Opportunity for Partnership

Simple, Low-Cost Method for Producing Submicron-Sized Tips for Field Emitters and Atomic Microscope Styli

Arrays of pointed structures or cones that can be used in a variety of electronic and mechanical equipment were produced by utilizing the low-cost method for producing submicron-sized tips for field emitters and atomic microscope styli.

NASA Goddard Space Flight Center seeks companies to license this method for producing arrays of pointed structures or cones used in a variety of electronic and mechanical equipment applications. This low-cost, simple method yields a template containing large numbers of cones that are uniform in size and equally spaced. This template then can be easily coated with metals or semiconductors to tailor the mechanical and electrical properties of the tip.

Micron- and submicron-sized pointed structures are used in electrical and mechanical equipment applications where sharp tips are needed. However, existing methods to produce these structures—materials synthesis and etching—are plagued with difficulties. The equipment (e.g., deep reactive ion etching) can be very expensive, and the resulting arrays are small with tips/cones of varying heights and aspect ratios. However, a researcher at NASA Goddard Space Flight Center has developed a new, cost-effective process for producing large numbers of uniform point structures.

This innovative process involves dropping or spinning a ferrofluid (i.e., a liquid containing Fe2O3 particles) onto a glass, quartz, or other substrate. A magnetic field is then applied using simple permanent or electro-magnets, causing the ferrofluid to form pointed structures that are uniformly aligned with a maximized aspect ratio. The ferrofluid then is dried at room temperature. The result is a template that can serve as a substrate for subsequent film growth through any standard thin-film deposition technique, including evaporation, sputtering or chemical vapor deposition. Templates have survived vacuum testing at 10–6 Torr. The conformal films applied to the template will reflect its pointed structure.

NASA’s ferrofluid technique may be particularly useful for creating emitters to be coated by wide bandgap semiconductors, which can absorb and emit electrons in the ultraviolet light bands. These materials, such as readily available ZnO, are an excellent alternative for the traditional large, high-voltage photocathode systems. Coating the templates created with Goddard’s technology with ZnO or other oxides avoids the oxidizing properties associated with metals typically used in photocathodes (e.g., tungsten, chromium). Therefore, the photocathodes are less susceptible to contamination, decay and radiation damage, and may be more chemically and structurally stable.

This technology is expected to provide a low-cost electron source useful in a wide range of electronics and mechanical equipment applications such as field emission displays, field emission devices, photocathodes, scanning tunneling microscopes, atomic force microscopes, far ultraviolet (UV) photolithography and low-power propulsion systems.

The benefits of this innovation include the following:

• Low cost: This method uses basic equipment and an inexpensive, commercially available material to produce the pointed-tip arrays.
• Versatile: The template can be formed on a variety of substrates (e.g., glass, quartz, sapphire) and can be coated with various materials (e.g., zinc oxide [ZnO] and other semi-conductors, metal).
• Scalable: Unlike other methods that yield arrays of limited size, this process has the potential for large-scale (>4") fabrication of pointed-tip arrays.
• Simple: This three-step process is an easy alternative to materials synthesis and etching techniques, which are the current standards for making pointed-tip arrays.
• Consistent: The method yields a template of needle-like tips uniformly aligned and with a high aspect ratio.

• Radically reconfigurable and scalable: Because the shape, size and volume of its elements can be controlled, the ART structure can take on multiple configurations and perform multiple tasks.
• Robust: The tetrahedral shape is the most stable geometric structure.
• Enhances control: As the size of each element gets smaller and the number of elements increases, the degree of freedom and level of control are greatly enhanced.
• Reduces mass: Having no hard body, the tetrahedron is lightweight and can be very compact but with the ability to expand as needed.
• Reduces power requirements: Its low mass has minimal power requirements. Future plans to incorporate nanotechnology will further decrease the required operational power density.
• Undifferentiated architecture eliminates need for dedicated components: The technology has the potential to reconfigure itself in response to its changing needs and environments, reducing the need for dedicated tools and components.
• Reduces failures: ART intrinsically is massively redundant; if one section is damaged, it has the potential—in an advanced form— for self-repair.

• Wheelchairs and other assistive devices: The effective ART skeletal/muscular frame system enables fluid motion over any terrain and supports performance of varied functions.
• Human performance enhancement and enablement: ART can function as an adaptive exoskeleton to enhance strength, reach and other functions.
• Robots: ART’s maneuverability and ability to reconfigure itself make it particularly useful in (but not limited to) situations where tasks must be performed in inhospitable environments (e.g., gathering environmental samples, finding and defusing bombs, search and recovery).
• Mining: ART can be configured for thin-vein mining applications.
• Toys and novelties: The unique abilities of the technology also open the door to a new era of toys and novelty items.

NASA Official: Janelle Turner • Web Design: Printing & Design Office, NASA Headquarters • Credits