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  • 1. Ahlund, John
    et al.
    Nilson, Katharina
    Palmgren, Pål
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Gothelid, Emmanuelle
    Schiessling, Joachim
    Göthelid, Mats
    Martensson, Nils
    Puglia, Carla
    Molecular growth determined by surface domain patterns2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 17, p. 6887-6890Article in journal (Refereed)
    Abstract [en]

    The growth of iron phthalocyanine (FePc) on InSb(001) c(8 x 2) at submonolayer coverage has been investigated with scanning tunneling microscopy (STM). FePc adsorbs flat centered on the In rows both at 70 K and at room temperature (RT). However, the shapes of the two-dimensional molecular islands are fundamentally different; while the RT growth results in chainlike structures along the [I 10] direction, as already observed for other Pc's adsorbed on the same surface, the islands are prolonged along [110], i.e., perpendicular to the substrate rows, at 70 K. These observations are explained on the basis of a recently observed new surface phase at low temperature, resulting in structural domains on the surface. The molecular growth front follows the propagating domain boundary that freezes at low temperature.

  • 2. Ai, Yuejie
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Song, Wei-Guo
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hydrophobicity and Hydrophilicity Balance Determines Shape Selectivity of Suzuki Coupling Reactions Inside Pd@meso-SiO2 Nanoreactor2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 19, p. 10244-10251Article in journal (Refereed)
    Abstract [en]

    Molecular sorting and catalysis directed by shape selectivity have been extensively applied in porous extended frameworks for a low-carbon, predictable, renewable component of modern industry. A comprehensive understanding of the underlying recognition mechanism toward different shapes is unfortunately still missing, owing to the lack of structural and dynamic information under operating conditions. We demonstrate here that such difficulties can be overcome by state-of-the-art molecular dynamics simulations which provide atomistic details that are not accessible experimentally, as exemplified by our interpretation for the experimentally observed aggregation induced shape selectivity for Suzuki C-C coupling reaction catalyzed by Pd particles in mesoporous silica. It is found that both aggregation ability and aggregating pattern of the reactants play the decisive role in controlling the shape selectivity, which are in turn determined by the balance between the hydrophobicity and hydrophilicity of the reactants, or in other words, by the balance between the noncovalent hydrogen bonding interaction and van der Waals forces. A general rule that allows prediction of the shape selectivity of a reactant has been proposed and verified against experiments. We show that molecular modeling is a powerful tool for rational design of new mesoporous systems and for the control of catalytic reactions that are important for the petrochemical industry.

  • 3. Alarcon, Hugo
    et al.
    Hedlund, Maria
    Johansson, Erik M. J.
    Rensmo, Hakan
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Modification of nanostructured TiO2 electrodes by electrochemical Al3+ insertion: Effects on dye-sensitized solar cell performance2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 35, p. 13267-13274Article in journal (Refereed)
    Abstract [en]

    Nanostructured TiO2 films were modified by insertion with aluminum ions using an electrochemical process. After heat treatment these films were found suitable as electrodes in dye-sensitized solar cells. By means of a catechol adsorption test, as well as photoelectron spectroscopy (PES), it was demonstrated that the density of Ti atoms at the metal oxide/electrolyte interface is reduced after Al modification. There is, however, not a complete coverage of aluminum oxide onto the TiO2, but the results rather suggest either the formation of a mixed Al-Ti oxide surface layer or formation of a partial aluminum oxide coating. No new phase could, however, be detected. In solar cells incorporating Al-modified TiO2 electrodes, both electron lifetimes and electron transport times were increased. At high concentrations of inserted aluminum ions, the quantum efficiency for electron injection was significantly decreased. Results are discussed at the hand of different models: A multiple trapping model, which can explain slower kinetics by the creation of additional traps during Al insertion, and a surface layer model, which can explain the reduced recombination rate, as well as the reduced injection efficiency, by the formation of a blocking layer.

  • 4. Al-Shammari, Rusul M.
    et al.
    Manzo, Michele
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Rice, James H.
    Rodriguez, Brian J.
    Tunable Wettability of Ferroelectric Lithium Niobate Surfaces: The Role of Engineered Microstructure and Tailored Metallic Nanostructures2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 12, p. 6643-6649Article in journal (Refereed)
    Abstract [en]

    An important aspect of optimizing micro- and optofluidic devices for lab on -a-chip systems is the ability to engineer materials properties including surface structure and charge to control wettability. Biocompatible ferroelectric lithium niobate (LN), which is well-known for acoustic and nonlinear optical applications, has recently found potential micro- and optofluidic applications. However, the tunable wettability of such substrates has yet to be explored in detail. Here, we show that the contact angle of LN substrates can be reproducibly tailored between similar to 7 degrees and similar to 421 degrees by controlling the surface topography and chemistry at the nano- and micrometer scale via ferroelectric domain and polarization engineering and polarization-directed photoassisted deposition of metallic nanostructures.

  • 5.
    Amft, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Walle, L. E.
    Ragazzon, D.
    Borg, A.
    Uvdal, P.
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Flerskalig materialmodellering.
    Sandell, A.
    A Molecular Mechanism for the Water-Hydroxyl Balance during Wetting of TiO22013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 33, p. 17078-17083Article in journal (Refereed)
    Abstract [en]

    We show that the formation of the wetting layer and the experimentally observed continuous shift of the H2O-OH balance toward molecular water at increasing coverage on a TiO2(110) surface can be rationalized on a molecular level. The mechanism is based on the initial formation of stable hydroxyl pairs, a repulsive interaction between these pairs, and an attractive interaction with respect to water molecules. The experimental data are obtained by synchrotron radiation photoelectron spectroscopy and interpreted with the aid of density functional theory calculations and Monte Carlo simulations.

  • 6. Araujo, Rafael B.
    et al.
    Banerjee, Amitava
    Ahujati, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala University, Sweden.
    Divulging the Hidden Capacity and Sodiation Kinetics of NaxC6Cl4O2: A High Voltage Organic Cathode for Sodium Rechargeable Batteries2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 26, p. 14027-14036Article in journal (Refereed)
    Abstract [en]

    In the current emerging sustainable organic battery field, quinones are seen as one of the prime candidates for application in rechargeable battery electrodes. Recently, C6Cl4O2, a modified quinone, has been proposed as a high voltage organic cathode. However, the sodium insertion mechanism behind the cell reaction remained unclear due to the nescience of the right crystal structure. Here, the framework of the density functional theory (DFT) together with an evolutionary algorithm was employed to elucidate the crystal structures of the compounds NaxC6Cl4O2 (x = 0.5, 1.0, 1.5 and 2). Along with the usefulness of PBE functional to reflect the experimental potential, also the importance of the hybrid functional to divulge the hidden theoretical capacity is evaluated. We showed that the experimentally observed lower specific capacity is a result of the great stabilization of the intermediate phase Na1.5C6Cl4O2. The calculated activation barriers for the ionic hops, are 0.68, 0.40, and 0.31 eV, respectively, for NaC6Cl4O2, Na1.5C6Cl4O2, and Na2C6Cl4O2. These results indicate that the kinetic process must not be a limiting factor upon Na insertion. Finally, the correct prediction of the specific capacity has confirmed that the theoretical strategy used, employing evolutionary simulations together with the hybrid functional framework, can rightly model the thermodynamic process in organic electrode compounds.

  • 7. Banerjee, R.
    et al.
    Novak, J.
    Frank, C.
    Girleanu, M.
    Ersen, O.
    Brinkmann, M.
    Anger, F.
    Lorch, C.
    Dieterle, J.
    Gerlach, A.
    Drnec, J.
    Yu, Shun
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials. Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany .
    Schreiber, F.
    Structure and Morphology of Organic Semiconductor-Nanoparticle Hybrids Prepared by Soft Deposition2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 9, p. 5225-5237Article in journal (Refereed)
    Abstract [en]

    We present an extensive structural analysis of hybrid architectures prepared by the soft incorporation of gold nanoparticles (AuNPs) within an organic semiconductor matrix of diindenoperylene (DIP). Such soft or noninvasive deposition of nanoparticles within organic semiconducting host matrices not only minimizes the influence of the deposition process on the order and properties of the organic host molecules, but also offers additional control in the process of incorporation. The hybrid structures were characterized by X-ray scattering techniques including grazing incidence small angle X-ray scattering (GISAXS), grazing incidence X-ray diffraction (GIXD), X-ray reflectivity (XRR), and complemented by atomic force microscopy (AFM), photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM) measurements. We show that different strategies of incorporating the nanoparticles in the host matrix lead to drastically different structure and morphologies. Particularly remarkable is the morphological change observed in the matrix of DIP as well as the AuNPs due to the influence of organic solvents, as evidenced by TEM tomography measurements, which revealed the exact location of the AuNPs within the organic host. It is also demonstrated that AuNPs can be successfully used as tunable templates for the growth of the organic semiconductors with desired island sizes and distances.

  • 8. Bareno, Javier
    et al.
    Shkrob, Ilya A.
    Gilbert, James A.
    Klett, Matilda
    Abraham, Daniel P.
    Capacity Fade and Its Mitigation in Li-Ion Cells with Silicon-Graphite Electrodes2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 38, p. 20640-20649Article in journal (Refereed)
  • 9. Bidermane, I.
    et al.
    Luder, J.
    Ahmadi, Sareh
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Grazioli, C.
    Bouvet, M.
    Brena, B.
    Martensson, N.
    Puglia, C.
    Witkowski, N.
    When the Grafting of Double Decker Phthalocyanines on Si(100)-2 x 1 Partly Affects the Molecular Electronic Structure2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 26, p. 14270-14276Article in journal (Refereed)
    Abstract [en]

    A combined X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT) study has been performed to characterize the adsorbate interaction of lutetium biphthalocyanine (LuPc2) molecules on the Si(100)-2 X 1 surface. Large molecule substrate adsorption energies are computed and are found to compete with the molecule molecule interactions of the double decker molecules. A particularly good matching between STM images and computed ones confirms the deformation of the molecule upon the absorption process. The comparison between DFT calculations and XP spectra reveals that the electronic distribution in the two plateaus of the biphthalocyanine are not affected in the same manner upon the adsorption onto the silicon surface. This finding can be of particular importance in the implementation of organic molecules in hybrid devices.

  • 10. Birke, R. L.
    et al.
    Lombardi, J. R.
    Saidi, W. A.
    Norman, P.
    Surface-Enhanced Raman Scattering Due to Charge-Transfer Resonances: A Time-Dependent Density Functional Theory Study of Ag13-4-Mercaptopyridine2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 37, p. 20721-20735Article in journal (Refereed)
    Abstract [en]

    We have used time-dependent density functional theory in conjunction with the CAM-B3LYP functional and MWB28/aug-cc-pVDZ basis set to determine non-, near-, and on-resonance Raman spectra for a complex formed by 4-mercaptopyridine (4-Mpy) binding with a Ag13 cluster via the thiolate Ag-S bond. Geometry optimizations of the Ag13-4-Mpy complex showed an on-top structure directly bound to one Ag atom with the ring of the molecule almost flat with respect to two Ag atoms of the complex. The corresponding B3LYP/MWB28/aug-cc-pVDZ geometry is also an on-top structure directly bound to one Ag atom, but the molecule is directed away from the surface. The near-resonance Raman calculations were carried out in the infinite lifetime approximation, while the on-resonant Raman excitation profiles were calculated with the complex polarization propagator (CPP) approach, introducing a half width at half-maximum spectral broadening of 0.2 eV. Calculation of the UV-vis spectra of the isolated 4-Mpy and of the Ag13-4-Mpy complex showed that binding shifts the spectra from deep in the UV to the visible region. Calculation of the near-resonance Raman spectra of the two structures of the complex at 410 (3.025 eV) and 425 nm (2.918 eV) showed a strong enhancement. A very large variation across vibrational modes by a factor of at least 103 was found for both the static chemical enhancement and charge-transfer (CT) enhancement mechanisms. This large variation in enhancement factor indicates that B-term Herzberg-Teller scattering is occurring because inactive or very low intensity modes in the static spectra of the molecule are much stronger in both the static and near-resonance spectra of the complex. From the excitation profile using the CPP method, an overall surface enhancement on the order 103 or higher was found for individual modes on excitation into a CT excited state. © 2016 American Chemical Society.

  • 11.
    Bjorkbacka, Asa
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Johnson, C. Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Leygraf, Christofer
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Role of the Oxide Layer in Radiation-Induced Corrosion of Copper in Anoxic Water2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 21, p. 11450-11455Article in journal (Refereed)
    Abstract [en]

    The influence of a pregrown copper oxide layer on radiation-induced corrosion of polished copper in pure anoxic water has been explored. The resulting amount of copper oxide formed during corrosion was measured with cathodic reduction, and the concentration of dissolved copper in solution was measured with inductively coupled plasma atomic emission spectroscopy. The identity of corrosion products and their topography was determined with Raman spectroscopy and scanning electron microscopy, respectively. Nonirradiated reference samples were analyzed for comparison. The results show that radiation-induced corrosion of copper in anoxic water is significantly more effective on preoxidized copper compared to polished copper. The total amount of oxidized copper exceeds the amount expected solely from radiation chemistry of water by more than 3 orders of magnitude. To explain this discrepancy a mechanism is suggested where the hydroxyl radical (HO center dot) is the main radiolytic oxidative species driving the corrosion process. If the thermodynamic driving force would be large enough (such as for the hydroxyl radical or its precursor, H2O+), the oxide layer could conduct electrons from the metal to the hydroxyl radicals formed at oxide surfaces. The formation of an oxide layer will then result in an increased reactive surface area partly accounting for the observed discrepancy.

  • 12.
    Bruhn, Benjamin
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Qejvanaj, Fatjon
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Sychugov, Ilya
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Blinking Statistics and Excitation-Dependent Luminescence Yield in Si and CdSe Nanocrystals2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 4, p. 2202-2208Article in journal (Refereed)
    Abstract [en]

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

  • 13.
    Cao, Hui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Jiang, Jun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ma, Jing
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Identification of switching mechanism in molecular junctions by inelastic electron tunneling spectroscopy2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 29, p. 11018-11022Article in journal (Refereed)
    Abstract [en]

    We present first-principles studies on electron transport properties of Pd-dithiolated oligoaniline-Pd molecular junctions. It is to demonstrate the possibility of using inelastic electron tunneling spectroscopy (IETS) to identify the switching mechanism in the molecular junction. Calculations have successfully reproduced the experimentally observed conductance switching behavior and the corresponding inelastic electron tunneling spectra. It is shown that the conductance switching is induced by conformation changes of the intercalated dithiolated oligoaniline in the junctions rather than oxidation/reduction as proposed earlier. Among three possible isomers, the low and high conductance states are related to two symmetrical structures. The possible involvement of asymmetric structure is discussed. It is revealed that chemical bonds between the terminal S atom and Pd electrodes are quite weak with relatively long bond distances.

  • 14.
    Cao, Xinrui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hu, Wei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Department of Chemical Physics, University of Science and Technology of ChinaHefei, China.
    Duan, Sai
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Department of Chemical Physics, University of Science and Technology of ChinaHefei, China .
    Feasible Catalytic Strategy for Writing Conductive Nanoribbons on a Single-Layer Graphene Fluoride2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 39, p. 22643-22648Article in journal (Refereed)
    Abstract [en]

    An accessible method for local reduction of graphene fluoride catalyzed by the Pt-coated nanotip with the assistance of a mixture of hydrogen and ethylene atmosphere is proposed and fully explored theoretically. Detailed mechanisms and roles of hydrogen and ethylene molecules in the cyclic reduction is discussed based on extensive first-principles calculations. It is demonstrated that the proposed cyclic reduction strategy is energetically favorable. This new strategy can be effectively applied in scanning probe lithography to fabricate electronic circuits at the nanoscale on graphene fluoride under mild conditions.

  • 15.
    Cao, Xinrui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Dehydrogenation of Propane to Propylene by a Pd/Cu Single-Atom Catalyst: Insight from First-Principles Calculations2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 2, p. 1016-1023Article in journal (Refereed)
    Abstract [en]

    The catalytic properties of the single-Pd-doped Cu55 nanoparticle toward propane dehydrogenation have been systemically investigated by first-principles calculations, and the possible reaction mechanisms and effects of the single and multiple Pd doping on the catalytic activity have been discussed. Calculations reveal that the low-energy catalytic conversion of propane to propylene by the Pd/Cu single-atom catalyst comprises the initial crucial C–H bond breaking at either the methyl or methylene group, the facile diffusion of detached H atoms on the Cu surface, and the subsequent C–H bond dissociation activation of the adsorbed propyl species. The single-Pd-doped Cu55 nanoparticle shows remarkable activity toward C–H bond activation, and the presence of relatively inactive Cu surface is beneficial for the coupling and desorption of detached H atoms and can reduce side reactions such as deep dehydrogenation and C–C bond breaking. The single-Pd-doped Cu55 cluster bears good balance between the maximum use of the noble metal and the activity, and it may serve as a promising single-atom catalyst toward selective dehydrogenation of propane.

  • 16.
    Cao, Xinrui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Study of the Electronic and Optical Properties of Hybrid Triangular (BN)(x)C-y Foams2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 38, p. 22181-22187Article in journal (Refereed)
    Abstract [en]

    The triangular foam is a newly designed 3D network structure only containing sp(2) bonding. The triangular carbon foam and its boron nitride analogue are predicted to be metallic and semiconducting, respectively (Chem. Commun. 2011, 47 (15), 4406-4408). Here a series of hybrid 3D network models from the BN- and C-doping of both carbon and BN foams have been designed. These newly designed hybrid (BN)(x)C-y foams are predicted to have comparable stability with their undoped crystalline networks, and the conversion between metallic and semiconducting behavior can be achieved by different doping patterns. Furthermore, these hybrid network structures have strong absorption in a wide range of UV region and relatively weak absorption in the visible-light range, and they should be quite promising for the design of electronic and optical devices.

  • 17. Cappel, U. B.
    et al.
    Gibson, E. A.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. Uppsala University, Sweden.
    Boschloo, G.
    Dye regeneration by Spiro-MeOTAD in solid state dye-sensitized solar cells studied by photoinduced absorption spectroscopy and spectroelectrochemistry2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 15, p. 6275-6281Article in journal (Refereed)
    Abstract [en]

    Photoinduced absorption (PIA) spectroscopy is presented as a tool for the systematic study of dye regeneration and pore filling in solid state dye-sensitized solar cells (DSC). Oxidation potentials and extinction coefficients for oxidized species of the perylene dye, ID28, on TiO(2) and of the hole conductor, 2,2'7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD), were determined by spectroelectrochemistry. The onset of oxidation of a solid film of spiro-MeOTAD was found to be 0.15 V versus Fc/Fc(+) and extinction coefficients of spiro-MeOTAD(+) were found to be 33 000 M(-1) cm(-1) at 507 nm and 8500 M(-1) cm-' at 690 nm. Electrons in TiO(2) films were shown to alter the ground-state absorption spectra of ID28 attached to TiO(2)-PIA measurements indicated a good contact between ID28 and spiro-MeOTAD for different spiro-MeOTAD concentrations for both 2- and 6-mu m thick TiO(2) films. We discuss the possibility of estimating the quality of pore filling from the positions of absorption peaks. Results suggested that with a spiro-MeOTAD concentration of 300 mg mL(-1) in chlorobenzene, a uniform distribution of spiro-MeOTAD in the pores of the 6-mu m thick TiO(2) film could be achieved.

  • 18. Cappel, Ute B.
    et al.
    Karlsson, Martin H.
    Pschirer, Neil G.
    Eickemeyer, Felix
    Schoeneboom, Jan
    Erk, Peter
    Boschloo, Gerrit
    Hagfeldt, Anders
    A Broadly Absorbing Perylene Dye for Solid-State Dye-Sensitized Solar Cells2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 33, p. 14595-14597Article in journal (Refereed)
    Abstract [en]

    We present a new perylene sensitizer, ID 176, for dye-sensitized solar cells (DSCs). The dye has the capability for very high photocurrents due to strong absorption from 400 to over 700 rim. Photocurrents Of LIP to 9 mA cm(-2) were achieved in solid-state DSCs employing the hole conductor 2,2’7,7’-tetrakis-(NN-di-p-methoxyphenylamine)-9,9’-spirobifluorene (spiro-MeOTAD), with a conversion efficiency of 3.2%. In contrast, the sensitizer did not perform well in conjunction with liquid iodide/tri-iodide electrolytes, suggesting a difference in the injection and regeneration mechanisms in these two types of dye-sensitized solar cells.

  • 19. Cappel, Ute B.
    et al.
    Smeigh, Amanda L.
    Plogmaker, Stefan
    Johansson, Erik M. J.
    Rensmo, Hakan
    Hammarstrom, Leif
    Hagfeldt, Anders
    Boschloo, Gerrit
    Characterization of the Interface Properties and Processes in Solid State Dye-Sensitized Solar Cells Employing a Perylene Sensitizer2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 10, p. 4345-4358Article in journal (Refereed)
    Abstract [en]

    We recently reported on a perylene sensitizer, ID176, which performs much better in solid state dye-sensitized solar cells than in those using liquid electrolytes with iodide/tri-iodide as the redox couple (J. Phys. Chem. C 2009, 113, 14595-14597). Here, we present a characterization of the sensitizer and of the TiO2/dye interface by UV-visible absorption and fluorescence spectroscopy, spectroelectrochemistry, photoelectron spectroscopy, electroabsorption spectroscopy, photoinduced absorption spectroscopy, and femtosecond transient absorption measurements. We report that the absorption spectrum of the sensitizer is red-shifted by addition of lithium ions to the surface due to a downward shift of the excited state level of the sensitizer, which is of the same order of magnitude as the downward shift of the titanium dioxide conduction band edge. Results from photoelectron spectroscopy and electrochemistry suggest that the excited state is largely located below the conduction band edge of TiO2 but that there are states in the band gap of TiO2 which might be available for photoinduced electron injection. The sensitizer was able to efficiently inject into TiO2, when a lithium salt was present on the surface, while injection was much less effective in the absence of lithium ions or in the presence of solvent. In the presence of the hole conductor 2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9’-spirobifluorene (spiro-MeOTAD) and LiTFSI, charge separation was monitored by the emergence of a Stark shift of the dye in transient absorption spectra, and both injection and regeneration appear to be completed within 1 ps. Regeneration by spiro-MeOTAD is therefore several orders of magnitude faster than regeneration by iodide, and ID176 can even be photoreduced by spiro-MeOTAD.

  • 20. Carrete, Jesus
    et al.
    Mingo, Natalio
    Tian, Guangjun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Baev, Alexander
    Prasad, Paras N.
    Thermoelectric Properties of Hybrid Organic-Inorganic Superlattices2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 20, p. 10881-10886Article in journal (Refereed)
    Abstract [en]

    We theoretically evaluate the thermoelectric transport coefficients of hybrid thiophene/SiGe superlattices and the effect of their chemical tuning via phenyl groups. Owing to the interplay between alloy scattering and phonon transmission at the molecular layers, very low thermal conductivities under 1 W/(m K) and values of ZT more than twice as large as those of bulk SiGe can be attained. These results highlight exciting possibilities of organic-inorganic hybrid systems, as compared to traditional inorganic thermoelectrics.

  • 21. Casalongue, Hernan G. Sanchez
    et al.
    Benck, Jesse D.
    Tsai, Charlie
    Karlsson, Rasmus K. B.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Kaya, Sarp
    Ng, May Ling
    Pettersson, Lars G. M.
    Abild-Pedersen, Frank
    Norskov, J. K.
    Ogasawara, Hirohito
    Jaramillo, Thomas F.
    Nilsson, Anders
    Operando Characterization of an Amorphous Molybdenum Sulfide Nanoparticle Catalyst during the Hydrogen Evolution Reaction2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 50, p. 29252-29259Article in journal (Refereed)
    Abstract [en]

    Molybdenum sulfide structures, particularly amorphous MoS3 nanoparticles, are promising materials in the search for cost-effective and scalable water-splitting catalysts. Ex situ observations show that the nanoparticles exhibit a composition change from MoS3 to defective MoS2 when subjected to hydrogen evolution reaction (HER) conditions, raising questions regarding the active surface sites taking part in the reaction. We tracked the in situ transformation of amorphous MoS3 nanoparticles under HER conditions through ambient pressure X-ray photoelectron spectroscopy and performed density functional theory studies of model MoSx systems. We demonstrate that, under operating conditions, surface sites are converted from MoS3 to MoS2 in a gradual manner and that the electrolytic current densities are proportional to the extent of the transformation. We also posit that it is the MoS2 edge-like sites that are active during HER, with the high activity of the catalyst being attributed to the increase in surface MoS2 edge-like sites after the reduction of MoS3 sites.

  • 22. Chen, Xingxing
    et al.
    Yang, Yuanqing
    Chen, Yu-Hui
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Zhejiang University, China.
    Blaikie, Richard J.
    Ding, Boyang
    Probing Plasmonic Gap Resonances between Gold Nanorods and a Metallic Surface2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 32, p. 18627-18634Article in journal (Refereed)
    Abstract [en]

    The plasmonic resonances in individual gold nanorods nanoscopically coupled to a gold film with different gap spacing have been experimentally and theoretically investigated. The spectral widths, wavelengths, and optical polarizabilities of the maxima in measured single-nanopartide scattering spectra are significantly modified as the gap distance changes in the sub-20 nm domain. Comparing the experimental data with numerical simulations reveals that these modifications arise from the complex hybridization of several dipolar and multipolar plasmon modes that are strongly localized at the gap. These plasmon gap modes have distinct resonant and spatial characteristics as a result of near-field interaction between the elongated nanorods and the gold film. Additionally, the excitation of these gap modes is highly dependent on the gap spacing. Finally, we also discuss influences of these plasmonic modes on absorption properties of the system and propose a potential application of the studied structures in facilitating photothermal conversion.

  • 23.
    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.

  • 24. Cheng, Ming
    et al.
    Yang, Xichuan
    Zhang, Fuguo
    Zhao, Jianghua
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Tuning the HOMO and LUMO Energy Levels of Organic Dyes with N-Carboxomethylpyridinium as Acceptor To Optimize the Efficiency of Dye-Sensitized Solar Cells2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 18, p. 9076-9083Article in journal (Refereed)
    Abstract [en]

    Different from traditional D-pi-A sensitizers (the traditional design concept of the organic dyes is the donor-pi-linker-acceptor structure), a series of organic dyes with pyridinium as acceptor have been synthesized in order to approach the optimal energy level composition in the TiO2-dye-iodide/triiodide system in the dye-sensitized solar cells. HOMO and LUMO energy level tuning is achieved by varying the conjugation units and the donating ability of the donor part. Detailed investigation on the relationship between the dye structure and photophysical, photoelectrochemical properties and performance of DSSCs is described. For TPA-based dyes, by substituting the 3-hexylthiophene group with a carbon-carbon double bond as pi-spacer, the bathochromic shift of absorption spectra and higher current density (J(sc)) are achieved. When the methoxyl and n-hexoxyl are introduced into CM301 to construct dyes CM302 and CM303, the absorption peak is red-shifted compared with that of CM301 due to the increase of the electron-donating ability. The devices fabricated with sensitizers CM302 and CM303 show higher J(sc) and open-circuit voltage (V-oc) than those of the device sensitized by CM301, which can be mainly attributed to the wider incident photon-to-current conversion efficiency (IPCE) response and the suppression of electron recombination between TiO2 film and electrolyte, respectively. The effects of different electron donors in DSSCs application are compared, and the results show that sensitizers with a phenothiazine (PTZ) electron-donating unit give a promising efficiency, which is even better than the TPA-based dyes. This is because the PTZ unit displayed a stronger electron-donating ability than the TPA unit (oxidation potential of 0.82 and 1.08 V vs the normal hydrogen electrode (NHE), respectively). For sensitizers CM306 and CM307, the introduction of 1,3- bis(hexyloxy)phenyl increases the donating ability of the donor part. Furthermore, the presence of long alkyl chains decreases the dye adsorption amount on the TiO2 surface, which diminishes dye aggregation and the electron recombination effectively, though, with less adsorption amount of dyes on TiO2, the device sensitized by dye CM307 obtained the best conversion efficiency of 7.1% (J(sc) = 13.6 mA.cm(-2), V-oc = 710 mV, FF = 73.6%) under AM 1.5G irradiation (100 mW.cm(-2)).

  • 25. Chirgwandi, Z. G.
    et al.
    Panas, I.
    Johansson, L. G.
    Norden, B.
    Willander, M.
    Winkler, D.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Properties of a Biophotovoltaic Nanodevice2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 48, p. 18717-18721Article in journal (Refereed)
    Abstract [en]

    Properties of an on-chip photovoltaic nanodevice are demonstrated. The dyes comprise green florescent proteins (GFP). Dependence of recently reported zero external potential bias (ZEPB) photocurrent (I) on temperature, power, and wavelength (lambda) is shown. Correlation between UV-vis spectrum of the GFP and the ZEPB I(lambda) of the device is reported. The temperature dependence suggests the ZEPB photocurrent to reflect a liquid crystal type ordering where the current declines monotonically with increasing temperature. The influence of an external bias on the photocurrent is demonstrated. The resulting light-induced current is analyzed in terms of resistive and quantum mechanical contributions.

  • 26. Choudhuri, I.
    et al.
    Patra, N.
    Mahata, A.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Pathak, B.
    B-N@Graphene: Highly Sensitive and Selective Gas Sensor2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 44, p. 24827-24836Article in journal (Refereed)
    Abstract [en]

    We have performed density functional theory (DFT) calculations to study the gas (CO, CO2, NO, and NO2) sensing mechanism of pure and doped (B, N, and B-N) graphene surfaces. The calculated adsorption energies of the various toxic gases (CO, CO2, NO, and NO2) on the pure and doped graphene surfaces show, doping improves adsorption energy and selectivity. The electronic properties of the B-Ngraphene surfaces change significantly compared to pure and B and Ngraphene surfaces, while selective gas molecules are adsorbed. So, we report B-N codoping on graphene can be highly sensitive and selective for semiconductor-based gas sensor.

  • 27. Christodoulou, C.
    et al.
    Giannakopoulos, A.
    Nardi, M. V.
    Ligorio, G.
    Oehzelt, M.
    Chen, L.
    Pasquali, L.
    Timpel, M.
    Giglia, A.
    Nannarone, S.
    Norman, P.
    Linares, M.
    Parvez, K.
    Müllen, K.
    Beljonne, D.
    Koch, N.
    Tuning the work function of graphene-on-quartz with a high weight molecular acceptor2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 9, p. 4784-4790Article in journal (Refereed)
    Abstract [en]

    Ultraviolet and X-ray photoelectron spectroscopies in combination with density functional theory (DFT) calculations were used to study the change in the work function (Φ) of graphene, supported by quartz, as induced by adsorption of hexaazatriphenylene-hexacarbonitrile (HATCN). Near edge X-ray absorption fine structure spectroscopy (NEXAFS) and DFT modeling show that a molecular-density-dependent reorientation of HATCN from a planar to a vertically inclined adsorption geometry occurs upon increasing surface coverage. This, in conjunction with the orientation-dependent magnitude of the interface dipole, allows one to explain the evolution of graphene Φ from 4.5 eV up to 5.7 eV, rendering the molecularly modified graphene-on-quartz a highly suitable hole injection electrode. © 2014 American Chemical Society.

  • 28. Cimatu, Katherine A.
    et al.
    Baldelli, Steven
    Chemical Microscopy of Surfaces by Sum Frequency Generation Imaging2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 38, p. 16575-16588Article in journal (Refereed)
    Abstract [en]

    Sum frequency generation imaging microscopy has been developed and implemented in different systems from self-assembled monolayer on metal surfaces to reaction of a metal surface upon exposure to a corrosive material (cyanide solution). It also helped the fundamental issues of heterogeneity to be understood by using mapping analysis that considers an acquired spectrum in a chosen region-of-interest to be independent of its neighboring ROIs. The construction of the microscope has been utilized and modified to accommodate the improvement of its spatial resolution, signal-to-noise ratio, and faster accumulation time. The latter aspect is more dependent toward the kind of sample to be analyzed. Finally, the current resolution of this diffraction-limited microscope is similar to 2 mu m and there is still some room for improvement to reach its ultimate resolution of similar to 800 nm. The main and final goal of this study is to provide chemical sensitivity, interfacial specificity, and a two-dimensional image based on the chemical properties of the adsorbed molecules on the surface and also the substrate itself.

  • 29.
    Dai, Jing
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Ferreira Fernandes, Ricardo Manuel
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. Univ Porto, CIQUP, Dept Chem & Biochem, Fac Sci, P-4169007 Porto, Portugal..
    Regev, Oren
    Ben Gurion Univ Negev, Dept Chem Engn, IL-84105 Beer Sheva, Israel.;Ben Gurion Univ Negev, Ilse Katz Inst Nanotechnol, IL-84105 Beer Sheva, Israel..
    Marques, Eduardo F.
    Univ Porto, CIQUP, Dept Chem & Biochem, Fac Sci, P-4169007 Porto, Portugal..
    Furo, Istvan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Dispersing Carbon Nanotubes in Water with Amphiphiles: Dispersant Adsorption, Kinetics, and Bundle Size Distribution as Defining Factors2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 42, p. 24386-24393Article in journal (Refereed)
    Abstract [en]

    Debundling and dispersing single-walled carbon nanotubes (SWNTs) is essential for applications, but the process is not well understood. In this work, aqueous SWNT dispersions were produced by sonicating pristine SWNT powder in the presence of an amphiphilic triblock copolymer (Pluronic F127) as dispersant. Upon centrifugation, one obtains a supernatant with suspended individual tubes and thin bundles and a precipitate with large bundles (and impurities). In the supernatant, that constitutes the final dispersion, we determined the dispersed SWNT concentration by thermogravi-metric analysis (TGA) and UV-vis spectroscopy, and the dispersant concentration by NMR The fraction of dispersant adsorbed at the SWNT surface was obtained by H-1 diffusion NMR Sigmoidal dispersion curves recording the concentration of dispersed SWNTs as a function of supernatant dispersant concentration were obtained at different SWNT loadings and sonication times. As SWNT bundles are debundled into smaller and smaller ones, the essential role of the dispersant is to sufficiently quickly cover the freshly exposed surfaces created by shear forces induced during sonication. Primarily kinetic reasons are behind the need for dispersant concentrations required to reach a substantial SWNT concentration. Centrifugation sets the size threshold below which SWNT particles are retained in the dispersion and consequently determines the SWNT concentration as a function of sonication time.

  • 30. Damm, Signe
    et al.
    Carville, Nigel
    Rodriguez, Brian
    Manzo, Michele
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    James, Rice
    Plasmon enhanced Raman from Ag nanopatterns made using periodically poled lithium niobate and periodically proton exchanged template methods2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 50, p. 26543-26550Article in journal (Refereed)
    Abstract [en]

    We study Ag nanopattern arrays formed using ferroelectric lithography based on two separate approaches, i.e., periodically poled lithium niobate (PPLN) and periodically proton exchanged (PPE) template methods. We demonstrate that such nanoarrays are plasmon active. Raman spectroscopy was applied to study molecular probe 4-aminothiophenol (4-ABT) absorbed onto a silver nanostructured array. The observed Raman spectra show peaks arising from b2 modes, which occur for plasmon enhanced Raman from 4-ABT in place of a1 modes, which occur in normal Raman scattering. We demonstrate that the PPLN and PPE substrates possess different plasmonic properties with PPE creating a stronger SERS signal relative to PPLN substrates.

  • 31.
    Datta, Abheek
    et al.
    Okinawa Inst Sci & Technol OIST Grad Univ, Nanoparticles Design Unit, 1919-1 Tancha, Onna Son, Okinawa 9040495, Japan..
    Porkovich, Alexander J.
    Okinawa Inst Sci & Technol OIST Grad Univ, Nanoparticles Design Unit, 1919-1 Tancha, Onna Son, Okinawa 9040495, Japan..
    Kumar, Pawan
    Okinawa Inst Sci & Technol OIST Grad Univ, Nanoparticles Design Unit, 1919-1 Tancha, Onna Son, Okinawa 9040495, Japan..
    Nikoulis, Giorgos
    Aristotle Univ Thessaloniki, Dept Phys, GR-54124 Thessaloniki, Greece..
    Kioseoglou, Joseph
    Aristotle Univ Thessaloniki, Dept Phys, GR-54124 Thessaloniki, Greece..
    Sasaki, Toshio
    Okinawa Inst Sci & Technol OIST Grad Univ, Imaging Sect, 1919-1 Tancha, Onna Son, Okinawa 9040495, Japan..
    Steinhauer, Stephan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Grammatikopoulos, Panagiotis
    Okinawa Inst Sci & Technol OIST Grad Univ, Nanoparticles Design Unit, 1919-1 Tancha, Onna Son, Okinawa 9040495, Japan..
    Sowwan, Mukhles
    Okinawa Inst Sci & Technol OIST Grad Univ, Nanoparticles Design Unit, 1919-1 Tancha, Onna Son, Okinawa 9040495, Japan..
    Single Nanoparticle Activities in Ensemble: A Study on Pd Cluster Nanoportals for Electrochemical Oxygen Evolution Reaction2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 43, p. 26124-26135Article in journal (Refereed)
    Abstract [en]

    Comprehensive understanding of the electrochemical activity of single nanoparticles (NPs) is in critical need for opening new avenues in the broad field of electrochemistry. Published reports on single-NP electrocatalysts typically include complicated and difficult methods of synthesis and characterization; moreover, these methods usually fail to provide a reliable way to measure the activities of individual NPs within larger ensembles of particles, i.e., in real-life nanocatalyst systems. In the present work, we synthesized from the gas phase Pd NPs that act as nanoportals for electron transfer within surface-oxidized Mg thin films. The physical synthesis method provided excellent control over the deposition density and, hence, enabled the design of a system where each individual open nanoportal forms an independent active single-NP electrode (SNPE). Being uncoupled from one another, these SNPEs contribute separately toward the total electrocatalytic activity while simultaneously providing a measure of their average, individual activities. We were thus able to fabricate a stable, steady-state electrode for the electrochemical oxygen evolution reaction (OER) and to study the activity and stability of the SNPEs over a period of 20 days; the former depended on the size of the NPs, while the latter depended on the SNPEs' resistance to aerial oxidation. The remarkable stability of the ensemble catalysts under OER conditions proves that this concept can be used for further studies on the activities of different single NPs in numerous real-life systems.

  • 32.
    Diesen, Veronica
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Formation of H2O2 in TiO2 Photocatalysis of Oxygenated and Deoxygenated Aqueous Systems: A Probe for Photocatalytically Produced Hydroxyl Radicals2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 19, p. 10083-10087Article in journal (Refereed)
    Abstract [en]

    The formation of H2O2 in oxygenated and deoxygenated aqueous solutions using immobilized TiO2 illuminated by black light (365 nm) was studied to verify the presence of hydroxyl radicals in TiO2 photocatalysis. In oxygen containing systems, formation of H2O2 proceeds through reduction of molecular oxygen by conduction band electrons or by recombination of hydroxyl radicals. In oxygen free solutions recombination of hydroxyl radicals constitutes the only pathway to H2O2 formation. Detection of H2O2 in absence of oxygen therefore serves as an indicator for hydroxyl radical formation. The H2O2 concentration was determined using the Ghormley triiodide method. It was found that a significant amount of H2O2 was produced in the deoxygenated aqueous solutions supporting the hypothesis of hydroxyl radical production in photocatalysis. To further elucidate the origin of the H2O2, experiments using the radical scavenger tris(hydroxymethyL)aminomethane (Tris) were conducted. The results showed that the H2O2 concentration increased in the oxygenated system as Tris protects the H2O2 from decomposition by hydroxyl radicals. In the deoxygenated system, no H2O2 could be detected due to hydroxyl radical scavenging by Tris, which prevents H2O2 formation. The results presented support the hypothesis that the hydroxyl radical is the primary oxidant in aqueous TiO2 photocatalysis.

  • 33. Dixit, M.
    et al.
    Maark, T. A.
    Ghatak, K.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Pal, S.
    Scandium-decorated MOF-5 as potential candidates for room-temperature hydrogen storage: A solution for the clustering problem in MOFs2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 33, p. 17336-17342Article in journal (Refereed)
    Abstract [en]

    Transition-metal-based systems show promising binding energy for hydrogen storage but suffer from clustering problem. The effect of light transition metal (M = Sc, Ti) decoration, boron substitution on the hydrogen storage properties of MOF-5, and clustering problem of metals has been investigated using ab initio density functional theory. Our results of solid-tate calculations reveal that whereas Ti clusters strongly Sc atoms do not suffer from this problem when decorating MOF-5. Boron substitution on metal-decorated MOF-5 enhances the interaction energy of both the metals with MOF-5. Sc-decorated MOF-5 shows a hydrogen storage capacity of 5.81 wt % with calculated binding energies of 20-40 kJ/mol, which ensures the room-temperature applicability of this hydrogen storage material.

  • 34. Djouambi, Nadia
    et al.
    Bougheloum, Chafika
    Messalhi, Abdelrani
    Bououdina, Mohamed
    Banerjee, Amitava
    Chakraborty, Sudip
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    New Concept on Photocatalytic Degradation of Thiophene Derivatives: Experimental and DFT Studies2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 27, p. 15646-15651Article in journal (Refereed)
    Abstract [en]

    In this study, the photocatalytic degradation of seven sulfur compounds (2-methylthiophene, 3-methylthiophene, 2-phenylthiophene, 3-phenylthiophene, 2,5-diphenylthiophene, 2-(2-thienyl) pyridine, and 2-(3-thienyl) pyridine in semiaqueous medium are compared to thiophene. The apparent-reaction-rate constant (k) is found to decrease in the following order: 2,5-diphenylthiophene > 2-(2-thienyl) pyridine > 2-penhylthiophene methylthiophene > 3-penhylthiophene > 2-methylthiophene > 2-(3-thienyl) pyridine > 3-thiophene. From the data obtained by UV light absorption (lambda(max)) measurements and electronic structure calculations (frontier orbitals energy, global hardness, and global softness), the kinetic parameters of the reaction have been determined. Among the studied compounds, thiophene with a high lambda(max) and low calculated LUMO-HOMO gap energy has showed higher activity under UV irradiation. Interestingly, a lower activity is observed with low lambda(max) and high LUMO-HOMO gap energy. This demonstrates, for the first time, that the reactivity depends essentially on the thermodynamic stability of the sulfur compound rather than on the nature or the position of the substituent on the ring.

  • 35. Dong, Jingfeng
    et al.
    Wang, Mei
    Zhang, Pan
    Yang, Songqiu
    Liu, Jianyong
    Li, Xueqiang
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Promoting Effect of Electrostatic Interaction between a Cobalt Catalyst and a Xanthene Dye on Visible-Light-Driven Electron Transfer and Hydrogen Production2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 30, p. 15089-15096Article in journal (Refereed)
    Abstract [en]

    The readily obtained noble-metal-free molecular catalyst systems, with xanthene dyes (Rose Bengal, RB(2-); Eosin Y, EY(2-); and Eosin B, EB(2-)) as photosensitizers, [Co(bpy)(3)]Cl(2) as catalyst, and triethylamine as sacrificial electron donor, are highly active for visible-light-driven (lambda > 450 nm) hydrogen production from water. The turnover frequency is up to 54 TON/min versus RB(2-) with a RB(2-)/[Co(bpy)(3)]Cl(2) molar ratio of 1:10 in CH(3)CN/H(2)O under optimal conditions in the first half hour of irradiation (lambda > 450 rim), and the turnover number is up to 2076 versus RB(2-). Comparative studies show the following: (1) The photocatalytic H(2)-evolving activity of the cationic cobalt complex [Co(bpy)(3)]Cl(2), is apparently higher than the neutral cobaloxime complexes with xanthene dyes as potosensitizers, and also much higher than the analogous system of [Ru(bpy)(3)]Cl(2)/[Co(bpy)(3)]Cl(2). (2) The UV-vis absorptions of xanthene dyes are red shifted to different extents upon addition of [Co(bpy)(3)]Cl(2) to the aqueous or CH(3)CN/H(2)O solutions of these dyes, while no change was observed in UV-vis absorptions of photosensitizer with addition of the cobaloximes to the aqueous solution of RB(2-) or addition of [Co(bpy)(3)]Cl(2) to the aqueous solution of [Ru(bpy)(3)]Cl(2). (3) The fluorescence of RB(2-) is significantly quenched by [Co(bpy)(3)]Cl(2), but not by the cobaloximes. These special performances of [Co(bpy)(3)]Cl(2) are attributed to the electrostatically attractive interaction between the anionic organic dyes and the cationic cobalt catalyst. The probable mechanism for photoinduced hydrogen production catalyzed by the system of RB(2-), [Co(bpy)(3)]Cl(2), and triethylamine is discussed in detail on the basis of fluorescence. fand transient absorption spectroscopic studies. "

  • 36.
    Duan, Sai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ai, Yue-Jie
    Hu, Wei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Roles of Plasmonic Excitation and Protonation on Photoreactions of p-Aminobenzenethiol on Ag Nanoparticles2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 13, p. 6893-6902Article in journal (Refereed)
    Abstract [en]

    There is increasing evidence that surface plasmons could catalyze photochemical reactions of organic molecules on metal surfaces. However, due to the complex interactions among the substrate, the adsorbate, the environment, and the incident light, the existence and the underlying mechanism of such catalytic processes have been under intense debate. Here we present a systematic first principles study on one of the most studied and controversial systems, namely, p-aminobenzenethiol (PATP) adsorbed on silver nanoparticles. Our calculations have confirmed that the observed surface-enhanced Raman scattering (SERS) bands at 1142, 1391, and 1440 cm(-1) of PATP on silver surfaces belong to its coupling reaction product, 4,4'-dimercaptoazobenzene (DMAB). It is found that the deprotonation or protonation of N atoms is the key initial step for the transformations between PATP and DMAB. The photodecomposition reaction from DMAB to PATP can occur only under the conditions that both proton transfer and plasmonic excitations have taken place. Moreover, in addition to the widely suggested hot-electron injection mechanism of plasmon, a new photochemical channel has been revealed in the decomposition of DMAB molecules under suitable incident light. This may open up an entire new type of chemical reaction in surface chemistry that we call plasmonic photochemistry. Our theoretical calculations provide consistent interpretations for the experimentally observed pH-,wavelength-,and electrode potential dependence of the SERS spectra of PATP/DMAB adsorbed on silver surfaces. Our findings highlight the important role of theoretical investigations for better understanding of complex processes involved in photochemical reaction of surface adsorbates.

  • 37.
    Duan, Sai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Wu, De-Yin
    Xu, Xin
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Tian, Zhong-Qun
    Structures of Water Molecules Adsorbed on a Gold Electrode under Negative Potentials2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 9, p. 4051-4056Article in journal (Refereed)
    Abstract [en]

    Two stable conformations of water hexamer Clusters on gold electrode under negative potentials have been identified by density functional theory calculations. Both form a ring Structure but with different orientations of free CH bonds. Ill one of the Structures, labeled as F-Type, four free OH bonds of the water molecules point toward the gold surface and remain stable over a wide range of the negative potential. The other Structure, labeled as S-Type, starts with five Such free OH bonds pointing toward the gold surface at the low negative potential and ends LIP with six of them at higher negative potential. From the energetic point of view, the S-Type Structure is more stable than the F-Type under the same Potential. By comparing the calculated Raman spectra with the experiment, it is found that S-Type Structures are the most possible surface adsorption state of water molecules at the electrochemical interface under very negative electrode potentials. It is believed that such a novel water Structure Could also exist Oil other negative charged Surfaces.

  • 38. Edvinsson, Tomas
    et al.
    Li, Chen
    Pschirer, Neil
    Schoeneboom, Jan
    Eickemeyer, Felix
    Sens, Ruediger
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Herrmann, Andreas
    Muellen, Klaus
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Intramolecular charge-transfer tuning of perylenes: Spectroscopic features and performance in Dye-sensitized solar cells2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 42, p. 15137-15140Article in journal (Refereed)
    Abstract [en]

    Five novel perylene molecules with different intramolecular charge-transfer (ICT) characters have been synthesized. The relation between the ICT character for different donating groups and the results for their electro- and photochemical properties as well as their performance in nanostructured dye-sensitized solar cells (nDSC) are reported. With the stronger donors, we obtain a shift of the lowest unoccupied molecular orbital (LUMO) to more negative potential versus normal hydrogen electrode (NHE) as well as an increase the charge separation in the dye upon excitation. Ab initio calculations were used to analyze the effects on orbital energies and electron distribution with the different donors. Incorporating the dyes in nDSCs, we see a drastical improvement in the performance for the more polar dyes. In particular, we find a much improved photovoltage because of higher LUMO levels, allowing conduction band tuning in the TiO2 as well as a contribution from the permanent dipoles in the dyes. The photocurrent improves remarkably with increasing ICT character of the dyes. The external quantum efficiency reached over 70%, and the overall solar-to-electrical energy conversion efficiency was improved to almost 4% for the dye with highest ICT character, which can be compared with devices with the standard N719 dye (Ru(dcbPY)(2)(NCS)(2)) showing 6% under similar conditions. The performance is a significant improvement compared to previous reports for perylenes and lifts the performance from modest to promising. Initial stability tests show that the dye with the highest performance was spectrally stable after more than 2000 h of irradiation in a solar-cell device.

  • 39.
    Eita, Mohamed
    et al.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Wagberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Thin Films of Zinc Oxide Nanoparticles and Poly(acrylic acid) Fabricated by the Layer-by-Layer Technique: a Facile Platform for Outstanding Properties2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 7, p. 4621-4627Article in journal (Refereed)
    Abstract [en]

    The incorporation of nanoparticles into polyelectrolytes thin films opens the way to a broad range of applications depending on the functionality of the nanoparticles. In this work, thin films of ZnO nanoparticles and poly(acrylic acid) (PAA) were built up using the layer-by-layer technique. The thickness of a 20-bilayer film is about 120 nm with a surface roughness of 22.9 nm as measured by atomic force microscopy (AFM). Thin ZnO/PAA films block UV radiation starting at a wavelength of 361 nm due to absorption by ZnO although the films are highly transparent. Due to their high porosity, these thin films show a broadband antireflection in the visible region, and thus they provide selective opacity in the UV region and enhanced transmittance in the visible region up to the near-infrared region. They are also superhydrophilic due to their high porosity and surface roughness.

  • 40. Ekström, U.
    et al.
    Ottosson, H.
    Norman, Patrick
    Linköping University, Sweden.
    Characterization of the chemisorption of methylsilane on a au(1,1,1) surface from the silicon K- And L-edge spectra: A theoretical study using the four-component static exchange approximation2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 37, p. 13846-13850Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectra (NEXAFS) of methylsilane, isolated and chemisorbed to a Au(1,1,1) surface, are determined in the fully relativistic four-component static exchange approximation - both the K- and the L-edge of silicon are addressed in this investigation. In the fully chemisorbed structure, three H(Si) atoms have been cleaved off when Si binds in the hollow site of Au forming three Si - Au bonds of normal length. As due to die tri-coordinated chemisorption, the onsets of the K- and L-edge NEXAFS absorption bands occur some 2.0 and 2.5 eV lower in energy, respectively. The spin-orbit splittings in the silicon 2p-shell are not significantly changed due to adsorption. A partly chemisorbed methylsilane with only one H(Si) bond cleaved was also studied, and it is shown that the polarization dependence in the surface spectra contains details that can be used experimentally to identify the surface coordination of silicon. The red-shifts in the XPS silicon 1s (2p) spectra upon surface binding are 0.95 (0.65) and 1.15 (0.83) eV for the mono- and tricoordinated system, respectively.

  • 41. Ellis, Hanna
    et al.
    Eriksson, Susanna K.
    Feldt, Sandra M.
    Gabrielsson, Erik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Lohse, Peter W.
    Lindblad, Rebecka
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Rensmo, Håkan
    Boschloo, Gerrit
    Hagfeldt, Anders
    Linker Unit Modification of Triphenylamine-Based Organic Dyes for Efficient Cobalt Mediated Dye-Sensitized Solar Cells2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 41, p. 21029-21036Article in journal (Refereed)
    Abstract [en]

    Linker unit modification of donor-linker-acceptor-based organic dyes was investigated with respect to the spectral and physicochemical properties of the dyes. The spectral response for a series of triphenylamine (TPA)-based organic dyes, called LEG1-4, was shifted into the red wavelength region, and the extinction coefficient of the dyes was increased by introducing different substituted dithiophene units on the pi-conjugated linker. The photovoltaic performance of dye-sensitized solar cells (DSCs) incorporating the different dyes in combination with cobalt-based electrolytes was found to be dependent on dye binding. The binding morphology of the dyes on the TiO2 was studied using photoelectron spectroscopy, which demonstrated that the introduction of alkyl chains and different substituents on the dithiophene linker unit resulted in a larger tilt angle of the dyes with respect to the normal of the TiO2-surface, and thereby a lower surface coverage. The good photovoltaic performance for cobalt electrolyte-based DSCs found here and by other groups using TPA-based organic dyes with a cyclopentadithiophene linker unit substituted with alkyl chains was mainly attributed to the extended spectral response of the dye, whereas the larger tilt angle of the dye with respect to the TiO2-surface resulted in less efficient packing of the dye molecules and enhanced recombination between electrons in TiO2 and Co(III) species in the electrolyte.

  • 42.
    Elwinger, Fredrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Pourmand, Payam
    KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Diffusive Transport in Pores. Tortuosity and Molecular Interaction with the Pore Wall2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 25, p. 13757-13764Article in journal (Refereed)
    Abstract [en]

    The self-diffusion of neat water, dimethyl sulfoxide (DMSO), octanol, and the molecular components in a water-DMSO solution was measured by H-1 and H-2 NMR diffusion experiments for those fluids imbibed into controlled pore glasses (CPG). Their highly interconnected structure is scaled by pore size and shows invariant pore topology independent of the size. The nominal pore diameter of the explored CPGs varied from 7.5 to 72.9 nm. Hence, the about micrometer mean-square diffusional displacement during the explored diffusion tithes was much larger than the individual pore size, and the experiment yielded the average diffusion coefficient Great care was taken to establish the actual pore: volumes of the CPGs. Transverse relaxation experiments processed by inverse Laplace transformation were performed to verify that the liquids explored filled exactly the available pore volume. Relative to the respective diffusion coefficients obtained in bulk phases, we observe a reduction in the diffusion coefficient that is independent of pore size for the larger pores and becomes stronger toward the smaller pores. Geometric tortuosity governs the behavior at larger pore sizes, while the interaction with pore walls becomes the dominant factor at our smallest pore diameter. Deviation from the trends predicted by the Renkin equation indicates that the interaction with the pore wall is not a just simple steric one but is in part dependent on the specific features of the molecules explored here.

  • 43.
    El-Zohry, Ahmed M.
    et al.
    Uppsala Univ, Dept Chem, Angstrom Labs, Box 523, SE-75120 Uppsala, Sweden..
    Karlsson, Karl Martin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Gigantic Relevance of Twisted Intramolecular Charge Transfer for Organic Dyes Used in Solar Cells2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 42, p. 23998-24003Article in journal (Refereed)
    Abstract [en]

    Within this work, we emphasis on the importance of twisted intramolecular charge transfer (TICT) process in organic dyes based on triphenyl amine moiety to achieve high performance in dye-sensitized solar cells. Through the comparison between two recent made dyes, Ll and L1Fc, on different semiconductors (TiO2, and ZrO2), we could spectrally and dynamically detect for the first time the formation of TICT state for Ll on ZrO2 after localized charge transfer (LCT) state population, and an electron injection process from TICT state on TiO2. However, for the excited L1Fc dye, the ultrafast electron transfer from ferrocene (Fc) moiety to the Ll unit quenched the formation of TICT state in L1Fc on semiconductors, leading instead to an electron injection process from the LCT state. The electron injection from TICT state in Ll associated with structural rearrangements on TiO2 leads to slow recombination process and an efficiency improvement of about 325%, compared to solar cells based on L1Fc dye, in which TICT state formation is hindered. Similar electron dynamics are obtained for Ll on TiO2 upon physically hindering the TICT process by adding polymer matrix. The presence of TICT state for Ll dye and similar triphenyl amine dyes aids to reconstruct the kinetic profile for these dyes on semiconductor surfaces, and to redesign organic dyes accordingly for higher efficiency in solar cells.

  • 44. Emanuelsson, Rikard
    et al.
    Löfas, Henrik
    Zhu, Jun
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Grigoriev, Anton
    Ottosson, Henrik
    In Search of Flexible Molecular Wires with Near Conformer-Independent Conjugation and Conductance: A Computational Study2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 11, p. 5637-5649Article in journal (Refereed)
    Abstract [en]

    Oligomers of 1,4-disila/germa/stannacyclohexa-2,5-dienes as well as all-carbon 1,4-cyclohexadienes connected via E-E single bonds (E = C, Si, Ge, or Sn) were studied through quantum chemical calculations in an effort to identify conformationally flexible molecular wires that act as molecular "electrical cords" hang conformer-independent conjugative and conductive properties. Our oligomers display neutral hyperconjugative interactions (sigma/pi-conjugation) between adjacent sigma(E-E) and pi(C=C) bond orbitals, and these interactions do not change with conformation. The energies and spatial distributions of the highest occupied molecular orbitals of methyl-, silyl-, and trimethylsilyl (TMS)-substituted 1,4-disilacyclohexa-2,5-diene dimers, and stable conformers of trimers and tetramers, remain rather constant upon Si-Si bond rotation. Yet, steric congestion may be a concern in some of the oligomer types. The calculated conductances for the Si-containing tetramers are similar to that of a sigma-conjugated linear all-anti oligosilane (a hexadecasilane) with equally many bonds in the conjugated paths. Moreover, the Me-substituted 1,4-disilacyclohexadiene tetramer has modest conductance fluctuations with Si-Si bond rotations when the electrode-electrode distance is locked (variation by factor similar to 30), while the fluctuations under similar conditions are larger for the analogous TMS-substituted tetramer. When the electrode-electrode distance is changed several oligomers display small conductance variations within certain distance intervals, e.g., the mean conductance of TMS-substituted 1,4-disilacyclohexa-2,5-diene tetramer is almost unchanged over 9 A of electrode-electrode distances.

  • 45. Feldt, Sandra M.
    et al.
    Cappel, Ute B.
    Johansson, Erik M. J.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Characterization of Surface Passivation by Poly(methylsiloxane) for Dye-Sensitized Solar Cells Employing the Ferrocene Redox Couple2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 23, p. 10551-10558Article in journal (Refereed)
    Abstract [en]

    One-electron outer-sphere redox couples, such as ferrocene/ferrocenium, are an interesting alternative to the iodide/triiodide redox couple that is normally employed in dye-sensitized solar cells (DSCs) because they should reduce the driving force needed to regenerate the dye. Unfortunately, one-electron redox couples also show enhanced recombination with photoinjected electrons, and methods to inhibit this recombination are needed for functioning DSCs. In this study, dye-sensitized titanium dioxide surfaces were passivated by a trichloromethylsilane reaction in order to decrease the fast recombination rates when using the ferrocene redox couple. The formation and binding of poly(methylsiloxane) on the dye-sensitized TiO(2) surface was verified with infrared spectroscopy and photoelectron spectroscopy. Photoelectrochemical characterization of the silanization method showed that the treatment decreased the recombination rate of photoinjected electrons with ferrocenium and thereby improved the efficiency of the DSC. Transient absorption spectroscopy revealed, however, that the poly(methylsiloxane) coatings slowed down the regeneration of the oxidized dye by the ferrocene and prevented the regeneration of some of the dye molecules.

  • 46.
    Fernandes, Ricardo M.F.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, s/n, Porto, Portugal.
    Buzaglo, Matat
    Regev, Oren
    Marques, Eduardo
    Furo, Istvan
    Surface Coverage and Competitive Adsorption on Carbon Nanotubes2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, The Journal of Physical Chemistry C, ISSN 1932-7447, Vol. 119, no 38, p. 22190-22197Article in journal (Refereed)
    Abstract [en]

    The binding strength of dispersants to the surface of carbon nanotubes is of crucial importance for the efficiency of the dispersion process and for potential applications, yet data are scarce on this subject. Here we present the results of diffusion NMR experiments in dispersions of single-walled carbon nanotubes (SWNTs) prepared by either the polymer Pluronics F127 or the protein bovine serum albumin (BSA). The experiments detect the amount of F127 molecules adsorbed onto the SWNT surface. This quantity is recorded (i) in F127-SWNT dispersions to which BSA molecules are added and (ii) in BSA-SWNT dispersions to which F127 molecules are added. The data clearly show that F127 replaces BSA adsorbed at the SWNT surface, while BSA leaves the adsorbed F127 coverage intact. Consequently, F127 binds to the nanotube surface more strongly than BSA. Hence, we provide a way to categorize dispersants by adsorption strength. We also provide evidence showing that the nanotubes dispersed by BSA form loose aggregates where a large part of the surface is not in direct contact with the surrounding liquid. The results are discussed in relation to previous findings in the literature.

  • 47.
    Ferreira Fernandes, Ricardo Manuel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. Univ Porto, Portugal.
    Buzaglo, Matat
    Shtein, Michael
    Bar, Ilan Pri
    Regev, Oren
    Marques, Eduardo F.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Lateral Diffusion of Dispersing Molecules On Nanotubes As Probed by NMR2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 1, p. 582-589Article in journal (Refereed)
    Abstract [en]

    Noncovalent dispersion of carbon nanotubes is essential to most applications but still poorly understood at the molecular level. The interaction of the dispersing molecule with the nanotube, wrapping or nonwrapping, still awaits consensus. Herein, we have studied by H-1 NMR diffusometry some features of molecular dynamics in the system of carbon nanotubes dispersed by triblock copolymer Pluronics F127 in water. The diffusional decays obtained at different diffusion times, Delta, are not single-exponential and have a complex Delta-dependent profile, ultimately implying that the polymer is observed in two states: free (in unimeric form) and nanotube-bound. Fitting a two-site exchange model to the data indicates that at any instant, only a small fraction of polymers are adsorbed on the nanotubes, with polydisperse residence times in the range of 100-400 ms. Most significantly, we further provide an estimate of D = (3-8) x 10(-12) m(2) s(-1) the coefficient of lateral diffusion of the polymer along the nanotube surface, which is an order of magnitude slower than the corresponding self-diffusion coefficient in water. The emerging picture is that of a nonwrapping mode for the polymer-nanotube interaction.

  • 48.
    Fidalgo, Alexandre Barreiro
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Dahlgren, Björn
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Surface Reactions of H2O2, H-2, and O-2 in Aqueous Systems Containing ZrO22016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 3, p. 1609-1614Article in journal (Refereed)
    Abstract [en]

    In radiolysis of water, three molecular products are formed (H2O2, O-2, and H-2). It has previously been shown that aqueous hydrogen peroxide is catalytically decomposed on many oxide surfaces and that the decomposition proceeds via the formation of surface-bound hydroxyl radicals. In this work, we have investigated the behavior of aqueous H-2 and O-2 in contact with ZrO2. Experiments were carried out in an autoclave with high H2 pressure and low O-2 pressure (40 and 0.2 bar, respectively). In the experiments the concentration of H-abstracting radicals was monitored as a function of time using tris(hydroxymethyl)aminomethane (Tris) as scavenger and the subsequent formation of formaldehyde to probe radical formation. The plausible formation of H2O2 was also monitored in the experiments. In addition, density functional theory (employing the hybrid PBE0 functional) was used to search for reaction pathways. The results from the,experiments show that hydrogen-abstracting radicals: are formed in the aqueous H2O2-system in contact with solid ZrO2. Formation of H2O2 is also detected, and the time dependent production of hydrogen-abstracting radicals follows the time-dependent H2O2 concentration, strongly:indicating that the radicals are produced upon catalytic decomposition of H2O2. The DFT study implies that H2O2 formation proceeds via a pathway where HO2 is a key intermediate. It is interesting to note that all the stable molecular products from aqueous radiolysis are precursors of quite intriguing radical reactions at water/oxide interfaces.

  • 49. Fredin, Kristofer
    et al.
    Anderson, Kenrick F.
    Duffy, Noel W.
    Wilson, Gregory J.
    Fell, Christopher J.
    Hagberg, Daniel P.
    KTH, School of Chemical Science and Engineering (CHE).
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Bach, Udo
    Lindquist, Sten-Eric
    Effect on Cell Efficiency following Thermal Degradation of Dye-Sensitized Mesoporous Electrodes Using N719 and D5 Sensitizers2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 43, p. 18902-18906Article in journal (Refereed)
    Abstract [en]

    This work examines the comparative durability of two common dyes at temperatures that may be experienced during fabrication of dye-sensitized solar cells (DSCs) such as through the application of thermoplastics for encapsulation or the use of a molten solid-state hole conductor. Dye-sensitized electrodes were heated in an atmosphere of air or nitrogen and thereafter used as working electrodes in DSCs. Electrodes sensitized with N719 appeared more sensitive to thermal degradation than electrodes sensitized with D5, although absorbance measurements suggest similar first-order degradation rates for the two dyes. Intensity modulated photovoltage spectroscopy and intensity modulated photocurrent spectroscopy were used to measure the effect of heating on electron lifetime and transport. It was found that the electron diffusion length may.. be as low as 10% for heated samples, compared to that of the unheated counterpart, and therefore, we assess recombination as an additional efficiency limiting process in our experiments.

  • 50.
    Fredin, Kristofer
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Gorlov, M.
    IVF Industrial Research and Development Corporation, Mölndal.
    Pettersson, Henrik
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    On the influence of anions in binary ionic liquid electrolytes for monolithic dye-sensitized solar cells2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 35, p. 13261-13266Article in journal (Refereed)
    Abstract [en]

    Five ion c liquids (ILs) of the general formula Im(+)A(-), where Im(+) = I -methyl-3-n-butyl-imidazolium, A(-) = I- (1), BF4- (2), SCN- (3), CF3CO2- (4), and CF(3)S0(3)(-) (5), were used in electrolytes for dye-sensitized monolithic solar cells. The properties of the electrolytes and various characteristics of the solar cell performance, such as electron transport and electron lifetime, were studied. The composition of the binary electrolytes, i.e., the different anions, have a significant effect on the viscosity, but only a modest effect of the measured diffusior. coefficient for triiodide. No significant effect of the electrolyte composition on the electron transport time in the mesoporous TiO2 film was found, while there was a pronounced effect on the electron lifetime. Monolithic solar cells with thiocyanate, IL 3, showed overall light-to-electricity conversion efficiency up to 5.6% in 250 W m(-2) simulated sunlight and have promising stability.

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