Essentially, they say, the tool is an electron version of the laser "optical tweezers" that have become a standard tool in biology, physics and chemistry for manipulating tiny particles. Except that electron beams could offer a thousand-fold improvement in sensitivity and resolution.
Optical tweezers were first described in 1986 by a research team at Bell Labs. The general idea is that under the right conditions, a tightly focused laser beam will exert a small but useful force on tiny particles. Not pushing them away, which you might expect, but rather drawing them towards the center of the beam. Biochemists, for example, routinely use the effect to manipulate individual cells or liposomes under a microscope.
If you just consider the physics, says NIST metallurgist Vladimir Oleshko, you might expect that a beam of focused electrons—such as that created by a transmission electron microscope (TEM)—could do the same thing. However that's never been seen, in part because electrons are much fussier to work with. They can't penetrate far through air, for example, so electron microscopes use vacuum chambers to hold specimens.
So Oleshko and his colleague, UVA materials scientist James Howe, were surprised when, in the course of another experiment, they found themselves watching an electron tweezer at work. They were using an electron microscope to study, in detail, what happens when a metal alloy melts or freezes. They were observing a small particle—a few hundred microns wide—of an aluminum-silicon alloy held just at a transition point where it was partially molten, a liquid shell surrounding a core of still solid metal. In such a small sample, the electron beam can excite plasmons, a kind of quantized wave in the alloy's electrons, that reveals a lot about what happens at the liquid-solid boundary of a crystallizing metal. "Scientifically, it's interesting to see how the electrons behave," says Howe, "but from a technological point of view, you can make better metals if you understand, in detail, how they go from liquid to solid."
"This effect of electron tweezers was unexpected because the general purpose of this experiment was to study melting and crystallization," Oleshko explains. "We can generate this sphere inside the liquid shell easily; you can tell from the image that it's still crystalline. But we saw that when we move or tilt the beam—or move the microscope stage under the beam—the solid particle follows it, like it was glued to the beam."
Potentially, Oleshko says, electron tweezers could be a versatile and valuable tool, adding very fine manipulation to wide and growing lists of uses for electron microscopy in materials science.** "Of course, this is challenging because it requires a vacuum," he says, "but electron probes can be very fine, three orders of magnitude smaller than photon beams—close to the size of single atoms. We could manipulate very small quantities, even single atoms, in a very precise way."
See video clip of effect at http://youtu.be/x1IMruGk8e0
* V.P. Oleshko and J.M. Howe. Are electron tweezers possible? Ultramicroscopy (2011) doi:10.1016/j.ultramic.2011.08.015.
** See, for example, the Jan. 19, 2011, Tech Beat story "NIST Puts a New Twist on the Electron Beam" at www.nist.gov/public_affairs/tech-beat/tb20110119.cfm#tem
Michael Baum | EurekAlert!
Magnetic tuning at the nanoscale
13.11.2019 | Helmholtz-Zentrum Dresden-Rossendorf
At future Mars landing spot, scientists spy mineral that could preserve signs of past life
13.11.2019 | Brown University
Carbon nanotubes (CNTs) are valuable for a wide variety of applications. Made of graphene sheets rolled into tubes 10,000 times smaller than a human hair, CNTs have an exceptional strength-to-mass ratio and excellent thermal and electrical properties. These features make them ideal for a range of applications, including supercapacitors, interconnects, adhesives, particle trapping and structural color.
New research reveals even more potential for CNTs: as a coating, they can both repel and hold water in place, a useful property for applications like printing,...
If you've ever tried to put several really strong, small cube magnets right next to each other on a magnetic board, you'll know that you just can't do it. What happens is that the magnets always arrange themselves in a column sticking out vertically from the magnetic board. Moreover, it's almost impossible to join several rows of these magnets together to form a flat surface. That's because magnets are dipolar. Equal poles repel each other, with the north pole of one magnet always attaching itself to the south pole of another and vice versa. This explains why they form a column with all the magnets aligned the same way.
Now, scientists at ETH Zurich have managed to create magnetic building blocks in the shape of cubes that - for the first time ever - can be joined together to...
Quantum-based communication and computation technologies promise unprecedented applications, such as unconditionally secure communications, ultra-precise...
In two experiments performed at the free-electron laser FLASH in Hamburg a cooperation led by physicists from the Heidelberg Max Planck Institute for Nuclear physics (MPIK) demonstrated strongly-driven nonlinear interaction of ultrashort extreme-ultraviolet (XUV) laser pulses with atoms and ions. The powerful excitation of an electron pair in helium was found to compete with the ultrafast decay, which temporarily may even lead to population inversion. Resonant transitions in doubly charged neon ions were shifted in energy, and observed by XUV-XUV pump-probe transient absorption spectroscopy.
An international team led by physicists from the MPIK reports on new results for efficient two-electron excitations in helium driven by strong and ultrashort...
An international research group has observed new quantum properties on an artificial giant atom and has now published its results in the high-ranking journal Nature Physics. The quantum system under investigation apparently has a memory - a new finding that could be used to build a quantum computer.
The research group, consisting of German, Swedish and Indian scientists, has investigated an artificial quantum system and found new properties.
05.11.2019 | Event News
30.10.2019 | Event News
02.10.2019 | Event News
13.11.2019 | Physics and Astronomy
13.11.2019 | Physics and Astronomy
13.11.2019 | Materials Sciences