Prof. Ophelia K. C. Tsui      

Department of Physics, Boston University

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Atomic Force Microscopic Nanolithography

As academic and industrial research are geared towards specimens of smaller size, there is tremendous demand for new technologies that could make samples with smaller feature size without compromising the equipment cost and accessibility.  Atomic force microscopic (AFM) local oxidation is one that possesses all these perks. The equipment used - AFM ¡V is a bench-top equipment, the operation does not require a clean-room environment, and it could produce sample features ~10 nm.

We have used the AFM local oxidation method to make nanostructures in a large variety of materials including aluminium, gold, titanium, and silicon. Figure 1 illustrates the principle of the method. During operation, a dc bias voltage is applied between the AFM tip and the sample (Al, say) that were brought into close proximity. The resulting electric field causes local oxidation of the region underneath the tip. The voltage-carrying tip could thus be programmed to draw an oxide pattern on the sample surface. Upon finishing, one may dip the sample into a chemical to selectively etch away regions that are not oxidized to enhance the pattern structure.

Fig. 1

Figure 2 is a gallery showing some nanostructures we have fabricated. The major technical advancement we accomplished is to successfully interface the AFM local oxidation technique with other microfabrication techniques such as photolithography, which are needed to make the nanostructure device accessible to macroscopic electrical leads.  Our method is illustrated in Figs. 3a and 3b. The report of this work, published in J. Vac. Sci. Tech. B, 21(1), 162-167 (2003), was selected by the Virtual Journal of Nanoscale Science & Technology Vol. 7(3), 2003 for highlight.

 

Fig. 2

        

Fig. 3(a)                                                                         Fig. 3(b)             

Key Publication:

"Fabrication of Mesoscopic Devices Using Atomic Force Microscopic Electric Field Induced Oxidation", F. K. Lee, G. H. Wen, X. X. Zhang, O.K.C. Tsui, J. Vac. Sci. Tech. B, 21, 162-167 (2003).

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      

Last revised on 28 May 2007.