Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Light triggers gold in unexpected way

03.12.2018

Rice University lab discovers mechanism to control output of a nanoscale antenna

Rice University researchers have discovered a fundamentally different form of light-matter interaction in their experiments with gold nanoparticles.


Circularly polarized light delivered at a particular angle to C-shaped gold nanoparticles produced a plasmonic response unlike any discovered before, according to Rice University researchers. When the incident-polarized light was switched from left-handed (blue) to right-handed (green) and back, the light from the plasmons switched almost completely on and off.

Credit: Link Research Group/Rice University

They weren't looking for it, but students in the lab of Rice chemist Stephan Link found that exciting the microscopic particles just right produced a near-perfect modulation of the light they scatter.

The discovery may become useful in the development of next-generation, ultrasmall optical components for computers and antennas.

A paper about the research appears in the American Chemical Society journal ACS Nano.

The work springs from the complicated interactions between light and plasmonic metal particles that absorb and scatter light extremely efficiently. Plasmons are quasiparticles, collective excitations that move in waves on the surface of some metals when excited by light.

The Rice researchers were studying pinwheel-like plasmonic structures of C-shaped gold nanoparticles to see how they responded to circularly polarized light and its rotating electric field, especially when the handedness, or the direction of rotation of the polarization, was reversed. They then decided to study individual particles.

"We stripped it back into the simplest possible system where we only had a single arm of the pinwheel, with a single incident light direction," said Lauren McCarthy, a graduate student in the Link lab. "We weren't expecting to see anything. It was a complete surprise when I put this sample on the microscope and rotated my polarization from left- to right-handed. I was like, 'Are these turning on and off?' That's not supposed to happen."

She and co-lead author Kyle Smith, a recent Rice alumnus, had to go deep to figure out why they saw this "giant modulation."

At the start, they knew shining polarized light at a particular angle onto the surface of their sample of gold nanoparticles attached to a glass substrate would create an evanescent field, an oscillating electromagnetic wave that rides the surface of the glass and traps the light like parallel mirrors, an effect known as a total internal reflection.

They also knew that circularly polarized light is composed of transverse waves. Transverse waves are perpendicular to the direction the light is moving and can be used to control the particle's visible plasmonic output. But when the light is confined, longitudinal waves also occur. Where transverse waves move up and down and side to side, longitudinal waves look something like blobs being pumped through a pipe (as illustrated by shaking a Slinky).

They discovered the plasmonic response of the C-shaped gold nanoparticles depends on the out-of-phase interactions between both transverse and longitudinal waves in the evanescent field.

For the pinwheel, the researchers found they could change the intensity of the light output by as much as 50 percent by simply changing the handedness of the circularly polarized light input, thus changing the relative phase between the transverse and longitudinal waves.

When they broke the experiment down to individual, C-shaped gold nanoparticles, they found the shape was important to the effect. Changing the handedness of the polarized input caused the particles to almost completely turn on and off.

Simulations of the effect by Rice physicist Peter Nordlander and his team confirmed the explanation for what the researchers observed.

"We knew we had an evanescent field and we knew it could be doing something different, but we didn't know exactly what," McCarthy said. "That didn't become clear to us until we got the simulations done, telling us what the light was actually exciting in the particles, and seeing that it actually matches up with what the evanescent field looks like.

"It led to our realization that this can't be explained by how light normally operates," she said. "We had to adjust our understanding of how light can interact with these sorts of structures."

The shape of the nanoparticle triggers the orientation of three dipoles (concentrations of positive and negative charge) on the particles, McCarthy said.

"The fact that the half-ring has a 100-nanometer radius of curvature means the entire structure takes up half a wavelength of light," she said. "We think that's important for exciting the dipoles in this particular orientation."

The simulations showed that reversing the incident-polarized light handedness and throwing the waves out of phase reversed the direction of the center dipole, dramatically reducing the ability of the half-ring to scatter light under one-incident handedness. The polarization of the evanescent field then explains the almost complete turning on and off effect of the C-shaped structures.

"Interestingly, we have in a way come full circle with this work," Link said. "Flat metal surfaces also support surface plasmons like nanoparticles, but they can only be excited with evanescent waves and do not scatter into the far field. Here we found that the excitation of specifically shaped nanoparticles using evanescent waves produces plasmons with scattering properties that are different from those excited with free-space light."

###

David Ruth 713-348-6327 david@rice.edu

Mike Williams 713-348-6728 mikewilliams@rice.edu

Co-authors of the paper are Rice assistant research professor Alessandro Alabastri, postdoctoral fellow Luca Bursi and alumnus Wei-Shun Chang. Link is a professor of chemistry and of electrical and computer engineering. Nordlander is a professor of physics and astronomy, of electrical and computer engineering and of materials science and nanoengineering. Link and Nordlander are members of Rice's Laboratory for Nanophotonics.

The Robert A. Welch Foundation and the National Science Foundation supported the research.

Read the abstract at https://pubs.acs.org/doi/10.1021/acsnano.8b07060.

This news release can be found online at https://news.rice.edu/2018/11/29/light-triggers-gold-in-unexpected-way/

Follow Rice News and Media Relations via Twitter @RiceUNews.

Related materials:

Link Research Group: http://slink.rice.edu

Nordlander Nanophotonics Group: http://nordlander.rice.edu

Wiess School of Natural Sciences: https://naturalsciences.rice.edu

Images for download:

https://news-network.rice.edu/news/files/2018/11/1203_POLARIZE-1-WEB-2gx76br.jpg

Rice University researchers studying the effect of light on pinwheels (left) and single C-shaped (right) gold nanoparticles have found an unknown effect on single particles. Stimulating the particles just right produced a near-perfect modulation of the light they scatter via their plasmonic response. The discovery may become useful in the development of chips for next-generation optical components for computers and antennas. (Credit: Link Research Group/Rice University)

https://news-network.rice.edu/news/files/2018/11/1203_POLARIZE-2-WEB-2f3rpn0.jpg

Circularly polarized light delivered at a particular angle to C-shaped gold nanoparticles produced a plasmonic response unlike any discovered before, according to Rice University researchers. When the incident-polarized light was switched from left-handed (blue) to right-handed (green) and back, the light from the plasmons switched almost completely on and off. (Credit: Link Research Group/Rice University)

https://news-network.rice.edu/news/files/2018/11/1203_POLARIZE-3-WEB-29pw029.jpg

As seen under the objective lens of a microscope, Rice University researchers discovered that circularly polarized light -- right-handed circularly polarized (RCP) is shown here -- had the ability to dramatically modify the plasmonic output of C-shaped gold nanoparticles. The light input triggered the modification by shifting the phase relationship of transverse and longitudinal waves in an evanescent field exciting the particle. That in turn controlled the level of plasmonic response. The letter k represents the direction of light input on the particle after it passes through a prism. (Credit: Link Research Group/Rice University)

https://news-network.rice.edu/news/files/2018/11/1203_POLARIZE-4-WEB-2222blk.jpg

Rice University graduate student Lauren McCarthy adjusts the polarizer she used to discover a fundamentally different form of light-matter interaction in experiments with gold nanoparticles. (Credit: Jeff Fitlow/Rice University)

Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,962 undergraduates and 3,027 graduate students, Rice's undergraduate student-to-faculty ratio is just under 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for lots of race/class interaction and No. 2 for quality of life by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl.com/RiceUniversityoverview.

Media Contact

David Ruth
david@rice.edu
713-348-6327

 @RiceUNews

http://news.rice.edu 

David Ruth | EurekAlert!

More articles from Physics and Astronomy:

nachricht Astronomy student discovers 17 new planets, including Earth-sized world
28.02.2020 | University of British Columbia

nachricht Explained: Why water droplets 'bounce off the walls'
27.02.2020 | University of Warwick

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: High-pressure scientists in Bayreuth discover promising material for information technology

Researchers at the University of Bayreuth have discovered an unusual material: When cooled down to two degrees Celsius, its crystal structure and electronic properties change abruptly and significantly. In this new state, the distances between iron atoms can be tailored with the help of light beams. This opens up intriguing possibilities for application in the field of information technology. The scientists have presented their discovery in the journal "Angewandte Chemie - International Edition". The new findings are the result of close cooperation with partnering facilities in Augsburg, Dresden, Hamburg, and Moscow.

The material is an unusual form of iron oxide with the formula Fe₅O₆. The researchers produced it at a pressure of 15 gigapascals in a high-pressure laboratory...

Im Focus: From China to the South Pole: Joining forces to solve the neutrino mass puzzle

Study by Mainz physicists indicates that the next generation of neutrino experiments may well find the answer to one of the most pressing issues in neutrino physics

Among the most exciting challenges in modern physics is the identification of the neutrino mass ordering. Physicists from the Cluster of Excellence PRISMA+ at...

Im Focus: Therapies without drugs

Fraunhofer researchers are investigating the potential of microimplants to stimulate nerve cells and treat chronic conditions like asthma, diabetes, or Parkinson’s disease. Find out what makes this form of treatment so appealing and which challenges the researchers still have to master.

A study by the Robert Koch Institute has found that one in four women will suffer from weak bladders at some point in their lives. Treatments of this condition...

Im Focus: A step towards controlling spin-dependent petahertz electronics by material defects

The operational speed of semiconductors in various electronic and optoelectronic devices is limited to several gigahertz (a billion oscillations per second). This constrains the upper limit of the operational speed of computing. Now researchers from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, and the Indian Institute of Technology in Bombay have explained how these processes can be sped up through the use of light waves and defected solid materials.

Light waves perform several hundred trillion oscillations per second. Hence, it is natural to envision employing light oscillations to drive the electronic...

Im Focus: Freiburg researcher investigate the origins of surface texture

Most natural and artificial surfaces are rough: metals and even glasses that appear smooth to the naked eye can look like jagged mountain ranges under the microscope. There is currently no uniform theory about the origin of this roughness despite it being observed on all scales, from the atomic to the tectonic. Scientists suspect that the rough surface is formed by irreversible plastic deformation that occurs in many processes of mechanical machining of components such as milling.

Prof. Dr. Lars Pastewka from the Simulation group at the Department of Microsystems Engineering at the University of Freiburg and his team have simulated such...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

70th Lindau Nobel Laureate Meeting: Around 70 Laureates set to meet with young scientists from approx. 100 countries

12.02.2020 | Event News

11th Advanced Battery Power Conference, March 24-25, 2020 in Münster/Germany

16.01.2020 | Event News

Laser Colloquium Hydrogen LKH2: fast and reliable fuel cell manufacturing

15.01.2020 | Event News

 
Latest News

New molten metal hybrid filters from TU Freiberg will make components even safer and more resistant in the future

28.02.2020 | Materials Sciences

Polymers get caught up in love-hate chemistry of oil and water

28.02.2020 | Life Sciences

Two NE tree species can be used in new sustainable building material

28.02.2020 | Architecture and Construction

VideoLinks
Science & Research
Overview of more VideoLinks >>>