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Title: Plane-strain bulge test for nanocrystalline copper thin films

Abstract

Free-standing nanocrystalline Cu films with grain size around 39 nm are fabricated by thermal evaporation and characterized by the plane-strain bulge test. Young's modulus and yield stress at a 0.2% offset are about 110-130 GPa and 400 MPa, respectively. Results show that the strength of the n-Cu films is largely independent of film thickness at a strain rate less than 10{sup -5} s{sup -1}. No grain growth is observed and the predominant plastic deformation mechanism is grain boundary sliding accompanied by dislocation mechanisms.

Authors:
 [1];  [1];  [2];  [1];  [1]
  1. Columbia University
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Shared Research Equipment Collaborative Research Center
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931755
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Scripta Materialia; Journal Volume: 57; Journal Issue: 6
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 77 NANOSCIENCE AND NANOTECHNOLOGY; COPPER; NANOSTRUCTURES; DISLOCATIONS; GRAIN SIZE; STRAIN RATE; THIN FILMS; YOUNG MODULUS; YIELD STRENGTH

Citation Formats

Wei, Xiaoding, Lee, Dongyun, Shim, Sang Hoon, Chen, Xi, and Kysar, Jeffrey. Plane-strain bulge test for nanocrystalline copper thin films. United States: N. p., 2007. Web. doi:10.1016/j.scriptamat.2007.05.012.
Wei, Xiaoding, Lee, Dongyun, Shim, Sang Hoon, Chen, Xi, & Kysar, Jeffrey. Plane-strain bulge test for nanocrystalline copper thin films. United States. doi:10.1016/j.scriptamat.2007.05.012.
Wei, Xiaoding, Lee, Dongyun, Shim, Sang Hoon, Chen, Xi, and Kysar, Jeffrey. Mon . "Plane-strain bulge test for nanocrystalline copper thin films". United States. doi:10.1016/j.scriptamat.2007.05.012.
@article{osti_931755,
title = {Plane-strain bulge test for nanocrystalline copper thin films},
author = {Wei, Xiaoding and Lee, Dongyun and Shim, Sang Hoon and Chen, Xi and Kysar, Jeffrey},
abstractNote = {Free-standing nanocrystalline Cu films with grain size around 39 nm are fabricated by thermal evaporation and characterized by the plane-strain bulge test. Young's modulus and yield stress at a 0.2% offset are about 110-130 GPa and 400 MPa, respectively. Results show that the strength of the n-Cu films is largely independent of film thickness at a strain rate less than 10{sup -5} s{sup -1}. No grain growth is observed and the predominant plastic deformation mechanism is grain boundary sliding accompanied by dislocation mechanisms.},
doi = {10.1016/j.scriptamat.2007.05.012},
journal = {Scripta Materialia},
number = 6,
volume = 57,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • A new analysis of the deflection of square and rectangular membranes of varying aspect ratio under the influence of a uniform pressure is presented. The influence of residual stresses on the deflection of the membranes is examined. Expressions have been developed that allow one to measure residual stresses and Young's moduli. By testing both square and rectangular membranes of the same film, it is possible to determine Poisson's ratio of the film. Using standard micromachining techniques, free-standing films of LPCVD silicon nitride were fabricated and tested as a model system. The deflection of the silicon nitride films as a functionmore » of film aspect ratio is very well predicted by the new analysis. Young's modulus of the silicon nitride films is 222[plus minus]3 GPa and Poisson's ratio is 0.28[plus minus]0.05. The residual stress varies between 120 and 150 MPa. Young's modulus and hardness of the films were also measured by means of nanoindentation, yielding values of 216[plus minus]10 GPa and 21.0[plus minus]0.9 GPa, respectively.« less
  • Analysis and sample preparation techniques for the bulge test have been improved to the point where the test can provide reliable and accurate measurements of the mechanical properties of thin films. Ag--Pd multilayer films of variable bilayer period were prepared for this study and characterized by cross-section transmission electron microscopy and by x-ray methods. The films were tested in the bulge test to determine their biaxial moduli. The data show no peak in biaxial modulus at a critical composition wavelength and no nonlinear elastic behavior. They do show a slight trend toward increasing elastic modulus with increasing strength of (111)more » crystallographic texture. These findings refute a previous report of the supermodulus'' effect in this system and add to the evidence that the effect is caused by artifacts of the mechanical testing technique. Methods for eliminating such artifacts are discussed.« less
  • Since its first application to thin films in the 1950's the bulge test has become a standard technique for measuring thin film mechanical properties. While the apparatus required for the test is simple, interpretation of the data is not. Failure to recognize this fact has led to inconsistencies in the reported values of properties obtained using the bulge test. For this reason we have used the finite element method to model the deformation behavior of a thin film in a bulge test for a variety of initial conditions and material properties. In this paper we will review several of themore » existing models for describing the deformation behavior of a circular thin film in a bulge test, and then analyze these models in light of the finite element results. The product of this work is a set of equations and procedures for analyzing bulge test data that will improve the accuracy and reliability of this technique.« less
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