A methodology for determining mechanical properties of freestanding thin films and MEMS materials

Espinosa, Horacio D.; Prorok, Barton C.; Fischer, M.

doi:10.1016/s0022-5096(02)00062-5

Cited by 301 publications

(202 citation statements)

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“…Direct experimental observations of the deformation mechanisms mentioned above while the materials behavior is measured quantitatively is difficult at the nanoscale even with the recent novel existing approaches (24)(25)(26)(27)(28). We overcome the difficulty by developing microinstrumentation that combines quantitative tensile testing of thin films with the qualitative capabilities of the transmission electron microscope (TEM) so that one can simultaneously measure the stress-strain states in solids and observe the deformation mechanisms during materials testing.…”

Section: Experimental Methodsmentioning

confidence: 99%

Deformation mechanisms in free-standing nanoscale thin films: A quantitative in situ transmission electron microscope study

Haque

Saif

2004

Proc. Natl. Acad. Sci. U.S.A.

241

115

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We have added force and displacement measurement capabilities in the transmission electron microscope (TEM) for in situ quantitative tensile experimentation on nanoscale specimens. Employing the technique, we measured the stress-strain response of several nanoscale free-standing aluminum and gold films subjected to several loading and unloading cycles. We observed low elastic modulus, nonlinear elasticity, lack of work hardening, and macroscopically brittle nature in these metals when their average grain size is 50 nm or less. Direct in situ TEM observation of the absence of dislocations in these films even at high stresses points to a grain-boundary-based mechanism as a dominant contributing factor in nanoscale metal deformation. When grain size is larger, the same metals regain their macroscopic behavior. Addition of quantitative capability makes the TEM a versatile tool for new fundamental investigations on materials and structures at the nanoscale.N anomechanical behavior of materials has gained considerable attention because of the ever-shrinking dimensions of thin-film materials in microelectronics, data storage, and microelectromechanical sensors͞actuators, and also the advancements in bulk nanostructured materials. Mechanical properties of materials are influenced by their length-scales. For example, yield stress of polycrystalline metals increases with a decrease in grain size [Hall-Petch behavior (1, 2)], and strain-gradientdependent strengthening (3-6) occurs when the specimen size is reduced to the micrometer scale. Dislocations have been attributed to cause both of these behaviors as long as the grain size or the thickness is Ͼ100 nm. At smaller length-scales, straingradient-dependent strengthening disappears (7) and reverse Hall-Petch behavior is observed (8-13). Another less understood size effect observed at nanoscale is the reduction of Young's modulus, which has been attributed to specimen density (13) and grain boundary compliance (14,15). Models that attempt to explain the nanoscale size effect are of two basic types: (i) models describing nanocrystalline materials as twophase composites with grain interiors and boundaries, where the mechanical properties are averaged by simple ''rule of mixtures '' (16, 17); and (ii) models considering dislocation motion (10,18,19), grain boundary sliding (20, 21), and diffusion (12, 22) as competing deformation mechanisms. Although the literature has compelling evidence of these size-effects, the underlying deformation mechanisms are not yet well understood (23). Experimental MethodsDirect experimental observations of the deformation mechanisms mentioned above while the materials behavior is measured quantitatively is difficult at the nanoscale even with the recent novel existing approaches (24-28). We overcome the difficulty by developing microinstrumentation that combines quantitative tensile testing of thin films with the qualitative capabilities of the transmission electron microscope (TEM) so that one can simultaneously measure the stress-strain state...

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Section: Experimental Methodsmentioning

confidence: 99%

Deformation mechanisms in free-standing nanoscale thin films: A quantitative in situ transmission electron microscope study

Haque

Saif

2004

Proc. Natl. Acad. Sci. U.S.A.

241

115

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“…Fracture strength is another important bulk parameter, particularly for MEMS/NEMS devices where moving components are subject to impact. Therefore, the fracture strength of UNCD, and silicon for comparison, was measured using a membrane deflection technique (MDT) developed by Espinosa's Group at Northwestern University [21]. These measurements provide quantitative information on mechanical properties such as Young's modulus, residual stress state, and yield and/or fracture strength.…”

Section: Bulk and Surface Propertiesmentioning

confidence: 99%

Are Diamonds a MEMS' Best Friend?

Auciello

Pacheco²,

Sumant³

et al. 2007

IEEE Microwave

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“…[6][7][8][9][10] The latest DDD results based on Frank networks also demonstrate the "staircaselike" stress-strain behavior and provide an explanation for the starvation argument first proposed in Ref. 1 3.…”

mentioning

confidence: 86%

Comment on “Effects of focused ion beam milling on the nanomechanical behavior of a molybdenum-alloy single crystal” Appl. Phys. Lett. 91, 111915 (2007)

Greer

Espinosa

Ramesh

et al. 2008

Applied Physics Letters

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A methodology for determining mechanical properties of freestanding thin films and MEMS materials

Cited by 301 publications

References 19 publications

Deformation mechanisms in free-standing nanoscale thin films: A quantitative in situ transmission electron microscope study

Deformation mechanisms in free-standing nanoscale thin films: A quantitative in situ transmission electron microscope study

Are Diamonds a MEMS' Best Friend?

Comment on “Effects of focused ion beam milling on the nanomechanical behavior of a molybdenum-alloy single crystal” Appl. Phys. Lett. 91, 111915 (2007)

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