Scientists discover that a single layer of tiny diamonds increases electron emission 13,000-fold

December 10, 2015
Nick Melosh, an associate professor at SLAC and Stanford, holds a model of a diamondoid. Credit: SLAC National Accelerator Laboratory

They sound like futuristic weapons, but electron guns are actually workhorse tools for research and industry: They emit streams of electrons for electron microscopes, semiconductor patterning equipment and particle accelerators, to name a few important uses.

Now scientists at Stanford University and the Department of Energy's SLAC National Accelerator Laboratory have figured out how to increase these electron flows 13,000-fold by applying a single layer of diamondoids – tiny, perfect diamond cages – to an electron gun's sharp gold tip.

The results, published today in Nature Nanotechnology, suggest a whole new approach for increasing the power of these devices. They also provide an avenue for designing other types of electron emitters with atom-by-atom precision, said Nick Melosh, an associate professor at SLAC and Stanford who led the study.

Diamondoids are interlocking cages made of carbon and hydrogen atoms. They're the smallest possible bits of diamond, each weighing less than a billionth of a billionth of a carat. That small size, along with their rigid, sturdy structure and high chemical purity, give them useful properties that larger diamonds lack.

SLAC and Stanford have become one of the world's leading centers for diamondoid research. Studies are carried out through SIMES, the Stanford Institute for Materials and Energy Sciences, and a lab at SLAC is devoted to extracting diamondoids from petroleum.

In 2007, a team led by many of the same SIMES researchers showed that a single layer of diamondoids on a metal surface could emit and focus into a tiny beam with a very narrow range of energies.

The research team used tiny nanopillars of germanium wire as stand-ins for the tips of electron guns in experiments aimed at improving electron emission. This image was made with a scanning electron microscope – one of a number of devices that use emitted electrons. Credit: Karthik Narasimha/Stanford

The new study looked at whether a diamondoid coating could also improve emissions from electron guns.

One way to increase the power of an electron gun is to make the tip really sharp, which makes it easier to get the electrons out, Melosh said. But these sharp tips are unstable; even tiny irregularities can affect their performance. Researchers have tried to get around this by coating the tips with chemicals that boost , but this can be problematic because some of the most effective ones burst into flames when exposed to air.

For this study, the scientists used tiny nanopillars of germanium wire as stand-ins for electron gun tips. They coated the wires with gold and then with diamondoids of various sizes.

Germanium nanopillars were coated with gold and then with diamondoids of various sizes. The scientists got the best results by coating the pillars with diamondoid molecules that consist of four “cages;” this increased the emission of electrons from the tips 13,000-fold. Credit: Karthik Narasimha/Stanford

When the scientists applied a voltage to the nanowires to stimulate the release of electrons from the tips, they found they got the best results from tips coated with diamondoids that consist of four "cages." These released a whopping 13,000 times more electrons than bare gold tips.

Further tests and computer simulations suggest that the increase was not due to changes in the shape of the tip or in the underlying gold surface. Instead, it looks like some of the diamondoid molecules in the tip lost a single electron – it's not clear exactly how. This created a positive charge that attracted electrons from the underlying surface and made it easier for them to flow out of the tip, Melosh said.

"Most other molecules would not be stable if you removed an electron; they'd fall apart," he said. "But the cage-like nature of the diamondoid makes it unusually stable, and that's why this process works. Now that we understand what's going on, we may be able to use that knowledge to engineer other materials that are really good at emitting electrons."

Diamondoid structures tested in the experiment; the two on the bottom, which consist of four “cages” with carbon atoms at each corner, produced the biggest gains in electron emission. The chemical tags at the bottom of each molecule were added to help the diamondoids stick to the gold surface of the nanopillars. Credit: Karthik Narasimha/Stanford

SIMES researchers Nick Melosh, left, and Jeremy Dahl in a Stanford laboratory with equipment used to perform diamondoid experiments. Credit: SLAC National Accelerator Laboratory

Explore further: Tiny 3-D structures nanoimprinted on the end of an optical fiber

More information: Karthik Thimmavajjula Narasimha et al. Ultralow effective work function surfaces using diamondoid monolayers, Nature Nanotechnology (2015). DOI: 10.1038/nnano.2015.277

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5 comments

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cgsperling
1 / 5 (1) Dec 10, 2015
Could this effect possibly be used to increase efficiency of solar cells?
tpb
1 / 5 (1) Dec 10, 2015
Diamondoid electron emitters and quantum dot light emitters, for a thin, high efficiency video screen. LCD's because of the polarizers and color filters are incredibly inefficient. This combination should beat LCD displays for power consumption and color fidelity.
NoStrings
2 / 5 (4) Dec 10, 2015
Sad day today at phys.org. All bogus news. A locust inspired robot that could be a high school fair project, oxygen from comets - surprise, really?, rehash of phonon tunneling without a good explanation. And now this...

The doped diamond films were known for decades to emit electrons with close to 0 ionization potential. The phenomenon was seriously considered at one time for building hardened microscopic vacuum tube based computers for military uses. Specifically, EMP and radiation hardened. And WITH COLD CATHODE, no power wasted on heating one. It never picked up because no chip manufacturer found it worth their while. So, it is no new discovery. Just look at those too mugs on the photo; another scotch, fellas?

Now 3...2...1... give me a dumdass comment like all of the ones above.
Wolf358
not rated yet Dec 10, 2015
Did anyone consider it as a "free" electron collector? From the images, it has a huge surface area at the molecular level; It seems like it could extract some serious charge from a good dry breeze.
knowphiself
not rated yet Dec 28, 2015
wasn't this one of the plot ideas in the film "diamonds are forever" for use on the diamond coated satellite weapon.....
Maybe this technique could be used in the micro channel plates m.c.p's of image intensifiers for night vision... a next or last generation of intensifier tube;
before they all go digital eg such as ccd cmos and microbolometrers chip arrays... imho.

p.s merry xmas to all

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