Nano-Patterning Processes and Material Systems

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Photolithography remains one of the most versatile methods for patterning materials. However, it has not been widely applied in nano-science because the smallest features that can be obtained using conventional optical systems have dimensions on the order of the wavelength of the excitation radiation. Sub-wavelength-aperture scanning probe tips, of the type used for near-field scanning optical microscopy (NSOM), can be used to photo-excite regions that are much smaller than the diffraction limit. A type of near-field scanning optical lithography (NSOL) has been reported in which piezoelectrically scanned NSOM tips are used to pattern serially a photosensitive surface with nanometer precision. NSOL should be a tremendously powerful tool for nano-science and technology because (1) it enables sub-wavelength-sized features to be patterned with nanometer-precision and (2) it can be adapted for patterning the wide range of materials for which conventional photolithographic processes exist. We will develop methods for patterning materials onto surfaces by NSOL and adapt these processes for the fabrication of multilayer 3D photonic crystals and other nano-photonic structures. We are also investigating methods of achieving the same using atomic force microscopy tips as a surface nano-patterning tool.

Figure 1. Illustration of a nano-fabrication scheme based on surface patterning using an atomic force microscope (AFM) tip.

Figure 2. Schematic of a nano-patterning approach based on near-field scanning optical lithography.

Multi-Photon Three-Dimensional Microfabrication

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Multi-photon three-dimensional microfabrication (3DM) is a photolithographic technique that enables topologically complex 3D micro-structures with feature size as small as 1 um or less to be generated in a single exposure step by nonlinear photo-patterning in a material. The photo-patterning is initiated by coherent multi-photon excitation (MPE). The material may be a glass, a polymerizable resin, or even a heterogeneous composite, such as a resin containing dispersed nano-particles. 3DM offers great promise as a tool for generating complex micro-devices, such as MEMS, micro-fluidics, and micro-optical components.

We are developing new material systems for 3DM and applying the technique for generating a wide range of functional micro-structures. Of particular interest are micro-structures that interact with or sense biological species and that mimic a biological function. The limiting resolution, or the dimensions of the smallest feature that can be generated, is determined by the optical parameters of the excitation geometry and the physical and chemical response of the material to MPE. We are exploring new optical configurations to improve the resolution in 3DM. Examples of my work in 3DM can be found in the publications below.

Figure 3. Sequence of steps involved in the generation of a free-standing microstructure by multi-photon 3DM.

Figure 4. Opto-mechanical setup for multi-photon 3DM.

"An efficient two-photon-generated photoacid applied to positive-tone 3D microfabrication." W. Zhou, S. M. Kuebler, K. L. Braun, T. Yu, J. K. Cammack, C. K. Ober, J. W. Perry, and S. R. Marder, Science, 296, 1106-1109 (2002). [Download PDF]

"Optimizing two-photon initiators and exposure conditions for three-dimensional lithographic microfabrication." S.M. Kuebler, M. Rumi, T. Watanabe, K. Braun, B. H. Cumpston, A. A. Heikal, L. L. Erskine, S. Thayumanavan, S. Barlow, S. R. Marder, and J. W. Perry, J. Photopolym. Sci. Technol., 14, 657-668 (2001). [Download PDF]

"Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication." B.H. Cumpston, S. P. Ananthavel, S. Barlow, D. L. Dyer, J. E. Ehrlich, L. L. Erskine, A. A. Heikal, S. M. Kuebler, I.-Y. S. Lee, McCord-Maughon, D. J. Qin, H. R. Roeckel, M. Rumi, X. -L. Wu, S. R. Marder, and J. W. Perry. Nature, 398, 51-54 (1999). [Download PDF]

For More Information

Stephen M. Kuebler
Department of Chemistry
University of Central Florida
Orlando, FL 32816