Allis Prize Highlights the Importance of Ionized Gases to Modern Life

Although plasmas are used throughout electronics research and manufacturing today, it took decades for their industrial potential to be realized.

By Liz Boatman | April 12, 2024

Plasmas — like those found in plasma cutters — are used across industries.

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Across the universe, plasma — a gas so energetic that its electrons have been stripped from atomic nuclei — is the most common state of matter. But on Earth, plasma only occurs naturally in a few instances, like in auroras near our planet’s magnetic poles or in bolts of lightning.

Even so, a century ago, scientists weren’t quite sure what plasma was, much less whether it could have useful applications if harnessed.

Today, industrial applications of partially and completely ionized gases, like plasma, have touched many parts of our world: in the fabrication of computer chips, the purification of drinking water, the adhesion of the surface of films, and even in spacecraft thrusters.

APS recognizes advances in plasma science with the Will Allis Prize for the Study of Ionized Gases. Allis, an American theoretical physicist, “made seminal contributions to the science of ionized gases,” establishing “basic concepts that describe how these systems behave,” says Rick Gottscho, a chemist and the executive vice president of Lam Research, which specializes in advanced technologies for semiconductor manufacturing.

After becoming an APS Fellow in 1936, Allis explored the feasibility of building a nuclear fusion engine, eventually co-founding the APS Gaseous Electronics Conference, which still runs today.

Chemical engineer David B. Graves, the 2014 Allis Prize recipient and a professor at Princeton University, says Allis’ work motivated his own early research on particle-in-cell and fluid simulations of plasma. Allis’ 20th-century contributions to physicists’ understanding of electron kinetics — how electrons move in different environments — proved foundational for industrial applications of plasma, Graves says.

But Graves also notes the impact of another American physicist: Irving Langmuir, whose work predates Allis’. After contributing to the development of atomic structure theory, Langmuir discovered atomic hydrogen and applied it in a new welding process, and invented the gas-filled incandescent lamp. Langmuir was the first to call the state of matter “plasma,” which reminded him of blood plasma. His contributions are recognized today, in part, by physicists’ reliance on the Langmuir probe for characterizing electrons in plasma, says Graves.

Although Langmuir studied plasma through the 1920s, it took decades for widespread interest in its industrial applications to emerge. “The biggest single change in the 20th century was the growth of the semiconductor industry in the 1970s,” Graves says.

Following the invention of the transistor and the integrated circuit, both in the 1950s, NASA’s demands during the space race and the “calculator wars” of the 1960s and 1970s — fierce competition between companies like Texas Instruments and Hewlett-Packard — sparked rapid advances in semiconductor technology.

Today, semiconductors are ubiquitous components of modern electronics, forming the basis of modern computer chips. “As chip technology becomes even smaller and more precise, the challenges we face become greater and more complex,” says Gottscho.

Ionized gases play a key role in many steps of semiconductor manufacturing, he says — from photon production for lithography to the etching of fine-scale circuit patterns on thin films, and even treatments for smoothing surfaces.

The plasma used in semiconductor manufacturing is not like the plasma in the sun. While the temperature of solar plasma can reach 15 million degrees Celsius, the plasmas used in semiconductor manufacturing can be much closer to room temperature. For this reason, they’re known as cold or low-temperature plasmas.

This type of plasma “has different energies for the different components,” says Graves. “Electrons especially are very hot, on the order of tens of thousands of degrees, whereas neutral species and ions are close to room temperature.”

“This gives all sorts of special properties in low temperature plasmas,” he says, “and these can be leveraged in multiple applications” — even cancer therapies and the treatment of wounds.

This potential has inspired far-reaching collaborations. Beyond his basic research, Graves works with private sector companies, like Lam, to better understand the utility of plasmas in their industrial processes, including the development of electronic materials.

Collaboration like this is also what led to the creation of the Allis Prize in 1989. Gottscho played a key role in establishing the prize while he was still at Bell Labs. Another founding supporter of the prize was General Electric, the company where Langmuir first enclosed a light-emitting resistive filament in a glass tube filled with gas, to prolong the filament’s lifetime. Langmuir’s invention was the precursor to the modern incandescent light bulb.

Recent gifts from Micron Technology, Intel Corporation, and Lam Research have helped APS expand the Allis Prize from a biannual award to an annual one, offering each recipient $10,000.

Graves says there’s another good reason for these companies to support the prize: Many physics, chemistry, and engineering students ultimately pursue careers at them. Nineteen of Graves’ own former grad students or postdocs have worked for Lam Research at one point or another in their careers.

Graves says he sees a lot of opportunities for young physicists in industry, especially those who can stretch beyond their own disciplines. “Physics students need to realize that applications [of technologies] always involve many factors, not just physics,” he says. “Although physics is the essential foundational field, people must be willing to dive deeply into a new field and learn things that are not necessarily in their formal educational field.”

This can sometimes differ from a research career in a physics department, so students must set the right expectations for a job in industry.

Good things can come to those who do. “[It’s an] extraordinarily rich field, both intellectually and practically,” Graves says. “Plasma physicists can have an enormous impact on society.”

Liz Boatman is a science writer based in Minnesota.