Lithographically Fabricated 10-Micron Scale Autonomous Motors
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Lithographically Fabricated 10-Micron Scale Autonomous Motors Yang Wang1, Shih-to Fei1, Vincent H. Crespi2, Ayusman Sen,1 and Thomas E. Mallouk1* 1 Department of Chemistry, Pennsylvania State University, University Park, PA, 16802, U.S.A. 2 Department of Physics, Pennsylvania State University, University Park, PA, 16802, U.S.A ABSTRACT Self-propulsion and directed movement of nano- and micro-particles can in principle provide novel components for applications in microrobotics and MEMS. Our research involves the design of catalytic propulsion systems and the control of colloidal movement based on this principle. We have designed autonomous nanomotors that mimic biological motors by using catalytic reactions to generate forces derived from chemical gradients. Through architectural control of bimetallic catalytic particles, we have recently developed systems that undergo more complex movement. For example, we have constructed 10-micron scale rotary motors by contact lithography. In these chiral motors, bimetallic Au-Pt patterns are free-standing and move in the pattern predicted by theory. These studies demonstrate that by designing the proper architecture, one can tailor the pattern of movement to specific applications, such as changing from translational to rotational movement. The potential for elaboration of these designs to more complex micro-machine assemblies is discussed. INTRODUCTION We describe the lithographic fabrication of catalytic propulsion systems in various new designs that control/tailor movement patterns from translational to rotational at the 10µm scale. Nano- and sub-microscale autonomous moving systems have attracted substantial interest because of potential applications in powered assembly, delivery vehicles, MEMS, robotics, fluidics, and sensing. Nano- and microscale movement driven by catalysis is as expanding area that follows from the recent discovery of autonomous nanomotors that mimic biological motors by using catalytic reactions to generate forces derived from chemical gradients1,2. Templategrown bimetallic nanorods can move at speeds up to 30µm/s by catalyzing the decomposition of hydrogen peroxide. An electrokinetic mechanism for powered movement has been proposed for these systems 3,4, and several subsequent studies have expanded on the idea to demonstrate enzymatically catalyzed and rapid directional movement 5, 6. A signficant restriction in nanomotor research is that they generally rod - shaped, although some interesting efforts have been made to modify the nanorod geometry 7, 8 to achieve more complex movement such as rotation. The template growth of nanorods thus significantly limits the possible applications for this system. One way to address this problem is to use contact lithography, which provides the freedom to design and fabricate microscale object that have arbitrary planar geometries. One concern in designing new nano- and micromotor shapes is the issue of scaling. Catalytic nanomotors work in the low Reynolds number regime, and at larger length scales, ine
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