Suppression of size-dependent softening effects in sub-micron nanocrystalline ruthenium columnar structures

Sub-micron scale nanocrystalline ruthenium columnar structures with average grain sizes of approximately 4 nm were fabricated by using electron beam lithography and electroplating techniques. Small scale ruthenium columns with several different cross-sectional geometries - solid core, keyhole, hollow, and x-shaped, were successfully manufactured. Uniaxial compressive plastic flow stress results of these ruthenium specimens revealed that they are not sensitive to the column diameters investigated, i.e. size independent. This suggests that the mechanical strength size dependence of nanocrystalline previously reported in literature may be suppressed or reduced if the grain size is significantly smaller than the external structure dimension. In addition, results indicated that the mechanical strengths of ruthenium nanocrystalline structures are not influenced by the cross-sectional geometry of the specimens.