Pressure effects in AlAs/Inx Ga1-xAs/GaAs resonant tunnelling diodes for application in micromachined sensors

This paper reports the current-voltage characteristics of [001]-oriented AlAs/InxGa1-xAs/GaAs resonant tunnelling diodes （RTDs） as a function of uniaxial external stress applied parallel to the [110] and the [1^-10] orientations, and the output characteristics of the GaAs pressure sensor based on the pressure effect on the RTDs. Under [110] stress, the resonance peak voltages of the RTDs shift to more positive voltages. For [1^-10] stress, the peaks shift toward more negative voltages. The resonance peak voltage is linearly dependent on the [110] and [1^-0] stresses and the linear sensitivities are up to 0.69 mV/MPa, -0.69 mV/MPa respectively. For the pressure sensor, the linear sensitivity is up to 0.37 mV/kPa.

Pressure effect on the electron mobility in AlAs/GaAs quantum wells

By taking the influence of optical phonon modes into account, this paper adopts the dielectric continuum phonon model and force balance equation to investigate the electronic mobility parallel to the interfaces for AlAs/GaAs semiconductor quantum wells （QWs） under hydrostatic pressure. The scattering from confined phonon modes, interface phonon modes and half-space phonon modes are analysed and the dominant scattering mechanisms in wide and narrow QWs are presented. The temperature dependence of the electronic mobility is also studied in the temperature range of optical phonon scattering being available. It is shown that the electronic mobility reduces obviously as pressure increases from 0 to 4GPa, the confined longitudinal optical （LO） phonon modes play an important role in wide QWs, whereas the interface optical phonon modes are dominant in narrow QWs, the half-space LO phonon modes hardly influence the electronic mobility expect for very narrow QWs.

Star Grain Regression Analysis under Spin Effect and Chamber Pressure Effect

The angular acceleration due to the spin effect increases the burning rate of solid propellant and changes the motor performance by increasing the operating pressure and decreasing the burning time. So it is important to know the grain regression taken place in the solid propellant rocket motor in the acceleration field. This study represents the grain regression analysis of two-dimensional axis-symmetric star grain configuration of the solid propellant rocket motor with spin induced acceleration effect and pressure effect on burn rate using geometrical and numerical analysis. While the rocket is spinning, the burn rates on each point of the propellant surface are different with its radial distance, acceleration vector angle and surface slope. With the different burn rates on the propellant surface, we analyze the propellant surface perimeter and port area, and these results are compared with those of constant burn rate and burn rate affected by the chamber pressure.

Pressure effect on magnetic phase transition and spin-glass-like behavior of GdCo_2B_2

We systematically investigate the effect of pressure on the magnetic properties of GdCo2B2 on the basis of alternating current（AC） susceptibility,AC heat capacity and electrical resistivity measurements under pressures up to 2.2 GPa.A detailed magnetic phase diagram under pressure is determined.GdCo2B2 exhibits three anomalies that apparently reflect magnetic phase transitions,respectively,at temperatures TC= 20.5 K,T1= 18.0 K and TN= 11.5 K under ambient pressure.Under pressures up to 2.2 GPa,these anomalies are observed to slightly increase at TCand T1,and they coincide with each other above 1.6 GPa.Conversely,they decrease at TN and disappear under pressures higher than 1.4 GPa.The results indicate that the low-temperature magnetic phases can be easily suppressed by pressure.Moreover,the spin-glass-like behavior of GdCo2B2 is examined in terms of magnetization,aging effect and frequency dependence of AC susceptibility.A separation between the zero-field-cooled（ZFC） and field-cooled（FC） magnetization curves becomes evident at a low magnetic field of 0.001 T.A long-time relaxation behavior is observed at 4 K.The freezing temperature Tfincreases with frequency increasing.

Pressure Effect on Crystallization of Zr_(55)Cu_(30)Al_(10)Ni_5 Bulk Metallic Glass

The effect of pressure on the variation of the crystallization phases of the Zr55Cu30Al10Ni5 bulk glass and its thermal stability under high pressure annealing was investigated by X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The mode of crystallization and products of crystallization of the Zr55Cu30Al10Ni5 bulk glass were quite different under different pressure. At ambient pressure, the crystallization products consisted of NiZr2 and CuZr2, while at pressure of 1 GPa and 3 GPa, the alloys crystallized into NiZr2 and Cu10Zr7, respectively. The alloy was nearly not crystallized and only a small amount of Cu10Zr7 was precipitated under 5 GPa. DSC proved that the mode of the crystallization under high pressure was different from that at ambient pressure.

Pressure Effects on Thermodynamics of Phase Behavior in Polystyrene/Methylcyclohexane Solutions

The calculations presented in this paper are based on the Sanchez-Lacombe（SL）lattice fluid theory.The interaction energy parameter,g12/k,required in this approach was obtained by fitting the cloud points of polystyrene（PS）/methylcyclohexane（MCH）polymer solutions under pressure.The SL lattice fluid theory was used to calculate the spinodals,the binodals,and the Flory-Huggins（FH）interaction parameter of the solutions.The calculated results show that the SL lattice fluid theory can describe the dependences of thermodynamics of PS/MCH solutions on temperature and pressure very well.However,the calculated enthalpy and the excess volume changes indicate that the Clausius-Clapeyron equation cannot be suitable to describe pressure effect on PS/MCH solutions.Further analysis on the thermodynamics of this system under pressure shows that the role of entropy is more important than the excess volume in the present case.

Hydrostatic pressure effect on the electron mobility in a ZnSe/Zn_(1-x)Cd_xSe strained heterojunction

With a memory function approach, this paper investigates the electronic mobility parallel to the interface in a ZnSe/Zn1-xCdxSe strained heterojunction under hydrostatic pressure by considering the intersubband and intrasubband scattering from the optical phonon modes. A triangular potential approximation is adopted to simplify the potential of the conduction band bending in the channel side and the electronic penetrating into the barrier is considered by a finite interface potential in the adopted model. The numerical results with and without strain effect are compared and analysed. Meanwhile, the properties of electronic mobility under pressure versus temperature, Cd concentration and electronic density are also given and discussed, respectively. It shows that the strain effect lowers the mobility of electrons while the hydrostatic pressure effect is more obvious to decrease the mobility. The contribution induced by the longitudinal optical phonons in the channel side is dominant to decide the mobility. Compared with the intrasubband scattering it finds that the effect of intersubband scattering is also important for the studied material.

Pressure Effects on the Charge Carrier Transportation of BaF_2 Nanocrystals

The charge transport behavior of barium fluoride nanocrystals is investigated by in situ impedance measurement up to 35 GPa. It is found that the parameters change discontinuously at about 6.9 GPa, corresponding to the phase transition of BaF2 nanocrystals under high pressure. The charge carriers in BaF2 nanocrystals include both Fions and electrons. Pressure makes the electronic transport more difficult. The defects at grains dominate the electronic transport process. Pressure could make the charge-discharge processes in the Fm3m phase more difficult.

Diamond growth in a high temperature and high pressure Fe–Ni–C–Si system:Effect of synthesis pressure

Pressure is one of the necessary conditions for diamond growth.Exploring the influence of pressure on growth changes in silicon-doped diamonds is of great value for the production of high-quality diamonds.This work reports the morphology,impurity content and crystal quality characteristics of silicon-doped diamond crystals synthesized under different pressures.Fourier transform infrared spectroscopy shows that with the increase of pressure,the nitrogen content in the C-center inside the diamond crystal decreases.X-ray photoelectron spectroscopy test results show the presence of silicon in the diamond crystals synthesized by adding silicon powder.Raman spectroscopy data shows that the increase in pressure in the Fe-Ni-C-Si system shifts the Raman peak of diamonds from 1331.18 cm^(-1)to 1331.25 cm^(-1),resulting in a decrease in internal stress in the crystal.The half-peak width decreased from 5.41 cm^(-1)to 5.26 cm^(-1),and the crystallinity of the silicon-doped diamond crystals improved,resulting in improved quality.This work provides valuable data that can provide a reference for the synthesis of high-quality silicon-doped diamonds.

A numerical simulation study on the evolutionary characteristics of the damage process of karst soil cavity under positive pressure effect

Positive pressure effect is the result of rapid urban development in recent years,which leads to over-exploitation of karst groundwater,coupled with the emergence of extreme weather(such as heavy rainfall,the increase in the duration of heavy rainfall),leading to the sharp rise of karst water level,the gas in the karst cavity can not be discharged in time to form a high positive pressure in the soil cavity and promote the destruction of the soil layer,which then induces a series of phenomena,such as karst subsidence.As a new collapse mechanism,the positive pressure effect causes geological disasters that seriously affect the safety of people's lives and properties in karst regions.In order to study the damage characteristics and evolution characteristics of karst soil cavities under positive pressure effect,this study is based on the ASCII text provided by FLAC itself,and the orthotropic simulation computation compilation program,which realizes the finite element analysis in FLAC3D,and focuses on the inhomogeneous change of soil displacement,redistribution of stresses,and plastic damage of karst soil cavities in different evolution stages under the action of positive pressure,and summarizes the characteristics and laws of stress,strain and damage in plastic zone of karst soil cave at different stages of evolution.The results will play a positive role in further investigating the potential mechanical effects,development mechanism and critical warning conditions during the evolution of covered karst soil caves,and also have important scientific research value in deepening the theory of prevention and control of collapse disasters in covered karst soil caves.

Effect of Co-solvent and Pressure on the Thermal Decomposition of 2,2′Azobis-(isobutyronitrile) in Supercritical CO_2

The thermal decomposition of 2, 2'-azobis (isobutyronitrile) (AIBN) in supercritical CO2 with cosolvent methanol or cyclohexane has been studied by using UV/Vis spectroscopic method at 335.15 K and at 12.0 MPa and 14.0 MPa. Both of the cosolvents can accelerate the decomposition rate, and the effect of methanol is more significant than that of the cyclohexane.

Density-functional theory study of the effect of pressure on the elastic properties of CaB_6

Under high pressure, the long believed single-phase material CaB6 was latterly discovered to have a new phase tI56. Based on the density-functional theory, the pressure effects on the structural and elastic properties of CaB6 are obtained. The calculated bulk, shear, and Young’s moduli of the recently synthesized high pressure phase tI56-CaB6 are larger than those of the low pressure phase. Moreover, the high pressure phase of CaB6 has ductile behaviors, and its ductility increases with the increase of pressure. On the contrary, the calculated results indicate that the low pressure phase of CaB6 is brittle. The calculated Debye temperature indicates that the thermal conductivity of CaB6 is not very good. Furthermore, based on the Christoffel equation, the slowness surface of the acoustic waves is obtained.

Confining pressure effect on dynamic response of high rockfill dam

Studies show that the dynamic properties of rockfill are strongly dependent on the confining pressure.Therefore,confining pressure effect has become a very important factor in the seismic analysis of high rockfill dam.The relationships of dynamic shear modulus versus dynamic shear strain and damping ratio versus dynamic shear strain had been improved to a certain degree on the basic of widely used Hardin-Drnevich constitutive model in this paper.Then a new model that could consider confining pressure effect has been established.Regression analysis was carried out of the dynamic triaxial experimental data of the damming materials in the Changheba hydropower station of Sichun Province,China.The results show that,the new model can fit the test data well under various confining pressures.A corresponding computational procedure was compiled and applied in the dynamic response analysis of the Changheba Dam.Comparing the calculation results between the new constitutive model and the ordinary Hardin-Drnevich model,it can be seen that the result is conservative to some extent without considering confining pressure effect.

Pressure effects on the electrical transport and anharmonic lattice dynamics of r-GeTe:A first-principles study

Various strategies for thermoelectric material optimization have been widely studied and used for promoting electrical transport and suppressing thermal transport.As a nontraditional method,pressure has shown great potential,as it has been applied to obtain a high thermoelectric figure of merit,but the microscopic mechanisms involved have yet to be fully explored.In this study,we focus on r-GeTe,a lowtemperature phase of GeTe,and investigate the pressure effects on the electronic structure,electrical transport properties and anharmonic lattice dynamics based on density functional theory(DFT),the Boltzmann transport equations(BTEs)and perturbation theory.Electronic relaxation times are obtained based on the electron-phonon interaction and the constant relaxation time approximation.The corresponding electrical transport properties are compared with those obtained from previous experiments.Hydrostatic pressure is shown to increase valley degeneracy,decrease the band effective mass and enhance the electrical transport property.At the same time,the increase in the low-frequency phonon lifetime and phonon group velocity leads to an increase in lattice thermal conductivity under pressure.This study provides insight into r-GeTe under hydrostatic pressure and paves the way for a high-pressure strategy to optimize transport properties.

Effects of Pressure, Solvent, and Substituent on the Thermal Isomerization of 2-Oxo- spiro[diazirine-3,3'-indoline]

The kinetic effects of pressure, solvent, and substituent on the thermal isomerization from 2 oxospiro[diazirine 3,3 indoline] to 3 diazo 2 oxo indoline have been examined. The rate constants of the thermal isomerization increased with increasing external pressure and were related to the σ + P substituent constant of Hammett correlation. The results suggest that the thermal isomerization proceeds via a dipolar transition state involving heterolytic bond fission. However, the kinetic solvent effects on the thermal isomerization were not observed. The special solvent effects were discussed on the basis of the linear free energy relationship.

Simultaneous studies of pressure effect on charge transport and photophysical properties in organic semiconductors:A theoretical investigation

High-mobility and strong luminescent materials are essential as an important component of organic photodiodes,having received extensive attention in the field of organic optoelectronics.Beyond the conventional chemical synthesis of new molecules,pressure technology,as a flexible and efficient method,can tune the electronic and optical properties reversibly.However,the mechanism in organic materials has not been systematically revealed.Here,we theoretically predicted the pressure-depended luminescence and charge transport properties of high-performance organic optoelectronic semiconductors,2,6-diphenylanthracene(DPA),by first-principle and multi-scale theoretical calculation methods.The dispersion-corrected density functional theory(DFT-D)and hybrid quantum mechanics/molecular mechanics(QM/MM)method were used to get the electronic structures and vibration properties under pressure.Furthermore,the charge transport and luminescence properties were calculated with the quantum tunneling method and thermal vibration correlation function.We found that the pressure could significantly improve the charge transport performance of the DPA single crystal.When the applied pressure increased to 1.86 GPa,the hole mobility could be doubled.At the same time,due to the weak exciton coupling effect and the rigid flat structure,there is neither fluorescence quenching nor obvious emission enhancement phenomenon.The DPA single crystal possesses a slightly higher fluorescence quantum yield~0.47 under pressure.Our work systematically explored the pressure-dependence photoelectric properties and explained the inside mechanism.Also,we proposed that the exte rnal pressure would be an effective way to improve the photoelectric perfo rmance of organic semiconductors.

Pressure tuning of the anomalous Hall effect in the kagome superconductor CsV_(3)Sb_(5)

Controlling the anomalous Hall effect(AHE)inspires potential applications of quantum materials in the next generation of electronics.The recently discovered quasi-2D kagome superconductor CsV_(3)Sb_(5) exhibits large AHE accompanying with the charge-density-wave(CDW)order which provides us an ideal platform to study the interplay among nontrivial band topology,CDW,and unconventional superconductivity.Here,we systematically investigated the pressure effect of the AHE in CsV_(3)Sb_(5).Our high-pressure transport measurements confirm the concurrence of AHE and CDW in the compressed CsV_(3)Sb_(5).Remarkably,distinct from the negative AHE at ambient pressure,a positive anomalous Hall resistivity sets in below 35 K with pressure around 0.75 GPa,which can be attributed to the Fermi surface reconstruction and/or Fermi energy shift in the new CDW phase under pressure.Our work indicates that the anomalous Hall effect in CsV_(3)Sb_(5) is tunable and highly related to the band structure.

EFFECT OF PRESSURE ON CRYSTALLIZATION CHARACTERISTICS AND CRYSTALLIZED MICROSTRUCTURE OF AMORPHOUS Al_(85)Ni_(10)Y_(5) ALLOY

The crystallization behaviour of amorphous Al_(85)Ni_(10)Y_(5) alloy under high pressure was investigated.Results showed that the amorphous state can be preserved when the alloy is treated under high pressure at temperature below 325℃,the polytropic crystallization takes place when the alloy is treated at 325〜520 ℃ and 3〜6GPa for 1 min;the crystallizing product is nanometer scale supersaturated fee-Al solid solution particles dispersed in amorphous matrix;under 1 GPa pressure amorphous allloy crystallizes in an eutectic way,the crystallizing products are fee-Al,Al_(3)Y,Al_(3)Ni,AlNiY equilibrium crystalline phases etc.High pressure appreciably changes the crystallization mode and the products,elevates the crystallizing temperature.

The effective pressure law for permeability of clay-rich sandstones

To study the relative sensitivity of permeability to pore pressure Pp and confining pressure Pc for clay-rich rocks, permeability measurements were performed on samples of four clay-rich sandstones. A new method （hereafter denoted the ＂slide method＂） was developed and used for analyzing the permeability data obtained. The effective pressure coefficients for permeability nk were calculated. The values of nk were found to be greater than 1.0 and insensitive to changes in pressure. These results confirmed observations previously made on clay-rich rocks. Also, the coefficients nk obtained had different characteristics for different samples because of differences in the types of clay they contained. The effective pressure law （σeff=Pc-nkPp） determined using the slide method gave better results about k（oefr） than classic Terzaghi＇s law （σeff=Pc-nkPp）.