In-situ electrical probing of zones of nanoindentation-induced phases of silicon
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1146-NN02-06
In-situ electrical probing of zones of nanoindentation-induced phases of silicon S. Ruffell1, J. E. Bradby1, J. S. Williams1, R. C. Major2, O. L. Warren2 1 Department of Electronic Materials Engineering, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200, Australia 2 Hysitron Inc., 10025 Valley View Road, Minneapolis, MN 55344, USA ABSTRACT Phase transformed zones of silicon have been formed by nanoindentation both at the micro- and nanoscale and electrically probed using an in-situ measurement system. Zones composed of the high pressure crystalline phases (Si-III/Si-XII) have higher conductivity than those of amorphous silicon (a-Si). At the microscale probing laterally across the surface shows that the conductivity varies within the zones composed of the high pressure phases. The sensitivity to the different conductivities of the two phases allows mapping within the zones. Finally, at the nanoscale the conductivity of the high pressure phase zones can be correlated with the position of the pop-out associated with the formation of the phases. The zones have higher conductivity when the pop-out occurs earlier on unloading and we suggest that this is due to the reduction in trace volumes of a-Si formed during the early portion of the unloading cycle. INTRODUCTION Nanoindentation-induced phase transformations of silicon have attracted significant interest over recent years [1-7]. During indentation loading, diamond-cubic Si-I undergoes a transformation to the β-Sn phase (Si-II) at a pressure of ~11 GPa. During unloading this phase undergoes further transformations to either amorphous Si (a-Si) or a mixture of two high pressure phases (Si-III and Si-XII) in polycrystalline form. The latter phase transformation is favoured for slow unloading conditions and the phases are believed to form by a nucleation and growth mechanism with large volumes forming on occurrence of a so-called pop-out event. Therefore, the indentation process creates a sub-surface volume of either a-Si or a mixture of SiIII and Si-XII depending on unloading conditions, with size and shape determined by indenter geometry and maximum load. These phase transformations have been well characterized but the physical mechanisms that drive them and the exact transformation pathways are not fully understood. Little is known about the electrical properties of the end-phases in particular the high pressure crystalline phases (Si-III/Si-XII). Electrical characterization of the end-phases is intrinsically difficult due to the size of the zones created by indentation and the mixed nature of the high pressure phases, each of which is thought to have different electrical properties. A promising method that has been shown to have high sensitivity, is in-situ electrical characterization using a conductive indenter tip [8-10]. Furthermore, this method of characterizing the end-phases may provide greater insight into the phase transformation pathways which occur during the indentation process. The aim of this stud
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