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  • 151.
    Liu, Peng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Nisar, Jawad
    Sa, Baisheng
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Pathak, Biswarup
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Anion-Anion Mediated Coupling in Layered Perovskite La2Ti2O7 for Visible Light Photocatalysis2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 27, s. 13845-13852Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Anionic-anionic (N-N, P-P, N-P, and C-S) mediated coupling can be introduced in the layered perovskite La2Ti2O7 structure for visible light photocatalysis. The anionic-anionic codoped La2Ti2O7 systems lower the band gap much more than their respective monodoping systems. Moreover, the electronic band positions of the doped systems with respect to the water oxidation/reduction potentials show that codoped (N-N, N-P, and C-S) systems are more promising candidates for visible-light photocatalysis. The calculated defect formation energy shows that the codoped systems are more stable than their respective monodoped systems.

  • 152.
    Loiko, Pavel
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Pollnau, Markus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Stochastic Model of Energy-Transfer Processes Among Rare-Earth Ions. Example of Al2O3:Tm3+2016Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 46, s. 26480-26489Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Energy-transfer processes strongly affect the performance of lanthanide-doped photonic devices. In this work, we introduce a simple stochastic model of energy-transfer processes and successfully apply it to the example of cross-relaxation (CR) and energy-transfer upconversion (ETU) in amorphous Al2O3:Tm3+ waveguides on silicon intended for lasers operating at similar to 2 mu m. The stochastic model is based on the rate-equation formalism and considers two spectroscopically distinct ion classes, namely single ions and ions with neighbors (pairs and clusters), with the corresponding ion fractions being dependent on the doping concentration. We prove that a more accurate description of the luminescence properties of amorphous Al2O3:Tm3+ is obtained when accounting for the presence of these distinct ion classes. Based on the developed model, we derive microscopic CR and ETU parameters of C-CR = 5.83 X 10(-38) cm(6) s(-1), C-ETU1 = 0.93 x 10(-40) cm(6) s(-1), and C-Eru2 = 7.81 x 10(-40) cm(6) s(-1), and determine the laser quantum efficiency eta(q) of excitation of Tm3+ ions in the upper laser level. For the maximum Tm3+ concentration of 5.0 X 10(20) cm(-3) studied experimentally in this investigation, eta(q) reaches 1.73. Furthermore, the transition cross sections at the pump and laser wavelengths are determined. For the H-3(6) -> F-3(4) transition, the maximum stimulated-emission cross section is sigma(e) = 0.47 X 10(-20) cm(2) at 1808 nm.

  • 153.
    Lousada, Claudio M.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Johansson, Adam Johannes
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Mechanism of H2O2 Decomposition on Transition Metal Oxide Surfaces2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 17, s. 9533-9543Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We performed an experimental and density functional theory (DFT) investigation of the reactions of H2O2 with ZrO2, TiO2, and Y2O3. In the experimental study we determined the reaction rate constants, the Arrhenius activation energies, and the activation enthalpies for the processes of adsorption and decomposition of H2O2 on the surfaces of nano- and micrometersized particles of the oxides. The experimentally obtained enthalpies of activation for the decomposition of H2O2 catalyzed by these materials are 30 +/- 1 kJ.mol(-1) for ZrO2, 34 +/- 1 kJ.mol(-1) for TiO2, and 44 +/- 5 kJ.mol(-1) for Y2O3. In the DFT study, cluster models of the metal oxides were used to investigate the mechanisms involved in the surface process governing the decomposition of H2O2. We compared the performance of the B3LYP and M06 functionals for describing the adsorption energies of H2O2 and HO center dot onto the oxide surfaces as well as the energy barriers for the decomposition of H2O2. The DFT models implemented can describe the experimental reaction barriers with good accuracy, and we found that the decomposition of H2O2 follows a similar mechanism for all the materials studied. The average absolute deviation from the experimental barriers obtained with the B3LYP functional is 6 kJ.mol(-1), while with the M06 functional it is 3 kJ.mol(-1). The differences in the affinity of the different surfaces for the primary product of H2O2 decomposition, the HO radical, were also addressed both experimentally and with DFT. With the experiments we found a trend in the affinity of HO center dot toward the surfaces of the oxides, depending on the type of oxide. This trend is successfully reproduced with the DFT calculations. We found that the adsorption energy of HO center dot varies inversely with the ionization energy of the metal cation present in the oxide.

  • 154.
    Lousada, Claudio M.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Kinetics, Mechanism, and Activation Energy of H2O2 Decomposition on the Surface of ZrO22010Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 25, s. 11202-11208Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The kinetics, mechanism, and activation energy of H2O2 decomposition in ZrO2 particle suspensions were studied. The obtained first-order and second-order rate constants for the decomposition of H2O2 in the presence of ZrO2 at T = 298.15 K produced the values k(1) = (6.15 +/- 0.04) x 10(-5) s(-1) and k(2) = (2.39 +/- 0.09) x 10(-10) m.s(-1), respectively. The dependency of the reaction first-order rate constant with temperature was studied; consequently, the activation energy for the reaction was obtained in the temperature interval 294.15-353.15 K having yielded the value E-a = 33 +/- 1.0 kJ.ma(-1). The dependency of the zeroth-order reaction rate constant with pH was investigated and discussed. A mechanistic study encompassing the investigation of the dynamics of formation of hydroxyl radicals during the course of the reaction was performed. A version of the modified Hantzsch method was applied for this purpose, and it was verified that the dynamics of formation of hydroxyl radicals during the reaction are in good agreement with the proposed reaction mechanism.

  • 155.
    Lousada, Claudio M.
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Sophonrat, Nanta
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Weihong, Yang
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Energi- och ugnsteknik. KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Tillämpad termodynamik och kylteknik.
    Mechanisms of Formation of H, HO, and Water and of Water Desorption in the Early Stages of Cellulose Pyrolysis2018Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 23, s. 12168-12176Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Here, we report the results from a combined first-principles and experimental investigation of the initial stages of decomposition of cellulose during heating in pyrolysis. Density functional theory calculations with periodic boundary conditions were performed to investigate the formation of H and HO radicals and of the molecular products H2O, H-2, and H2O2 originating from their recombination. The stabilization that alcohol groups impart to adjacent C-radicals and the allylic recombination of unpaired electrons of neighboring C-radicals play decisive roles in the decomposition mechanism. This makes the simultaneous formation of H-center dot from C2 and HO center dot from C3 the most favorable process. The recombination of these radicals to form water leads to an additional stabilization of the reaction. The computed temperature-dependent reactions Gibbs' free energies reveal that desorption of H2O from intact cellulose occurs at T = 147 degrees C and that gas-phase water forms spontaneously from the decomposition of cellulose at T = 282 degrees C. These results are in excellent agreement with our experimental study of the pyrolysis done with pyrolysis gas chromatography/mass spectrometry at different temperatures. The experiments show that upon heating, a small amount of water is released from cellulose at 210 degrees C, and a considerably larger amount starts to be released at 280 degrees C.

  • 156.
    Lousada, Claudio Miguel
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Johansson, Adam Johannes
    Korzhavyi, Pavel A
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialteknologi.
    Thermodynamics of H2O Splitting and H-2 Formation at the Cu(110)-Water Interface2015Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, nr 25, s. 14102-14113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We used density functional theory to investigate the sequential oxidation of the (110) surface of fcc copper triggered by the dehydrogenation of molecularly adsorbed water the reactions studied did not involve any oxygen besides that present in the water molecules. According to the obtained Gibbs free energies, the formation of half a inonolayer of HO and the corresponding amount of hydrogen gas is spontaneous (Delta(r)G(0) < 0) starting from a monolayer of adsorbed water at Cu(110) The subsequent dehydrogenation steps necessary to ultimately form one monolayer of O atoms are nonspontaneous (Delta(r)G(o) > 0). We present a computationally efficient approach which shows good accuracy for determining the solvation energy of the Cu(110) surface, deviating only by 0.014 eV from literature data. The solvation effect imparts additional stabilization to several oxygen-containing species adsorbed at the Cu(110) surface. Additionally, we investigated the effect of an overlayer of water molecules at the surface where the dehydrogenation of H2O takes place. We found that even though the Gibbs free energy changes associated with the first steps of dehydrogenation of H2O at the Cu surface do not differ substantially from those without an additional water layer, subsequent dehydrogenation steps are favored by as much as 1.6 eV. In view of these results we discuss the importance of the hydrogen-bonding network formed when an overlayer of H2O is present in determining the reactivity of surface species. Additionally, we found a considerable effect of the second water layer on the surface relaxation, which differs significantly from the case where no second water layer is present. The hydrogen-bonding network has an important role in affecting the chemistry of the surface species but also in stabilizing the surface itself, which in turn affects the surface relaxation. These findings shed additional light on the modeling of surface processes in solution, which have implications for corrosion science and catalysis.

  • 157. Lu, Zhansheng
    et al.
    Kullgren, Jolla
    Yang, Zongxian
    Hermansson, Kersti
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Sulfidation of Ceria Surfaces from Sulfur and Sulfur Diffusion2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 15, s. 8417-8425Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Even very low levels of sulfur contaminants can degrade the catalytic performance of cerium oxide. Here, the interaction of atomic sulfur with the ceria (111) and (110) surfaces has been studied using first-principles methods. Two sulfoxy species are identified: oxido-sulfate(2-) species (SO2-) on both the CeO2(111) and (110) surfaces and hyposuffite (SO22-) on the (110) surface. Sulfide (S2-) is formed when a surface or a subsurface oxygen atoms is replaced by sulfur. These sulfide species are more stable at the surface. Furthermore, sulfite (SO32-) structures are found when sulfur is made to replace one Ce in the ceria (111) and (110) surfaces. The calculated sulfur diffusion barriers are larger than 1.4 eV for both surfaces, and thus sulfur is essentially immobile, providing a possible explanation for the sulfidation phenomena of the ceria-based catalyst. Thus, we find three different species from interaction of S with ceria which are all, due to their strong binding, capable of poisoning the surface, reduced or unreduced. Our results suggest that under reducing conditions sulfur is likely to be found in the (111) surface (replacing oxygen) but on the (110) surface (as SO22-).

  • 158. Löfås, H.
    et al.
    Orthaber, A.
    Jahn, B. O.
    Rouf, A. M.
    Grigoriev, A.
    Ott, S.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ottosson, H.
    New class of molecular conductance switches based on the [1,3]-silyl migration from silanes to silenes2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 21, s. 10909-10918Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    On the basis of first-principles density functional theory calculations, we propose a new molecular photoswitch which exploits a photochemical [1,3]-silyl(germyl) shift leading from a silane to a silene (a Si=C double bonded compound). The silanes investigated herein act as the OFF state, with tetrahedral saturated silicon atoms disrupting the conjugation through the molecules. The silenes, on the other hand, have conjugated paths spanning over the complete molecules and thus act as the ON state. We calculate ON/OFF conductance ratios in the range of 10-50 at a voltage of +1 V. In the low bias regime, the ON/OFF ratio increases to a range of 200-1150. The reverse reaction could be triggered thermally or photolytically, with the silene being slightly higher in relative energy than the silane. The calculated activation barriers for the thermal back-rearrangement of the migrating group can be tuned and are in the range 108-171 kJ/mol for the switches examined herein. The first-principles calculations together with a simple one-level model show that the high ON/OFF ratio in the molecule assembled in a solid state device is due to changes in the energy position of the frontier molecular orbitals compared to the Fermi energy of the electrodes, in combination with an increased effective coupling between the molecule and the electrodes for the ON state.

  • 159. Löfås, Henrik
    et al.
    Ernanuelsson, Rikard
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120, Uppsala, Sweden .
    Grigoriev, Anton
    Ottosson, Henrik
    Conductance through Carbosilane Cage Compounds: A Computational Investigation2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 42, s. 21692-21699Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Silicon is still the dominating material in microelectronics, yet primarily conjugated hydrocarbons are investigated in the field of single-molecule electronics even though linear oligosilanes are a-conjugated. A drawback with the latter is their high conformational flexibility which strongly affects conductance. Here we report on a first principles density functional theory investigation of a series of rigid [2.2.2]bicyclic carbosilanes with 3, 2, 1, or 0 disilanylene bridges, providing all-silicon paths for charge transport. It is explored if these paths can be seen as independent and equivalent current paths acting as parallel resistors. For high conductance through the carbosilanes they need to be anchored to the gold electrodes via groups that are matched with the a-conjugated paths of the oligosilane cage segment, and we find that silyl (SiH3) groups are better matched than thiophenol groups. Even for the carbosilane with three disilanylene bridges we find that the most transmitting conductance channel is not equally distributed on the three parallel bridges. In addition, there is significant communication between the various pathways, which results in destructive interference lowering the conductance. Taken together, the different disilanylene bridges in the cage compounds do not act as parallel resistors.

  • 160. Mahabal, Manasi S.
    et al.
    Deshpande, Mrinalini D.
    Hussain, Tanveer
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Sensing Characteristics of Phosphorene Monolayers toward PH3 and AsH3 Gases upon the Introduction of Vacancy Defects2016Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 36, s. 20428-20436Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Motivated by the exceptional interest of researchers in two-dimensional nanostructures, the current study deals with the structural, electronic, optical, and gas sensing properties of recently synthesized monolayer phosphorene. Van der Waals induced first-principles calculations were performed to study the binding mechanism of pristine and defected phosphorene towards the toxic gases PH3 and AsH3. The preferential sites and orientations of these molecules on the phosphorene sheet were determined, and a detailed analysis of the adsorption energetics was performed. Both of the gas molecules interact weakly with the phosphorene sheet, with AsH3 the binding was slightly stronger than PH3. The creation of defects such as monovacancies and divacancies in the phosphorene sheet was found to significantly enhance the adsorption mechanism. The adsorption energies of both PH3 and AsH3 improved by factors of four and three, respectively, as compared to their values on pristine phosphorene. The adsorption mechanism was further investigated by plotting the band structure and density of states. We also studied the optical properties and the static dielectric matrices of these nanostructures using density functional perturbation theory. Our findings showed that defected phosphorene with vacancies can be considered as an efficient sensor for toxic gases.

  • 161.
    Mahani, Mohammad Reza
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Mirsakiyeva, Amina
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Delin, Anna
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. KTH, Centra, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Breakdown of Polarons in Conducting Polymers at Device Field Strengths2017Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, nr 19, s. 10317-10324Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Conducting polymers have become standard engineering materials used in many electronic devices. Despite this, there is a lack of understanding of the microscopic origin of the conducting properties, especially at realistic device field strengths. We present simulations of doped poly(p-phenylene) (PPP) using a Su-Schrieffer-Heeger (SSH) tight-binding model, with the electric field included in the Hamiltonian through a time-dependent vector potential via Peierls substitution of the phase factor. We find that polarons typically break down within less than a picosecond after the field has been switched on, already for electric fields as low as around 1.6 mV/angstrom. This is a field strength common in many flexible organic electronic devices. Our results challenge the relevance of the polaron as charge carrier in conducting polymers for a wide range of applications.

  • 162. Makhal, A.
    et al.
    Sarkar, S.
    Bora, T.
    Baruah, S.
    Dutta, Joydeep
    School of Engineering and Technology, Asian Institute of Technology,.
    Raychaudhuri, A. K.
    Pal, S. K.
    Role of resonance energy transfer in light harvesting of zinc oxide-based dye-sensitized solar cells2010Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 23, s. 10390-10395Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this contribution we have studied the dynamics of light harvesting of ZnO nanoparticles (NPs) to a surface adsorbed sensitizing dye (SD) N719. By using the picosecond resolved Forster resonance energy transfer (FRET) technique we have explored that the excited ZnO NPs resonantly transfer visible optical radiation to the SD N719. The consequence of the energy transfer on the performance of the overall efficiency of a model ZnO NP-based dye-sensitized solar cell (DSSC) has also been explored. We have demonstrated that the overall efficiency of a ZnO NP-based solar cell significantly depends on the presence of high-energy photons in the solar radiation. In a control experiment on a model TiO2 NP-based solar cell it has been demonstrated that the presence of high-energy photon has a minimal effect on the performance of the cell as the TiO2 NPs are incapable of harvesting high-energy photons from solar radiation. The possibility of the back electron transfer from the excited NPs to the SD has also been investigated by studying the NPs in the presence of an ideal electron accepting organic molecule, benzoquinone (BQ). The time constants and nonradiative rate constant obtained for the ZnO/N719 system are found to be different from those of the ZnO/BQ system, which rules out the possibility of back electron transfer from ZnO NPs to SD N719. Moreover, the observed FRET dynamics in the light harvesting process of the nanocrystalites may be efficient in the further use of the nanoparticles in the development of new photodevices.

  • 163.
    Marinado, Tannia
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Edvinsson, Tomas
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Boschloo, Gerrit
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Influence of π-Conjugation Units in Organic Dyes for Dye-Sensitized Solar Cells2007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 4, s. 1853-1860Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two organic dyes with the general structure donor-conjugated chain-acceptor (D-pi-A) have been investigated as sensitizers for nanocrystalline TiO2 solar cells. The electron donor and acceptor groups were pyrrolidine and cyano acrylic acid, respectively. The conjugated chain of 2-cyano-3-{5-[2-(4-pyrrolidin-1-ylphenyl)vinyl]thiophen-2-yl}acrylic acid contains one phenyl ring and a thiophene unit and is therefore denoted PT, while for 2-cyano-3-{5 -[2-(5-pyrrolidin-1-ylthiophen-2-yl)vinyl]thiophen-2-yl}acrylic acid the phenyl ring is replaced by a second thiophene unit (TT). Solar-to-electrical energy conversion efficiencies under simulated AM 1.5 irradiation (1000 W m(-2)) of 2.3% were obtained for solar cells based on PT but of less than 0.05% for those based on TT. The reasons for the dramatic difference of the efficiencies were analyzed. Photoinduced absorption measurements revealed that the TT dye was not properly regenerated by redox electrolyte after electron injection. This sluggish regeneration is probably due to the 0.3 V less positive HOMO level for TT dye compared to the PT dye, resulting in a lower driving force for regeneration of the oxidized dye by iodide in the electrolyte. In addition, regeneration of the oxidized TT dye and electron injection from the excited TT dye may be poor due to formation of dye aggregates/complexes, as FT-IR measurements show an excess of not properly and/or unidentate bound TT dye molecules instead of bidentate bound PT dye molecules. The results highlight that small structural change of dyes results in significant changes in redox energies and binding features, affecting dramatically the performance of these dyes in dye-sensitized solar cells.

  • 164.
    Marinado, Tannia
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Hahlin, Maria
    Jiang, Xiao
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Quintana, Maria
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Johansson, Erik M J
    Gabrielsson, Erik
    Plogmaker, Stefan
    Hagberg, Daniel P
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Boschloo, Gerrit
    Zakeeruddin, M
    Gratzel, Michael
    Siegbahn, Hans
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Rensmo, Håkan
    Surface Molecular Quantification and Photoelectrochemical Characterization of Mixed Organic Dye and Coadsorbent Layers on TiO2 for Dye-Sensitized Solar Cells2010Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 27, s. 11903-11910Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Different molecular layers on TiO2 were prepared by using the p-dimethylaniline triphenylamine based organic dye, D29, together with the coadsorbents decylphosphonic acid (DPA), dineohexyl bis(3,3-dimethylbutyl)phosphinic acid (DINHOP), and chenodeoxycholic acid (CDCA). The surface molecular structure of dye and coadsorbent layers on TiO2 was investigated by photoelectron spectroscopy (PES). A focus was to determine the surface molecular concentrations using characteristic photoelectron core levels. Dye-sensitized solar cells (DSCs) were prepared from the same substrate and were further characterized by photoelectrochemical methods. Together the investigation gives information on the arrangement of the mixed molecular layer and a first insight to the extent to which the coadsorbents exchange with dye molecules on the TiO2 surface for the examined conditions.

  • 165. Moia, Davide
    et al.
    Cappel, Ute B.
    Leijtens, Tomas
    Li, Xiaoe
    Telford, Andrew M.
    Snaith, Henry J.
    O’Regan, Brian C.
    Nelson, Jenny
    Barnes, Piers R. F.
    The Role of Hole Transport between Dyes in Solid-State Dye-Sensitized Solar Cells2015Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, nr 33, s. 18975-18985Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In dye-sensitized solar cells (DSSCs) photo-generated positive charges are normally considered to be carried away from the dyes by a separate phase of hole-transporting material (HTM). We show that there can also be significant transport within the dye monolayer itself before the hole reaches the HTM. We quantify the fraction of dye regeneration in solid-state DSSCs that can be attributed to this process. By using cyclic voltammetry and transient anisotropy spectroscopy, we demonstrate that the rate of interdye hole transport is prevented both on micrometer and nanometer length scales by reducing the dye loading on the TiO2 surface. The dye regeneration yield is quantified for films with high and low dye loadings (with and without hole percolation in the dye monolayer) infiltrated with varying levels of HTM. Interdye hole transport can account for >50% of the overall dye regeneration with low HTM pore filling. This is reduced to about 5% when the infiltration of the HTM in the pores is optimized in 2 mu m thick films. Finally, we use hole transport in the dye monolayer to characterize the spatial distribution of the HTM phase in the pores of the dyed mesoporous TiO2.

  • 166.
    Monti, Susanna
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Carravetta, Vincenzo
    Li, Cui
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    A Computational Study of the Adsorption and Reactive Dynamics of Diglycine on Cu(110)2014Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 7, s. 3610-3619Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Adsorption of diglycine on the Cu(110) interface in the gas phase at medium coverage is investigated by means of classical all-atom reactive molecular dynamics simulations (ReaxFF) with a focus on preferential binding arrangements and peptide dynamics. Differently from earlier studies, where the slab model was frozen during all calculations, the constraints on the substrate have, in this investigation, been removed, and the atoms can readjust their location in response to the local environment and to the characteristics of the chosen copper face. Relaxation and reconstruction are indeed observed. The results are compared with the data sampled for the perfect slab where the position of every atom of the interface is kept fixed at the bulk geometry. In line with previous studies, the most stably adsorbed molecules are connected to the copper layer through all their oxygen atoms and the terminus nitrogen, adopting an on-top position at an average distance of about 2 A from the interface. In the case of surface reconstruction other strong binding modes are identified together with favorable arrangements which are reinforced by the tight packing ability of the peptides and by their positioning at the step edge of a terrace. There, at the terrace, backbone atoms are found in direct contact with the substrate. On the perfect slab chiral footprints and typical self-assembling arrangements (parallel and antiparallel beta-sheet structures) are recognized, but they disappear on the reconstructed model.

  • 167. Monti, Susanna
    et al.
    Carravetta, Vincenzo
    Zhang, Wenhua
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Yang, Jinlong
    Effects due to interadsorbate interactions on the dipeptide/TiO2 surface binding mechanism investigated by molecular dynamics simulations2007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 21, s. 7765-7771Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Classical molecular dynamics simulations, supported by ab initio periodic calculations, were carried out to investigate peptide adsorption mechanisms onto a rutile (110) TiO2 layer in the presence of water molecules. Different binding modes, comprising multiple coordination to the titanium atoms, of several conformers, simultaneously adsorbed upon the surface, were analyzed in detail. In agreement with experimental and theoretical findings, peptide carbonyl oxygens and nitrogens were found to be possible coordination atoms. Local effects were responsible of adsorption and desorption events and intermolecular interactions induced conformational changes and reorientations of the molecules with respect to the surface that produced both strongly and weakly adsorbed species.

  • 168.
    Monti, Susanna
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Li, Cui
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Carravetta, Vincenzo
    Dropping a droplet of cysteine molecules on a rutile (110) interface: Reactive versus nonreactive classical molecular dynamics simulations2015Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, nr 12, s. 6703-6712Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two different types of classical molecular dynamics approaches, based on reactive and nonreactive force-field parametrizations, are used to investigate the adsorption process of a nanodroplet of cysteine molecules onto a perfect and a defective rutile (110) surface in the gas phase. Three molecular samples made of different cysteine species, namely, one neutral and two zwitterionic models, are tested in order to check how much the starting configurations can bias the description of the deposition onto the surface and if the initial composition of the droplet can influence the final mixture and adsorption arrangements. The present comparison between the two classical computational strategies is useful to identify and suggest the most appropriate approach to depict the behavior of hybrid materials, which cannot be treated at the quantum dynamical level because of the prohibitive computational cost. The complex interaction mechanisms between the molecules of the isolated droplet far from the slab and when it is spread on the inorganic interface are represented reliably and effectively by the reactive dynamics, which is revealed to be a powerful and more appropriate methodology, in comparison with standard molecular dynamics, to disclose all the aspects connected with the process of adsorption. Indeed, differently from the usual nonreactive molecular dynamics, simulations based on reactive force fields do not require any arbitrary assumption on the nature of the adsorbed units and include chemical reactivity. This is often fundamental to identify the most relevant biomolecular species interacting with the inorganic supports and the proton exchange mechanisms acting at the interface.

  • 169.
    Monti, Susanna
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Pastore, Maria Chiara
    Li, Cui
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    De Angelis, Filippo
    Carravetta, Vincenzo
    Theoretical Investigation of Adsorption, Dynamics, Self-Aggregation, and Spectroscopic Properties of the D102 Indoline Dye on an Anatase (101) Substrate2016Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 5, s. 2787-2796Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A coherent account of adsorption modes, dynamics, self aggregation, and spectroscopic properties of an indoline organic dye adsorbed on TiO2 anatase (101) substrates is reported. The study is performed by combining reactive molecular dynamics (reaxFF) simulations with time-dependent density functional theory calculations, and the reliability of the results is assessed through comparison with theoretical and experimental data available in the literature. The use of a theoretical multilevel approach has proven to be crucial to gain a deep understanding, at an atomistic level, of the morphology and electronic properties of dye-sensitized heterogeneous interfaces. A realistic description of the functionalized anatase (101) interface, where a variety of binding modes are present, has been achieved by means of extensive molecular dynamics simulations of the adsorption of dye clusters made of different molecular units on medium/large size TiO2 anatase slabs. Our results disclose that the main driving forces toward formation of ordered surface aggregates are pi stacking and T-shaped interactions between the aromatic rings of the donor moiety of the molecules, as well as the tendency to maximize the anchoring points with the surface. The dye aggregates were found to be organized in domains, characterized by a different orientation of the packing units, and, in the high coverage limit, presenting a certain degree of short-to-medium range order.

  • 170. Morandeira, Ana
    et al.
    Boschloo, Gerrit
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Hammarstrom, Leif
    Coumarin 343-NiO films as nanostructured photocathodes in dye-sensitized solar cells: Ultrafast electron transfer, effect of the I-3(-)/I- redox couple and mechanism of photocurrent generation2008Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, nr 25, s. 9530-9537Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanoporous, p-type NiO films were sensitized with coumarin 343 (C343), and the photoinduced electron transfer dynamics was studied in the presence of different concentrations of electrolyte (I-3(-)/I- in propylene carbonate). Electron transfer from the valence band of NiO to the excited C343 is very fast, occurring on time scales from hundreds of femtoseconds to a few picoseconds, but also the subsequent recombination is quite rapid, on the time scale of tens of picoseconds. Nevertheless, formation of an intermediate, attributed to I2-I NiO(+), was observed on the picosecond time scale. Simultaneously the reduced dye was converted back to the C343 ground state, indicating that recombination could be intercepted by 13 reduction. Consistent with that interpretation, we observed oxidized NiO and depletion Of 13 persisting on the millisecond time scale. Complete dye-sensitized solar cells (DSSCs) with these films as photocathode gave up to 10-11% incident photon to current conversion efficiency at the C343 visible absorption maximum, which is the highest value reported for a p-type DSSC. Our results elucidate the main mechanism for photocurrent generation in this p-type DSSC, which is important for the understanding and development of these rarely studied counterpart of conventional n-type "Gratzel cells".

  • 171. Morandeira, Ana
    et al.
    Fortage, Jerome
    Edvinsson, Tomas
    Le Pleux, Loic
    Blart, Errol
    Boschloo, Gerrit
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Hanmiarstrom, Leif
    Dobel, Fabrice
    Improved photon-to-current conversion efficiency with a nanoporous p-type NiO electrode by the use of a sensitizer-acceptor dyad2008Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, nr 5, s. 1721-1728Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A peryleneimide sensitizer and a covalently linked peryleneimide-naphthalenediimide dyad were prepared and characterized by absorption and emission spectroscopies, electrochemistry, and spectroelectrochemistry. These compounds were chemisorbed on nanoporous nickel oxide electrodes and then studied by femtosecond transient absorption spectroscopy in the presence of a redox active electrolyte (I-3(-)/I-). In both compounds, upon excitation of the peryleneimide unit, an electron is efficiently ejected from the valence band of NiO to the dye with an average time constant of approximately 0.5 ps. In the case of the dyad, the excess electron is shifted further onto the naphtalenediimide unit, creating a new charge separated state. The latter exhibits a substantial retardation of the charge recombination between the hole and the reduced molecule compared with the peryleneimide sensitizer. The photoaction spectra of a sandwich dye-sensitized solar cell (DSSC) composed of NiO films and these new dyes were recorded, and the absorbed-photon to current conversion efficiency (APCE) was three times higher with the dyad than with the peryleneimide dye: 45%. The maximum APCE of approximately 45% is the highest value reported for a DSSC based on a nanostructured metal oxide p-type semiconductor.

  • 172. Mudedla, S. K.
    et al.
    Singam, E. R. Azhagiya
    Sundar, J. Vijay
    Pedersen, Morten N.
    Murugan, N. Arul
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Kongsted, Jacob
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Subramanian, V.
    Enhancement of Internal Motions of Lysozyme through Interaction with Gold Nanoclusters and its Optical Imaging2015Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, nr 1, s. 653-664Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Understanding the interaction of gold nanoclusters with proteins has important ramifications in various fields. We present a study of the interaction between gold nanoclusters and lysozyme investigated using classical molecular dynamics and center-of-mass pulling simulations. The results reveal that the gold nanoclusters induce significant structural changes in lysozyme. Because the internal motions of lysozyme are related to its function, the changes in these internal motions have been quantified using principal component analysis of the molecular dynamics trajectories. The internal motions of lysozyme that are important for its function have been altered because of the interaction with the gold nanocluster. We have also explored how these induced changes in the lysozyme structure affect specific optical properties of the gold nanocluster using the complex polarization propagator method within the time-dependent density functional theory framework, which is of relevance for studies of the optical imaging of lysozyme using gold nanoclusters as molecular probes.

  • 173. Naqvi, S. R.
    et al.
    Hussain, T.
    Luo, W.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Exploring Doping Characteristics of Various Adatoms on Single-Layer Stanene2017Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, nr 14, s. 7667-7676Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have performed first-principles calculations based on density functional theory to investigate the doping characteristics of 31 different adatoms on stanene monolayer, which includes the elements of alkali metals (AM), alkaline earth metals (AEM), transition metals (TMs), and groups III-VII. The most stable configurations of all the dopants have been explored by calculating and comparing binding energies of all the possible binding sites. To comment on the uniform distribution of adatoms on stanene, the adsorption energies (E-ads) of adatoms have been compared with their experimental cohesive energies (E-c,) in the bulk phase.A further comparison reveals that the binding energies of most of the studied adatoms on stanene are much stronger than other group IV monolayers. Apart from structural and binding characteristics, bond lengths, adatom adatom distance, charge-transfer mechanism, electronic properties, and work function have also been explored in pristine and doped monolayers. The strong adsorption of adatoms on stanene, tunable electronic properties, and formation of dumbbell structures in the case of AEM and TM shows that doped stanene sheets are worth further exploration.

  • 174.
    Natarajan Arul, Murugan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Dasgupta, I.
    Chakraborty, A.
    Ganguli, N.
    Kongsted, J.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    How crucial are finite temperature and solvent effects on structure and absorption spectra of Si10?2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 50, s. 26618-26624Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have investigated finite temperature and solvent effects on the structure, and optical absorption properties of the Si10 cluster, as a model for functionalized clusters used in biomedical applications. Among the many isomers possible for Si10 clusters we have studied tetracapped trigonal prism (TCTP) with C3v symmetry, which previously has been reported to be the global minimum structure, using the Car-Parrinello hybrid QM/MM technique. We observe that Si10 remains to be in the TCTP structure in the gas phase, while in solvents we see dominant population of a distorted TCTP conformer which has a similar structure like TCTP except for one of the surface atoms changing its face center position to the edge. We find that there is frequent conformational transitions between these two structures. In the presence of solvents, the interatomic distances are lowered significantly compared to the case of gas phase. While solvent effects appear not to be very significant for the prediction of the excitation energy in the silicon cluster, we find that temperature effects have a substantial influence on its structure and optical properties.

  • 175. Nilson, Katharina
    et al.
    Åhlund, John
    Shariati, Masumeh-Nina
    Göthelid, Emmanuelle
    Palmgren, Pål
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Schiessling, Joachim
    Berner, Simon
    Mårtensson, Nils
    Puglia, Carla
    Rubidium Doped Metal-Free Phthalocyanine Monolayer Structures on Au(111)2010Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 28, s. 12166-12172Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Scanning tunneling microscopy (STM) studies of monolayer of metal-free phthalocyanine (H2Pc) adsorbed on Au(111) have shown ordered arrangement of the molecules on the surface. Evaporation of H2Pc onto the Au(111) surface and post annealing of the sample to 670 K results in a densely packed structure of the molecules. The monolayer is characterized by molecules adsorbed with the molecular plane parallel to the substrate surface in a square adsorption unit cell. Furthermore, the high resolution images revealed the orientation of individual molecules. The H2Pc/Au(111) system has also been doped by rubidum and compared to the undoped layers. The Rb affects the molecular adsorption geometry, and a hexagonal unit cell is found for the coadsorption of H2Pc and Rb. Upon doping, highly ordered Rb-induced protrusions are observed at the benzene site of adsorbed molecules.

  • 176.
    Ning, Zhijun
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Tian, Haining
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Qin, Haiyan
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Zhang, Qiong
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Fu, Ying
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Wave-Function Engineering of CdSe/CdS Core/Shell Quantum Dots for Enhanced Electron Transfer to a TiO2 Substrate2010Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 35, s. 15184-15189Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we have synthesized a series of core/shell quantum dots (QDs) for the purpose of enhancing the electron transfer from the dots to a TiO2 substrate. We make use of the fact that CdSe is a small-bandgap material compared with CdS; therefore, in a common CdSe/CdS core/shell QD, the photo-excited electron is confined deeply in the CdSe core. By special construction of the CdS/CdSe core/shell QDs, referred as reversed type-I, the electron wave function will distribute largely in the shell region. This facilitates the transfer of the electron from the QD to the TiO2 substrate, resulting in significantly improved electron-injection efficiency. Such an enhanced electron-injection efficiency was confirmed by fluorescence lifetime decay measurements, showing the largest lifetime reduction after that the QDs were adsorbed on the TiO2 surface. The reversed type-I CdS/CdSe QDs show a much higher photon-to-current conversion efficiency than type-I CdSe/CdS and CdSe QDs without shell. Furthermore, by chemical-bath depositing of CdS on the QD-sensitized electrode to form a quantum-well structure, the electron recombination between the QDs and the redox couple was reduced, hence further enhancing the electron-injection efficiency. The absorbed-photon-to-current efficiency of the quantum well CdS/CdSe/CdS sensitized solar cells reaches a value as high as 60%.

  • 177. Ning, Zhijun
    et al.
    Zhang, Qiong
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Pei, Hongcui
    Luan, Jiangfeng
    Lu, Changgui
    Cui, Yiping
    Tian, He
    Photovoltage Improvement for Dye-Sensitized Solar Cells via Cone-Shaped Structural Design2009Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 23, s. 10307-10313Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, three truexene-based dyes with 2-cyanoacrylic acid as acceptor and starburst triarylamine as donor (S5, S6, and S7) were conveniently synthesized and used for dye-sensitized solar cells (DSSCs). A compact sensitizer layer is molecular interfacially engineered on the TiO2 surface via cone-shaped sensitizers. As a result, the approach of the electrolyte to the TiO2 surface is blocked significantly by the compact sensitizer layer formed and the charge recombination in the DSSCs is proved to be retarded effectively. The monochromatic incident photon-to-current conversion efficiency of these sensitizers is near 90%. In addition, S7-sensitized solar cells yield an open-circuit voltage of 752 mV and it fill factor of 0.70, which are even higher than those of N719 under the same conditions.

  • 178.
    Nissfolk, Jark
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Marinado, Tannia
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Fabregat-Santiago, Francisco
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Quintana, Maria
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Identification of factors giving low fill factor in ZnO based dye sensitized solar cellsIngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455Artikel i tidskrift (Övrigt vetenskapligt)
  • 179.
    Nissfolk, Jarl
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Revisiting the electron transport models in dye sensitized solar cells: film thickness studyIngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455Artikel i tidskrift (Övrigt vetenskapligt)
  • 180.
    Nordstrand, Johan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Dutta, Joydeep
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Dynamic Langmuir Model: A Simpler Approach to Modeling Capacitive Deionization2019Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 26, s. 16479-16485Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Capacitive deionization (CDI) is emerging as an environment-friendly and energy-efficient water desalination option for meeting the growing global demand for drinking water. It is important to develop models that can predict and optimize the performance of CDI systems with respect to key operational parameters in a simple way. Such models could open up modeling studies to a wider audience by making modeling more accessible to researchers. We have developed the dynamic Langmuir model that can describe CDI in terms of a few fundamental macroscopic properties. Through extensive comparisons with data from the literature, it is shown that the model could describe and predict charge storage, ion adsorption, and charge efficiency for varying input ion concentrations, applied voltages, electrolyte compositions, electrode asymmetries, and electrode precharges in the equilibrium state. We conclude that the model could accurately describe a wide range of key features while being a simpler approach than the commonly applied theories for modeling CDI.

  • 181.
    Osella, Silvio
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Minoia, Andrea
    Beljonne, David
    Combined Molecular Dynamics and Density Functional Theory Study of Azobenzene-Graphene Interfaces2016Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 12, s. 6651-6658Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic properties of graphene can be tuned in a dynamic way from physical adsorption of molecular photoswitches. Here, we first investigate the formation of 4-(decyloxy)azobenzene molecular monolayers on a single graphene layer through molecular dynamics (MD) simulations and assess the associated change in work function (WF) at the density functional theory (DFT) level. We show that the major contribution to the WF shift arises from electrostatic effects induced by the azobenzene electric dipole component normal to graphene and that the conformational distribution of the molecular switches in either their trans or cis forms can be convoluted into WF distributions for the hybrid systems. We next use this strategy to build a statistical ensemble for the work functions of graphene decorated with fluorinated azobenzene derivative designed to maximize the change in WF upon photoswitching. These findings pave the way to the possible use of photoswitchable graphene-based hybrid materials as optically controlled memories for light-assisted programming and high-sensitive photosensors.

  • 182.
    Pakeetood, Patompob
    et al.
    Kasetsart Univ, Fac Sci, Dept Phys, Bangkok 10900, Thailand..
    Reunchan, Pakpoom
    Kasetsart Univ, Fac Sci, Dept Phys, Bangkok 10900, Thailand.;Commiss Higher Educ, Thailand Ctr Excellence Phys, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand..
    Boonchun, Adisak
    Kasetsart Univ, Fac Sci, Dept Phys, Bangkok 10900, Thailand.;Commiss Higher Educ, Thailand Ctr Excellence Phys, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand..
    Limpijumnong, Sukit
    Inst Promot Teaching Sci & Technol, 924 Sukhumvit Rd, Bangkok 10110, Thailand..
    Munprom, Ratiporn
    Kasetsart Univ, Fac Engn, Dept Mat Engn, Bangkok 10900, Thailand..
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, Mat Theory Div, Box 530, SE-75121 Uppsala, Sweden..
    T-Thienprasert, Jiraroj
    Kasetsart Univ, Fac Sci, Dept Phys, Bangkok 10900, Thailand.;Commiss Higher Educ, Thailand Ctr Excellence Phys, 328 Si Ayutthaya Rd, Bangkok 10400, Thailand..
    Hybrid-Functional Study of Native Defects and W/Mo-Doped in Monoclinic-Bismuth Vanadate2019Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, nr 23, s. 14508-14516Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Monoclinic scheelite (ms) BiVO4 is recognized as one of the most promising photocatalyst materials due to its band gap as well as band-edge positions. Several theoretical and experimental works have been dedicated to improving the photocatalytic activity of ms-BiVO4. It has been reported that doping ms-BiVO4 with either W or Mo can enhance its photocatalytic activity compared to the undoped one. Further, codoping with W and Mo can improve the photocatalytic activity. Here, we systematically investigate all native and W/Mo-related defects in ms-BiVO4 by using density functional theory with hybrid functional. For undoped ms-BiVO4, we reveal that vacancies are the most dominant intrinsic defects and these defects compensate themselves leading to moderate n-type conductivity in O-poor growth condition. For W/Mo-doped ms-BiVO4, W and Mo are likely to substitute for V atom under all crystal growth conditions. While W v defect is a shallow donor, Mo v defect creates a defect level below the conduction band edge. This implies that doping with W can gain more photocatalytic efficiency, which agrees well with experiment. Interestingly, we find that two donors, i.e., W v and Mo v defects, prefer to form a complex defect becoming a shallow double donor. This can improve the electrical conductivity of W/Mo-codoped ms-BiVO4, which helps enhance its photocatalytic performance. In addition, the formation of donor-donor complexes is quite stable and helps improve material property.

  • 183.
    Palmgren, Pål
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Nilson, K.
    Yu, Shun
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Hennies, F.
    Angot, T.
    Nlebedim, Cajetan Ikenna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Layet, J. -M
    Le Lay, G.
    Götelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Strong interactions in dye-sensitized interfaces2008Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, nr 15, s. 5972-5977Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Phthalocyanines (Pcs) are capable of converting sunlight into electric energy when adsorbed on TiO2 in a dye-sensitized solar cell. Of special interest in this type of cell is the energy level alignment as well as how molecules adsorb on the surface as it determines the output of the cell. We investigated the FePc-TiO2(110) interface using scanning tunneling microscopy, synchrotron-based photoelectron spectroscopy, and X-ray absorption spectroscopy. We found a strong coupling of the first-layer FePc to the substrate resulting in an alteration of the electronic structure and charge transfer from the molecules. The FePc in the second layer is not severely affected by the bonding to the surface and has bulk-like electronic properties. The growth of FePc thin films proceeds in a layer plus island mode, and the molecular plane is parallel to the surface. The energy level alignment at the interface is determined, and the lowest unoccupied molecular orbital is found above the conduction band minimum of the oxide substrate.

  • 184.
    Perumal, Sathya
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Minaev, Boris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Triplet State Phosphorescence in Tris(8-hydroxyquinoline) Aluminum Light Emitting Diode Materials2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 7, s. 3446-3455Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Time-dependent density functional theory (TD-DFT) with the quadratic response technique is applied to the tris(8-hydroxyquinoline) aluminum complex (Alq(3)) to calculate spin orbit coupling (SOC) effects and the main mechanism of the Alq(3) phosphorescence. This compound exhibits weak phosphorescence which provides additional emission in organic light emitting diodes (OLEDs) besides the main fluorescence band. The phosphorescence affords to overcome the efficiency limit imposed by the formation of triplet excitons in the emissive layer of OLEDs. The zero-field splitting (ZFS) parameters are also calculated taking into account the spin spin coupling in the first-order perturbation theory and the SOC in the second order. On the basis of the results obtained, we propose that an efficient spin-polarized injection and transport in long channels of Alq(3), which have been recently achieved with new hybrid organic inorganic interfaces, can proceed with the triplet electronic state admixture to the charge carriers. Our results also indicate that weak spin orbit coupling may be responsible for the room-temperature magneto-resistance at the ferromagnetic-Alq(3) interfaces and the spin-dependent charge transport.

  • 185.
    Pevere, Federico
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sychugov, Ilya
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Sangghaleh, Fatemeh
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Fucikova, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Linnros, Jan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Biexciton Emission as a Probe of Auger Recombination in Individual Silicon Nanocrystals2015Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, nr 13, s. 7499-7505Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 186. Philippe, Bertrand
    et al.
    Jacobsson, T. Jesper
    Correa-Baena, Juan-Pablo
    Jena, Naresh K.
    Banerjee, Amitava
    Chakraborty, Sudip
    Cappel, Ute B.
    Uppsala University, Sweden.
    Ahuja, Rajeev
    Hagfeldt, Anders
    Odelius, Michael
    Rensmo, Håkan
    Valence Level Character in a Mixed Perovskite Material and Determination of the Valence Band Maximum from Photoelectron Spectroscopy: Variation with Photon Energy2017Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, nr 48, s. 26655-26666Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A better understanding of the electronic structure of perovskite materials used in photovoltaic devices is essential for their development and optimization. In this investigation, synchrotron-based photoelectron spectroscopy (PES) was used to experimentally delineate the character and energy position of the valence band structures of a mixed perovskite. The valence band was measured using PES with photon energies ranging from ultraviolet photoelectron spectroscopy (21.2 eV) to hard X-rays (up to 4000 eV), and by taking the variation of the photoionization cross sections into account, we could experimentally determine the inorganic and organic contributions. The experiments were compared to theoretical calculations to further distinguish the role of the different anions in the electronic structure. This work also includes a thorough study of the valence band maximum and its position in relation to the Fermi level, which is crucial for the design and optimization of complete solar cells and their functional properties.

  • 187. Prasongkit, Jariyanee
    et al.
    Amorim, Rodrigo G.
    Chakraborty, Sudip
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Scheicher, Ralph H.
    Amornkitbamrung, Vittaya
    Highly Sensitive and Selective Gas Detection Based on Silicene2015Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, nr 29, s. 16934-16940Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent advances in the fabrication of silicene devices have raised exciting prospects for practical applications such as gas sensing. We investigated the gas detection performance of silicene nanosensors for four different gases (NO, NO2, NH3, and CO) in terms of sensitivity and selectivity, employing density functional theory and nonequilibrium Greens function method. The structural configurations, adsorption sites, binding energies and charge transfer of all studied gas molecules on silicene nanosensors are systematically discussed in this work. Our results indicate that pristine silicene exhibits strong sensitivity for NO and NO2, while it appears incapable of sensing CO and NH3. In an attempt to overcome sensitivity limitations due to weak van der Waals interaction of those latter gas molecules on the device, we doped pristine silicene with either B or N atoms, leading to enhanced binding energy as well as charge transfer, and subsequently a significant improvement of sensitivity. A distinction between the four studied gases based on the silicene devices appears possible, and thus these promise to be next-generation nanosensors for highly sensitive and selective gas detection.

  • 188. Prasongkit, Jariyanee
    et al.
    Grigoriev, Anton
    Pathak, Biswarup
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Scheicher, Ralph H.
    Theoretical Study of Electronic Transport through DNA Nucleotides in a Double-Functionalized Graphene Nanogap2013Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, nr 29, s. 15421-15428Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Graphene nanogaps and nanopores show potential for the purpose of electrical DNA sequencing, in particular because single-base resolution appears to be readily achievable. Here, we evaluated from first principles the advantages of a nanogap setup with functionalized graphene edges. To this end, we employed density functional theory and the non-equilibrium Green's function method to investigate the transverse conductance properties of the four nucleotides occurring in DNA when located between opposing functionalized graphene electrodes. In particular, we determined the electrical tunneling current variation as a function of the applied bias and analyzed the associated differential conductance at a voltage which appears suitable to distinguish between the four nucleotides. Intriguingly, we predict for one of the nucleotides (deoxyguanosine monophosphate) a negative differential resistance effect.

  • 189. Privalov, Timofei
    et al.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Svensson, Per H.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    Kloo, Lars A.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Oorganisk kemi.
    A Study of the Interactions between I-/I-3(-) Redox Mediators and Organometallic Sensitizing Dyes in Solar Cells2009Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, nr 2, s. 783-790Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Specific interactions of the I-/I-3(-) redox mediators with the reduced and oxidized dye, Ru(4,4'-dicarboxy2,2'-bipyridyl)(2)(NCS)(2), referred to as N3 or Ru(dcbpy)(2)(NCS)(2), have been studied by means of density functional theory (DFT) with the focus on the charge transfer process involving {dye(+) I-} adducts; computations had been performed with a series of density functionals (gradient-corrected density functional BP86, and the hybrid density functionals B3LYP, MPW1K, B3PW1K, and MPW1PW91). Different pathways leading to (dye(+) I-) adducts have been studied. First, mechanistic insights into the interaction of I- with Ru-III (dcbpy)(2)(NCS)(2) via an SCN- ligand directly giving rise to Ru-II(dcbpy)(2)(NCS)(2)I](0) have been obtained with the distinctive S-I bonding. Second, the binding of I- to the N3 dye cation via I(-)dcbpy interactions has been analyzed. We also report experimental and computational evidence that sheds light on the interaction of the redox mediator with bipyridyl moieties. Evidence for a charge transfer process in the presence of only one I- anion in the outer coordination sphere of the ruthenium center has been identified. Finally, geometries and electronic structures of plausible intermediates have been computationally analyzed based on an innersphere interaction between the metal center and the redox mediator, including a two-step regeneration reaction: Ru-III (dcbPy)(2)(NCS)(2)](+) + I- -> Ru-III(dcbpy)(2)(NCS)I](+) + SCN-, followed by the interaction of a second I- with the intermediate Ru-III(dcbpy)(2)(NCS)I](+) complex. Conclusive evidence of a charge-transfer process that gives rise to the regenerated Ru-II complex, where I- interacts with the intermediate Ru-III (dcbpy)(2)(NCS)I](+) complex has been identified.

  • 190.
    Qian, Zhao
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hudson, M. Sterlin Leo
    Raghubanshi, Himanshu
    Scheicher, Ralph H.
    Pathak, Biswarup
    Araujo, C. Moyses
    Blomqvist, Andreas
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Srivastava, O. N.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Excellent Catalytic Effects of Graphene Nanofibers on Hydrogen Release of Sodium alanate2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 20, s. 10861-10866Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    One of the most technically challenging barriers to the widespread commercialization of hydrogen-fueled devices and vehicles remains hydrogen storage. More environmentally friendly and effective nonmetal catalysts are required to improve hydrogen sorption. In this paper, through a combination of experiment and theory, we evaluate and explore the catalytic effects of layered graphene nanofibers toward hydrogen release of light metal hydrides such as sodium alanate. Graphene nanofibers, especially the helical kind, are found to considerably improve hydrogen release from NaAlH4, which is of significance for the further enhancement of this practical material for environmentally friendly and effective hydrogen storage applications. Using density functional theory, we find that carbon sheet edges, regardless of whether they are of zigzag or armchair type, can weaken Al-H bonds in sodium alanate, which is believed to be due to a combination of NaAlH4 destabilization and dissociation product stabilization. The helical form of graphene nanofibers, with larger surface area and curved configuration, appears to benefit the functionalization of carbon sheet edges. We believe that our combined experimental and theoretical study will stimulate more explorations of other microporous or mesoporous nanomaterials with an abundance of exposed carbon edges in the application of practical complex light metal hydride systems.

  • 191.
    Qiang, Fu
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Jinlong, Yang
    Yi, Luo
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    A first principles study on the dissociation and rotation processes of a single O2 molecule on the Pt(111) surface2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 14, s. 6864-6869Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Through density functional theory calculations, a detailed description on the dissociation and rotation processes of a single oxygen molecule adsorbed on the Pt(111) surface has been provided. Both dissociation and rotation reaction pathways have been identified, and some interesting phenomena related to the scanning tunneling microscopy experiments are finally explained. It is found that the prior occupation of oxygen atom on the metastable hcp-hollow site after O2 dissociation is originated from the particular structure of the intermediate state, and the low energy barrier of the O2 rotation can be attributed to an effective pathway. The experimentally observed noninteger power-law dependence of the rotation rate as a function of the current has been accurately determined by a newly developed statistical model for the inelastic electron tunneling. By considering the randomness of multielectron inelastic tunneling processes, it is found that the noninteger exponent comes from a statistical contribution of various n-electron events.

  • 192.
    Qin, Hai-Yan
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Shang, X. -J
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Ning, Z. -J
    Fu, Tao
    Zhejiang Univ, Hangzhou, Zhejiang, Peoples R China.
    Niu, Z. -C
    Chinese Acad Sci, Beijing, Peoples R China .
    Brismar, Hjalmar
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Cellens fysik.
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Fu, Ying
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Observation of Bunched Blinking from Individual CdSe/CdS and CdSe/ZnS Colloidal Quantum Dots2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 23, s. 12786-12790Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Blinking and time correlation between fluorescences of neighboring negatively charged CdSe/CdS and CdSe/ZnS colloidal quantum dots have been studied experimentally. A tendency of synchronous blinking, that is, a bunching effect, is clearly observed from two neighboring QDs with a spatial separation up to 1.1 mu m. We believe that our observations will help to better understand the mechanisms for the blinking.

  • 193.
    Qin, Peng
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Wiberg, Joanna
    Gibson, Elizabeth A.
    Linder, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Li, Lin
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Albinsson, Bo
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Synthesis and Mechanistic Studies of Organic Chromophores with Different Energy Levels for p-Type Dye-Sensitized Solar Cells2010Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 10, s. 4738-4748Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of donor-pi-acceptor dyes with different electron-withdrawing groups were designed and synthesized for p-type dye-sensitized Solar cells. The modification of dye structures shows significant influence on the photophysical, electrochemical, and photovoltaic performance of the dyes. DSSCs based on these dyes show maximum 63% and minimum 6% of incident monochromatic photon-to-current conversion efficiencies. The two dyes with the highest (P1) and lowest (P3) efficiencies were Studied by femtosecond transient absorption spectroscopy, which shows a fast injection rate of more than (250 fs)(-1) for both dyes. Such fast injection corresponds to more than 90% injection efficiency. The photoinduced absorption Spectroscopy Study of sensitized NiO films in the presence of electrolyte showed poor regeneration of 113 due to all insufficient driving force. This, together with aggregation of the dye on the NiO film, explained the poor solar cell performance.

  • 194. Quintana, Maria
    et al.
    Edvinsson, Tomas
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Boschloo, Gerrit
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Comparison of dye-sensitized ZnO and TiO2 solar cells: Studies of charge transport and carrier lifetime2007Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, nr 2, s. 1035-1041Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanocrystalline particles of ZnO and TiO2 of approximately equal size (-15 nm) were used to prepare mesoporous electrodes for dye-sensitized solar cells. Electron transport in the solar cells was studied using intensity-modulated photocurrent spectroscopy and revealed very similar results for ZnO and TiO2. Apparent activation energies for electron transport in nanostructured ZnO of <= 0.1 eV were calculated from the temperature dependence of transport times under short-circuit conditions. The lifetime of electrons in the nanostructured semiconductors was evaluated from open-circuit voltage decay and intensity-modulated photovoltage spectroscopy. Significantly longer lifetimes were obtained with ZnO. Despite the reduced recombination, ZnO-based solar cells performed worse than TiO2 cells, which was attributed to a lower electron injection efficiency from excited dye molecules and/or a lower dye regeneration efficiency. The internal voltage in the nanostructured ZnO film under short-circuit conditions was about 0.23 V lower than the open-circuit potential at the same light intensity. Results may be explained using a multiple trapping model, but as electrons are usually only shallowly trapped in ZnO, an alternative view is presented. If there is significant doping of the ZnO, resulting band bending in the nanocrystals will form energy barriers for electron transport and recombination that can explain the observed properties.

  • 195.
    Rahm, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Tyrode, Eric
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Johnson, Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära.
    The Molecular Surface Structure of Ammonium and Potassium Dinitramide: A Vibrational Sum Frequency Spectroscopy and Quantum Chemical Study2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 21, s. 10588-10596Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vibrational sum frequency spectroscopy (VSFS) and quantum chemical modeling have been employed to investigate the molecular surface structure of ammonium and potassium dinitramide (ADN and KDN) crystals. Identification of key vibrational modes was made possible by performing density functional theory calculations of molecular clusters. The surface of KDN was found to be partly covered with a thin layer of the decomposition product KNO3, which due to its low thickness was not detectable by infrared and Raman spectroscopy. In contrast, ADN exhibited an extremely inhomogeneous surface, on which polarized dinitramide anions were present, possibly together with a thin layer of NH4NO3. The intertwined use of theoretical and experimental tools proved indispensable in the analysis of these complex surfaces. The experimental verification of polarized and destabilized dinitramide anions stresses the importance of designing surface-active polymer support, stabilizers, and/or coating agents, in order to enable environmentally friendly ADN-based solid-rocket propulsion.

  • 196. Ramzan, M.
    et al.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hybrid density functional and molecular dynamics study of promising hydrogen storage materials: Double metal amidoboranes and metal amidoborane ammoniates2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 33, s. 17351-17359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the recently synthesized materials, Na2Mg-(NH 2BH 3) 4, NaLi(NH 2BH 3) 2, Mg(NH 2BH 3) 2·NH 3, and Ca-(NH 2BH 3) 2·2NH 3, are studied, which were found suitable for hydrogen storage applications. The hybrid density exchange-correlation functional is employed to explore the structural and electronic properties of these materials using the first-principles method on the basis of density functional theory calculations. From the detailed study of electronic structures, it is found that the mixed cation amidoboranes and [NH 3] molecules play an important role in the dehydrogenation process. Bader charge analysis is performed to show the charge distribution between the constituent atoms. The corresponding electron densities and related properties of these compounds are also calculated. Furthermore, ab initio molecular dynamics simulations are performed to study the diffusion of hydrogen in these compounds, which consist of boron, nitrogen, and hydrogen atoms. The common features of these compounds are also revealed by explaining the electronic properties. Finally, it is shown that the mobility of hydrogen in Na 2Mg(NH 2BH 3) 4 and NaLi(NH 2BH 3) 2 is slightly higher than that in Mg(NH 2BH 3) 2·NH 3 and Ca(NH 2BH 3) 2·2NH 3 at the same temperatures.

  • 197. Ramzan, Muhammad
    et al.
    Lebegue, Sebastien
    Kang, Tae W.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hybrid Density Functional Calculations and Molecular Dynamics Study of Lithium Fluorosulphate, A Cathode Material for Lithium-Ion Batteries2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 5, s. 2600-2603Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we use hybrid density functional theory to calculate the electronic structure of lithium fluorosulphate (LiFeSO4F), which has been found recently to be an excellent cathode material for lithium-ion,batteries by Recham et al. (Nat. Mater. 2010, 9, 68). We calculate the average intercalation voltage of the corresponding battery, and we also analyze the electron charge distribution through Bader's analysis. Our results are in good agreement with the available experimental values. Then we studied the Li-diffusion in lithium fluorosulphate with ab initio molecular dynamics and found it to be three-dimensional.

  • 198. Ramzan, Muhammad
    et al.
    Silvearv, Fredrik
    Lebegue, Sebastien
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Electronic Structure from First-Principles of LiBH(4)center dot NH(3), Sr(NH(2)BH(3))(2), and Li(2)Al(BH(4))(5)center dot 6NH(3) for Hydrogen Storage Applications2011Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 40, s. 20036-20042Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of compounds containing boron, nitrogen, and hydrogen atoms, namely, LiBH(4)center dot NH(3), Sr(NH(2)BH(3))(2), and Li(2)Al(BH(4))(5)center dot 6NH(3), were synthesized recently, and found to be promising for hydrogen storage. We have conducted the corresponding ab initio calculations using density functional theory and analyzed the corresponding electron density as well as derived properties. Also, molecular dynamics simulations were performed to study the diffusion of hydrogen in this series of compounds. We found that despite having widely different crystal structures and difference in their chemical composition, these compounds share common features at the level of their electronic structure. Moreover, diffusion of hydrogen appears to be more favorable in LiBH(4)center dot NH(3) than in Sr(NH(2)BH(3))(2) and Li(2)Al(BH(4))(5)center dot 6NH(3).

  • 199. Raymand, David
    et al.
    Jacobsson, T. Jesper
    Hermansson, Kersti
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Edvinsson, Tomas
    Investigation of Vibrational Modes and Phonon Density of States in ZnO Quantum Dots2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 12, s. 6893-6901Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ability to understand the phonon behavior in small metal oxide nanostructures and their surfaces is of great importance for thermal and microelectronic applications in successively smaller devices. Here the development of phonons in successively larger ZnO wurtzite quantum dots (QDs) is investigated. Raman spectroscopic measurements for particles from 3 to 11 nm reveal that the E-2 Raman active optical phonon at 436 cm(-1) is the first mode to be developed with a systematic increase with particle size. We also find a broad phonon band at 260-340 attributed to surface vibrations. The E-1-LO mode at 585 cm(-1) is the next to be developed while still being strongly suppressed in the confined particles. Other modes found in bulk ZnO are not developed for particles below 11 nm. Results from density functional theory showed an excellent agreement with the experimental molecular vibrations in the zinc acetate precursor and phonon modes in bulk ZnO. To elucidate the vibration behavior and phonon development in the ZnO QDs under nonzero temperature conditions and incorporating surface reconstruction, we performed reactive force field calculations. We show that the experimentally developed phonon modes in the QDs are the ones expected from dynamic theory. In particular, we show that the surface phonon modes in the very outermost surface (5 angstrom) can explain the observed broad phonon band and give the precise relation between the intensity of the surface and bulk phonons as the particle size increases. Calculations with temperatures between 50K and 1000K also show distinction of temperature effects in the material and that the phonon peaks are not generally shifted when the system is heated and quantum confined but instead reveal a dependence on the symmetry of the phonon mode.

  • 200.
    Rosén, Tomas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center. SUNY Stony Brook.
    Brouzet, Christophe
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Roth, Stephan V.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. DESY.
    Lundell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center. KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Söderberg, Daniel
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Centra, Wallenberg Wood Science Center.
    Three-Dimensional Orientation of Nanofibrils in Axially Symmetric Systems Using Small-Angle X-ray Scattering2018Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, nr 12, s. 6889-6899Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The increased availability and brilliance of new X-ray facilities have in the recent years opened up the possibility to characterize the alignment of dispersed anisotropic nanoparticles in various microfluidic applications, from hydrodynamic self-assemblies to flows in complex geometries. In such applications, it is vital to study the alignment of the nanoparticles in the flow, as this in turn affects the final properties of the self-assembled superstructures or those of the flow itself. Small-angle X-ray scattering (SAXS) is a well-suited characterization technique for this but typically provides the alignment in a projected plane perpendicular to the beam direction. In this work, we demonstrate a simple method to reconstruct the full three-dimensional orientation distribution function from a SAXS experiment through the assumption that the azimuthal angle of the nanoparticles around the flow direction is distributed uniformly, an assumption that is valid for a large range of nanoparticle flow processes. For demonstration purposes, the experimental results from previous works on hydrodynamic self-assembly of cellulose nanofibrils (CNFs) into filaments have been revised, resulting in a small correction to the presented order parameters. The results are then directly compared with simple numerical models to describe the increased alignment of CNFs both in the flowing system and during the drying of the filament. The proposed reconstruction method will allow for further improvements of theoretical or numerical simulations and consequently open up new possibilities for optimizing assembly processes, which include flow alignment of elongated nanoparticles.

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