Controlling Self-assembled Surface Features in Thin Films by Surface Tension and Elasticity.

Self-assembly;Thin Film;Surface Tension;Long-range Order;Templated Dewetting;Elastocapillary Densification;Mechanical Engineering;Engineering;Mechanical Engineering

Zhao, ZhouzhouSangi Reddy, Pramod ;

University of Michigan

关键词: Self-assembly;    Thin Film;    Surface Tension;    Long-range Order;    Templated Dewetting;    Elastocapillary Densification;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/97938/zzzhao_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Precise control over the self-assembled surface features, such as pattern, order and feature size, is crucial to the device performance. However, most current self-assembly methods have inadequate control over defects. Motivated by this challenge, this work aims to investigate and propose mechanisms for efficient and robust fabrication of well-defined micro and nanostructures by self-assembly. Specifically, the coupling of surface tension and elasticity is the focus of this work. First, I proposed two mechanisms to improve the long-range order in self-assembled nanostructures. The first mechanism is called sequential activation of self-assembly, in which the self-assembly was initiated in a small mobile region to form a seed pattern, and then the mobile region was shifted gradually. The second mechanism called the spontaneous propagation of self-assembly utilizes the ordered pattern in the growth front to trigger self-assembly in the propagation front zone. Both mechanisms enable the delivery of local order information to distance by spontaneous propagation and may apply to other self-assembled systems. Next, I studied the formation of self-assembled nanoparticles during dewetting of templated thin films. Recent experiments showed that anodic aluminum oxide (AAO) membranes, which have uniform nanoscale pore size and spacing, can influence the dewetting of iron thin films into organized arrays of nanoparticles. Our simulations show that the AAO pore position variations and the initial film thicknesses have strong influence on the order of nanoparticles, while AAO pore size variations have relatively weak effect on the order. Two coarsening mechanisms are further identified to explain the changes in particle order parameter and size distribution. Last, I investigated the mechanisms of elastocapillary densification of pre-patterned vertically aligned carbon nanotube (CNT) forests. The bending mechanism in bilaterally symmetric structures is revealed by considering competition between axial forces and lateral forces. The shape change in cross-section of relatively short CNT forests is explained as a substrate effect. In addition, the nonlinear lateral mechanical behavior of CNT forests is captured by finite element modeling of a contact problem between a pair of curved beams.