Microfabrication
The ability to create and manipulate structures at micron and nanometer length scales is an essential aspect of nanotechnology. We are exploring several diverse areas related to fabrication. Three of these are described here.
Nano-tweezers
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We are designing and fabricating an electromechanical device for manipulation and electrical probing of nano-scale objects (Figures 1 and 2). The device consists of micro-scale flexures and actuators that generate nano-scale motion; and nano-scale structure that interact with the nano world. Our device is designed to work in conjunction with the AFM and will be used to image the sample as well.
Currently there is no versatile, practical experimental tool for use at this scale. Our goal is to have a cheap and consistently reproducible experimental device. Hence, we are designing this device to be completely batch fabricated start to finish. Despite the lack of batch lithography at this scale, we have developed unique processes that allow for nano-scale feature size and single nano-scale pitch using standard microfabrication.
To ensure consistency between our nano-tweezers, we have developed self compensating devices that can withstand a range of process and subsequent structure variations and still provide the same performance characteristics. This robust design method also has extensive utility in other commercial MEMs applications where repeatability of performance and reliability are essential.
Photothermal Lithography
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We are exploring alternatives to traditional photolithography in an effort to push the boundaries of micro- and nano-fabrication. In traditional photolithography, light is used to transfer patterns from a mask to a wafer. The minimum feature size this method can achieve is proportional to the wavelength of light used in the exposure process. In an ongoing effort to pack more features into smaller spaces, the standard approach has been to use increasingly shorter wavelengths of light. Unfortunately, in many applications this is becoming prohibitively expensive because of the technical challenges inherent in creating new materials and optics required to manipulate this light.
Our process relies on optical to thermal energy conversion and as a result, the resolution is decoupled from the optical wavelength. We are carrying out thermal modeling and the development of a prototype system. The basic concept of our scheme is shown in Figure 3; some very preliminary results are shown in Figure 4.
Electromagnetic Metamaterials
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Metamaterials, man-made structures with unique electromagnetic properties, are an active area of research. Influencing electromagnetic waves at or near optical frequencies will require the fabrication of two and three dimensional nanostructures.
We have done research on the simple fabrication of thin film roll-up structures for developing a metamaterial with a negative magnetic permeability in the Tera Hertz range. If successful, this would contribute an essential element to the development of a LHM (Left-Handed Material), which would have unique electromagnetic properties not observed in any naturally occurring material. We have been able to fabricate double roll-up structures, or "nanoscrolls", comprised of silicon dioxide and nickel that are 100 microns long and 2 microns in diameter. We expect to see negative permeability in such structures.