Novel Studies of Topological Order and Pinning Effects in Colloidal Crystals

9804083林这个实验研究项目集中在胶体晶体中的拓扑有序和钉扎效应。讨论了三个经典问题：1)公度和非公度相和相变，2)随机钉扎势中弹性晶格的拓扑序的稳定性，3)Peierls-Nabarro势对边缘位错和熔化动力学的影响。这些问题在表面科学、自组装纳米结构材料、低维电子系统、无序超导体、固体微观力学和统计力学的基础研究中都会遇到。胶体悬浮液是本研究的媒介。实验使用数字视频显微镜，结合先进的光学镊子技术，研究限制在两个玻璃片之间的胶体颗粒的静力学和动力学。在玻璃载玻片上，将使用光刻技术制作作为胶体颗粒的猝灭的周期性或随机钉扎势的介观结构。我们将使用光学镊子来研究胶体晶体对局部变形的弹性和塑性响应。这项拟议的研究将使本科生的物理课程受益，并将使学生接触到先进的微制造技术、光学、图像分析和凝聚态物理。这一研究项目本质上是跨学科的，涉及学生，他们接受了为在工业、政府实验室或学术界的职业生涯做准备的出色培训。本实验研究项目主要研究二维弹性晶体的基本力学性质。二维晶体是有序的阵列，与中国棋盘或弹簧上的大理石阵列有一些相似之处。问题是，如果推动一个或几个对象，整个阵列会发生什么；阵列是平滑扭曲还是解体。一个相关的问题是，如果在均匀外力的作用下，晶格的几个位置被压住，会有什么反应。阵列是继续移动、停止(固定)还是断开。这项工作中的实验实际上将在胶体晶体上进行，这是一种弱结合的有序分子阵列。这些晶体相对容易在实验上处理，因为分子间作用力较弱，分子相对较大。关于这样一个模型系统的结果可望适用于许多其他情况。本文讨论了胶体晶体的三个经典问题：1)公度和非公度相和相变；2)弹性晶格在随机钉扎势中的拓扑序的稳定性；3)Peierls-Nabarro势对边缘位错和熔化动力学的影响。这些问题在表面科学、自组装纳米结构材料、低维电子系统、无序超导体、固体微观力学和统计力学的基础研究中都会遇到。胶体悬浮液是本研究的媒介。实验使用数字视频显微镜，结合先进的光学镊子技术，研究限制在两个玻璃片之间的胶体颗粒的静力学和动力学。在玻璃载玻片上，将使用光刻技术制作作为胶体颗粒的猝灭的周期性或随机钉扎势的介观结构。我们将使用光学镊子来研究胶体晶体对局部变形的弹性和塑性响应。这项拟议的研究将有益于本科生的物理课程，并将使学生接触到先进的微制造技术、光学、图像分析和凝聚态物理。这一研究项目本质上是跨学科的，涉及学生，他们接受了为在工业、政府实验室或学术界的职业生涯做准备的出色培训。***

w:\awards\awards96\*.doc 9804083 Ling This experimental research project focuses on topological order and pinning effects in colloidal crystals. Three classical problems are addressed: 1) commensurate and incommensurate phases and phase transitions, 2) stability of topological order of an elastic lattice in a random pinning potential, 3) effects of a Peierls-Nabarro potential on edge dislocations and melting kinetics. These problems are encountered in surface science, self- assembled nanostructure materials, low dimensional electron systems, disordered superconductors, micromechanics of solids, and fundamental studies of statistical mechanics. Colloidal suspensions are the media for the present study. Experiments employ digital video microscopy, in combination with advanced optical tweezers technology, to study the statics and dynamics of colloidal particles confined between two glass slides. On the glass slides, a mesoscopic structure which acts as a quenched periodic or random pinning potential for the colloidal particles will be made using lithographic techniques. An optical tweezer will be used to study the elastic and plastic responses of a colloidal crystal to a local distortion. The proposed research will benefit the undergraduate physics program, and will expose students to advanced microfabrication technology, optics, image analysis and condensed matter physics. This research program is interdisciplinary in nature and involves students, who receive excellent training in preparation for careers in industry, government laboratories or academia. %%% This experimental research project focuses on basic mechanical properties of two-dimensionsal elastic crystals. Two-dimensional crystals are ordered arrays, with some similarity to an array of marbles on a Chinese checker board, or a bedspring. The sort of question is what happens t o the overall array if one or a few of the objects are pushed; does the array smoothly distort or does it come apart. A related question is the response if, in the presence of a uniform external force, a few locations of the lattice are pinned down. Does the array continue to move, does it stop (pinned), or does it break up. The experiments in this work actually will be done on colloidal crystals, which are weakly bound ordered arrays of molecules. These crystals are relatively easy to deal with experimentally because the intermolecular forces are weak and the molecules are relatively large. The results on such a model system are expected to be applicable to many other situations. In the present work on colloidal crystals, three classical problems are addressed: 1) commensurate and incommensurate phases and phase transitions, 2) stability of topological order of an elastic lattice in a random pinning potential, 3) effects of a Peierls-Nabarro potential on edge dislocations and melting kinetics. These problems are encountered in surface science, self-assembled nanostructure materials, low dimensional electron systems, disordered superconductors, micromechanics of solids, and fundamental studies of statistical mechanics. Colloidal suspensions are the media for the present study. Experiments employ digital video microscopy, in combination with advanced optical tweezers technology, to study the statics and dynamics of colloidal particles confined between two glass slides. On the glass slides, a mesoscopic structure which acts as a quenched periodic or random pinning potential for the colloidal particles will be made using lithographic techniques. An optical tweezer will be used to study the elastic and plastic responses of a colloidal crystal to a local distortion. The proposed research will benefit the undergraduate physics program, and will expose stude nts to advanced microfabrication technology, optics, image analysis and condensed matter physics. This research program is interdisciplinary in nature and involves students, who receive excellent training in preparation for careers in industry, government laboratories or academia. ***