溶液法晶体生长中薄表面层形成及生长机理研究

Crystal growth from solution is a typical thermodynamic phase transition process which must follow the basic laws of thermodynamics. However, there exists one strange phenomenon appeared in the crystal growth, known as the thin surface layer growth phenomenon, which is not explained reasonably up till now. This phenomenon is against the thermodynamic law that the Gibbs free energy in the system with constant temperature and pressure should become more and more small. A study on this problem by the aid of theory analyses, experiments and numerical simulation in the present project possesses an important scientific significance and academic value. Proceed with the edge of the crystal, a model of step generation at the edge is proposed. By calculating the density fluctuation using statistical thermodynamics method and linear stability analysis, combining with in situ and ex situ micro observation on the surface morphology and numerical simulation, the mechanism of the step generation at the edge and the thin surface layer formation will be explored. A hypothetic about the growth of the thin surface layer is proposed and checked out by the experiments, it is expected that a new explanation can be given. A search for the method of suppressing the formation and growth of the thin surface layer is carried out in order to improve the process of the capping of the z-cut seed. If some obvious progress can be achieved, it is an important practical significance for those countries like China, in which, the growth of KDP crystal still depends on the conventional method.

溶液法晶体生长是一个典型的热力学一级相变过程，应遵循热力学基本原理。但溶液法晶体生长中出现的薄表面层生长现象，是一个至今未能给予合理解释的奇特现象。它有悖于热力学的基本原理，即定温定压系统中自发过程朝吉布斯自由能降低的方向进行。本项目通过理论分析、实验并结合数值模拟对该问题开展研究，具有重要的学术价值和科学意义。项目从棱边台阶产生机制入手，提出一个棱边台阶产生模型； 通过统计热力学密度涨落计算和线性稳定性分析，结合晶面近棱边区域实时和非实时的显微观察实验和数值模拟，探寻台阶在棱边产生的原因，进而分析薄表面层形成机理；提出一个薄表面层生长假说，并通过薄表面层生长实验予以检验，希望从新的视角对薄表面层生长机制给予阐释；探寻一种抑制薄表面层形成和生长的方法，以改善成帽过程，提高晶体的利用率，如果该方法能取得进展，对于像我国这样仍利用传统生长方法生长KDP晶体的国家来说，有重要的现实意义。

溶液法晶体生长是典型的热力学一级相变过程，应遵循热力学基本原理。但溶液法晶体生长中出现的薄表面层生长现象，是一个至今未能给予合理解释的奇特现象。它似有悖于热力学的基本原理，即定温定压系统中自发过程朝吉布斯自由能降低的方向进行。本项目通过理论分析、实验并结合数值模拟对该问题开展研究。首先从棱边棱角在薄表面层生长中的特殊作用考虑，开展了棱边棱角特殊处理后薄表面层生长实验，用光学显微镜和扫描电子显微镜观察薄表面层形成初期的特性实验，结合数值模拟对薄表面层形成和生长机理给予了分析。开展了各种非完整形态晶体薄表面层生长实验。进行了薄表面层生长动力学理论计算。对z切片、非完整晶体、喷流和带锥台托盘下溶液流动及物质输运开展了三维时相关数值模拟。获得了一些有重要意义的结果：发现棱角作为相邻棱边及晶面联接的重要部分, 在 Z 切片对其原有形态的“判断”中起“信息传导作用”，而棱边在薄表面层形成和生长中是物质基础；提出了非完整晶体恢复中薄表面层生长的最小凸多面体原理；发现非完整晶体似乎有“感知”能力并存在“恢复势”，“恢复势”是薄表面层生长的驱动力，而棱边棱角处的过饱和度并不高，过饱和度应不是薄表面层生长的驱动力。获得了体扩散机制下薄表面层生长速度和动力学系数的表达式，找到了薄表面层稳定生长的动力学条件；获得了薄表面层生长的临界厚度及形成能。