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Goray L.,Saint Petersburg Academic University | Lubov M.,RAS Ioffe Physical - Technical Institute
Optics Express | Year: 2015

Combined computer simulations of the growth of multilayer mirrors and their exact differential reflection coefficients in the soft-x-ray- EUV range have been conducted. The proposed model describes the variation of the surface roughness of the multilayer Al/Zr mirror boundary profiles taking into account a random noise source. Theoretically calculated Al/Zr boundary profiles allow one to know real rough boundary statistics including rms roughnesses and correlation lengths and, to obtain rigorously EUV specular and diffuse reflection coefficients. The proposed integrated approach opens up a way to performing exact theoretical studies similar in accuracy to results obtained by quantitative microscopy investigations of nanoreliefs and synchrotron radiation measurements. © 2015 Optical Society of America.


Voronov D.L.,Lawrence Berkeley National Laboratory | Goray L.I.,Saint Petersburg Academic University | Warwick T.,Lawrence Berkeley National Laboratory | Yashchuk V.V.,Lawrence Berkeley National Laboratory | Padmore H.A.,Lawrence Berkeley National Laboratory
Optics Express | Year: 2015

A grand challenge in soft x-ray spectroscopy is to drive the resolving power of monochromators and spectrometers from the 104 achieved routinely today to well above 105. This need is driven mainly by the requirements of a new technique that is set to have enormous impact in condensed matter physics, Resonant Inelastic X-ray Scattering (RIXS). Unlike x-ray absorption spectroscopy, RIXS is not limited by an energy resolution dictated by the core-hole lifetime in the excitation process. Using much higher resolving power than used for normal x-ray absorption spectroscopy enables access to the energy scale of soft excitations in matter. These excitations such as magnons and phonons drive the collective phenomena seen in correlated electronic materials such as high temperature superconductors. RIXS opens a new path to study these excitations at a level of detail not formerly possible. However, as the process involves resonant excitation at an energy of around 1 keV, and the energy scale of the excitations one would like to see are at the meV level, to fully utilize the technique requires the development of monochromators and spectrometers with one to two orders of magnitude higher energy resolution than has been conventionally possible. Here we investigate the detailed diffraction characteristics of multilayer blazed gratings. These elements offer potentially revolutionary performance as the dispersive element in ultrahigh resolution x-ray spectroscopy. In doing so, we have established a roadmap for the complete optimization of the grating design. Traditionally 1st order gratings are used in the soft x-ray region, but we show that as in the optical domain, one can work in very high spectral orders and thus dramatically improve resolution without significant loss in efficiency. ©2015 Optical Society of America.


Goray L.I.,Saint Petersburg Academic University
Proceedings of the International Conference Days on Diffraction 2015, DD 2015 | Year: 2015

A general expression derived from Poynting's theorem reports the well-posedness of energy conservation for a weak formulation of diffraction by lossy anisotropic inhomogeneous one-and biperiodic gratings. Formulas allow direct absorption calculus with the same rigor as solutions of Maxwell's equations, i.e. via distributions employed to describe the field. Absorption integrals, valid for any rigorous method, are expressed using the near field and conductivity tensors in the volume or on the surface restricting a grating domain between uniform medias. © 2015 IEEE.


Ng K.W.,University of California at Berkeley | Ko W.S.,University of California at Berkeley | Tran T.-T.D.,University of California at Berkeley | Chen R.,University of California at Berkeley | And 6 more authors.
ACS Nano | Year: 2013

The heterogeneous integration of III-V optoelectronic devices with Si electronic circuits is highly desirable because it will enable many otherwise unattainable capabilities. However, direct growth of III-V thin film on silicon substrates has been very challenging because of large mismatches in lattice constants and thermal coefficients. Furthermore, the high epitaxial growth temperature is detrimental to transistor performance. Here, we present a detailed studies on a novel growth mode which yields a catalyst-free (Al,In)GaAs nanopillar laser on a silicon substrate by metal-organic chemical vapor deposition at the low temperature of 400 °C. We study the growth and misfit stress relaxation mechanism by cutting through the center of the InGaAs/GaAs nanopillars using focused ion beam and inspecting with high-resolution transmission electron microscopy. The bulk material of the nanopillar is in pure wurtzite crystal phase, despite the 6% lattice mismatch with the substrate, with all stacking disorders well confined in the bottom-most transition region and terminated horizontally. Furthermore, InGaAs was found to be in direct contact with silicon, in agreement with the observed crystal orientation alignment and good electrical conduction across the interface. This is in sharp contrast to many III-V nanowires on silicon which are observed to stem from thin SiNx, SiO2, or SiO2/Si openings. In addition, GaAs was found to grow perfectly as a shell layer on In0.2Ga 0.8As with an extraordinary thickness, which is 15 times greater than the theoretical thin-film critical thickness for a 1.5% lattice mismatch. This is attributed to the core-shell radial geometry allowing the outer layers to expand and release the strain due to lattice mismatch. The findings in this study redefine the rules for lattice-mismatched growth on heterogeneous substrates and device structure design. © 2012 American Chemical Society.


Goray L.I.,Saint Petersburg Academic University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

The paper reports on development of an integral and nondestructive technique of characterization of low-dimensional periodically arranged nanocrystals (LDPAN) by spectroscopic scatterometry in the UV-IR ranges. Some approaches to the solution of direct and inverse problems in scatterometry are addressed. For the solution of the direct problem, the author has chosen the universal method of boundary integral equations, which has demonstrated a broad range of applicability and a high accuracy. Cases are analyzed in which a complicated three-dimensional diffraction problem involving 2D gratings can be reduced to a two-dimensional one with 1D gratings, or multilayer mirrors with plane boundaries. An algorithm is proposed for the solution of a system of nonlinear operator equations with an arbitrary, but limited set of unknown LDPAN structural parameters, and a given set of measured values of diffraction efficiency. The functional to be minimized in the course of solution of the inverse problem is identified, and methods of its regularization and for monitoring the accuracy of the solution are proposed. A Fortran code written with the use of the Löwenberg-Markwardt gradient method has turned out an efficient way to the solution of model problems for a Si grating with a trapezoidal profile. © 2011 SPIE.


Kaliteevski M.A.,RAS Ioffe Physical - Technical Institute | Lazarenko A.A.,Saint Petersburg Academic University
Technical Physics Letters | Year: 2013

It was widely accepted that embedding of metallic layers into optoelectronic structures is detrimental to lasing due to the absorption in the metal. However, recently macroscopic optical coherence and lasing was observed in microcavities with an intra-cavity single metallic layer. Here we propose the design of the of microcavity-type structure with two or more intra-cavity metallic layers which could serve as contacts for electrical pumping. The design of optical modes based on utilizing peculiarities of Tamm plasmon provides vanishing absorption due to the fixing of the node of the electric field of optical mode to metallic layers. Proposed design can be used for fabrication of vertical cavity lasers with intra-cavity metallic contacts. © 2013 Pleiades Publishing, Ltd.


Beznogov M.V.,Saint Petersburg Academic University | Yakovlev D.G.,RAS Ioffe Physical - Technical Institute
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

We calculate interdiffusion coefficients in a two-component, weakly or strongly coupled ion plasma (gas or liquid, composed of two ion species immersed into a neutralizing electron background). We use an effective potential method proposed recently by Baalrud and Daligaut [Phys. Rev. Lett. 110, 235001 (2013)PRLTAO0031-900710.1103/PhysRevLett.110.235001]. It allows us to extend the standard Chapman-Enskog procedure of calculating the interdiffusion coefficients to the case of strong Coulomb coupling. We compute binary diffusion coefficients for several ionic mixtures and fit them by convenient expressions in terms of the generalized Coulomb logarithm. These fits cover a wide range of plasma parameters spanning from weak to strong Coulomb couplings. They can be used to simulate diffusion of ions in ordinary stars as well as in white dwarfs and neutron stars. © 2014 American Physical Society.


News Article | April 28, 2016
Site: www.cemag.us

A group of scientists from ITMO University has put forward a new approach to effective manipulation of light at the nanoscale based on hybrid metal-dielectric nanoantennas. The new technology is a driver for developing new platform for ultradense optical data recording and for producing a wide range of optical nanodevices capable of localizing, enhancing and manipulating light at the nanoscale. The results of the study were published in Advanced Materials. Nanoantenna is a device that converts freely propagating light into localized light – compressed into several tens of nanometers. The localization enables scientists to effectively control light at the nanoscale. This is one of the reasons why nanoantennas may become the fundamental building blocks of future optical computers that rely on photons instead of electrons to process and transmit information. This inevitable replacement of the information carrier is related to the fact that photons surpass electrons by several orders of magnitude in terms of information capacity, require less energy, rule out circuit heating and ensure high velocity data exchange. Until recently, the production of planar arrays of hybrid nanoantennas for light manipulation was considered an extremely painstaking process. A solution to this problem was found by ITMO University researchers in collaboration with colleagues from Saint Petersburg Academic University and Joint Institute for High Temperatures in Moscow. The researchers were the first who developed a technique for creating such arrays of hybrid nanoantennas and for high-accuracy adjustment of individual nanoantennas within the array. It was made by subsequently combining two production stages: lithography and precise exposure of the nanoantenna to a femtosecond laser – ultrashort impulse laser. The practical application of hybrid nanoantennas lies, in particular, within the field of ultradense data recording. Modern optical drives can record information with density around 10 Gbit/inch2, which equals to the size of a single pixel of a few hundred nanometers. Although such dimensions are comparable to the size of the nanoantennas, the scientists propose to additionally control their color in the visible spectrum.  This procedure leads to the addition of one more ‘dimension’ for data recording, which immediately increases the entire data storage capacity of the system. Apart from ultradense data recording, the selective modification of hybrid nanoantennas can help create new designs of hybrid metasurfaces, waveguides and compact sensors for environmental monitoring. In the nearest future, the research group plans to focus on the development of such specific applications of their hybrid nanoantennas. The nanoantennas are made of two components: a truncated silicon cone and a thin golden disk located on its` top. The researchers demonstrated that, thanks to nanoscale laser reshaping, it is possible to precisely modify the shape of the golden particle without affecting the silicon cone. The change in the shape of the golden particle results in changing optical properties of the nanoantenna as a whole due to different degrees of resonance overlap between the silicon and golden nanoparticles. “Our method opens a possibility to gradually switch the optical properties of nanoantennas by means of selective laser melting of the golden particles. Depending on the intensity of the laser beam the golden particle will either remain disc-shaped, convert into a cup or become a globe. Such precise manipulation allows us to obtain a functional hybrid nanostructure with desired properties in the flicker of a second,” comments Sergei Makarov, one of the authors of the paper and researcher at the Department of Nanophotonics and Metamaterials of ITMO University. Contrary to conventional heat-induced fabrication of nanoantennas, the new method allows to adjust individual nanoantennas within the array and exert precise control over overall optical properties of the hybrid nanostructures. “Our concept of asymmetric hybrid nanoantennas unifies two approaches that were previously thought to be mutually exclusive: plasmonics and all-dielectric nanophotonics. Our hybrid nanostructures inherited the advantages of both approaches – localization and enhancement of light at the nanoscale, low optical losses and the ability to control the scattering power pattern. Furthermore using of laser reshaping helps us precisely and quickly change the optical properties of such structures and perhaps even record information with extremely high density,” concludes Dmitry Zuev, lead author of the study and researcher at the Department of Nanophotonics and Metamaterials of ITMO University.


News Article | December 21, 2016
Site: phys.org

Schematic sketches of UV generation from (a) smooth and (c) nanostructured Si film. (b) Principle of Si film laser-induced nanostructuring. Credit: ITMO University Russian researchers have developed a new material that converts infrared light to ultrashort pulses of ultraviolet. For this purpose, the scientists exposed silicon film to a laser so that its relief adjusted under the light wavelength and made properties of the material resonant. The result was a cheap and easy-to-make metasurface as effective as existing ones. The new technology is applicable in compact UV generators for biophotonics and medicine, and also devices for ultradense data processing in optical communications. The study was published in Nanoscale. Biological media can reflect, absorb, scatter and re-emit light waves. Each of these processes contains information about micro- and macrostructure of the media, as well as shape and motion of its components. In this regard, deep ultraviolet is a promising tool for biology and medicine. Its application includes laser diagnostics and control of fast processes in cells, laser therapy and surgery at the molecular level. Researchers from ITMO University and Saint Petersburg Academic University have developed a new method for nanostructures fabricating, which is able to convert infrared light to deep ultraviolet. The structure is a film with a regular massive of nanolumps – metasurface. It is generated by radiating silicon film, whose thickness is 100 nanometers, with ultrashort or femtosecond laser pulses that form its relief. On the film surface, the laser smelts such nanolumps, which resonate only with its wavelength and thus allow more radiation to be turned into ultraviolet. In other words, the laser adjusts metasurface to itself. When the relief is formed, the scientists reduce the power so the film starts converting radiation without deformation. The researchers have managed not only to convert infrared light into violet, but also to get deep ultraviolet. Such radiation is strongly localized, has very short wavelength and distributes as femtosecond pulses. "For the first time, we've created a metasurface that stably emits femtosecond pulses of high power in the ultraviolet range," notes Anton Tsypkin, assistant of ITMO's Department of Photonics and Optical Information Technology. "Such light can be applied in biology and medicine, as femtosecond pulses affect biological objects more precisely." For example, using deep UV, researchers can image a molecule during its chemical transformation and understand how to manage it. "A femtosecond compared to a second is almost like a second compared to the lifetime of the universe. It's even faster than the vibration of atoms in molecules. So such short pulses can tell us a lot about matter structure in motion," says first author Sergey Makarov, senior research associate of ITMO's Department of Nano-Photonics and Metamaterials. The new technology may also find applications in optical communications. "Using ultrashort laser pulses for data transmission, we will make the flow denser and enhance its speed. It will increase the performance of systems for transferring and processing information. Additionally, we can integrate such metasurfaces into an optical chip to change beam frequency. This will help separate data flows and enable major computing at the same time," comments Anton Tsypkin. The metasurface obtained in this way is a monolithic structure, as opposed to being assembled of isolated particles, as it was before. It conducts heat better and thus lives longer without overheating. In photonics, researchers always have to search for compromise. Standard nonlinear crystals used for ultraviolet generation are big, but can convert up to 20 percent of radiation. Such efficiency is higher than that of metasurfaces, but laser pulses lengthen inside crystals. "This happens because a laser beam contains many wavelengths that differ from each other only by several decades of nanometers. Such variance is enough to make some waves surpass others. In order to make pulses ultrashort again, additional expensive devices are required," explains Makarov. Thin structures such as metasurfaces do not allow laser pulses to misalign, but still have a low efficiency. Furthermore, both metasurfaces and crystals are usually expensive and difficult to make. However, in the new study, the scientists have managed to make metasurface fabrication much easier and cheaper, and at the same time, these surfaces are as effective as their expensive counterparts. Explore further: Versatile optical laser will enable innovative experiments at atomic-scale measurements More information: S. V. Makarov et al. Self-adjusted all-dielectric metasurfaces for deep ultraviolet femtosecond pulse generation, Nanoscale (2016). DOI: 10.1039/C6NR04860A


News Article | April 29, 2016
Site: www.nanotech-now.com

Abstract: A group of scientists from ITMO University in Saint Petersburg has put forward a new approach to effective manipulation of light at the nanoscale based on hybrid metal-dielectric nanoantennas. The new technology promises to bring about a new platform for ultradense optical data recording and pave the way to high throughput fabrication of a wide range of optical nanodevices capable of localizing, enhancing and manipulating light at the nanoscale. The results of the study were published in Advanced Materials. Nanoantenna is a device that converts freely propagating light into localized light - compressed into several tens of nanometers. The localization enables scientists to effectively control light at the nanoscale. This is one of the reasons why nanoantennas may become the fundamental building blocks of future optical computers that rely on photons instead of electrons to process and transmit information. This inevitable replacement of the information carrier is related to the fact that photons surpass electrons by several orders of magnitude in terms of information capacity, require less energy, rule out circuit heating and ensure high velocity data exchange. Until recently, the production of planar arrays of hybrid nanoantennas for light manipulation was considered an extremely painstaking process. A solution to this problem was found by researchers from ITMO University in collaboration with colleagues from Saint Petersburg Academic University and Joint Institute for High Temperatures in Moscow. The research group has for the first time developed a technique for creating such arrays of hybrid nanoantennas and for high-accuracy adjustment of individual nanoantennas within the array. The achievement was made possible by subsequently combining two production stages: lithography and precise exposure of thenanoantenna to a femtosecond laser - ultrashort impulse laser. The practical application of hybrid nanoantennas lies, in particular, within the field of ultradense data recording. Modern optical drives can record information with density around 10 Gbit/inch2, which equals to the size of a single pixel of a few hundred nanometers. Although such dimensions are comparable to the size of the nanoantennas, the scientists propose to additionally control their color in the visible spectrum. This procedure leads to the addition of yet another 'dimension' for data recording, which immediately increases the entire data storage capacity of the system. Apart from ultradense data recording, the selective modification of hybrid nanoantennas can help create new designs of hybrid metasurfaces, waveguides and compact sensors for environmental monitoring. In the nearest future, the research group plans to focus on the development of such specific applications of their hybrid nanoantennas. The nanoantennas are made of two components: a truncated silicon cone with a thin golden disk located on top. The researchers demonstrated that, thanks to nanoscale laser reshaping, it is possible to precisely modify the shape of the golden particle without affecting the silicon cone. The change in the shape of the golden particle results in changing optical properties of the nanoantenna as a whole due to different degrees of resonance overlap between the silicon and golden nanoparticles. "Our method opens a possibility to gradually switch the optical properties of nanoantennas by means of selective laser melting of the golden particles. Depending on the intensity of the laser beam the golden particle will either remain disc-shaped, convert into a cup or become a globe. Such precise manipulation allows us to obtain a functional hybrid nanostructure with desired properties in the flicker of a second," comments Sergey Makarov, one of the authors of the paper and researcher at the Department of Nanophotonics and Metamaterials of ITMO University. Contrary to conventional heat-induced fabrication of nanoantennas, the new method raises the possibility of adjusting individual nanoantennas within the array and exerting precise control over overall optical properties of the hybrid nanostructures. "Our concept of asymmetric hybrid nanoantennas unifies two approaches that were previously thought to be mutually exclusive: plasmonics and all-dielectric nanophotonics. Our hybrid nanostructures inherited the advantages of both approaches - localization and enhancement of light at the nanoscale, low optical losses and the ability to control the scattering power pattern. In turn, the use of laser reshaping helps us precisely and quickly change the optical properties of such structures and perhaps even record information with extremely high density," concludes Dmitry Zuev, lead author of the study and researcher at the Department of Nanophotonics and Metamaterials of ITMO University. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

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