FRACTUREBETWEENSELF-ASSEMBLEDMONOLAYERS S.R. Na1, B. Doynov1, A. Hassan2, K. M. Liechti1 and M.J. Krische2 1Aerospace Engineering and Engineering Mechanics 2Chemistry and Biochemistry The University of Texas at Austin Austin, TX 78712 kml@mail.utexas.edu While it is intuitive that molecular interaction should correlate to the mechanical properties of a material, it has only recently become possible to make the measurements necessary to trace the effects of molecular interaction across length scales to properties at the level of the material. The utility of “classical” polymeric adhesives is underscored by their widespread use in primary structural applications ranging from aerospace, automotive, and civil structures to biomedical implants and microelectronic devices. To date, the vast majority of the efforts directed toward improving the strength and durability of adhesives have been largely empirical. At the same time, the drive towards miniaturization in MEMS and NEMS devices and nano patterning means that an understanding of adhesion and fracture at smaller and smaller scales needs to be developed. This actually provides an opportunity to decrease the amount of empiricism as the number of variables is essentially decreased. The paper describes the development of an experiment with associated analysis to determine the toughness of a molecular level adhesive joining two silicon strips. Si (111) surfaces were coated with amine and carboxy-terminated self-assembled monolayers (SAMs). The silicon beams were pressed together to form miniature laminated beam specimens which were then separated using a specially developed high vacuum fracture tester. The deposition of the SAMs and associated spectroscopic, scanning probe and ellipsometric diagnostics are described. The delaminations between the silicon strips and the associated normal crack opening displacements (NCOD) were measured via infra-red crack opening interferometry. The fracture toughness of the specimens was measured. Traction-separation laws were extracted from measurements of crack opening displacements and an associated fracture analysis. These compared favorably with traction-separation laws based on potentials for ionic bonding. Proceedings of the SEM Annual Conference June 7-10, 2010 Indianapolis, Indiana USA ©2010 Society for Experimental Mechanics Inc. 267 T. Proulx (ed.), MEMS and Nanotechnology, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series 2, DOI 10.1007/978-1-4419-8825-6_38, © The Society for Experimental Mechanics, Inc. 2011
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