Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Ultrafast sonograms shed new light on rapid phase transitions

09.03.2012
An international team of physicists has developed a method for taking ultrafast ‘sonograms’ that can track the structural changes that take place within solid materials in trillionth-of-a-second intervals as they go through an important physical process called a phase transition.

Common phase transitions include the melting of candle wax before it burns and dissolving sugar in water. They are purely structural changes that produce dramatic changes in a material’s physical properties and they play a critical role both in nature and in industrial processes ranging from steel making to chip fabrication.

The researchers have applied thismethod to shed new light on the manner in which vanadium dioxide, the material that undergoes the fastest phase transition known, shifts between its transparent and reflective phases.

Many of these transitions, like that in vanadium dioxide, take place so rapidly that scientists have had difficulty catching them in the act. “This means that there is a lot that we still don’t know about the dynamics of these critical processes,” said Professor of Physics Richard Haglund, who directed the team of Vanderbilt researchers who were involved.

To build a more complete picture of this phenomenon in vanadium dioxide (VO2), one of the most unusual phase-change materials known, Vanderbilt researchers collaborated with physicists at the Fritz Haber Institute of the Max Planck Society in Berlin, who have developed the powerful new technique for obtaining a more complete picture of ultrafast phase changes. Details of the method, which can track the structural changes that take place within materials at intervals of less than a trillionth of a second, are reported in the Mar. 6 issue of the journal Nature Communications.

Vanadium dioxide shifts from a transparent, semiconducting phase to a reflective, metallic phase in the time it takes a beam of light to travel a tenth of a millimeter. This phase change can be caused by heating the material above 150 degrees Fahrenheit (65 degrees Celsius) or by hitting it with a pulse of laser light.

VO2 is one of a class of materials now being considered for use in faster computer memory. When mixed with suitable additives, it makes a window coating that blocks infrared transmission on hot days and reduces heat loss during cool periods. In addition, it has potential applications in optical shutters, sensors and cameras.

“With this new technique, we were able to see a lot of details that we’ve never seen before,” said Haglund. These details include how the electrons in the material rearrange first and then are followed by the movement of the much more massive atoms as the material shifts from its semiconductor to metallic-phase orientation. These details provide new information that can be used to design high-speed optical switches using this unique material.

The new method is a variation on a standard method known as ‘pump-and-probe.’ It uses an infrared laser that can produce powerful pulses of light that only last for femtoseconds (millionths of a trillionth of a second). When these pump pulses strike the surface of thetarget material, they generate high-frequency atomic vibrations determined by the material’s composition and phase. These vibrations change during a phase transition so they can be used to identify and track the transition in time.

At the same time, the physicists split off a small fraction of the infrared beam (the probe), convert it into white light and use it to illuminate the surface of the target. It turns out that these lattice vibrations produce changes in the material’s surface reflectivity. As a result, the physicists can track what is happening inside the material by mapping the changes taking place on its surface.

The situation is analogous to hitting a gong with thousands of tiny microscopic hammers. The sound each hammer makes depends on the composition and arrangement of the atoms in the part of the gong where it hits. If the composition and arrangement of the atoms changes in one of these areas, then the sound the hammer makes also changes.

“The real power of this technique is that it is sensitive to atomic changes inside the material which are usually observed using expensive large-scale X-ray sources. Now we can do the experiment optically and in the lab on a tabletop,” said Simon Wall, an Alexander von Humbolt fellow at the Fritz Haber Institute.

Vanderbilt graduate students Kannatassen Appavoo and Joyeeta Nag fabricated and characterized the vanadium dioxide thin films; Simon Wall, Daniel Wegkamp, Laura Foglia, Julia Stähler and Martin Wolf at the Fritz Haber Institute directed the laser experiments and subsequent data analysis.

The project was funded by grants from the Alexander von Humboldt Foundation and the National Science Foundation.

Visit Research News @ Vanderbilt for more research news from Vanderbilt University.

David F. Salisbury | Vanderbilt University
Further information:
http://www.vanderbilt.edu

More articles from Physics and Astronomy:

nachricht SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University

nachricht Molecule flash mob
19.01.2017 | Technische Universität Wien

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: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>