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Direct Imprinting of Porous Substrates
This easily adoptable technology consists of an inexpensive and reproducible method to imprint micron and sub-micron features into porous materials by pressing a reusable stamp directly into the porous material. This method of direct imprinting (DIP™) has the potential to enable an entirely new class of low-cost porous nanomaterial based devices.
Challenges in Patterning of Porous Materials
• Porous materials offer a large internal surface area and highly tunable pore dimensions, making them particularly interesting for use in a variety of applications including photovoltaics, integrated optics, drug-delivery, and sensing of biological and chemical species
• The majority of methods used in the patterning of porous materials require equipment that is often bulky and expensive to operate
• The techniques that do avoid cumbersome equipment, such as dry-removal soft lithography, sacrifice mechanical integrity, speed of fabrication and pattern complexity
This technology presents a simple, direct-to-device technique to mechanically deform porous silicon to produce well-defined microstructures. Since the porous material is composed in part of air, the material can be easily crushed or compressed. Taking advantage of this property, a stamp (e.g. solid silicon) crushes the porous substrate in selective regions and the debris is washed away, revealing a patterned porous structure. This stamping process happens in a matter of seconds and can be rapidly reproduced. The stamp pattern is transferred to the porous material with high fidelity with a vertical resolution of below 5nm and lateral resolution of below 100 nm. The stamp is made by standard lithographic methods, but once it is made the stamp can be reused indefinitely, greatly reducing the cost of the process and increasing production speed.
Unique Features and Competitive Advantages
• No heating, curing, or intermediary coating layer is required in this process
• Solid stamps are reusable and do not wear significantly over time
• The stamping process occurs on a time scale of seconds at room temperature making this a straightforward, costeffective, and high-throughput process
• The stamping process is applicable to a number of substrates including porous silicon, porous silica, porous alumina, and porous gold
• This process offers a wide range of potential applications in areas such as photovoltaics, drug-delivery, chemical sensing, and optoelectronics
Top view SEM images of porous nanomaterials patterned with DIPS. (a) pSi grating (Λ=750 nm) with submicrometer sized features. The mean pore diameter is approximately 20-30 nm. (b) Free standing porous silicon microparticles fabricated by performing DIPS with a silicon grating stamp, rotating 90 degrees and stamping again. In this image, the particles are sitting on the original stamp used to define them. (c) pSi imprinted with 3μm font “Vanderbilt” text. (d) Imprinted and nonimprinted regions of a TiO2-NTA.
Intellectual Property and Development Status
US (20110056398A1) and Canadian Patent applications have been filed
J. D. Ryckman, M. Liscidini, J. E. Sipe, and S. M. Weiss, "Direct imprinting of porous substrates: A rapid and lowcost approach for patterning porous materials," Nano Letters., 2011, 11, 1857–1862.
J. D. Ryckman, Y. Jiao, and S. M. Weiss, "Threedimensional patterning and morphological control of porous nanomaterials by gray-scale direct imprinting," Scientific Reports 3, 1502 (2013).
Lab home Page with list of publications and ongoing research portfolio: http://eecs.vuse.vanderbilt.edu/research/vuphotonics/research.html
Additional images and video: "Stamping out low cost nanodevices" Vanderbilt News, May. 31, 2011
Inventors:Sharon WeissJudson RyckmanMarco LiscidiniJohn Sipe