Effect of the Compressive Stress for the Growth of Cubic-BN Film

In this work,it is found that the compressive stress on the surface of cubic-BN(c-BN)film is all smaller than that inside c-BN film and after a longer period,the depositing matter mainly is of hexagonal-BN phase rather than c-BN phase,those just are the reason why a pure thicker c-BN film cannot,as yet,be obtained.Up to now the lowest IR peak position of 1004.7cm-1 detected from a broken and part delaminated c-BN film may be one close to the stressless c-BN.

Orthogonal Alignment InAs Islands Formation on GaAs Tensile Strained Layer Grown on (001) InP Substrate by Low Pressure Metal-Organic Chemical Vapor Deposition

Nucleation control is one of the key questions in quantum dots preparation and application.This paper reports the experimental results of orthogonal alignment InAs islands formed on(001)InP substrate by low-pressure metal-organic chemical vapor deposition.As a nucleation control layer,the tensile strained GaAs epilayer with orthogonal trench structure was grown firstly on(001)InP substrate under Stranski-Krastanov growth mode.Then,the InAs islands were grown selectively on the trench edges by using strain effect.This growth technique results in the formation of orthogonal alignment InAs islands without any preprocessing technique prior to the growth.

Atomic Force Microscopy on the Ga_(0.16)In_(0.84)As_(0.80)Sb_(0.20)Epilayer Grown by Metalorganic Chemical Vapor Deposition

The atomic force microscopy study was made on the quaternary Ga_(0.16)In_(0.84)As_(0.80)Sb_(0.20) epilayer prepared on GaSb substrate by metalorganic chemical vapor deposition.The island-like defects were found on the substrate surface pretreated chemically.With the growth process going,these island-like defects could be buried by the epilayer.In the initial stage,two-dimensional-growth-mode was followed.When the epilayer thickness reached 70nm,three-dimensional(3D)-growth-mode occurred and the perfect 3D islands were observed.

Theoretical Prediction for Structural Stabilities and Optical Properties of SrS, SrSe and SrTe under High Pressure

An investigation on the structural stabilities and electronic properties of SrX （X =S, Se and Te） under high pressure is conducted using the first-principles calculation based on density functional theory （DFT） with the plane wave basis set as implemented in the CASTEP code. Our results demonstrate that the sequence of the pressure-induced phase transition of the three compounds is the NaCl-type （B1） structure （Fm3rn） to the CsC1- type （B2） structure （Pm3m）. The phase transition and the metallization pressures are determined theoretically. The pressure effect on the optical properties is discussed. The results are compared with the previous calculations and experimental data.

A new technology for controlling in-situ oxygen fugacity in diamond anvil cells and measuring electrical conductivity of anhydrous olivine at high pressures and temperatures

We present a novel technique for controlling oxygen fugacity,which is broadly used to in-situ measure the electrical conductivities in minerals and rocks during diamond anvil cell experiments.The electrical conductivities of olivine are determined under controlled oxygen fugacity conditions(Mo–MoO2)at pressures up to 4.0 GPa and temperatures up to 873 K.The advantages of this new technique enable the measuring of the activation enthalpy,activation energy,and activation bulk volume in the Arrhenius relationship.This provides an improved understanding of the mechanism of conduction in olivine.Electrical conduction in olivine is best explained by small polaron movement,given the oxygen fugacity-dependent variations in conductivity.

In-Situ High Pressure Raman Spectrum and Electrical Property of PbMoO4

In-situ high pressure Raman spectra and electrical conductivity measurements of scheelite-structure compound PbMoO4 are presented. The Raman spectrum of PbMoO4 is determined up to 26.5 GPa on a powdered sample in a diamond anvil cell （DAC） under nonhydrostatic conditions. The PbMoO4 gradully experiences the trans- formation from the crystal to amorphous between 9.2 and 12.5 GPa. The crystal to amorphous transition may be due to the mechanical deformation and the crystalographic transformation. Furthermore, the electrical conductivity of PbMoO4 is in situ measured accurately using a microcircuit fabricated on a DAC based on the van der Pauw method. The results show that the electrical conductivity of PbMoO4 increases with increases of pressure and temperature. At 26.5 GPa, the electrical conductivity value of PbMoO4 at 295K is 1.93 - 10-4 S/cm, while it raises by one order of magnitude at 430K and reached 3.33 - 10-3 S/cm. However, at 430K, compared with the electrical conductivity value of PbMoO4 at 26.5 GPa, it drops by about two order magnitude at 7.4 GPa and achieves 2.81 × 10^-5 S/cm. This indicates that the effect of pressure on the electrical conductivity of PbMoO4 is more obvious than that of temperature.

Electron Transport Property of CdTe under High Pressure and Moderate Temperature by In-Situ Resistivity Measurement in Diamond Anvil Cell

In situ resistivity measurement has been performed to investigate the electron transport property of powered CdTe under high pressure and moderate temperature in a designed diamond anvil cell. Several abnormal resistivity changes can be found at room temperature when the pressure increases from ambient to 33 GPa. The abnormal resistivity changes at about 3.8 GPa and 10 GPa are caused by the structural phase transitions to the rock-salt phase and to the Cmcm phase, respectively. The other abnormal resistivity changes at about 6.5 GPa, 15.5 GPa, 22.2 GPa and about 30 GPa never observed before are due to the electronic phase transitions of CdTe. The origin of the abnormal change occurred at about 6.5 GPa is discussed. The temperature dependence of the resistivity of CdTe shows its semiconducting behaviour at least before 11.3 GPa.

Direct Deposition of Polycrystalline Diamond Films on the Si(100) Mirror Surface by Hot Filament Chemical Vapor Deposition

High quality diamond films have been deposited on Si(100) mirror surface without using any surface pretreatment such as abrasive diamond scratching,diamond-like carbon predeposition or oil treatment.The experiments are carried out in the hot filament chemical vapour deposition system by using the mixture of methane,hydrogen and oxygen.The films show the well-defined facets and are confirmed by Raman spectroscopy and scanning electron microscopy to be high quality diamond films.In this deposition process,higher substrate temperature,high filament temperature and oxygen addition play the important roles in diamond nucleation on the mirror-smooth Si(100) surface.

Processing YCo_(5) Permanent Magnetic Submicron Flakes by Surfactant-Assisted High-Energy Ball Milling

YCo_(5) alloy is processed by surfactant-assisted high-energy ball milling. Oleic acid is used as the surfactant and is 20% of the starting powder.The resultant particles are flakes of several microns in length and width,and 20-200nm in thickness. The flakes have significant crystallographic anisotropy and the c-axis (also easy magnetization axes) is perpendicular to the flake's surface. Maximum coercivity of 192kA/m is obtained in the sample milled for 100 min.Excess milling results in the appearance of Fe and deteriorates the permanent magnetic properties seriously.

A study on the electrical property of HgSe under high pressure

Using a microcircuit fabricated on a diamond anvil cell, we have measured in-situ conductivity of HgSe under high pressures, and investigated the temperature dependence of conductivity under several different pressures. The result shows that HgSe has a pressure-induced transition sequence from a semimetal to a semiconductor to a metal, similar to that in HgTe. Several discontinuous changes in conductivity are observed at around 1.5, 17, 29 and 49GPa, corresponding to the phase transitions from zinc-blende to cinnabar to rocksalt to orthorhombic to an unknown structure, respectively. In comparison with HgTe, it is speculated that the unknown structure may be a distorted CsCl structure. For the cinnabar-HgSe, the energy gap as a function of pressure is obtained according to the temperature dependence of conductivity. The plot of the temperature dependence of conductivity indicates that the unknown structure of HgSe has an electrical property of a conductor.

Superconductivity in Heavily Boron-Doped Diamond Films Prepared by Electron Assisted Chemical Vapour Deposition Method

Heavily boron-doped thick diamond films with higher superconducting transition temperatures have been prepared by electron assisted chemical vapour deposition method. The results of scanning electron microscopy, Raman spectroscopy, x-ray diffraction, and Hall effect indicate that the films have nice crystalline facets, a notable decrease in the growth rate, and an increase in the tensile stress. Meanwhile, the film resistivity decreases with the increase of the carrier concentration. Our measurements show that the films with 4.88×10^20 cm^-3 and 1.61×10^21 cm^-3 carrier concentration have superconductivity, with onset temperatures of 9.7 K （8.9K for zero resistance） and 7.8 K （6.1 K for zero resistance）, respectively.

In-Situ Conductivity Measurement of BaF2 under High Pressure and High Temperature

We perform the in-situ conductivity measurement on BaF2 at high pressure using a microcircuit fabricated on a diamond anvil cell. The results show that BaF2 initially exhibits the electrical property of an insulator at pressure below 25 GPa, it transforms to a wide energy gap semiconductor at pressure from 25 to 30 GPa, and the conductivity increases gradually with increasing pressure from 30 GPa. However, the metallization predicted by theoretical calculation at 30-33 GPa cannot be observed. In addition, we measure the temperature dependence of the conductivity at several pressures and obtain the relationship between the energy gap and pressure. Based on the experimental data, it is predicted that BaF2 would transform to a metal at about 87 GPa and ambient temperature. The conductivity of BaF2 reaches the order of 10^-3Ω^-1 cm^-1 at 37 GPa and 2400 K, the superionic conduction is not observed during the experiments, indicating the application of pressure elevates greatly the transition temperature of the superionic conduction.

Crystal field analysis of the magnetic properties of RFe11Ti and RFe11TiH （R=Sm, Tb, Ho）

The crystalline-electric-field parameters Anm for RFe11Ti and RFe11TiH （R=Sm, Tb, Ho） are evaluated by fitting calculations to the magnetization curves measured on the single crystals or on magnetically aligned powder samples at 4.2K and higher temperatures. Interstitial hydrogen atom in RFe11Ti has been found to have a significant effect on crystalline-electric-field parameters Anm. By using the parameters of exchange field 2μBHex estimated from inelastic neutron scattering experiments and the fitted Anm, the calculations can reproduce the experimental curves well.

Morphology Change of Metastable Regrown Graphite with Boron Additive under HPHT

By temperature gradient method under high pressure and high temperature （HPHT）, with NiMnCo alloy as the solvent metal, at diamond-stable region of about 5.4 GPa and 1500 K, metastable regrown graphite crystals of different morphology were synthesized. With B as an additive incorporated into the NiMnCo-C system, metastable regrown graphite crystals of sphere-like shape were firstly obtained under HPHT. If the growth system does not contain B, sheet-like regrown graphite crystals, most with regular hexagonal morphology, are grown upwards and standing vertically in the metal solvent. When B additive of 1.0 wt pct was added into carbon source （graphite powder）, all metastable regrown graphite crystals took on the habit of regular sphere-like morphology, and were grown by a spiral layer growth mechanism.

Effect of Seed Sizes on Growth of Large Synthetic Diamond Crystals

For the growth of large synthetic diamond crystals by temperature gradient method （TGM）, the grit sizes of seed crystals have great effects on the growth rate and quality of large grown crystals. Because of the limited area of seed surfaces, the maximum diffusion flux of carbon source, which could be absorbed by the seed, is related to the seed size. And with increasing the seed sizes, the growth rates also increase markedly. However, the seed sizes should be lower than a certain value, which determines the crystal quality directly. For example, with NiMnCo alloy as the metal solvent, when the seed size increases from 0.5 to 1.8 mm, the growth rate increases greatly from about 1.1 to 3.2 mg/h; when the size is beyond 2.0 mm, more and more metal inclusions would be incorporated into the grown crystals, and the crystal quality is destroyed heavily. Finite element analysis （FEA） shows that, due to the special assembly of growth cell, the diffusion of carbon source in the metal solvent is very inhomogeneous, which could be substantiated directly by the appearances and shapes of large grown crystals and the remains of carbon source. And this inhomogeneous diffusion of carbon source would be very harmful to the growth of large diamond crystals, especially when large-size seed crystals are used.

Crystal field analysis of the magnetization curves of R2Fe17 and R2Fe17H3 （R=Tb,Ho,Er）

In this paper the values of the crystalline-electric-field parameters Anm for R2Fel7 and R2Fe17H3 （R=Tb,Ho,Er） are evaluated by fitting calculations to the magnetization curves measured on the single crystal at several temperatures. The fitted Anm for R2Fe17 are strikingly different from those for the corresponding R2Fe17H3. The energy gaps between the lowest four energy levels for Ho ions in Ho2Fe17 can be reproduced by using the fitted Anm and exchange field 2μBHex, which estimated from the fit of the temperature dependence of the spontaneous magnetization combined with inelastic neutron scattering experiment.

Characteristics of grain growth of microarc oxidation coatings on pure titanium

Grainy titania coatings are prepared by microarc oxidation on pure titanium （TA2） substrates in a Na2SiO3NaF electrolytic solution. The coating thickness is measured by an optical microscope with a CCD camera. Scanning electron microscope （SEM） and x-ray diffraction （XRD） are employed to characterize the microstructure and phase composition of coatings. The results show that the coating thickness increases linearly as the treatment time increases. The coatings are mainly composed of anatase and rutile （TiO2）. With the increase of treatment time, the predominant phase composition varies from anatase to rutile, which indicates that phase transformation of anatase into rutile occurs in the oxidizing process. Meanwhile, the size of grains existing on the coating surface increases and thus the surface becomes much coarser.

Study of Diamond Nucleation on Porous Silicon

Diamond films have been deposited on porous silicon with microwave plasma chemical vapour deposition method.Nucleation density and site have been observed and analyzed by using scanning electron micrography.Experimental results showed that the nucleation density changes with the porosity and the nucleation occurs mostly on the edge of the pores.Reasons of these phenomena are discussed.

Diamond Nuclei on the Silicon Mirror Surface by Direct-Current Glow Discharge Chemical Vapor Deposition

A new method is proposed for generation of high density diamond nuclei in the dc glow discharge chemical vapor deposition.Application of dc negative valtage together with high methane content has been found to generate diamond nuclei as high as 10^(10)/cm^(2) on mirror-polished Si wafer.It has been indicated that carbon over-saturation,negative voltage and hydrogen play an important role in this new pretreatment process.

Cubic Boron Nitride Films with Low Stress

We report a cubic boron nitride(c-BN)film with low stress.Infrared(IR)peak position of c-BN at 1006.3cm-1measured by IR spectroscopy shows that the c-BN film has very low internal stress which leads to an excellent adhesion.Transmission electron microscope micrograph indicates the only BN phase on the surface of the film is c-BN phase.It is clearly seen from IR spectra that the intermediate layer between the substrate and the c-BN layer is of the molecular crystal explosion boron nitride,hexagonal boron nitride,and wurtzic boron nitride.