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 A better way to weigh millions of solitary stars
15.12.2017 | Vanderbilt University

nachricht A chip for environmental and health monitoring
15.12.2017 | Friedrich-Alexander-Universität Erlangen-Nürnberg

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: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Engineers program tiny robots to move, think like insects

15.12.2017 | Power and Electrical Engineering

One in 5 materials chemistry papers may be wrong, study suggests

15.12.2017 | Materials Sciences

New antbird species discovered in Peru by LSU ornithologists

15.12.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>