Measurements of submicron spheres and pillars of silicon single crystals have exhibited a strain-hardening capacity equal to or greater than their metallic counterparts. Stress-strain characteristics are reported for diameters ranging from 40 to 400 nm. Evaluations were performed with nanoindentation-based atomic force, scanning and transmission electron microscopies. Values of strain-hardening exponents up to unity in nanospheres are attributed to a size effect variation on the rate of increase of contact area with deformation. A surface-mediated dislocation nucleation concept is shown to be consistent with length scale effects partially modified by geometry as well as size. It is proposed, but not proven, that the modification relates to greater constraint in compact spheres as opposed to tall pillars.
Bibliographical noteFunding Information:
The authors would like to acknowledge the Abu Dhabi-Minnesota Institute for Research Excellence a partnership with the Petroleum Institute, NSF/DMR- 0946337, and NSF/CTS-0506748 for funding. Some of the pillars described in this work were provided by Sergiy Krylyuk and Albert Davydov of the Metallurgy Division, MML at NIST Gaithersburg. D.S. and J.N. would additionally like to acknowledge Hysitron, Inc. Parts of this work were carried out in the Institute of Technology Characterization Facility, University of Minnesota, a member of the NSF-funded Materials Research Facilities Network.
- Nanoparticle compression