Cui Bo, Wu Lin, Chou Stephen Y
NanoStructure Laboratory, Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA.
Nanotechnology. 2008 Aug 27;19(34):345303. doi: 10.1088/0957-4484/19/34/345303. Epub 2008 Jul 15.
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.
作者们开发了一种利用纳秒脉冲激光熔化来制造尖锐且高纵横比金属尖端的方法。将覆盖有薄铬（Cr）膜的石英晶片放置在另一个晶片之上，两者之间有亚微米级的间隙，且Cr膜面向第二个晶片。然后从石英晶片背面发射准分子激光脉冲（波长308nm，脉冲持续时间20ns），瞬间（几百纳秒）熔化Cr膜。发现熔融的Cr膜能够自形成连接两个晶片的离散金属柱。分离两个晶片后，在断裂的柱颈部形成纳米尖端。所获得的最尖锐尖端的顶点直径为10nm，高度为180nm。两个晶片之间Cr柱的自形成归因于紧密相邻的两个晶片的功函数差异所产生的有吸引力的静电力。该技术可扩展到其他金属，并且通过将金属预先图案化为相同的孤立台面并精确控制两个晶片之间的间隙，可以获得周期性均匀的尖端阵列。
