Time-resolved X-ray Studies of Kinetics of Metastable Materials

在许多技术应用中，亚稳态材料的使用正变得非常普遍。在这种情况下，原子排列通常具有中等范围的有序，这有点像晶体结构，但它们并不处于真正的热力学平衡状态。亚稳结构的动力学行为，特别是它们与平衡长程有序态的关系，目前还知之甚少。利用动力学临界现象的概念来研究非平衡过程的理论已经取得了很大的进展，但直接探讨微观机制的实验工作却很少。我们建议利用强大的时间分辨x射线漫射新技术对这一领域进行深入研究。该研究利用了x射线源（高亮度同步辐射）和探测器（快速二维ccd）的最新发展，有望彻底改变时间分辨研究。研究的目的是确定动力学的普遍特征，这些特征可以纳入非平衡结构过程的一般定量描述。这些研究选择了两个模型系统；重点研究具有重要光电应用价值的薄膜异质结构的快速热退火，以及电化学沉积枝晶和薄膜结构的生长和弛豫机制。

The use of materials in metastable states is becoming very pervasive in many technological applications. Very often the atomic arrangements in such cases have intermediate-range order somewhat characteristic of crystalline structure but they are not in true thermodynamic equilibrium. The kinetic behavior of metastable structures, and especially their relation to the equilibrium long-range ordered state, is quite poorly understood at present. There has been substantial progress in the theory of non-equilibrium processes using the concepts of kinetic critical phenomena, but little experimental work which probes directly the microscopic mechanisms. We propose a thorough study of this area utilizing powerful ne techniques in time-resolved x-ray diffuse scattering. The research exploits the recent developments in x-ray sources (very brightness synchrotron radiation) and detectors (fast two- dimensional CCDs) which are expected to revolutionize time- resolved studies. The goal of the research is to identify universal features of the kinetics which can be incorporated into a general quantitative description of non-equilibrium structural processes. Two model systems have been chosen for these studies; the research will focus on the rapid thermal annealing of thin- film heterostructures which have important optoelectronic applications, and the growth and relaxation mechanisms of electrochemically deposited dendrites and thin film structures.