Light triggers gold in unexpected way

November 30, 2018, Rice University
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

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

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 to see how they responded to circularly polarized light and its rotating , 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."

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

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 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.

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

When they broke the experiment down to individual, C-shaped , 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.

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
"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 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 ."

Explore further: A new twist in the properties of light

More information: Kyle W. Smith et al, Exploiting Evanescent Field Polarization for Giant Chiroptical Modulation from Achiral Gold Half-Rings, ACS Nano (2018). DOI: 10.1021/acsnano.8b07060

Related Stories

A new twist in the properties of light

April 25, 2014

Light has some well-established dynamical properties that have defined our understanding of electromagnetic radiation for over a century. Two of the most fundamental of these properties are that photons of light carry momentum ...

Twisted crystals point way toward active optical materials

September 29, 2011

(PhysOrg.com) -- A nanoscale game of "now you see it, now you don't" may contribute to the creation of metamaterials with useful optical properties that can be actively controlled, according to scientists at Rice University.

Recommended for you

Engineers produce smallest 3-D transistor yet

December 10, 2018

Researchers from MIT and the University of Colorado have fabricated a 3-D transistor that's less than half the size of today's smallest commercial models. To do so, they developed a novel microfabrication technique that modifies ...

New traffic rules in 'Graphene City'

December 6, 2018

In the drive to find new ways to extend electronics beyond the use of silicon, physicists are experimenting with other properties of electrons, beyond charge. In work published today (Dec 7) in the journal Science, a team ...

Artificial synapses made from nanowires

December 6, 2018

Scientists from Jülich together with colleagues from Aachen and Turin have produced a memristive element made from nanowires that functions in much the same way as a biological nerve cell. The component is able to save and ...

26 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Nik_2213
5 / 5 (2) Nov 30, 2018
Is this curious effect limited to gold, with its anomalous colour and related properties due to relativistic modification by high nuclear mass, or do more 'ordinary' metal nano-particles behave likewise ?
Jeffhans1
5 / 5 (2) Nov 30, 2018
Sounds like they are figuring out some of the tricks that let mantis shrimp see light in ways we couldn't imagine until now. I doubt the shrimp use gold nanoparticles in their eyes, so another structure must do something similar.
antialias_physorg
5 / 5 (6) Nov 30, 2018
s this curious effect limited to gold

No. Gold is just used because it doesn't react with anything much - so you can get pristine structures and don't have to worry about oxidized surfaces or the like screwing up your experiments. Theoretically you should be able to get the same effect with any electrical conductor.

due to relativistic modification by high nuclear mass

The nuclear mass doesn't do anything in terms of "relativistiv modification" (whatever that is supposed to mean). The color of gold is due to a relativistic effect - but that effect happens due to the orbitals of the electrons (more specifically electrons orbiting so fast that they exhibit relativistic contraction and absorb a slightly different color than other metals do...though 'orbiting fast' is a bit iffy due to it being more of a electron-probability cloud. It's complicated. )
rrwillsj
1.7 / 5 (3) Nov 30, 2018
Me? If I was working in that laboratory during this research? I'd bet the effectiveness of their techniques would be dependent on much of the gold "accidentally" fell into my pockets!
Anonym133065
1 / 5 (2) Dec 01, 2018
So maybe the Great Pyramid of Giza had the golden tip to function as a switchable beacon.. Anyway very interesting findings!
rrwillsj
5 / 5 (1) Dec 01, 2018
I despair that annoyingmousie was able to come up with a comment about this article , even more stupid than mine!
Captain Stumpy
3.7 / 5 (3) Dec 01, 2018
So maybe the Great Pyramid of Giza had the golden tip to function as a switchable beacon..
dafuq?
meerling
not rated yet Dec 03, 2018
"... the gold 'accidentally' fell into my pockets... "

If you combined all the gold in that lab, I wouldn't be surprised if it was less than $40 worth.
They are working with nanoparticles after all.
antialias_physorg
5 / 5 (1) Dec 03, 2018
There's stuff in any lab that is worth a LOT more than its weight in gold. But don't worry. All that stuff is quite safe.
Scientist don't care about money. Do you honestly think they'd remain scientists with the low pay and atrocious working hours instead of getting a well paid job in the private sector for long if they were in it for the money? When's the last time you've seen a scientist (even the most senior ones) drive around in a Ferrari and park it in front of their lush mansions?
Anonym133065
not rated yet Dec 03, 2018

I despair that annoyingmousie was able to come up with a comment about this article , even more stupid than mine!


Refering to a finding from July this year from July 31, 2018 by Anastasia Komarova, ITMO University which was also published on phys.org. Look it up at www,phys.org/news/2018-07-reveals-great-pyramid-giza-focus.html. My assumption sounds well like dafuq but moreover both findings let arise new questions when combined

Captain Stumpy
not rated yet Dec 03, 2018
@anon133065
Refering to a finding from July this year
erm... but even considering that article or paper, what dafuq would sheep/goat herders and farmers be using "a switchable beacon" for?

it may be a functional land-nav reference, but it's limited in size and to visibility conditions, so it's not going to work well considering the aforementioned article and Komarova study as the culture and technology of the time didn't utilise the EM in any way, excepting visible light from fires - and that is assuming the aforementioned singular study is validated
Steelwolf
not rated yet Dec 03, 2018
Anon, there are plenty of people here that have an automatic knee-jerk reaction at the very mention of some topics, pyramids and the science of them (which modern scientists tell you they plainly do not know what pyramids do or were for, since tombs appears to be outside their actual primary function.)

https://m.phys.org/news/2018-07-reveals-great-pyramid-giza-focus.html

The fact that we Don't Know, along with earlier wild ideas, to some people is going to come across as automatic 'woo', and so they make fun of it an anything they can connect to it out of their OWN conspiracy theories or notions, rather than what You may be pointing out. They are diligent with their strawmen as well as ignoring the plain meanings of the proofs you DO find, they will find Some way to troll you even if you are absolutely, 100% correct, their minds have closed on certain subjects and they consider any such science to answer these questions as Woo, and thus not worth their time. But trolling is.
Anonym133065
not rated yet Dec 03, 2018
That's why I was really looking forward to the reactions. It was my first comment in an Scientific Forum. But I already expected such kind of answers. Just listen to mainstream archaeology and they will tell you that the Pyramids of Giza are fully researched although Projects like ScanPyramids revealed through Thermograpghy and Myon Measurements that there are several hidden chambers. The copper wires from the King Chamber were probably connected to the (golden) tip.
Captain Stumpy
not rated yet Dec 03, 2018
@anon133065
That's why I was really looking forward to the reactions
so, you were intentionally trolling, like steel et al

gotcha

.

@steel
to some people is going to come across as automatic 'woo
no
the woo, in this case, was a nonsensical assumption that golden tip on the pyramid was "a switchable beacon" when there is absolutely no empirical evidence to suggest anything

moreover, it's not logical to assume that a primitive society sans the ability to manipulate the EM spectrum is using the aforementioned pyramid to manipulate the spectrum as a beacon
their minds have closed on certain subjects
not if there is evidence

just because you believe it to be true doesn't mean it is
and repeating your lie doesn't make it truer

Steelwolf
not rated yet Dec 03, 2018
Ahh, the ASSumption that it was a primitive society that built the pyramids. What has been found and shown, beyond any doubt, is that the stone cutting tools used by the primitives that found the original pyramid and the solid stone sarcophagi, and added cruder work decorations to what they found, and claimed it as their own. The original stonework in in excess of 12-14k years ago, or more.

Astro-archaeology, using the stars movement to chart back to what the sky Would have been when the Sphinx was built was in the age of Leo, and it lines up properly with the constellation Leo along the causeway, and the 90 degree line to that, lined up by the pyramids themselves, are the belt stars in the constellation of Orion. So they left the date of their building in the siting of the whole set of buildings.

I dont know about gold tip, I do consider them a lasting info repository, to pass on word of catastrophe from sky in the form of meteor and cometary impacts, which HAPPENS.
Captain Stumpy
not rated yet Dec 03, 2018
@steel
the ASSumption that it was a primitive society that built the pyramids
there is absolutely no evidence whatsoever to suggest otherwise

Their society or nation may well have had mad engineering skills, but the only record we have of any engineering skills is in the pyramids themselves, so there is still absolutely no evidence of engineering beyond moving, cutting and lifting rock
Astro-archaeology
this is relevant to dating and that the society used stars as navigational or other aids. most primitive cultures did likewise as it's a fantastic way to get bearings at night

hell, it's still used in land-nav and seamanship
I do consider them a lasting info repository
the pyramids?
to pass on word of catastrophe from sky in the form of meteor and cometary impacts, which HAPPENS
dafuq?

I saw a boat...
Steelwolf
not rated yet Dec 03, 2018
One of the stone sarcophagi that was cut wrong happens to be in Cairo Museum, and it shows a cut went offline, so they discarded the item partially made. Taking close look at the cut marks and measuring radius of the cuts (one from on top, crooked, one from the bottom that was cut straight) that the cutting wheels had to be 6' in diameter and were using powered cutting tools with either corundum or diamond level tech.

In addition to the straight cuts there were Tube-sawn pieces, some with the plug intact, some showing the tube-sawing as a drill technique to remove stone in an area so it can be further carved.

But working in Andesite and Granite, these stones were beyond the ability of 'primitives' to be working with in this manner.

Primitives found them later, adorned, moved and re-used many of them. But their origin is very much in question still. The end of the last ice age raised sea level 400 ft, dated to "near the time" @13 KYA, and Dynastic Egypt @ only 6 KYA.
Steelwolf
not rated yet Dec 03, 2018
All religious temples tend to draw our eyes to the sky. All religions recount The Great Flood, that washed away ALL the Peoples aside from Noah and his family. All around the world there is the Same Story, modified mostly only by what group survives. It points to a small handful of humans who either prepared and built and 'Ark' or were lucky enough to be on the only mountain that did not subside.

But they all talk about the Wicked Ones who peopled the Earth Before, in their ignorance and arrogance they Ignored the warnings of the heavens.

The time period celebrated, World Wide, as the Days of the Dead lines up with the peak of the Taureid Meteor Shower, which we know to be the remains of a comet that broke up like Shoemaker-Levi-9 that plowed into Jupiter.

Burkle Crater in the Indian Ocean dates to near 6K years ago, at 12 miles across in 1200 ft of water. Debris deposits can be seen on Madagascar, India, Sri Lanka and West Australian coast dated to that time. The Deluge.
Steelwolf
not rated yet Dec 03, 2018
Due to precession of the Equinox, the constellations change over time, for Modern History we have been warned of the Taurid system. But when the pyramids appear to have really been built, the equinox would have had Leo in view instead.

So, all the astronomical precision, including the math that shows the pyramid builders knew the size of the Earth very closely, as well as it's orbit and it's rate of precession of the equinox. They left very specific clues by way of how they aligned their buildings, and it is nowhere near 'primitive' as our later survivors of the catastrophe, thousands of years later, and we STILL have these enduring "myths" of a high tech civilization before our own, which, now that we have the tools ourselves, we can see the effects they had and the mistakes they made and left, in the waste tailings from the build, what tech level they Really Had, and when.

Whether you want to believe or not, Meteors happen, think Chelyabinsk of recent fame.
Steelwolf
not rated yet Dec 03, 2018
But that is far from the plasmons and evanescent wave-forms they are finding with the gold nano-particles. Finding that light/matter interactions bring rise to a mixed effect in matter that, as a wave, diminishes geometrically, the smallest portion observable is going to be able to increase our understanding of what both 'light' and 'matter' really are. Observations down to the sub-photon regime is within reach with this sort of advance.
Captain Stumpy
not rated yet Dec 03, 2018
@steel
But working in Andesite and Granite, these stones were beyond the ability of 'primitives' to be working with in this manner
ASSumption
https://en.oxford...rimitive

But they all talk about the Wicked Ones who peopled the Earth Before
are you being religious? or do you have something more than ASSumption?
All religious temples tend to draw our eyes to the sky
not all religions

of course, considering the primitive necessity of knowing the stars for various navigational aids and seasonal tracking also can be a reason why any religion may want to focus on them, especially as they're limited in the ability to explain them without appeals to [x]
Whether you want to believe or not, Meteors happen
nonsensical comment in light of Chelyabinsk, Wabar, Tenoumer, Meteor Crater, the moon, etc

relevance?
Captain Stumpy
not rated yet Dec 03, 2018
@steel
Observations down to the sub-photon regime is within reach with this sort of advance.
how will this work?

do you realise what "sub-photon" means?
https://readingfe...-photon/

https://briankobe...e-of-it/

https://en.wikipe...operties

Steelwolf
not rated yet Dec 03, 2018
I only re-stated that which is in various recordings, in various forms, from Sumerian Clay tablets on, concerning the stories of the flood. The fact is THEY used those terms, and stated there was a higher degree of civilization that they had lost due to the catastrophe of the Heavens filling with fires and the waters of the land rising to put them out...Actual clay tablet history.

And their timing of these events happens to coincide with the records we have geographically, stratigraphically and being able to cross reference them to our various, regions histories and from separate civilizations.

A young civilization, in a small geographic area, could be wiped out in an instant from a Tunguska type event, and that is SMALL on cosmic scales. And we get at least one Tunguska every 20 years or so.

People used to be boggled and said things microscopic could not exist, yet look at where we are today. Sub-photonic matter might just power the i-phone for 2200.
Captain Stumpy
not rated yet Dec 03, 2018
@steel
I only re-stated that which is in various recordings, in various forms, from Sumerian Clay tablets on, concerning the stories of the flood
stories of a flood aren't evidence of a global catastrophe
this is best demonstrated by the distribution of animals as well as places like Oz
Actual clay tablet history
no, their interpretation of what happened, so eyewitness testimony at best (and we know how unreliable that is)

of course, "a higher degree of civilization" could also mean they had better sanitary conditions and a different government, so "a higher degree of civilization", being subjective, isn't indicative of anything other than "different from the author"
People used to be boggled
irrelevant and not indicative of anything, especially concerning science

all science is on the cutting edge between what is known and what is not known
originalxaxx
not rated yet Dec 03, 2018
It's a breakthrough!
If it's repeated and found by other workers.
Steelwolf
not rated yet Dec 05, 2018
This article here actually details a smaller such impact and some of the consequences, such as the land being poisoned etc from the impact:

https://phys.org/...ead.html

And while they state this coincides with right place and time frame for Sodom and Gommorah, they go and make the modern mistake of associating the cities with sex practices, when the reasons stated in the bible, at the time sodomy was the ostentatious presentation of wealth, and overbearing greed. It may have picked up the sexual connotations from the slaves, which were said to be finely and alluringly dressed as decoration and proof of wealth for their owners. Conspicuous Consumption was more the problem than sexual escapades, but in any case, when a comet or meteor from the skies strike, it is much akin to "The Fist of God" as many primitives would immediately imagine, with the world ending.

As I said, Think Chelyabinsk, they Happen!

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.