Pop-in events induced by spherical indentation in compound semiconductors
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M.V. Swainb) Biomaterials Science Research Unit, Department of Mechanical and Mechatronic Engineering, and Faculty of Dentistry, The University of Sydney, Eveleigh, NSW 1430, Australia (Received 16 June 2003; accepted 31 October 2003)
Details of the elastic–plastic transitions in crystalline compound semiconductors have been examined using spherical indentation. Two cubic (InP and GaAs) and two hexagonally structured semiconductors (ZnO and GaN) have been studied. A series of indentations have been made in each material at a number of different loads. The resulting load–penetration curves exhibited one or more discontinuities on loading (so called pop-in events). The load at which the initial pop-in event occurred has been measured along with the corresponding indenter extension. The elastic and elastic–plastic response of each material to spherical indentation has been calculated and compared with the experiment. By taking the difference between the elastic and elastic–plastic penetration depths, it has been found that the pop-in extension at each load could be predicted for each material. The detailed deformation behavior of each of the materials during indentation has also been discussed.
I. INTRODUCTION
It is now widely recognized that features in nanoindentation load–penetration curves can provide valuable insights into the response of materials during deformation.1–8 For example, prominent features in the load– penetration curve can be associated with microstructural events including cracking, film delamination, and the generation and propagation of dislocations.1–9 On nanoindentation loading, a discontinuity in the measured depth is commonly referred to as a pop-in event with a similar discontinuity on unloading called a pop-out event. The pop-in event usually represents the sudden yielding of a material under load. It is routinely observed in samples with a crystalline structure and has widely been associated with the onset of plasticity.1–8 Previous indentation studies have observed a pop-in event in the loading curves taken from the compound semiconductors GaAs, InP, GaN, and ZnO.8,10–19 It has been shown that the mode of deformation in these compound semiconductors10–12 does not involve a phase transformation, as has been previously observed in Si.20 a
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www. mrs.org/publications/jmr/policy.html 380
J. Mater. Res., Vol. 19, No. 1, Jan 2004
Unlike Si, no discontinuities have been reported in the unloading curves (pop-out events) from these compound semiconductors at room temperature.10,18,19 Previous transmission electron microscopy (TEM) studies of GaAs,10,21–23 InP,10,18,19,22,24 GaN,11,25 and ZnO12 after indentation have shown that these materials deform by the generation and propagation of dislocations. No evidence has been observed tha
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