing through the diode due to back scattering at anode(collector)and carrier heating at higher bias.At a bias of 1.0 V,the current density obtained from experimental result,MC and DD simulation models are 1.35,1.12 and1.77μA/μm^2 respectively.The reduction in current over conventional model,is compensated to a certain extent because less charge settles in the potential well and so the barrier is slightly reduced.The DD model results in higher currents under the same bias and conditions.However,at very low bias specifically,up to 0.3 V without any carrier heating effects,the DD and MC models look pretty similar as experimental results.The significant differences observed in the I-V characteristics of the DD and MC models at higher biases confirm the importance of energy transport when considering these devices.
基金the National Natural Science Foundation of China(Nos.51901027,51971130,51771113 and 51671128)the China Postdoctoral Science Foundation(No.2018M643408)the Natural Science Foundation of Chongqing,China(No.Xm T2019012)。
文摘Mg-13.1 Gd-1.6 Ag-0.4 Zr(wt%)alloy was either iso-thermally extruded at 350℃ or differentialthermally extruded with respectively pre-heated billet at 500℃ and die at 350℃.The iso-thermal extrusion leads to a near fully recrystallized structure and a[0001]//ED(extrusion direction)texture.In contrast,the differential-thermally extruded alloy develops a bimodal-grained structure composed of fine equiaxed recrystallized grains and coarse elongated unrecrystallized grains with a0110//ED texture.The differential-thermally extruded alloy has a higher number density of precipitates after postextrusion ageing than that of the iso-thermally extruded counterpart.Moreover,precipitation in the differential-thermally extruded alloy is further enhanced with cold rolling before ageing.Finally,the alloy obtains room temperature tensile yield strength of 421 MPa and ultimate tensile strength of 515 MPa via differential-thermal extrusion,cold rolling and ageing,mainly ascribed to the coupled strengthening from the bimodal-grained structure and enhanced precipitation.Strength of the alloy is noticeably higher than those of Mg-Gd(-Y)-Ag extruded alloys with similar compositions reported previously and is comparable to those of other high-strength Mg wrought alloys.The findings suggest that differentialthermal extrusion plus strain ageing is a suitable approach for achieving high strength in age-hardenable Mg alloys.
基金supported by Key Projects of the National Science&Technology Pillar Program(No.2011BAE13B03)the Fundamental Research Funds for the Central Universities(No.N110502001)
文摘In this paper, the texture and microstructure evolution of drawn-torsion and drawn-annealing-torsion ferrite wires are studied by electron back scattering diffraction （EBSD） in order to investigate the special torsion texture evolution. Compared to the simulation results, the stable texture components {110}〈 110 〉 and {110}〈112〉 in both drawn-torsion and drawn-annealing-torsion wires display different evolution processes. The texture of the drawn-annealing-torsion wire fits to the Taylor model. A special texture evolution is found in drawn-torsion wires, related to the grain shape, and the heterogeneous deformation. A new plastic deformation viewpoint is suggested based on the special microstructure of drawn ferrite wire.
