In situ measurement of bulk modulus and yield response of glassy thin films via confined layer compression

The measurement of thin film mechanical properties free from substrate influence remains one of the outstanding challenges in nanomechanics. Here, a technique based on indentation of a supported film with a flat punch whose diameter is many times the initial film thickness is introduced. This geomet...

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Bibliographic Details
Published in:Journal of materials research 2020-03, Vol.35 (6), p.644-653
Main Authors: Brazil, Owen, de Silva, Johann P., Chowdhury, Mithun, Yoon, Heedong, McKenna, Gregory B., Oliver, Warren C., Kilpatrick, Jason, Pethica, John B., Cross, Graham L. W.
Format: Article
Language:English
Subjects:
Applied and Technical Physics
Biomaterials
Bulk modulus
Deformation
Diameters
Film thickness
Geometry
In situ measurement
Indentation
Inorganic Chemistry
Load
Materials Engineering
Materials research
Materials Science
Mechanical properties
Modulus of elasticity
Nanomechanics and Testing
Nanotechnology
Parameters
Poisson's ratio
Polymethyl methacrylate
Polystyrene resins
Room temperature
Selenium
Strain
Substrates
Thin films
Yield strength
Yield stress
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Summary:The measurement of thin film mechanical properties free from substrate influence remains one of the outstanding challenges in nanomechanics. Here, a technique based on indentation of a supported film with a flat punch whose diameter is many times the initial film thickness is introduced. This geometry generates a state of confined uniaxial strain for material beneath the punch, allowing direct access to intrinsic stress versus strain response. For simple elastic–plastic materials, this enables material parameters such as elastic modulus, bulk modulus, Poisson’s ratio, and yield stress to be simultaneously determined from a single loading curve. The phenomenon of confined plastic yield has not been previously observed in thin films or homogeneous materials, which we demonstrate here for 170–470 nm thick polystyrene (PS), polymethyl-methacrylate (PMMA) and amorphous Selenium films on silicon. As well as performing full elastic-plastic parameter extraction for these materials at room temperature, we used the technique to study the variation of yield stress in PS to temperatures above the nominal glass transition of 100 °C.
ISSN:0884-2914
2044-5326
DOI:10.1557/jmr.2020.42