Nanoswitches Toggled by Light

Microscopic fissures in a tiny crystal open and close—on command. Researchers led by Ahmed H. Zewail successfully used ultrafast electron microscopy (UEM) to observe nanoscopic structures at their “exercises”, as they report in the journal Angewandte Chemie. Such switchable nanochannels could be useful for future nanoelectronics and nanoscopic “machines”.

Zewail and his team at the California Institute of Technology (Pasadena, USA) are renowned for their work in ultrafast science and technology. Zewail received the Nobel Prize in Chemistry in 1999 for the development of ultrafast laser techniques that are capable of revealing the motions of individual atoms within a molecule during a reaction.

The most recent development to spring from Zewail’s Laboratory is ultrafast electron microscopy. This technique is a combination of a femtosecond optical system (a femtosecond equals 10-15 seconds) with a high-resolution electron microscope; the result is a new tool with extremely high resolution in time as well as in space.

Zewail and his team have now discovered that needle-shaped microcrystals of copper and the organic compound TCNQ (7,7,8,8-tetracyanoquinodimethane, C12H4N4 ), a crystalline, quasi-one-dimensional semiconductor, exhibit optomechanical phenomena that could be of use in nanoelectronic applications.

The investigation showed that these crystals stretch out to become longer (but not wider) when they are irradiated with laser pulses in the microscope. If the irradiation is switched off, they contract back to their original size. This effect was most obvious when one of these needles was broken by the shock of a short, strong laser pulse: A small crack of some ten to one hundred nanometers forms at the break. When the crystal is stretched out under irradiation, the nanoscale channel closes up; upon contraction, it reappears. The phenomenon is reversible, as confirmed by UEM.

Why do these micromaterials stretch under light? Within the crystal, the negatively charged TCNQ ions are arranged so that their central, flat, six-membered rings are piled up on top of each other in the long direction of the needle. The energy of a laser pulse excites electrons; part of this energy is transferred, resulting in uncharged TCNQ molecules. For the uncharged TCNQ, the stacked arrangement is no longer favorable, they now require more space and cause the crystal to grow longer. The degree of stretching depends on the strength of the energy absorbed.

“Our fundamental in situ UEM observations, which reveal the behavior of nanoscopic matter in space and time, opens up new areas to explore, especially in materials science, nanotechnology, and biology,” says Zewail.

Citation: Ahmed H. Zewail, Controlled Nanoscale Mechanical Phenomena Discovered with Ultrafast Electron Microscopy, Angewandte Chemie International Edition 2007, 46, No. 48, 9206–9210, doi: 10.1002/anie.200704147

Source: Angewandte Chemie

Related stories:

Fast quantum computer building block created
(PhysOrg.com) -- The fastest quantum computer bit that exploits the main advantage of the qubit over the conventional bit has been demonstrated by researchers at University of Michigan, U.S. Naval Research Laboratory and the University of California at San Diego.
FLASH Imaging Redux: Nano-Cinema is Born
Flash imaging of nanoscale objects undergoing ultrafast changes is now a technical possibility, according to a recent paper published in the June 22 edition of Nature Photonics. The results are a direct precursor to research that will be conducted using SLAC’s Linac Coherent Light Source (LCLS).
A look into the nanoscale
Lawrence Livermore National Laboratory researchers have captured time-series snapshots of a solid as it evolves on the ultra-fast timescale.

Ultrafast look into atoms and molecules
New record in ultrafast metrology: Physicists at Max-Planck Institute of Quantum Optics and the Ludwig-Maximilians-University Munich are the first to produce light pulses lasting only 80 attoseconds.

The Photonic Beetle: Nature Builds Diamond-Like Crystals For Future Optical Computers
Researchers have been unable to build an ideal “photonic crystal” to manipulate visible light, impeding the dream of ultrafast optical computers. But now, University of Utah chemists have discovered that nature already has designed photonic crystals with the ideal, diamond-like structure: They are found in the shimmering, iridescent green scales of a beetle from Brazil.
Ultrafast electron microscopy reveals switchable nanochannels in materials
Microscopic fissures in a tiny crystal open and close—on command. Researchers led by Ahmed H. Zewail successfully used ultrafast electron microscopy (UEM) to observe nanoscopic structures at their “exercises”, as they report in the journal Angewandte Chemie. Such switchable nanochannels could be useful for future nanoelectronics and nanoscopic “machines”.
Michigan laser beam believed to set record for intensity
If you could hold a giant magnifying glass in space and focus all the sunlight shining toward Earth onto one grain of sand, that concentrated ray would approach the intensity of a new laser beam made in a University of Michigan laboratory.
World's only ultrafast electron microscope takes 4-D 'movies' of molecules
A unique electron microscope that can help create four-dimensional “movies” of molecules may hold the answers to research questions in a number of fields including chemistry, biology, and physics, according to an article scheduled for the Dec. 24 issue of Chemical & Engineering News, ACS’ weekly newsmagazine.

News discussion:

Nanotechnology news