Tag Archives: nanoantenna

The reddest red and Schrödinger’s red pixel

Caption: Schrödinger’s red pixel by quasi-bound-states in-the-continuum Credit: 123RF

Science keeps moving. First, there was the June 2022 news and, then, there was the August 2022 news.

A June 8, 2022 Agency for Science, Technology and Research (A*STAR) press release (also on EurekAlert but published June 7, 2022 as an ‘article highlight’) announces more research into structural colour along with some colour theory from Erwin Schrödinger,

The brilliant and often iridescent colours that we see in some species of birds, beetles and butterflies arise from a regular arrangement of nanostructures that scatter selective wavelengths of light more strongly to generate colour. These colours are called structural colours, which usually range from blues to greens, and even magenta. However, vibrant or saturated reds are elusive and notably absent from the structural colour range in both natural and synthetic realms.

To achieve highly saturated reds, the material needs to absorb light from all wavelengths shorter than ~600 nm and reflect the remaining longer wavelengths, doing both as completely as possible. This sharp transition from absorption to reflection was prescribed theoretically by none other than Erwin Schrödinger of quantum theory fame. However, the physics of resonators tell us that high-order optical resonances in blue will also occur as soon as we have a fundamental resonance in red. This combination of blue and red thus results in the magenta observed in nature. It is therefore challenging to achieve the Schrödinger’s red pixel, which would produce the most saturated red in the world. Current nanoantenna-based approaches are insufficient to simultaneously satisfy the above conditions.

Researchers from the Agency for Science, Technology and Research’s (A*STAR) Institute of Materials Research and Engineering (IMRE), National University of Singapore (NUS) and Singapore University of Technology and Design (SUTD) have collaborated to design and realise reds at the ultimate limit of saturation as predicted by theory, where the team worked together on conceptualisation methodology, fabrications, characterisations and simulations. This research was published in Science Advances on 23 February 2022.

The design consists of regularly arranged silicon nanoantennas in the shape of ellipses. These produce possibly the most saturated and brightest reds with ~80% reflectance, exceeding the reds in the standard red, green and blue gamut (sRGB) and other well-known red pigments, e.g. cadmium red .

The nanoantennas support two partially overlapping quasi bound-states-in-the-continuum modes, where the optimal dimensions of the silicon nanoantenna arrays are derived by using a gradient descent algorithm to enable the antennas to achieve sharp spectral edges at red wavelengths. At the same time, high-order modes at blue or green wavelengths are suppressed via engineering the substrate‑induced diffraction channels and the absorption of amorphous silicon.

Potential uses for Schrödinger’s red include developing a polarisation dependent encryption method, with plans to scale up the Schrödinger’s red pixel for applications like functional nanofabrication devices such as optical spectrometers and reflective displays with high colour saturation.

“With this new design that can achieve the most saturated and brightest reds, we can exploit its sensitivity to polarisation and illumination angle on potential applications for information encryption. This proposed concept and design methodology could also be generalised to other Schrödinger’s colour pixels. The highly-saturated red achieved could be potentially scaled up through methods such as deep ultraviolet and nano-imprint lithography, to reach the dimensions of reflective displays based on multilayer film configuration, which could lead to potential applications like compact red filters, highly saturated reflective displays, nonlocal metasurfaces, and miniaturised spectrometers”, said Dr. Dong Zhaogang, Deputy Department Head of Nanofabrication at A*STAR’s IMRE.

“The creation of the record-high saturation and brightness in red opens up possibilities for a plethora of applications related to anti-counterfeiting technologies, high-calibre colour display and more, which were previously perceived as unachievable with structural colour. It showcases a wonderful synergy between conceptual breakthrough, powerful algorithm and advanced nanofabrication”, said Prof. Cheng-Wei Qiu, Dean’s Chair Professor at NUS.

“This work in structural colours goes to show that we can sometimes outdo evolution through clever use of the tools in nanofabrication and accurate optical simulations”, said Prof. Joel Yang, Provost Chair Professor and Associate Professor in Engineering Product Development at SUTD.

Here’s a link to and a citation for the paper,

Schrödinger’s red pixel by quasi-bound-states-in-the-continuum by Zhaogang Dong, Lei Jin, Soroosh Daqiqeh Rezaei, Hao Wang, Yang Chen, Febiana Tjiptoharsono, Jinfa Ho, Sergey Gorelik, Ray Jia Hong Ng, Qifeng Ruan, Cheng-Wei Qiu and Joel K. W. Yang. Science Advances Vol 8, Issue 8 DOI: 10.1126/sciadv.abm4512 Published 23 Feb 2022

This paper is open access.

Math error, colour theory, and perception

An August 10, 2022 news item on phys.org announced a math error made by Erwin Schrödinger and others,

A new study corrects an important error in the 3D mathematical space developed by the Nobel Prize-winning physicist Erwin Schrödinger and others, and used by scientists and industry for more than 100 years to describe how your eye distinguishes one color from another. The research has the potential to boost scientific data visualizations, improve TVs and recalibrate the textile and paint industries.

“The assumed shape of color space requires a paradigm shift,” said Roxana Bujack, a computer scientist with a background in mathematics who creates scientific visualizations at Los Alamos National Laboratory. Bujack is lead author of the paper by a Los Alamos team in the Proceedings of the National Academy of Sciences on the mathematics of color perception.

“Our research shows that the current mathematical model of how the eye perceives color differences is incorrect. That model was suggested by Bernhard Riemann and developed by Hermann von Helmholtz and Erwin Schrödinger—all giants in mathematics and physics—and proving one of them wrong is pretty much the dream of a scientist,” said Bujack.

While the Los Alamos National Laboratory work was published in April 2022 (online) and May 2022 (in print), their news announcement doesn’t seem to have been made until August. I can’t be certain but I believe this should have an impact on the work from A*STAR as that team’s paper cites: E. Schrödinger, Theorie der Pigmente von größter Leuchtkraft. Ann. Phys. 367, 603–622 (1920).

An August 10, 2022 Los Alamos National Laboratory (LANL) news release (also on EurekAlert) provides more information about the discovery,

Modeling human color perception enables automation of image processing, computer graphics and visualization tasks.

“Our original idea was to develop algorithms to automatically improve color maps for data visualization, to make them easier to understand and interpret,” Bujack said. So the team was surprised when they discovered they were the first to determine that the longstanding application of Riemannian geometry, which allows generalizing straight lines to curved surfaces, didn’t work.

To create industry standards, a precise mathematical model of perceived color space is needed. First attempts used Euclidean spaces—the familiar geometry taught in many high schools; more advanced models used Riemannian geometry. The models plot red, green and blue in the 3D space. Those are the colors registered most strongly by light-detecting cones on our retinas, and—not surprisingly—the colors that blend to create all the images on your RGB computer screen.

In the study, which blends psychology, biology and mathematics, Bujack and her colleagues discovered that using Riemannian geometry overestimates the perception of large color differences. That’s because people perceive a big difference in color to be less than the sum you would get if you added up small differences in color that lie between two widely separated shades.

Riemannian geometry cannot account for this effect.

“We didn’t expect this, and we don’t know the exact geometry of this new color space yet,” Bujack said. “We might be able to think of it normally but with an added dampening or weighing function that pulls long distances in, making them shorter. But we can’t prove it yet.”

Here’s a link to and a citation for the paper,

The non-Riemannian nature of perceptual color space by Roxana Bujack, Emily Teti, Jonah Miller, Elektra Caffrey, and Terece L. Turton. Proceedings of the National Academy of Sciences (PNAS) 119 (18) e2119753119 DOI: https://doi.org/10.1073/pnas.2119753119 Published: April 29, 2022

This paper is behind a paywall.

Rice University (Texas) researchers ‘soften’ a buckyball (buckminster fullerene)

A Jan. 16, 2014 Rice University news release landed in my mailbox this morning and revealed that researchers have ‘detuned’ or softened the atomic bonks in a molecule known as a buckminster fullenere (aka, buckyball),

Rice University scientists have found they can control the bonds between atoms in a molecule.

The molecule in question is carbon-60, also known as the buckminsterfullerene and the buckyball, discovered at Rice in 1985. The scientists led by Rice physicists Yajing Li and Douglas Natelson found that it’s possible to soften the bonds between atoms by applying a voltage and running an electric current through a single buckyball.

“This doesn’t mean we’re going to be able to arbitrarily dial around the strength of materials or anything like that,” Natelson said. “This is a very specific case, and even here it was something of a surprise to see this going on.

“But in general, if we can manipulate the charge distribution on molecules, we can affect their vibrations. We can start thinking, in the future, about controlling things in a better way.”

The effect appears when a buckyball attaches to a gold surface in the optical nano antenna used to measure the effects of an electric current on intermolecular bonds through a technique called Raman spectroscopy.

Natelson’s group built the nano antenna a few years ago to trap small numbers of molecules in a nanoscale gap between gold electrodes. Once the molecules are in place, the researchers can chill them, heat them, blast them with energy from a laser or electric current and measure the effect through spectroscopy, which gathers information from the frequencies of light emitted by the object of interest.

With continuing refinement, the researchers found they could analyze molecular vibrations and the bonds between the atoms in the molecule. That ability led to this experiment, Natelson said.

Natelson compared the characteristic vibrational frequencies exhibited by the bonds to the way a guitar string vibrates at a specific frequency based on how tightly it’s wound. Loosen the string and the vibration diminishes and the tone drops.

The nano antenna is able to detect the “tone” of detuned vibrations between atoms through surface-enhanced Raman spectroscopy (SERS), a technique that improves the readings from molecules when they’re attached to a metal surface. Isolating a buckyball in the gap between the gold electrodes lets the researchers track vibrations through the optical response seen via SERS.

When a buckyball attaches to a gold surface, its internal bonds undergo a subtle shift as electrons at the junction rearrange themselves to find their lowest energetic states. The Rice experiment found the vibrations in all the bonds dropped ever so slightly in frequency to compensate.

“Think of these molecules as balls and springs,” Natelson said. “The atoms are the balls and the bonds that hold them together are the springs. If I have a collection of balls and springs and I smack it, it would show certain vibrational modes.

“When we push current through the molecule, we see these vibrations turn on and start to shake,” Natelson said. “But we found, surprisingly, that the vibrations in buckyballs get softer, and by a significant amount. It’s as if the springs get floppier at high voltages in this particular system.” The effect is reversible; turn off the juice and the buckyball goes back to normal, he said.

The researchers used a combination of experimentation and sophisticated theoretical calculations to disprove an early suspicion that the well-known vibrational Stark effect was responsible for the shift. The Stark effect is seen when molecules’ spectral responses shift under the influence of an electric field. The Molecular Foundry, a Department of Energy User Facility at Lawrence Berkeley National Laboratory, collaborated on the calculations component.

Natelson’s group had spied similar effects on oligophenylene vinylene molecules used in previous experiments, also prompting the buckyball experiments. “A few years ago we saw hints of vibrational energies moving around, but nothing this clean or this systematic. It does seem like C-60 is kind of special in terms of where it sits energetically,” he said.

The discovery of buckyballs, which earned a Nobel Prize for two Rice professors, kick-started the nanotechnology revolution. “They’ve been studied very well and they’re very chemically stable,” Natelson said of the soccer-ball-shaped molecules. “We know how to put them on surfaces, what you can do to them and have them still be intact. This is all well understood.” He noted other researchers are looking at similar effects through the molecular manipulation of graphene, the single-atomic-layer form of carbon.

“I don’t want to make some grand claim that we’ve got a general method for tuning the molecular bonding in everything,” Natelson said. “But if you want chemistry to happen in one spot, maybe you want to make that bond really weak, or at least make it weaker than it was.

“There’s a long-sought goal by some in the chemistry community to gain precise control over where and when bonds break. They would like to specifically drive certain bonds, make sure certain bonds get excited, make sure certain ones break. We’re offering ways to think about doing that.”

Here’s a link to the abstract and a citation for the paper,

Voltage tuning of vibrational mode energies in single-molecule junctions by Yajing Li, Peter Doak, Leeor Kronik, Jeffrey B. Neatonc, and Douglas Natelsona. PNAS.  doi: 10.1073/pnas.1320210111

This paper is behind a paywall so you need either a subscription to the journal or access to a research library with a subscription or, alternatively, there are two short-term rental options (which for reasons that escape me were difficult to access) here.

As business models go, I don’t believe that aspect of the PNAS model is going to prove successful. Why not make all the options available from the page containing the abstract as do other academic publishers?

Getting back to the buckyball, the researchers have provided an image to illustrate their work,

Rice University scientists discovered the bonds in a carbon-60 molecule – a buckyball – can be "detuned" when exposed to an electric current in an optical antenna. (Credit: Natelson Group/Rice University)

Rice University scientists discovered the bonds in a carbon-60 molecule – a buckyball – can be “detuned” when exposed to an electric current in an optical antenna. (Credit: Natelson Group/Rice University)

Electricity without a current

My imagination fails at the thought of electricity without a current luckily there’s a consortium of scientists at Finland’s Tampere University of  Technology (TUT) who have no trouble with their imaginations, according to the Sept. 12, 2012 news item on Nanowerk (Note: I have removed a link from the following excerpt),

The Academy of Finland has granted €1.6 million to a consortium based at Tampere University of Technology (TUT) under the “Programmable Materials” funding scheme. The project runs from 1 September 2012 to 31 August 2016 and is entitled “Photonically Addressed Zero Current Logic through Nano-Assembly of Functionalised Nanoparticles to Quantum Dot Cellular Automata” ( PhotonicQCA).

The Sept. 12, 2012 news release from TUT which originated the news item explains the ideas and work which support the notion of electricity without current,

The key idea behind the project is the so-called quantum dot cellular automaton (QCA). In QCAs, pieces of semiconductor so small that single electronic charges can be measured and manipulated are arranged into domino like cells. Like dominos, these cells can be arranged so that the position of the charges in one cell affects the position of the charges in the next cell, which allows making logical circuits out of these “quantum dominos”. But, no charge flows from one cell to the next, i.e. no current. This, plus the extremely small size of QCAs, means that they could be used to make electronic circuits at densities and speeds not possible now. However, realisation of the dots and cells and making electrical connections to them has been a huge challenge.

Professors Donald Lupo from Department of Electronics, Mircea Guina and Tapio Niemi from Optoelectronics Research Centre (ORC), and Nikolai Tkachenko and Helge Lemmetyinen from Department of Chemistry and Bioengineering, want to investigate a completely new approach. They want to attach tailor-made molecules, optical nanoantennas, to the quantum dots, which can inject a charge into a dot or enable charge transfer between the dots when light of the right wavelength shines on them. This concept will be combined with the expertise at TUT’s Optoelectronics Research Centre concerning “site-specific epitaxy”, i.e. growing the quantum dots in the right place using nanofabrication techniques, which would enable a solid-state technology platform compatible with standard electronic circuits. If this works, then someday QCAs could be written and read with light.

Project coordinator, Professor Donald Lupo says: “As far as we can tell, no one has ever tried anything like this before. It’s a completely new idea. It was our excellent inter-departmental communication that identified a unique combination of know-how that let us come up with this concept. It’s highly risky because of many technological challenges, but the potential is amazing; being able to get rid of electrical connections and write and read nanoelectronic circuits using only light would be a huge breakthrough”.

Reading the Programmable Materials page on the Academy of Finland website provided some clues for what they hope to achieve with this ‘electricity’ project is all about,

The FinnSight 2015 report published in 2006 underscores the fact that materials research is a cross-disciplinary exercise: new materials are increasingly being developed on a multidisciplinary platform. The report also urges Finnish materials research to step up its efforts to explore the more advanced properties of new materials that are still partly unknown.

Most new materials today are typically static by nature. They are composed of components that have a specific function or quality, but they do not respond to their environment as such. Programmable materials, by contrast, are composed of components that respond in a specific, programmed way to environmental stimuli and signals. Depending on the initial state or code of these components, it is possible to produce various complex, even macroscopic, structures in a controlled way.

Programmable materials represent a new emerging research field in which Finland can play a pioneering role. The programmable properties of different materials are continuing to develop with advances in such fields as nano- and biotechnology, and programmable materials may completely revolutionise applications of functional materials.

Materials programming is an emerging, all-new field of research. The aim of this programme is to work with the best international research teams and solidify Finland’s position at the international forefront of research. The strongest countries in this field include the United States, Japan, Russia, India and certain European countries. In addition, China has a strong emerging materials research field.

I threw in that last paragraph because I find their analysis of the international scene quite interesting and notice they list three of the BRICS (Brazil, Russia, India, China, ans South Africa) countries as leaders in this emergent field.

Getting back to this specific ‘electricity’ project, it sounds as if they’re working on an electrical component which could be made to operate when a light is shone on it in a process that reminiscent of photosynthesis (Wikipedia essay on photosynthesis) where a plant converts light into chemical energy.

Are we creating a Star Trek world? T-rays and tricorders

There’s been quite a flutter online (even the Huffington Post has published a piece) about ‘Star Trek-hand-held medical scanners’ becoming possible due to some recent work in the area of T-rays. From the Jan. 20, 2012 news item on Nanowerk,

Scientists who have developed a new way to create a type of radiation known as Terahertz (THz) or T-rays – the technology behind full-body security scanners – say their new, stronger and more efficient continuous wave T-rays could be used to make better medical scanning gadgets and may one day lead to innovations similar to the “tricorder” scanner used in Star Trek.

In a study published recently in Nature Photonics (“Greatly enhanced continuous-wave terahertz emission by nano-electrodes in a photoconductive photomixer” [behind a paywall]), researchers from the Institute of Materials Research and Engineering (IMRE), a research institute of the Agency for Science, Technology and Research (A*STAR) in Singapore and Imperial College London in the UK have made T-rays into a much stronger directional beam than was previously thought possible and have efficiently produced T-rays at room-temperature conditions. This breakthrough allows future T-ray systems to be smaller, more portable, easier to operate, and much cheaper.

For anyone who’s not familiar with ‘Star Trek world’ and tricorders, here’s a brief description from a Wikipedia essay about tricorders,

In the fictional Star Trek universe, a tricorder is a multifunction handheld device used for sensor scanning, data analysis, and recording data.

David Freeman in his Jan. 21, 2012 article for the Huffington Post about the research puts it this way,

Trekkies, take heart. A scientific breakthrough involving a form of infrared radiation known as terahertz (THz) waves could lead to handheld medical scanners reminiscent of the “tricorder” featured on the original Star Trek television series.

What’s the breakthrough? Using nanotechnology, physicists in London and Singapore found a way to make a beam of the”T-rays”–which are now used in full-body airport security scanners–stronger and more directional.

Here’s how the improved T-ray technology works (from the Jan. 20, 2012 news item on Nanowerk),

In the new technique, the researchers demonstrated that it is possible to produce a strong beam of T-rays by shining light of differing wavelengths on a pair of electrodes – two pointed strips of metal separated by a 100 nanometre gap on top of a semiconductor wafer. The unique tip-to-tip nano-sized gap electrode structure greatly enhances the THz field and acts like a nano-antenna that amplifies the THz wave generated. The waves are produced by an interaction between the electromagnetic waves of the light pulses and a powerful current passing between the semiconductor electrodes from the carriers generated in the underlying semiconductor. The scientists are able to tune the wavelength of the T-rays to create a beam that is useable in the scanning technology.

Lead author Dr Jing Hua Teng, from A*STAR’s IMRE, said: “The secret behind the innovation lies in the new nano-antenna that we had developed and integrated into the semiconductor chip.” ….

Research co-author Stefan Maier, a Visiting Scientist at A*STAR’s IMRE and Professor in the Department of Physics at Imperial College London, said: “T-rays promise to revolutionise medical scanning to make it faster and more convenient, potentially relieving patients from the inconvenience of complicated diagnostic procedures and the stress of waiting for accurate results. Thanks to modern nanotechnology and nanofabrication, we have made a real breakthrough in the generation of T-rays that takes us a step closer to these new scanning devices. …”

It’s another story about handheld (or point-of-care) diagnostic devices and I have posted on this topic previously:

  • Jan. 4, 2012 about work in Alberta;
  •  Dec. 22, 2011 on grants to scientists in the US and Canada working on these devices;
  •  Aug. 4, 2011 about a diagnostic device the size of a credit card;
  •  Mar. 1, 2011 about nanoLAB from Stanford University (my last sentence in that posting “It’s not quite Star Trek yet but we’re getting there.”); and,
  •  Feb. 5, 2011 about the Argento and PROOF initiatives.

I see I had four articles last year and this year (one month old), I already have two articles on these devices. It reflects my own interest, as well as, the amount work being done in this area.