On the preparation and mechanical testing of nano to micron-scale specimens

Over the past two decades, means allowing to probe experimentally the mechanical behavior of materials specimens only a few micrometers or less in diameter have multiplied, largely owing to the widespread adoption and versatility of focused ion beam (FIB) milling for the preparation of small-scale test specimens. Despite its remarkable capabilities, the ion bombardment that is employed during FIB milling operations does not leave machined surfaces unscathed: it may induce a series of alterations in the near-surface microstructure of materials, which vary in severity depending on the material being milled, or milling parameters, or the type of ion used. These alterations in turn can strongly influence the local behavior, and as a result measured mechanical properties, of the milled material. In the first part of this manuscript, we review the different forms that FIB-induced microstructural alterations can take and their influence on small-scale mechanical test results. In the second part, we present alternative strategies that have been used to circumvent the issue. These include the use of entirely different small-scale sample fabrication processes, as well as approaches that do use FIB-milling but put effort in the test design to minimize or avoid the formation of FIB-induced defects in regions where micromechanical test data are collected. The advent of such methods can enhance our understanding of FIB-induced defects on the mechanical behavior of microsamples by comparing the results with those from ion-milled samples. This, in turn, should improve our ability to interpret test data when FIB-milling is the only method available for microsample production.