A gem of a laboratory will develop next generation diamond sensors and bring the world of quantum physics to light
Newswise – The novel design for a next-generation diamond sensor with capabilities ranging from magnetic resonance imaging (MRI) of individual molecules to the detection of slight anomalies in the earth’s magnetic field to guide aircraft that do not have access to global positioning systems (GPS) by a collaboration of scientists led by the US Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL).
At the head of the collaboration to develop a new quantum sensor is David Graves, Associate Laboratory Director for Low Temperature Plasma Surface Interactions at PPPL, who works closely with co-designer Nathalie. de Leon from Princeton University, a renowned expert in quantum hardware, and the physicist Alastair Stacey from the Royal Melbourne Institute of Technology (RMIT) in Australia will work together.
The award was one of 10 critically reviewed DOE microelectronics grants for national laboratories. “Microelectronics is key to tomorrow’s technologies,” said Energy Secretary Jennifer M. Granholm, “and with the DOE’s world-class scientists at the helm, they can help bring our clean energy future to life and keep America one step ahead to be “our economic competitors.”
The award brings PPPL, traditionally a fusion-focused research laboratory, completely into the often bizarre world of quantum physics. “This is the beginning of an entirely new activity for the laboratory that will make us a leader in the use of plasma to make diamond to enhance sensors,” said Steve Cowley, director of PPPL. “It’s also a wonderful example of how the lab, led by David Graves, works with Princeton University and Professor Nathalie de Leon and physicist Alastair Stacey in Melbourne.”
The development of diamond sensors requires the synthesis of designer diamond material that begins with a diamond seed that is built up through the gradual deposition of plasma-enhanced vapor. The trick is to replace carbon atoms in the growing material with nitrogen atoms and vacancies – a combination called NV centers in diamonds. This combination creates the sensor and is commonly referred to as the color center because it glows red when a light shines on it.
Difficult material design
The tricky material design requires the extremely careful doping or implantation of nitrogen atoms along with the creation of voids in the color center. The doping is done with microwave reactors that generate the plasma-enhanced vapors that enlarge the diamond. These reactors are somewhat similar to the microwave ovens used in households, but they are modified to ignite plasmas. “Such reactors are very delicate and peculiar,” said Graves. “You have to get the process just right for doping to work.” =
The PPPL project will follow the path proposed by Stacey from Australia’s RMIT, who stated that increasing the number of simultaneously addressed color centers will make the sensor more sensitive. However, the traditional method of doing this by increasing the density of the centers results in defects in the diamond which degrade the properties of the color centers and thus limit sensor improvement. To avoid this problem, he suggested adding the innovative step of co-doping the diamond with phosphorus plasma to increase the density without electrical interference.
The plasma must be carefully controlled in order to successfully introduce both dopants, and this requires significant advances in plasma physics and chemistry. Key plasma researchers include PPPL physicists Yevgeny Raitses and Igor Kaganovich, heads of the PPPL Plasma Nanosynthesis Laboratory, who will study plasma used in the synthesis of diamond sensors. Plasma, the fourth physical state that makes up 99 percent of the visible universe, consists of free electrons and atomic nuclei or ions.
Plasmas at room temperature
Kaganovich and his team will model the plasmas at room temperature and perform quantum chemical calculations of diamond growth, while Raitses will use state-of-the-art diagnostics to measure the chemical species or substances in the plasma. The plasma studies help in choosing the synthesis conditions. The low-temperature or cold plasmas examined are comparable to the million-degree fusion plasmas that have been the hallmark of PPPL research.
“The basic idea is to combine plasma science with modeling the surface chemistry of the plasma and conducting experiments to grow the diamond,” said Graves. “We also want to understand the science behind how to build and operate a plasma reactor in order to obtain this highly specialized and defect-free material for useful quantum sensors.”
The plan is to purchase two commercial reactors to jointly dope the diamond at PPPL: one for light phosphorus doping and one for heavy phosphorus doping. The combination will allow for a range of doping concentrations, Graves said.
The development process brings all employees together. The Princetons de Leon group will carry out measurements that include the so-called coherence properties of the diamond’s color centers. Such properties relate to the length of time in which electrons in the color center rotate in quantum superposition or simultaneously up and down in order to activate the sensor.
“Close cooperation between diamond synthesis, plasma modeling and quantum measurement will enable a new dimension in quantum sensors,” said de Leon. “These research areas are usually completely separate research communities, and I am excited to see what we can achieve together.”
In the meantime, Stacey will conduct measurements of the doping properties and growth of the diamond crystal, starting with the seed crystal. “The seed is a piece of existing high-purity single crystal diamond,” said Stacey. “We often add just a tiny bit of new diamond, just like a new layer on the surface, but that new layer has precisely engineered properties [such as doping agents and increased densities] which did not have the original seed. “
Graves points out the importance of the project for PPPL. “It’s a big step,” he said. “It’s our first competition [quantum] Proposal. It’s a pretty big deal for PPPL to be awarded a grant in an area like this that is so different from our traditional research, and I think it’s symbolically important. “
PPPL, located on Princeton University’s Forrestal campus in Plainsboro, NJ, is dedicated to discovering new insights into the physics of plasmas – ultra-hot, charged gases – and developing practical solutions for generating fusion energy. The laboratory is administered by the University for the US Department of Energy’s Office of Science, which is the United States’ single largest contributor to basic research in the physical sciences and works to address some of the most pressing challenges of our time. More information is available at energy.gov/science(Link is external).