Fabrication of high aspect ratio metal nanotips by nanosecond pulse laser melting

The authors have developed an approach to fabricate sharp and high aspect ratio metal tips using nanosecond pulse laser melting. A quartz wafer covered with a thin chromium (Cr) film was placed on top of a second wafer with a sub-micrometer gap between them and the Cr film facing the second wafer. Then an excimer laser pulse (308?nm wavelength, 20?ns pulse duration) was shone from the back of the quartz wafer and melted the Cr film momentarily (several hundred nanoseconds). It is found that the molten Cr films can self-form discrete metal pillars connecting the two wafers. After separating the two wafers, nanotips were formed at the broken pillar necks. The sharpest tip achieved has an apex diameter 10?nm and height 180?nm. The self-formation of Cr pillars between the two wafers was attributed to the attractive electrostatic force caused by the work function difference of two wafers that were in close proximity. This technique could be extended to other metals, and a periodic uniform tip array could be obtained by pre-patterning the metal into identical isolated mesas and precisely controlling the gap between the two wafers.