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  • 1. Bhattacharya, K.
    et al.
    El-Sayed, R.
    Andón, F. T.
    Mukherjee, S. P.
    Gregory, J.
    Li, H.
    Zhao, Yinchen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Seo, W.
    Fornara, A.
    Brandner, B.
    Toprak, Muhammet Sadaka
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Leifer, K.
    Star, A.
    Fadeel, B.
    Lactoperoxidase-mediated degradation of single-walled carbon nanotubes in the presence of pulmonary surfactant2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 91, p. 506-517Article in journal (Refereed)
    Abstract [en]

    Carbon nanotubes (CNTs) may elicit inflammatory responses following pulmonary exposure. Conversely, enzymatic biodegradation of CNTs by inflammatory cells has also been reported. The aim of this study was to study the degradation of oxidized single-walled CNTs (ox-SWCNTs) by lactoperoxidase (LPO), a secreted peroxidase present in the airways, and whether pulmonary surfactant affects this biodegradation. To this end, ox-SWCNTs were incubated in vitro with recombinant bovine LPO + H<inf>2</inf>O<inf>2</inf> + NaSCN in the presence and absence of porcine lung surfactant (Curosurf®) and biodegradation was monitored using UV-Vis-NIR spectroscopy, Raman spectroscopy, and scanning electron microscopy. The interaction of recombinant LPO with bundles of ox-SWCNTs was confirmed by atomic force microscopy. Cell-free biodegradation of ox-SWCNTs was also observed ex vivo in murine bronchoalveolar lavage fluid in the presence of H<inf>2</inf>O<inf>2</inf> + NaSCN. Our study provides evidence for biodegradation of ox-SWCNTs with a lung surfactant 'bio-corona' and expands the repertoire of mammalian peroxidases capable of biodegradation of ox-SWCNTs. These findings are relevant to inhalation exposure to these materials, as LPO serves as an important component of the airway defense system.

  • 2. Bhattacharya, Kunal
    et al.
    El-Sayed, Ramy
    Andon, Fernando T.
    Mukherjee, Sourav P.
    Gregory, Joshua
    Li, Hu
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Seo, Wanji
    Fornara, Andrea
    Brandner, Birgit
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Leifer, Klaus
    Star, Alexander
    Fadeel, Bengt
    Lactoperoxidase-mediated degradation of single-walled carbon nanotubes in the presence of pulmonary surfactant (vol 91, pg 506, 2015)2015In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 95, p. 766-766Article in journal (Refereed)
  • 3.
    Doddapaneni, Venkatesh
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Ye, Fei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Gati, R.
    Edin, Hans
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Improving Uv Radiation Absorption by Copper Oxide NPs/PMMA Nanocomposites for Electrical Switching Applications2015In: Powder metallurgy and metal ceramics, ISSN 1068-1302, E-ISSN 1573-9066, Vol. 54, no 7-8, p. 397-401Article in journal (Refereed)
    Abstract [en]

    Nanocomposites based on the radiation absorbing polymer (PNCs) are of interest for a variety of applications including circuit breakers, UV-shielding windows, contact lenses, and glasses among others. Such PNCs can be made by incorporating suitable radiation absorbing nanoparticles into a polymeric matrix by in situ polymerization. In this study, spherical nanoparticles (5-6 nm) of oleic acid (OA) surface modified cupric oxide (CuO) are synthesized and used to improve the ultra-violet (UV) radiation absorption property of a polymer matrix, i.e., polymethylmethacrylate (PMMA). The synthesis of spherical CuO nanoparticles, surface modification using OA, dispersion of CuO nanoparticles with different concentrations in PMMA, and UV radiation absorption property of the resultant PNC are investigated. Two different PNCs are produced using OA modified CuO nanoparticles with different concentrations. As synthesized CuO nanoparticles and OA modified CuO nanoparticles are examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) techniques. The UV absorption edges are evaluated from the UV-Vis absorption spectra by using UV-Visible absorption spectroscopy. The results show that the UV radiation absorption of the PNC with higher concentration of CuO nanoparticles is improved compared with PMMA and the absorption edge moved towards longer wavelengths i.e., from 271 to 281 nm. These PNCs are successful in arc interruption process by absorbing a broad range of radiation emitted from high-energy copper arcs produced in the circuit breakers.

  • 4. El-Sayed, Ramy
    et al.
    Bhattacharya, Kunal
    Gu, Zonglin
    Yang, Zaixing
    Weber, Jeffrey K.
    Li, Hu
    Leifer, Klaus
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Zhou, Ruhong
    Fadeel, Bengt
    Single-Walled Carbon Nanotubes Inhibit the Cytochrome P450 Enzyme, CYP3A42016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 21316Article in journal (Refereed)
    Abstract [en]

    We report a detailed computational and experimental study of the interaction of single-walled carbon nanotubes (SWCNTs) with the drug-metabolizing cytochrome P450 enzyme, CYP3A4. Dose-dependent inhibition of CYP3A4-mediated conversion of the model compound, testosterone, to its major metabolite, 6 beta-hydroxy testosterone was noted. Evidence for a direct interaction between SWCNTs and CYP3A4 was also provided. The inhibition of enzyme activity was alleviated when SWCNTs were pre-coated with bovine serum albumin. Furthermore, covalent functionalization of SWCNTs with polyethylene glycol (PEG) chains mitigated the inhibition of CYP3A4 enzymatic activity. Molecular dynamics simulations suggested that inhibition of the catalytic activity of CYP3A4 is mainly due to blocking of the exit channel for substrates/products through a complex binding mechanism. This work suggests that SWCNTs could interfere with metabolism of drugs and other xenobiotics and provides a molecular mechanism for this toxicity. Our study also suggests means to reduce this toxicity, eg., by surface modification.

  • 5. Karlsson, M.
    et al.
    Wang, Q.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Zhao, W.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Iakimov, T.
    Ali, A.
    Yakimova, R.
    Syväjärvi, M.
    Ivanov, I. G.
    Wafer-scale epitaxial graphene on SiC for sensing applications2015In: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2015Conference paper (Refereed)
    Abstract [en]

    The epitaxial graphene-on-silicon carbide (SiC-G) has advantages of high quality and large area coverage owing to a natural interface between graphene and SiC substrate with dimension up to 100 mm. It enables cost effective and reliable solutions for bridging the graphene-based sensors/devices from lab to industrial applications and commercialization. In this work, the structural, optical and electrical properties of wafer-scale graphene grown on 2'™'™ 4H semi-insulating (SI) SiC utilizing sublimation process were systemically investigated with focus on evaluation of the graphene'™s uniformity across the wafer. As proof of concept, two types of glucose sensors based on SiC-G/Nafion/Glucose-oxidase (GOx) and SiC-G/Nafion/Chitosan/GOx were fabricated and their electrochemical properties were characterized by cyclic voltammetry (CV) measurements. In addition, a few similar glucose sensors based on graphene by chemical synthesis using modified Hummer'™s method were also fabricated for comparison. © 2015 SPIE.

  • 6.
    Khachatourian, Malek Adrine
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. IUST-Iran University of Science and Technology, Iran.
    Golestani-Fard, F.
    Sarpoolaky, H.
    Vogt, Carmen
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Green synthesis of Y2O3:Eu3+ nanocrystals for bioimaging2015In: Materials Research Society Symposium Proceedings, Materials Research Society, 2015, Vol. 1720, p. 59-64Conference paper (Refereed)
    Abstract [en]

    Rare earth (e.g., Eu, Er, Yb, Tm) doped Y<inf>2</inf>O<inf>3</inf> nanocrystals are promising fluorescent bioimaging agents which can overcome well known problems of currently used organic dyes like photobleaching, phototoxicity, and light scattering. Furthermore, the alternative quantum dots (QDs) composed of heavy metals (e.g., CdSe) possess inherently low biocompatibility due to the heavy metal content. In the present work, monodisperse spherical Y<inf>2</inf>O<inf>3</inf>:Eu3+ nanocrystals were successfully synthesized by microwave assisted urea precipitation method followed by thermochemical treatment. This is a green, fast and reproducible synthesis method, which is surfactant and hazardous precursors free. The as prepared particles were non-aggregated, spherical particles with a narrow size distribution. The calcined particles have a polycrystalline structure preserving the monodispersity and the spherical morphology of the as prepared particles. After calcination of Y(OH)CO<inf>3</inf>:Eu3+ precursors at 900°C for 2 hours, a highly crystalline cubic Y<inf>2</inf>O<inf>3</inf> structure was obtained. The Y<inf>2</inf>O<inf>3</inf>:Eu3+ spherical particles showed a strong red emission peak at 613nm due to the 5D<inf>0</inf>-7F<inf>2</inf> forced electric dipole transition of Eu3+ ions under UV excitation (235 nm) as revealed by the photoluminescence analysis (PL). The effect of reaction time on size and photoluminescence properties of calcined particles and also the effect of reaction temperature and pressure on the size and the yield of the precipitation process have been studied. The intense red fluorescent emission, excellent stability and potential low toxicity make these QDs promising for applications in bio-related areas such as fluorescence cell imaging or fluorescence bio labels.

  • 7.
    Lobov, G. S.
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Marinins, A.
    KTH, School of Information and Communication Technology (ICT).
    Etcheverry, S.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT).
    Vasileva, Elena
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sugunan, A.
    Laurell, F.
    Thylén, Lars
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wosinski, L.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT).
    Toprak, M. S.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Direct birefringence and transmission modulation via dynamic alignment of P3HT nanofibers in an advanced opto-fluidic component2017In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 7, no 1, p. 52-61Article in journal (Refereed)
    Abstract [en]

    Poly-3-hexylthiophene (P3HT) nanofibers are semiconducting high-aspect ratio nanostructures with anisotropic absorption and birefringence properties found at different regions of the optical spectrum. In addition, P3HT nanofibers possess an ability to be aligned by an external electric field, while being dispersed in a liquid. In this manuscript we show that such collective ordering of nanofibers, similar to liquid crystal material, significantly changes the properties of transmitted light. With a specially fabricated opto-fluidic component, we monitored the phase and transmission modulation of light propagating through the solution of P3HT nanofibers, being placed in the electric field with strength up to 0.1 V/μm. This report describes a technique for light modulation, which can be implemented in optical fiber-based devices or on-chip integrated components.

  • 8.
    Lobov, Gleb S.
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Marinins, Aleksandrs
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, Jiantong
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Thylen, Lars
    KTH, School of Biotechnology (BIO).
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Ostling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Size Impact of Ordered P3HT Nanofibers on Optical Anisotropy2016In: Macromolecular Chemistry and Physics, ISSN 1022-1352, E-ISSN 1521-3935, Vol. 217, no 9, p. 1089-1095Article in journal (Refereed)
    Abstract [en]

    Poly-3-hexylthiophene (P3HT) nanofibers are 1D crystalline structures with semiconductor properties. When P3HT nanofi bers are dispersed in nonconducting solvent, they react to external alternate electric field by aligning along the field lines. This can be used to create layers of ordered nanofi bers and is referred to as alternating current poling method. P3HT nanofi bers with three different size distributions are fabricated, using self-assembly mechanism in marginal solvents, and used for the alignment studies. Anisotropic absorption of oriented 2 mu m long nanofi bers exponentially increases with the magnitude of applied field to a certain asymptotic limit at 0.8 V mu m(-1), while 100-500 nm long nanofi bers respond to electric field negligibly. Effective optical birefringence of oriented 2 mu m long nanofi bers is calculated, based on the phase shift at 633 nm and the average layer thickness, to be 0.41. These results combined with further studies on real-time control over orientation of P3HT nanofi bers in liquid solution or host system are promising in terms of exploiting them in electroabsorptive and electrorefractive applications.

  • 9.
    Lobov, Gleb S.
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Marinins, Aleksandrs
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, Jiantong
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Sugunan, A.
    Thylén, Lars
    KTH, School of Biotechnology (BIO). Hewlett-Packard Laboratories, United States.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT).
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Electric field induced optical anisotropy of P3HT nanofibers in a liquid solution2015In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 5, no 11, p. 2642-2647Article in journal (Refereed)
    Abstract [en]

    The nanofiber morphology of regioregular Poly-3- hexylthiophene (P3HT) is a 1D crystalline structure organized by π - π stacking of the backbone chains. In this study, we report the impact of electric field on the orientation and optical properties of P3HT nanofibers dispersed in liquid solution. We demonstrate that alternating electric field aligns nanofibers, whereas static electric field forces them to migrate towards the cathode. The alignment of nanofibers introduces anisotropic optical properties, which can be dynamically manipulated until the solvent has evaporated. Time resolved spectroscopic measurements revealed that the electro-optical response time decreases significantly with the magnitude of applied electric field. Thus, for electric field 1.3 V ·μm-1 the response time was measured as low as 20 ms, while for 0.65 V ·μm-1 it was 110-150 ms. Observed phenomenon is the first mention of P3HT supramolecules associated with electrooptical effect. Proposed method provides real time control over the orientation of nanofibers, which is a starting point for a novel practical implementation. With further development P3HT nanofibers can be used individually as an anisotropic solution or as an active component in a guest-host system.

  • 10.
    Lobov, Gleb S.
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT).
    Marinins, Aleksandrs
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, Jiantong
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Sugunan, A.
    Thylen, Lars
    KTH, School of Biotechnology (BIO).
    Wosinski, L.ech
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Fotonik och mikrovågsteknik, FMI.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Popov, Sergei Yu
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Electro-optical response of P3HT nanofibers in liquid solution2015In: Asia Communications and Photonics Conference, ACPC 2015, 2015Conference paper (Refereed)
    Abstract [en]

    AC electric poling introduces in P3HT nanofibers anisotropic electro-optical response and birefringence. Along with birefringence, such material exhibits strong amplitude modulation which makes it more efficient alternative to liquid crystals. © 2015 OSA.

  • 11.
    Lobov, Gleb
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT).
    Marinins, Aleksandrs
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, Jiantong
    KTH, School of Information and Communication Technology (ICT).
    Sugunan, A.
    Thylén, Lars
    KTH, School of Biotechnology (BIO). Hewlett-Packard Laboratories, United States.
    Wosinski, L.ech
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Fotonik och mikrovågsteknik, FMI.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Toprak, Muhammet
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Dynamic Manipulation of Optical Anisotropy of Suspended Poly-3-hexylthiophene Nanofibers2016In: Advanced Optical Materials, ISSN 2195-1071, Vol. 4, no 10, p. 1651-1656Article in journal (Refereed)
    Abstract [en]

    Poly-3-hexylthiophene (P3HT) nanofibers are 1D crystalline semiconducting nanostructures, which are known for their application in photovoltaics. Due to the internal arrangement, P3HT nanofibers possess optical anisotropy, which can be enhanced on a macroscale if nanofibers are aligned. Alternating electric field, applied to a solution with dispersed nanofibers, causes their alignment and serves as a method to produce solid layers with ordered nanofibers. The transmission ellipsometry measurements demonstrate the dichroic absorption and birefringence of ordered nanofibers in a wide spectral range of 400–1700 nm. Moreover, the length of nanofibers has a crucial impact on their degree of alignment. Using electric birefringence technique, it is shown that external electric field applied to the solution with P3HT nanofibers can cause direct birefringence modulation. Dynamic alignment of dispersed nanofibers changes the refractive index of the solution and, therefore, the polarization of transmitted light. A reversible reorientation of nanofibers is organized by using a quadrupole configuration of poling electrodes. With further development, the described method can be used in the area of active optical fiber components, lab-on-chip or sensors. It also reveals the potential of 1D conducting polymeric structures as objects whose highly anisotropic properties can be implemented in electro-optical applications.​

  • 12.
    Lobov, Gleb
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Marinins, Aleksandrs
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Li, Jiantong
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Sugunan, A.
    Thylén, Lars
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Optical birefringence from P3HT nanofibers in alternating electric field2014In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2014Conference paper (Refereed)
    Abstract [en]

    AC poling allowing to control the orientation of P3HT nanofibers, result in strong optical birefringence with promising implementation in a novel type of optical modulator, without necessary embedding into any hosting matrix, e.g. liquid crystal.

  • 13.
    Sugunan, Abhilash
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Mitra, Somak
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Dong, Lin
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Shanghua
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Marcinkevicius, Saulius
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Synthesis of tetrahedral quasi-type-II CdSe-CdS core-shell quantum dots2011In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 22, no 42, p. 425202-Article in journal (Refereed)
    Abstract [en]

    Synthesis of colloidal nanocrystals of II-VI semiconductor materials has been refined in recent decades and their size dependent optoelectronic properties have been well established. Here we report a facile synthesis of CdSe-CdS core-shell heterostructures using a two-step hot injection process. Red-shifts in absorption and photoluminescence spectra show that the obtained quantum dots have quasi-type-II alignment of energy levels. The obtained nanocrystals have a heterostructure with a large and highly faceted tetrahedral CdS shell grown epitaxially over a spherical CdSe core. The obtained morphology as well as high resolution electron microscopy confirms that the tetrahedral shell have a zinc blende crystal structure. A phenomenological mechanism for the growth and morphology of the nanocrystals is discussed.

  • 14.
    Zhao, Wei
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Acreo Swedish ICT AB, Sweden.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Karlsson, Mikael
    Wang, Qin
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Evaluation of Zinc Oxide Nano-Microtetrapods for Biomolecule Sensing Applications2015In: MICRO+NANO MATERIALS, DEVICES, AND SYSTEMS, SPIE - International Society for Optical Engineering, 2015, article id UNSP 966833Conference paper (Refereed)
    Abstract [en]

    Zinc oxide tetrapods (ZnO-Ts) were synthesized by flame transport synthesis using Zn microparticles. This work herein reports a systematical study on the structural, optical and electrochemical properties of the ZnO-Ts. The morphology of the ZnO-Ts was confirmed by scanning electron microscopy (SEM) as joint structures of four nano-microstructured legs, of which the diameter of each leg is 0.7-2.2 mu m in average from the tip to the stem. The ZnO-Ts were dispersed in glucose solution to study the luminescence as well as photocatalytic activity in a mimicked biological environment. The photoluminescence (PL) intensity in the ultraviolet (UV) region decreased with linear dependence on the glucose concentration up to 4 mM. The ZnO-Ts were also attached with glucose oxidase (GOx) and over coated with a thin film of Nafion to form active layers on Si/SiO2/Au substrate for electrochemical glucose sensing. The attachment of GOx and the coating of Nafion onto ZnO-Ts were confirmed by Fourier transform infrared spectroscopy (FT-IR). Furthermore, the current response of the active layers based on ZnO-Ts was investigated by cyclic voltammetry (CV) in various glucose concentration conditions. Stable current response of glucose was detected with linear dependence on the glucose concentration up to 12 mM, which confirms the potential of ZnO-Ts for biomolecule sensing applications.

  • 15.
    Zhao, Yichen
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Semiconducting Polymer Nanofibers and Quantum Dot based Nanocomposites for Optoelectronic Applications2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nanostructured materials have attracted a broad interest in various technologies such as optoelectronics. In this thesis, nanostructured semiconductor nanocrystals, including inorganic and organic materials, were fabricated by solution based methods. The reaction conditions were optimized to control the size and morphology of the obtained nanocrystals. The optical and photoelectric properties of nanocrystals were evaluated for potential optoelectronic applications.

    Colloidal CdSe quantum dots (QDs) were synthesized via thermolysis method and layers of CdS was further grown on the core CdSe QDs to form a core-shell heterostructure quantum dots (HQDs). The optical properties of HQDs were evaluated and showed the characteristics of quasi-type-II alignment of energy levels, which has potential for excitonic solar cell (XSC) application.

    Nanofibers of the semiconducting polymer poly-(3-hexylthiophene) (P3HT) were synthesized via a modified whisker method. In order to control the size (both the length and the diameter) of nanofibers, we systematically studied the ratio between mixture solvents and the solute concentration. In addition, the degradation processes of P3HT nanofibers on different substrates under various environments were investigated. We found that the degradation of P3HT nanofibers can be effectively suppressed by using the substrate of higher conductivity. A nanocomposite consisting of HQDs and P3HT nanofibers was fabricated and its photoelectric properties were evaluated by I-V measurements. A ‘turn-on’ voltage was found and revealed the localization of excited holes within the HQDs, which confirmed the quasi-type-II alignment between core and shell energy levels.

    In addition, we aligned the P3HT nanofibers by applying the external electric field. Alternating current (AC) and direct current (DC) induced alignments of P3HT nanofibers were investigated respectively to study the effects of different electric fields on the alignment behavior. It was determined that the AC electric field allowed a better alignment of nanofibers. Moreover, two different lengths of P3HT nanofibers were aligned and their absorption spectra were measured. Under polarized light beams, we observed a better aligned pattern in the case of longer nanofibers, shown as a higher dichroic ratio calculated from optical absorption spectra. These aligned nanofibers may find applications in optoelectronic devices.

  • 16.
    Zhao, Yichen
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Lobov, Gleb
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Sugunan, Abhilash
    Chemistry, Materials and Surfaces Unit, SP Technical Research Institute of Sweden.
    Karlsson, Mikael
    Department of Sensor system, Acreo Swedish ICT AB.
    Marinins, Aleksandrs
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Delekta, Szymon Sollami
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Wang, Qin
    Department of Sensor system, Acreo Swedish ICT AB.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Electrical Field Induced Alignment of P3HT NanofibersManuscript (preprint) (Other academic)
    Abstract [en]

    Abstract: Poly 3-hexylthiophene (P3HT) is one of the most studied conjugated polymers for organic solar cell applications due to its light weight, flexible processing methods and low cost fabrication. However, the hole mobility in P3HT is still relatively low compared to that of the inorganic semiconductors, which is one of the main challenges to achieve better performance of organic solar cells. The P3HT nanofibers with aligned by inducing an external electric field have been studied to improve the hole mobility in P3HT nanofibers. Here we present an AC electric field (1.3 V/µm, 50 Hz) induced alignment of P3HT nanofibers with two different lengths. The optical absorption spectra of aligned nanofibers were measured under different polarizations of incident light. The longer nanofibers showed higher dichroic raitos than that of shorter nanofibers, revealing a better alignment pattern. The photoconductivity of non-aligned and aligned P3HT nanofibers were measured and compared, where the aligned P3HT nanofibers showed a ~270% higher dark current than that of non-aligned sample. Moreover, the current measured under the illumination showed ~110% enhancement in the aligned P3HT nanofibers while only ~70% enhancement was obseved in non-aligned nanofibers, revealing that the alignment process have the potential to improve the mobility for optoelectronic applications. 

  • 17.
    Zhao, Yichen
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Sugunan, A.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Synthesis of nanostructured antimony telluride for thermoelectric applications2015In: Materials Research Society Symposium Proceedings, Elsevier, 2015, Vol. 1742, p. 1-6Conference paper (Refereed)
    Abstract [en]

    Thermoelectric (TE) materials have been studied during past decades since they can generate electricity directly from waste heat. Antimony chalcogenides (Sb2M3, M = S, Se, Te) are well known as one of the promising candidates among the inorganic TE materials. We report on the synthesis of Sb2Te3 nanoparticle via thermolysis method. A systematic study was done to investigate the effect of reaction time and ratio between the precursors as well as the method of cooling on the morphology and composition of obtained nanoparticles. The ratio between precursors was varied to study the effect on the morphology. Furthermore, the high purity phase Sb2Te3 was obtained by a rapid cooling process.

  • 18.
    Zhao, Yichen
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Rihtnesberg, David B.
    Wang, Qin
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Size-tuneable synthesis of photoconducting poly-(3-hexylthiophene) nanofibres and nanocomposites2012In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 7, p. 1546-1550Article in journal (Refereed)
    Abstract [en]

    Poly-(3-hexylthiophene) (P3HT) has been applied in many fields such as organic solar cells, printed electronic circuits, due to superior semiconducting properties compared to other semiconducting polymers. The presence of p-p interaction causes regio-regular P3HT to form ordered lamellar stacks during crystallisation. Here we report a simple room temperature, solution based method to synthesise P3HT nanofibres with controllable sizes. Our method is based on differing solubility of P3HT in various solvents. In a mixed solvent environment, we could control the precipitation of P3HT to obtain nanofibres with various diameters by varying the ratios of the solvents. We found that the lengths of the nanofibres could be controlled with concentration of the solution. Other methods to obtain nanofibres of P3HT invariably involves heating and controlled cooling which makes reproducibility and morphology control difficult. Furthermore, we synthesised a nanocomposite consisting of P3HT nanofibres and quasi-type-II quantum dots and evaluated the photoelectric properties of the nanofibres as well as the nanocomposites using interdigitated gold microelectrodes.

  • 19.
    Zhao, Yichen
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Sugunan, Abhilash
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. SP Tech Res Inst Sweden, Chem Mat & Surfaces Unit, Sweden.
    Schmidt, Torsten
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Fornara, Andrea
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Relaxation is the key to longer life: suppressed degradation of P3HT films on conductive substrates2014In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 2, no 33, p. 13270-13276Article in journal (Refereed)
    Abstract [en]

    Here we show the dependence of the degree of degradation of poly-3-hexylthiophene (P3HT) films on the conductivity of the supporting substrate. P3HT is widely used for organic solar cells and electronic devices because it allows simple, low cost fabrication and has potential for the fabrication of flexible devices. However, P3HT is known to have a relatively low photostability, and investigating the photodegradation mechanism is an active research field. We find that P3HT films on conductive substrates show significantly retarded degradation and retain their chemical and morphological features when compared to similar films on glass substrates. This 'substrate effect' in retarding the degradation of P3HT films is evident even upon prolonged exposure to air for up to five months.

  • 20.
    Zhao, Yichen
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Sugunan, Abhilash
    Wang, Qin
    Yang, Xuran
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Rihtnesberg, David B.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Direct Determination of Spatial Localization of Carriers in CdSe-CdS Quantum Dots2015In: Journal of Nanomaterials, ISSN 1687-4110, E-ISSN 1687-4129, article id 321354Article in journal (Refereed)
    Abstract [en]

    Colloidal quantum dots (QDs) have gained significant attention due to their tunable band gap, simple solution processability, ease of scale-up, and low cost. By carefully choosing the materials, core-shell heterostructure QDs (HQDs) can be further synthesized with a controlled spatial spread of wave functions of the excited electrons and holes for various applications. Many investigations have been done to understand the exciton dynamics by optical characterizations. However, these spectroscopic data demonstrate that the spatial separation of the excitons cannot distinguish the distribution of excited electrons and holes. In this work, we report a simple and directmethod to determine the localized holes and delocalized electrons in HQDs. The quasi-type-II CdSe-CdS core-shell QDs were synthesized via a thermolysis method. Poly(3-hexylthiophene) (P3HT) nanofiber and ZnO nanorods were selected as hole and electron conductor materials, respectively, and were combined with HQDs to form two different nanocomposites. Photoelectrical properties were evaluated under different environments via a quick and facile characterization method, confirming that the electrons in the HQDs were freely accessible at the surface of the nanocrystal, while the holes were confined within the CdSe core.

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