Very sharp and well-defined rigid diamond indenters are critical for accurate sub-10 nm nanoindentation mechanical property measurements. The focused ion beam milling technique is adopted to create such a very sharp diamond indenter. With ion milling patterning, a spherical well-defined super tip is obtained at the apex of the indenter, with a radius of 53.4 nm. This sharpened indenter is applied to sub-10 nm nanoindentation measurements on fused quartz and silicon (100) samples. The elastic moduli measured at sub-10 nm depths are consistent with literature bulk values. In addition, the measured hardness values are qualitatively consistent with indentation experiments using conventional larger radii indenters. Finally, due to the small size of the indenter tip, the transition from elastic to plastic contact occurs at very shallow contact depths. (C) 2004 American Vacuum Society.