Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Manipulating and Detecting Ultrahigh Frequency Sound Waves

12.06.2014

Berkeley Lab Researchers Demonstrate Advance in Controlling Nano-scale Vibrations at 10 GHz

An advance has been achieved towards next generation ultrasonic imaging with potentially 1,000 times higher resolution than today’s medical ultrasounds. Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have demonstrated a technique for producing, detecting and controlling ultrahigh frequency sound waves at the nanometer scale.


Gold plasmonic nanostructures shaped like Swiss-crosses can convert laser light into ultrahigh frequency (10GHz) sound waves.

Through a combination of subpicosecond laser pulses and unique nanostructures, a team led by Xiang Zhang, a faculty scientist with Berkeley Lab’s Materials Sciences Division, produced acoustic phonons – quasi-particles of vibrational energy that move through an atomic lattice as sound waves – at a frequency of 10 gigahertz (10 billion cycles per second).

By comparison, medical ultrasounds today typically reach a frequency of only about 20 megahertz (20 million cycles per second.) The 10GHz phonons not only promise unprecedented resolution for acoustic imaging, they also can be used to “see” subsurface structures in nanoscale systems that optical and electron microscopes cannot.

“We have demonstrated optical coherent manipulation and detection of the acoustic phonons in nanostructures that offer new possibilities in the development of coherent phonon sources and nano-phononic devices for chemical sensing, thermal energy management and communications,” says Zhang, who also holds the Ernest S. Kuh Endowed Chair Professor at the University of California (UC) Berkeley. In addition, he directs the National Science Foundation’s Nano-scale Science and Engineering Center, and is a member of the Kavli Energy NanoSciences Institute at Berkeley.

Zhang is the corresponding author of a paper describing this research in Nature Communications. The paper is titled “Ultrafast Acousto-plasmonic Control and Sensing in Complex Nanostructures.” The lead authors are Kevin O’Brien and Norberto Daniel Lanzillotti-Kimura, members of Zhang’s research group. Other co-authors are Junsuk Rho, Haim Suchowski and Xiaobo Yin.

Acoustic imaging offers certain advantages over optical imaging. The ability of sound waves to safely pass through biological tissue has made sonograms a popular medical diagnostic tool. Sound waves have also become a valuable tool for the non-destructive testing of materials. In recent years, ultrahigh frequency sound waves have been the subject of intense scientific study. Phonons at GHz frequencies can pass through materials that are opaque to photons, the particles that carry light. Ultrahigh frequency phonons also travel at the small wavelengths that yield a sharper resolution in ultrasound imaging.

The biggest challenge has been to find effective ways of generating, detecting and controlling ultrahigh frequency sound waves. Zhang, O’Brien, Lanzillotti-Kimura and their colleagues were able to meet this challenge through the design of nanostructures that support multiple modes of both phonons and plasmons. A plasmon is a wave that rolls through the conduction electrons on the surface of a metal.

“Through the interplay between phonons and localized surface plasmons, we can detect the spatial properties of complex phonon modes below the optical wavelength,” O’Brien says. “This allows us to detect complex nanomechanical dynamics using polarization-resolved transient absorption spectroscopy.”

Plasmons can be used to confine light in subwavelength dimensions and are considered to be good candidates for manipulating nanoscale mechanical motion because of their large absorption cross-sections, subwavelength field localization, and high sensitivity to geometry and refractive index changes.

“To generate 10 GHz acoustic frequencies in our plasmonic nanostructures we use a technique known as picosecond ultrasonics,” O’Brien says. “Sub-picosecond pulses of laser light excite plasmons which dissipate their energy as heat. The nanostructure rapidly expands and generates coherent acoustic phonons. This process transduces photons from the laser into coherent phonons.”

To detect these coherent phonons, a second laser pulse is used to excite probe surface plasmons. As these plasmons move across the surface of the nanostructure, their resonance frequency shifts as the nanostructure geometry becomes distorted by the phonons. This enables the researchers to optically detect mechanical motion on the nanoscale.

“We’re able to sense ultrafast motion along the different axes of our nanostructures simply by rotating the polarization of the probe pulse,” says Lanzillotti-Kimura. “Since we’ve shown that the polarization of the pump pulse doesn’t make a difference in our nanostructures due to hot electron diffusion, we can tailor the phonon modes which are excited by designing the symmetry of the nanostructure.”

The plasmonic nanostructures that Zhang, O’Brien, Lanzillotti-Kimura and their colleagues designed are made of gold and shaped like a Swiss-cross. Each cross is 35 nanometers thick with horizontal and vertical arm lengths of 120 and 90 nanometers, respectively. When the two arms oscillate in phase, the crosses generate symmetric phonons. When the arms oscillate out of phase, anti-symmetric phonons are generated.

“The phase differences in the phonon modes produce an interference effect that allow us to distinguish between symmetric and anti-symmetric phonon modes using localized surface plasmons,” O’Brien says. “Being able to generate and detect phonon modes with different symmetries or spatial distributions in a structure improves our ability to detect nanoscale motion and is a step towards some potential applications of ultrahigh frequency acoustic phonons.”

By allowing researchers to selectively excite and detect GHz mechanical motion, the Swiss-cross design of the plasmonic nanostructures provides the control and sensing capabilities needed for ultrahigh frequency acoustic imaging. For the material sciences, the acoustic vibrations can be used as nanoscale “hammers” to impose physical strains along different axes at ultrahigh frequencies. This strain can then be detected by observing the plasmonic response. Zhang and his research group are planning to use these nanoscale hammers to generate and detect ultrafast vibrations in other systems such as two-dimensional materials.

This research was supported by the DOE Office of Science through the Energy Frontier Research Center program.


Additional Information

For more about the research of Xiang Zhang go here

Xiang Zhang can be reached for comment at: 510-643-4578.

###

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science.  For more, visit www.lbl.gov.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Lynn Yarris | Eurek Alert!
Further information:
http://newscenter.lbl.gov/2014/06/11/ultrahigh-frequency-sound-waves/

Further reports about: Energy Frequency GHz Laboratory Sound Ultrahigh acoustic energy nanoscale nanostructure sensing waves

More articles from Physics and Astronomy:

nachricht LIGO confirms RIT's breakthrough prediction of gravitational waves
12.02.2016 | Rochester Institute of Technology

nachricht Milestone in physics: gravitational waves detected with the laser system from LZH
12.02.2016 | Laser Zentrum Hannover e.V.

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: Production of an AIDS vaccine in algae

Today, plants and microorganisms are heavily used for the production of medicinal products. The production of biopharmaceuticals in plants, also referred to as “Molecular Pharming”, represents a continuously growing field of plant biotechnology. Preferred host organisms include yeast and crop plants, such as maize and potato – plants with high demands. With the help of a special algal strain, the research team of Prof. Ralph Bock at the Max Planck Institute of Molecular Plant Physiology in Potsdam strives to develop a more efficient and resource-saving system for the production of medicines and vaccines. They tested its practicality by synthesizing a component of a potential AIDS vaccine.

The use of plants and microorganisms to produce pharmaceuticals is nothing new. In 1982, bacteria were genetically modified to produce human insulin, a drug...

Im Focus: The most accurate optical single-ion clock worldwide

Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock which attains an accuracy which had only been predicted theoretically so far. Their optical ytterbium clock achieved a relative systematic measurement uncertainty of 3 E-18. The results have been published in the current issue of the scientific journal "Physical Review Letters".

Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock...

Im Focus: Goodbye ground control: autonomous nanosatellites

The University of Würzburg has two new space projects in the pipeline which are concerned with the observation of planets and autonomous fault correction aboard satellites. The German Federal Ministry of Economic Affairs and Energy funds the projects with around 1.6 million euros.

Detecting tornadoes that sweep across Mars. Discovering meteors that fall to Earth. Investigating strange lightning that flashes from Earth's atmosphere into...

Im Focus: Flow phenomena on solid surfaces: Physicists highlight key role played by boundary layer velocity

Physicists from Saarland University and the ESPCI in Paris have shown how liquids on solid surfaces can be made to slide over the surface a bit like a bobsleigh on ice. The key is to apply a coating at the boundary between the liquid and the surface that induces the liquid to slip. This results in an increase in the average flow velocity of the liquid and its throughput. This was demonstrated by studying the behaviour of droplets on surfaces with different coatings as they evolved into the equilibrium state. The results could prove useful in optimizing industrial processes, such as the extrusion of plastics.

The study has been published in the respected academic journal PNAS (Proceedings of the National Academy of Sciences of the United States of America).

Im Focus: New study: How stable is the West Antarctic Ice Sheet?

Exceeding critical temperature limits in the Southern Ocean may cause the collapse of ice sheets and a sharp rise in sea levels

A future warming of the Southern Ocean caused by rising greenhouse gas concentrations in the atmosphere may severely disrupt the stability of the West...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Symposium on Climate Change Adaptation in Africa 2016

12.02.2016 | Event News

Travel grants available: Meet the world’s most proficient mathematicians and computer scientists

09.02.2016 | Event News

AKL’16: Experience Laser Technology Live in Europe´s Largest Laser Application Center!

02.02.2016 | Event News

 
Latest News

LIGO confirms RIT's breakthrough prediction of gravitational waves

12.02.2016 | Physics and Astronomy

Gene switch may repair DNA and prevent cancer

12.02.2016 | Life Sciences

Using 'Pacemakers' in spinal cord injuries

12.02.2016 | Medical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>