Abstract-Terahertz-driven polymerization of resists in nanoantennas

Woongkyu Park, Youjin Lee, Taehee Kang, Jeeyoon Jeong,  Dai-Sik Kim

https://www.nature.com/articles/s41598-018-26214-w


Plasmon-mediated polymerization has been intensively studied for various applications including nanolithography, near-field mapping, and selective functionalization. However, these studies have been limited from the near-infrared to the ultraviolet regime. Here, we report a resist polymerization using intense terahertz pulses and various nanoantennas. The resist is polymerized near the nanoantennas, where giant field enhancement occurs. We experimentally show that the physical origin of the cross-linking is a terahertz electron emission from the nanoantenna, rather than multiphoton absorption. Our work extends nano-photochemistry into the terahertz frequencies.

Can Israeli Start-up Oryx Oust Lidar From Self-Driving Cars?

(MY NOTE: I kept meaning to post this. It's from 2016, but remains an interesting story. IMO. )

By Mark Harris

https://spectrum.ieee.org/cars-that-think/transportation/sensors/can-israeli-startup-oryx-oust-lidar-from-selfdriving-cars

Lidar has been the best thing to happen to self-driving cars—and also the worst. Installing a bank of lasers on the roof means a car can capture millions of points of information every second, rapidly building up a 3D image of the world around it.

The problem is that until recently, lidar units were more expensive than the cars that carried them. High performance units on Google’s early vehicles cost $70,000; devices with shorter range and a narrower field of view, from lidar pioneer Velodyne, can still cost thousands.

There is always the option of going without lidar altogether, as Tesla has done. Its cars rely on cheaper radar, video, and ultrasonic sensors. But the fatal crash of a Model S this summer while its Autopilot system was engaged shows that this solution is far from ideal.

What autonomous car makers really want is a dirt cheap and utterly reliable sensor that complements radar and video cameras. And Israeli start-up Oryx Vision thinks it might have just what they’re looking for.

Oryx’s technology, coherent optical radar, splits the difference between radar and lidar. Like a lidar, it uses a laser to illuminate the road ahead, but like a radar it treats the reflected signal as a wave rather than a particle.

The laser in question is a long-wave infrared laser, also called a terahertz laser because of the frequency at which it operates. Because human eyes cannot focus light at this frequency, Oryx can use higher power levels than can lidar designers. Long-wave infrared light is also poorly absorbed by water and represents only a tiny fraction of the solar radiation that reaches Earth. This means the system should not be blinded by fog or direct sunlight, as lidar systems and cameras can be.

One of the potential cost savings of Oryx’s technology comes from the fact that its laser does not need to be steered with mechanical mirrors or a phased array in order to capture a scene. Simple optics spread the laser beam to illuminate a wide swathe in front of the vehicle. (Oryx would not say what the system’s field of view will be, but if it is not 360 degrees like rooftop lidars, a car will need multiple Oryx units facing in different directions.)

The clever bit—and what has prevented anyone from building a terahertz lidar before now—is what happens when the light bounces back to the sensor. A second set of optics direct the incoming light onto a large number of microscopic rectifying nanoantennas. These are what Oryx’s co-founder, David Ben-Bassat, has spent the past six years developing.

Incoming light creates an AC response in the antenna that is rectified—in other words, converted into a DC signal. Rani Wellingstein, Oryx’s other founder, says the system has a million times the sensitivity of traditional lidar. Because the antennas treat incoming light as a wave, they can also detect Doppler shift—the change in frequency due to the relative motion of whatever it bounced off—and thus determine the velocities of other objects in or near the roadway.

Each nanoantenna is just five square micrometers; they will ultimately be fabricated directly onto integrated circuits using a thin-film chip manufacturing processes. This will make it fairly simple for the signals to be fed into a machine learning system that can classify objects in the scene.

While Oryx has already built many millions of experimental nanoantennas, it has yet to fabricate them into an integrated circuit. Within a year, it intends to build a 300-pixel demonstration unit, then a 10,000-pixel chip containing a quarter of a million nanoantennas, and finally a 100,000-pixel, multi-million-nanoantenna device suitable for in-car use.

“Today, radars can see to 150- or 200 meters, but they don’t have enough resolution. Lidar provides great resolution but is limited in range to about 60 meters, and to as little as 30 meters in direct sunlight,” says Wellingstein. He expects Oryx’s coherent optical radar to accurately locate debris in the road at 60 meters, pedestrians at 100 meters, and motorcycles at 150 meters—significantly better than the performance of today’s sensor systems.

Image: Oryx

If they can scale it, the technology developed by Oryx’s founders may best radar and lidar in both range and resolution

   

The Oryx setup could be cheap, too. If the company can get its (still unproven) fabrication process to scale, it thinks making millions of nanoantennas will be little harder than producing conventional semiconductor chips. The company recently announced a $17 million Series A funding round and has already been talking with autonomous vehicle companies, including Nutonomy, which recently launched a pilot self-driving taxi service in Singapore.

“The idea seems reasonable, but I'd be skeptical until they have a working prototype,” says Joe Funke, an engineer who has worked on autonomous systems at several vehicle start-ups, including Lucid Motors. “There will always be use cases for cheaper, high range sensors,” says Funke. “If nothing else, longer range enables higher operating speeds.”

But don’t write off lidar just yet. Following a $150 million investment by Ford and Chinese search giant Baidu this summer, Velodyne expects an “exponential increase in lidar sensor deployments.” The cost of the technology is still dropping, with Velodyne estimating that one of its newer small-form lidars will cost just $500 when made at scale.

Solid-state lidars are also on the horizon, with manufacturers including Quanergy, Innoluce, and another Israeli start-up, Innoviz, hinting at sub-$100 devices. Osram recently said that it could have a solid-state automotive lidar on the market as soon as 2018, with an eventual target price of under $50. Its credit card–size lidar may be able to detect pedestrians at distances up to 70 meters.

That’s not quite as good as Oryx promises, but is probably fine for all but the very fastest highway driving. The window for disrupting lidar’s grip on autonomous vehicles is closing fast.

This story was corrected to give proper details of Oryx nanoantenna integration plans.

Abstract-Nanoantenna with Geometric Diode for Energy Harvesting

Hosam Ali El-Araby, Hend Abd El-Azem Malhat, Saber Helmy Zainud-Deen,

https://link.springer.com/article/10.1007/s11277-017-5159-2

A graphene based geometrical diodes coupled with nanoantennas for infrared (IR) energy harvesting has been introduced. The geometrical diode is an electronic device in which the current flow through it is controlled by its geometry. The I–V characteristics of the graphene based geometrical diodes are calculated by the Monte Carlo simulation. Different shapes of graphene geometrical diodes, arrowhead, modified staircase, and quarter-elliptical geometries have been examined. The equivalent impedance, capacitance, and responsitivity of each geometric diode have been calculated. The radiation characteristics of nanoantenna designed at 20.5 THz have been investigated. The IR harvesting using nanoantenna coupled with the graphene geometric diode has been calculated and interpreted. Full-wave simulation for the nanoantenna coupled to the geometric diode has been introduced. The DC voltage collected by the nanoantenna and rectified using the geometrical diode has been calculated.

Abstract-A sub-terahertz broadband detector based on a GaN high-electron-mobility transistor with nanoantennas

Haowen Hou1,2, Zhihong Liu1, Jinghua Teng3, Tomás Palacios4 and Soo-Jin Chua1,2

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=5119501665943236159

We report a sub-terahertz (THz) detector based on a 0.25-µm-gate-length AlGaN/GaN high-electron-mobility transistor (HEMT) on a Si substrate with nanoantennas. The fabricated device shows excellent performance with a maximum responsivity (R v) of 15 kV/W and a minimal noise equivalent power (NEP) of 0.58 pW/Hz0.5 for 0.14 THz radiation at room temperature. We consider these excellent results as due to the design of asymmetric nanoantennas. From simulation, we show that indeed such nanoantennas can effectively enhance the local electric field induced by sub-THz radiation and thereby improve the detection response. The excellent results indicate that GaN HEMTs with nanoantennas are future competitive detectors for sub-THz and THz imaging applications.

SpectroscopyNOW-Last Month's Most Accessed Feature: Invisibility cloak: Hiding the microscopic

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http://www.spectroscopynow.com/ir/details/highlight/14de329bf14/Last-Months-Most-Accessed-Feature-Invisibility-cloak-Hiding-the-microscopic.html

Cloaking device

A microscopic invisibility cloak based on brick-like blocks of gold nanoantennae could pave the way to a flexible device for making an object invisible in visible light.

Invisibility cloaks have been a staple of science fiction and fantasy for decade, who, after all, has not mused on what they might get up to if they could make themselves invisible? For several years camouflage covers that resemble the background environment to help hide a person were the best option, leafy greens allowing a soldier to crawl through undergrowth undetected perhaps, except when night-vision or thermal imaging is in place. Aircraft can be made "stealth" to hide them from the reflective waves of a radar tower but they can still be spotted as they fly by at altitude with a decent set of binoculars and a good eye.

In recent years, however, meta materials have emerged that might take invisibility to the next level. There have been demonstrations of infrared and other forms of invisibility but now, researchers at the US Department of Energy's Lawrence Berkeley National Laboratory and the University of California Berkeley have come up with a microscopic invisibility cloak that can hide a three dimensional object from the microscope's viewfinder. The team suggest that the principle should work on the macroscopic level to once it is scaled up.

Concealing to appeal

The team has worked with gold nanoantennae to fabricate a flexible skin a mere 80 nanometres in thickness that can be wrapped around a three-dimensional object of arbitrary shape the size of a clump of biological cells. Adopting the underlying lumps and bumps of the object. The meta-engineered surface of the skin cloak allows it to re-route reflected light waves so impinge on it so that the object's lumps and bumps are rendered invisible to optical detection when the cloak is activated.

"This is the first time a 3D object of arbitrary shape has been cloaked from visible light," explains meta materials expert Xiang Zhang, director of Berkeley Lab's Materials Sciences Division. "Our ultra-thin cloak now looks like a coat. It is easy to design and implement, and is potentially scalable for hiding macroscopic objects," he adds.

Zhang, working with Xingjie Ni, Zi Jing Wong, Michael Mrejen and Yuan Wang, point out that that it is the scattering of electromagnetic radiation, whether that is visible light, infrared, X-ray, or another band in the spectrum, and its interaction with matter that enables us to detect and observe objects. The researchers explains that the rules that govern these interactions in natural materials can be circumvented using meta materials whose optical properties arise from their physical structure rather than their chemical composition. The surface of a butterfly's wing has no coloured pigment, it's surface texture interacts with visible light to cause iridescence that gives rise to its beautiful colours and patterns and so might be thought of as a natural meta material.

For the past ten years, Zhang and his research group have been pushing the boundaries of how light interacts with fabricated meta materials. They have managed to curve the path of light or bend it backwards, creating negative refractive index meta materials, a phenomenon not seen before in nature, and to render objects optically undetectable. In the past, their meta material-based optical carpet cloaks were bulky and hard to scale-up, and entailed a phase difference between the cloaked region and the surrounding background that made the cloak itself detectable, although what it was concealing could not be detected, which defeats the object of being invisible one has to say.

Skin to carpet

"Creating a carpet cloak that works in air was so difficult we had to embed it in a dielectric prism that introduced an additional phase in the reflected light, which made the cloak visible by phase-sensitive detection," explains team member and co-lead author Ni, who has recently moved to Pennsylvania State University. "Recent developments in meta surfaces, however, allow us to manipulate the phase of a propagating wave directly through the use of sub-wavelength sized elements that locally tailor the electromagnetic response at the nanoscale, a response that is accompanied by dramatic light confinement."

In their experiments, the team shone red light struck on a sample object with an area of about 1300 square micrometres. When it was sheathed in the gold nanoantennae skin cloak, light reflected from the object's surface produced the same effect as if the light were simply reflecting from a plane mirror. The 3D object cloaked in this way is thus invisible even by phase-sensitive detection. The team points out that their cloaking device can be turned on or off simply by switching the polarization of the nanoantennae.

"A phase shift provided by each individual nanoantenna fully restores both the wavefront and the phase of the scattered light so that the object remains perfectly hidden," explains Wong. Ironically, this ability to manipulate the interactions of light and a meta material for invisibility hints at a future of high resolution optical microscopes and superfast optical computers and as a component of a future 3D display technology. Conversely, such a device could be used for security through obscurity applications allowing microscopic components to be hidden for privacy or security applications. purposes.

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Science 2015, 349, 1310-1314: "An ultrathin invisibility skin cloak for visible light"

Article by David Bradley

• Read more about David and our other columnists >>>

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

Abstract-Terahertz-triggered phase transition and hysteresis narrowing in a nanoantenna patterned vanadium dioxide film

ZACHARY J. THOMPSON, Andrew J. Stickel, YOUNG-GYUN JEONG, SANGHOON HAN, BYUNG HEE SON, MICHAEL J. PAUL, BYOUNGHWAK LEE, ALI MOUSAVIAN, GIWAN SEO, Hyun-Tak Kim, Yun-Shik Lee, and Dai-Sik Kim

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/acs.nanolett.5b01970

Publication Date (Web): August 24, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b01970

We demonstrate that high-field THz pulses trigger transient insulator-to-metal transition in a nanoantenna patterned vanadium dioxide thin film. THz transmission of vanadium dioxide instantaneously decreases in the presence of strong THz fields. The transient THz absorption indicates that strong THz fields induce electronic insulator-to-metal transition without causing a structural transformation. The transient phase transition is activated on the sub-cycle time scale during which the THz pulse drives the electron distribution of vanadium dioxide far from equilibrium and disturb the electron correlation. The strong THz fields lower the activation energy in the insulating phase. The THz-triggered insulator-to-metal transition gives rise to hysteresis loop narrowing, while lowering the transition temperature both for heating and cooling sequences. THz nanoantennas enhance the field-induced phase transition by intensifying the field strength and improve the detection sensitivity via antenna resonance. The experimental results demonstrate a potential that plasmonic nanostructures incorporating vanadium dioxide can be the basis for ultrafast, energy-efficient electronic and photonic devices.

Abstract-Miniaturized tunable terahertz antenna based on graphene

1. Tao Zhou^1,*, 
2. Zhiqun Cheng¹, 
3. Hongfang Zhang¹, 
4. Martine Le Berre², 
5. Liviu Militaru²and
6. Francis Calmon²

http://onlinelibrary.wiley.com/doi/10.1002/mop.28450/abstract

Article first published online: 24 MAY 2014

DOI: 10.1002/mop.28450

Copyright © 2014 Wiley Periodicals, Inc.

A tunable terahertz nanoantenna based on graphene is presented. The proposed antenna has a characteristic of dynamic frequency reconfiguration, high miniaturization, easy integration, low reflection coefficient, and good omnidirectional radiation pattern. The attractive properties of the graphene antenna has the potential to be used in nanoscale wireless communications and sensing systems. 
© 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1792–1794, 2014

Ultrathin wafer of silicon and gold focuses telecom wavelengths without distortion

A new ultrathin, flat lens focuses light without imparting the optical distortions of conventional lenses. Credit: Artist's rendition courtesy of Francesco Aieta.

 http://phys.org/news/2012-08-ultrathin-wafer-silicon-gold-focuses.html#jCp
(Phys.org)—August 23, 2012 – Applied physicists at the Harvard School of Engineering and Applied Sciences (SEAS) have created an ultrathin, flat lens that focuses light without imparting the distortions of conventional lenses.

At a mere 60 nanometers thick, the flat lens is essentially two-dimensional, yet its focusing power approaches the ultimate physical limit set by the laws of diffraction.

Operating at telecom wavelengths (i.e., the range commonly used in fiber-optic communications), the new device is completely scalable, from near-infrared to terahertz wavelengths, and simple to manufacture. The results have been published online in the journal Nano Letters.

Enlarge

Left: A micrograph of the flat lens (diameter approximately 1 mm) made of silicon. The surface is coated with concentric rings of gold optical nanoantennas (inset) which impart different delays to the light traversing the lens. Right:The colored rings show the magnitude of the phase delay corresponding to each ring. (Image courtesy of Francesco Aieta.)

"Our flat lens opens up a new type of technology," says principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS. "We're presenting a new way of making lenses. Instead of creating phase delays as light propagates through the thickness of the material, you can create an instantaneous phase shift right at the surface of the lens. It's extremely exciting."

Capasso and his collaborators at SEAS create the flat lens by plating a very thin wafer of silicon with an nanometer-thin layer of gold. Next, they strip away parts of the gold layer to leave behind an array of V-shaped structures, evenly spaced in rows across the surface. When Capasso's group shines a laser onto the flat lens, these structures act as nanoantennas that capture the incoming light and hold onto it briefly before releasing it again. Those delays, which are precisely tuned across the surface of the lens, change the direction of the light in the same way that a thick glass lens would, with an important distinction.

The flat lens eliminates optical aberrations such as the "fish-eye" effect that results from conventional wide-angle lenses. Astigmatism and coma aberrations also do not occur with the flat lens, so the resulting image or signal is completely accurate and does not require any complex corrective techniques.

The array of nanoantennas, dubbed a "metasurface," can be tuned for specific wavelengths of light by simply changing the size, angle, and spacing of the antennas.

"In the future we can potentially replace all the bulk components in the majority of optical systems with just flat surfaces," says lead author Francesco Aieta, a visiting graduate student from the Università Politecnica delle Marche in Italy. "It certainly captures the imagination."

Journal reference: Nano Letters  

Provided by Harvard University  

'Nanoantennas' Show Promise in Optical Innovations

The image in the upper left shows a schematic for an array of gold "plasmonic nanoantennas" able to precisely manipulate light in new ways, a technology that could make possible a range of optical innovations such as more powerful microscopes, telecommunications and computers. At upper right is a scanning electron microscope image of the structures. The figure below shows the experimentally measured refraction angle versus incidence angle for light, demonstrating how the nanoantennas alter the refraction. (Credit: Purdue University Birck Nanotechnology Center image)

http://www.sciencedaily.com/releases/2011/12/111222142459.htm

ScienceDaily (Dec. 22, 2011) — Researchers have shown how arrays of tiny "plasmonic nanoantennas" are able to precisely manipulate light in new ways that could make possible a range of optical innovations such as more powerful microscopes, telecommunications and computers.

The researchers at Purdue University used the nanoantennas to abruptly change a property of light called its phase. Light is transmitted as waves analogous to waves of water, which have high and low points. The phase defines these high and low points of light.

"By abruptly changing the phase we can dramatically modify how light propagates, and that opens up the possibility of many potential applications,"said Vladimir Shalaev, scientific director of nanophotonics at Purdue's Birck Nanotechnology Center and a distinguished professor of electrical and computer engineering.
Findings are described in a paper to be published online on Dec. 22 in the journal Science.
The new work at Purdue extends findings by researchers led by Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at the Harvard School of Engineering and Applied Sciences. In that work, described in an October Science paper, Harvard researchers modified Snell's law, a long-held formula used to describe how light reflects and refracts, or bends, while passing from one material into another.
"What they pointed out was revolutionary," Shalaev said.
Until now, Snell's law has implied that when light passes from one material to another there are no abrupt phase changes along the interface between the materials. Harvard researchers, however, conducted experiments showing that the phase of light and the propagation direction can be changed dramatically by using new types of structures called metamaterials, which in this case were based on an array of antennas.
The Purdue researchers took the work a step further, creating arrays of nanoantennas and changing the phase and propagation direction of light over a broad range of near-infrared light. The paper was written by doctoral students Xingjie Ni and Naresh K. Emani, principal research scientist Alexander V. Kildishev, assistant professor Alexandra Boltasseva, and Shalaev.
The wavelength size manipulated by the antennas in the Purdue experiment ranges from 1 to 1.9 microns.
"The near infrared, specifically a wavelength of 1.5 microns, is essential for telecommunications," Shalaev said. "Information is transmitted across optical fibers using this wavelength, which makes this innovation potentially practical for advances in telecommunications."
The Harvard researchers predicted how to modify Snell's law and demonstrated the principle at one wavelength.
"We have extended the Harvard team's applications to the near infrared, which is important, and we also showed that it's not a single frequency effect, it's a very broadband effect," Shalaev said. "Having a broadband effect potentially offers a range of technological applications."
The innovation could bring technologies for steering and shaping laser beams for military and communications applications, nanocircuits for computers that use light to process information, and new types of powerful lenses for microscopes.
Critical to the advance is the ability to alter light so that it exhibits "anomalous" behavior: notably, it bends in ways not possible using conventional materials by radically altering its refraction, a process that occurs as electromagnetic waves, including light, bend when passing from one material into another.
Scientists measure this bending of radiation by its "index of refraction." Refraction causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside. Each material has its own refraction index, which describes how much light will bend in that particular material. All natural materials, such as glass, air and water, have positive refractive indices.
However, the nanoantenna arrays can cause light to bend in a wide range of angles including negative angles of refraction.
"Importantly, such dramatic deviation from the conventional Snell's law governing reflection and refraction occurs when light passes through structures that are actually much thinner than the width of the light's wavelengths, which is not possible using natural materials," Shalaev said. "Also, not only the bending effect, refraction, but also the reflection of light can be dramatically modified by the antenna arrays on the interface, as the experiments showed."
The nanoantennas are V-shaped structures made of gold and formed on top of a silicon layer. They are an example of metamaterials, which typically include so-called plasmonic structures that conduct clouds of electrons called plasmons. The antennas themselves have a width of 40 nanometers, or billionths of a meter, and researchers have demonstrated they are able to transmit light through an ultrathin "plasmonic nanoantenna layer" about 50 times smaller than the wavelength of light it is transmitting.
"This ultrathin layer of plasmonic nanoantennas makes the phase of light change strongly and abruptly, causing light to change its propagation direction, as required by the momentum conservation for light passing through the interface between materials," Shalaev said.
The work has been funded by the U.S. Air Force Office of Scientific Research and the National Science Foundation's Division of Materials Research.