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  • 1. Bratkovsky, Alexander
    et al.
    Ponizovskaya, Ekaterina
    Wang, Shih-Yuan
    Holmström, Petter
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    A metal-wire/quantum-dot composite metamaterial with negative epsilon and compensated optical loss2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 19, p. 193106-Article in journal (Refereed)
    Abstract [en]

    Numerical simulations of a binary mixture of quantum dots exhibiting gain with silver nanorods are performed, showing the feasibility of lossless negative epsilon operation for realistic material structures and parameters.

  • 2. Chen, Yun
    et al.
    Molnar, Mátyás
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Li, Li
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Friberg, Peter
    Gan, Li-Ming
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Characterization of VCAM-1-Binding Peptide-Functionalized Quantum Dots for Molecular Imaging of Inflamed Endothelium2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 12, p. e83805-Article in journal (Refereed)
    Abstract [en]

    Inflammation-induced activation of endothelium constitutes one of the earliest changes during atherogenesis. New imaging techniques that allow detecting activated endothelial cells can improve the identification of persons at high cardiovascular risk in early stages. Quantum dots (QDs) have attractive optical properties such as bright fluorescence and high photostability, and have been increasingly studied and developed for bio-imaging and bio-targeting applications. We report here the development of vascular cell adhesion molecule-1 binding peptide (VCAM-1 binding peptide) functionalized QDs (VQDs) from amino QDs. It was found that the QD fluorescence signal in tumor necrosis factor alpha (TNF-alpha) treated endothelial cells in vitro was significantly higher when these cells were labeled with VQDs than amino QDs. The VQD labeling of TNF-alpha-treated endothelial cells was VCAM-1 specific since pre-incubation with recombinant VCAM-1 blocked cells' uptake of VQDs. Our ex vivo and in vivo experiments showed that in the inflamed endothelium, QD fluorescence signal from VQDs was also much stronger than that of amino QDs. Moreover, we observed that the QD fluorescence peak was significantly blue-shifted after VQDs interacted with aortic endothelial cells in vivo and in vitro. A similar blue-shift was observed after VQDs were incubated with recombinant VCAM-1 in tube. We anticipate that the specific interaction between VQDs and VCAM-1 and the blue-shift of the QD fluorescence peak can be very useful for VCAM-1 detection in vivo.

  • 3.
    Chen, Zhihui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Yu, Zhongyuan
    Improving efficiency of quantum dot infrared photodetector by using photonic crystal framework in the active layer2011Conference paper (Refereed)
    Abstract [en]

    Photonic crystal structure as a framework in both substrate and active layer in quantum dot infrared photodetector is used to improve the interaction between photons and QDs.

  • 4.
    Chen, Zhihui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Hellström, Staffan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ning, Zhijun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Yu, Z-Y
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Exciton Polariton Contribution to the Stokes Shift in Colloidal Quantum Dots2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 13, p. 5286-5293Article in journal (Refereed)
    Abstract [en]

    We study the exciton polariton contribution to the Stokes shift in colloidal quantum dots (QDs). By detailed quantum mechanical description of light-matter interaction and temporal analysis of incident electromagnetic field across the QD using the finite-difference time-domain method, we have shown that the optical excitation of an exciton in the QD and its coupling with the excitation radiation (i.e., exciton polariton) induce strong variations in the dielectric constant of the QD which contribute significantly to the Stokes shift and cause modifications 50 in the absorption spectrum that agrees well with experiments.

  • 5.
    Chen, Zhi-Hui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hellström, Staffan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Yu, Zhong-Yuan
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Comb-shaped photonic crystal structure for efficient broadband light diffraction and funnelling in solar cells2012In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 99, p. 316-320Article in journal (Refereed)
    Abstract [en]

    We present a comb-shaped photonic-crystal (PhC) rods-lattice structure of broadband light diffraction and funnelling for solar cell applications. It is shown that the photonic band of this PhC structure is very dispersive over a broad bandwidth so that light will be efficiently diffracted in the wavelength region of solar radiation. The PhC structure also creates resonance modes leading to further diffraction and funnelling of light so that the light propagates in many pathways in the whole PhC lattice region, which will greatly facilitate light-matter interaction when light-absorbing elements are embedded in the PhC structure. The proposed structure is also valid for photodetection applications.

  • 6.
    Chen, Zhihui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hellström, Staffan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Yu, Zhong-Yuan
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Time-resolved photocurrents in quantum well/dot infrared photodetectors with different optical coupling structures2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 4, p. 043502-Article in journal (Refereed)
    Abstract [en]

    Temporal developments of photocurrents excited by an infrared radiation pulse in quantum well/dot infrared photodetectors with different optical coupling structures have been theoretically studied. It is shown that the light diffraction in a conventional reflective grating structure is a near-field effect containing severe crosstalk from neighboring pixels. A concave reflector not only eliminates the crosstalk but also strongly diffracts and focuses the incident electric field into deep active layers, which significantly increases the photocurrents in the photodetectors.

  • 7.
    Chen, Zhihui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Yu, Z. -Y
    Liu, Y. -M
    Lu, P. -F
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Multiple beam splitting to free space from a V groove in a photonic crystal waveguide2011In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 102, no 4, p. 857-861Article in journal (Refereed)
    Abstract [en]

    We present multiple-beam splitting to free space from a V groove in a two-dimensional photonic crystal waveguide (PCW) with a few additional dielectric rods at the exit of the PCW. Numerical study shows that 'one-beam-in to two-beams-out' (one-to-two, also denoted as Y-shaped), one-to-three, and one-to-five beam splittings can be easily realized over a wide bandwidth, and the split beams have remarkable properties such as symmetric energy distributions and high directional transmissions. Off-axis directional emission can also be achieved by simple displacements of the additional rods at the exit of the PCW.

  • 8.
    de Melo, Fernando Menegatti
    et al.
    Univ Sao Paulo, Supramol Nanotech Lab, Dept Chem, BR-05508000 Sao Paulo, SP, Brazil..
    Grasseschi, Daniel
    Univ Prebiteriana Mackenzie, Machg Graphene & Nanomat Res Ctr, BR-01303907 Sao Paulo, SP, Brazil..
    Brandao, Bruno B. N. S.
    Univ Sao Paulo, Supramol Nanotech Lab, Dept Chem, BR-05508000 Sao Paulo, SP, Brazil..
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Toma, Henrique E.
    Univ Sao Paulo, Supramol Nanotech Lab, Dept Chem, BR-05508000 Sao Paulo, SP, Brazil..
    Superparamagnetic Maghemite-Based CdTe Quantum Dots as Efficient Hybrid Nanoprobes for Water-Bath Magnetic Particle Inspection2018In: ACS Applied Nano Materials, ISSN 2574-0970, Vol. 1, no 6, p. 2858-2868Article in journal (Refereed)
    Abstract [en]

    Fluorescent water-based cadmium telluride quantum dots (QDs) and citrate-functionalized maghemite nanoparticles (MghNPs) were synthesized and assembled together (MghNPs@QDs) through electrostatic interactions by using cetyltrimethylammonium bromide (CTAB) as a linker and steric spacer to minimize the Forster resonance energy transfer (FRET) restriction. A whole family of hybrid and multifunctional nanoparticles has been successfully obtained, exhibiting good performance in nondestructive water-bath magnetic particle inspection (MPI) assays.

  • 9.
    Fontana, Jacopo Maria
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cellular Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Yin, Huijuan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cellular Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Chen, Yun
    Florez, Ricardo
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cellular Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cellular Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cellular Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Transport and release of colloidal 3-mercaptopropionic acid-coated CdSe-CdS/ZnS core-multishell quantum dots in human umbilical vein endothelial cells2017In: International Journal of Nanomedicine, ISSN 1176-9114, E-ISSN 1178-2013, Vol. 12, p. 8615-8629Article in journal (Refereed)
    Abstract [en]

    Colloidal semiconductor quantum dots (QDs) have been extensively researched and developed for biomedical applications, including drug delivery and biosensing assays. Hence, it is pivotal to understand their behavior in terms of intracellular transport and toxicological effects. In this study, we focused on 3-mercaptopropionic acid-coated CdSe-CdS/ZnS core-multishell quantum dots (3MPA-QDs) converted from the as-grown octadecylamine-coated quantum dots (ODA-QDs) and their direct and dynamic interactions with human umbilical vein endothelial cells (HUVECs). Live cell imaging using confocal fluorescence microscopy showed that 3MPAQDs first attached to and subsequently aggregated on HUVEC plasma membrane similar to 25 min after QD deposition. The aggregated QDs started being internalized at similar to 2 h and reached their highest internalization degree at similar to 24 h. They were released from HUVECs after similar to 48 h. During the 48 h period, the HUVECs responded normally to external stimulations, grew, proliferated and wound healed without any perceptible apoptosis. Furthermore, 1) 3MPA-QDs were internalized in newly formed LysoTracker-stained early endosomes; 2) adenosine 5'-triphosphateinduced [Ca2+](i) modulation caused a transient decrease in the fluorescence of 3MPA-QDs that were attached to the plasma membrane but a transient increase in the internalized 3MPA-QDs; and 3) fluorescence signal modulations of co-stained LysoTracker and QDs induced by the lysosomotropic agent Gly-Phe-beta-naphthylamide were spatially co-localized and temporally synchronized. Our findings suggest that 3MPA-QDs converted from ODA-QDs are a potential nontoxic fluorescent probe for future use in clinical applications. Moreover, the photophysical strategy and techniques reported in this work are easily applicable to study of direct interactions between other nanoparticles and live cells; contributing to awareness and implementation of the safe applications of nanoparticles.

  • 10.
    Fu, Kai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Kinetic Monte Carlo study of metal organic chemical vapor deposition growth mechanism of GaSb quantum dots2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 101906Article in journal (Refereed)
    Abstract [en]

    The growth dynamics of self-assembled GaSb quantum dots (QDs) on GaAs substrate in the strain-induced Stranski-Krastanov mode was investigated using kinetic Monte Carlo method. The strain induced by the lattice mismatch between the epitaxial material and the substrate was shown to be directly responsible for the QD formation and the transition of growth mode from two dimensional to three dimensional.

  • 11.
    Fu, Kai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Strain-induced Stranski-Krastanov three dimensional growth mode of GaSb quantum dot on GaAs substrate2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, no 181913Article in journal (Refereed)
    Abstract [en]

    The growth dynamics of self-assembled GaSb quantum dots (QDs) on GaAs substrate was investigated using kinetic Monte Carlo method. The strain induced by the lattice mismatch between the epitaxial material and the substrate was shown to be directly responsible for the three-dimensional QD formation. Different geometries of the initial seeds on the surface which are equally favorable from an energy point of view can result in different GaSb nanostructures (nanostrips and nanoring).

  • 12.
    Fu, Kai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Zhang, R.
    Kinetic Monte Carlo study of metal organic chemical vapor deposition growth dynamics of GaN thin film at microscopic level2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 10, p. 103524-Article in journal (Refereed)
    Abstract [en]

    Group III nitrides, especially gallium nitride (GaN), have many applications. The materials are usually grown by metal organic chemical vapor deposition (MOCVD) technology. By combining the computational fluid dynamics and kinetic Monte Carlo method, we present a multiscale modeling of fluid dynamics, thermodynamics, and molecular dynamics to study the chemical and physical growth process of GaN in a standard MOCVD reactor, which shows a general agreement with experimental results. The theoretical model thus provides us with a fundamental guideline for optimizing GaN MOCVD growth at the microscopic level.

  • 13.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Energy band structure and spectral gain characteristics of dilute-nitride zinc blende InGaNAs quantum wells embedded in GaAs and GaNAs barriers2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 100, no 7Article in journal (Refereed)
    Abstract [en]

    The spectral gain characteristics of dilute-nitride zinc blende InxGa1-xNyAs1-y quantum wells embedded in GaNy1As1-y1 barriers have been investigated experimentally and theoretically. Two samples, both with the gain peak at 1300 nm, were studied for comparison. One has a high nitrogen concentration in the quantum well with the surrounding barriers being pure GaAs. The other has a lower and uniform nitrogen concentration in the quantum well and the barriers (GaNAs barriers). Measurements show the redshift of the gain peak induced by the incorporation of nitrogen and difference in the spectral gain characteristics. The energy band structures and spectral gain characteristics are analyzed theoretically using the standard eight-band k center dot p theory. It is shown that the introduction of nitrogen atoms in the GaAs barriers reduces the barrier height for the central quantum well so that the energy sublevels in the conduction band becomes condensed. The condensation of the conduction-band energy sublevels reduces the peak gain and makes the gain spectrum narrower, in agreement with measurements.

  • 14.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Photonic energy band structure of excitonic quantum dot dimer system2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 5Article in journal (Refereed)
    Abstract [en]

    We study the energy dispersion of a photonic crystal composed of two types of excitonic quantum dots (QD dimer system), type-I QDs at their ground states while type-II QDs are already excited. The excitation and de-excitation of the exciton states in the QDs by an external electromagnetic field contribute extra dielectric polarizations with respect to the background material, thus a contrast in the dielectric constant and the eventual formation of the photonic dispersion. By assuming periodic boundary conditions, it has been shown that the photonic dispersion of the QD dimer system is composed of modified but still characteristic dispersions of the two types of QDs in their separate photonic crystal formats. Starting from the transparent condition of type-II QDs, the photonic structure of the QD dimer system evolves from the one of type-I QDs to the composite dimer system. The modification due to the radiative interaction between the two types of the QDs is symmetric with respect to the change in the excitation degree of type-II QDs (increase/decrease the excitation degree from transparent status so that type-II QDs become optically gain/lossy). It is thus concluded that the transport of an external electromagnetic field is normal in the QD dimer system and achieving a lossless negative-dielectric material at a single frequency is possible by using the QD dimer system.

  • 15.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. Department of Applied Physics.
    Physical Models of Semiconductor Quantum Devices2014Book (Refereed)
  • 16.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Berglind, Eilert
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Optical transmission and waveguiding by excitonic quantum dot lattices2006In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 23, no 11, p. 2441-2447Article in journal (Refereed)
    Abstract [en]

    Metal-dielectric-metal configurations of optical waveguides have a very high laterally packaging density at the cost of high optical loss. Photonic crystals based on refractive-index-modulation materials have been used in optics, e.g., two materials having different refractive indices form a well-defined Bragg refraction mirror. Such a waveguide has lower loss but also lower packaging density. From the outset of these two notions, we propose a photonic-crystal device based on the exciton-polariton effect in a three-dimensional array of semiconductor quantum dots (QDs) for ultradense optical planar circuit applications. Excitons are first photogenerated in the QDs by the incident electromagnetic field, the exciton-polariton effect in the QD photonic crystal then induces an extra optical dispersion in QDs. The high contrast ratio between the optical dispersions of the QDs and the background therefore creates clear photonic bandgaps. By carefully designing the QD size and the QD lattice structure, perfect electromagnetic field reflection can be obtained at a specific wavelength in the lossless case, thus providing the fundamental basis for ultradense optical waveguide applications.

  • 17.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Engstrom, O.
    Electron wave packet transmission through a Si quantum wire under the influence of an ionized impurity scattering potential2006In: Journal of Nanoelectronics and Optoelectronics, ISSN 1555-130X, Vol. 1, no 1, p. 108-113Article in journal (Refereed)
    Abstract [en]

    By solving the three-dimensional Schrodinger equation in the time domain, we study the wave packet transport through a Si quantum nano wire embedded in silicon dioxide. The temporal behaviour of the wave packet under the influence of an ionized impurity located in the system has been clearly revealed. In general, the presence of an impurity potential deteriorates the coherence transmission of the wave packet along the quantum wire. However, the large effective mass of the electrons in Si material largely overcomes the scattering potential induced by a positively charged impurity, which traps only a small fraction of a wave packet when the wave vector of the transporting wave packet resonantly matches with the characteristic length of the scattering potential. The repulsive potential of a negatively charged impurity strongly reflects the low-energy wave packet transmission. We conclude that the dominating impurity scattering process limiting ballistic transport in these nano wires will be determined by negatively charged impurities located at the Si-SiO2 interface.

  • 18.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Han, Tiantian
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Dynamic analysis of multiple-photon optical processes in semiconductor quantum dots2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 39, p. 9071-9082Article in journal (Refereed)
    Abstract [en]

    Semiconductor quantum dots (QDs) have been gaining much attention because of their outstanding properties for multiple-photon microscopy applications. By solving nonperturbatively the time-dependent Schrodinger equation, it has been shown that the large number of energy states densely compacted in both the conduction and valence bands of the QD greatly enhance the inter-band and intra-band optical couplings between two energy states induced by multiple photons from ultra-fast and ultra-intense lasers. The multiphoton absorption processes are further enhanced by many energy relaxation processes in commonly used semiconductors, which are generally represented by the relaxation energy in the order of tens of meV. Numerical calculation of multiphoton processes in QDs agrees with experimental demonstration. After proper designing, QDs can be activated by infrared radiation to emit radiation in the visible optical regime (up-conversion) for bioimaging applications.

  • 19.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Han, Tiantian
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Multiphoton excitation of quantum dots by ultrashort and ultraintense laser pulses2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 88, no 22, p. 221114-1-221114-3Article in journal (Refereed)
    Abstract [en]

    Multiphoton optical processes in semiconductor quantum dots (QDs) excited by ultrafast (femtosecond) and ultraintense (GW/cm(2)) lasers are considered as the ultimate tags for cellular bioimaging. By solving the time-dependent Schrodinger equation unperturbatively, experimentally observed strong multiphoton excitation is reproduced when optical transitions among all confined states and a few hundred more extended states are taken into account. Model calculations indicate a significant excitation of a CdS QD of 3.7 nm in radius by a 100 fs laser pulse with a 10 GW/cm(2) peak optical power. The excitation rate is almost constant between 1300 and 560 nm, a useful region for bioimaging.

  • 20.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Han, Tiantian
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Lin, L.
    Institute of Modern Optics, Nankai University.
    Chen, P.
    Institute of Modern Optics, Nankai University.
    Liu, Y.
    Institute of Modern Optics, Nankai University.
    Tang, G.-Q.
    Institute of Modern Optics, Nankai University.
    Wu, J.
    National Lab. for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences.
    Yue, Y.
    National Lab. for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences.
    Dai, N.
    National Lab. for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences.
    Design of semiconductor CdSe core ZnS/CdS multishell quantum dots for multiphoton applications2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 17, p. 173102-1-173102-3Article in journal (Refereed)
    Abstract [en]

    Optical properties of colloidal II-VI semiconductor CdSe cores with ZnS and CdS multishell quantum dots (QDs) have been studied by experimental characterization and theoretical analysis. Due to the large number of energy states densely compacted in both conduction and valence bands of the quantum dots, strong interband and intraband optical couplings are induced by the multiphoton excitation, implicating an efficient fluorescence of such II-VI-based core-multishell CdSe QDs. This fact in combination with the advantage of the size tolerance of II-VI QDs with respect to the narrow fluorescence bandwidth make these systems excellent candidates for applications using fluorescence induced by multiphoton excitation.

  • 21.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Hellström, Staffan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Nonlinear optical properties of quantum dots: Excitons in nanostructures2009In: Journal of nonlinear optical physics and materials, ISSN 0218-8635, Vol. 18, no 2, p. 195-226Article, review/survey (Refereed)
    Abstract [en]

    We review the concepts of excitons and excitonic polaritons, their nonlinear optical properties in nanostructures and their applications within integrated electronics and optoelectronics. Various theoretical aspects of excitons and excitonic polaritons are introduced, followed by a summary of their experimental and application-specific development in nanostructures at the electronic and photonic engineering levels. A number of technical applications are highlighted.

  • 22.
    Fu, Ying
    et al.
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Jussi, Johnny Israelsson
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Elmlund, Louise
    Swedish Natl Forens Ctr, SE-58194 Linkoping, Sweden..
    Dunne, Simon
    Swedish Natl Forens Ctr, SE-58194 Linkoping, Sweden..
    Wang, Qin
    RISE Res Inst Sweden AB, Box 1070, SE-16425 Kista, Sweden..
    Brismar, Hjalmar
    KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Intrinsic blinking characteristics of single colloidal CdSe-CdS/ZnS core-multishell quantum dots2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 3, article id 035404Article in journal (Refereed)
    Abstract [en]

    Fluorescence blinking of single colloidal semiconductor quantum dots (QDs) has been extensively studied, and several sophisticated models have been proposed. In this work, we derive Heisenberg equations of motion to carefully study principal transition processes, i.e., photoexcitation, energy relaxation, impact ionization and Auger recombination, radiative and nonradiative recombinations, and tunneling between core states and surface states, of the electron-hole pair in single CdSe-CdS/ZnS core-multishell QDs and show that the on-state probability density distribution of the QD fluorescence obeys the random telegraph signal theory because of the random radiative recombination of the photoexcited electron-hole pair in the QD core, while the off-state probability density distribution obeys the inverse power law distribution due to the series of random walks of the photoexcited electron in the two-dimensional surface-state network after the electron tunnels from the QD core to the QD surface. These two different blinking characteristics of the single QD are resolved experimentally by properly adjusting the optical excitation power and the bin time.

  • 23.
    Fu, Ying
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Jussi, Johnny
    KTH, School of Engineering Sciences (SCI), Applied Physics. 1989.
    Qin, Wang
    RISE Acreo AB.
    Brismar, Hjalmar
    KTH, Superseded Departments (pre-2005), Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Liu, Yushen
    College of Physics and Electronic Engineering, China..
    Yang, Xifeng
    College of Physics and Electronic Engineering, China..
    Chen, Yun
    University of Gothenburg, Sweden..
    Endocytic pathway of vascular cell adhesion molecule 1 in human umbilical vein endothelial cell identified in vitro by using functionalized nontoxic fluorescent quantum dots2019In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 297, article id 126702Article in journal (Refereed)
    Abstract [en]

    Studies about vascular cell adhesion molecule 1 (VCAM1) in tumor growth, metastasis, and angiogenesis suggest that targeting VCAM1 expression is an attractive strategy for diagnosis and anti-tumor therapy. However, the endocytic pathway of VCAM1 in vascular cells has not been well characterized. In this study we visualize the endocytic pathway of tumor necrosis factor α (TNFα) induced VCAM1 in human umbilical vein endothelial cell (HUVEC) in vitro using 5-carboxyfluorescein labeled VCAM1 binding peptides and fluorescent water-dispersible 3-mercaptopropionic acid (3MPA)-coated CdSe-CdS/Cd0.5Zn0.5S/ZnS core–multishell nontoxic quantum dots (3MPA-QDs) functionalized with VCAM1 binding peptides. Clear key in vitro observations are as follows: (a) 3MPA-QDs functionalized with VCAM1 binding peptides, denoted as VQDs, adhered and aggregated cumulatively to cell membrane around 2 h after VQD deposition to cell culture medium and were found in lysosomes in TNFα-treated HUVECs approximately 24 h after VQD deposition; (b) VQDs remained in TNFα-treated HUVECs for the whole 16 days of the experimental observation period; (c) quite differently, 3MPA-QDs were endocytosed then exocytosed by HUVECs via endosomes in about 24–48 h after 3MPA-QD deposition. Our study suggests that VCAM1 molecules, initially expressed on cell membrane induced by TNFα treatment, are internalized into lysosomes. This provides a novel means to deliver materials to lysosomes such as enzyme replacement therapy. Moreover, our meticulous sensing methodology of devising fluorescent nontoxic QDs advances biosensing technique for studying cellular activities in vitro and in vivo.

  • 24.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Lu, W
    Jiang, J
    Wang, MK
    Yang, XP
    Wu, G
    Fan, YH
    Li, YG
    Nonperturbative dynamic photon absorption of quantum wells2006In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 99, no 10Article in journal (Refereed)
    Abstract [en]

    Optical photoresponse of quantum wells in the nonperturbative regime has been studied by high-power and ultrafast-oscillating free-electron laser (FEL) experiments, which revealed a profound deviation of the nonlinear power from conventional perturbative multiple photon absorption processes. By combining the experimental and theoretical works we have shown that the nonperturbative solution of the time-dependent Schrodinger equation is essential to understand the experimental observations. Optical transitions of electrons are dynamic. One photon is absorbed or emitted when an electron transits from one electron state to the other. The rates of absorption and emission are proportional to the time interval in the femtosecond time scale. In the picosecond time scale, multiphoton processes emerge. The strong and fast-oscillating FEL source intensifies the dynamic photon absorption and emission processes in the quantum wells, resulting in a much enhanced nonlinearity in the photoresponse spectrum.

  • 25.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Multiple-photon spectrum of CdS semiconductor quantum dot for bioimaging2006In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 2, p. 842-845Article in journal (Refereed)
    Abstract [en]

    We study the dynamic processes of multiple-photon absorption and emission in a semiconductor quantum dot. By the non-perturbative time-dependent Schrodinger equation, it is shown that electrons in the quantum dot can be optically excited from the valence band to the conduction band via multiphoton processes, leaving holes in the valence band. The radiative recombination of the conduction-band electrons with the valence-band holes results in optical emission of a single photon having an energy which is larger than the input photon energy, resulting in the high-photon-energy luminescence from the quantum dot activated by low-energy photons to emit radiation in the visible optical regime for bioimaging application.

  • 26.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Photonics (Closed 20120101).
    Optical properties of nanostructures2011Book (Other academic)
    Abstract [en]

    Nanotechnology has been named as one of the most important areas of forthcoming technology because it promises to form the basis of future generations of electronic and optoelectronic devices. From the point of view of technical physics, all these developments greatly reduce the geometric sizes of devices, and thus the number of active electrons in the system. Quantum mechanical considerations about electronic states, electron transports, and various scattering processes, including light-matter interaction, are thus crucial. However, the theoretical study is extremely difficult. The authors' first numerical simulation work about a three-dimensional energy band structure calculation in 1995 took more than 6 months to complete for one bias configuration of a nanoscale metal-oxide-semiconductor field-effect transistor. With today's computation workstations the CPU time is reduced to less than 24 hours. This book discusses electrons and photons in and through nanostructures by the first-principles quantum mechanical theories and fundamental concepts (a unified coverage of nanostructured electronic and optical components) behind nanoelectronics and optoelectronics, the material basis, physical phenomena, device physics, as well as designs and applications. The combination of viewpoints presented in the book can help foster further research and cross-disciplinary interaction needed to surmount the barriers facing future generations of technology design.

  • 27.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    A lossless negative dielectric constant from quantum dot exciton polaritons2008In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, no 5, p. 1551-1555Article in journal (Refereed)
    Abstract [en]

    Prospects for a lossless negative dielectric constant material for optical devices are studied. Simulations show that with sufficient gain, a mixture of two semiconductor quantum dots (QDs) can produce an effective dielectric constant that is lossless and negative. This permits, in concept, arbitrarily small scaling of the optical mode volume, a major goal in the field of nanophotonics. The proposed implementation of a lossless negative dielectric constant material based on colloidal QDs opens a tractable path.

  • 28.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Yang, CL
    Modification of absorption spectrum of GaAs/AlGaAs quantum well infrared photodetector by postgrowth adjustment2006In: Hongwai yu haomibo xuebao, ISSN 1001-9014, Vol. 25, no 1, p. 1-5Article in journal (Refereed)
    Abstract [en]

    Quantum well intermixing techniques modify the geometric shape of quantum wells to allow postgrowth adjustments. The tuning effect on the optical response property of a GaAs/AlGaAs quantum well infrared photodetector (QWIP) induced by the interdifussion of Al atoms was studied theoretically. By assuming an improvement of the heterointerface quality and an enhanced Al interdiffusion caused by postgrowth intermixings, the photoluminescence spectrum shows a blueshifted, narrower and enhanced photoluminescence peak. The infrared optical absorption spectrum also shows the expected redshift of the response wavelength. However, the variation in the absorption peak intensity depends on the boundary conditions of the photo generated carriers. For high-quality QWIP samples, the mean free path of photocarriers is long so that the photocarriers are largely coherent when they transport across quantum wells. In this case, the enhanced Al interdiffusion can significantly degrade the infrared absorption property of the QWIP. Special effects are therefore needed to maintain and/or improve the optical properties of the QWIP device during postgrowth treatments.

  • 29.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Zeng, Yong
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Berglind, Eilert
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Nanoscale excitonic-plasmonic optical waveguiding by metal-coated quantum dots2006In: Proceedings of International Symposium on Biophotonics, Nanophotonics and Metamaterials, 2006, p. 426-431Conference paper (Refereed)
    Abstract [en]

    A three-dimensional metal-coated semiconductor-quantum-dot (QD) nanoscale lattice structure is designed for optical waveguiding. It is based on three notions: i) Excitons are first photogenerated in the QDs by the incident electromagnetic field which is the optical wave to be guided: ii) The exciton-polariton effect in the QD structure induces an extra optical dispersion in the QDs: iii) The high contrast ratio between the optical dispersions of the QDs and the background material creates clear photonic bandgaps. By carefully designing the QD size and the QD lattice structure, perfect electromagnetic field reflection can be obtained for the incident wave in the lossless case, thus providing the fundamental basis of QDs for optical waveguide applications. Metal coating at the QD surface generates a surface plasmon spatially confined in the QD so that the exciton generation becomes enhanced for a better dielectric modulation.

  • 30.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Zeng, Yong
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Surface-plasmon-assisted electromagnetic field enhancement in semiconductor quantum dots2007In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 87, no 2, p. 167-169Article in journal (Refereed)
    Abstract [en]

    The temporal development of incident electromagnetic plane waves across semiconductor quantum dots (QDs) is analyzed by the finite-difference time-domain method. By coating the QDs using thin metal films, surface plasmon polaritons (SPPs) can be created. As illustration, our modeling approach is applied to fluorescent multiphoton quantum dots made of cadmium sulphide of particular size (3.7 nm) and energy band gap (2.67 eV). When such a QD is coated by a metal film, a dipole-formed SPP is generated at the external surface of the coated QD by the incident electromagnetic wave with a photon energy of 1.34 eV corresponding to a two-photon process. When the thickness of the metal film is 0.37 nm, the peak intensity of the SPP oscillates through both the thin metal film and the core QD, resulting in an electromagnetic field inside the QD enhanced by a factor of 10, and thus an increased two-photon excitation that can be useful for bioimaging applications. Further increasing the metal film thickness blockades the SPP initially generated at the external surface of the coated QD from penetrating through the metal film, reducing the electromagnetic field inside the QD.

  • 31.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Zhou, Y. -H
    Su, H.
    Boey, F. Y. C.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512). Nanyang Technological University, Singapore .
    Reply to "comment on 'impact ionization and auger recombination rates in semiconductor quantum dots'"2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 39, p. 16860-16860Article in journal (Refereed)
  • 32.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Zhou, Y. H.
    Su, Haibin
    Boey, F. Y. C.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Impact Ionization and Auger Recombination Rates in Semiconductor Quantum Dots2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 9, p. 3743-3747Article in journal (Refereed)
    Abstract [en]

    Impact ionization and Auger recombination in nanoscale spherical quantum dots (QDs) have been Studied theoretically. It is shown that due to the strong quantum confinement of both electrons in the conduction band and holes ill the valence band. impact ionization and Auger recombination energies in these QDs call be oil the order of a few millielectronvolts when various selection rules are fulfilled, which are Much higher than spontaneous radiative emission energies. This explains the experimentally reported high Occurrence rates of the multiple exciton generation (MEG) effect in QDs. However, due to quantum confinement, the energy States are discrete in QDs, especially for low-energy states where the densities of states are low. This implies that only a limited number of high-energy electron states call interact with (i.e., impact ionize) low-energy hole states in QDs having certain values of radii due to the energy conservation requirement. This explains the vastly scattered experimental data and difficulties ill Utilizing the MEG effect in practice.

  • 33.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Optical Properties of Quantum Dot Nano-composite Materials Studied by Solid-State Theory Calculations2012In: Handbook of Computational Chemistry / [ed] J. Leszczynski, Springer Berlin/Heidelberg, 2012, p. 869-899Chapter in book (Refereed)
    Abstract [en]

    This chapter reviews the fundamental concepts of excitons and excitonic polaritons and their extraordinary optical properties in quantum dot nano-composite materials. By starting with the optical excitation of an exciton in the nanostructure we show that the effective dielectric constant of the nanostructure becomes significantly modified due to the exciton generation and recombination, resulting in high positive and negative dielectric constants. We also discuss single exciton generation by multiple photons and multiple exciton generation by single photon. All these nonlinear optical properties of quantum dot nano-composite materials offer novel possibilities and are expected to have deep impact in nanophotonics.

  • 34.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Andersson, J. Y.
    Asplund, C.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101).
    Optical reflection from excitonic quantum-dot multilayer structures2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 18, p. 183117-Article in journal (Refereed)
    Abstract [en]

    We study theoretically and experimentally the optical reflection from excitonic quantum-dot (QD) multilayer structures composed of InAs QDs in a GaAs substrate. Quantum mechanical and finite-difference time-domain numerical calculations indicate that the incident radiation in the optical reflectance measurement photoexcites the InAs QDs which then form excitonic dipoles. The excitonic dipole modifies significantly the dielectric constant of the QD, which results in a reflectance peak in the vicinity of the excitonic energy, as observed experimentally.

  • 35.
    Fu, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Kowalewski, Jacob
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Wu, J.
    Yue, Y.
    Dai, N.
    Thylén, Lars
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics. KTH, School of Information and Communication Technology (ICT), Centres, Kista Photonics Research Center, KPRC.
    Radiative and nonradiative recombination of photoexcited excitons in multi-shell-coated CdSe/CdS/ZnS quantum dots2009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 86, no 3, p. 37003-Article in journal (Refereed)
    Abstract [en]

    Colloidal quantum dots (QDs) have been widely studied for nanophotonics and bioimaging applications for which the lifetime of their fluorescence is of critical importance. We report experimental and theoretical characterizations of dynamic optical properties of multi-shell-coated CdSe/CdS/ZnS QDs. Quantum-mechanical studies of fundamental optical excitations and Monte Carlo simulations of energy relaxation mechanisms indicate that the excitonic states are densely compacted in the QDs and are easily photoexcited by the laser pulse in the presence of nonradiative electron-phonon interactions. For spherical QDs, the decay time of spontaneous radiative emission of individual photoexcited excitonic states with zero angular momenta is found to be only tens of picoseconds. In our multi-shell QDs, high-energy excitonic states of nonzero angular momenta have to go through a number of nonradiative electron-phonon interaction steps in order to relax to zero-angular-momentum excitonic states for radiative emission, resulting in an effective fluorescence peak at about 2 ns in the photoncount-time relationship. This explains the measured long average fluorescence lifetime of 3.6 ns. Such a long lifetime facilitates the applications of colloidal QDs in areas such as QD-based solar cells, bioimaging and metamaterials.

  • 36. Gan, Zhixing
    et al.
    Wu, Xinghong
    Xu, Hao
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Zhang, Ning
    Nie, Shouping
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Electron transition pathways of photoluminescence from 3C-SiC nanocrystals unraveled by steady-state, blinking and time-resolved photoluminescence measurement2016In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 27Article in journal (Refereed)
    Abstract [en]

    The cubic phase SiC nanocrystals (3C-SiC NCs) have been extensively studied for electronics and photonics applications. In this work we study the electron transition pathways of photoluminescence (PL) from 3C-SiC NCs. It is found through measuring the steady-state, blinking and time-resolved PL spectra that surface passivation by glycerol improved the steady-state PL intensity (it does not modify the emission wavelength) and the NCs fluoresced more steadily. The PL decay lifetimes are shown to be the same when the detection wavelength is modified to scan the broad PL peak, implying that the broad PL peak is originated from the distribution of NCs' sizes. Furthermore, the PL decay lifetimes are not modified by the surface passivation. It is concluded that for PL, the electron is photoexcited from the ground state in the NC to a high-energy excited state, relaxes to the first excited state then radiatively recombines to the ground state to emit a photon. The photoexcited electron at the high-energy excited state could transit to the surface state, resulting in a reduced PL intensity and a decreased on-state dwell time in the blinking trajectory. The PL decay lifetime data implies that the two principal electron transition pathways of (a) high-energy excited state double right arrow the first excited state double right arrow the ground state, and (b) high-energy excited state double right arrow surface state double right arrow the ground state are independent from each other. We strongly believe that such a deep knowledge about 3C-SiC NCs will open new doors to harness them for novel applications.

  • 37. Gan, Zhixing
    et al.
    Xu, Hao
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Photon Reabsorption and Nonradiative Energy-Transfer-Induced Quenching of Blue Photoluminescence from Aggregated Graphene Quantum Dots2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 51, p. 29432-29438Article in journal (Refereed)
    Abstract [en]

    A deep understanding of the photoluminescence (PL) from aggregated graphene quantum dots (GQDs) is very important for their practical applications. Here the PL spectra from GQDs solutions at different concentrations are studied. We find that the intensity of the green emission (ca. 530560 nm) linearly relies on the concentration of GQDs, whereas the blue PL (ca. 425 nm) intensity is below the linear relationship, indicating a concentration-induced partial quenching of blue PL. Confocal fluorescence images explicitly demonstrate the aggregation of GQDs at high concentration. The concentration-induced PL quenching is successfully interpreted by a model of photon reabsorption and nonradiative energy transfer, indicating that, at the aggregated states, the excited electrons of GQDs may nonradiatively relax to ground states through couplings with neighboring ones. Simulated fluorescence decay results show that the energy transfer between neighboring GQDs results in a prolonged dwell time of electron on high-energy state and thus increases the decay time of 425 nm emission, while 550 nm emission remains unaffected, which is consistent with the experimental results. This work will contribute to a deep understanding on PL of GQDs and is also of huge importance to extend GQDs applications.

  • 38.
    Han, Tiantian
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Dai, N.
    Optical properties of multi-coated CdSe/CdS/ZnS quantum dots for multiphoton applications2008In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 11, p. 115104-Article in journal (Refereed)
    Abstract [en]

    CdSe-core CdS/Cd(0.5)Zn(0.5)S/ZnS multishell quantum dots (QDs) were synthesized by using the successive ion layer adsorption and reaction method, and their optical properties were characterized experimentally. Based on probability calculations of the time-dependent Schrodinger equation, a kinetic Monte Carlo method was used to simulate and analyse the absorption and spontaneous emission spectra of multiphoton-excited QDs. It has been shown that the blue shift of the photoluminescence peak of the core CdSe QD after coating is most probably due to the Zn diffusion during the synthesis of the ZnS coating layer.

  • 39.
    Han, Tiantian
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Wang, S.-M.
    Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology.
    Larsson, A.
    Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology.
    Structural analysis of dilute-nitride zinc blende InxGa1−xNyAs1−y cluster by a semiempirical quantum chemistry study2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 12, p. 123707-1-123707-6Article in journal (Refereed)
    Abstract [en]

    We have studied the total energy of a series of dilute-nitride zinc blende Inx Ga1-x Ny As1-y cluster configurations using a semiempirical quantum chemistry method. It was found that In-N bonding is favorable from an energy point of view when the N atom is substitutional (replacing an As atom at the regular zinc blende lattice site) and the In mole fraction is smaller than 25%. In-N bonding is always favorable when the N atom is interstitial. Furthermore, an analysis of the incorporation of N-N pairs showed that substitutional incorporation is favored over interstitial. In addition, the dissociation of a N-N pair was found to depend on the local environment, being either In rich or In-free, along the dissociation trajectory when the average In mole fraction is high. The theoretical results are in agreement with experimental results.

  • 40.
    Han, Tiantian
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Dynamic photon emission from multiphoton-excited semiconductor quantum dots2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 9, p. 093703-1-093703-6Article in journal (Refereed)
    Abstract [en]

    The dynamic process of multiphoton optical transitions in semiconductor quantum dots (QDs) has been studied by a Monte Carlo scheme. The scheme includes optical transitions of all electrons, initially occupying the valence-band confined states in the QD, among the confined states in valence and conduction bands. The optical transition probabilities are calculated by the time-dependent Schrodinger equation, and nonradiative phonon scattering processes have been included. Assisted by a two-photon excitation by a continuous-wave laser (one photon energy equals half of the QD energy band gap), an assembly of the QDs shows an emission peak around the band gap in the optical emission spectrum, while an ultrafast pulsed laser, whose photon energy is below the QD band gap, also induces a similar narrow but weaker emission peak, which results in a nonstrict multiphoton excitation condition for many potential applications including biophotonics. Extension of the theoretical study to the spherical CdS/Cd0.5Zn0.5S/ZnS-multicoated CdSe QD has reproduced the experimental absorption and multiphoton emission spectra.

  • 41.
    Han, Tiantian
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Radiative emission from multiphoton-excited semiconductor quantum dots2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 6, p. 063712-1-063712-6Article in journal (Refereed)
    Abstract [en]

    Optical transitions in CdS semiconductor quantum dots (QDs) have been studied by the Monte Carlo method based on probability calculations of the time-dependent Schrodinger equation. It has been demonstrated that excited by a continuous-wave laser, an assembly of CdS QDs, whose radii range from 2 to 5 nm centered at 3.7 nm, shows an emission peak around 2.65 eV in the optical emission spectrum, which corresponds to optical transitions among degenerate sublevels close to the ground sublevels in the conduction and valence bands of a CdS QD having a radius of 3.7 nm. For resonant one-photon excitation, the emission peak is very sharp, while for resonant two-photon excitation, the emission peak becomes blueshifted and broadened. The inclusion of the nonradiative electron-phonon processes makes the two-photon excitation peak significantly sharper and shows a better agreement with experimental work, thus demonstrating the upconversion luminescence of the QDs required for many applications including bioimaging.

  • 42.
    Han, Tiantian
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Han, P.
    Key Laboratory of Advanced Photonic and Electronic Materials, Department of Physics, Nanjing University.
    Qin, Z.
    Key Laboratory of Advanced Photonic and Electronic Materials, Department of Physics, Nanjing University.
    Zhang, R.
    Key Laboratory of Advanced Photonic and Electronic Materials, Department of Physics, Nanjing University.
    Room-temperature photoluminescence of doped 4H-SiC film grown on AlN/Si(100)2007In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 86, no 1, p. 145-149Article in journal (Refereed)
    Abstract [en]

    Well-defined room-temperature photoluminescence (PL) was observed from 4H-SiC films on AlN/Si(100) complex substrates grown at temperatures below 1150 degrees C by the chemical vapor deposition method. The PL spectrum consists of three major emission peaks in the vicinities of 3.03, 3.17 and 3.37 eV. By the combination of experimental measurements and theoretical analysis, the origins of the PL emission peaks have been identified and associated with N donors, Al acceptors in the 4H-SiC films and the band-to-band transition between the second minimum of the conduction band and the top of valance band of the 4H-SiC. The room-temperature SiC PL can be much utilized for optoelectronic high-power, high-frequency and high-temperature applications in the ultraviolet spectral regime.

  • 43.
    Han, Tiantian
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Jiang, Jun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Gao, Bin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Quantum chemistry study of energy band structures of GaAs nano clustersManuscript (Other academic)
  • 44.
    Hellstrom, Staffan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Dynamic optical response of an excitonic quantum dot studied by solving the self-consistent Maxwell-Schrodinger equations nonperturbatively2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 24, p. 245305-Article in journal (Refereed)
    Abstract [en]

    The optical excitation of a quantum dot in real-world working conditions is studied by self-consistent solution of the time-dependent Schrodinger equation coupled to the Maxwell equations by the finite-difference time domain method, resulting in a polarization modification which is the basis for the enhanced light-matter interaction in many nanoscale devices. The commonly used perturbational analysis approach is compared to the results and found to be an acceptable approximation even for intense femtosecond pulse excitations where using the perturbative approach is risky. This allows device designers and simulators to confidently use the simpler and faster perturbative results in their work.

  • 45.
    Hellström, Staffan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Chen, Zhihui
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Soltanmoradi, R.
    Wang, Q.
    Andersson, J. Y.
    Increased photocurrent in quantum dot infrared photodetector by subwavelength hole array in metal thin film2010In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 23, p. 231110-Article in journal (Refereed)
    Abstract [en]

    Photocurrent enhancement in quantum dot (QD) infrared photodetector (QDIP) with an optical grating of subwavelength hole array in a thin metal film has been studied by calculating the transmission and diffraction of the infrared optical field through the grating and the light-matter interaction between the transmitted optical field and electrons confined in the QD. It is shown that due to the small aspect ratio of realistic QDs in QDIPs, the light diffraction due to the surface plasmon effect at the metal-semiconductor surface and the photonic subwavelength hole array structure is dominant in increasing the photocurrent.

  • 46.
    Hellström, Staffan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Enhanced electromagnetic field transfer across semiconductor-and-metal-nanoparticle oligomeric planar structure through exciton-plasmoninteractionsManuscript (preprint) (Other academic)
  • 47.
    Hou, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Wang, W. P.
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences.
    Li, N.
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences.
    Lu, W.
    National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Effects of series and parallel resistances on the current-voltage characteristics of small-area air-bridge resonant tunneling diode2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 104, no 7Article in journal (Refereed)
    Abstract [en]

    We have studied experimentally and theoretically the effects of series and parallel resistances on the current-voltage (I-V) characteristics of the resonant tunneling diode (RTD) in the format of a small-area freestanding air bridge. It has been shown by standard quantum mechanical considerations that the I-V characteristics consists of a simple resonant current peak (without bistability) and the voltage at the current peak is quite low, whereas experiments show not only a much high current-peak voltage, but also the bistability. Furthermore, experimental peak-to-valley ratio is in general quite low. By analyzing material and device structures, it has been demonstrated that the series resistance in the RTD contacts shifts the peak in current to higher voltage, it also creates the experimentally observed bistability effect in the region of the tunneling resonance. The parallel resistance induces a leakage current and reduces the peak-to-valley ratio. We have further performed similar analyses to many RTD structures reported in the literature and the conclusions remain the same.

  • 48.
    Hou, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Wang, W. -P.
    Li, N.
    Xu, W. -L.
    Lu, W.
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Carrier wave-packet transport under the influence of charged quantum dot in small-area resonant tunneling diodes2008In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, no 13, p. 132108-Article in journal (Refereed)
    Abstract [en]

     It was shown experimentally that charging InAs quantum dots (QDs) embedded in a small-area GaAs/AlAs double-barrier resonant tunneling diode (RTD) effectively modified the carrier transport properties of the RTD. By adopting and comparing the one-dimensional plane-wave and three-dimensional (3D) wave-packet transport theories we show that the electron transports in the QDRTD device are in the form of 3D wave packets, which are strongly affected by the 3D long-range Coulomb potential induced by charged InAs QDs. This explains well experimental data and indicates that the 3D wave-packet transport model is more appropriate for the QDRTD device.

  • 49.
    Jiang, Jun
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Gao, Bin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Han, Tiantian
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ab initio study of energy band structures of GaAs nanoclusters2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, no 9Article in journal (Refereed)
    Abstract [en]

    Electronic states and optical transitions of hydrogen terminated GaAs nanoclusters up to 16.9 nm in diameter were studied using a large-scale quantum chemistry approach called central insertion scheme by which the quantum confinement effect is shown to quantitatively agree with experimental results. The ab initio study further reveals that the effective mass of the conduction-band electron (valence-band hole) in the GaAs nanocluster is larger (smaller) than the bulk material value.

  • 50. Karimi, M.
    et al.
    Heurlin, M.
    Limpert, S.
    Jain, V.
    Zeng, X.
    Geijselaers, I.
    Nowzari, A.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Samuelson, L.
    Linke, H.
    Borgström, M. T.
    Pettersson, H.
    Intersubband Quantum Disc-in-Nanowire Photodetectors with Normal-Incidence Response in the Long-Wavelength Infrared2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 1, p. 365-372Article in journal (Refereed)
    Abstract [en]

    Semiconductor nanowires have great potential for realizing broadband photodetectors monolithically integrated with silicon. However, the spectral range of such detectors has so far been limited to selected regions in the ultraviolet, visible, and near-infrared regions. Here, we report on the first intersubband nanowire heterostructure array photodetectors exhibiting a spectrally resolved photoresponse from the visible to long-wavelength infrared. In particular, the infrared response from 3 to 20 μm is enabled by intersubband transitions in low-bandgap InAsP quantum discs synthesized axially within InP nanowires. The intriguing optical characteristics, including unexpected sensitivity to normal incident radiation, are explained by excitation of the longitudinal component of optical modes in the photonic crystal formed by the nanostructured portion of the detectors. Our results provide a generalizable insight into how broadband nanowire photodetectors may be designed and how engineered nanowire heterostructures open up new, fascinating opportunities for optoelectronics.

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