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Article

Elastic Moduli of Ultrathin Amorphous Polymer Films

Supporting Info

Christopher M. Stafford,*^† Bryan D. Vogt,^† Christopher Harrison,^†^§ Duangrut Julthongpiput,^† and Rui Huang^‡

Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, and Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, Texas 78712

Macromolecules, 2006, 39 (15), pp 5095–5099

DOI: 10.1021/ma060790i

Publication Date (Web): June 28, 2006

Corresponding author: Fax +1 (301) 975-4924; e-mail chris.stafford@ nist.gov.

†

National Institute of Standards and Technology.

Present address: Sensor Physics Department, Schlumberger-Doll Research, Ridgefield, CT 06877.

Present address: Assembly Technology Development, Intel Corporation, Chandler, AZ 85226.

‡

University of Texas.

Abstract

The elastic moduli of ultrathin poly(styrene) (PS) and poly(methylmethacrylate) (PMMA) films of thickness ranging from 200 nm to 5 nm were investigated using a buckling-based metrology. Below 40 nm, the apparent modulus of the PS and PMMA films decreases dramatically, with an order of magnitude decrease compared to bulk values for the thinnest films measured. We can account for the observed decrease in apparent modulus by applying a composite model based on the film having a surface layer with a reduced modulus and of finite thickness. The observed decrease in the apparent modulus highlights issues in mechanical stability and robustness of sub-40 nm polymer films and features.

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