A Galvorn Case Study

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Air Force Research Laboratory (AFRL) is a scientific research and development detachment of the United States Air Force Materiel Command. Their work to advance field emission technology is seeing promising results thanks to Galvorn.

electrons

Field Emission Challenges

Field emission cathodes, which emit electrons under a strong electric field, face several challenges.

  1. Performance: One key issue is achieving consistent and stable electron emission, as performance can degrade due to surface irregularities or contamination on the cathode material. 
  2. Durability: Another challenge is durability—high electric fields and current densities can cause material wear or breakdown over time. Efficiently managing heat dissipation is also critical, as excessive temperatures can alter the cathode's properties. 
  3. Complex Production: Additionally, fabricating cathodes with precise nanoscale features, like sharp tips for enhanced emission, remains technically complex and costly. Finally, scaling up for practical applications, such as in vacuum electronics or displays, requires balancing performance with manufacturability. 

DexMat’s work with AFRL on this dual-use technology, is addressing these hurdles by using  Galvorn.

Field Emission Benefits with Galvorn

Faster, More Efficient Repetition Rates

The conductivity enables lower turn-on voltages, meaning it is faster to power and thus increases the repetition rate of the device.

350x More Directed Energy

Galvorn produced 350x more current per equivalent field strength (measured in volts per unit length) under DC testing in a laboratory setting. In other words, Galvorn is 350x more productive at turning current into directed energy.

Scalable Manufacturing

The development of the cathode was straightforward, simply requiring Galvorn to be knitted into the correct size and shape for the device. This is in contrast to the current state-of-the-art flocked carbon fiber cathodes, which are both complex and expensive to produce. Previous work on Galvorn CNT fibers and Galvorn CNT fiber cathode manufacturing, supported by feedback and funding from the Air Force Research Laboratory (AFRL), has demonstrated that using CNT fibers in field emission cathodes can result in scalable production. These cathodes can be produced faster, more reliably, and at a lower cost than the current state-of-the-art.

Surface Geometry Matters!

Field emission is improved by a spikey cathode surface. Researchers have traditionally arranged individual CNTs or other carbon materials to achieve this surface geometry, but Galvorn enables a simpler and faster way to achieve better results.

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How Galvorn Enables Better Field Emission

Galvorn initially has no tall, pointy surface structures: the solid carbon material is densely packed and highly aligned CNTs. When used as a cathode material the CNTs in Galvorn run smoothly parallel to the cathode surface.  

Image Source: Advanced space charge limited field emission cathodes

Microscopic photo of advanced space charge limited field emission cathodes

Charging the device with voltages sufficient for field emission creates bursts in the material, causing a build-up of electric charge in the fiber skin. The negatively charged CNT bundles repel each other and peel away from the surface. This results in an exfoliated, fibrillated structure with many thin CNT bundle tips, which ultimately enables Galvorn's great field emission. Additionally, as these fibrils burn out, a lot of charge simply builds up in a different spot, which then also fibrillates. This phenomenon explains how Galvorn has proven to be a remarkably durable cathode source.

AFRL has discovered several key benefits to using Galvorn

Galvorn is a durable and effective cathode source for field emission applications due to its unique properties and structural transformation during the emission process. These developments have positive implications for several commercial applications:

  • Electron microscopy: creates images by reflecting electrons off tiny structures.
  • Displaying information: lights up screens in areas struck by electrons.
  • Discharging unwanted voltages: neutralizes charges on spacecraft or satellites.
  • Creating radiation: generates electromagnetic waves with a controlled frequency.
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