Nanostructure Fabrications with Top-Down Techniques

Speaker:   Prof. Ling Xie

Time:       10:15-11:00, July 11

Location:  SIST 1A 200

Host:       Prof. Tao Wu

Abstract:

In this talk I will first present a few of ways to construct nanoscale structures using top-down fabrication approaches. Several nanostructures shaped by these ways are demonstrated, such as nano-wires, nanotubes with a variety of materials and shapes, silicon nanowires, ultra-narrow (~10 nm) high aspect ratio trenches, diamond nanopillars, etc. The advantages using top-down approaches include precisely controlling nanotube distribution patterns, geometric shapes, and dimensions. These intentionally designed and precisely controlled nanostructures could offer a broader range of applications in drug delivering, bio-sensing, optoelectronics, etc.

Then I will talk about crystallographic direction-dependent dry etching. The crystallographic orientation dependent wet etch of single crystalline silicon in potassium hydroxide (KOH) allows a range of shapes formed and has significant impacts on MEMS (microelectromechanical systems), AFM (atomic force microscopy), and microfluidics. Here, a crystal direction dependent dry etching principle in an inductively-coupled plasma reactive ion etcher is presented, which allows to selectively reveal desired crystal planes in monocrystalline diamond by controlling the etching conditions. The principle is demonstrated when the kinetic energy of incident ions on diamond surfaces is reduced below a certain threshold leading to anisotropic etching and faceting along specific crystal planes. Using the principle, monolithic diamond nanopillars for magnetometry using nitrogen vacancy centers are fabricated. In these nanopillars, a half-tapering angle up to 21° is achieved, the highest angle reported, which leads to a high photon efficiency and high mechanical strength of the nanopillar. These results represent the first demonstration of crystallographic orientation dependent reactive ion etch principle, which opens a new window for shaping specific nanostructures which is at the heart of nanotechnology. It is believed that this principle will prove to be valuable for structuring and patterning of other single crystal materials as well.

Bio:

Ling Xie is a Principal Research Scientist at the Harvard Center for Nanoscale Systems (CNS). She received her MS and PhD in Materials Science and Engineering from the University of Wisconsin-Madison and worked for Eastman Kodak Company on CCD image sensors and Lucent Technologies, Inc on 3D optical switches before joining Harvard University in 2004. Her research focuses on micro/nano fabrication techniques, using state-of-the-art-technologies to construct micro and nano structures, such as micro/nano tubes with a variety of materials and shapes, silicon nanowires, ultra-narrow (~10 nm) high aspect ratio trenches, diamond nanopillars, etc. Through a collaboration with the Professor Amir Yacoby Group at Harvard, Ling and the team developed the crystallographic orientation dependent reactive ion etch in single crystal diamond, which opens a new window for shaping specific nanostructures, which lies at the heart of nanotechnology. Ling specializes in MEMS fabrication, reactive ion etch (RIE), chemical vapor deposition (CVD), physical vapor deposition (PVD), and thin film characterization. She has been facilitating the CNS seminar series since 2008.