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Electronic structure, mechanical and optical properties of ternary semiconductors Si <sub/>1-x</sub> Ge <sub/>x</sub> C (X?=?0, 0.25, 0.50, 0.75, 1)
摘要： The electronic structure of silicon carbide with increasing germanium content have been examined using first principles calculations based on density functional theory. The structural stability is analysed between two different phases, namely, cubic zinc blende and hexagonal phases. The zinc blende structure is found to be the stable one for all the Si1-xGexC semiconducting carbides at normal pressure. Effect of substitution of Ge for Si in SiC on electronic and mechanical properties is studied. It is observed that cubic SiC is a semiconductor with the band gap value 1.243 eV. The band gap value of SiC is increased due to the substitution of Ge and the band gap values of Si 0.75 Ge 0.25 C, Si 0.50 Ge 0.50 C, Si 0.25 Ge 0.75 C and GeC are 1.322 eV, 1.413 eV, 1.574 eV and 1.657 eV respectively. As the pressure is increased, it is found that the energy gap gets decreased for Si1-x GexC (X = 0, 0.25, 0.50, 0.75, 1). The elastic constants satisfy the Born – Huang elastic stability criteria. The bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are also calculated and compared with the other available results.
关键词： mechanical properties,electronic structure,optical properties,First principles study
更新于2025-09-23 15:23:52
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On the mechanisms of tip-force induced switching in ferroelectric thin films: The crossover of depolarization, shear strain and flexoelectricity
摘要： The recent observation of mechanical switching of ferroelectric polarization has placed the mechanical manipulation of ferroelectrics on an equal footing with the conventional electrical manipulation. However, discussions on the exact switching mechanisms due to mechanical loads are ongoing for the complexity in experimental situations. In this work, based on continuum mechanical and thermodynamic modeling and simulation, we analyze the mechanisms of tip-force induced switching in ferroelectric thin films. The roles of depolarization, shear strain and flexoelectricity in mechanical switching, both in normal and sliding loading modes, are separated out and the switching characteristics are analyzed. The depolarization field in the film is demonstrated to enable bidirectional switching. The coupling between shear strain and polarization components is shown to be important in the sliding loading mode. A great influence of flexoelectricity-modified polarization boundary condition on the switching process is revealed. The previous speculation that the switching process experiences an intermediate paraelectric phase is proved. The regulation of loading force, misfit strain, temperature and film thickness on the switching are further given for each mechanism. Taking all of the three mechanisms into account, we present the phase diagrams of mechanical switching for films in an initial upward or downward polarization state. The revealed characteristics of various switching mechanisms should provide useful guidelines for their verification in experiments, and the tunability of the switching by various influencing factors is instructive for the design and optimization of ferroelectric devices via mechanical engineering.
关键词： shear strain,mechanical switching,ferroelectrics,flexoelectricity,depolarization
更新于2025-09-23 15:23:52
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Comprehensive investigation of surface quality and mechanical properties in CO2 laser drilling of GFRP composites
摘要： The present paper aims to study different laser drilling/cutting parameters including laser intensity, cutting speed, and gas pressure in order to achieve minimum surface roughness (Ra), heat-affected zone (HAZ), taper angle (TA), and maximum tensile strength (TS) of the laser-drilled glass fiber-reinforced plastic (GFRP) laminate. Full factorial design of experiment method and analysis of variance were adopted to investigate the effect of each parameter on the responses, and in addition, the surface roughness and tensile strength were compared with that of conventional drilling. The morphology of the laser-drilled holes was studied through the scanning electron microscopy (SEM). It was found that optimum laser drilling parameters can yield higher tensile strength and lower surface roughness in drilled GFRP laminate compared to the conventional drilling. Moreover, multi-response optimization was carried out on the results in order to obtain maximum tensile strength, minimum HAZ, minimum surface roughness, and minimum taper angle. The results revealed that the laser intensity, cutting speed, and assist gas pressure should be set at 2.04 W/cm2, 8 mm/s, and 4 bar, respectively, to obtain higher tensile strength and surface integrity. The results drawn from this study can be applied to improve the surface quality and mechanical properties of laser drilling of FRP materials especially in aircraft part manufacturing.
关键词： FRP,HAZ,Laser machining,Mechanical properties,Fiber-reinforced polymer composite
更新于2025-09-23 15:23:52
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A novel growth strategy of TiO<sub>2</sub> anodic films using surface residual stress as driving force
摘要： The relationship between residual stress and growth behavior of anodic titanium oxide films (TiO2) was investigated in terms of defect chemistry and the nanocrystalline materials thermodynamic. The results showed that the surface residual stress can be controlled by acting on the duration of the surface mechanical attrition treatment (SMAT). When samples are processed by grinding for 30 min, the residual stress value reaches a maximum of 73.13 MPa, approximately 7.2 times higher than the one obtained with untreated sample. Under these conditions, the thickness of the anodic film was about 1200 nm, three times that of the TA2 anodic film. Furthermore, the results of electrochemical tests showed that following the surface mechanical attrition treatment, the anodic film show lower density vacancies, higher resistance to the diffusion of Cl-, higher density, and an improved corrosion resistance when compared to TA2. Generally speaking, the growth behavior of the anodic film can be improved by identifying the suitable residual stress.
关键词： Surface mechanical attrition treatment,Anodic oxidation,Corrosion resistance,Growth mechanism
更新于2025-09-23 15:23:52
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Laser impact welding: Investigation on microstructure and mechanical properties of molybdenum-copper welding joint
摘要： Due to their excellent properties, molybdenum and copper are widely used in the electronics industry. However, the welding of molybdenum and copper is difficult, which limits their application prospects in the field of microelectronics devices. This paper describes a novel method for Mo/Cu welding in micro devices: laser impact welding (LIW). The experimental results found that welding improved with the increase of laser energy. The springback and interface wave in the welding area were observed by optical microscope and scanning electron microscope (SEM) and the results showed that the shapes of the interface wave were flat and zigzag. Energy dispersive spectroscopy (EDS) showed little or no diffusion of elements at the welding interface. Tensile shear test results of the welded specimens showed that there were two kinds of failure forms: solder joint failure and solder joint edge failure. The nano-hardness of the materials in the welding area increased compared with the raw materials.
关键词： Laser impact welding,Springback,Interface wave,Molybdenum,Mechanical properties,Copper
更新于2025-09-23 15:23:52
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[IEEE 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - Shanghai (2018.8.8-2018.8.11)] 2018 19th International Conference on Electronic Packaging Technology (ICEPT) - A cost-effective and high performance assembly technology for interconnecting the Cu/Al bilayer electrode and lead wire of ZnO varistor using a low Ag-containing solder paste
摘要： In this paper, the spreading ability of solder pastes with different Ag contents on Ag and Cu/Al bilayer electrodes was investigated in detail. The mechanical performance (i.e., stripping force) and microstructure of 'lead-wire/solder/electrode/ZnO' joints were characterized. The electrical property of ZnO varistors soldered by various solder pastes was also analysed. Results show that the low Ag-containing solder paste with the assistance of the flux having appropriate activity exhibits similar spreading ability on Ag and Cu/Al bilayer electrodes with the high Ag-containing solder paste. Moreover, the difference in Ag content of solder pastes has little influence on the stripping force of the solder joints and the surge performance of ZnO varistors. High activity of the solder paste may lead to severe corrosion of Ag electrode and decrease in the stripping force of the joints, and low activity of the solder paste brings the problem of inadequate removal of oxide films on the Cu/Al bilayer electrode, which leads to poor soldering quality and lower stripping force of the joints. ZnO varistors with Cu/Al bilayer electrodes have superior surge performance over those with Ag electrodes.
关键词： Cu/Al bilayer electrode,ZnO varistor,mechanical performance,spreading ability,low Ag-containing solder paste
更新于2025-09-23 15:22:29
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Novel polyelectrolyte–Al2O3/SiO2 composite nanoabrasives for improved chemical mechanical polishing (CMP) of sapphire
摘要： A new type of polyelectrolyte–Al2O3/SiO2 composite nanoparticle with excellent dispersibility and superior polishing performance was successfully fabricated using a facile method. Silica acted as a bifunctional molecule by attaching to alumina via covalent bond and adsorbing polyelectrolytes by electrostatic interaction. The material removal rate of the polyelectrolyte–Al2O3/SiO2 abrasive was 30% higher than that of the pure Al2O3 abrasive. In addition, the sapphire surface was much smoother. The material removal mechanism was investigated during CMP using the microcontact and wear model. The enhanced removal rate was mainly attributed to the well-dispersed particles, which can accelerate mechanical removal process. The remarkably smooth surface was due to the decrease in penetration depth of the abrasive into the wafer. The results of this study provided a feasible strategy to satisfy the high efficiency and damage-free polishing requirements for sapphire planarization.
关键词： chemical mechanical polishing,composite abrasives,polyelectrolyte,surface roughness,sapphire,material removal rate
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Ultrasonics Symposium (IUS) - Kobe, Japan (2018.10.22-2018.10.25)] 2018 IEEE International Ultrasonics Symposium (IUS) - Accelerated Aging Procedures of Bending Piezoelectric Structures Using Electrical Stress Induced Approaches
摘要： Efficient AgInGaS quantum dot-based energy harvesting devices using electrical and mechanical approaches
关键词： energy harvesting,quantum dots,optoelectronics,AgInGaS,mechanical stress
更新于2025-09-23 15:22:29
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[IEEE 2017 IEEE Workshop on Recent Advances in Photonics (WRAP) - Hyderabad (2017.12.18-2017.12.19)] 2017 IEEE Workshop on Recent Advances in Photonics (WRAP) - Differential Pressure Sensor Using Integrated Optical MEMS and Double Ring Resonator
摘要： In this work, we designed and simulated a differential pressure sensor using a double ring resonator with radius 5μm and 4μm placed on the fixed of a cantilever beam with dimensions 100μm x 30μm x 5μm. The stress induced on the cantilever changes the refractive index in the waveguide which results in the shift of the resonant wavelength. A sensitivity of 15.544pm/kPa is achieved. The sensor is operated at wavelength equal to 1.55μm and can be used for aircraft, medicine and automobile.
关键词： Cantilever beam,Opto-mechanical effect,Differential pressure sensor,Double ring resonator
更新于2025-09-23 15:22:29
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Phonon-assisted tunneling in direct-bandgap semiconductors
摘要： In tunnel ?eld-effect transistors, trap-assisted tunneling (TAT) is one of the probable causes for degraded subthreshold swing. The accurate quantum-mechanical (QM) assessment of TAT currents also requires a QM treatment of phonon-assisted tunneling (PAT) currents. Therefore, we present a multi-band PAT current formalism within the framework of the quantum transmitting boundary method. An envelope function approximation is used to construct the electron-phonon coupling terms corresponding to local Fr?hlich-based phonon-assisted inter-band tunneling in direct-bandgap III-V semiconductors. The PAT current density is studied in up to 100 nm long and 20 nm wide p-n diodes with the 2- and 15-band material description of our formalism. We observe an inef?cient electron-phonon coupling across the tunneling junction. We further demonstrate the dependence of PAT currents on the device length, for our non-self-consistent formalism which neglects changes in the electron distribution function caused by the electron-phonon coupling. Finally, we discuss the differences in doping dependence between direct band-to-band tunneling and PAT current.
关键词： phonon-assisted tunneling,quantum-mechanical modeling,tunnel ?eld-effect transistors,electron-phonon coupling,direct-bandgap semiconductors
更新于2025-09-23 15:22:29