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  • 1.
    Dai, Jin
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Dyakov, Sergey A.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Enhanced near-field radiative heat transfer between corrugated metal plates: Role of spoof surface plasmon polaritons2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 3, article id 035419Article in journal (Refereed)
    Abstract [en]

    We demonstrate with the finite-difference time-domain method that radiative heat transfer between two parallel gold plates can be significantly enhanced by engraving periodic grooves with a subwavelength width on the plate surfaces. The enhancement increases with a decrease in the separation distance at near-field regime and it can be further efficiently improved by having a supercell with multiple grooves with different depths. We attribute this near-field enhancement to coupling of thermally excited spoof surface plasmon polaritons, a type of artificial surface wave inherent to structured metal surfaces [J. B. Pendry, L. Martin-Moreno, and F. J. Garcia-Vidal, Science 305, 847 (2004)]. The frequency-dependent contribution to the heat transfer, or transmission-factor spectrum, is confirmed by calculating the dispersion relation of guided modes by the two parallel corrugated plates through a finite-element method. Especially, the photonic density of states derived from the dispersion relation is found to have excellent agreement to the transmission-factor spectrum.

  • 2.
    Dyakov, Sergey A.
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Dai, Jin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Qiu, M.
    Thermal radiation dynamics in two parallel plates: The role of near field2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 4, p. 045414-Article in journal (Refereed)
    Abstract [en]

    The temperature dynamics of the radiative heat propagation in a multilayer structure is theoretically treated with a formalism combining the scattering matrix and Green's-functions methods. The time evolution of the temperature of parallel plates of silicon carbide in vacuum is simulated for different interplate distances and thicknesses of plates. The characteristic radiative heat exchange time and temperature of the plates at stationary state are determined from the time evolutions. The threshold interplate distance which separates heating and cooling regimes for the sink plate is found. We show that the variation of the interplate distance allows us to control the relaxation processes in the system of absorber and emitter.

  • 3.
    Dyakov, Sergey A.
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Dai, Jin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Near field thermal memory based on radiative phase bistability of VO22015In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 48, no 30, article id 305104Article in journal (Refereed)
    Abstract [en]

    We report the concept of a near-field memory device based on the radiative bistability effect in the system of two closely separated parallel plates of SiO2 and VO2 which exchange heat by thermal radiation in vacuum. We demonstrate that the VO2 plate, having metal-insulator transition at 340 K, has two thermodynamical steady-states. One can switch between the states using an external laser impulse. We show that due to near-field photon tunneling between the plates, the switching time is found to be only 5 ms which is several orders lower than in case of far field.

  • 4.
    Dyakov, Sergey A.
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Dai, Jin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Thermal self-oscillations in radiative heat exchange2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 6, article id 064103Article in journal (Refereed)
    Abstract [en]

    We report the effect of relaxation-type self-induced temperature oscillations in the system of two parallel plates of SiO2 and VO2 which exchange heat by thermal radiation in vacuum. The nonlinear feedback in the self-oscillating system is provided by metal-insulator transition in VO2. Using the method of fluctuational electrodynamics, we show that under the action of an external laser of a constant power, the temperature of VO2 plate oscillates around its phase transition value. The period and amplitude of oscillations depend on the geometry of the structure. We found that at 500 nm vacuum gap separating bulk SiO2 plate and 50 nm thick VO2 plate, the period of self-oscillations is 2 s and the amplitude is 4K, which is determined by phase switching at threshold temperatures of phase transition.

  • 5.
    Dyakov, Sergey
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Trinity College Dublin.
    Baldycheva, A.
    Perova, T. S.
    Li, G. V.
    Astrova, E. V.
    Gippius, N. A.
    Tikhodeev, S. G.
    Surface states in the optical spectra of two-dimensional photonic crystals with various surface terminations2012In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 11, p. 115126-1151268Article in journal (Refereed)
    Abstract [en]

    Reflection and transmission spectra of two-dimensional photonic crystal slabs, fabricated by photoelectrochemical etching of deep macropores and trenches in Si, are investigated theoretically and experimentally. It is shown that the presence of an unstructured silicon interfacial layer between the air and the photonic crystal structure can give rise to surface (Tamm) states within the TE and TM photonic stop bands. In the presence of roughness of inner surfaces of air pores, the surface states show up as dips within the stop bands in the reflection spectrum. The calculated electromagnetic near-field distribution demonstrates the vortices between the upper pores at the frequency of the surface mode. The experimental reflection and transmission spectra are in a good agreement with theoretical calculations performed by the Fourier modal method in the scattering matrix form.

  • 6.
    Dyakov, Sergey
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Trinity College Dublin.
    Perova, T. S.
    Miao, C. Q.
    Xie, Y. -H
    Cherevkov, S. A.
    Baranov, A. V.
    Influence of the buffer layer properties on the intensity of Raman scattering of graphene2013In: Journal of Raman Spectroscopy, ISSN 0377-0486, E-ISSN 1097-4555, Vol. 44, no 6, p. 803-809Article in journal (Refereed)
    Abstract [en]

    Using a model of oscillating dipoles, we simulate the intensity of the G-band in the Raman signal from structures consisting of graphene, separated by an arbitrary buffer layer from a substrate. It is found that a structure with an optimized buffer layer refractive index and thickness exhibits a Raman signal which is nearly 50 times more intense than that from the same structure with a non-optimized buffer layer. The theoretical simulations are verified by Raman measurements on structures consisting of a layer of graphene on SiO2 and Al2O3 buffer layers. The optical contrast of the single graphene layer is calculated for an arbitrary buffer layer. It was found that both the Raman intensity and optical contrast can be maximized by varying the buffer layer thickness.

  • 7.
    Dyakov, Sergey
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Skolkovo Institute of Science and Technology, Russia.
    Zhigunov, D. M.
    Marinins, Aleksandrs
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Shcherbakov, M. R.
    Fedyanin, A. A.
    Vorontsov, A. S.
    Kashkarov, P. K.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Zhejiang University, China.
    Zacharias, M.
    Tikhodeev, S. G.
    Gippius, N. A.
    Optical properties of silicon nanocrystals covered by periodic array of gold nanowires2016In: Physical Review B, ISSN 2469-9950, Vol. 93, no 20, article id 205413Article in journal (Refereed)
    Abstract [en]

    Extinction and photoluminescence spectra are experimentally and theoretically studied for a periodic array of gold nanowires deposited on top of a dielectric substrate containing silicon nanocrystals. Quasiguided modes are observed in the substrate resulting in modification of optical properties of silicon nanocrystals. Our calculations of extinction and photoluminescence spectra are in good agreement with experimental results. The periodicity provides a powerful tool for achieving a high photoluminescence outcoupling efficiency of silicon nanocrystals.

  • 8.
    Dyakov, Sergey
    et al.
    Department of Electronic and Electrical Engineering, Trinity College Dublin, Ireland.
    Zhigunov, D.M.
    Hartel, A.
    Zacharias, M.
    Perova, T.S.
    Timoshenko, V.Y.
    Enhancement of photoluminescence signal from ultrathin layers with silicon nanocrystals2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 6, p. 061908-1-061908-4Article in journal (Refereed)
    Abstract [en]

    Using the model of oscillating dipoles, we simulated the photoluminescence intensity of a triple-layered structure where the silicon nanocrystals layer was enclosed by buffer and capping silicon dioxide layers. It was found that a structure with an optimized buffer layer thickness exhibited photoluminescence which was approximately 20 times more intense than that from the structure without a buffer layer. Theoretical simulations were verified by photoluminescence measurements for the corresponding structures with silicon nanocrystals fabricated by plasma enhanced chemical vapour deposition.

  • 9. Hiller, D.
    et al.
    Zelenina, A.
    Gutsch, S.
    Dyakov, Sergey
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Lopez-Conesa, L.
    Lopez-Vidrier, J.
    Estrade, S.
    Peiro, F.
    Garrido, B.
    Valenta, J.
    Korinek, M.
    Trojanek, F.
    Maly, P.
    Schnabel, M.
    Weiss, C.
    Janz, S.
    Zacharias, M.
    Absence of quantum confinement effects in the photoluminescence of Si3N4-embedded Si nanocrystals2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 20, p. 204301-Article in journal (Refereed)
    Abstract [en]

    Superlattices of Si-rich silicon nitride and Si3N4 are prepared by plasma-enhanced chemical vapor deposition and, subsequently, annealed at 1150 degrees C to form size-controlled Si nanocrystals (Si NCs) embedded in amorphous Si3N4. Despite well defined structural properties, photoluminescence spectroscopy (PL) reveals inconsistencies with the typically applied model of quantum confined excitons in nitride-embedded Si NCs. Time-resolved PL measurements demonstrate 10(5) times faster time-constants than typical for the indirect band structure of Si NCs. Furthermore, a pure Si3N4 reference sample exhibits a similar PL peak as the Si NC samples. The origin of this luminescence is discussed in detail on the basis of radiative defects and Si3N4 band tail states in combination with optical absorption measurements. The apparent absence of PL from the Si NCs is explained conclusively using electron spin resonance data from the Si/Si3N4 interface defect literature. In addition, the role of Si3N4 valence band tail states as potential hole traps is discussed. Most strikingly, the PL peak blueshift with decreasing NC size, which is often observed in literature and typically attributed to quantum confinement (QC), is identified as optical artifact by transfer matrix method simulations of the PL spectra. Finally, criteria for a critical examination of a potential QC-related origin of the PL from Si3N4-embedded Si NCs are suggested.

  • 10. Schnabel, M.
    et al.
    Löper, P.
    Canino, M.
    Dyakov, Sergey A.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Allegrezza, M.
    Bellettato, M.
    López-Vidrier, J.
    Hernández, S.
    Summonte, C.
    Garrido, B.
    Wilshaw, P. R.
    Janz, S.
    Electrical and optical characterisation of silicon nanocrystals embedded in SiC2014In: Gettering and Defect Engineering in Semiconductor Technology XV, Scitec Publications Ltd , 2014, p. 480-485Conference paper (Refereed)
    Abstract [en]

    Silicon nanocrystals (Si NCs) are a promising candidate for the top cell of an all-Si tandem solar cell with a band gap from 1.3-1.7 eV, tuneable by adjusting NC size. They are readily produced within a Si-based dielectric matrix by precipitation from the Si excess in multilayers of alternating stoichiometric and silicon-rich layers. Here we examined the luminescence and transport of Si NCs embedded in SiC. We observed luminescence that redshifts from 2.0 to 1.5 eV with increasing nominal NC size. Upon further investigation, we found that this redshift is to a large extent due to Fabry-Pérot interference. Correction for this effect allows an analysis of the spectrum emitted from within the sample. We also produced p-i-n solar cells and found that the observed I-V curves under illumination could be well-fitted by typical thin-film solar cell models including finite series and parallel resistances, and a voltage-dependent current collection function. A minority carrier mobility-lifetime product on the order of 10-10 cm2/V was deduced, and a maximum open-circuit voltage of 370 mV achieved.

  • 11. Schnabel, M.
    et al.
    Summonte, C.
    Dyakov, Sergey A.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Canino, M.
    Lopez-Conesa, L.
    Loeper, P.
    Janz, S.
    Wilshaw, P. R.
    Absorption and emission of silicon nanocrystals embedded in SiC: Eliminating Fabry-Perot interference2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 4, article id 045307Article in journal (Refereed)
    Abstract [en]

    Silicon nanocrystals embedded in SiC are studied by spectrophotometry and photoluminescence (PL) spectroscopy. Absorptivities are found to be affected by residual Fabry-Perot interference arising from measurements of reflection and transmission at locations of different film thickness. Multiple computational and experimental methods to avoid these errors in thin film measurements, in general, are discussed. Corrected absorptivity depends on the quantity of Si embedded in the SiC but is independent of the Si crystallinity, indicating a relaxation of the k-conservation criterion for optical transitions in the nanocrystals. Tauc gaps of 1.8-2.0 and 2.12 eV are determined for Si nanoclusters and SiC, respectively. PL spectra exhibit a red-shift of similar to 100 nm per nm nominal Si nanocluster diameter, which is in agreement with quantum confinement but revealed to be an artifact entirely due to Fabry-Perot interference. Several simple experimental methods to diagnose or avoid interference in PL measurements are developed that are applicable to all thin films. Corrected PL is rather weak and invariant with passivation, indicating that non-paramagnetic defects are responsible for rapid non-radiative recombination. They are also responsible for the broad, sub-gap PL of the SiC, and can wholly account for the form of the PL of samples with Si nanoclusters. The PL intensity of samples with Si nanoclusters, however, can only be explained with an increased density of luminescent defects in the SiC due to Si nanoclusters, efficient tunneling of photogenerated carriers from Si nanoclusters to SiC defects, or with emission from a-Si nanoclusters. Films prepared on Si exhibit much weaker PL than the same films prepared on quartz substrates.

  • 12.
    Soltanmoradi, Reyhaneh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Dyakov, Sergey A.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Wang, Q.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. State Key Laboratory of Modern Optical Instrumentation, Department of Optical Engineering, Zhejiang University, China.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Multi-resonator structure based on continuous silver thin films for transparent conductors2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 6, p. 061110-Article in journal (Refereed)
    Abstract [en]

    A type of metal-dielectric multilayered structures is investigated theoretically and experimentally for achieving optical transparency with a high electrical conductivity. The structure in our demonstrated case comprises of two coupled metal-dielectric-metal planar optical resonators with metal-layer thicknesses near to its skin depth. Simulations show that the maximum transmittance for visible light can easily reach 90% for silver-based structures. Experimentally, the sample fabricated exhibits a transmission window with a bandwidth of 150 nm and a maximum transmittance of 76% around 643 nm wavelength at normal incidence. Its sheet resistance is measured to be less than 10 Omega/square, much smaller than that of common indium-tin-oxide films. Transparent conductors functioning for blue light and even for the whole visible light are also shown to be theoretically possible. Owing to their simple fabrication procedure as well as design flexibility, such a layered structure can serve as a compelling alternative as transparent conductors for optoelectronic devices, especially for liquid-crystal displays and light-emitting diodes.

  • 13. Tolmachev, Vladimir A.
    et al.
    Zharova, Yulia A.
    Perova, Tatiana S.
    Melnikov, Vasily A.
    Dyakov, Sergey A.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Univ Dublin, Ireland.
    Optical Spectra of Composite One-Dimensional Photonic Crystals With Extended Stop Bands Based on a Si-Air Structure2015In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 33, no 17, p. 3577-3583Article in journal (Refereed)
    Abstract [en]

    The optical spectra of composite one-dimensional photonic crystals (1-D PCs), fabricated by microstructuring of Si, are investigated. The composite PC is based on a Si-air structure and consists of two periodic 1-D PCs with various lattice constants a with a(1) = 2.7 mu m and a(2) = 4 mu m and various filling fractions f. The PCs are fabricated using photolithography followed by anisotropic chemical etching of (1 1 0) Si. Reflection and transmission spectra of this structure are measured using a Fourier transform infrared spectrometer combined with an IR microscope. The transmission spectra obtained demonstrate extended photonic stop bands (SBs), with characteristic transmission bands between the SBs. Theoretical and experimental transmission results indicate that the position of the extended SBs does not depend on the sequence of the individual PCs within the composite structure. In general, the calculated electric field distribution in the composite structure is similar to that of the individual PC components.

  • 14. Zelenina, A.
    et al.
    Dyakov, Sergey A.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Hiller, D.
    Gutsch, S.
    Trouillet, V.
    Bruns, M.
    Mirabella, S.
    Löper, P.
    Lopez-Conesa, L.
    Lopez-Vidrier, J.
    Estrade, S.
    Peiro, F.
    Garrido, B.
    Bläsing, J.
    Krost, A.
    Zhigunov, D. M.
    Zacharias, M.
    Structural and optical properties of size controlled Si nanocrystals in Si3N4 matrix: The nature of photoluminescence peak shift2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 18, p. 184311-Article in journal (Refereed)
    Abstract [en]

    Superlattices of Si3N4 and Si-rich silicon nitride thin layers with varying thickness were prepared by plasma enhanced chemical vapor deposition. After high temperature annealing, Si nanocrystals were formed in the former Si-rich nitride layers. The control of the Si quantum dots size via the SiNx layer thickness was confirmed by transmission electron microscopy. The size of the nanocrystals was well in agreement with the former thickness of the respective Si-rich silicon nitride layers. In addition X-ray diffraction evidenced that the Si quantum dots are crystalline whereas the Si3N4 matrix remains amorphous even after annealing at 1200 degrees C. Despite the proven Si nanocrystals formation with controlled sizes, the photoluminescence was 2 orders of magnitude weaker than for Si nanocrystals in SiO2 matrix. Also, a systematic peak shift was not found. The SiNx/Si3N4 superlattices showed photoluminescence peak positions in the range of 540-660nm (2.3-1.9 eV), thus quite similar to the bulk Si3N4 film having peak position at 577nm (2.15 eV). These rather weak shifts and scattering around the position observed for stoichiometric Si3N4 are not in agreement with quantum confinement theory. Therefore theoretical calculations coupled with the experimental results of different barrier thicknesses were performed. As a result the commonly observed photoluminescence red shift, which was previously often attributed to quantum-confinement effect for silicon nanocrystals, was well described by the interference effect of Si3N4 surrounding matrix luminescence.

  • 15. Zelenina, A.
    et al.
    Sarikov, A.
    Zhigunov, D. M.
    Weiss, C.
    Zakharov, N.
    Werner, P.
    Lopez-Conesa, L.
    Estrade, S.
    Peiro, F.
    Dyakov, Sergey A.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Zacharias, M.
    Silicon nanocrystals in SiNx/SiO2 hetero-superlattices: The loss of size control after thermal annealing2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 24, p. 244304-Article in journal (Refereed)
    Abstract [en]

    Superlattices containing 3 nm thick silicon rich silicon nitride sublayers and 3 nm and 10 nm thick SiO2 barriers were prepared by plasma enhanced chemical vapor deposition. Despite the as-prepared samples represented a well-kept multilayer structure with smooth interfaces, the high temperature annealing resulted in the total destruction of multilayer structure in the samples containing 3 nm SiO2 barriers. Energy-filtered transmission electron microscopy images of these samples indicated a silicon nanoclusters formation with sizes of 2.5-12.5 nm, which were randomly distributed within the structure. Although in the sample with 10 nm SiO2 barriers some fragments of the multilayer structure could be still observed after thermal annealing, nevertheless, the formation of large nanocrystals with diameters up to 10 nm was confirmed by dark field transmission electron microscopy. Thus, in contrast to the previously published results, the expected size control of silicon nanocrystals was lost. According to the FTIR results, the thermal annealing of SiNx/SiO2 superlattices led to the formation of silicon nanocrystals in mostly oxynitride matrix. Annealed samples demonstrated a photoluminescence peak at 885 nm related to the luminescence of silicon nanocrystals, as confirmed by time-resolved photoluminescence measurements. The loss of nanocrystals size control is discussed in terms of the migration of oxygen atoms from the SiO2 barriers into the silicon rich silicon nitride sublayers. A thermodynamic mechanism responsible for this process is proposed. According to this mechanism, the driving force for the oxygen migration is the gain in the configuration entropy related to the relative arrangements of oxygen and nitrogen atoms.

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