Effects of alternating current imposition and alkaline earth elements on modification of primary Mg_2Si crystals in hypereutectic Mg-Si alloy

The effects of alternating current imposition and/or alkaline earth elements on modification of the primary Mg2Si crystals in the hypereutectic Mg-Si alloy were investigated.An alternating current of 60 A with frequency of 1 kHz was applied into the hypereutectic Mg-Si melt which was alloyed with alkaline earth elements or not in the fixed temperature range from 700 to 630℃. The results show that the primary Mg2Si crystals could be refined by imposing alternating current or adding alkaline elements. Compared with the samples treated by adding 0.4%Ca or 0.4%Sr,higher modification efficiency could be obtained for the samples treated by imposing alternating current.No further modification efficiency could be obtained for the samples treated by imposing alternating current combined with 0.4%Ca or 0.4%Sr addition.

Fe-3%Si大尺寸合金单晶的制备及磁感系数的计算

以取向Fe-3%Si合金热轧板为原材料,采用二次再结晶法制备了尺寸大于200 mm的合金单晶。随机选取3个单晶样品剪切成7个与轧向成不同角度、尺寸为50 mm×50 mm的样品,分别对所选样品进行单晶定向,并对每个样品的横、纵向磁性能进行了测量。以单晶定向结果为依据,计算每个单晶在晶体学坐标架下的极角和辐角,提出了一种单晶磁感系数的计算方法,并基于该方法以单晶磁性能实测值及其在晶体学坐标架下的极角和辐角为输入条件,测算了Fe-3%Si合金单晶磁感应强度系数并验证了其可靠性。采用该方法对{110}晶面平行于板面的任意方向单晶的磁感应强度进行了计算,为开展多晶材料磁性能计算提供了理论依据。

p-Si/n-Ga_(2)O_(3)异质结制备与特性研究

本实验采用金属有机化学气相沉积(MOCVD)工艺,在p(111)型Si衬底上制备了p-Si/n-Ga_(2)O_(3)结构的PN结。通过X射线衍射仪、原子力显微镜等对样品进行了晶体结构、表面形貌、表面粗糙度等的表征分析;通过磁控溅射与蒸镀方法在样品上生长Ti/Au电极并进行I-V特性曲线、开启电压、开关电流比、反向饱和电流、理想因子、零偏压下的势垒高度等结特性测试,研究了掺杂浓度与薄膜厚度对PN结特性的影响,并对其原因进行了分析;通过二步生长法和缓冲层温度优化实验,减少了Si衬底与β-Ga_(2)O_(3)之间的晶格失配与热失配带来的影响,对薄膜与器件特性进行了优化。最终获得了表面粗糙度最低可达到4.21 nm的高质量n型β-Ga_(2)O_(3)薄膜,以及具有较低理想因子(42.1)的PN结。

Determination of Structure and Polarity of Si C Single Crystal by X-Ray Diffraction Technique

Structure and polarity of the Si C single crystal have been analyzed with the four- circle X- ray diffraction method by a double- crystal diffractom eter.The hexagonal{ 10 15 } pole figure shows that this Si C sam ple has a6 H modification.The difference between the integrated intensities m easured byω scan in the triple- axis diffraction set- up finds some convincing evidence that the surface is either a Si- terminated face or C- terminated face.The experi- mental ratios of| F( 0 0 0 L) | 2 / | F( 0 0 0 L) | 2 are in good agreem entwith the calculated ones after the dispersion cor- rections to the atomic scattering factors( L=6 ,12 and18,respectively) .Thus,this m easurem ent technique is con- venient for the application of the materials with remarkable surface polarity.

Effect of Growth Parameters on Core Length of Φ76．2mm Heavily Sb－doped Si Crystals

An M-shaped interface was observed in the top part of Φ76. 2 mm , (111) , dislocation-free, heavily Sb-doped Si single crystals, which is beneficial for crystals to keep dislocation-free condition at the beginning ofbody growth. Effects of seed rotation, crucible rotation , crown shape and growth rate on M-shaed interfacewere studied. Under proper conditions, impurity core length can be shortened from 6 cm to 1 cm , the yield israised by more than 5 %.

Effect of thermal shield and gas flow on thermal elastic stresses in 300mm silicon crystal

The thermal elastic stresses induced in 300 mm Si crystal may be great troubles because it can incur the generation of dislocations and undesirable excessive residual stresses. A special thermal modeling tool, CrysVUn, was used for numerical analysis of thermal elastic stresses and stress distribution of 300 mm Si crystal under the consideration of different thermal shields and gas flow conditions. The adopted governing partial equations for stress calculation are Cauchy′s first and second laws of motion. It is demonstrated that the presence and shape of thermal shield, the gas pressure and velocity can strongly affect von Mises stress distribution in Si crystal. With steep-wall shield, however, the maximal stress and ratio of high stress area are relatively low. With slope-wall shield or without shield, both maximal stress and ratio of high stress area are increased in evidence. Whether thermal shields are used or not, the increase of gas flow velocity could raise the stress level. In contrast, the increase of gas pressure cannot result in so significant effect. The influence of thermal shield and gas flow should be attributed to the modification of heat conduction and heat radiation by them.

Mechanical properties and structure of zirconia-mullite ceramics prepared by in-situ controlled crystallization of Si-Al-Zr-O amorphous bulk

Zirconia-mullite nano-composite ceramics were fabricated by in-situ controlled crystallization of Si-Al-Zr-O amorphous bulk, which were first treated at 900-1000 ℃ for nucleation, then treated at higher temperature for crystallization to obtain ultra-fine zirconia-mullite composite ceramics. The effects of treating temperature and ZrO2 addition on mechanical properties and microstructure were analyzed. A unique structure in which there are a lot of near equiaxed t-ZrO2 grains and fine yield-cracks has been developed in the samples with 15% zirconia addition treated at 1 150 ℃ . This specific microstructure is much more effective in toughening ceramics matrix and results in the best mechanical properties. The flexural strength and fracture toughness are 520 MPa and 5.13 MPa·m1/2, respectively. Either higher zirconia addition or higher crystallization temperature will produce large size rod-like ZrO2 and mullite grains, which are of negative effect on mechanical properties of this new composite ceramics.

Activation of silicon quantum dots and coupling between the active centre and the defect state of the photonic crystal in a nanolaser

A new nanolaser concept using silicon quantum dots （QDs） is proposed. The conduction band opened by the quantum confinement effect gives the pumping levels. Localized states in the gap due to some surface bonds on Si QDs can be formed for the activation of emission. An inversion of population can be generated between the localized states and the valence band in a QD fabricated by using a nanosecond pulse laser. Coupling between the active centres formed by localized states and the defect states of the two-dimensional （2D） photonic crystal can be used to select the model in the nanolaser.

COLD-ROLLING AND RECRYSTALLIZATION OF (110)[110] IRON-SILICON SINGLE CRYSTALS

After70-90% cold-rolling,strong{111}〈110〉and weak {111},〈112〉 cold-rolled tex- tures and perfect{111}〈112〉 recrystallization texture were obtained in Fe-Si single crys- tals.The cold-rolled textures with different orientations possesses different ability for recov- ery because of the difference of dislocation structure and store energy alter cold-rolling.The recovery taking place at{111}〈112〉orientation region was prior to that at{111}〈110〉 orientation region.hese subgrains with{111}〈112〉 orientation became recrvstallization nuclei during their growth at expending the surrounding matrix which was sluggish in recovery process.The development of recrystallization textures may be suggested as a process of “nucleation in-situ-selective growth”.The formation of(111)textures in low carbon steel sheets has been discussed in the light of this suggestion.

Dislocation Behaviour near the Crack Tip in Bulk Fe-3% Si Single Crystal

An investigation has been made of the disloca- tion distribution and dislocation free zone near the crack tip in bulk Fe-3% Si single crystal during deformation in SEM.It has been found that a number of dislocations were emitted from the crack tip during deformation.After that,the dislocations moved rapidly away from the crack tip,which indi- cated that they were strongly repelled by the stress field at the crack tip.Between the crack tip and the plastic zone there is a region of dislocation-free, which is referred to as dislocation-free zone (DFZ). The length of DFZs is roughly estimated 100 μm which is much longer than that found in thin foil specimen.The variation of dislocation density as a function of the distance from the crack tip was measured,which showed that the dislocations are inversely piled up in the plastic zone.The length of DFZs increased with both the length of pre-crack and the amplitude of applied stress.

Crystallization of Fe_(78)Si_9B_(13) Bulk Crystaline/ Amorphous(c/a) Composite

A metallic crystalline/amorphous （c/a） bulk composite was prepared by the slow cooling method after remelting the amorphous Fe78Si9B13 ribbon. By X-ray diffraction （XRD）, differential scanning calorimetry （DSC） and scanning electron microscope （SEM）, the composite consists of the primary dendrite α-Ee （without Si） as well as the amorphous matrix. After being anneal at 800 K, the uniform spheroid particles are formed in the c/a composite, which does not form in the amorphous ribbon under the various annealing process. Energy dispersive analysis of X-rays （EDAX）, SEM and XRD were applied to give more detailed information. The formation and evolution of the particle may stimulate the possible application of the Fe-matrix amorphous alloy.

Determination of the Nucleation Region Location of Si Nano-Crystal Grains Prepared by Pulsed Laser Ablation through Changing Position of Substrates

To determine the nucleation region location of Si nano-crystal grains, pulsed laser ablation of Si target is performed in Ar gas of 10 Pa at room temperature with laser fluence of 4 J/cm2, the substrates are located horizontal under ablation spot with different vertical distance. Characteristics of deposited grains are described by scanning electron microscopy, Raman scattering and X-ray diffraction spectra, the results indicate that deposition position on substrates in a certain range is relative to target surface, which changes according to different vertical distance of substrates to ablation spot. Grain size increased?at first and then decreased with addition of lateral distances to target in the range, but the integral distribution rule was independent of position of substrates. Combining with hydrodynamics model, nucleation division model, thermokinetic equation and flat parabolic motion, spatial nucleation region location of grains is obtained through numerical calculations, which is 2.7 mm-43.2 mm to target surface along the plume axis.

Crystallization of amorphous silicon beyond the crystallized polycrystalline silicon region induced by metal nickel

Crystallization of amorphous silicon（a-Si） which starts from the middle of the a-Si region separating two adjacent metal-induced crystallization（MIC） polycrystalline silicon（poly-Si） regions is observed. The crystallization is found to be related to the distance between the neighboring nickel-introducing MIC windows. Trace nickel that diffuses from the MIC window into the a-Si matrix during the MIC heat-treatment is experimentally discovered, which is responsible for the crystallization of the a-Si beyond the MIC front. A minimum diffusion coefficient of 1.84×10^-9cm^2/s at 550℃ is estimated for the trace nickel diffusion in a-Si.

FORMABILITY AND CRYSTAL TYPES OF RARE EARTH-SILICON CONTAINING TERNARY COMPOUNDS

By pattern recognition chemical bond parameter method, the formability of NaZn13 type and BaCd11 type ternary compounds in RE-M Si （RE=La-Lu, M is any metallic element） systems has been investigated. And the existence of unknown ternary compounds is predicted by the pattern recognition method.

Study on Optical Activities of A3BGa3Si2O14 Crystals

Four crystals with the general formula of A3BGa3Si2O14 （A = Ca^2＋, Sr^2＋; B=Nb^5＋ , Ta^5＋） grown by using the Czoehralsky technique were reported. They are all uniaxial and belong to 32 point group. Their transmission, rotatory angle and specific rotation dispersion were investigated by speetrophotometer and compared with LGS. The transmission spectra show that they are transparent in the visible wavelength region beyond 294 nm and infrared region, and their transmission are all larger than that of LGS.The transmission spectra between parallel polasizers show that they have large optical activities which are larger than that of LGS. Of the four crystals, Sr3NbGa3Si2O14 has the largest optical activity ： 240.75 （°）·mm^-1 at 0.30 μm wavelength, 34.73 （°） ·mm^-1 at 0. 633 μm wavelength. The Bohzmann＇s coefficients of these crystals were calculated, which were in good agreement with earlier measurement in other reference.

STUDIES OF OXYGEN ADSORPTION AND INITIAL OXIDATION ON SINGLE CRYSTAL Mn_5Si_3(111) SURFACE

Kinetics of oxygen adsorption on single crystal Mn5Si3 （111） surface and initial surface oxidation were investigated. Oxygen chemisorbs dissociatively at room temperature on Mn and Si atoms. A fast oxidation of Si atoms occurs followed by oxidation of Mn atoms at RT. The MnO2 was reduced by Si atoms and the SiO was oxidized further to SiO2 during the sample heating.

CRYSTALLIZATION AND HARDNESS CHANGE OF RAPIDLY SOLIDIFIED Fe-C-Si-Mo ALLOYS

Crystallization behavior of rapidly solidified Fe-C-Si-Mo alloy ribbons made by single rol- ler method together with their changes in phase and hardness have been studied by X-ray diffraction and SEM.The results show that the alloys attribute their very high Vickers hardness to numerous fine carbides formed during crystallization.

Investigation of Photonic Band Gap in Si-Based One-Dimensional Photonic Crystal

A one-dimensional silicon based photonic crystal with nonlinear defect layers is examined. The linear and nonlinear optical properties are analyzed. The transmission spectrum was obtained by applying the optical transfer matrix formalism to the photonic crystal. The various transmittance peaks obtained with the defect layers are investigated. The nature of the transmittance peak is analyzed with the number of defect layers.

Solution-based metal induced crystallization of a-Si

This paper investigates a simplified metal induced crystallization （MIC） of a-Si, named solution-based MIC （SMIC）. The nickel inducing source was formed on a-Si from salt solution dissolved in de-ionized water or ethanol, a-Si thin film was deposited with low pressure chemical vapour deposition or plasma enhanced chemical vapour deposition as precursor material for MIC. It finds that the content of nickel source formed on a-Si can be controlled by solution concentration and dipping time. The dependence of crystallization rate of a-Si on annealing time illustrated that the linear density of nickel source was another critical factor that affects the crystallization of a-Si, besides the diffusion of nickel disilicide. The highest electron Hall mobility of thus prepared S-MIC poly-Si is 45.6 cm^2/（V· s）. By using this S-MIC poly-Si, thin film transistors and display scan drivers were made, and their characteristics are presented.

Crystallization Behaviour of Laser Synthesized Nanometric Amorphous Si_3N_4 Powders

The crystallization behaviour of the laser synthesized nanometric amorphous Si3N4 powders with the particle size of 15 nm in diameter has been studied between 1200° and 1700℃ by XRD,TEM and FTIR techniques. A small amount of β-Si3N4 formed at 1250℃ and increased slowly until the α- β transformation happened at 1700℃, whereas α-Si3N4 appeared at 1300℃ andincreased rapidly between 1500-1600℃. The formation of β phase at the lower temperature was caused by the nitridation of free Si due to the preexisted β-nuclei in the Si3N4 particles, whereasthe α phase was formed by solid crystallization from the amorphous matrix. There were α and β SiC formed at 1700℃ due to the presence of Sio and Co gases in the system. FTIR analysis shows that two new IR absorption at 1356 and 1420 cm-1, and an overall strong absorption in wide wavenumber range resulted from the powders annealed at 1600 and 1700℃ respectively