Ändra sökning
Avgränsa sökresultatet
23456 201 - 250 av 277
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 201. Sarkar, S.
    et al.
    Makhal, A.
    Lakshman, K.
    Bora, T.
    Dutta, Joydeep
    Asian Institute of Technology, Klong Luang, Thailand.
    Kumar Pal, S.
    Dual-sensitization via electron and energy harvesting in CdTe quantum dots decorated ZnO nanorod-based dye-sensitized solar cells2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 27, s. 14248-14256Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Different-sized, 3-mercaptopropionic acid (MPA) stabilized CdTe quantum dots (QDs) have been prepared in aqueous solution, and potential cosensitization of such QDs in ZnO nanorod (NR)-based dye-sensitized solar cells (DSSCs) has been established. The results presented in this study highlight two major pathways by which CdTe QDs may contribute to the net photocurrent in a DSSC: (1) a direct injection of charge carriers from QDs to ZnO semiconductor via photoinduced electron transfer (PET) and (2) an indirect excitation of the sensitizing dye (SD) N719 molecules by funneling harvested light via Förster resonance energy transfer (FRET). The steady-state and picosecond-resolved luminescence measurements were combined to clarify the process of PET and FRET from the excited QDs to ZnO NR and SD N719, respectively. On the basis of these advantages, the short-circuit current density and the photoconductivity of the QD-assembled DSSCs with distinct architectures are found to be much higher than DSSCs fabricated with N719 sensitizer only.

  • 202. Sarkar, Soumik
    et al.
    Makhal, Abhinandan
    Baruah, Sunandan
    Mahmood, Mohammad A
    Dutta, Joydeep
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Pal, Samir K
    Nanoparticle-Sensitized Photodegradation of Bilirubin and Potential Therapeutic Application2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 17, s. 9608-9615Artikel i tidskrift (Refereegranskat)
  • 203. Schiessling, Joachim
    et al.
    Grigoriev, A.
    Stener, Mauro
    Kjeldgaard, Lisbeth
    Balasubramanian, Thiagarajan
    Decleva, Piero
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Nordgren, Joseph
    Bruhwiler, Paul A.
    The Role of Charge-Charge Correlations and Covalent Bonding in the Electronic Structure of Adsorbed C-60: C-60/A12010Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 43, s. 18686-18692Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aromatic molecules are central components of model systems for molecular electronics, with C-60 one of the most studied. Upon adsorption on (metallic) substrates a splitting of the frontier orbitals is commonly observed, with a strong dependence on substrate material, but little dependence on substrate structure. We report the detailed photoelectron angle dependence of C-60/A1(110) over a wide range of energy, finding a strong remnant molecular character. In particular, certain HOMO-derived suborbitals couple strongly, and others weakly, with the metal, which results in final state charging for those weakly coupled. C Is data correlate well with the assignments made on this basis, as does the comparison of ground state partial densities-of-states (PDOS) to photoelectron spectra. Detailed analysis of the PDOS supports a rough division into surface-near and surface-far components, in agreement with the molecular picture. The component spectral widths are attributed to intramolecular vibrational coupling, which is suggested to aid in the electronic decoupling of certain suborbitals from the substrate, facilitating the observed final state charging.

  • 204. Scholin, Rebecka
    et al.
    Quintana, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi (stängd 20110630). KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Johansson, Erik M. J.
    Hahlin, Maria
    Marinado, Tannia
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi (stängd 20110630). KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Hagfeldt, Anders
    Rensmo, Håkan
    Preventing Dye Aggregation on ZnO by Adding Water in the Dye-Sensitization Process2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 39, s. 19274-19279Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    ZnO based dye-sensitized solar cells have been studied using N719 and Z-907 as sensitizing dyes, with and without including water to the dye solution. The solar cells have been characterized with photoelectric measurements and the interface between the dye and the ZnO surface has been studied using photoelectron spectroscopy. It was shown that water in the dye solution greatly reduces surface dye aggregation and thereby enhances the solar cell performance for N719. For Z-907 where no sign of dye aggregation could be found, the presence of water had minor effect on the surface structure and solar cell performance.

  • 205. Shah, F. U.
    et al.
    Holmgren, A.
    Rutland, Mark W.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap. RISE Research Institutes of Sweden, Bioscience and Materials.
    Glavatskih, S.
    Antzutkin, O. N.
    Interfacial Behavior of Orthoborate Ionic Liquids at Inorganic Oxide Surfaces Probed by NMR, IR, and Raman Spectroscopy2018Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 34, s. 19687-19698Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Absorption modes and the reactivity of nonhalogenated ionic liquids (ILs) at inorganic oxide surfaces of γ-Al2O3, MgO, and SiO2 particles were characterized using multinuclear (11B, 31P, and 29Si) solid-state magic-angle-spinning NMR, FTIR, and Raman spectroscopy. ILs are composed of the trihexyl(tetradecyl)phosphonium cation, [P6,6,6,14]+, and bis(mandelato)borate, [BMB]-, or bis(salicylato)borate, [BScB]-, anions. Spectroscopic measurements were performed on room-temperature (298 K) samples and samples exposed to 15 h at 373 K. The single-pulse 11B NMR data of heated [P6,6,6,14][BMB] mixed with the inorganic oxides showed a significant change in the spectra of the anion for all three oxides. In contrast, no such spectral changes were detected for heated [P6,6,6,14][BScB] mixed with the inorganic oxides. 31P MAS NMR data for the IL/metal oxide systems revealed interactions between [P6,6,6,14]+ and the surfaces of oxides. A significant intensity of 31P CP-MAS NMR signals indicated a low mobility of cations in these systems. The existence of strongly adhered surface layers of ILs on SiO2 particles was also confirmed by 1H-29Si CP-MAS NMR spectroscopy. FTIR and Raman spectroscopic data revealed strong interactions between the anions and the inorganic surfaces, and there is a strong correlation with the data obtained from NMR spectroscopy. Although their chemical structures are rather similar, the [BScB]- anion is more stable than the [BMB]- anion at the inorganic oxide surfaces.

  • 206.
    Shambetova, Nestan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Chen, Yun
    Xu, Hao
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Cellens fysik.
    Li, Li
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Solandt, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Zhou, Yuhua
    Wang, Jingbo
    Su, Haibin
    Brismar, Hjalmar
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Cellens fysik.
    Fu, Ying
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Cellens fysik.
    Acid dissociation of 3-mercaptopropionic acid coated CdSe-CdS/Cd0.5Zn0.5S/ZnS core-multishell quantum dot and strong ionic interaction with Ca2+ ion2016Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By devising careful electrophoresis, it was shown that at pH below 7.0, the electrophoretic mobility of 3-mercaptopropionic acid (3MPA) coated CdSe-ZnS core-shell quantum dots (denoted as QD-3MPA) was very small. At pH above 7.0, QD-3MPA migrated toward the anode, implying acid dissociation, and the degree of which was proportional to the pH value. QD-3MPA's electrophoretic mobility was impaired after adding sufficient Ca2+ ions to the QD solution and revived when a similar amount of Ca2+ chelators (ethylene glycol tetraacetic acid, EGTA) was added. This demonstrated that acid dissociation and its pH dependence of 3MPA on the QD surface are critical factors in understanding the electric and optical properties of QDs. The acid dissociated QD-3MPA interacted strongly with Ca2+, forming a charge neutral QD-3MPA Ca2+ complex in the absence of EGTA. First-principles study confirmed the observed experimental evidence. The strong ionic interaction between acid dissociated QD-3MPA and Ca2+ is critical for developing reliable QD-based biosensing assays. Moreover, the strategy and techniques reported in this work are easily applicable to other fluorescent biomarkers and therefore can be important for advancing in vivo and in vitro imaging, sensing, and labeling.

  • 207. Shariati, Masumeh-Nina
    et al.
    Luder, Johann
    Bidermane, Ieva
    Ahmadi, Sareh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Göthelid, Emmanuelle
    Palmgren, Pål
    Sanyal, Biplab
    Eriksson, Olle
    Piancastelli, Maria Novella
    Brena, Barbara
    Puglia, Carla
    Photoelectron and Absorption Spectroscopy Studies of Metal-Free Phthalocyanine on Au(111): Experiment and Theory2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 14, s. 7018-7025Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adsorption of monolayers and multilayers of metal-free phthalocyanine molecules on the Au(111) (root 3 x 22) reconstructed surface has been investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). Our results for the monolayer show that the molecules are arranged tightly onto the surface with their molecular plane parallel to it. In addition, the X-ray absorption spectra of the monolayer have been modeled by density functional theory, which could enlighten new aspect of the interaction between molecules and substrate. The XAS results evidence that also in the multilayer the molecules keep the orientation with the molecular plane parallel to the surface. These results are discussed in the framework of moleculemolecule/moleculeadsorbate interactions.

  • 208. Shukla, Vivekanand
    et al.
    Warna, John
    Jena, Naresh K.
    Grigoriev, Anton
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Toward the Realization of 2D Borophene Based Gas Sensor2017Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, nr 48, s. 26869-26876Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To the league of rapidly expanding 2D materials, borophene is a recent addition. Herein, a combination of ab initio density functional theory (DFT) and nonequilibrium Green's function (NEGF) based methods is used to estimate the prospects of this promising elemental 2D material for gas sensing applications. We note that the binding of target gas molecules such as CO, NO, NO2, NH3, and CO2 is quite strong on the borophene surface. Interestingly, our computed binding energies are far stronger than several other reported 2D materials like graphene, MoS2, and phosphorene. Further rationalization of stronger binding is made with the help of charge transfer analysis. The sensitivity of the borophene for these gases is also interpreted in terms of computing the vibrational spectra of the adsorbed gases on top of borophene, which show dramatic shift from their gas phase reference values. The metallic nature of borophene enables us to devise a setup considering the same substrate as electrodes. From the computation of the transmission function of system (gas + borophene), appreciable changes in the transmission functions are noted compared to pristine borophene surface. The measurements of current-voltage (I-V) characteristics unambiguously demonstrate the presence and absence of gas molecules (acting as ON and OFF states), strengthening the plausibility of a borophene based gas sensing device. As we extol the extraordinary sensitivity of borophene, we assert that this elemental 2D material is likely to attract subsequent interest.

  • 209.
    Si, Wenping
    et al.
    Paul Scherrer Inst, Lab Multiscale Mat Expt, CH-5232 Villigen, Switzerland.;Tianjin Univ, Sch Mat Sci & Engn, Minist Educ, Key Lab Adv Ceram & Machining Technol, Tianjin 300072, Peoples R China..
    Tehrani, Zahra Pourmand
    Paul Scherrer Inst, Lab Multiscale Mat Expt, CH-5232 Villigen, Switzerland..
    Haydous, Fatima
    Paul Scherrer Inst, Lab Multiscale Mat Expt, CH-5232 Villigen, Switzerland.
    Marzari, Nicola
    Ecole Polytech Fed Lausanne, Theory & Simulat Mat THEOS, CH-1015 Lausanne, Switzerland.;Ecole Polytech Fed Lausanne, Natl Ctr Computat Design & Discovery Novel Mat MA, CH-1015 Lausanne, Switzerland..
    Castelli, Ivano E.
    Tech Univ Denmark, Dept Energy Convers & Storage, Fysikvej 309, DK-2800 Lyngby, Denmark..
    Pergolesi, Daniele
    Paul Scherrer Inst, Lab Multiscale Mat Expt, CH-5232 Villigen, Switzerland.;Paul Scherrer Inst, Electrochem Lab, CH-5232 Villigen, Switzerland..
    Lippert, Thomas
    Paul Scherrer Inst, Lab Multiscale Mat Expt, CH-5232 Villigen, Switzerland.;Swiss Fed Inst Technol, Dept Chem & Appl Biosci, Lab Inorgan Chem, CH-8093 Zurich, Switzerland..
    Yttrium Tantalum Oxynitride Multiphases as Photoanodes for Water Oxidation2019Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 43, s. 26211-26217Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The perovskite yttrium tantalum oxynitride is theoretically proposed as a promising semiconductor for solar water splitting because of the predicted band gap and energy positions of band edges. In experiments, however, we show here that depending on the processing parameters, yttrium tantalum oxynitrides exist in multi phases, including the desired perovskite YTaON2, defect fluorite YTa(O,N,square)(4), and N-doped YTaO4. These multiphases have band gaps ranging between 2.13 and 2.31 eV, all responsive to visible light. The N-doped YTaO4, perovskite main phase, and fluorite main phase derived from crystalline fergusonite oxide precursors exhibit interesting photoelectrochemical performances for water oxidation, while the defect fluorite derived from low-crystallized scheelite-type oxide precursors shows negligible activity. Preliminary measurements show that loading an IrOx, cocatalyst on N-doped YTaO4 significantly improves its photoelectrochemical performance, encouraging further studies to optimize this new material for solar fuel production.

  • 210.
    Soldemo, Markus
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Halldin Stenlid, Joakim
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Besharat, Zahra
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Ghadami Yazdi, Milad
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Önsten, Anneli
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Leygraf, Christofer
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Göthelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    The Surface Structure of Cu2O(100)2016Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 8, s. 4373-4381Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Despite the industrial importance of copper oxides, the nature of the (100) surface of Cu2O has remained poorly understood. The surface has previously been subject to several theoretical and experimental studies, but has until now not been investigated by atomically resolved microscopy or high-resolution photoelectron spectroscopy. Here we determine the atomic structure and electronic properties of Cu2O(100) by a combination of multiple experimental techniques and simulations within the framework of density functional theory (DFT). Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) characterized the three ordered surface structures found. From DFT calculations, the structures are found to be energetically ordered as (3,0;1,1), c(2 x 2), and (1 x 1) under ultrahigh vacuum conditions. Increased oxygen pressures induce the formation of an oxygen terminated (1 x 1) surface structure. The most common termination of Cu2O(100) has previously been described by a (3 root 2 x root 2)R45 degrees unit cell exhibiting a LEED pattern with several missing spots. Through atomically resolved STM, we show that this structure instead is described by the matrix (3,0;1,1). Both simulated STM images and calculated photoemission core level shifts compare favorably with the experimental results.

  • 211.
    Soldemo, Markus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Materialfysik, MF.
    Halldin Stenlid, Joakim
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Besharat, Zahra
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Materialfysik, MF.
    Johansson, N.
    Önsten, Anneli
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Materialfysik, MF.
    Knudsen, J.
    Schnadt, J.
    Göthelid, Mats
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Materialfysik, MF.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Weissenrieder, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Materialfysik, MF.
    Interaction of Sulfur Dioxide and Near-Ambient Pressures of Water Vapor with Cuprous Oxide Surfaces2017Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, nr 43, s. 24011-24024Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interaction of water vapor and sulfur dioxide (SO2) with single crystal cuprous oxide (Cu2O) surfaces of (100) and (111) termination was studied by photoelectron spectroscopy (PES) and density functional theory (DFT). Exposure to near-ambient pressures of water vapor, at 5 × 10-3 %RH and 293 K, hydroxylates both Cu2O surfaces with OH coverage up to 0.38 copper monolayers (ML) for (100) and 0.25 ML for (111). O 1s surface core level shifts indicate that the hydroxylation lifts the (3,0;1,1) reconstruction of the clean (100) surface. On both clean Cu2O terminations, SO2 adsorbs to unsaturated surface oxygen atoms to form SO3 species with coverage, after a saturating SO2 dose, corresponding to 0.20 ML on the Cu2O(100) surface and 0.09 ML for the Cu2O(111) surface. Our combined DFT and PES results suggest that the SO2 to SO3 transformation is largely facilitated by unsaturated copper atoms at the Cu2O(111) surface. SO3-terminated surfaces exposed to low doses of water vapor (≤100 langmuirs) in ultrahigh vacuum show no adsorption or reaction. However, during exposure to near-ambient pressures of water vapor, the SO3 species dissociate, and sulfur replaces a Cu2O lattice oxygen in a reaction that forms Cu2S. The hydroxylation of the Cu2O surfaces is believed to play a central role in the reaction.

  • 212.
    Soldemo, Markus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Vandichel, Matthias
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Competence Ctr Catalysis, SE-41296 Gothenburg, Sweden.;Aalto Univ, Dept Chem & Mat Sci, Sch Chem Engn, Sch Sci, Espoo 02150, Finland.;Aalto Univ, Dept Appl Phys, Sch Chem Engn, Sch Sci, Espoo 02150, Finland..
    Gronbeck, Henrik
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Competence Ctr Catalysis, SE-41296 Gothenburg, Sweden..
    Weissenrieder, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Initial Fe3O4(100) Formation on Fe(100)2019Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 26, s. 16317-16325Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The initial oxidation of Fe(100) at 400 degrees C has been studied by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and low-energy electron diffraction, in combination with density functional theory calculations. The first observed well-ordered surface oxide is formed at a coverage of similar to 3 oxygen atoms per unreconstructed surface Fe(100) atom. STM shows that this surface oxide is terminated by straight atomic rows exhibiting a p(2 X 1) periodicity. However, already for oxide films with a coverage of similar to 4 oxygen atoms (corresponding to one Fe3O4 unit cell thickness), wiggly atomic rows appear similar to the c(2 X 2) reconstructed Fe3O4 (100)-surface with the Fe3O4 unit vectors rotated 45 degrees to Fe(100). The wiggly rows are a consequence of subsurface cation iron vacancies, which previously have been observed for bulk surfaces. The formation of subsurface vacancies is supported by the XPS O is signature, which is modeled by considering the core-level shifts for all oxygen atoms in the film. Throughout the oxidation series, the microscopy results reveal a layer-by-layer (Frank-van der Merwe) growth.

  • 213.
    Song, Xiuneng
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Hua, Weijie
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ma, Yong
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Wang, Chuankui
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Theoretical Study of Core Excitations of Fullerene-Based Polymer Solar Cell Acceptors2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 45, s. 23938-23944Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles simulations for the C K-edge X-ray photoelectron (XPS) and near-edge X-ray fine-structure (NEXAFS) spectra of representative polymer solar cell acceptor (PSCA) molecules have been carried out with special focuses on the [6,6]-phenyl-Cn+1-butyric acid methyl ester (PCnBM, n = 60, 70, 84). In the XPS spectra, evident red shift of core binding energies are observed in PCnBM as compared to the corresponding fullerene C-n, which is due to weak electronic charge transfer from the side chain to the fullerene backbone and consequently increased electron screening. Special emphasis is paid to a spectral peak at ca. 284.7 eV, which is caused by resonances of phenyl-ring carbons in the side chain and is important in characterizing the electronic structures of different PSCA molecules. Additionally, we propose a modified version of the building block (MBB) approach for quick estimation of the NEXAFS spectra, which is useful when computational resources are limited or massive systems are under study. This method is based on our component analysis on the side chain and fullerene backbone parts and adds only a further empirical fine-tuning after the conventional BB approach. Our calculated results are in good agreement with available experiments.

  • 214.
    Song, Xiuneng
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ma, Yong
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Wang, Chuankui
    Shandong Normal University, Shandong, Peoples R China.
    Dietrich, Paul M.
    BAM Fed Inst Mat Res & Testing, Berlin, Germany .
    Unger, Wolfgang E. S.
    BAM Fed Inst Mat Res & Testing, Berlin, Germany .
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Effects of Protonation, Hydrogen Bonding, and Photodamaging on X-ray Spectroscopy of the Amine Terminal Group in Aminothiolate Monolayers2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 23, s. 12649-12654Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The amine head group, NH2, in aminothiolate monolayers can often generate unexpectedly rich structures in its N K-edge X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra that are difficult to assign. We have carried out density functional theory (DFT) calculations to study the XPS and NEXAFS of amine head group in four different aminothiolate monolayers, namely aliphatic 11-aminoundecane-1-thiol (AUDT), aromatic 4-aminobenzenethiol (ABT) and araliphatic 4-aminophenylbutane-1-thiol (APBT) and 3-(4”-amino-1,1’:4’,1”-terphenyl-4-yl)propane-1-thiol (ATPT), with the focus on structure changes caused by protonation, hydrogen bonding and X-ray damaging. Spectra of all possible saturated and unsaturated species, as well as X-ray damage products, such as imine, nitrile, azo species and cumulative double bonds, have been thoroughly examined. It is found that extra spectral structures observed in the experimental XPS spectra are not resulted from protonation, but from the formation of a primary ammonium. The X-ray excitation can induce cross linking between two neighboring molecules to form different complexes that contribute to the π features in NEXAFS spectra.

  • 215.
    Sprunken, Dan
    et al.
    NTT Basic Research Labs.
    Omi, Hiroo
    NTT Basic Research Labs.
    Furukawa, Kazuaki
    NTT Basic Research Labs.
    Nakashima, Hiroshi
    NTT Basic Research Labs.
    Sychugov, Ilya
    NTT Basic Research Labs.
    Kobayashi, Yoshihiro
    NTT Basic Research Labs.
    Torimitsu, Keiichi
    NTT Basic Research Labs.
    Influence of the Local Environment on Determining Aspect-Ratio Distributions of Gold Nanorods in Solution Using Gans Theory2007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, s. 14299-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

    1.

  • 216. Srepusharawoot, P.
    et al.
    Scheicher, R. H.
    Araujo, C. M.
    Blomqvist, A.
    Pinsook, U.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab Initio Study of Molecular Hydrogen Adsorption in Covalent Organic Framework-12009Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 19, s. 8498-8504Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The adsorption energies of hydrogen molecules at all possible adsorption sites of covalent organic framework-1 (COF-1) are studied by density functional theory (DFT) and second-order Moller-Plesset perturbation theory (MP2). The most favorable adsorption sites from our DFT results are on the top of an oxygen atom for the B3O3 ring and on the top of the center of the C-C bond for the benzene ring when a single H-2 is interacting with the COF-1. The adsorption energy trend obtained from the DFT calculations is found to be in good agreement with the MP2 binding energy trend. The binding preferences are slightly changed when high hydrogen loading is considered. H-2 molecules prefer to be trapped on the top of the carbon atoms of the benzene ring and also on the top of the oxygen atoms of the B3O3 ring. These findings are confirmed by hydrogen center-of-mass distribution results obtained using molecular dynamics simulations. Moreover, our DFT results reveal that the hydrogen adsorption energies are boosted when we increase the number of hydrogen loadings due to attractive H-2-H-2 interactions. In addition, the nonavailability of the remaining adsorption sites in the COF-1 leads to a reduction of the H-2 mobility.

  • 217.
    Stenlid, Joakim H.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Johansson, A. Johannes
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Local Lewis Acidity of (TiO2)(n) (n=7-10) Nanoparticles Characterized by DFT-Based Descriptors: Tools for Catalyst Design2017Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, nr 49, s. 27483-27492Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transition metal oxide nanoparticles are common materials in a multitude of applications including heterogeneous catalysis, solar energy harvesting, and energy storage. Understanding the particles' interplay with their surroundings is key to their efficient usage and design. Herein two DFT-based descriptors are used to study local reactivity on (TiO2)(n) (n = 7-10) nanoparticles. The local electron attraction energy [E(r)] and the electrostatic potential [V(r)], evaluated on isodensity surfaces, are able to identify and rank Lewis acidic sites on the particles with high accuracy when compared to the interaction energies of the Lewis bases H2O, H2S, NH3, and CO. These interactions are characterized as mainly electrostatically controlled. Given the local character, low computational cost, and excellent performance of the E-s(r) and V-s(r) descriptors, they are anticipated to find widespread use in nanoparticle research and development.

  • 218.
    Sthoer, Adrien
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap. kth.
    Tyrode, Eric
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Yt- och korrosionsvetenskap.
    Interactions of Na+ Cations with a Highly Charged Fatty Acid Langmuir Monolayer: Molecular Description of the Phase Transition2019Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    Vibrational sum frequency spectroscopy has been used to study the molecular properties upon compression of a highly charged arachidic acid Langmuir monolayer, which displays a first-order phase transition plateau in the surface pressure - molecular area (π-A) isotherm. By targeting vibrational modes from the carboxylic acid headgroup, alkyl chain, and interfacial water molecules, information regarding the surface charge, surface potential, type of ion pair formed, and conformational order of the monolayer could be extracted. The monolayer was found to be fully charged before reaching the 2D-phase transition plateau, where partial reprotonation, as well as the formation of COO⎺ Na+ contact-ion pairs, started to take place. After the transition, three headgroup species, mainly hydrated COO⎺, COOH, and COO⎺ Na+ contact-ion pairs could be identified and their proportions quantified. Comparison with theoretical models shows that predictions from the Gouy Chapman model are only adequate for the lowest surface charge densities (<-0.1 C/m2). In contrast, a modified Poisson-Boltzmann (MPB) model that accounts for finite-size of the cation, captures many of the experimental observables, including the partial reprotonation, and surface potential changes upon compression. The experimental results provide a quantitative molecular insight that could be used to test potential extensions to the theory.

  • 219. Sugiharto, A. B.
    et al.
    Johnson, Claes Magnus
    Dunlop, I. E.
    Roke, S.
    Delocalized surface modes reveal three-dimensional structures of complex biomolecules2008Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, nr 20, s. 7531-7534Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Interfaces are important for many processes in chemistry, physics, and biology. Crucial to their properties are the details of the three-dimensional structure of the participating (macro) molecules. Vibrational Sum Frequency Generation (VSFG) is a tool specifically suited to probing the first few atomic layers of an interface. Traditionally, interfaces are probed by mapping localized vibrational modes. Here, we show that the three-dimensional structure of large interfacial biomolecules can be probed by measuring delocalized vibrational backbone modes, which appear to be extremely sensitive to changes in the skeletal structure. We demonstrate that for three different films of chemically identical poly(lactic acid) polymer, we can observe dramatic changes in the three-dimensional arrangement of the surface molecular backbones. This type of information could not be obtained from probing only localized group modes.

  • 220.
    Sychugov, Ilya
    et al.
    National Institute for Materials Science.
    Nakayama, Yoshiko
    National Institute for Materials Science.
    Mitsuishi, Kazutaka
    National Institute for Materials Science.
    Composition Control of Electron Beam Induced Nanodeposits by Surface Pretreatment and Beam Focusing2009Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 52, s. 21516-21519Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 221. Szutkowski, Kosma
    et al.
    Stilbs, Peter
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Jurga, Stefan
    Proton chemical exchange in aqueous solutions of dodecylammonium chloride: Effects of micellar aggregation2007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 43, s. 15613-15619Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Proton chemical exchange was studied in aqueous solutions of dodecylammonium chloride (DDAC1) for two selected concentrations, 18 and 33 wt %. The Fourier transform Carr-Pureell-Meiboom-Gill (CPMG) NMR method combined with the Carver and Richards model for T-2 dispersion curve analysis were employed to evaluate the temperature dependence of the proton exchange rates k(ex). An increase of the energy barrier height Delta G double dagger for the proton chemical exchange between water and ammonium cation (-NH3+) was observed as the DDAC1 concentration was increased. Results are complementary to previous studies of aggregation phenomena for various n-alkylammonium chlorides.

  • 222. Tan, Qin
    et al.
    Yang, Xichuan
    Cheng, Ming
    Wang, Haoxin
    Wang, Xiuna
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. State Key Laboratory of Fine Chemicals, Dalian, China .
    Application of Small Molecule Donor Materials Based on Phenothiazine Core Unit in Bulk Heterojunction Solar Cells2014Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 30, s. 16851-16855Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A D-pi-A type small molecule PTZ1 and an A-pi-D-pi-A type small molecule PTZ2 with phenothiazine as the central building block and dicyanovinyl as the electron-withdrawing end-group have been designed and synthesized. Compared with D-pi-A type donor material PTZ1, the donor material PTZ2 with A-pi-D-pi-A configuration shows much wider response to solar light. The donor material PTZ1 possesses more positive highest occupied molecular orbital level, and higher V obtained for devices with PTZ1/PC71BM blend as the active layer. An improved efficiency of 3.25% was obtained for the PTZ2/PC71BM based solar cells.

  • 223.
    Tan, Shijing
    et al.
    Univ Sci & Technol China, Microscale & Synerget Innovat Ctr Quantum Informa, Hefei Natl Res Ctr Phys Sci, Hefei 230026, Anhui, Peoples R China.;Royal Inst Technol, Sch Engn Sci Chem Biotechnol & Hlth, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden..
    Feng, Hao
    Univ Sci & Technol China, Microscale & Synerget Innovat Ctr Quantum Informa, Hefei Natl Res Ctr Phys Sci, Hefei 230026, Anhui, Peoples R China..
    Ji, Yongfei
    Royal Inst Technol, Sch Engn Sci Chem Biotechnol & Hlth, Dept Theoret Chem & Biol, S-10691 Stockholm, Sweden..
    Zheng, Qijing
    Univ Sci & Technol China, Microscale & Synerget Innovat Ctr Quantum Informa, Hefei Natl Res Ctr Phys Sci, Hefei 230026, Anhui, Peoples R China..
    Shi, Yongliang
    Univ Sci & Technol China, Microscale & Synerget Innovat Ctr Quantum Informa, Hefei Natl Res Ctr Phys Sci, Hefei 230026, Anhui, Peoples R China..
    Zhao, Jin
    Univ Sci & Technol China, Microscale & Synerget Innovat Ctr Quantum Informa, Hefei Natl Res Ctr Phys Sci, Hefei 230026, Anhui, Peoples R China..
    Zhao, Aidi
    Univ Sci & Technol China, Microscale & Synerget Innovat Ctr Quantum Informa, Hefei Natl Res Ctr Phys Sci, Hefei 230026, Anhui, Peoples R China..
    Yang, Jinlong
    Univ Sci & Technol China, Microscale & Synerget Innovat Ctr Quantum Informa, Hefei Natl Res Ctr Phys Sci, Hefei 230026, Anhui, Peoples R China..
    Luo, Yi
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Wang, Bing
    Univ Sci & Technol China, Microscale & Synerget Innovat Ctr Quantum Informa, Hefei Natl Res Ctr Phys Sci, Hefei 230026, Anhui, Peoples R China..
    Hou, J. G.
    Univ Sci & Technol China, Microscale & Synerget Innovat Ctr Quantum Informa, Hefei Natl Res Ctr Phys Sci, Hefei 230026, Anhui, Peoples R China..
    Visualizing Elementary Reactions of Methanol by Electrons and Holes on TiO2(110) Surface2018Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 50, s. 28805-28814Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Direct visualization and comparison of the elementary reactions induced by electrons and holes are of importance for finding a way to conduct chemical reactions and reaction sequences in a controllable manner. As a semiconductor, TiO2 provides a playground to perform the measurements, and moreover, the information can be useful for design of high-performance TiO2-based catalysts and photocatalysts. Here, we present our investigation on the elementary reactions of CH3OH on TiO2 surface through visualization of specific elementary steps by highly controllable electron and hole injection using scanning tunneling microscopy. The distinct sequential routes and their kinetics, namely, breaking C-O and O-H bonds by electrons and breaking O-H and C-H bonds by holes, respectively, have been experimentally identified and well elucidated by density functional theory calculations. Our nonlocal h-injection experimental and theoretical results suggest that the delocalized holes in the TiO2 substrate should be responsible for the temperature-dependent h-route reactions. The locally triggered e-route reaction is associated with the fact that the location of the unoccupied hybridization states is much higher than that of the conduction band onset. Our findings resolve the long-standing debate about the intermediate species and reaction mechanism in photocatalytic oxidation of CH3OH. Our proposed protocol offers a powerful means to study elementary reactions induced by electrons and holes on a semiconductor surface in general.

  • 224. Teng, Chao
    et al.
    Yang, Xichuan
    Yang, Chao
    Li, Shifeng
    Cheng, Ming
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD. KTH, Skolan för kemivetenskap (CHE), Kemi.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Molecular Design of Anthracene-Bridged Metal-Free Organic Dyes for Efficient Dye-Sensitized Solar Cells2010Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 19, s. 9101-9110Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of metal-free organic dyes bridged by anthracene-containing pi-conjugations were designed and synthesized as new chromophores for the application of dye-sensitized solar cells (DSCs). Detailed investigations on the relationship between the dye structures, photophysical properties, electrochemical properties, and performances of DSCs are described. With the introduction of the anthracene moiety, together with a triple bond for the fine-tuning of molecular planar configurations and to broaden absorption spectra, the short-circuit photocurrent densities (J(sc)) and open-circuit photovoltages (V-oc) of DSCs were improved to a large extent. The improvement of J(sc) is attributed to much broader absorption spectra of the dyes with the anthracene moiety. Electrochemical impedance spectroscopy (EIS) analysis reveals that the introduction of the anthracene moiety suppresses the charge recombination arising from electrons in TiO2 films with I-3(-) ions in the electrolyte, thus improving V-oc considerably. On the basis of optimized molecular structures and DSC test conditions, the dye TC501 shows a prominent solar energy conversion efficiency (eta) up to 7.03% (J(sc) = 12.96 mA . cm(-2), V-OC = 720 mV, ff = 0.753) under simulated AM 1.5 irradiation (100 mW . cm(-2)).

  • 225. Teng, Chao
    et al.
    Yang, Xichuan
    Yang, Chao
    Tian, Haining
    Li, Shifeng
    Wang, Xiuna
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Influence of Triple Bonds as pi-Spacer Units in Metal-Free Organic Dyes for Dye-Sensitized Solar Cells2010Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 25, s. 11305-11313Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Four metal-free organic sensitizers (TC101-TC104) with triple bonds in pi-spacers and five reference dyes (TC, TC105, TPC1, D5, and TH208) without triple bonds were applied in dye-sensitized solar cells to study the influence of triple bonds as pi-spacer units on their photoelectrochemical properties and dye-sensitized solar cells (DSCs) performance. Results show that the introduction of triple bond could red-shift the dye's absorption spectrum due to the enhancement of the pi-spacer. However, the spectrum red-shift is much less than that of the introduction of double bond because of more electronegativity of triple bond. The incident photon-to-current conversion efficiency reveals that the electron transfer yield (Phi(nu)(ET)) of DSCs becomes larger with the introduction of triple bond. Electrochemical impedance spectroscopy analysis reveals that the introduction of triple bond almost does not change the electron lifetimes in TiO2 films but decreases the effective diffusion lengths.

  • 226.
    Thiyam, Priyadarshini
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Fiedler, J.
    Buhmann, S. Y.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Brevik, I.
    Bostrom, M.
    Parsons, D. F.
    Ice Particles Sink below the Water Surface Due to a Balance of Salt, van der Waals, and Buoyancy Forces2018Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 27, s. 15311-15317Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    According to the classical Archimedes' principle, ice floats in water and has a fraction of its volume above the water surface. However, for very small ice particles, other competing forces such as van der Waals forces due to fluctuating charge distributions and ionic forces due to salt ions and charge on the ice surface also contribute to the force balance. The latter crucially depends on both the pH of the water and the salt concentration. We show that a bulge in the air-water interface due to interaction of surface tension with the rising ice particle becomes significant when the particle radius is greater than 50-100 mu m. The role of these forces in governing the initial stages of ice condensation has never been considered. Here, we show that small ice particles can only form below an exclusion zone, from 2 nm (in high salt concentrations) up to 1 mu m (in pure water at pH 7) thick, under the water surface. This distance is defined by an equilibrium of upward buoyancy forces and repulsive van der Waals forces. Ionic forces due to salt and ice surface charge push this zone further down. Only after growing to a radius larger than 10 pm, will the ice particles eventually float toward the water surface in agreement with the simple intuition based on Archimedes' principle. Our result is the first prediction of observable repulsive van der Waals forces between ice particles and the water surface outside a laboratory setting. We posit that it has consequences on the biology of ice water as we predict an exclusion zone free of ice particles near the water surface which is sufficient to support the presence of bacteria.

  • 227.
    Tian, Guangjun
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. University of Science and Technology of China.
    Isomer-Dependent Franck-Condon Blockade in Weakly Coupled Bipyridine Molecular Junctions2014Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 27, s. 14853-14859Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Franck-Condon blockade is an attractive functionality of molecular junctions, but its tunability is still a challenge that has not been fully addressed. We show here from first-principles calculations that the electron-vibration coupling strength of a weekly coupled bipyridine molecular junction can be largely tuned from weak to strong coupling regime through isomerization. Electron transport properties of four bipyridine isomers, namely 2,6'-bipyridine, 2,4'-bipyridine, 2,2'-bipyridine, and 4,4'-bipyridine, have been exclusively examined. A very strong Franck-Condon blockade is found to be associated with 2,2'-bipyridine and 4,4'-bipyridine molecules and should be observable experimentally. A gate-controlled conductance switch is proposed for a molecular junction with a 4,4'-bipyridine molecule. Our calculations have clearly demonstrated that bipyridine isomers are excellent candidates for the experimental study of vibration-mediated transport properties in a single molecule.

  • 228. Tian, Haining
    et al.
    Yang, Xichuan
    Chen, Ruikui
    Zhang, Rong
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Sunt, Licheng
    Effect of different dye baths and dye-structures on the performance of dye-sensitized solar cells based on triphenylamine dyes2008Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, nr 29, s. 11023-11033Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of triphenylamine dyes were designed and synthesized as photosensitizers for the application of organic dye-sensitized solar cells (DSSCs). Different substituted phenylene units, 2,2';5',2 ''-terthiophene (TT) and dithieno[3,2-b;2',3'-d]thiophene (DTT) serve as the pi-spacers, and the electron acceptors employ the cyanoacrylic acid or rhodanine-3-acetic acid units. Detailed investigation on the relationship between the dye structure, and photophysical, photoelectrochemical properties and performance of DSSCs is described here. By substituting the phenylene group with electron-withdrawing units as pi-spacers or replacing the cyanoacrylic acid with rhodanine-3-acetic acid units as electron acceptors, the bathochromic shift of absorption spectra are achieved. The significant differences in the redox potential of these dyes are also influenced by small structure changes. Furthermore, the different dye baths for semiconductor sensitization have a crucial effect on the performance of the DSSCs due to the different absorbed amount, absorption spectra and binding modes of anchored dyes on TiO2 surface in various solvents. On the basis of optimized dye bath and molecular structure, TPC1 shows a prominent solar-to-electricity conversion efficiency (eta), 5.33% (J(SC) = 9.7 mA.cm(-2), V-OC = 760 mV, ff = 0.72), under simulated AM 1.5G irradiation (100 mW.cm(-2)). Density functional theory has employed to study the electron distribution and the intramolecular charge transfer (HOMO -> LUMO) of the dyes. From the calculation results of the selected dyes, we can also find the cyanoacrylic acid unit is better than the rhodanine-3-acetic acid unit as electron acceptor. Also, the electron-withdrawing groups on phenylene units as pi-spacers show the negative effect on the performance of the organic DSSCs.

  • 229. Tiseanu, C.
    et al.
    Parvulescu, V. I.
    Cojocaru, B.
    Pemartin, K.
    Sanchez-Dominguez, M.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    In situ Raman and time-resolved luminescence investigation of the local structure of ZrO 2 in the amorphous to crystalline phase transition2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 31, s. 16776-16783Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The local structure of europium doped and impregnated ZrO 2 in the amorphous state and during crystallization is investigated by in situ X-ray diffraction and in situ Raman, high-resolution transmission electron microscopy (HRTEM) and time-resolved photoluminescence spectroscopy. From Raman spectra excited at three different wavelengths (λ ex= 488, 514, and 633 nm), both phonon modes of ZrO 2 and photoluminescence (PL) corresponding to europium electronic transitions were investigated. In the as-synthetized state, samples were X-ray and Raman amorphous with few tetragonal (also monoclinic) crystallites being observed under HRTEM microscopy. In situ XRD patterns show that all samples crystallize in the tetragonal phase around 450 °C. The time-resolved PL spectra of europium doped and impregnated ZrO 2 show spectral dynamics with time delay after lamp/laser pulse which is assigned to the coexistence of the different amorphous and crystalline components or unreacted europium precursor. From in situ Raman spectra, crystallization was detected at 300-350 °C, monitoring for the characteristic tetragonal-like 5D 0- 7F 2 emission of europium at 606 nm. The ratio of tetragonal to amorphous emission increased abruptly from ca. 2-4% at 300-400 °C to almost 25% at 400-450 °C, whereas at 500 °C the emission is mostly tetragonal. A similar trend was found with the ex situ calcined samples, but relative strong tetragonal emission was observed at lower temperature in the range of 350 to 400 °C.

  • 230.
    Tissot, Heloise
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Wang, Chunlei
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Stenlid, Joakim Halldin
    Stockholm Univ, Albanova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Panahi, Mohammad
    Koc Univ, TUPRAS Energy Ctr KUTEM, TR-34450 Istanbul, Turkey.;Koc Univ, Chem Dept, TR-34450 Istanbul, Turkey..
    Kaya, Sarp
    Koc Univ, TUPRAS Energy Ctr KUTEM, TR-34450 Istanbul, Turkey.;Koc Univ, Chem Dept, TR-34450 Istanbul, Turkey..
    Soldemo, Markus
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Ghadami Yazdi, Milad
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Brinck, Tore
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Tillämpad fysikalisk kemi.
    Weissenrieder, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Interaction of Atomic Hydrogen with the Cu2O(100) and (111) Surfaces2019Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 36, s. 22172-22180Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reduction of Cu2O by hydrogen is a common preparation step for heterogeneous catalysts; however, a detailed understanding of the atomic reaction pathways is still lacking. Here, we investigate the interaction of atomic hydrogen with the Cu2O(100):(3,0;1,1) and Cu2O(111):(root 3 x root 3)R30 degrees surfaces using scanning tunneling microscopy (STM), low-energy electron diffraction, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). The experimental results are compared to density functional theory simulations. At 300 K, we identify the most favorable adsorption site on the Cu2O(100) surface: hydrogen atoms bind to an oxygen site located at the base of the atomic rows intrinsic to the (3,0;1,1) surface. The resulting hydroxyl group subsequently migrates to a nearby Cu trimer site. TPD analysis identifies H-2 as the principal desorption product. These observations imply that H-2 is formed through a disproportionation reaction of surface hydroxyl groups. The interaction of H with the (111) surface is more complex, including coordination to both Cu+ and O-CUS sites. STM and XPS analyses reveal the formation of metallic copper clusters on the Cu2O surfaces after cycles of hydrogen exposure and annealing. The interaction of the Cu clusters with the substrate is notably different for the two surface terminations studied: after annealing, the Cu clusters coalesce on the (100) termination, and the (3,0;1,1) reconstruction is partially recovered. Clusters formed on the (111) surface are less prone to coalescence, and the (root 3 x root 3)R30 degrees reconstruction was not recovered by heat treatment, indicating a weaker Cu cluster to support interaction on the (100) surface.

  • 231.
    Tissot, Heloise
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Wang, Chunlei
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Sterdid, Joakim Halldin
    Stockholm Univ, Albanova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Tillämpad fysikalisk kemi.
    Weissenrieder, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    The Surface Structure of Cu2O(100): Nature of Defects2019Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 13, s. 7696-7704Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Cu2O(100) surface is most favorably terminated by a (3,0;1,1) reconstruction under ultrahigh-vacuum conditions. As most oxide surfaces, it exhibit defects, and it is these sites that are focus of attention in this study. The surface defects are identified, their properties are investigated, and procedures to accurately control their coverage are demonstrated by a combination of scanning tunneling microscopy (STM) and simulations within the framework of density functional theory (DFT). The most prevalent surface defect was identified as an oxygen vacancy. By comparison of experimental results, formation energies, and simulated STM images, the location of the oxygen vacancies was identified as an oxygen vacancy in position B, located in the valley between the two rows of oxygen atoms terminating the unperturbed surface. The coverage of defects is influenced by the surface preparation parameters and the history of the sample. Furthermore, using low-energy electron beam bombardment, we show that the oxygen vacancy coverage can be accurately controlled and reach a complete surface coverage (1 per unit cell or 1.8 defects per nm(2)) without modification to the periodicity of the surface, highlighting the importance of using local probes when investigating oxide surfaces.

  • 232.
    Trybula, Marcela E.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Polish Academy of Sciences, Krakow, 30-059, Poland.
    Korzhavyi, Pavel A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Atomistic Simulations of Al(100) and Al(111) Surface Oxidation: Chemical and Topological Aspects of the Oxide Structure2019Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 1, s. 334-346Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The chemical and topological aspects of short- and medium-range atomic ordering on oxidized Al(100) and Al(111) surfaces have been studied by employing reactive force field-based molecular dynamics (ReaxFF-MD) simulations as a function of O-2 gas density at 300 K. We found two oxide film growth regimes, compatible with experimental and recent modeling data. Trend of changes in oxide film thickness with increasing oxygen gas density agrees with available literature data, while slightly thicker oxide film forms on the Al(100) substrate. Chemical descriptors of short- and medium-range correlation manifest difference in atom environment between two ultrathin oxide films as Al-[3,Al-4] and O-[2,O-3]-coordinated species dominate. In turn, a highly liquid-like structure of ultrathin oxide film develops on the Al(100) surface compared to an amorphous nature of the Al(111) oxide film with slightly lower thickness. Three-dimensional analysis of oxide structures reveals a medium-range atomic order formed by the arrangement of dominating corner-sharing configurations over edge-sharing ones with some deviation from the ideal polyhedral units. Three-fold ring is in majority over 2-, 4-, and 5-fold ones, in conjunction with a 2-fold ring forming the most frequent ring linkage. The high-n ring structure can be treated as a measure of a certain degree of "free volume", incorporated in the oxide film during its growth on the Al(100) or Al(111) surfaces and can initiate nanostructure formation in anodic oxide film. Such diversity in ring abundance also explains the lower mass density of the oxide films compared to crystalline alumina compounds.

  • 233.
    Tyrode, Eric
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi.
    Corkery, Robert
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi.
    Charging of Carboxylic Acid Monolayers with Monovalent Ions at Low Ionic Strengths: Molecular Insight Revealed by Vibrational Sum Frequency Spectroscopy2018Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 50, s. 28775-28786Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The charging of arachidic acid Langmuir monolayers as a function of subphase pH and monovalent ion concentration below 100 mM was investigated using vibrational sum frequency spectroscopy. Molecular information was obtained by targeting the vibrational modes of the carboxylic acid headgroups, alkyl chains, and water molecules in the immediate surface and diffuse double layers. The surface charge in the monolayer was experimentally determined by monitoring the hydrated carboxylate stretching modes. The charging behavior was found to be in excellent agreement with that predicted by Gouy-Chapman theory using a thermodynamic pK(a) of 5.1 +/- 0.2. This resulted in an apparent pK(a) of similar to 10.8 when the only ions present in solution were those associated with adjusting the pH. Water molecules with a preferred orientation in the immediate surface region were found to primarily interact with the uncharged carboxylic acid moiety, decreasing in number as the monolayer further deprotonated. Contributions from water molecules in the diffuse double layer, partly aligned by the exponentially decaying surface electric field, closely followed the predictions of a recently proposed theoretical framework that accounts for interference and screening effects. Finally, the charging of the monolayer was experimentally found to be independent of the identity of either the monovalent cation (i.e., Li+, Na+, Rb+) or anion (i.e., F-, Cl-, I-) at low salt concentrations.

  • 234.
    Tyrode, Eric
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Hedberg, Jonas
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära.
    A Comparative Study of the CD and CH Stretching Spectral Regions of Typical Surfactants Systems Using VSFS: Orientation Analysis of theTerminal CH3 and CD3 Groups2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, s. 1080-1091Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A systematic comparison between the vibrational spectra in the CD and CH stretching regions of four deuterated and perprotonated surfactants adsorbed at the liquid/vapor interface has been carried out using vibrational sum frequency spectroscopy (VSFS). Bulk IR and polarized Raman spectra of hexane and its deuterated analogue have also been obtained for reference. Due to differences in the Fermi resonances, the relative positions and intensities of the spectral features, including conformational order indicators vary between the CD and CH regions. The commonly used sum frequency (SF) order indicator for perprotonated molecules, which involves the amplitude ratio of the symmetric CH3 r(+)/ symmetric CH2 d(+) bands is not directly transposable to the CD region. Instead, the ratio between the asymmetric CH3 r(-)/ antisymmetric CD2 d(-) bands is proposed as a more suitable alternative. Using as a starting point the SF spectra from the upright all-trans monolayer of dodecanol and its deuterated analogue, the theoretically modeling of the terminal methyl group orientation has been critically evaluated. The orientational analysis in the CD region gives significantly more reliable and consistent results, mainly because of the relative simplicity in unambiguously resolving the concerned peaks in the SF spectra.

  • 235.
    Tyrode, Eric
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Johnson, Claes Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Rutland, Mark W
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Claesson, Per M
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Structure and hydration of poly(ethylene oxide) surfactants at the air/liquid interface. A vibrational sum frequency spectroscopy study2007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 31, s. 11642-11652Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Adsorption layers of penta(ethylene oxide) n-dodecyl ether (C12E5) at the air/liquid interface have been studied using the surface-sensitive technique vibrational sum frequency spectroscopy (VSFS). The CH and COC stretching vibrations of the surfactant molecule, as well as the OH stretching vibrations of the surface water molecules, have been targeted to obtain a comprehensive picture of the adsorption process. The concentration range studied comprises different adsorption regimes, starting from the neat water surface until attaining the saturated liquid expanded monolayer when approaching the critical micellar concentration (cmc). The surfactant molecules were found to first adsorb to the air-liquid interface with their hydrocarbon tails preferentially orientated close to the surface plane, surrounded by patches of unperturbed surface water. These patches were only seen to disappear at areas per molecule close to 65 A(2), coinciding with a sudden change in the orientation of the surfactant alkyl chains, which adopted a more upright configuration. Nonetheless, gauche defects in the hydrocarbon tails were observed along the whole concentration range, even above the cmc. Moreover, the poly(ethylene oxide) headgroup was seen to induce a significant structuring of the water molecules in direct proximity to the surfactant monolayer, despite being themselves substantially disordered. Comparison of the hydration fingerprint region is made with another non-ionic surfactant with a sugar-based headgroup. The temperature effect in the VSFS spectra of C12E4 and C12E8 solutions has also been considered, and the results are discussed in terms of the different models proposed to explain the peculiar temperature dependence of ethylene oxide-based surfactants and polymers in water.

  • 236.
    Tyrode, Eric
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Johnson, Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära.
    Rutland, Mark
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Day, James P. R.
    Bain, Colin D.
    A study of the adsorption of ammonium perfluorononanoate at the air-liquid interface by vibrational sum-frequency spectroscopy2007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 1, s. 316-329Artikel i tidskrift (Refereegranskat)
    Abstract [en]

     Vibrational sum frequency spectroscopy (VSFS) has been used to study the adsorption of ammonium perfluorononanoate (APFN) at the air-liquid interface, specifically targeting the C-F and carboxylate stretches. In the spectral region extending from 1050 to 1850 cm(-1), three major peaks situated at 1369, 1408, and similar to 1665 cm(-1) were detected under the polarization combinations ssp, ppp, and sps. The first of these peaks was assigned to CF3 stretching vibrations after a detailed comparison with other surfactant molecules with different degrees of fluorination, while the last two resonant features were assigned to symmetric and antisymmetric carboxylate stretching vibrations. From the combined analysis of the VSFS, ellipsometry, and previous FTIR measurements, a consistent physical model for the adsorption of APFN to the liquid surface is proposed. At low surface coverages the APFN molecules lie essentially flat on the surface. At concentrations from 1 mM to the critical micellar concentration (molecular areas < 70 angstrom(2)) the mean orientation of both the surfactant head group and terminal CF3 group remained constant. The formation of surface micelles at higher concentrations is consistent with the experimental data.

  • 237.
    Tyrode, Eric
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Liljeblad, Jonathan F. D.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Water Structure Next to Ordered and Disordered Hydrophobic Silane Monolayers: A Vibrational Sum Frequency Spectroscopy Study2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 4, s. 1780-1790Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vibrational sum frequency spectroscopy (VSFS) has been used to study the structure of water incontact to fused silica surfaces, hydrophobically modified with series of alkyl trichlorosilanemonolayers of varying degrees of order. The interfacial molecular structural information wascomplemented using total internal reflection (TIR) Raman spectroscopy. The silane moleculesconsisted of octadecyltrichlorosilane (OTS) and its shorter chain analogue with eight carbonatoms. The VSFS spectra show a direct correlation between monolayer order and the intensity ofthe free OH mode, characteristic of straddling water molecules vibrating in direct contact to thehydrophobic layer, with a concurrent reduction of the bands associated with hydrogen bondedwater molecules. The results imply that the structure of water in the most ordered monolayers isnot much affected beyond the first layer of water molecules, with bulk isotropic propertiesbecoming apparent already at sub-nanometer distances from the surface. Contact anglemeasurements with both water and hexadecane were also performed in an effort to relatemacroscopically measureable parameters to the molecular surface structure provided by VSFSand TIR Raman. Only the receding contact angles, and in particular those with hexadecane, werefound to correlate with the monolayer order. Finally, to obtain an additional insight into the waterstructure in direct contact to an ordered hydrophobic surface, isotopic dilution experiments withD2O were also performed. They indicate that the vibrational coupling mechanism of watermolecules at the hydrophobized solid/water interface is different from what has been observed atthe liquid/vapor interface.

  • 238. Vahlberg, C.
    et al.
    Linares, M.
    Norman, Patrick
    Linköping University, Sweden.
    Uvdal, K.
    Phenylboronic ester- and phenylboronic acid-terminated alkanethiols on gold surfaces2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 1, s. 796-806Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, it is shown that a well-organized monolayer of phenylboronic ester-terminated thiol (BOR-capped) on gold surfaces can be prepared. Our results also show that the BOR-capped molecular system can be cleaved directly on the surface, resulting in an unprotected BOR-uncapped monolayer with the boronic acid functional groups available for coordination to diol molecules in the ambient media. The monolayers of BOR-capped and BOR-uncapped were characterized using infrared spectroscopy, near edge X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, and contact angle goniometry. The X-ray photoelectron spectroscopy results showed that both BOR-capped and BOR-uncapped are chemically linked to the gold substrate. According to the infrared spectroscopy results, the main component of the C=O vibrational mode present in the amide moiety is perpendicular oriented relative to the gold surface normal for the BOR-capped molecular system. The near edge X-ray absorption fine structure spectroscopy resonance peak located at approximately 285 eV, assigned to π 1* transitions, was used to estimate the average tilt angle of the vector parallel to the π* orbitals of the aromatic ring relative to the gold surface normal. The average tilt angle is estimated to be approximately 63° for the BOR-capped monolayer on gold surfaces. The aromatic ring of the BOR-uncapped molecule has a more tilted orientation compared to the BOR-capped one. The experimental infrared spectroscopy and near edge X-ray absorption fine structure spectroscopy results were supported with theoretical modeling including calculations of vibrational modes and of excitation processes.

  • 239. Vahlberg, C.
    et al.
    Linares, M.
    Villaume, S.
    Norman, Patrick
    Linköping University, Sweden.
    Uvdal, K.
    Noradrenaline and a thiol analogue on gold surfaces: An infrared reflection-absorption spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy study2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 1, s. 165-175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Self-assembled monolayers and multilayers of a noradrenaline analogue (Nor-Pt) on gold substrates as well as multilayers of noradrenaline have been investigated by means of the molecular orientation, the molecule-surface interaction, the molecular composition and the functional group availability for further biointeraction processes, using X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRAS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. A chemical shift (1.7 eV) of the S 2p peak to lower binding energies is observed, in the XPS spectrum, indicating that the Nor-Pt molecules are chemisorbed onto the gold substrate. The IR results show that Nor-Pt adsorbate has the C=O stretching vibration modes parallel oriented relative to the gold substrate. The average tilt angle of the aromatic ring relative to the gold surface normal is determined to be approximately 51°, based on the NEXAFS measurements on Nor-Pt monolayers. The experimental results and assignments are supported with theoretical studies where we use the building block principle in the spectral analysis and compare with the measurements of noradrenaline and Nor-Pt. The theoretical calculations are shown to be useful; for angle dependence NEXAFS studies as resonances with fully φ* or σ* character are preferred for correct analysis.

  • 240. Varga, A.
    et al.
    Endrődi, Balázs
    University of Szeged, Hungary.
    Hornok, V.
    Visy, C.
    Janáky, C.
    Controlled Photocatalytic Deposition of CdS Nanoparticles on Poly(3-hexylthiophene) Nanofibers: A Versatile Approach to Obtain Organic/Inorganic Hybrid Semiconductor Assemblies2015Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, s. 28020-28027Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To efficiently harness the possible synergies, stemming from the combination of organic conducting polymers and inorganic semiconductors; sophisticated assembling methods are required to control the composition and morphology at the nanoscale. In this proof-of-concept study, we demonstrate the in situ photocatalytic deposition of CdS nanoparticles on poly(3-hexylthiophene) (P3HT) nanofibers, exploiting the semiconducting nature of this polymer. The formation of the hybrid assembly was monitored by UV-vis and Raman spectroscopy, Energydispersive X-ray microanalysis, and X-ray diffraction (XRD). Transmission electron microscopic studies and AFM images confirmed that both the particle size and the loading can be tuned by the deposition time. Photoelectro chemical studies revealed the facile transfer of photogenerated electrons from P3HT to CdS, as well as that of the holes from CdS to P3HT. It is believed that ensuring intimate contact between the components in these nanohybrids will open new avenues in various application schemes, e.g., solar energy conversion.

  • 241.
    Vargas-Florencia, Dulce
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Furo, Istvan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Edvinsson, Tomas
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Pores in nanostructured TiO2 films. Size distribution and pore permeability2007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 21, s. 7605-7611Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanoporous films of crystalline anatase with intended application in dye-sensitized photovoltaic cells were investigated by NMR cryoporometry, NMR diffusiometry, electron microscopy, and X-ray diffraction. The nanoparticles from which the films were subsequently sintered were prepared in two ways, one with an acidic and one with a basic aqueous process environment and along different temperature regimes. The average morphology was similar in all films as indicated by the roughly identical < 2 kappa V/S > values where kappa is the mean curvature of the pore surface and S/V denotes the surface-to-volume ratio. Self-diffusion of water in the pores is strongly reduced with respect to that of bulk and is influenced both by micrometer-scale obstructions to molecular displacement and by pore-size effect in pore interconnectivity. The investigated samples exhibit different transport regimes as concerning those phenomena. In this initial study performed on a limited set of samples, we found no linear correlation between particle and pore sizes. Instead, total porosity is controlled by particle-particle jamming which, together with particle size polydispersity, may also dominate the effects that lead to the observed pore size distributions for the different samples. The rich variation of structural effects and transport properties among the few prepared films call for further studies in order to find an optimal film structure.

  • 242. Vegelius, J. R.
    et al.
    Kvashnina, K. O.
    Hollmark, H.
    Klintenberg, M.
    Kvashnin, Y. O.
    Soroka, Inna L.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Werme, L.
    Butorin, S. M.
    X-ray Spectroscopic Study of Cu2S, CuS, and Copper Films Exposed to Na2S Solutions2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 42, s. 22293-22300Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic structure of copper sulfides was studied using X-ray absorption at Cu K and L-2,L-3 and S L-2,L-3 edges and X-ray emission spectroscopy at S L-2,L-3 thresholds. The experimental data were compared with results of local density approximation calculations taking into account the calculated valence band contributions and core-level chemical shifts between inequivalent sites. The presence of divalent Cu was detected in CuS with X-ray absorption spectroscopy in the high-energy-resolution fluorescence detection (HERFD) mode. The S L-2,L-3 emission spectrum of CuS was found to be significantly broader than that of Cu2S due to contributions from inequivalent S sites. This difference in the spectral width was used to distinguish between sulfide species formed on the Cu foil exposed to Na2S solutions. The Cu-S interaction processes for Cu films of different thicknesses exposed to Na2S solutions were monitored in situ using X-ray absorption spectroscopy in the HERFD mode at the Cu K edge. It was found that Cu ions were diffusing in the sulfide and entering the solution. The rate at which Cu ions enter the solution via diffusion was estimated on the basis of the results for a 1000 angstrom thick film.

  • 243.
    von Schenck, Henrik
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Kumar, Neil
    Klug, Christopher A.
    Sinfelt, John H.
    NMR study of the chemisorption and decomposition of methylamine on Rh/SiO22007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 21, s. 7783-7794Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nuclear magnetic resonance (NMR) studies of the interaction of methylamine with the rhodium surface in a Rh/SiO2 catalyst at temperatures in the range of 253-298 K reveal two principal features in both the C-13 and N-15 spectra. One feature is a resonance occurring at a frequency very close to the resonance frequency for methylamine gas. This feature is attributed to methylamine molecules adsorbed without dissociation. Because the methylamine is not removed from the catalyst surface by evacuation to 10(-6) Torr, its interaction with the surface is reasonably strong. The silica support does not retain methylamine after such an evacuation, and therefore, the adsorbed methylamine is associated with the rhodium. The other feature in both the C-13 and N-15 spectra is a very broad resonance occurring downfield of the resonance for the nondissociatively adsorbed methylamine. It is attributed to partially dehydrogenated surface species designated by the generalized formula (CN)H-x. Incipient scission of carbon-nitrogen bonds is observed at room temperature. As the temperature is increased above room temperature, the extent of scission of the carbon-nitrogen bonds increases. Ammonia, methane, and higher-carbon-number hydrocarbons then appear in the gas phase. The nondissociatively adsorbed methylamine is continuously transformed into the species (CN)H-x, thereby releasing hydrogen on the surface. The hydrogen is consumed in the production of the ammonia and methane observed in the gas phase. Ammonia is formed much more readily than methane or the other hydrocarbons, with the result that the species remaining on the surface are rich in carbon relative to nitrogen.

  • 244.
    Von Schenck, Henrik
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Kumar, Neil
    Klug, Christopher A.
    Sinfelt, John H.
    NMR study of the chemisorption and surface chemistry of methylamine on Pd/SiO22008Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, nr 8, s. 3042-3048Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Results of an investigation of the interaction of methylamine with a Pd/SiO2 catalyst utilizing nuclear magnetic resonance (NMR) spectroscopy are presented. Two sets of experiments were conducted. In one set, a sample of catalyst was initially exposed to (CH3NH2)-C-13-N-15 at 77 K and then subjected to a lengthy equilibration period at 190 K. A C-13 spectrum at 77 K obtained on the sample at this point exhibited a single symmetric line at a frequency very close to the resonance frequency for methylamine in the absence of the catalyst. The line is attributed to methylamine adsorbed without dissociation. In C-13 spectra obtained at 77 K on the sample after each of a series of subsequent annealing periods at successively higher temperatures in the range 253-298 K, the line exhibited a gradual broadening on the downfield side. Deconvolution of the spectra resolved the original symmetric line from a very broad downfield line attributed to partially dehydrogenated surface species designated by the formula (CN)H-x. In the second set of experiments, (CH3NH2)-C-13-N-15 was adsorbed on a sample of catalyst at 298 K. The sample was then annealed at successively higher temperatures in the range 325-450 K. Deconvolution of the C-13 spectra obtained at 298 K after the various annealing periods revealed extensive formation of dimethylamine, reaching a maximum after the annealing period at 400 K. Ammonia and methane were first detected in the N-15 and C-13 spectra, respectively, after the annealing period at 375 K. During the annealing periods at 425 and 450 K, the dimethylamine decomposed almost completely, leaving only methane, ammonia, and residual surface species.

  • 245.
    Wang, Baochang
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kanhere, Pushkar D.
    Chen, Zhong
    Nisar, Jawad
    Pathak, Biswarup
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Anion-Doped NaTaO3 for Visible Light Photocatalysis2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 44, s. 22518-22524Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we have employed DFT and HSE06 methods to study the doping effects on the NaTaO3 photocatalyst. N, S, C, and P monodoping and N-N, C-S, P-P, and N-P codoping have been studied. The redopants' formation energies have been calculated, and we find S monodoping is energetically more favorable than any other elemental doping. The mechanism of anion doping on the electronic properties of NaTaO3 is discussed. We find the band gap reduces significantly if we dope with anionic elements whose p orbital energy is higher than the O 2p orbitals. N and S can shift the valence band edge upward without losing the ability to split water into H-2 and O-2. Double-hole-mediated codoping can decrease the band gap significantly. On the basis of our calculations, codoping with N-N, C-S, and P-P could absorb visible light. However, they can only decompose water into H-2 when the valence band edge is above the water oxidation level.

  • 246.
    Wang, Chunlei
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Tissot, Heloise
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Escudero, Carlos
    Alba Synchrotron Light Source, Carrer Llum 2-26, Barcelona 08290, Spain..
    Perez-Dieste, Virginia
    Alba Synchrotron Light Source, Carrer Llum 2-26, Barcelona 08290, Spain..
    Stacchiola, Dario
    Brookhaven Natl Lab, Ctr Funct Nanomat, Upton, NY 11973 USA..
    Weissenrieder, Jonas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Redox Properties of Cu2O(100) and (111) Surfaces2018Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 50, s. 28684-28691Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Intense research efforts are directed toward Cu and Cu2O based catalysts as they are viewed as potential replacements for noble metal catalysts. However, applications are hampered by deactivation, e.g., through facile complete oxidation to CuO. Despite the importance of the redox processes for Cu2O catalysts, a molecular level understanding of the deactivation process is still lacking. Here we study the initial stages of oxidization of well-defined Cu2O bulk single crystals of (100) and (111) termination by means of synchrotron radiation X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). Exposure of the (100) surface to 1 mbar O-2 at 25 degrees C results in the formation of a 1.0 monolayer (ML) CuO surface oxide. The surface is covered by 0.7 ML OH groups from trace moisture in the reaction gas. In contrast, neither hydroxylation nor oxidation was observed on the (111) surface under similar mild exposure conditions. On Cu2O(111) the initial formation of CuO requires annealing to similar to 400 degrees C in 1 mbar 02, highlighting the markedly different reactivity of the two Cu2O surfaces. Annealing of the (100) surface, under ultrahigh vacuum conditions, to temperatures up to similar to 225 degrees C resulted in removal of the OH groups (0.46 ML decrease) at a rate similar to a detected increase in CuO coverage (0.45 ML increase), suggesting the reaction path 2OH(adsorbed) + CU2Osolid -> H2Ogas + 2CuO(solid). STM was used to correlate the observed changes in surface chemistry with surface morphology, confirming the surface hydroxylation and CuO formation. The STM analysis showed dramatic changes in surface morphology demonstrating a high mobility of the active species under reaction conditions.

  • 247. Wang, Guang-Wei
    et al.
    Ma, Yong
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Shandong Normal Univ, Peoples R China.
    Song, Xiu-Neng
    Jiang, Shou-Zhen
    Yue, Wei-Wei
    Wang, Chuan-Kui
    Luo, Yi
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Univ Sci & Technol China, Peoples R China.
    Theoretical Isomer Identification of Three C-56 Fullerenes and Their Chlorinated Derivatives by XPS and NEXAFS Spectra2016Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 25, s. 13779-13786Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The C Is X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy for three C-56 fullerene isomers and their chlorinated derivatives have been theoretically simulated by means of density functional theory (DFT). Compared with XPS, the NEXAFS spectra present remarkable dependence on the structures of all the studied molecules and thus can be used to identify the three C-56 isomers and chlorinated species. The spectra of the chlorinated species present significant variations compared with the pristine fullerenes. The spectral components of carbon atoms of different local environment have been investigated as well. The spectra of carbons saturated by chlorine atoms exhibit a shift toward higher energies compared with the others.

  • 248. Wang, Richard B.
    et al.
    Koerbel, Sabine
    Saha, Santanu
    Botti, Silvana
    Skorodumova, Natalia V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. Uppsala University, Sweden.
    Structure and Optical Properties of Small (TiO2)(n) Nanoparticles, n=21-242017Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, nr 17, s. 9528-9536Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recently, nanostructured TiO2 ("black TiO2") has been discovered to absorb visible light, which makes, it an efficient material for water splitting. Hydrogenization has been proposed to be at the origin of this beneficial electronic structure of black TiO2. Here, we investigate, using ab initio methods, alternative mechanisms related to structure modifications in nanoclusters that could be responsible for absorption in the visible range. To that end, we apply a combination of computational structure prediction using simulated annealing and minima-hopping methods based on density-functional theory to predict low-energy configurations and time-dependent density-functional theory (TDDFT) using a hybrid functional with optimized Hartree Fock content to obtain optical absorption edges.

  • 249. Wersäll, Martin
    et al.
    Verre, Ruggero
    Svedendahl, Mikael
    Chalmers University of Technology, Sweden.
    Johansson, Peter
    Käll, Mikael
    Shegai, Timur
    Directional Nanoplasmonic Antennas for Self-Referenced Refractometric Molecular Analysis2014Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 36, s. 21075-21080Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Localized surface-plasmon resonance (LSPR) sensors are typically based on tracing resonance peak shifts that precisely follow changes in the local refractive index. Such measurements usually require a spectrometer, a stable light source, and an accurate LSPR position tracing technique. As a simple but efficient alternative, we investigated a self-referenced single-wavelength sensing scheme based on angle-dependent and highly directional radiation patterns originating from a monolayer of asymmetric gold nanodimers. We found that one could easily trace a model biotinneutravidin recognition reaction as well as minute bulk refractive index changes, by measuring the intensity ratio between the light scattered in two different directions with respect to the dimers. The refractometric resolution of the methodology was estimated to be on the order of Delta n approximate to 10(-5) RIU. These results may be particularly useful for label-free biosensing applications that require a combination of simple and cost-effective optical readout with a reasonable sensitivity.

  • 250. Wiberg, Joanna
    et al.
    Marinado, Tannia
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Hagberg, Daniel P.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Albinsson, Bo
    Effect of Anchoring Group on Electron Injection and Recombination Dynamics in Organic Dye-Sensitized Solar Cells2009Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 9, s. 3881-3886Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the field of dye-sensitized solar cells, the number of different sensitizing dyes is increasing rapidly. To produce low-cost dyes, much work is being directed toward synthesizing all-organic, ruthenium-free dyes with high extinction coefficients and broad absorption bands with large solar spectrum overlap. One of the best dyes, the polyene-diphenylaniline dye D5L2A1, has a rather blue absorption with an IPCE onset at around 650 nm, but it still has an energy conversion efficiency of almost 6%. To increase the overlap with the solar spectrum, the cyanoacrylic acid anchoring group was changed to rhodanine-3-acetic acid in complex D5L2A3. This gave an IPCE onset at around 750 nm, but unfortunately, it also decreased the overall efficiency to a modest 1.7%. By femtosecond transient absorption, we show that the electron injections into TiO2 for the two dyes are ultrafast and indistinguishable with our time resolution (< 200 fs). However, charge recombination is also ultrafast, with different fractions of a ca. 500-fs component for the two dyes. Yet, the fraction of the faster decay component is larger for D5L2A3 than for D5L2A1. Here, we provide an interpretation of the implications of changing anchoring group. We believe that a lack of electron density oil the binding oxygens of the D5L2A3 LUMO, due to the rhodanine group, promotes a higher probability for electron injection to short-lived surface trap states compared to the situation for the fully conjugated D5L2A1.

23456 201 - 250 av 277
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf