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  • 1.
    Berglund, Lars
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Li, Yuanyuan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Fu, Qiliang
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Yang, Min
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Modification of transparent wood for photonics functions2018In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 255Article in journal (Other academic)
  • 2.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Qejvanaj, Fatjon
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Blinking Statistics and Excitation-Dependent Luminescence Yield in Si and CdSe Nanocrystals2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 4, p. 2202-2208Article in journal (Refereed)
    Abstract [en]

    ON-OFF intermittency or blinking is a phenomenon observed in single quantum emitters, which reduces their overall light emission. Even though it seems to be a fundamental property of quantum dots (QDs), substantial differences can be found in the blinking statistics of different nanocrystals. This work compares the blinking of numerous single, oxide-capped Si nanocrystals with that of CdSe/ZnS core-shell nanocrystals, measured under the same conditions in the same experimental system and over a broad range of excitation power densities. We find that ON- and OFF-times can be described by exponential statistics in Si QDs, as opposed to power-law statistics for the CdSe nanocrystals. The type of blinking (power-law or monoexponential) does not depend on excitation but seems to be an intrinsic property of the material system. Upon increasing excitation power, the duty cycle of Si quantum dots remains constant, whereas it decreases for CdSe nanocrystals, which is readily explained by blinking statistics. Both ON-OFF and OFF-ON transitions can be regarded as light-induced in Si/SiO2 QDs, while the OFF-ON transition in CdSe/ZnS nanocrystals is not stimulated by photons. The differences in blinking behavior in these systems will be discussed.

  • 3.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Valenta, Jan
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Mitsuishi, Kazutaka
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Transition from silicon nanowires to isolated quantum dots: Optical and structural evolution2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 4, p. 045404-Article in journal (Refereed)
    Abstract [en]

    The evolution of the structural and optical properties of a silicon core in oxidized nanowalls is investigated as a function of oxidation time. The same individual nanostructures are characterized after every oxidation step in a scanning electron microscope and by low-temperature photoluminescence, while a representative sample is also imaged in a transmission electron microscope. Analysis of a large number of recorded single-dot spectra and micrographs allows to identify delocalized and localized exciton emission from a nanowire as well as confined exciton emission of a nanocrystal. It is shown how structural transitions from one-to zero-dimensional confinement affect single-nanostructure optical fingerprints.

  • 4.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Valenta, Jan
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Mitsushi, Kazutaka
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Transition fromsilicon nanowires to isolated quantum dots: Optical and structural evolution2009Manuscript (preprint) (Other (popular science, discussion, etc.))
  • 5. Chulapakorn, T.
    et al.
    Primetzhofer, D.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Suvanam, Sethu Saveda
    KTH, School of Information and Communication Technology (ICT).
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Impact of H-uptake by forming gas annealing and ion implantation on photoluminescence of Si-nanoparticles2018In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 215, no 3, article id 1700444Article in journal (Refereed)
    Abstract [en]

    Silicon nanoparticles (SiNPs) are formed by implanting 70 keV Si+ into a SiO2-film and subsequent thermal annealing. SiNP samples are further annealed in forming gas. Another group of samples containing SiNP is implanted by 7.5 keV H+ and subsequently annealed in N2-atmosphere at 450 °C to reduce implantation damage. Nuclear reaction analysis (NRA) is employed to establish depth profiles of the H-concentration. Enhanced hydrogen concentrations are found close to the SiO2surface, with particularly high concentrations for the as-implanted SiO2. However, no detectable uptake of hydrogen is observed by NRA for samples treated by forming gas annealing (FGA). H-concentrations detected after H-implantation follow calculated implantation profiles. Photoluminescence (PL) spectroscopy is performed at room temperature to observe the SiNP PL. Whereas FGA is found to increase PL under certain conditions, i.e., annealing at high temperatures, increasing implantation fluence of H reduces the SiNP PL. Hydrogen implantation also introduces additional defect PL. After low-temperature annealing, the SiNP PL is found to improve, but the process is not found equivalently efficient as conventional FGA.

  • 6.
    Chulapakorn, T.
    et al.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Ottosson, M.
    Uppsala Univ, Dept Chem, Angstrom Lab, Inorgan Chem, POB 538, SE-75121 Uppsala, Sweden..
    Primetzhofer, D.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    Moro, M. V.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT).
    Luminescence of silicon nanoparticles from oxygen implanted silicon2018In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 86, p. 18-22Article in journal (Refereed)
    Abstract [en]

    Oxygen with a kinetic energy of 20 keV is implanted in a silicon wafer (100) at different fluences, followed by post-implantation thermal annealing (PIA) performed at temperatures ranging from 1000 to 1200 degrees C, in order to form luminescent silicon nanoparticles (SiNPs) and also to reduce the damage induced by the implantation. As a result of this procedure, a surface SiOx layer (with 0 < x < 2) with embedded crystalline Si nanoparticles has been created. The samples yield similar luminescence in terms of peak wavelength, lifetime, and absorption as recorded from SiNPs obtained by the more conventional method of implanting silicon into silicon dioxide. The oxygen implantation profile is characterized by elastic recoil detection (ERD) technique to obtain the excess concentration of Si in a presumed SiO2 environment. The physical structure of the implanted Si wafer is examined by grazing incidence X-ray diffraction (GIXRD). Photoluminescence (PL) techniques, including PL spectroscopy, time-resolved PL (TRPL), and photoluminescence excitation (PLE) spectroscopy are carried out in order to identify the PL origin. The results show that luminescent SiNPs are formed in a Si sample implanted by oxygen with a fluence of 2 x 10(17) atoms cm(-2) and PIA at 1000 degrees C. These SiNPs have a broad size range of 6-24 nm, as evaluated from the GIXRD result. Samples implanted at a lower fluence and/or annealed at higher temperature show only weak defect-related PL. With further optimization of the SiNP luminescence, the method may offer a simple route for integration of luminescent Si in mainstream semiconductor fabrication.

  • 7. Chulapakorn, T.
    et al.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Suvanam, Sethu Saveda
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Linnros, Jan T.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Primetzhofer, D.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    MeV ion irradiation effects on the luminescence properties of Si-implanted SiO2-thin films2016In: Physica Status Solidi (C) Current Topics in Solid State Physics, ISSN 1862-6351, Vol. 13, no 10-12, p. 921-926Article in journal (Refereed)
    Abstract [en]

    The effects of MeV heavy ion irradiation at varying fluence and flux on excess Si, introduced in SiO2 by keV ion implantation, are investigated by photoluminescence (PL). From the PL peak wavelength (λ) and decay lifetime (τ), two PL sources are distinguished: i) quasi-direct recombination of excitons of Si-nanoparticles (SiNPs), appearing after thermal annealing (λ &gt; 720 nm, τ ∼ μs), and ii) fast-decay PL, possibly due to oxide-related defects (λ ∼ 575-690 nm, τ ∼ ns). The fast-decay PL (ii) observed before and after ion irradiation is induced by ion implantation. It is found that this fast-decay luminescence decreases for higher irradiation fluence of MeV heavy ions. After thermal annealing (forming SiNPs), the SiNP PL is reduced for samples irradiated by MeV heavy ions but found to stabilize at higher level for higher irradiation flux; the (ii) band vanishes as a result of annealing. The results are discussed in terms of the influence of electronic and nuclear stopping powers.

  • 8. Chulapakorn, T.
    et al.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Suvanam, Sethu Saveda
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Wolff, M.
    Primetzhofer, D.
    Possnert, G.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits. Uppsala University, Sweden.
    Si-nanoparticle synthesis using ion implantation and MeV ion irradiation2015In: Physica Status Solidi (C) Current Topics in Solid State Physics, ISSN 1862-6351Article in journal (Refereed)
    Abstract [en]

    A dielectric matrix with embedded Si-nanoparticles may show strong luminescence depending on nanoparticles size, surface properties, Si-excess concentration and matrix type. Ion implantation of Si ions with energies of a few tens to hundreds of keV in a SiO<inf>2</inf> matrix followed by thermal annealing was identified as a powerful method to form such nanoparticles. The aim of the present work is to optimize the synthesis of Si-nanoparticles produced by ion implantation in SiO<inf>2</inf> by employing MeV ion irradiation as an additional annealing process. The luminescence properties are measured by spectrally resolved photoluminescence including PL lifetime measurement, while X-ray reflectometry, atomic force microscopy and ion beam analysis are used to characterize the nanoparticle formation process. The results show that the samples implanted at 20%-Si excess atomic concentration display the highest luminescence and that irradiation of 36 MeV 127I ions affects the luminosity in terms of wavelength and intensity. It is also demonstrated that the nanoparticle luminescence lifetime decreases as a function of irradiation fluence.

  • 9.
    Elfström, Niklas
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Juhasz, Robert
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Engfeldt, Torun
    KTH, School of Biotechnology (BIO).
    Eriksson Karlström, Amelie
    KTH, School of Biotechnology (BIO).
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Surface Charge Sensitivity of Silicon Nanowires: Size Dependence2007In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 7, no 9, p. 2608-2612Article in journal (Refereed)
    Abstract [en]

    Silicon nanowires of different widths were fabricated in silicon on insulator (SOI) material using conventional process technology combined with electron-beam lithography. The aim was to analyze the size dependence of the sensitivity of such nanowires for biomolecule detection and for other sensor applications. Results from electrical characterization of the nanowires show a threshold voltage increasing with decreasing width. When immersed in an acidic buffer solution, smaller nanowires exhibit large conductance changes while larger wires remain unaffected. This behavior is also reflected in detected threshold shifts between buffer solutions of different pH, and we find that nanowires of width > 150 nm are virtually insensitive to the buffer pH. The increased sensitivity for smaller sizes is ascribed to the larger surface/volume ratio for smaller wires exposing the channel to a more effective control by the local environment, similar to a surrounded gate transistor structure. Computer simulations confirm this behavior and show that sensing can be extended even down to the single charge level.

  • 10.
    Hormozan, Yashar
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    High-resolution x-ray imaging using a structured scintillator2016In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 43, no 2, p. 696-701Article in journal (Refereed)
    Abstract [en]

    Purpose: In this study, the authors introduce a new generation of finely structured scintillators with a very high spatial resolution (a few micrometers) compared to conventional scintillators, yet maintaining a thick absorbing layer for improved detectivity. Methods: Their concept is based on a 2D array of high aspect ratio pores which are fabricated by ICP etching, with spacings (pitches) of a few micrometers, on silicon and oxidation of the pore walls. The pores were subsequently filled by melting of powdered CsI(Tl), as the scintillating agent. In order to couple the secondary emitted photons of the back of the scintillator array to a CCD device, having a larger pixel size than the pore pitch, an open optical microscope with adjustable magnification was designed and implemented. By imaging a sharp edge, the authors were able to calculate the modulation transfer function (MTF) of this finely structured scintillator. Results: The x-ray images of individually resolved pores suggest that they have been almost uniformly filled, and the MTF measurements show the feasibility of a few microns spatial resolution imaging, as set by the scintillator pore size. Compared to existing techniques utilizing CsI needles as a structured scintillator, their results imply an almost sevenfold improvement in resolution. Finally, high resolution images, taken by their detector, are presented. Conclusions: The presented work successfully shows the functionality of their detector concept for high resolution imaging and further fabrication developments are most likely to result in higher quantum efficiencies.

  • 11.
    Li, Yuanyuan
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Vasileva, Elena
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Optically Transparent Wood: Recent Progress, Opportunities, and Challenges2018In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 6, no 14, article id 1800059Article, review/survey (Refereed)
    Abstract [en]

    Transparent wood is an emerging load-bearing material reinvented from natural wood scaffolds with added light management functionalities. Such material shows promising properties for buildings and related structural applications, including its renewable and abundant origin, interesting optical properties, outstanding mechanical performance, low density, low thermal conductivity, and great potential for multifunctionalization. In this study, a detailed summary of recent progress on the transparent wood research topic is presented. Remaining questions and challenges related to transparent wood preparation, optical property measurements, and transparent wood modification and applications are discussed.

  • 12.
    Liu, Lige
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. Beijing Inst Technol, Sch Phys, Beijing Key Lab, Nanophoton & Ultrafine Optoelect Syst, 5 South St Zhongguancun, Beijing 100081, Peoples R China.
    Deng, Luogen
    Beijing Inst Technol, Sch Phys, Beijing Key Lab, Nanophoton & Ultrafine Optoelect Syst, 5 South St Zhongguancun, Beijing 100081, Peoples R China..
    Huang, Sheng
    Beijing Inst Technol, Sch Mat Sci & Engn, 5 South St Zhongguancun, Beijing 100081, Peoples R China..
    Zhang, Pei
    KTH, School of Engineering Sciences (SCI), Applied Physics. Zhengzhou Univ Light Ind, Sch Elect & Informat Engn, Henan Key Lab Informat Based Elect Appliances, Zhengzhou 450002, Henan, Peoples R China.
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Zhong, Haizheng
    Beijing Inst Technol, Sch Mat Sci & Engn, 5 South St Zhongguancun, Beijing 100081, Peoples R China..
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Photodegradation of Organometal Hybrid Perovskite Nanocrystals: Clarifying the Role of Oxygen by Single-Dot Photoluminescence2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 4, p. 864-869Article in journal (Refereed)
    Abstract [en]

    Photostability has been a major issue for perovskite materials. Understanding the photodegradation mechanism and suppressing it are of central importance for applications. By investigating single-dot photoluminescence spectra and the lifetime of MAPbX(3) (MA = CH3NH3+, X = Br, I) nanocrystals with quantum confinement under different conditions, we identified two separate pathways in the photodegradation process. The first is the oxygen-assisted light-induced etching process (photochemistry). The second is the light-driven slow charge-trapping process (photophysics), taking place even in oxygen-free environment. We clarified the role of oxygen in the photodegradation process and show how the photoinduced etching can be successfully suppressed by OSTE polymer, preventing an oxygen-assisted reaction.

  • 13. Luo, Jun-Wei
    et al.
    Li, Shu-Shen
    Sychugov, Ilya
    Pevere, Federico
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material- och nanofysik.
    Zunger, Alex
    Absence of redshift in the direct bandgap of silicon nanocrystals with reduced size2017In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 12, no 10, p. 930-932Article in journal (Refereed)
  • 14.
    Marinins, Aleksandrs
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Udalcovs, A.
    Ozolins, O.
    Pang, X.
    Veinot, J.
    Jacobsen, G.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    All-optical intensity modulation in polymer waveguides doped with si quantum dots2018In: Optics InfoBase Conference Papers, Optical Society of America, 2018Conference paper (Refereed)
    Abstract [en]

    We demonstrate all-optical intensity modulation in integrated PMMA optical waveguides doped with silicon quantum dots. The 1550 nm probe signal is absorbed by free carriers excited in silicon quantum dots with 405 nm pump light.

  • 15.
    Marinins, Aleksandrs
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Zhenyu
    Chen, Hongzheng
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Veinot, Jonathan G. C.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Photostable Polymer/Si Nanocrystal Bulk Hybrids with Tunable Photoluminescence2016In: ACS Photonics, E-ISSN 2330-4022, Vol. 3, no 9, p. 1575-1580Article in journal (Refereed)
    Abstract [en]

    Solid polymer/Si nanocrystal bulk nanocomposites were fabricated from solutions of alkene- and hydride-terminated silicon nanocrystals (NCs) in toluene. The photoluminescence peak position of hydride-terminated SiNCs before polymerization was tuned by photoassisted hydrofluoric acid etching. Optical properties of obtained PMMA/NC hybrids, such as quantum yield, luminescence lifetime, and dispersion factor, were evaluated over time. Photostability of these transparent bulk polymer/SiNC hybrids over months was confirmed. The emission covers the visible to near-infrared range with a quantum yield of similar to 30-40% for yellow-red nanocomposites.

  • 16.
    Omanakuttan, Giriprasanth
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Stergiakis, Stamoulis
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sahgal, Abhishek
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sun, Yan-Ting
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Epitaxial lateral overgrowth of GaxIn1-xP toward direct GaxIn1-xP/Si heterojunction2017In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 214, no 3Article in journal (Refereed)
    Abstract [en]

    The growth of GaInP by hydride vapor phase epitaxy (HVPE) was studied on planar GaAs, patterned GaAs for epitaxial lateral overgrowth (ELOG), and InP/Si seed templates for corrugated epitaxial lateral overgrowth (CELOG). First results on the growth of direct GaInP/Si heterojunction by CELOG is presented. The properties of GaxIn(1-x)P layer and their dependence on the process parameters were investigated by X-ray diffraction, including reciprocal lattice mapping (XRD-RLM), scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDS), photoluminescence (PL), and Raman spectroscopy. The fluctuation of Ga composition in the GaxIn(1-x)P layer was observed on planar substrate, and the strain caused by the composition variation is retained until relaxation occurs. Fully relaxed GaInP layers were obtained by ELOG and CELOG. Raman spectroscopy reveals that there is a certain amount of ordering in all of the layers except those grown at high temperatures. Orientation dependent Ga incorporation in the CELOG, but not in the ELOG GaxIn(1-x)P layer, and Si incorporation in the vicinity of direct GaxIn(1-x)P/Si heterojunction from CELOG are observed in the SEM-EDS analyses. The high optical quality of direct GaInP/Si heterojunction was observed by cross-sectional micro-PL mapping and the defect reduction effect of CELOG was revealed by high PL intensity in GaInP above Si.

  • 17.
    Omanakuttan, Giriprasanth
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Stergiakis, Stamoulis
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sahgal, Abhishek
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sun, Yan-Ting
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Epitaxial lateral overgrowth of GaxIn1-xP towards coherent GaxIn1-xP/Si heterojunction by hydride vapor phase epitaxy2016In: 2016 Compound Semiconductor Week, CSW 2016 - Includes 28th International Conference on Indium Phosphide and Related Materials, IPRM and 43rd International Symposium on Compound Semiconductors, ISCS 2016, IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    Epitaxial lateral overgrowth (ELOG) of GaInP on GaAs by hydride vapor phase epitaxy (HVPE) is carried out as a pre-study to obtain GaInP/Si heterointerface. We present first results on the growth of GaInP/Si by a modified ELOG technique, corrugated epitaxial lateral overgrowth (CELOG).

  • 18.
    Omi, Hiroo
    et al.
    NTT Basic Research Lab.
    Sychugov, Ilya
    NTT Basic Research Lab.
    Kobayashi, Yoshihiro
    NTT Basic Research Lab.
    Murashita, Toru
    NTT Basic Research Lab.
    New Microscope Combines Optical and Electrical Excitation into a Single Scanning Tunneling Microscope Unit for Simultaneous Characterization of Near-Field Luminescence from Individual Nanostructures2009In: Kenbikyo, ISSN 1349-0958, Vol. 44, p. 174-Article, review/survey (Refereed)
  • 19.
    Pevere, Federico
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Bruhn, Benjamin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sangghaleh, Fatemeh
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Hormozan, Yashar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Effect of X-ray irradiation on the blinking of single silicon nanocrystals2015In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 212, no 12Article in journal (Refereed)
    Abstract [en]

    Photoluminescence (PL) intermittency (blinking) observed for single silicon nanocrystals (Si-NCs) embedded in oxide is usually attributed to trapping/de-trapping of carriers in the vicinity of the NC. Following this model, we propose that blinking could be modified by introducing new trap sites, for example, via X-rays. In this work, we present a study of the effect of X-ray irradiation (up to 65 kGy in SiO) on the blinking of single Si-NCs embedded in oxide nanowalls. We show that the luminescence characteristics, such as spectrum and life-time, are unaffected by X-rays. However, substantial changes in ON-state PL intensity, switching frequency, and duty cycle emerge from the blinking traces, while the ON- and OFF- time distributions remain of mono-exponential character. Although we do not observe a clear monotonic dependence of the blinking parameters on the absorbed dose, our study suggests that, in the future, Si-NCs could be blinking-engineered via X-ray irradiation.

  • 20.
    Pevere, Federico
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Sangghaleh, Fatemeh
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Bruhn, Benjamin
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Rapid Trapping as the Origin of Nonradiative Recombination in Semiconductor Nanocrystals2018In: ACS Photonics, E-ISSN 2330-4022, Vol. 5, no 8, p. 2990-2996Article in journal (Refereed)
    Abstract [en]

    We demonstrate that nonradiative recombination in semiconductor nanocrystals can be described by a rapid luminescence intermittency, based on carrier tunneling to resonant traps. Such process, we call it "rapid trapping (blinking)", leads to delayed luminescence and promotes Auger recombination, thus lowering the quantum efficiency. To prove our model, we probed oxide- (containing static traps) and ligand- (trap-free) passivated silicon nanocrystals emitting at similar energies and featuring monoexponential blinking statistics. This allowed us to find analytical formulas and to extract characteristic trapping/detrapping rates, and quantum efficiency as a function of temperature and excitation power. Experimental single-dot temperature-dependent decays, supporting the presence of one or few resonant static traps, and ensemble saturation curves were found to be very well described by this effect. The model can be generalized to other semiconductor nanocrystals, although the exact interplay of trapping/detrapping, radiative, and Auger processes may be different, considering the typical times of the processes involved.

  • 21.
    Pevere, Federico
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sangghaleh, Fatemeh
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Fucikova, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Biexciton Emission as a Probe of Auger Recombination in Individual Silicon Nanocrystals2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 13, p. 7499-7505Article in journal (Refereed)
    Abstract [en]

    Biexciton emission from individual silicon nanocrystals was detected at room temperature by time-resolved, single-particle luminescence measurements. The efficiency of this process, however, was found to be very low, about 10-20 times less than the single exciton emission efficiency. It decreases even further at low temperature, explaining the lack of biexciton emission line observations in silicon nanocrystal single-dot spectroscopy under high excitation. The poor efficiency of the biexciton emission is attributed to the dominant nonradiative Auger process. Corresponding measured biexciton decay times then represent Auger lifetimes, and the values obtained here, from tens to hundreds of nanoseconds, reveal strong dot-to-dot variations, while the range compares well with recent calculations taking into account the resonant nature of the Auger process in semiconductor nanocrystals.

  • 22.
    Pevere, Federico
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    von Treskow, Carl
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Marino, Emanuele
    Van der Waals – Zeeman Institute, University of Amsterdam, The Netherlands.
    Anwar, Monib
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Bruhn, Benjamin
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    X-ray radiation hardness and influence on blinking in Si and CdSe quantum dots2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 113, no 25, article id 253103Article in journal (Refereed)
    Abstract [en]

    We study the effect of X-ray irradiation on the photoluminescence (PL) efficiency and intermittency (blinking) of single Si/SiO2 and CdSe/CdZnS quantum dots (QDs). Our results show that the PL efficiency of Si nanocrystals is not significantly altered up to a cumulative fluence of 10(20) photons/m(2) (corresponding to similar to 300 kGy of absorbed dose in SiO2), while CdSe particles become completely dark already after a 17 times lower fluence. In both types of QDs, the statistical nature of blinking ON- and OFF-times remains unaltered: mono-exponential for Si and power-law for CdSe QDs. However, the evolution of the blinking parameters with absorbed dose depends on the choice of material. On average, both ON- and OFF-time constants do not vary in Si nanocrystals, highlighting their radiation hardness. Instead, the ON-time exponent increases while the OFF-time exponent decreases with the increasing dose for CdSe dots, confirming their efficiency quenching. Ensemble measurements did not show PL spectral changes neither indicated removal of surface ligands in irradiated CdSe dots. Thus, ionization-generated non-radiative centers in the core-shell system modify blinking of CdSe dots and eventually rapidly quench their emission, in contrast to robust Si/SiO2 nanocrystals. Our study is important for the future use of luminescent QDs in harsh environments, such as space, and the engineering of their blinking properties via ionizing radiation.

  • 23.
    Popov, Sergei
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Marinins, Aleksandrs
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Yan, Max
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Vasileva, Elena
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Li, Yuanyuan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Biocomposites.
    Udalcovs, Aleksejs
    RISE Acreo AB, Stockholm, Sweden..
    Ozolins, Oskars
    RISE Acreo AB, Stockholm, Sweden..
    Polymer photonics and nano-materials for optical communication2018In: 2018 17TH WORKSHOP ON INFORMATION OPTICS (WIO), Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

    Polymer materials offer process compatibility, design flexibility, and low cost technology as a multi-functional platform for optical communication and photonics applications. Design and thermal reflowing technology of low loss polymer waveguides, as well as demonstration of transparent wood laser are presented in this paper.

  • 24.
    Sangghaleh, Fatemeh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Bruhn, Benjamin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Optical absorption cross section and quantum efficiency of a single silicon quantum dot2013In: Nanotechnology VI, SPIE - International Society for Optical Engineering, 2013, p. 876607-Conference paper (Refereed)
    Abstract [en]

    Direct measurements of the optical absorption cross section (sigma) and exciton lifetime are performed on a single silicon quantum dot fabricated by electron beam lithography (EBL), reactive ion etching (RIE) and oxidation. For this aim, single photon counting using, an avalanche photodiode detector (APD) is applied to record photoluminescence (PL) intensity traces under pulsed excitation. The PL decay is found to be of a mono-exponential character with a lifetime of 6.5 mu s. By recording the photoluminescence rise time at different photon fluxes the absorption cross could be extracted yielding a value of 1.46x10(-14)cm(2) under 405 nm excitation wavelength. The PL quantum efficiency is found to be about 9% for the specified single silicon quantum dot.

  • 25.
    Sangghaleh, Fatemeh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Bruhn, Benjamin
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Non-radiative decay in Si/SiO2 quantum dots in transition from dark to bright exciton statesManuscript (preprint) (Other academic)
  • 26.
    Sangghaleh, Fatemeh
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Yang, Zhenyu
    Veinot, Jonathan G C
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Near-Unity Internal Quantum Efficiency of Luminescent Silicon Nanocrystals with Ligand Passivation.2015In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 9, no 7, p. 7097-7104Article in journal (Refereed)
    Abstract [en]

    Spectrally resolved photoluminescence (PL) decays were measured for samples of colloidal, ligand-passivated silicon nanocrystals. These samples have PL emission energies with peak positions in the range 1.4-1.8 eV and quantum yields of 30-70%. Their ensemble PL decays are characterized by a stretched-exponential decay with a dispersion factor of 0.8, which changes to an almost monoexponential character at fixed detection energies. The dispersion factors and decay rates for various detection energies were extracted from spectrally resolved curves using a mathematical approach that excluded the effect of homogeneous line width broadening. Since nonradiative recombination would introduce a random lifetime variation, leading to a stretched-exponential decay for an ensemble, we conclude that the observed monoexponential decay in size-selected ensembles signifies negligible nonradiative transitions of a similar strength to the radiative one. This conjecture is further supported as extracted decay rates agree with radiative rates reported in the literature, suggesting 100% internal quantum efficiency over a broad range of emission wavelengths. The apparent differences in the quantum yields can then be explained by a varying fraction of "dark" or blinking nanocrystals.

  • 27.
    Schmidt, Torsten
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Zhang, Miao
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Roxhed, Niclas
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Nanopore arrays in a silicon membrane for parallel single-molecule detection: fabrication2015In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, no 31, article id 314001Article in journal (Refereed)
    Abstract [en]

    Solid state nanopores enable translocation and detection of single bio-molecules such as DNA in buffer solutions. Here, sub-10 nm nanopore arrays in silicon membranes were fabricated by using electron-beam lithography to define etch pits and by using a subsequent electrochemical etching step. This approach effectively decouples positioning of the pores and the control of their size, where the pore size essentially results from the anodizing current and time in the etching cell. Nanopores with diameters as small as 7 nm, fully penetrating 300 nm thick membranes, were obtained. The presented fabrication scheme to form large arrays of nanopores is attractive for parallel bio-molecule sensing and DNA sequencing using optical techniques. In particular the signal-to-noise ratio is improved compared to other alternatives such as nitride membranes suffering from a high-luminescence background.

  • 28.
    Sprunken, Dan
    et al.
    NTT Basic Research Labs.
    Omi, Hiroo
    NTT Basic Research Labs.
    Furukawa, Kazuaki
    NTT Basic Research Labs.
    Nakashima, Hiroshi
    NTT Basic Research Labs.
    Sychugov, Ilya
    NTT Basic Research Labs.
    Kobayashi, Yoshihiro
    NTT Basic Research Labs.
    Torimitsu, Keiichi
    NTT Basic Research Labs.
    Influence of the Local Environment on Determining Aspect-Ratio Distributions of Gold Nanorods in Solution Using Gans Theory2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, p. 14299-Article in journal (Refereed)
    Abstract [en]

    We apply Gans theory to fit the absorption spectra of gold nanorods with aspect ratios R < 2.5 in solution using both the longitudinal and transversal surface plasmon resonance absorption peaks and the dielectric constant of the medium as a fitting parameter. By fitting the broadened absorption peaks using the absorption spectra of a set of nanorods with a range of aspect ratios, we determine the size distribution of the nanorods in solution. The optimum value of dielectric constant is substantially higher than the dielectric constant of the solvent, which is most likely due to a change in the effective dielectric constant in the vicinity of the nanorods. The validity of our method is confirmed by comparing the calculated size  distributions with transmission electron microscope images, and we obtain a good agreement between the experiments and our calculations. Furthermore, several other recent experimental results are compared with our fitting method, and we find that the discrepancy between Gans theory and those experimental results can be explained by using higher values of dielectric constant.

    1.

  • 29.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Analytical Description of a Luminescent Solar Concentrator Device2019In: Optica, Vol. 6, p. 1046-1049Article in journal (Refereed)
  • 30.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Synthesis and properties of single luminescent silicon quantum dots2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Silicon is an ubiquitous electronic material and the discovery of strong room temperature luminescence from porous Si in 1990 raised hopes it may find a new lease of life in the emerging field of optoelectronics. First, the luminescence was shown to be emitted from nanostructures remained in a porous Si network. Later the same emission was shown from Si nanocrystals and the concept of a Si quantum dot emerged. Yet a number of different models have been proposed for the origin of light emission. Some involved interface states between a Si nanocrystal and the surrounding shell, while others considered the effect of quantum confinement in an indirect bandgap semiconductor.

    In this work a single Si nanocrystal was addressed to shed light on the mechanism of luminescence. Nanocrystals were prepared using e-beam lithography with subsequent etching and oxidation of silicon nanopillars. In particular, the non-uniform oxidation in self-limiting regime was successfully used to form a single nanocrystal inside nanopillars. This preparation method allowed optical probing of a single nanocrystal with far-field optics.

    Results revealed sharp luminescence spectra at low temperatures with a linewidth less than the corresponding thermal broadening. This property is a signature of energy level discreetness, which is, in turn, a straightforward consequence of the quantum confinement model. Another effect observed was a random on-off blinking, which is also regarded as a hallmark of single fluorescent objects. This effect appeared to be dependent on the excitation power density suggesting the involvement of Auger-assisted ionization in the dynamics of nanocrystal luminescence. In addition, it was shown how a change in the optical mode density affects the main parameters of luminescence from Si nanocrystals, such as the radiative lifetime, the quantum efficiency and the total yield.

    Finally, in order to clarify the influence of morphological properties, such as size or shape, of a Si quantum dot on its luminescence, combined low-temperature photoluminescence and transmission electron microscopy investigations were initiated. A method was developed using focused ion beam preparation for such a joint characterization.

    To conclude, the work gives support to the quantum confinement effect in explaining the light emission mechanism from nano-sized Si, as well as highlights the importance of morphological structure in the luminescence process.

  • 31.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Elfström, Niklas
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Effect of photonic bandgap on luminescence from silicon nanocrystals2007In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, no 13, p. 1878-1880Article in journal (Refereed)
    Abstract [en]

    The modification of the luminescence of silicon nanocrystals experiencing the effect of a photonic bandgap in a 2D photonic crystal was investigated. The time-integrated photoluminescence spectra detected in the plane of the photonic crystal revealed a dip in the light emission corresponding to the wavelength of the bandgap, whose position changes according to the geometry of the prepatterned pillar array. The calculated emission pattern for a pointlike dipole placed in such a structure suggests an inhibition of the spontaneous emission rate at certain directions as a physical reason for the observed modification of luminescence.

  • 32.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Fucikova, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Pevere, Federico
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Yang, Zhenyu
    Veinot, Jonathan G. C.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Ultranarrow Luminescence Linewidth of Silicon Nanocrystals and Influence of Matrix2014In: ACS Photonics, E-ISSN 2330-4022, Vol. 1, no 10, p. 998-1005Article in journal (Refereed)
    Abstract [en]

    The luminescence linewidth of individual silicon nanocrystals was characterized by single-dot spectroscopy, and an ultranarrow linewidth of similar to 200 mu eV at 10 K was found. This value is, in fact, limited by system resolution and represents only the upper limit of the homogeneous linewidth. In addition, the effect of the matrix was investigated for nanocrystals coated with organic ligands, embedded in silicon dioxide, as well as for nanocrystals with only a thin passivating layer. It was found that, depending on the matrix, the room-temperature bandwidth may vary by an order of magnitude, where values as small as similar to 12 meV (similar to 5 nm) at 300 K were detected for nanocrystals with a thin passivation. The observed values for silicon nanocrystals are similar and even surpass some of those for direct-band-gap quantum dots. The narrow linewidth at room temperature enables the use of silicon nanocrystals for nontoxic narrow-band labeling of biomolecules and for application as phosphors in white-light-emitting devices.

  • 33.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Galeckas, Augustinas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Elfström, Niklas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Wilkinson, Andrew
    Elliman, Rob
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Effect of substrate proximity on luminescence yield from Si nanocrystals2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 89, no 11, p. 111124-Article in journal (Refereed)
    Abstract [en]

    The influence of the proximity of a high refractive index substrate on the luminescence of Si nanocrystals was investigated by time-integrated and time-resolved photoluminescence. The luminescence yield was found to be ∼2.5 times larger for emitters distanced from the substrate compared to those in proximity with the substrate, while luminescence decay measurements revealed only a slight increase in the luminescence lifetime (∼15%). Results are discussed in terms of local density of optical modes surrounding a pointlike light emitter with important implications for the collection efficiency of luminescence and the estimation of internal quantum efficiency for a quantum dot.

  • 34.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Juhasz, Robert
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Galeckas, Augustinas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Valenta, Jan
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Single dot optical spectroscopy of silicon nanocrystals: Low temperature measurements2005In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 27, no 5, p. 973-976Article in journal (Refereed)
    Abstract [en]

    Single dot spectroscopy allows studying properties of a single nanocrystal avoiding inhomogeneous broadening of the emission band. Here, data obtained by this technique for Si nanocrystals fabricated by electron beam lithography, plasma etching and subsequent size-reduction by oxidation are presented. First, blinking (on–off intermittence) of the luminescence was observed for most individual nanocrystals, although some exhibited relatively stable luminescence. As a result of the quantum confinement effect spectra with different emission wavelengths for different nanocrystals were recorded. While at room temperature the full width at half-maximum of the nanocrystal emission peaks was measured to be 100–150 meV, at 80 K the linewidth for some dots appeared to be about 25 meV only. The observed temperature dependence of the homogeneous linewidth may lead to an understanding of the exciton–phonon interaction in indirect band-gap quantum dots.

  • 35.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Juhasz, Robert
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Valenta, Jan
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Narrow luminescence linewidth of a silicon quantum dot2005In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, no 8, p. 087405 (1)-087405 (4)Article in journal (Refereed)
    Abstract [en]

    Single-dot luminescence spectroscopy was used to study the emission linewidth of individual silicon nanocrystals from low temperatures up to room temperature. The results show a continuous line narrowing towards lower temperatures with a linewidth as sharp as 2 meV at 35 K. This value, clearly below the thermal broadening at this temperature, proves the atomiclike emission from silicon quantum dots subject to quantum confinement. The low temperature measurements further reveal a similar to6 meV replica, whose origin is discussed. In addition, an similar to60 meV TO-phonon replica was detected, which is only present in a fraction of the dots.

  • 36.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Juhasz, Robert
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Valenta, Jan
    Zhang, A.
    Pirouz, P.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Light emission from silicon nanocrystals: probing a single quantum do2006In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, no 15, p. 5249-5253Article in journal (Refereed)
    Abstract [en]

    Analysis of low-temperature photoluminescence measurements performed on single silicon nanocrystals is presented. The luminescence emission linewidth of Si nanocrystals is found to be less than thermal broadening at low temperature, confirming the atomic-like nature of their energetic states. Beside the main peak the low-temperature spectra reveal a similar to 6 meV replica, the origin of which is discussed. For some of the investigated dots, we also observe a similar to 60 meV transverse optical (TO) phonon replica. The regular arrangement of individual nanocrystals used in this work enables combined high-resolution transmission electron microscopy (TEM) and low-temperature photoluminescence characterization of the same single quantum dot.

  • 37.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Juhász, Róbert
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Valenta, Jan
    Luminescence blinking of a Si quantum dot in a SiO2 shell2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 11, p. 115331-1-115331-5Article in journal (Refereed)
    Abstract [en]

    The phenomenon of on-off luminescence intermittency - blinking - in silicon nanocrystals was studied using a single-dot microphotoluminescence technique. From recordings of the luminescence intensity trace, on- and off-time distributions were extracted revealing exponential behavior, as expected for systems with blinking of a purely random nature. The corresponding switching rates for on-off and off-on processes exhibit different dependence on the excitation intensity. While the on-off switching rate grows quadratically with the excitation, the inverse process is nearly pumping power independent. Experimental findings are interpreted in terms of a dot "charging" model, where a carrier may become trapped in the surrounding matrix due to thermal and Auger-assisted processes. Observed blinking kinetics appear to be different from that of porous silicon particles.

  • 38.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Optical Properties of a Silicon Nanocrystal2009In: Nanocrystals: Properties, Preparation and Applications / [ed] Hongquig Hu, New York: Nova Science , 2009, p. 197-216Chapter in book (Refereed)
    Abstract [en]

    Basic optical properties of a silicon nanocrystal are discussed based on results from single-dot spectroscopy experiments. Luminescence linewidth and its temperature behavior, time dependency of the intensity trace and strong variations from dot-to-dot are particularly addressed. It appears that the fundamental optical features of a silicon nanocrystal are similar to that of its direct bandgap semiconductor counterpart, while in general preserving the indirect bandgap structure of bulk silicon. One of possible ways to modify its characteristics is to alter the local density of optical modes (LDOS) around this nano-emitter. The influence of LDOS is discussed based on experimental observations of substrate proximity and photonic bandgap effects. It is shown how the silicon nanocrystal excitation lifetime, luminescence yield and quantum efficiency can be modified in this way. By proper ‘nano-engineering’ this may lead to enhanced radiative properties useful for future applications.

  • 39.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lu, J.
    Elfström, Niklas
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Structural imaging of a Si quantum dot: Towards combined PL and TEM characterization2006In: Journal of Luminescence, ISSN 0022-2313, E-ISSN 1872-7883, Vol. 121, no 2, p. 353-Article in journal (Refereed)
    Abstract [en]

    Individual silicon quantum dots were fabricated by electron-beam lithography, plasma etching and a two-step oxidation process. This enables photoluminescence (PL) from individual dots at various temperatures to be detected and spectrally resolved using a sensitive charge-coupled device camera-imaging system, as reported previously. The regular array-like arrangement of oxidized pillars containing individual nanocrystals, in principle, enables combined transmission electron microscopy (TEM) and low-temperature PL characterization of the same Si quantum dot. To this end, a technique employing focused ion beam was developed for preparation of the pillar/nanocrystal of interest for TEM. It is shown that silicon quantum dots of several nanometers in size can be characterized using such a method.

  • 40.
    Sychugov, Ilya
    et al.
    National Institute for Materials Science.
    Nakayama, Yoshiko
    National Institute for Materials Science.
    Mitsuishi, Kazutaka
    National Institute for Materials Science.
    Composition Control of Electron Beam Induced Nanodeposits by Surface Pretreatment and Beam Focusing2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 52, p. 21516-21519Article in journal (Refereed)
    Abstract [en]

    Cross-sectional transmission electron microscopy with elemental analysis was used to investigate shape and composition of nanostructures fabricated by electron beam induced deposition. The nanostructures were deposited on a thin edge of the silicon membrane allowing characterization without intermediate distorting preparation steps, such as focused ion beam milling. The effect of the surface carbon contaminants and the electron beam focusing on nanostructure composition was studied. It is shown how carbon content of nanostructures can be reduced by sample preheating, forming metal nanostructures with higher purity advantageous for circuitry and lithography applications.

  • 41.
    Sychugov, Ilya
    et al.
    National Institute for Materials Science.
    Nakayama, Yoshiko
    National Institute for Materials Science.
    Mitsuishi, Kazutaka
    National Institute for Materials Science.
    Manifold Enhancement of Electron Beam Induced Deposition Rate at Grazing Incidence2010In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 21, no 2, p. 025303-Article in journal (Refereed)
    Abstract [en]

    It is shown how a significant drawback of the electron beam induced deposition technique, namely its low deposition rate, can be circumvented. By tilting a sample, a larger part of the primary electron beam energy becomes dissipated closer to the interface. This in turn increases the emission of secondary electrons, largely responsible for the deposition of the adsorbed molecule components on the surface. An order of magnitude increase in the deposition rate is reported in the fabrication of metal nanowires from organic precursor gas.

  • 42.
    Sychugov, Ilya
    et al.
    National Institute for Materials Science.
    Nakayama, Yoshiko
    National Institute for Materials Science.
    Mitsuishi, Kazutaka
    National Institute for Materials Science.
    Measuring interface electrostatic potential and surface charge in a scanning electron microscope2009In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 27, no 6, p. 2357-2360Article in journal (Refereed)
    Abstract [en]

    A novel method for electrostatic potential measurements at the interface is described. It involves placing a two-dimensional grid below the sample and observing it in a scanning electron microscope. Primary electron beam displacement, caused by surface charges, can be then measured for every grid knot. Using geometric parameters of the setup, a quantitative mapping of the potential can be extracted. It is shown that this method can achieve a tens of millivolt sensitivity and a submicron spatial resolution in electrostatic potential measurements.

  • 43.
    Sychugov, Ilya
    et al.
    National Institute for Materials Science.
    Nakayama, Yoshiko
    National Institute for Materials Science.
    Mitsuishi, Kazutaka
    National Institute for Materials Science.
    Sub-10 nm crystalline silicon nanostructures by electron beam induced deposition lithography2010In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 21, no 28, p. 285307-Article in journal (Refereed)
    Abstract [en]

    A novel top-down approach for the controllable fabrication of semiconductor nanostructures exhibiting quantum effects is described. By decomposing metal-rich precursor gas molecules with an electron beam, a sub-10 nm metal pattern can be formed and subsequently transferred to a semiconductor substrate. In such a way monocrystalline silicon nanodots and nanowires are produced as revealed by transmission electron microscopy. It is also shown how through controlled thermal or chemical oxidation the nanostructure surface can be passivated. By providing direct access to the sub-10 nm size range this method possesses promising potential for application in the quantum dot and nanoelectronics fields.

  • 44.
    Sychugov, Ilya
    et al.
    NTT Basic Research Labs.
    Omi, Hiroo
    NTT Basic Research Labs.
    Kobayashi, Yoshihiro
    NTT Basic Research Labs.
    On the Role of Substrate in Light Harvesting Experiments2008In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 33, no 16, p. 1807-1809Article in journal (Refereed)
    Abstract [en]

    An analysis of the emitted light distribution for a single emitter located at the planar interface of two optical media was performed. The interface of a varying refractive index substrate with air was considered, which is a common case in luminescence microscopy (spectroscopy) experiments. A modification of the radiative recombination rate induced by the variation of the substrate together with the emitted radiation spatial redistribution were taken into account. Simulation results show that the collection efficiency of the emitted light can vary several times depending on the substrate choice and the emitter intrinsic quantum efficiency.

  • 45.
    Sychugov, Ilya
    et al.
    NTT Basic Research Lab.
    Omi, Hiroo
    NTT Basic Research Lab.
    Murashita, Toru
    NTT Basic Research Lab.
    Kobayashi, Yoshihiro
    NTT Basic Research Lab.
    Modeling Tip Performance for Combined STM-luminescence and aperture-SNOM Scanning Probe: Spatial Resolution and Collection Efficiency2008In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 254, no 23, p. 7861-7863Article in journal (Refereed)
    Abstract [en]

    Finite-element simulations of the performance of the tip intended for use in combined aperture-SNOM and the scanning tunneling microscope (STM)-luminescence microscopy are presented. Tip geometry and the role of the opening in the protective metal coating were addressed. It is shown that the tip shape can affect transmittance for the excitation SNOM mode by nearly two orders of magnitude and the metal coating can enhance collection efficiency for the STM-luminescence mode. Desired tip configuration can be chosen based on the interplay between the improving collection efficiency and the deteriorating spatial resolution with increasing opening size.

  • 46.
    Sychugov, Ilya
    et al.
    NTT Basic Research Labs.
    Omi, Hiroo
    NTT Basic Research Labs.
    Murashita, Toru
    NTT Basic Research Labs.
    Kobayashi, Yoshihiro
    NTT Basic Research Labs.
    Optical and Electrical Characterization at the Nanoscale by a Transparent Tip of a Scanning Tunneling Microscope2009In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 20, no 14, p. 145706-Article in journal (Refereed)
    Abstract [en]

    A new type of scanning probe microscope, combining features of the scanning tunnelling microscope, the scanning tunnelling luminescence microscope with a transparent probe and the aperture scanning near-field optical microscope, is described. Proof-of-concept experiments were performed under ultrahigh vacuum conditions at varying temperature on GaAs/AlAs heterostructures.

  • 47.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Pevere, Federico
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Luo, Jun-Wei
    Zunger, Alex
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Single-dot absorption spectroscopy and theory of silicon nanocrystals2016In: Physical Review B, ISSN 2469-9950, Vol. 93, no 16, article id 161413Article in journal (Refereed)
    Abstract [en]

    Photoluminescence excitation measurements have been performed on single, unstrained oxide-embedded Si nanocrystals. Having overcome the challenge of detecting weak emission, we observe four broad peaks in the absorption curve above the optically emitting state. Atomistic calculations of the Si nanocrystal energy levels agree well with the experimental results and allow identification of some of the observed transitions. An analysis of their physical nature reveals that they largely retain the indirect band-gap structure of the bulk material with some intermixing of direct band- gap character at higher energies.

  • 48.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sangghaleh, Fatemeh
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Bruhn, Benjamin
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Pevere, Federico
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Luo, Jun-Wei
    Zunger, Alex
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Strong Absorption Enhancement in Si Nanorods2016In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 12, p. 7937-7941Article in journal (Refereed)
    Abstract [en]

    We report two orders of magnitude stronger absorption in silicon nanorods relative to bulk in a wide energy range. The local field enhancement and dipole matrix element contributions were disentangled experimentally by single-dot absorption measurements on differently shaped particles as a function of excitation polarization and photon energy. Both factors substantially contribute to the observed effect as supported by simulations of the light-matter interaction and atomistic calculations of the transition matrix elements. The results indicate strong shape dependence of the quasidirect transitions in silicon nanocrystals, suggesting nanostructure shape engineering as an efficient tool for overcoming limitations of indirect band gap materials in optoelectronic applications, such as solar cells.

  • 49.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Valenta, J.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Probing silicon quantum dots by single-dot techniques2017In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 28, no 7, article id 072002Article in journal (Refereed)
    Abstract [en]

    Silicon nanocrystals represent an important class of non-toxic, heavy-metal free quantum dots, where the high natural abundance of silicon is an additional advantage. Successful development in mass-fabrication, starting from porous silicon to recent advances in chemical and plasma synthesis, opens up new possibilities for applications in optoelectronics, bio-imaging, photovoltaics, and sensitizing areas. In this review basic physical properties of silicon nanocrystals revealed by photoluminescence spectroscopy, lifetime, intensity trace and electrical measurements on individual nanoparticles are summarized. The fabrication methods developed for accessing single Si nanocrystals are also reviewed. It is concluded that silicon nanocrystals share many of the properties of direct bandgap nanocrystals exhibiting sharp emission lines at low temperatures, on/off blinking, spectral diffusion etc. An analysis of reported results is provided in comparison with theory and with direct bandgap material quantum dots. In addition, the role of passivation and inherent interface/matrix defects is discussed.

  • 50.
    Sychugov, Ilya
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Valenta, J.
    Mitsuishi, K.
    Fujii, M.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Photoluminescence measurements of zero-phonon optical transitions in silicon nanocrystals2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 12, p. 125326-Article in journal (Refereed)
    Abstract [en]

    Optical transitions in silicon nanocrystals with different surface passivations were probed at low temperatures on a single-particle level. A type of quasidirect recombination process, different from the quantum-confined exciton transition, is identified. The luminescence spectra have different emission energies, but the contribution of a no-phonon transition is significantly higher than expected from the quantum-confinement model. Its relative strength was found to be temperature dependent, suggesting spatial localization of excitons as a possible origin.

12 1 - 50 of 61
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