Fracture mechanisms of GaAs under nanoscratching
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Fracture mechanisms of GaAs under nanoscratching J.-M. Solletti , M. Parlinska-Wojtan, J. Tharian 1, K. Wasmer 2, J. Michler 2, C. Ballif 3, D. Schulz 4 A. Karimi Faculty of Basic Science, IPMC, EPFL, CH-1015-Lausanne, Switzerland. 1 EMPA Überlandstrasse 129, CH-8600 Dübendorf. 2 EMPA Feuerwerkstrasse 39, CH – 3602 Thun. 3 University of Neuchâtel, A.-L. Breguet 2, CH-2000 Neuchâtel. 4 Bookham technologies plc, Binzstrasse 17 CH – 8045 Zürich.
ABSTRACT Nanoscratching on GaAs (001) by a pyramidal diamond tip (Berkovitch) indenter has been carried on under different loads, scratching velocities and directions. Plastic deformation and fractures induced by scratching have been investigated by atomic force microscopy (AFM), and by scanning and transmission electron microscopy (SEM and TEM, respectively). Surface images revealed radial and surface tensile cracks. Focused ion beam (FIB) milling of the contact area revealed median and shear fracture distribution in the volume. The different cracks were characterized for various scratching conditions in terms of their direction of propagation, extension and frequencies. Plastic deformations have been characterized by vertical displacement of material. No purely ductile zone was observed, GaAs deformation occurred by fractures and plastic strain. Their preponderances are discussed in terms of material properties.
INTRODUCTION Separation of gallium arsenide devices is generally achieved by cleavage. This necessitates a well-defined flaw that will expand only on the desired propagation plane under a wellcontrolled applied stress. Unfortunately, methods like nanoscatching induce a compulsory flaw for the cleavage but also other deleterious cracks that depend on the indenter geometry and loading conditions [1-2]. Under a sliding load with a Vickers indenter, GaAs deformed by slipping, and radial, lateral and median cracks were observed [1]. Recently, variable depth scratches were studied by SEM and positron annihilation spectroscopy showing a purely ductile deformation zone, followed by a brittle and then by an abrasive zone [2]. In this paper, we investigate more in details the fracture morphology and plastic deformation within the region surrounding the contact area by varying the scratching conditions.
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EXPERIMENTAL DETAILS The sample material was (001) oriented n-doped GaAs. A Berkovich diamond indenter tip was mounted in a Nano-XP apparatus from MTS to scratch the sample with the edge along the [110] and [100] directions. During scratching several parameters including normal and tangential loads as well as indenter penetration are recorded. Typical applied loads were below 80 mN, and the indenter velocities between 1 and 2000 µm/s. Surface deformation was observed by atomic force microscopy (AFM, Dimension 3000 from DI). Cross-sections were prepared by focused ion beam (FIB, FEI Strata DB 235) in order to investigate bulk fractures by SEM or TEM (Philips EM 430, LaB6 cathode operated at 300 kV). DISCUSSION AFM images of varying load scratches revealed rad
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