Thermo-Mechanical and Size-Dependent Behavior of Freestanding AuAg and Nanoporous-Au Beams
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0976-EE06-09
Thermo-Mechanical and Size-Dependent Behavior of Freestanding AuAg and NanoporousAu Beams Erkin Seker1, Jianzhong Zhu1, Hilary Bart-Smith2, Matthew Begley2,3, Robert Kelly3, Giovanni Zangari3, and Michael L. Reed1 1 Electrical and Computer Engineering, University of Virginia, Charlottesville, VA, 22904 2 Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA, 22904 3 Materials Science and Engineering, University of Virginia, Charlottesville, VA, 22904
ABSTRACT Nanoporous gold (np-Au), produced by selectively removing silver from an AuAg alloy, has recently gained considerable attention from the scientific community. Biocompatibility, chemical inertness, increased surface area, relatively low elastic modulus, and ease of synthesis make npAu an important candidate for biomedical, catalytic, and MEMS applications. Np-Au films also offer substantial ground for theoretical and empirical research, including mechanical characterization, fracture mechanics, and porosity evolution. Even though a significant effort has been directed towards exploring blanket np-Au films (i.e., foils, strips), to our knowledge no work has been done on fabricating or investigating freestanding np-Au structures (i.e., microbeams, cantilevers). Recently we have developed techniques to create freestanding clamped npAu beams with widths from 5 to 40 microns and lengths from 20 to 500 microns. The percentage yield was more than 97% for 2880 beams on a 2-inch wafer. A critical step in the fabrication process, necessary to prevent tensile failure of the beams during dealloying, is a thermal heat treatment prior to dealloying. The study of thermal treatment of beams at temperatures between 100°C and 600°C prior to dealloying revealed three distinct beam behavior regimes, namely quasi-elastic buckling, plastic buckling, and material interdiffusion. This paper will present the preliminary results from thermal treatment experiments particularly focusing on how beam dimensions affect percentage yield and beam fracture. INTRODUCTION Biocompatibility, chemical inertness, increased surface area, relatively low elastic modulus, and ease of synthesis make nanoporous gold (np-Au) an important candidate for biomedical, catalytic, and MEMS applications. The formation of the np-Au is realized by the rearrangement of Au atoms when Ag is chemically leached from AuAg alloy via a process know as dealloying [1]. Examples of previous research include fabrication of np-Au wires [2,3], application of npAu on quartz crystal sensors [4], production of thin np-Au membranes [5], atomistic behavior of porous matrix formation [6], nanoindentation of bulk np-Au discs [7], effects of halidecontaining electrolytes on critical potential and pore size [8], and compression tests on microfabricated posts via nanoindentation [9]. To our knowledge, freestanding np-Au structures were not realized. We have recently demonstrated the microfabrication of freestanding np-Au beams using conventional microfabrication techniques [10]. Freestanding structu
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