title: In situspectroscopic study of the plastic deformation of amorphous silicon under non-hydrostatic conditions induced by indentation.
abstract: Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied byin situRaman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generatedin situRaman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystallineβ-tin phase within the a-Si network.
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland, 20899; Mechanical Engineering Department, University of Maryland, College Park, Maryland, 20742.
authors.forename: Y B
authors.initials: YB
authors.lastname: Gerbig
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland, 20899.
authors.forename: C A
authors.initials: CA
authors.lastname: Michaels
authors.affiliation: Department of Electronic Materials Engineering, Research School of Physics and Engineering, Australian National University, Canberra 0200, Australia.
authors.forename: J E
authors.initials: JE
authors.lastname: Bradby
authors.affiliation: Chemical and Engineering Materials Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831.
authors.forename: B
authors.initials: B
authors.lastname: Haberl
authors.affiliation: Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland, 20899.
authors.forename: R F
authors.initials: RF
authors.lastname: Cook