Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Visualizing atomic-scale acoustic wavesin nanostructures

08.07.2008
Acoustic waves play many everyday roles - from communication between people to ultrasound imaging. Now the highest frequency acoustic waves in materials, with nearly atomic-scale wavelengths, promise to be useful probes of nanostructures such as LED lights.

However, detecting them isn't so easy.

Enter Lawrence Livermore National Laboratory scientists, who discovered a new physical phenomenon that enables them to see high frequency waves by combining molecular dynamics simulations of shock waves with an experimental diagnostic, terahertz (THz) radiation. (The hertz is the base unit of frequency. One hertz simply means one cycle per second. A terahertz is 10^12 hertz.).

The Livermore scientists performed computer simulations of the highest frequency acoustic waves forming spontaneously at the front of shock waves or generated by sub-picosecond pulse-length lasers.

They discovered that, under some circumstances, when such a wave crosses an interface between two materials, tiny electric currents are generated at the interface. These currents produce electromagnetic radiation of THz frequencies that can be detected a few millimeters away from the interface. Part of the wave is effectively converted to electromagnetic radiation, which propagates out of the material where it can be measured.

Most molecular dynamics simulations of shock waves connect to experiments through electronic properties, such as optical reflectivity.

"But this new approach connects to the much lower frequency THz radiation produced by the individual atoms moving around in the shock wave," said Evan Reed, lead author of a paper that appears in the July 7 edition of the journal, Physical Review Letters. "This kind of diagnostic promises to provide new information about shocked materials like the dynamics of crystals pushed to ultra-high strain rates."

Using molecular dynamics simulations, the team, made up of Livermore's Reed and Michael Armstrong in collaboration with Los Alamos National Laboratory colleagues shows that the time-history of the wave can be determined with potentially sub-picosecond, nearly atomic time and space resolution by measuring the electromagnetic field.

Reed and colleagues studied the effect for an interface between two thin films, which are used in LED (light-emitting diode) nanostructures, and are piezoelectric (electric currents that are generated when they are squeezed). Piezoelectric materials have been used for decades as arrival time gauges for shock-wave experiments but have been limited by electrical equipment that can only detect acoustic frequencies less than 10 gigathertz (GHz), precluding observation of the highest frequency acoustic waves. The new THz radiation technique can help improve the time resolution of such approaches.

The technique has other applications as well. It can be applied to determine the structure of many kinds of electronic devices that are constructed using thin film layered structures, such as field-effect transistors.

"The detection of high frequency acoustic waves also has been proposed for use in imaging of quantum dot nanostructures used in myriad optical devices, possibly including solar cells in the future," Reed said. "The technology is not there yet for that application, but our work represents a step closer."

Anne Stark | EurekAlert!
Further information:
http://www.llnl.gov

More articles from Physics and Astronomy:

nachricht New NASA study improves search for habitable worlds
20.10.2017 | NASA/Goddard Space Flight Center

nachricht Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Terahertz spectroscopy goes nano

20.10.2017 | Information Technology

Strange but true: Turning a material upside down can sometimes make it softer

20.10.2017 | Materials Sciences

NRL clarifies valley polarization for electronic and optoelectronic technologies

20.10.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>