基于离子束抛光的KDP晶体表面嵌入铁粉清洗研究

磁流变抛光技术是实现KDP晶体超精密加工的新方法,但磁流变液中的铁粉容易嵌入质软的KDP晶体表面.本文提出了利用基于低能离子溅射原理的离子束抛光技术去除KDP表面嵌入的铁粉.利用红外拉曼光谱和白光干涉仪分别分析了低能离子束抛光前后KDP晶体表面物质结构变化和表面粗糙度的变化;结果显示,低能离子束溅射不改变KDP晶体表面的组成结构,并改善了KDP晶体表面质量,因此离子束抛光可用于KDP晶体的加工;利用飞行时间二次离子质谱分析技术分别对单点金刚石车削、磁流变抛光和低能离子束抛光后的KDP晶体表面进行元素分析,结果显示低能离子束抛光可有效去除磁流变抛光在KDP晶体表面嵌入的铁粉.     

离子束作用下KDP晶体表面粗糙度研究

为了避免传统加工过程对KDP( Potassium dihydrogen phosphate)晶体表面产生损伤、嵌入杂质等降低晶体抗激光损伤阈值的不利因素,文章探索采用离子束抛光技术实现KDP晶体的加工.本文主要分析了离子束抛光作用下KDP晶体表面粗糙度的演变过程,采用垂直入射和倾斜45°入射两种方式研究KDP晶体表面粗糙度,利用倾斜45°入射的加工方式提高了KDP晶体的表面质量,其表面均方根粗糙度值由初始的3.07 nm减小到了1.95 nm,实验结果验证了离子束抛光加工KDP晶体的可行性.     

快速生长KDP晶体表面的光学显微实时观察

设计了一套溶液降温法晶体生长显微实时观察装置,对快速生长KDP晶体{101}和{100}表面形貌的演化过程进行了实时观测分析.测量了晶体表面生长层切向生长速度随溶液过饱和度的变化曲线,并利用台阶生长动力学方程计算了相关动力学参数.进行了Fe3+掺杂实验,结果表明Fe3+的存在会影响到不同晶面上生长层的动力学系数,从而改变KDP晶体表面生长层的切向生长速度.     

纳米尺度延性域干切削KDP晶体的无粘屑研究

为了避免使用切削液及其相应清洗工艺对KDP晶体表面产生雾化、引入杂质等降低晶体抗激光损伤阈值的不利因素,采用干切削技术对KDP晶体进行超精密切削.在干切削KDP晶体工艺中所遇到的难点是切削屑片易粘附已加工表面,由此产生屑片粘附点难清洗、易雾化等问题.本文提出了基于真空抽屑装置干切削KDP晶体的新工艺,重点解决了干切削工艺下KDP晶体表面粘屑现象,实现了无需清洗、无杂质的加工表面.在选择延性域切削参数条件下,取得了表面粗糙度为2.69 nm(Ra)的无粘屑、超光滑表面.     

典型阴离子杂质对KDP晶体电导特性的影响

针对KDP晶体生长过程中常出现的SO2-4,NO-3和Cl-杂质,采用传统法和快速法掺杂生长了一系列KDP晶体,研究了不同阴离子杂质掺杂对KDP晶体X和Z向的电导率的影响.结果表明,X向的电导率比Z向电导率高;未掺杂时,快速生长的KDP晶体比传统法生长的KDP晶体具有更高的电导率; SO2-4的掺杂增大了晶体在两个方向的电导率,且随着掺杂浓度的增加,晶体的电导率也相应增大;NO-3和Cl-对KDP晶体的电导率影响不大.分析认为,快速生长的KDP晶体具有更高的缺陷浓度,从而增大了晶体的电导率;SO2-4具有与PO3-4结构的相似性,从而能够取代部分PO3-4进入晶格,从而产生H+空位.H+空位的定向移动能增大晶体的电导率.而NO-3和Cl-与PO3-4结构差异较大,很难取代进入PO3-4晶格,因此NO-3和Cl-对KDP晶体的电导率影响不大.     

KDP晶体中包裹体形成机制的探讨

本文介绍了包裹体对KDP晶体质量的影响,并从两个方面探讨了KDP晶体生长过程中包裹体的形成机制.通过分析KDP晶体表面原子结构研究了不同杂质的吸附情况以及杂质对生长台阶的阻碍作用,通过分析晶体生长过程中流体动力学和质量输运条件的变化研究了旋转晶体的流体切应力和表面过饱和度,结果表明吸附杂质对生长台阶的阻碍和表面过饱和度的不均匀造成了生长台阶的弯曲和宏观台阶的形成,导致生长台阶形貌的不稳定是包裹体形成的重要原因.     

点状籽晶法生长KDP晶体中散射颗粒分布

在不同的溶液pH值条件下进行了点状籽晶法慢速和快速生长KDP晶体实验,发展了观察晶体中散射颗粒分布的激光层析技术,通过图像处理得到了KDP晶体内部(100)面完整的散射颗粒分部图,对不同生长速度、不同pH值条件下点状籽晶法生长的KDP晶体的散射颗粒分部做了对比.利用表面光学投影技术观察了晶体表面宏观形貌,并由此分析了不同生长条件下生长机制对散射颗粒分布的影响.测定了散射颗粒密度不同部位的晶体透过率.     

KDP晶体水溶液微结构和界面吸附行为研究

本文采用分子动力学模拟方法研究了磷酸二氢钾(KDP)晶体水溶液的微观分子结构以及生长基元的界面吸附行为.在分子动力学模拟中,水分子采用简单点电荷(三节点)模型,钾阳离子为带电硬球模型,磷酸二氢根离子采用七节点模型,计算了KDP水溶液的构型能,对比分析了(010)和(001)两个晶面的生长速率.研究结果发现:在饱和温度附近体系的局域粒子数密度有剧烈涨落,过饱和溶液的比热显著高于不饱和溶液的比热,表明在饱和温度以下KDP溶液经历了结晶相变过程;磷酸二氢根阴离子生长基元在(010)和(001)两个晶面生长行为的研究表明(010)面生长速率明显高于(001)面,得到了与实验和从头计算相符的结果.     

KDP晶体中散射颗粒形成机理的研究

本文在不同掺杂条件下,采用传统降温法生长了KDP晶体,利用超显微和透射电镜对KDP晶体中的散射颗粒进行了观察,在此基础上对其进行了分类.实验结果表明,不同种类散射颗粒的形成源于溶液中杂质与晶体化学键作用力的不同,造成这一结果的根本原因与KDP晶体的结构特性密切相关.     

硫酸盐对KDP晶体完整性的影响

本文利用高分辨X射线衍射技术,在"点籽晶"陕速生长法基础上,研究了掺杂K2SO4对KDP晶体锥面及柱面扇形结构完整性的影响.结果表明,在5×10-5的掺杂条件下,K2SO4对KDP晶体不同扇形区域的影响略有不同,其原因主要在于[SO42-]与KDP晶体各扇形相互作用不同有关.     

Investigation on the regeneration of Z‐cut KDP crystals

The regeneration of Z‐cut KDP crystals is explored by analyzing the growth of thin surface layers formed. The structural defects and crystalline perfection of the thin surface layers are evaluated by white‐beam synchrotron radiation topography and high‐resolution X‐Ray diffraction respectively. It shows that the thin surface layers have the same crystal structure as KDP crystal. There are large numbers of defects in thin surface layers and the crystalline quality is very poor. The growth velocity of thin surface layers is firstly accurately measured by a newly‐designed in‐situ crystal growth observation setup. It is found that the growth velocity of the thin surface layers strongly depends on the flow rate of the growth solution. The hindering effect of pyrophosphate (K₄P₂O₇) on the growth of the thin surface layers is discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

超大尺寸KDP/DKDP晶体研究进展

KDP/DKDP晶体具有生长方法简单、成本较低、光学性能良好等优点,而可生长出的超大尺寸KDP/DKDP晶体是目前唯一可用于高功率激光工程的单晶材料.但是在晶体的生长过程中存在很多影响因素,同时对晶体进行后处理也会影响晶体的性能,这都直接关系到超大尺寸KDP/DKDP晶体的实际应用.鉴于此,本文综述了近些年超大尺寸KD...     

Structural features of the KH<Subscript>2</Subscript>PO<Subscript>4</Subscript>: Cr single crystal

The precision X-ray structural investigation of KH₂PO₄ (KDP) crystal samples from different growth sectors of a single crystal containing chromium impurities is performed. It is demonstrated that the structure of the sample from the prismatic growth sector is more perfect than the structure of the sample from the pyramidal growth sector. The impurity trapping can lead to the formation of at least four different types of structural defects on the face of the pyramid, whereas only two of them can be formed on the face of the prism. A comparison with the relevant data for the “pure” KDP crystal shows that the number of defects and their character are approximately identical for all samples. The analysis of the IR spectra indicates that nitrate ions are contained in the samples from both growth sectors. Moreover, structurally bound water molecules and OH groups are revealed in the sample from the prismatic sector.     

The heteroepitaxial growth of KDP/ADP

Crystal growth rules of mixture crystals KADP (potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP)) have been analyzed based on the solubility product principle. The heteroepitaxial layers have been obtained by immersing KDP (ADP) substrate into the ADP (KDP) saturated solution at 313 K. The micromorphology indicates that small growing points on different planes show the self‐similar property compared to the bulk crystal's morphology. The process of epitaxial growth depends on not only form the lattice match but also form crystallizing kinetics which is the main influencing factor. Moreover, it can infer from the micromorphology on the surface of the mixed crystal that the dissolving of substrates will form mixed solution on epitaxial surface. What's more, corrosion phenomenon gets more and more evident with increasing times of epitaxial growth and it will be harder to form transparent epitaxial layers due to the increasing tension of epitaxial layers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

抛光加工参数对KDP晶体材料去除和表面质量的影响

针对软脆易潮解KDP功能晶体材料的加工难点,提出了一种基于潮解原理的无磨料化学机械抛光新方法,研制了一种非水基无磨料抛光液,该抛光液结构为油包水型微乳液.通过控制抛光液中的含水量可以方便地控制KDP晶体静态蚀刻率和抛光过程中材料的去除率.实验中还研究了不同加工参数对晶体材料去除率和已加工表面质量的影响.该抛光液的设计为易潮解晶体的超精密抛光加工提供了一条新的技术途径.     

Structural and mechanical properties of KН2PО4 single crystals with embedded nanoparticles and organic molecules

Single crystals of KDP crystals with embedded Urea molecules and TiO₂ nanoparticles have been grown from aqueous solution by the temperature lowering method. The effect of the organic molecules and nanoparticles on the structural and mechanical properties has been studied. It has been observed that addition of Urea molecules improves laser induced damage threshold and mechanical strength of the crystal, while TiO₂ nanoparticles have the opposite effect. The structure and composition of KDP:Urea crystal are studied by three‐crystal X‐ray diffraction analysis, which reveals the existence of a correlation between the increase of the microhardness value and the change of the crystal lattice parameter. The surface features of KDP:TiO₂ crystals are analyzed by scanning electron microscopy that reveals the presence of quasi‐equidistant growth bands caused by capture of the nanoparticles. It is shown that the rise of TiO₂ nanoparticles concentration up to 10⁻⁴ wt.% and higher resulted in 3‐fold reduction of the laser damage threshold of KDP:TiO₂ relative to pure KDP in [001] and [100] crystallographic directions. It is found that microhardness and fracture toughness decrease at the nanoparticles concentration of 10⁻³ wt.% due to crack formation at crystal lattice discontinuities. The grown crystals also have been subjected to dielectric studies.     

Rapid Z-plate seed regeneration of large size KDP crystal from solution

Regeneration process of a 330×330×20 mm³ Z-plate seed is carried out in a 1.5 metric tonnage volume crystallizer that placed in a water bath of temperature fluctuation less than ±0.02 °C within 10 days. The surface of the whole crystal was restored by the formation of a box-like structure filled with growth solution, and then the transparent layer of perfect tetragonal KDP crystal without inclusions, crack and milky regions just like those produced by traditional slow cooling technique can be grown from solution. After the regeneration, the height of KDP crystal is merely 0.5 times the side of plate seed. We found it that the optical transmission and laser damage threshold of the KDP crystals we grown are not significantly different from those of KDP crystals grown by traditional method.     

Partial ordering of glass networks adjacent to simulated glass–crystal interfaces

Interfaces between sodium lithium borosilicate glasses and the (100) and (110) surfaces of MgO and CaO crystals were simulated using a melt-quench procedure, employing classical pair potentials and molecular dynamics. The density of network forming species within the glass at these interfaces was considered as a function of distance from the plane of the interface and the positions of network formers were calculated in relation to sites in the crystal surface.For each interface, a strong correlation was found between the position and orientation of borate and silicate coordination polyhedra within the glass and particular positions of ions in the crystal surface, indicating that different partial ordering of the glass had occurred. In addition, examination of oxygen density profiles revealed a sequence of consistently spaced layers of increased density extending into the glass for all interfacial systems.