Novel Studies of Topological Order and Pinning Effects in Colloidal Crystals

w：\awards\awards96\*.doc 9804083 Ling 这个实验研究项目的重点是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）公度相和非公度相及相变，2）随机钉扎势下弹性晶格拓扑序的稳定性，3）Peierls-Nabarro势对刃位错的影响， 熔融动力学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。 胶体悬浮液是本研究的介质。 实验采用数字视频显微镜，结合先进的光镊技术，研究两个载玻片之间的胶体颗粒的静态和动态。 在载玻片上，将使用光刻技术制作介观结构，该介观结构充当胶体颗粒的淬灭周期性或随机钉扎电位。利用光镊研究胶体晶体对局部形变的弹性和塑性响应。拟议的研究将有利于本科物理课程，并将使学生接触到先进的微加工技术，光学，图像分析和凝聚态物理。该研究计划是跨学科的，涉及学生，他们接受了良好的培训，为工业，政府实验室或学术界的职业生涯做准备。 本实验研究课题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，与中国棋盘上的大理石阵列或弹簧有些相似。这类问题是，如果一个或几个对象被推，整个数组会发生什么;数组是否平滑地扭曲或分开。一个相关的问题是，如果在均匀外力的存在下，晶格的几个位置被钉住，那么响应是什么。阵列是否继续移动，是否停止（固定），或是否分解。这项工作中的实验实际上将在胶体晶体上进行，胶体晶体是弱结合的有序分子阵列。这些晶体在实验上相对容易处理，因为分子间的作用力很弱，分子相对较大。 这样一个模型系统的结果，预计将适用于许多其他情况。本文讨论了三个经典问题：1）公度相和非公度相及相变，2）随机钉扎势下弹性晶格拓扑有序的稳定性，3）Peierls-Nabarro势对刃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，统计力学的基础研究。 胶体悬浮液是本研究的介质。 实验 采用数字 视频 显微镜， 结合先进的光镊技术，研究胶体颗粒在两个载玻片之间的静态和动态。 在玻璃载玻片上，介观结构作为猝灭的周期性或随机钉扎电位， 胶体 粒子将使用 平版印刷技术利用光镊研究了纳米颗粒的弹性和 胶体晶体对局部变形的塑性响应。 本文的研究将有益于大学物理专业的教学 程序， 和 将暴露学生 到 先进的微加工技术，光学，图像分析和凝聚态物理。 该研究计划是跨学科的，涉及学生，他们接受了良好的培训，为工业，政府实验室或学术界的职业生涯做准备。 ***

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. ***