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Less is more when measuring fragile atomic bonds
THIS WEEK
MacGregor Campbell
IF YOU want to look at individual atoms, it helps to have a powerful microscope. But for delicate situations such as a lone atom on the edge of a sheet of carbon atoms, a high-energy beam can disturb the bonds that hold such atoms in place, making them difficult to study. Now, for the first time, a low-energy beam has been used to count these bonds. In the past, beams of highenergy electrons have been used to probe individual atoms. For example, such an electron beam was used to identify single atoms of so-called “rare earth” elements that were trapped inside buckyballs, round cages made of carbon atoms. By looking at the energy spectra of the electrons that bounced back, researchers could deduce the size of the atom inside, and so identify it. Probing atoms in other situations, however, may require more delicate methods. Kazu Suenaga and Masanori Koshino at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, wanted to make measurements on carbon atoms
Liar, liar! Brain circuit predicts others’ honesty A NEURAL circuit has been identified that allows people to predict whether someone is going to lie to them. The finding could help to explain why some people become paranoid. Humans have “theory of mind” – the ability to imagine what others are thinking and learn from their social habits. “We’re trying to find a specific circuit that performs social learning,” 14 | NewScientist | 18 December 2010
clinging to the edge of a sample of graphene – a sheet of carbon atoms arranged in a hexagonal mesh. In particular, they were interested in the number of bonds holding these edge atoms in place, as this can affect the graphene sheet’s electrical and chemical properties. In principle, the energy spectra of electrons scattered off an edge atom can be used to count the bonds. The trouble is that a high-energy electron beam can also rearrange the edge atoms, changing the very property we want to measure. Suenaga and Koshino took advantage of a new electron microscope that was capable of precisely resolving the spectra of scattered electrons, even if they were of relatively low energy. Using beams of electrons with around 40 per cent less energy than those in previous studies, the pair were able to resolve the spectra of electrons scattered by individual graphene edge atoms before any disruption to the bonds occurred. They found that these spectra were consistent with those produced in simulations of dangling carbon atoms linked
says Matthew Rushworth at the University of Oxford, who presented his work at a Cell Press LabLinks conference in London on 3 December. Rushworth’s team scanned volunteers’ brains while they chose one of two boxes to win points. They were sent advice on which box to choose from a second player who was sometimes dishonest. When the volunteers suspected they were being lied to, activity levels rose in the dorsomedial prefrontal cortex (DPFC), an area near the front of the brain. If the volunteer thought the player was telling the truth the
PASIEKA/spl
Less is more when measuring atoms
–Not so sturdy at the edges–
to the sheet by either one, two or three bonds. They used this to deduce how many bonds linked the individual edge atoms in their sample to the sheet (Nature, DOI: 10.1038/nature09664). Suenaga says the technique could also be used to measure the electronic properties of onedimensional chains of carbon atoms, which could be useful in
future nanocircuits. It might also be applied to silicon solar cells to determine which atoms are generating the most current. Ondrej Krivanek of Nion, an electron microscope maker in Seattle, Washington, who was not involved in the study, calls it “a tour de force”, applying novel techniques to “a problem of great technological interest”. n
activity remained low. If their suspicions were proved wrong, the activity changed “suggesting the volunteers needed to rethink their opinion of the second player”, says Rushworth. In effect, the activity was predicting how trustworthy the advice would be, then reacting to the results of that prediction (Nature, vol 456, p 245). Failures of this system could
explain why those with schizophrenia are often paranoid, says Chris Frith of University College London, who was not involved in the study. “People with schizophrenia show false prediction errors: they keep thinking their predictions are wrong,” he says. This leads to distrust and paranoia. Rushworth is now mapping the circuit using diffusion-weighted MRI, which tracks the movement of water through the brain, to find out which areas the DPFC is linked to. This might ultimately allow the design of targeted treatments for paranoia. Michael Marshall n
“In effect, the brain activity predicted how trustworthy the incoming advice was going to be”
MacGregor Campbell
IF YOU want to look at individual atoms, it helps to have a powerful microscope. But for delicate situations such as a lone atom on the edge of a sheet of carbon atoms, a high-energy beam can disturb the bonds that hold such atoms in place, making them difficult to study. Now, for the first time, a low-energy beam has been used to count these bonds. In the past, beams of highenergy electrons have been used to probe individual atoms. For example, such an electron beam was used to identify single atoms of so-called “rare earth” elements that were trapped inside buckyballs, round cages made of carbon atoms. By looking at the energy spectra of the electrons that bounced back, researchers could deduce the size of the atom inside, and so identify it. Probing atoms in other situations, however, may require more delicate methods. Kazu Suenaga and Masanori Koshino at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, wanted to make measurements on carbon atoms
Liar, liar! Brain circuit predicts others’ honesty A NEURAL circuit has been identified that allows people to predict whether someone is going to lie to them. The finding could help to explain why some people become paranoid. Humans have “theory of mind” – the ability to imagine what others are thinking and learn from their social habits. “We’re trying to find a specific circuit that performs social learning,” 14 | NewScientist | 18 December 2010
clinging to the edge of a sample of graphene – a sheet of carbon atoms arranged in a hexagonal mesh. In particular, they were interested in the number of bonds holding these edge atoms in place, as this can affect the graphene sheet’s electrical and chemical properties. In principle, the energy spectra of electrons scattered off an edge atom can be used to count the bonds. The trouble is that a high-energy electron beam can also rearrange the edge atoms, changing the very property we want to measure. Suenaga and Koshino took advantage of a new electron microscope that was capable of precisely resolving the spectra of scattered electrons, even if they were of relatively low energy. Using beams of electrons with around 40 per cent less energy than those in previous studies, the pair were able to resolve the spectra of electrons scattered by individual graphene edge atoms before any disruption to the bonds occurred. They found that these spectra were consistent with those produced in simulations of dangling carbon atoms linked
says Matthew Rushworth at the University of Oxford, who presented his work at a Cell Press LabLinks conference in London on 3 December. Rushworth’s team scanned volunteers’ brains while they chose one of two boxes to win points. They were sent advice on which box to choose from a second player who was sometimes dishonest. When the volunteers suspected they were being lied to, activity levels rose in the dorsomedial prefrontal cortex (DPFC), an area near the front of the brain. If the volunteer thought the player was telling the truth the
PASIEKA/spl
Less is more when measuring atoms
–Not so sturdy at the edges–
to the sheet by either one, two or three bonds. They used this to deduce how many bonds linked the individual edge atoms in their sample to the sheet (Nature, DOI: 10.1038/nature09664). Suenaga says the technique could also be used to measure the electronic properties of onedimensional chains of carbon atoms, which could be useful in
future nanocircuits. It might also be applied to silicon solar cells to determine which atoms are generating the most current. Ondrej Krivanek of Nion, an electron microscope maker in Seattle, Washington, who was not involved in the study, calls it “a tour de force”, applying novel techniques to “a problem of great technological interest”. n
activity remained low. If their suspicions were proved wrong, the activity changed “suggesting the volunteers needed to rethink their opinion of the second player”, says Rushworth. In effect, the activity was predicting how trustworthy the advice would be, then reacting to the results of that prediction (Nature, vol 456, p 245). Failures of this system could
explain why those with schizophrenia are often paranoid, says Chris Frith of University College London, who was not involved in the study. “People with schizophrenia show false prediction errors: they keep thinking their predictions are wrong,” he says. This leads to distrust and paranoia. Rushworth is now mapping the circuit using diffusion-weighted MRI, which tracks the movement of water through the brain, to find out which areas the DPFC is linked to. This might ultimately allow the design of targeted treatments for paranoia. Michael Marshall n
“In effect, the brain activity predicted how trustworthy the incoming advice was going to be”