Smoother Shank Profile for Atom Probe Specimens Prepared by the Multi-step Focused Ion Beam Milling

摘要

The focused ion beam (FIB) has been successfully used to prepare a range of atom probe specimens from metal alloys at site specific locations such as grain boundaries, thin ribbons, powders, and multilayer film materials [1, 2]. A 3-step process is commonly employed in which annular milling patterns of decreasing inner and outer radii are used to shape the end of the specimen and produce an apex of the required end radius. However, this method generates ledges at the shank of the specimens[3, 4]. The ledges act as a stress concentration sites and specimens were frequently found to fracture at such regions. Smoother shank profile of the specimen is therefore desirable, so as to reduce the chance of specimen failure at such points. In this work, we present an improved method to fabricate the specimens from planar multilayer thin films. The films were deposited onto etched Si posts, with dimensions of ～4-5μm in diameter and ～100μm in length, prepared by the lithographic patterning of a Si wafer [3]. Capping layers, e.g. Cu, Ni, and Fe, were deposited on top to protect the films of interest from implantation damage caused by the high energy ion beams. Individual posts were attached to the tip of sharpened metal wires, and subsequently sharpened by ion milling in a FEI FIB 200 instrument without further Pt deposition required.