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Physicists from the Moscow Institute of Physics and Technology (MIPT) have found that the two-dimensional form of carbon, known as graphene, might be the ideal material for manufacturing plasmonic devices capable of detecting explosive materials, toxic chemicals, and other organic compounds based on a single molecule, says an article published in Physical Review B.

 

Plasmons in constructing high-accuracy electronics and optics

 

Scientists have long been fascinated by the potential applications of a quasiparticle called the plasmon, a quantum of plasma oscillations. In the case of a solid body, plasmons are the oscillations of free electrons. Of special interest are the effects arising from the surface interactions of electromagnetic waves with plasmons—usually in the context of metals or semimetals, as they have a higher free electron density. Harnessing these effects could bring about a breakthrough in high-accuracy electronics and optics. One possibility opened up by plasmonic effects is the subwavelength light focusing, which increases the sensitivity of plasmonic devices to a point where they can distinguish a single molecule. Such measurements are beyond what any conventional (classical) optical devices can achieve. Unfortunately, plasmons in metals tend to lose energy quickly due to resistance, and for this reason they are not self-sustained, i.e. they need continuous excitation. Scientists are trying to tackle this issue by using composite materials with predefined microstructure, including graphene.

 

Graphene is an allotrope of carbon in the form of a two-dimensional crystal. It can be visualised as a one-atom-thick honeycomb lattice made of carbon atoms. Two MIPT graduates, Andre Geim and Konstantin Novoselov, were the first to isolate graphene, which won them a Nobel Prize in Physics. Graphene is a semiconductor with extremely high charge carrier mobility. Its electrical conductivity is also exceptionally high, which makes graphene-based transistors possible.

 

Theoretical physicists give the okay

 

Although, plasmonic devices have seemed an exciting prospect to pursue from the start, to take advantage of them, it was first necessary to find out whether the technology behind them was feasible. To do this, scientists had to find a numerical solution to the relevant quantum-mechanical equations. This was accomplished by a team of researchers at the Laboratory of Nanostructure Spectroscopy headed by Prof. Yurii Lozovik: they formulated and solved the necessary equation. Their research has led them to develop a quantum model that predicts plasmonic behaviour in graphene. As a result, the scientists described the operation of a surface-plasmon-emitting diode (SPED) and the nanoplasmonic counterpart of the laser—known as the spaser—whose construction involves a graphene layer.spaser_слайдер.png

Pic.: Design of the spaser with the graphene layer shown as a honeycomb lattice above the dielectric layer (blue). The spaser is optically pumped through the active (gain) medium shown in orange.

 

A spaser could be described as a device similar to a laser and operating on the same basic principle. However, to produce radiation, it relies on optical transitions in the gain medium, and the particles emitted are surface plasmons, as opposed to photons produced by a laser. An SPED is different from a spaser in that it is an incoherent source of surface plasmons. It also requires considerably lower pump power. Both devices would operate within the infrared region of the spectrum, which is useful for studying biological molecules.

 

‘The graphene spaser could be used to design compact spectral measurement devices capable of detecting even a single molecule of a substance, which is essential for many potential applications. Such sensors could detect organic molecules based on their characteristic vibrational transitions (‘fingerprints’), as the light emitted/absorbed falls into the medium infrared region, which is exactly where the graphene-based spaser operates,’ says Alexander Dorofeenko, one of the authors of the study.

Source news: https://mipt.ru/english/news/_sniffer_plasmons_could_detect_explosives?sphrase_id=143931

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In September 26 at the Institute of Physics of Kazan Federal University, a joint seminar was launched with researchers from Shahid Beheshti University of Tehran.

26 сентября в Институте физики КФУ начал свою работу совместный  семинар с исследователями из Университета им. Шахида Бехешти из Тегерана.

Основная цель форума – прямое общение между физиками Казанского университета и участниками семинара из Ирана и установление взаимовыгодного сотрудничества. Семинар начался с устных сессий; а во вторник, 27 сентября, запланировано посещение коллегами из Ирана лабораторий Института физики.

Тегеранский университет им. Шахида Бехешти  готовит студентов по различным отраслям – от гуманитарных до естественнонаучных – уже 57 лет. По данным различных рейтингов, он входит в 500 известных вузов мира. Его сотрудничество с российскими вузами ведет свою двухдесятилетнюю историю. А студенты из Ирана учатся в КФУ уже 2 года. Иранские ученые приехали лично познакомиться с коллегами из Казанского университета и надеются на дальнейшее сотрудничество.

 

Иранцы ,КФу, Институт физики, университет имени шахида бехешти

dr-hamidi

 

News source:http://kpfu.ru/news/irancy-247132.html

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Congratulations to Ms Borumand for her master thesis defense!

 

ms-borumand-en

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Congratulations to Mr Behjati for his master thesis defense!

1en-behjati

 

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Congratulations to Ms Jafari for her master thesis defense!

 

jafari-en

 

 

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Silicon holograms harness the full visible spectrum to bring holographic projections one step closer.

We can’t yet send holographic videos to Obi-Wan Kenobi on our droid, but researchers at Agency for Science, Technology and Research (A*STAR), Singapore, have got us a little bit closer by creating holograms from an array of silicon structures that work throughout the visible spectrum.

Many recent advances in hologram technology use reflected light to form an image; however the hologram made by Dong Zhaogang and Joel Yang from the A*STAR Institute of Materials Research and Engineering uses transmitted light. This means the image is not muddled up with the light source.

The team demonstrated the hologram of three flat images at wavelengths ranging from blue (480 nanometers) to red (680 nanometers). The images appeared in planes 50 microns apart for red and higher spacings for shorter wavelengths.

“In principle, it can be tuned to any wavelength,” says Yang.

Holograms can record three-dimensional images, which mean they can store large amounts of information in increasingly thin layers.

Recently, holograms that are mere hundredths of the thickness of a human hair have been made from metal deposited onto materials such as silicon. The holograms are created by nanoscale patterns of metal that generate electromagnetic waves that travel at the metal-silicon interface; a field called plasmonics.

Silicon holograms are slightly thicker than the metal-based ones, but have the advantage of being broadband. Plasmonic holograms only operate in the red wavelengths because they undergo strong absorption at blue wavelengths.

A disadvantage of the silicon holograms is their poor efficiency at only three per cent; however Dong estimates this could easily be tripled.

“The losses can be lowered by optimizing the growth method to grow polycrystalline silicon instead of amorphous silicon,” he says.

The hologram is an array of tiny silicon skyscrapers, 370 nanometers tall with footprints 190 nanometers by 100 nanometers. Unlike a city grid, however, the tiny towers are not laid out in neat squares but at varying angles.

The hologram operates with circularly polarized light, and the information is encoded on to the light beam by the varied angles of the skyscrapers. These alter the phase of the transmitted light through the ‘Pancharatnam-Berry effect’.

“What’s interesting about this hologram is that it controls only the phase of the light by varying the orientation of the silicon nanostructures. The amplitude is the same everywhere; in principle you can get a lot of light transmitted,” says Yang.

The A*STAR researchers focused on nanofabrication and measurements and collaborated with Cheng-Wei Qiu from National University of Singapore, whose team specializes in hologram design.


Story Source:

The above post is reprinted from materials provided by The Agency for Science, Technology and Research (A*STAR).Note: Content may be edited for style and length.


Journal Reference:

  1. Kun Huang, Zhaogang Dong, Shengtao Mei, Lei Zhang, Yanjun Liu, Hong Liu, Haibin Zhu, Jinghua Teng, Boris Luk’yanchuk, Joel K.W. Yang, Cheng-Wei Qiu. Silicon multi-meta-holograms for the broadband visible light. Laser & Photonics Reviews, 2016; 10 (3): 500 DOI:10.1002/lpor.201500314

News source: The Agency for Science, Technology and Research (A*STAR). “Silicon brings more color to holograms.” ScienceDaily. ScienceDaily, 12 August 2016. <www.sciencedaily.com/releases/2016/08/160812190822.htm>.

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Some “forbidden” light emissions are in fact possible, could enable new sensors and light-emitting devices.

David L. Chandler | MIT News Office
July 14, 2016

Emission spectra are a widely used method for identifying chemical compounds; the bright lines reveal the different frequencies of light that can be emitted by an atom. Here, a normal emission spectrum for an atom in a high-energy state (top) is compared to the emission from the same atom placed just a few nanometers (billionths of a meter) away from graphene that has been doped with charge carriers (bottom). For each energy-level transition, an orange line (or purple cloud) appears if that transition is estimated to be faster than one per microsecond — making it frequent enough to be observed.

Emission spectra are a widely used method for identifying chemical compounds; the bright lines reveal the different frequencies of light that can be emitted by an atom. Here, a normal emission spectrum for an atom in a high-energy state (top) is compared to the emission from the same atom placed just a few nanometers (billionths of a meter) away from graphene that has been doped with charge carriers (bottom). For each energy-level transition, an orange line (or purple cloud) appears if that transition is estimated to be faster than one per microsecond — making it frequent enough to be observed.

A new MIT study could open up new areas of technology based on types of light emission that had been thought to be “forbidden,” or at least so unlikely as to be practically unattainable. The new approach, the researchers say, could cause certain kinds of interactions between light and matter, which would normally take billions of years to happen, to take place instead within billionths of a second, under certain special conditions.

The findings, based on a theoretical analysis, are reported today in the journal Science in a paper by MIT doctoral student Nicholas Rivera, Department of Physics Professor Marin Soljačić, Francis Wright Davis Professor of Physics John Joannopoulos, and postdocs Ido Kaminer and Bo Zhen.

Interactions between light and matter, described by the laws of quantum electrodynamics, are the basis of a wide range of technologies, including lasers, LEDs, and atomic clocks. But from a theoretical standpoint, “Most light-matter interaction processes are ‘forbidden’ by electronic selection rules, which limits the number of transitions between energy levels we have access to,” Soljačić explains.

For example, spectrograms, which are used to analyze the elemental composition of materials, show a few bright lines against a mostly dark background. The bright lines represent the specific “allowed” energy level transitions in the atoms of that element that can be accompanied by the release of a photon (a particle of light). In the dark regions, which make up most of the spectrum, emission at those energy levels is “forbidden.”

With this new study, Kaminer says, “we demonstrate theoretically that these constraints can be lifted” using confined waves within atomically thin, 2-D materials. “We show that some of the transitions which normally take the age of the universe to happen could be made to happen within nanoseconds. Because of this, many of the dark regions of a spectrogram become bright once an atom is placed near a 2-D material.”

Electrons in an atom have discrete energy levels, and when they hop from one level to another they give off a photon of light, a process called spontaneous emission. But the atom itself is much smaller than the wavelength of the light that gets emitted — about 1/1,000 to 1/10,000 as big — substantially impairing the interactions between the two.

The trick is, in effect, to “shrink” the light so it better matches the scale of the atom, as the researchers show in their study. The key to enabling a whole range of interactions, specifically transitions in atomic states that relate to absorbing or emitting light, is the use of a two-dimensional material called graphene, in which light can interact with matter in the form of plasmons, a type of electromagnetic oscillation in the material.

These plasmons, which resemble photons but have wavelengths hundreds of times shorter, are very narrowly confined in the graphene, in a way that makes some kinds of interactions with that matter many orders of magnitude more likely than they would be in ordinary materials. This enables a variety of phenomena normally considered unattainable, such as the simultaneous emission of multiple plasmons, or two-step light-emitting transitions between energy levels, the team says.

This method can enable the simultaneous emission of two photons that are “entangled,” meaning they share the same quantum state even when separated. Such generation of entangled photons is an important element in quantum devices, such as those that might be used for cryptography.

Making use of these forbidden transitions could open up the ability to tailor the optical properties of materials in ways that had not been thought possible, Rivera says. “By altering these rules” about the relationship between light and matter, “it can open new doors to reshaping the optical properties of materials.”

Kaminer predicts that this work “will serve as a founding piece for the next generation of studies on light-matter interactions” and could lead to “further theoretical and experimental advances in many fields which rely on light-matter interactions, including atomic, molecular and optical physics, photonics, chemistry, optoelectronics, and many others.”

Beyond its scientific implications, he says, “this study has possible applications across multiple disciplines, since in principle it has potential to enable the full use of the periodic table for optical applications.” This could potentially lead to applications in spectroscopy and sensing devices, ultrathin solar cells, new kinds of materials to absorb solar energy, organic LEDs with higher efficiencies, and photon sources for possible quantum computing devices.

“From the standpoint of fundamental science, this work lays the groundwork for a subfield that just a few years ago was difficult to imagine and until now was largely unexplored,” Soljačić says.

“Two-dimensional materials confine fields to a surface and motion to a plane, making possible many effects that are orders-of-magnitude too weak to appear in a bulk volume,” says Jason Fleischer, an associate professor of electrical engineering at Princeton University, who was not involved in this research. This work, he says, “systematically explores how 2-D materials improve light-matter interactions, laying a theoretical foundation for faster electronic transitions, enhanced sensing, and better emission, including the compact generation of broadband and quantum light.”

The work was partly supported by the Army Research Office through the Institute for Soldier Nanotechnologies at MIT, and by the U.S. Department of Energy.

The link was sent to us by Ms. Asghari.

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Evangelia Vezouviou et al., have reported  a near infrared holographic glucose sensor. Real-time glucose monitoring has been beneficial in reducing health complications associated with diabetes as well as a decrease in mortality. This report describes a novel holographic platform, fabricated via laser ablation on chitosan hydrogel with gold nanoparticles with a replaying in visible and near IR. The sensor responded with a 12nm and 7nm shift in waveleng that glucose concentrations in the 0.70 mM range and in the visible and near IR, respectively, at pH 7.4 and an ionic strength of 154 mM. The sensor did not respond to potential interferences found in the interstitial fluid, such as fructose, vitamin C and lactate, at the irrespective normal concentrations and was stable to fluctuations in temperature, pH and ionic strength. The characteristics of this sensor suggest that it may be applicable for use as an implanted device for the real time monitoring of glucose concentrations in the interstitial fluid using near IR as the interrogating medium.

 

picNas

Holographic fabrication. A photosensitive emulsion (1) coated on a glass slide (2) is placed inside a tray with a 7° spacer (3) and facing towards a reflecting mirror (4).Upon exposure to the laser irradiation (5), the gold nanoparticle grains are arranged in fringes (6) align in parallel to the surface of the polymer, and are separated by half the distance of the wavelength they were exposed to. The diagram is not to scale.

 

 

Refrence:

Evangelia Vezouviou, Christopher R. Lowe – 2015 – Biosensors and Bioelectronics 68 ,371–381.

http://dx.doi.org/10.1016/j.bios.2015.01.014.

 

News sent to our group by Ms. Khajemiri

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If you want to measure the temperature at any point on an object’s surface, a thin coating of programmable material can do the job, say computer scientists.

  • January 11, 2016

The world is full of complex structures such as bridges, roads, wind turbines, power stations, and so on, that have to be carefully monitored to ensure their integrity.

Today, much of this work has to be done by engineers on the spot. That’s not so easy for objects that span hundreds, or even thousands, of kilometers, such as roads, or remote structures such as offshore wind turbines.

So a way of doing this remotely would be hugely valuable. Clearly it requires some kind of independent sensor that can measure the required property such as temperature or acidity, or cracking, and so on.

And indeed there are numerous gadgets for doing this. For example, optical fibers attached to or embedded in objects can measure the forces acting on it and sensors attached to these fibers can monitor temperature, acidity, and so on.

But these kinds of sensors do not provide global coverage—they cannot tell you the temperature at any point on the object. For that you need something more ambitious.

The dream would be to have a smart coating that does this job. This would be a “programmable material” that entirely coats an object in a thin layer. It would contain tiny particulate sensors that gather information about the surface, such as its temperature, and communicate it to their nearest neighbors.

While mathematicians have long pondered the properties of programmable materials, one question has stumped them. Is it possible to use a smart coating to determine the temperature at any point on an arbitrary object, even though the sensors have no knowledge of its overall geometry?

Today, we get an answer to this question thanks to the work of Zahra Derakhshandeh at Arizona State University in Tempe and a few pals. They’ve developed a series of algorithms that provide the mathematical framework that allows these particles to solve this problem.

To make this work, the particulate sensors and the coating must have certain properties. Derakhshandeh and co say the sensors must be able to move within the surface and to make, and break, communication bonds with their nearest neighbors. The object must have a geometry that allows a uniform coating.

Under those conditions, Derakhshandeh and co say that their framework functions as a universal coating algorithm for programmable matter. The particles need only have limited memory and communicate only over short distances and are entirely anonymous—in other words they are all equivalent.

That’s curious work that could one day lead to some useful applications in remote monitoring.

There is still work to be done, however. Given the task of measuring some property of the material at a specific point, one important problem is how quickly the algorithm can do this. To find out, the team suggests testing the algorithm in a simulation or with real programmable matter. It will be interesting to see how they get on.

Another important problem will be the energy efficiency of this kind of programmable matter. What kind of communications overhead does the coating problem impose and could the energy for this conceivably be harvested from the environment?

It’s still early days for programmable matter and for a universal coating. But the savings that Derakhshandeh and co’s algorithms might allow are considerable, given the cost of monitoring and maintaining off shore wind turbines, for example. That alone should guarantee further interest in this topic for the future.

Ref: http://arxiv.org/abs/1601.01008 : Universal Coating for Programmable Matter

https://www.technologyreview.com/s/545346/programmable-material-algorithm-solves-universal-coating-problem/

 

News sent to our group by Ms. Asghari

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Tugchin et al.,  study experimentally the excitation of the radially polarized conical surface plasmon polariton (SPP) in a fully metal-coated conically tapered M-profile fiber which works as a “plasmonic tip” for the scanning near-field optical microscope (SNOM). This structure extends the Kretschmann configuration to the conical geometry. In this plasmonic tip, the radially polarized waveguide mode, propagating inside the fiber, resonantly excites the radially polarized SPP on the metal surface, which consequently gets confined at the apex where the field oscillates longitudinally along the tip axis. We also demonstrate the reverse process, where a longitudinal field excites the radially polarized SPP mode which then resonantly excites the radially polarized waveguide mode. This plasmonic tip combines the advantageous properties of near-field optical probes. Though, it has the shape of an apertureless SNOM tip, it can simplify the detection/excitation procedure and suppresses the background signal by its fiber-based design. Unlike the sharp apertureless SNOM tips that detects only the longitudinal field component or aperture SNOM tips that detect mostly the transversal component, the plasmonic tip detects both longitudinal and transversal field in collection mode and backward-scattering mode, respectively. The plasmonic tip, with further improvements, can become an advanced tool in SNOM due to its ability for background-free near-field detection, ease of operation, and higher conversion efficiency from far-field to near-field than conventional tips.

The link of published paper can be found here:

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.5b00339?journalCode=apchd5


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