Fabrication and microstructure control of nanoscale mechanical testing specimens via electron beam lithography and electroplating

ABSTRACT It has been demonstrated that the mechanical properties of materials change significantly when external dimensions are confined to the nanoscale. Currently, the dominant fabrication method for mechanical testing specimens with nanometer dimensions is by using focused ion beam (FIB) milling, which results in inevitable Ga+ induced damage to the microstructure. Here, we report a FIB-less fabrication technique to create arrays of vertically oriented gold and copper nanopillars based on patterning polymethylmethacrylate by electron beam lithography and subsequent electroplating into the prescribed template. This fabrication process is capable of producing a wide range of microstructures: from single crystals and nanotwinned, to bi-, poly-, and nanocrystalline mechanical testing specimens with diameters from 750 down to 25 nm with the diameter range below 100 nm previously inaccessible by FIB. Over the past decade, the nanomechanics com-munity has renewed its interest in the investiga-tions of size-dependent mechanical properties due to the advancements in the instrumental resolution and in computational capabilities. In the case of single crystalline metals, the size effects manifest themselves as a pronounced increase in compressive strength when the external dimen-sions are reduced to the micrometer and submicrometer scale.1-14 To study the size-dependent material strengths