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

在许多技术应用中，亚稳态材料的使用变得非常普遍。在这种情况下，原子排列经常具有中程有序，这在某种程度上具有晶体结构的特征，但它们并不处于真正的热力学平衡。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对非平衡过程的理论研究已经取得了长足的进展，但直接探索微观机制的实验工作很少。我们建议利用时间分辨x射线扩散散射中强大的Ne技术对这一领域进行深入研究。这项研究利用了X射线源(非常明亮的同步辐射)和探测器(快速二维电荷耦合器件)的最新发展，预计这将给时间分辨研究带来革命性的变化。这项研究的目的是确定动力学的普遍特征，这些特征可以纳入对非平衡结构过程的一般定量描述。选择了两个模型系统进行这些研究，重点研究了具有重要光电应用的薄膜异质结的快速热退火，以及电化学沉积的树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.