涂覆法观测KH2PO4晶体Z切片薄表面层形成和生长特性

提出一种实验研究薄表面层形成和生长的涂覆法。利用该方法,以KH_2PO_4(KDP)晶体Z切片为载体,探究晶体的某些部位,比如(001)面、棱边、柱面在薄表面层形成以及生长过程中所起的作用。结果表明,当Z切片的(001)面上的棱边被覆盖,会首先以小晶锥的形式在(001)面形成新棱边,然后自新棱边沿(101)面切线方向出现薄表面层生长;当整个(001)面被覆盖,柱面生长一定时间并形成新棱边,之后也会出现薄表面层生长;当(001)面被涂覆分割,各分割部分能在各自的新棱边形成后以薄表面层方式形成独立的锥体,而在锥体间的棱边恢复后,独立锥体相应锥面能实现连接。可见,棱边是薄表面层形成的先决条件。对各种涂覆处理的Z切片通过光学显微镜实时观测,发现棱边在薄表面层形成中起关键作用,而柱面能提供台阶,在薄表面层生长中起重要作用;同时,得到了不同涂覆处理方式下薄表面层切向生长速度和动力学系数。     

非完整形态KH2PO4晶体薄表面层生长特性

实时观察了非完整形态的KH_2PO_4(KDP)晶体在过饱和溶液中以薄表面层生长形式恢复其结晶学形态的过程。提出了晶体形态恢复的"最小多面体原理",即:在自由生长系统中,对于非完整形态的KDP晶体,当其以薄表面层形式恢复其结晶学完整形态时,薄表面层将选择相应的奇异面方向生长,使晶体形态最终恢复为一个由各结晶学显露面所围成的体积最小的凸多面体。利用PBC理论分析了生长基元在非结晶学显露面上的附着情况并阐述了锥顶处薄表面层倒垂生长的原因。结果表明,薄表面层形成与晶体非完整结晶学形态及不均匀水动力学条件相关联。柱面凹角与非正常棱边及Z切片正常棱角均可诱发产生薄表面层,且薄表面层生长终止于其所在奇异面的正常结晶学晶棱。     

非完整形态KH2PO4晶体薄表面层生长特性

实时观察了非完整形态的KH2PO4 (KDP)晶体在过饱和溶液中以薄表面层生长形式恢复其结晶学形态的过程.提出了晶体形态恢复的“最小多面体原理”,即:在自由生长系统中,对于非完整形态的KDP晶体,当其以薄表面层形式恢复其结晶学完整形态时,薄表面层将选择相应的奇异面方向生长,使晶体形态最终恢复为一个由各结晶学显露面所围成的体积最小的凸多面体.利用PBC理论分析了生长基元在非结晶学显露面上的附着情况并阐述了锥顶处薄表面层倒垂生长的原因.结果表明,薄表面层形成与晶体非完整结晶学形态及不均匀水动力学条件相关联.柱面凹角与非正常棱边及Z切片正常棱角均可诱发产生薄表面层,且薄表面层生长终止于其所在奇异面的正常结晶学晶棱.     

棱角对NH4H2PO4晶体Z切片薄表面层生长影响的研究

本研究制备了具有不同形式棱角的NH₄H₂PO₄(ADP)晶体Z切片样品。通过实验, 观察不同Z切片薄表面层形成及生长特性, 并计算了不同棱角情况下薄表面层的切向生长速度V及其动力学系数β。结果表明, 正常棱角的缺失, 影响Z切片对其原有形态的“判断”, 进而影响薄表面层的形成及生长; 薄表面层在正常棱角处相遇形成相交角后, 将主要在相交角处形成并向棱边扩展生长, 表明棱角可能为薄表面层的主要生长源。此外, 计算结果显示, 正常棱角处薄表面层切向生长的平均生长动力学系数β_n为131.8 μm/s, 远大于棱角缺失后薄表面层切向生长的平均生长动力学系数β_a=11.6 μm/s, 即正常棱角缺失后, 薄表面层的切向生长速度将大大降低。     

流动对ZTS晶体(100)面台阶生长动力学影响的研究

通过利用光学显微镜对ZTS晶体(100)面的台阶推移过程进行实时观察,对不同溶液供应速度及不同过饱和度下的台阶生长动力学进行了研究。结果表明,随着溶液供应速度S的增大,台阶平均推移速率先增大后减小。溶液供应速度S≈1.2mL/min时,台阶平均推移速率达到最大。而在静止的生长溶液中,台阶平均推移速率随着过饱和度σ的增大呈非线性增大,同时确定了生长死区σd和台阶平均推移速率急剧增大时的临界过饱和度值σ*,并计算了不同过饱和度阶段的台阶动力学系数和台阶活化能。     

硫脲硫酸锌晶体（100）面台阶生长动力学实时研究

运用光学显微镜实时观测了硫脲硫酸锌晶体（100）面台阶推移过程。获得了不同过饱和度、不同台阶高度、不同生长时间、不同台阶边缘扭折密度下的台阶推移速率;应用＂净流量＂模型解释了不同台阶推移速率的差异与过饱和度之间的依赖关系,计算了生长单元与台阶融合活化能及单台阶的动力学系数。通过分析发现台阶推移速率随过饱和度增加而线性增加,随台阶高度增加而下降;同一台阶推移速率随时间变化的现象与台阶重组过程有关;而台阶边缘扭折密度则从根本上决定了台阶推移速率的大小和变化趋势。     

喷流转晶法KDP晶体生长系统的流动与传质模拟

提出了一种通过锥顶喷流改善KDP锥面过饱和度的晶体生长方法。采用有限体积法和滑移网格技术,对传统转晶法及喷流转晶法的KDP晶体生长过程进行了数值模拟。展示了两种生长方式下晶体表面过饱和度时均分布云图及均方差,分析了不同转速、不同喷流速度、不同晶体尺寸对晶面时均过饱和度及均方差的影响。结果表明:相比于传统转晶法,喷流转晶法晶体的锥面过饱和度提高且表面均匀性增加。提高喷流速度可以进一步提高锥面过饱和度,但其均方差却呈现先减小后增大的变化。旋转速度的增加能提高锥面过饱和度并减小其均方差。此外,晶体尺寸也会在一定程度上影响喷流的效果。     

pH值对ADP晶体(100)面生长的影响

通过对40℃、不同pH值和过饱和度下ADP晶体(100)面法向生长速度的研究,发现在同一过饱和度下,改变pH值后晶面的生长速度明显加快。实验数据显示,在过饱和度较低时,(100)面的生长以螺旋位错生长机制为主;过饱和度较高时,以二维成核生长机制为主,而且pH值的改变会促使ADP晶体在较低的过饱和度下就从位错生长机制向二维成核生长机制转变。利用实验数据计算出了不同pH值下、二维成核生长机制控制晶体生长时的台阶棱边能。最后,运用原子力显微镜(AFM)非实时观察了不同过饱和度、不同pH值下生长的ADP晶体(100)面的微观形貌,发现与正常pH值相比,在较低的过饱和度下,pH=2.5和5.0的晶面上就出现了二维核。     

ZTS晶体(100)面台阶聚并现象的AFM非实时研究

通过对301 K时,不同过饱和度以及掺杂2.5%(摩尔分数)尿素(σ=0.09)条件下生长的ZTS晶体进行AFM非实时扫描,对其(100)面的基本台阶以及聚并形成宏观台阶的形貌情况进行了研究。发现ZTS晶体(100)面在低过饱和度下(σ=0.03),以基本台阶推移为主,台阶高度约为0.553nm,近似为晶格参数a值的一半;在高过饱和度下(σ=0.09),以台阶聚并后的宏观台阶推移为主。而在同样的过饱和度下掺入尿素则会加剧台阶聚并的程度,该实验结果很好地符合了杂质诱导产生非对称台阶动力学系数理论模型。     

爆破作用下岩体顺倾软弱夹层的变形规律研究

当炮孔穿过含顺倾软弱夹层边坡时,爆炸冲击波与爆生气体不可避免地对软弱夹层产生推移、使其变形.利用ANSYS/LS-DYNA建立含软弱夹层的顺倾岩质边坡台阶爆破的有限元模型,分析了抵抗线、夹层初始厚度、夹层倾角这3个主要因素条件下,爆破作用下岩体顺倾软弱夹层的变形规律:1)随着抵抗线的增加,爆腔范围也越来越大,其厚度也随之越变越厚;2)夹层初始厚度越薄,爆破后夹层厚度增加率越大,同时也越容易被推移;3)随着夹层倾角的增加,夹层厚度峰值也随着增加,但其最终夹层厚度随夹层倾角的增加而减小.     

Helical anisotropic magnetic film

The magnetic coupling between the magnetization in two nonmagnetostrictive Ni-Fe layers separated by a SiO layer has been investigated by means of a transverse susceptibility measurement. The main results are that 1) the coupling energy Ec per Unit area of the multilayered film has a form ofE_{c}= -A cos (phi_{1}-phi_{2}), wherephi_{1}-phi_{2}is the angle between the magnetization vectors in the two Ni-Fe layers, and 2) the dependence of the coupling constant on the thickness b of the intermediate SiO layer can be interpreted quantitatively by the combination of the coupling energy due to Néel's topography model and that due to the magnetostatic interaction between the magnetic free poles appearing at the edges of the two Ni-Fe layers. The former coupling energy is given byE_{c1} = -frac{p}{2sqrt{2}}omega^{2}M^{2} exp(-sqrt{2}pb) cos (phi_{1}-phi_{2})wherep=2pi/LandLandware the wavelength and the amplitude of the undulation of the interface between Ni-Fe and SiO layers, respectively. The latter is given byE_{c2} = frac{2M^{2}D^{2}}{R} ln (frac{R}{D+b}) cos (phi_{1}-phi_{2})whereDis the thickness of each Ni-Fe layer, andRis the radius of the film.     

Stimulation of capillarity-driven grain boundary migration during sliding

Zinc bicrystals with originally flat 89° symmetric tilt boundary tilted at ∼45° to the tensile direction were strained at high temperature. The operation of crystallographic slip in both grains was suppressed by orientation of basal planes parallel and perpendicular to the tensile axis. The boundary migrated under the action of curvature driving force making its inclination angle close to 70° with respect to the lateral free surface. In the case of annealing with no load applied, a small boundary migration was observed at the edges of the sample. Initiation of grain-boundary sliding significantly increases the amount of boundary migration. It has been established that sliding can increase the reduced boundary mobility by more than an order of magnitude. Askar D. Mirzakhojaev—on leave from FSU-NHMFL, Tallahassee, FL 32310, USA.     

外应力场下NiAl合金微裂纹动态扩展的分子动力学模拟

目的 对NiAl合金中不同晶体取向的裂纹扩展动力学行为进行原子尺度研究,明晰在塑性变形过程     

TiO2和O-Al2O3晶体的生长习性

通过水热法制备粉体的实验观察到金红石、锐钛矿和α-Al2O3晶体的生长习性．采用配位多面体生长习性法则合理地解释了Ti O2和α-Al2O3的生长习性．其主要结果为α-Al2O3晶体的生长习性为平板{0001}，其各晶面的生长速度为：V｛0001 }＜V｛1123}；锐钛矿的生长习性为四面体，其各晶面的生长速度为V<010>=V<001>>V<010>>V<111>．而PBC理论很难合理地解释α-Al2 O3晶体的生长习性．     

Nano-Design für Makroschichten

Nano design for macroscopic coatings – new application potentials by PVD coatings up to 100 μm thickness Non-homogeneous coatings still limit the application of thicker layers due to defect growth and irregular layer thickness distribution along the surface of complex shaped components. Therefore, the layer thickness is usually limited to about 10 μm. In order to limit the surface roughness by the growing layer, multilayer coating systems are deposited by highly ionized plasmas. This allows significantly smoother layers to be produced, which until now could only be produced by mechanical finishing. Furthermore, by combining selected material systems and targeted parameter selection, structures can be deposited during coating, especially on edges, which result in a reduction of the cutting edge radius. In future, edge geometries should therefore be able to be specifically adjusted through the coating process.     

Transport Properties of the Tunnel Junctions Al1-xCox/{Al1-xCox-oxide}/Al

The oxides of Al1-xCox (x=0,0.25,0.5,0.75, and 1.0) alloys were chosen as barrier materials in this work. The tunnel junction consists of the bottom electrode Al1-xCox and the top electrode Al with an insulating layer { Al1-xCox-oxide} which was formed by natural oxidation in a baking-box at 333K. The oxidation time for forming an Al1-xCox-oxide layer on the surface of the bottom Al1-xCox layers were optimized.The resistance of Al1-xCox/{ Al1-xCox-oxide}/Al tunnel junctions varied between 101 and 106 Ω measured at 1 my and 4.2 K. The effective barrier height and width of insulating layers Al1-xCox-oxide ( x=0.25, 0.5, and 0.75 )varied between 0.6 and 2.7 eV and between 1.3 and 2.1 nm. It is shown that the thin oxide layer of Al1-xCox alloys can be chosen as barrier materials.     

Microstructure formation in electrochemically deposited Copper thin films

The influence of the electrochemical potential and deposition mode on the preferred orientation, morphology and microstructure of crystallites in electrochemically deposited (ECD) copper thin films was investigated using X‐ray diffraction (XRD), scanning electron microscopy (SEM) and the diffraction of back‐scattered electrons (EBSD). As a working electrode for the ECD process, thin gold layers were employed that were deposited on floating‐glass substrates in a vacuum evaporation process. With increasing negative electrochemical potential in the ECD process, the deposition mode changed from the charge transfer controlled one to the diffusion controlled one. At the highest electrochemical potentials, the copper deposition and the hydrogen release were running concurrently. The change of the deposition mode was accompanied by a change of the surface roughness of the thin films and by a change of the direction and degree of the preferred orientation of crystallites. The surface roughness of the deposited copper thin films increased with increasing electrochemical potential. Compact plate‐like crystallites with the preferred orientation {111} grew in the transport controlled deposition mode. Development of the {111} texture was supported by the {111} preferred orientation of the gold layers and by surface energy of copper, which is the lowest in the (111) plane. The diffusion controlled deposition mode was characterized by the growth of globular {110}‐oriented crystallites. The {110} texture resulted from the minimization of the anisotropic strain energy of copper via reduction of the structure defects in this deposition modus. For highest electrochemical potentials, the copper deposition run simultaneously with the development of hydrogen that resulted in growth of needle‐like crystallites with the {100} texture.