Area-selectively sputtering the RuO2 nanorods array

The RuO2 nanorods array is grown selectively on the SiO2-patterned sapphire (SA) wafers using reactive sputtering. The area-selectivity is attributed to an early nucleation of RuO2 and its fast surface coverage on SA (1 0 0) and (0 1 2), in contrast to the sluggish nucleation on glassy SiO2 in the initial sputtering period. The growth domain is explored by investigating the temperature windows at sputtering power 40, 50, and 60 W. The low-temperature bound is limited by the mobility of precursors on SiO2 surface, which enables the precursors to depart before aggregating into a large size to smear the non-growth region. The high-temperature bound is set by the horizontal growth which enlarges the rod width and deteriorates its one-dimensional feature. The temperature window shrinks with increasing sputtering power. The X-ray photoelectron spectra indicate the as-sputtered rod surface is ruthenium rich. The X-ray diffraction analysis shows that RuO2 growth on SA (1 0 0) and (0 1 2) follows the epitaxial relations between RuO2 and SA crystals.