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Manipulate atoms one by one with an electron beam

A new method can be useful for building quantum sensors and computers.

This diagram illustrates the controlled switching of phosphorus atom positions in a graphite layer using an electron beam, as shown by the research team.

This diagram illustrates the controlled switching of phosphorus atom positions in a graphite layer using an electron beam, as shown by the research team.

Researchers' politeness

The ultimate degree of engineering control would be the ability to create and manipulate materials at the most basic level by producing devices that are atoms with accurate control.

Now, scientists from MIT, Vienna University and several other institutions have taken a step in this direction by developing a method that can move atoms with a high focused electron beam and control their precise location and connection orientation. This discovery may eventually lead to new ways of creating quantum computing devices or sensors and introduce a new era of "atomic engineering," they say.

The advance was described today in the Science Advances journal in an article by MIT Professor of Nuclear Science and Engineering, Ju Li, Associate Professor Cong Su, Professor Tomas Susi from the University of Vienna and 13 others at MIT, University of Vienna, Oak Ridge National Laboratory China, Ecuador and Denmark.

"We use many nanotechnology tools," explains Li, who has a joint assignment in the field of materials science and engineering. But in the new study these tools are used to control processes that are still of lesser order. "The goal is to control one to several hundred atoms, control their positions, control their charging state, and control their electronic and nuclear spin states," he says.

While others have previously manipulated the positions of the individual atoms, even by creating a pure circle of atoms on the surface, this process involved collecting individual atoms on the needle tip of a scanning tunnel microscope, and then put them in place relatively slowly. mechanical process. The new process manipulates atoms using a relativistic electron beam in a scanning transmission electron microscope (STEM) so it can be electronically controlled electronically by magnetic lenses and does not require mechanical moving parts. This makes the process potentially much faster and can thus lead to practical applications.

Using electronic controls and artificial intelligence, "we think we can ultimately manipulate the atoms in microseconds," Li said. "It's much faster than we can manipulate them with mechanical probes. Also, it should be possible to have many electron beams working simultaneously on the same material. "

"This is an exciting new paradigm for manipulating the atom," says Susie.

Computer chips are typically made by "doping" a silicone crystal with other atoms needed to impart specific electrical properties, thus creating "defects" in the material – areas that do not retain the perfectly ordered crystal structure of silicon. But this process is scattered, Li explains, so there is no way to control the atomic precision where these atoms are going. The new system enables accurate positioning, he says.

The same electron beam can be used to break an atom from one position to another, and then "read" the new position to see if the atom has ended where it was intended, says Li. While positioning is determined largely by probabilities and not 100% accurate, the ability to determine the actual position makes it possible to choose only those who have completed the correct configuration.

Atomic Football

The force of a very focused electron beam, as wide as an atom, ejects the atom from its position, and by selecting the right angle of the beam, the researchers can determine where it will most likely end. "We want to use the beam to kill the atoms and essentially to play atomic football," the arthritic atoms say in the graphene field.

"Like football, it's not deterministic, but you can control probabilities," he says. – Like football, you always try to move on to the goal.

In team experiments, they mostly use phosphorus atoms, a commonly used additive, in a sheet of graphite, two-dimensional sheet of carbon atoms arranged in honeycomb. Phosphorous atoms ultimately replace the carbon atoms in parts of this pattern, thus changing the electronic, optical and other properties of the material in a way that can be predicted if the positions of these atoms are known.

Ultimately, the goal is to move multiple atoms in complex ways. "We hope to use the electron beam to move these supplements so we can make a pyramid or a defective complex where we can determine exactly where each atom sits," Li said.

This is the first time that different electron additive atoms have been manipulated in graphene. "Although we have previously worked with silicon impurities, phosphorus is potentially more interesting because of its electrical and magnetic properties, but as we have now found, it also behaves in a surprisingly different way. Every item can have new surprises and opportunities, "Susie adds.

The system requires precise beam and energy angle control. "Sometimes we have unwanted results if we are not careful," he says. For example, sometimes a carbon atom that was meant to remain in the "just leave" position, and sometimes the phosphor atom is locked in a position in the grid and "then, no matter how we change the angle of the beam, we can not influence its position. We have to find another ball. "

Theoretical framework

In addition to detailed experimental testing and observation of the effects of different angles and positions of rays and graphene, the team also developed a theoretical basis for predicting the effects, called primary cosmic formalism, which tracks the inertia of "football". "We did these experiments and give a theoretical framework on how to control this process," Li said.

The cascade of effects that originates from the original beam is carried out in multiple time scales, Li says, making observations and analyzes difficult to implement. The actual initial collision of the relativistic electron (moving about 45% of the light velocity) by atom is performed on a scale of zeptosenses – trillion parts of one billionth of a second – but the resulting motion and collisions of atoms in the lattice unfold in time scales from picoseconds or longer – billions of times longer.

Supplementary atoms, such as phosphorus, have non-zero nuclear spin which is a key property required for quantum-based devices because this spin state is easily influenced by elements in its environment such as magnetic fields. So the ability to position these atoms precisely in terms of position and relationship can be a key step in developing quantum processing information or reporting devices, Li said.

"This is an important advance in this area," said Alex Zettle, a professor of physics at the University of California at Berkeley who was not involved in this study. "The impinging atoms and defects in the crystal lattice are at the heart of the electronics industry. As solidifiers become smaller, up to the scale of the nanometer size, it becomes increasingly important to know exactly where an improper atom or defect is and what its atomic environment is. An extremely challenging goal is to have a scalable method for controlled manipulation or placement of individual atoms in the desired locations, as well as to accurately predict the effect this placement will have on the operation of the device. "

Zettl says that these researchers "have made significant progress towards this goal. They use a moderately energy-directed electron beam to force the desired rearrangement of the atoms, and observe in real-time, on a nuclear scale, what they are doing. The elegant theoretical treatise with impressive predictive power complements the experiments.

Besides MIT's lead team, international cooperation included researchers from the University of Vienna, University of the Chinese Academy of Sciences, Aarhus University in Denmark, Ecuador National Polytechnic School, Oak Ridge National Laboratory, and Sichuan University in China. The work was supported by the National Science Foundation, the American Army for Research through the MIT Institute of Nanotechnology, the Austrian Science Fund, the European Research Council, the Danish Independent Research Council, the Chinese Academy of Sciences, and the US Department of Energy.

/ University Edition. See all here.

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