聚甲基丙烯酸甲酯光子晶体的生长和结构分析

金属/半导体基光子晶体有重大的国防应用价值,其生长技术的核心是设计合适的方法将聚甲基丙烯酯甲酯(PMMA)微球组装成光子晶体。在目前垂直沉积法的基础上,通过控制甲基丙烯酸甲酯(MMA)和偶氮引发剂的反应,使用等温蒸发工艺开发了光子晶体的可控垂直沉积(CVD)技术。实验合成了高度单分散的PMMA微球,并将PMMA微球组装成了光子晶体;对试样进行扫描电镜研究发现,晶体内部排列有序度很高,表面层很完美平整,在3μm×5μm的有序区内仅有两个点缺陷;使用直径分别为294nm和345nm的PMMA微球,沉积出具有规则的周期性密堆积结构的光子晶体,试样的完美有序区范围在20μm以上。实验发现,在可控垂直沉积法的晶体生长过程中,光子晶体的生长方式为连续生长,生长界面为粗造界面。     

Observations of defect propagation in [100]-oriented opal-type photonic crystals

Charged colloidal suspensions have been used as experimental models for the study of crystal nucleation. Here we propose that the technique of template-assisted colloidal self-assembly can be used to visualize the effects of defect propagation in atomic crystal films produced using epitaxial growth. Templates with periodic line defects were used to grow [100]-oriented three-dimensional photonic crystals by means of the template-assisted colloidal self-assembly method, aided by capillary and gravitational forces. The defect propagation in the [100]-oriented photonic crystal was observed using scanning electron microscopy, both at the surface of the crystal and on cleaved facets. This method is useful in the understanding of defect propagation in the growth of colloidal films on templates - and the same approach may also prove useful for the understanding of atomic crystal growth on substrates with defects. Additionally, the deliberate incorporation of line defects may prove valuable as a way of introducing waveguide channels into three-dimensional photonic crystals.     

FEM simulations and experimental studies of the temperature field in a large diamond crystal growth cell

We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method (TGM) at high pressure and high temperature (HPHT). We employ both the finite element method (FEM) and in situ experiments. Simulation results show that the temperature in the center area of the growth cell continues to decrease during the process of large diamond crystal growth. These results are in good agreement with our experimental data, which demonstrates that the finite element model can successfully predict the temperature field variations in the growth cell. The FEM simulation will be useful to grow larger high-quality diamond crystal by using the TGM. Furthermore, this method will be helpful in designing better cells and improving the growth process of gem-quality diamond crystal.     

温度对Ib型和IIa型金刚石大单晶(100)表面特征的影响

本文在5.6 GPa, 1250–1340 ℃的条件下, 利用温度梯度法, 以FeNiMnCo 合金为触媒, 沿籽晶的(100)晶面成功合成了不同晶形的优质Ib型和IIa型金刚石大单晶. 利用激光拉曼附件显微镜, 分别对上述不同温度下合成的两类金刚石样品上表面(100)面的中心区域及棱角区域进行观察分析. 研究发现, Ib型和IIa型金刚石大单晶(100)晶面上从中心到棱角处黑色纹路的分布逐渐变黑变密集; 另外, 随着金刚石合成温度的升高, Ib型金刚石大单晶(100)面上黑色纹路由稀疏逐渐变稠密, 而IIa型金刚石大单晶的黑色纹路较为稀疏; Ib型金刚石大单晶的形貌特征表现为从低温晶体的不规则分布过渡到中温、高温晶体的典型树枝状分布. IIa型金刚石大单晶(100)面特征随温度变化规律与Ib型的类似. 这两类金刚石大单晶表面特征的差异可能是由于IIa 型金刚石具有比Ib型更小的生长速度和更少的氮含量. 最后, 对两类塔状金刚石大单晶进行拉曼光谱测试分析, 结果表明IIa型金刚石大单晶的品质较Ib型金刚石大单晶好.     

A phase-field/Monte-Carlo model describing organic crystal growth from solution

In this paper work we present a phase-field/Monte-Carlo hybrid algorithm for the simulation of solutal growth of organic crystals. The algorithm is subsequently used for an investigation of diffusion effects on the growth mechanisms. This method combines a two-scale phase-field model of the liquid phase epitaxial growth and a Monte-Carlo algorithm of the 2D nucleation and thus is faster than previous purely Monte Carlo simulations of crystal growth. The inclusion of supersaturation and diffusion in the method allows the study of crystal growth under various growth conditions. Parameters used in the hybrid algorithm are bound to the energetic parameters of crystal faces, which can be estimated from a detailed study of the actual crystal structure based on a connected nets analysis, which allows the prediction of the shape and morphology of real crystals. The study of the diffusion effect is carried out based on an example of a hydroquinone crystal, which grows from the water solution at various supersaturations. The dependencies of the growth rate and the nucleation rate on the supersaturation indicate the change of the growth mechanism from spiral growth to 2D nucleation. The difference in the growth rate for various faces is in agreement with the crystal morphologies derived from the attachment energy method and observed experimentally. The main result of the simulation is the evaluation of engineering limits for choosing appropriate external process conditions.     

新概念晶体提拉方法及其可能的应用简介

介绍了一种利用金属材料的热膨胀而产生的位移代替传统的机械电机提拉晶体的新方法,可以预见这种新型提拉方法既可以消除晶体提拉过程中由于拉速的不平滑而引进的晶体生长条纹,同时也可以作为研究晶体生长机理的有力工具,另一方面,该方法可以用来提拉这样的一灰晶体,这种晶体溶质的浓度周期地分布于其中,且其周期远小于用机械电机所提拉的晶体溶质浓度的周期,同时,另一种新颖的控温方式被首次提出,即先把金属棒加热膨胀至一定的长度再冷却使之收缩,由于这种控温方式温度波动极端微小,使得金属棒收缩所产生的位移随时间的变化率达到微观的平滑极限。     

籽晶尺寸对宝石级金刚石单晶生长的影响

本文在国产六面顶压机上,在5.6 GPa, 1250—1450℃的高压高温条件下,分别选用边长0.8, 1.5和2.2 mm三种尺寸的籽晶,系统开展了Ib型宝石级金刚石单晶的生长研究.文中系统考察了籽晶尺寸对宝石级金刚石单晶生长的影响.首先,考察了籽晶尺寸变化对宝石级金刚石单晶裂晶问题带来的影响.研究得到了籽晶尺寸变大,裂晶出现概率增加的晶体生长规律.其次,在25 h的生长时间内,考察了上述三种尺寸籽晶生长金刚石单晶时,生长时间与单晶极限生长速度的关系.得到了选用大尺寸籽晶,可以提高优质单晶合成效率、降低合成成本的研究结论.借助扫描电子显微镜和光学显微镜,对三种尺寸籽晶生长金刚石单晶的表面形貌进行了标定.最后,傅里叶微区红外测试,对三种尺寸籽晶生长宝石级金刚石单晶的N杂质含量进行了表征.研究得到了选用大尺寸籽晶实现快速生长金刚石的同时,晶体的N杂质含量会随之升高的晶体生长规律.     

Synthesis, crystal growth and characterization of a metal-organic nonlinear optical tri-allylthiourea mercury chloride single crystals

Metal-organic nonlinear optical material tri-allylthiourea mercury chloride single crystal was grown using low temperature solution growth method. The growth parameters such as pH and temperature were optimized for getting colorless single crystals. The X-ray rocking curve measurement shows that the grown crystal was free from internal structural grain boundaries. The structural, spectral, optical and thermal properties of the grown specimen were studied using various characterization techniques. The defects present in the grown crystals were studied with chemical etching analysis. The results show that the grown crystals are suitable candidates for nonlinear optical applications.     

Preparation and characterization of Y1−xPrxBa2Cu3O7−δ single crystals

We present a reliable method for growing single crystals of Y_1−xPr_xBa₂Cu₃O_7−δ high-T_c superconductors in ZrO₂ crucibles. This method results in crystals with greatly improved superconducting properties compared to crystals grown with the previously reported methods which use Al₂O₃ crucibles. We describe techniques for crystal growth in both Al₂O₃ and ZrO₂ crucibles using an excess of BaCo₃ and CuO as the flux. The crystals were characterized by means of DC magnetic-susceptibility measurements, electrical-resistivity measurements, and electron microprobe analysis. The effects of Al contamination on the conditions for crystal growth and on the superconducting properties of the crystals are found to be quite significant.     

氘化对KH2PO4晶体微观缺陷影响的正电子湮没研究

采用传统降温法从不同程度氘化(x=0, 0.51, 0.85)的生长溶液中生长氘化KH₂PO₄(KDP) 晶体, 利用正电子湮没技术(正电子寿命谱和多普勒展宽谱)、结合X射线衍射谱(XRD) 结构分析, 对KDP晶体氘化生长的微观缺陷进行了研究, 讨论了氘化程度对晶体内部微观结构特性、缺陷类型和浓度的影响. XRD结果显示晶胞参数a, b值随氘含量的增加而增加, c值无明显变化; 正电子寿命谱结果发现随着氘化浓度的提高, KDP晶体内部中性填隙缺陷以及氧缺陷不断增加, 引起晶体晶格畸变; 氢空位、K空位、杂质替位缺陷不断发生缔合反应形成复合缺陷, 缺陷浓度不断减少; 团簇、微空洞等大尺寸缺陷也在不断发生聚合反应, 缺陷浓度表现为不断减少. 多普勒实验结果表明随着氘化程度的提升, 晶体内部各类缺陷表现为同步变化. 实验结果表明, KDP晶体在低浓度氘化生长(50%以内)下缺陷反应较弱, 而在高浓度氘化(50%以上)下的缺陷反应显著增强.     

Non-steady state solidification of the Nd-123 superconducting oxides

Crystal growth of the melt-textured bulk Nd_1+xBa_2−xCu₃O_6+d (Nd123) superconducting oxides was investigated by employing isothermal undercooling solidification with hot-seeding in air. From the relationship between growth length and holding time, the Nd123 crystal was found to have almost stopped growing after a certain growth period, while the growth length increased proportionally to the holding time at an early stage of the crystal growth. As a result of quantitative analysis for the Nd123 crystal of which solidification was terminated, the distribution of the Nd/Ba substitution was observed to decrease in the Nd123 single crystal matrix from the seed crystal to the edge of the Nd123 crystals. Also, the substitution content at the edge of the Nd123 crystal, which corresponds to that at the final stage of the crystal growth, was found to be in good agreement with the minimum substitution of the Nd123 solid solution phase in the equilibrium phase diagram at this process temperature. These compositional changes could be explained using the equilibrium phase diagram as associated with the solid solution formation, which is responsible for the non-steady state solidification of the Nd123 crystals even for the isothermal undercooling processing.     

Nucleation studies and characterization of potassium thiocyanate added KDP crystals grown by seed rotation technique

The effect of the addition of potassium thiocyanate on potassium dihydrogen phosphate (KDP) crystals, grown from aqueous solution by the temperature lowering method using a microcontroller based seed rotation technique has been studied. As part of nucleation studies, metastable zone width, induction period and crystal growth rate of additive added KDP are determined and analyzed with the pure system. Dielectric measurements were carried out on pure and doped crystals at various temperatures ranging from 313 to 423 K and compared. The crystalline perfection of the grown crystal was studied by the high resolution X-ray diffraction analysis. The crystal grown from additive added solution was subjected to structural, optical transmission, second harmonic generation and hardness studies and the effect of additive on pure system is investigated.     

Studies on growth and characterization of l-alanine strontium chloride trihydrate single crystals for optical applications

The optically transparent nonlinear optical single crystals of l-alanine strontium chloride trihydrate (LASCT) were grown by slow evaporation solution growth method using water as solvent. The purity of the crystals was increased by the method of recrystallization. The grown crystals were analyzed by the single crystal X-ray diffraction pattern which proved that LASCT belongs to monoclinic crystal system. The presence of various functional groups and modes of vibrations were identified by FTIR spectroscopy. The optical absorption study confirms the suitability of the crystal for device applications. The thermal strength and the decomposition of the grown crystals were studied using TG/DTA analyses. The dielectric constant and dielectric loss measurements of the grown crystals at different frequencies of the applied field were measured and reported. The mechanical strength of the crystal is estimated by Vicker's hardness test. The nonlinear optical properties of the grown crystals were confirmed by second harmonic generation test which shows the suitability of NLO applications.     

Imaging of growth banding of minerals using 2-stage sectioning: application to accessory zircon

In the past, investigations of mineral growth were routinely carried out by the application of light-microscopic methods and, later on, by the production of single crystal sections and their documentation using specific imaging techniques (CL, BSEI, etc.). In the present work, a method is described which enables the precise sectioning of elongate crystals parallel and perpendicular to their longest axis. By examining backscattered electron images of parallel and perpendicular sections of the same grain, growth of all faces may be evaluated without major geometric correction. The new technique is applied to zircon crystals of a granitoid exposed in the southwestern Bohemian Batholith, Austria. For the studied zircon population, pyramidal and prism development during crystal growth is worked out very clearly by the imaging procedure. Besides its significance in crystal studies, the introduced method could also find a use in material science for the growth study of synthetic mineral phases.     

光子晶体中基于有效折射率接近零的光束准直出射

利用平面波展开法(PWM)和时域有限差分法(FDTD)研究了二维正方格子光子晶体靠近禁带边沿附近频率光波的传输特性.研究发现,若有效折射率接近于零,可出现光束从晶体表面准直出射的现象,且光束的出射方向只与晶体表面的取向有关,而与晶格取向无关.这种现象与自准直现象有很大不同.     

Fabrication and growth rate estimation of PrBa2Cu3O7−δ single crystal by the modified top seeded crystal pulling method

Recently, we succeeded in fabricating single crystals of PrBa₂Cu₃O_7−δ by a modified top seeded crystal pulling method called the SRL-CP (Solute Rich Liquid-Crystal Pulling) method. Y₂O₃ and MgO polycrystalline crucibles and a MgO single crystal crucible were used to grow the single crystals. The crystal growth temperature was set in the range of 968°C to 972°C. The grown crystals were identified as PrBa₂Cu₃O_7−δ by X-ray diffraction. In the case of using Y₂O₃ crucibles the composition of the grown crystals was Y_xPr_1−xBa₂Cu₃O_7−δ (0.48 < x < 0.57) and in the case of using MgO crucibles a relatively small amount of Mg contamination to the grown crystals occurred at a typical concentration of approximately 1 at.% of the sum of cations. According to the crystal growth model of the SRL-CP method [1–5], a maximum growth rate of 1.7 × 10⁻⁵ cm/s was calculated with the aid of the phase diagram studies we reported earlier [6]. This value is reasonably in agreement with the experimental results.     

光子晶体表面结构的改变对成像的影响

负折射率材料因为其奇异的特性成为广泛研究的对象,尤其是光子晶体平板的完美成像.硅材料以其良好的物理性质成为当今集成光学领域中应用最广的材料之一.本文以硅介质柱在空气中周期性排列构成六角结构的光子晶体平板为例,运用平面波展开法进行光子晶体能带计算并运用时域有限差分法模拟改变光子晶体平板成像并讨论表面结构对成像的影响.光子晶体平板等效折射率为-1时,通过改变上下侧最外层介质柱的半径或是侧向移动最外层介质柱发现:当光子晶体平板表面结构发生改变时光子晶体平板仍能成像但像点强度发生变化.当光子晶体平板表面结构的改变在一定范围时,所成像的位置发生改变且位置变化符合光子晶体成像经典的Veselago关系;当光子晶体表面结构的变化超过该范围时,所成像与物的相位发生反相同时像点位置发生"巨变",此时Veselago关系已不成立.数值模拟表明:光子晶体平板表面结构的改变可以有效地改变该光子晶体平板所成像的强度、位置和相位.     

Epitaxy: the motion picture

The engineering of many modern electronic devices demands control over a crystal down to the thickness of a single layer of atoms—and future demands will be even more challenging. Such control is achieved by the method of crystal growth known as epitaxy, and that makes this method the subject of intense study. More than that, recent advances are revolutionizing our knowledge of how surfaces grow. In fact, growing surfaces show a beautifully rich variety of phenomena, many of which are only now beginning to be uncovered. In the past few years many surface imaging techniques have been used to give us a close look at how crystals grow—while they are growing. The purpose of this article will be to illustrate some of the ways real surfaces grow and change as revealed by some of the latest in situ microscopic imaging technologies.

It is often said that crystal growth is more of an art than a science. Here we will show that it is emphatically both.     

不同方法DKDP晶体生长和损伤阈值

生长方法是影响DKDP晶体生长和光损伤阈值的一个重要因素。分别采用传统降温法和点籽晶快速生长法,利用同种原料从氘化程度为85%的溶液生长了DKDP晶体,并选取部分Ⅱ类3倍频晶片进行3倍频光损伤阈值和透过性能测试。实验表明,不同生长方法对DKDP晶体的损伤阈值以及DKDP晶体的生长速度的影响效果正好相反,即由于生长溶液过饱和度的差别,点籽晶快速生长法晶体生长速度为传统方法的10倍,但晶体损伤阈值下降了50%,且紫外波段透过性能下降明显。     

Studies on optical,mechanical, dielectric properties of bisthiourea nickel bromide NLO single crystal

Bisthiourea nickel bromide (BTNB) single crystal has been grown by solution growth technique at room temperature. The crystal structure and lattice parameters were determined for the grown crystal by single crystal X-ray diffraction studies. Optical constants like band gap, refractive index, reflectance, extinction coefficient and electric susceptibility were determined from UV–vis-NIR spectrum. Nonlinear optical property was discussed to confirm the SHG efficiency of the grown crystal. The mechanical strength of the grown crystal was analyzed using Vickers microhardness tester. The dielectric constant and dielectric loss of bisthiourea nickel bromide are measured in the frequency range of 50 Hz to 5 MHz at different temperatures. The ac conductivity studies were carried out on bisthiourea nickel bromide crystals. In order to investigate the growth mechanism and surface features, etching studies are carried out for the crystal. Photoconductivity studies were carried out on bisthiourea nickel bromide crystals.