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  • 1. Ahmed, Towfiq
    et al.
    Haraldsen, Jason T.
    Zhu, Jian-Xin
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Institute for Materials Science, Los Alamos National Laboratory, United States.
    Next-Generation Epigenetic Detection Technique: Identifying Methylated Cytosine Using Graphene Nanopore2014In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 5, no 15, p. 2601-2607Article in journal (Refereed)
    Abstract [en]

    DNA methylation plays a pivotal role in the genetic evolution of both embryonic and adult cells. For adult somatic cells, the location and dynamics of methylation have been very precisely pinned down with the 5-cytosine markers on cytosine-phosphate-guanine (CpG) units. Unusual methylation on CpG islands is identified as one of the prime causes for silencing the tumor suppressant genes. Early detection of methylation changes can diagnose the potentially harmful oncogenic evolution of cells and provide promising guideline for cancer prevention. With this motivation, we propose a cytosine methylation detection technique. Our hypothesis is that electronic signatures of DNA acquired as a molecule translocates through a nanopore would be significantly different for methylated and nonmethylated bases. This difference in electronic fingerprints would allow for reliable real-time differentiation of methylated DNA. We calculate transport currents through a punctured graphene membrane while the cytosine and methylated cytosine translocate through the nanopore. We also calculate the transport properties for uracil and cyanocytosine for comparison. Our calculations of transmission, current, and tunneling conductance show distinct signatures in their spectrum for each molecular type. Thus, in this work, we provide a theoretical analysis that points to a viability of our hypothesis.

  • 2. Amaya, Andrew J.
    et al.
    Pathak, Harshad
    Modak, Viraj P.
    Laksmono, Hartawan
    Loh, N. Duane
    Sellberg, Jonas A.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Sierra, Raymond G.
    McQueen, Trevor A.
    Hayes, Matt J.
    Williams, Garth J.
    Messerschmidt, Marc
    Boutet, Sebastien
    Bogan, Michael J.
    Nilsson, Anders
    Stan, Claudiu A.
    Wyslouzil, Barbara E.
    How Cubic Can Ice Be?2017In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 8, no 14, p. 3216-3222Article in journal (Refereed)
    Abstract [en]

    Using an X-ray laser, we investigated the crystal structure of ice formed by homogeneous ice nucleation in deeply supercooled water nanodrops (r approximate to 10 nm) at similar to 225 K The nanodrops were formed by condensation of vapor in a supersonic nozzle, and the ice was probed within 100 mu s of freezing using femtosecond wide-angle X-ray scattering at the Linac Coherent Light Source free-electron X-ray laser. The X-ray diffraction spectra indicate that this ice has a metastable, predominantly cubic structure; the shape of the first ice diffraction peak suggests stacking-disordered ice with a cubicity value, chi, in the range of 0.78 +/- 0.05. The cubicity value determined here is higher than those determined in experiments with micron-sized drops but comparable to those found in molecular dynamics simulations. The high cubicity is most likely caused by the extremely low freezing temperatures and by the rapid freezing, which occurs on a similar to 1 mu s time scale in single nanodroplets.

  • 3. Beye, Martin
    et al.
    Oberg, Henrik
    Xin, Hongliang
    Dakovski, Georgi L.
    Dell'Angela, Martina
    Foehlisch, Alexander
    Gladh, Jorgen
    Hantschmann, Markus
    Hieke, Florian
    Kaya, Sarp
    Kuehn, Danilo
    LaRue, Jerry
    Mercurio, Giuseppe
    Minitti, Michael P.
    Mitra, Ankush
    Moeller, Stefan P.
    Ng, May Ling
    Nilsson, Anders
    Nordlund, Dennis
    Norskov, Jens
    Ostrom, Henrik
    Ogasawara, Hirohito
    Persson, Mats
    Schlotter, William F.
    Sellberg, Jonas A.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Wolf, Martin
    Abild-Pedersen, Frank
    Pettersson, Lars G. M.
    Wurth, Wilfried
    Chemical Bond Activation Observed with an X-ray Laser2016In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 18, p. 3647-3651Article in journal (Refereed)
    Abstract [en]

    The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of those orbitals and the energetic difference between the two reflect the strength of the bonding interaction. Weakening the bond is expected to reduce this energetic splitting, but the transient character of bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free electron laser to directly observe the decreased bonding antibonding splitting following bond-activation using an ultrashort optical laser pulse.

  • 4. Bialik, Erik
    et al.
    Stenqvist, Bjorn
    Fang, Yuan
    Ostlund, Asa
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Lindman, Björn
    Lund, Mikael
    Bernin, Diana
    Ionization of Cellobiose in Aqueous Alkali and the Mechanism of Cellulose Dissolution2016In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 24, p. 5044-5048Article in journal (Refereed)
    Abstract [en]

    Cellulose, one of the most abundant renewable resources, is insoluble in most common solvents but dissolves in aqueous alkali under a narrow range of conditions. To elucidate the solubilization mechanism, we performed electrophoretic NMR on cellobiose, a subunit of cellulose, showing that cellobiose acts as an acid with two dissociation steps at pH 12 and 13.5. Chemical shift differences between cellobiose in NaOH and NaCl were estimated using 2D NMR and compared to DFT shift differences upon deprotonation. The dissociation steps are the deprotonation of the hemiacetal OH group and the deprotonation of one of four OH groups on the nonreducing anhydroglucose unit. MD simulations reveal that aggregation is suppressed upon charging cellulose chains in solution. Our findings strongly suggest that cellulose is to a large extent charged in concentrated aqueous alkali, a seemingly crucial factor for solubilization. This insight, overlooked in the current literature, is important for understanding cellulose dissolution and for synthesis of new sustainable materials.

  • 5. Cappel, Ute B
    et al.
    Dowland, Simon A
    Reynolds, Luke X
    Dimitrov, Stoichko
    Haque, Saif A
    Charge Generation Dynamics in CdS: P3HT Blends for Hybrid Solar Cells.2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 24, p. 4253-7Article in journal (Refereed)
    Abstract [en]

    Development of design rules for hybrid inorganic-organic solar cells through understanding charge generation and recombination dynamics is an important pathway for the improvement of solar cell conversion efficiencies. In this Letter, we study the dynamics of charge generation in CdS:polymer blends by transient absorption spectroscopy. We show that charge generation following excitation of the inorganic component is highly efficient and can occur up to a few nanoseconds after excitation, allowing for diffusion of charges within the inorganic component to an interface. In contrast, charge generation following excitation of the organic component occurs on subpicosecond time scales but suffers from two loss processes, incomplete exciton dissociation and geminate recombination.

  • 6. Céolin, D.
    et al.
    Rueff, J. -P
    Zimin, Andrei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Federal University, Russian Federation.
    Morin, P.
    Kimberg, Victor
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Federal University, Russian Federation.
    Polyutov, S.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Federal University, Russian Federation.
    Gelmukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Federal University, Russian Federation.
    Far-Zone Resonant Energy Transfer in X-ray Photoemission as a Structure Determination Tool2017In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 8, no 12, p. 2730-2734Article in journal (Refereed)
    Abstract [en]

    Near-zone Förster resonant energy transfer is the main effect responsible for excitation energy flow in the optical region and is frequently used to obtain structural information. In the hard X-ray region, the Förster law is inadequate because the wavelength is generally shorter than the distance between donors and acceptors; hence, far-zone resonant energy transfer (FZRET) becomes dominant. We demonstrate the characteristics of X-ray FZRET and its fundamental differences with the ordinary near-zone resonant energy-transfer process in the optical region by recording and analyzing two qualitatively different systems: high-density CuO polycrystalline powder and SF6 diluted gas. We suggest a method to estimate geometrical structure using X-ray FZRET employing as a ruler the distance-dependent shift of the acceptor core ionization potential induced by the Coulomb field of the core-ionized donor.

  • 7. da Silva, Aderson Miranda
    et al.
    Mocellin, Alexandra
    Monti, Susanna
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Cui
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Marinho, Ricardo R. T.
    Medina, Aline
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Carravetta, Vincenzo
    de Brito, Arnaldo Naves
    Surface-Altered Protonation Studied by Photoelectron Spectroscopy and Reactive Dynamics Simulations2015In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 5, p. 807-811Article in journal (Refereed)
    Abstract [en]

    The extent to which functional groups are protonated at aqueous interfaces as compared to bulk is deemed essential to several areas in chemistry and biology. The origin of such changes has been the source of intense debate. We use X-ray photoelectron spectroscopy and all-atom reactive molecular dynamics simulations as two independent methods to probe, at the molecular scale, both bulk and surface distributions of protonated species of cysteine in an aqueous solution. We show that the distribution of the cysteine species at the surface is quite different from that in the bulk. We argue that this finding, however, cannot be simply related to a change in the extent of proton sharing between the two conjugate acid/base pairs that may occur between these two regions. The present theoretical simulations identify species at the surface that are not present in the bulk.

  • 8. Di Meo, F.
    et al.
    Pedersen, M. N.
    Rubio-Magnieto, J.
    Surin, M.
    Linares, M.
    Norman, P.
    DNA electronic circular dichroism on the inter-base pair scale: An experimental-theoretical case study of the at homo-oligonucleotide2015In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 3, p. 355-359Article in journal (Refereed)
    Abstract [en]

    A successful elucidation of the near-ultraviolet electronic circular dichroism spectrum of a short double-stranded DNA is reported. Time-dependent density functional theory methods are shown to accurately predict spectra and assign bands on the microscopic base-pair scale, a finding that opens the field for using circular dichroism spectroscopy as a sensitive nanoscale probe of DNA to reveal its complex interactions with the environment. (Chemical Equation Presented). © 2015 American Chemical Society.

  • 9. Fahleson, Tobias
    et al.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Norman, Patrick
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Linköping University, Sweden.
    A Polarization Propagator for Nonlinear X-ray Spectroscopies2016In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 11, p. 1991-1995Article in journal (Refereed)
    Abstract [en]

    A complex polarization propagator approach has been developed to third order and implemented in density functional theory (DFT), allowing for the direct calculation of nonlinear molecular properties in the X-ray wavelength regime without explicitly addressing the excited-state manifold. We demonstrate the utility of this propagator method for the modeling of coherent near-edge X-ray two-photon absorption using, as an example, DFT as the underlying electronic structure model. Results are compared with the corresponding near edge X-ray absorption fine structure spectra, illuminating the differences in the role of symmetry, localization, and correlation between the two spectroscopies. The ramifications of this new technique for nonlinear X-ray research are briefly discussed.

  • 10.
    Farahani, Pooria
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Vacher, Morgane
    Valentini, Alssio
    Frutos, Luis M.
    Fdez. Galvan, Ignacio
    Karlsson, Hans
    Lindh, Roland
    How Do Methyl Groups Enhance the Triplet Chemiexcitation Yield ofDioxetane?2017In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 8, p. 3790-3794Article in journal (Refereed)
    Abstract [en]

    Chemiluminescence is the emission of light as aresult of a nonadiabatic chemical reaction. The present work isconcerned with understanding the yield of chemiluminescence,in particular how it dramatically increases upon methylation of1,2-dioxetane. Both ground-state and nonadiabatic dynamics(including singlet excited states) of the decomposition reactionof various methyl-substituted dioxetanes have been simulated.Methyl-substitution leads to a significant increase in thedissociation time scale. The rotation around the O−C−C−Odihedral angle is slowed; thus, the molecular system stayslonger in the “entropic trap” region. A simple kinetic model isproposed to explain how this leads to a higher chemiluminescence yield. These results have important implications for the designof efficient chemiluminescent systems in medical, environmental, and industrial applications.

  • 11.
    Harczuk, Ignat
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    First Hyperpolarizability of Collagen Using the Point Dipole Approximation2016In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 11, p. 2132-2138Article in journal (Refereed)
    Abstract [en]

    The application of localized hyperpolarizabilities to predict a total protein hyperpolarizability is presented for the first time, using rat-tail collagen as a demonstration example. We employ a model comprising the quadratic Applequist point-dipole approach, the so-called LoProp transformation, and a procedure with molecular fractionation using conjugate caps to determine the atomic and bond contributions to the net beta tensor of the collagen [(PPG)(10)](3) triple-helix. By using Tholes exponential damping modification to the dyadic tensor in the Applequist equations, a correct qualitative agreement with experiment is found. The intensity of the beta(HRS) signal and the depolarization ratios are best reproduced by decomposing the LoProp properties into the atomic positions and using Tholes exponential damping with the original damping parameter. Some ramifications of the model for general protein property optimization are briefly discussed.

  • 12.
    Huttmann, Felix
    et al.
    Univ Cologne, Inst Phys 2, Zulpicher Str 77, D-50937 Cologne, Germany..
    Rothenbach, Nico
    Univ Duisburg Essen, Fak Phys, Lotharstr 1, D-47057 Duisburg, Germany.;Ctr Nanointegrat Duisburg Essen CENIDE, Lotharstr 1, D-47057 Duisburg, Germany..
    Kraus, Stefan
    Univ Cologne, Inst Phys 2, Zulpicher Str 77, D-50937 Cologne, Germany..
    Ollefs, Katharina
    Univ Duisburg Essen, Fak Phys, Lotharstr 1, D-47057 Duisburg, Germany.;Ctr Nanointegrat Duisburg Essen CENIDE, Lotharstr 1, D-47057 Duisburg, Germany..
    Arruda, Lucas M.
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany..
    Bernien, Matthias
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany..
    Thonig, Danny
    Uppsala Univ, Dept Phys & Astron, Mat Theory, SE-75120 Uppsala, Sweden..
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Fransson, Jonas
    Uppsala Univ, Dept Phys & Astron, Mat Theory, SE-75120 Uppsala, Sweden..
    Kummer, Kurt
    European Synchrotron Radiat Facil, 71 Ave Martyrs,CS40220, F-38043 Grenoble 9, France..
    Brookes, Nicholas B.
    European Synchrotron Radiat Facil, 71 Ave Martyrs,CS40220, F-38043 Grenoble 9, France..
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, Mat Theory, SE-75120 Uppsala, Sweden.;Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden..
    Kuch, Wolfgang
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany..
    Michely, Thomas
    Univ Cologne, Inst Phys 2, Zulpicher Str 77, D-50937 Cologne, Germany..
    Wende, Heiko
    Univ Duisburg Essen, Fak Phys, Lotharstr 1, D-47057 Duisburg, Germany.;Ctr Nanointegrat Duisburg Essen CENIDE, Lotharstr 1, D-47057 Duisburg, Germany..
    Europium Cyclooctatetraene Nanowire Carpets: A Low-Dimensional, Organometallic, and Ferromagnetic Insulator2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 5, p. 911-917Article in journal (Refereed)
    Abstract [en]

    We investigate the magnetic and electronic properties of europium cyclooctatetraene (EuCot) nanowires by means of low-temperature X-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM) and spectroscopy (STS). The EuCot nanowires are prepared in situ on a graphene surface. STS measurements identify EuCot as an insulator with a minority band gap of 2.3 eV. By means of Eu M-5,M-4 edge XMCD, orbital and spin magnetic moments of (-0.1 +/- 0.3)mu(B) and (+7.0 +/- 0.6)mu(B), respectively, were determined. Field-dependent measurements of the XMCD signal at the Eu M-5 edge show hysteresis for grazing X-ray incidence at 5 K, thus confirming EuCot as a ferromagnetic material. Our density functional theory calculations reproduce the experimentally observed minority band gap. Modeling the experimental results theoretically, we find that the effective interatomic exchange interaction between Eu atoms is on the order of millielectronvolts, that magnetocrystalline anisotropy energy is roughly half as big, and that dipolar energy is approximately ten times lower.

  • 13. Kullgren, Jolla
    et al.
    Hermansson, Kersti
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Broqvist, Peter
    Supercharged Low-Temperature Oxygen Storage Capacity of Ceria at the Nanoscale2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 4, p. 604-608Article in journal (Refereed)
    Abstract [en]

    We provide an explanation for the experimental finding of a dramatically enhanced low-temperature oxygen storage capacity for small ceria nanoparticles. At low temperature, small octahedral ceria nanoparticles will be understoichiometric at both oxidizing and reducing conditions without showing explicit oxygen vacancies. Instead, rather than becoming stoichiometric at oxidizing conditions, such particles are stabilized through oxygen adsorption forming superoxo (O-2(-)) ions and become in this way supercharged with oxygen. The supercharging effect is size-dependent and largest for small nanoparticles where it gives a direct increase in the oxygen storage capacity and simultaneously provides a source of active oxygen species at low temperatures.

  • 14. Li, Hua
    et al.
    Cooper, Peter K.
    Somers, Anthony E.
    Rutland, Mark W.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.
    Howlett, Patrick C.
    Forsyth, Maria
    Atkin, Rob
    Ionic Liquid Adsorption and Nanotribology at the Silica-Oil Interface: Hundred-Fold Dilution in Oil Lubricates as Effectively as the Pure Ionic Liquid2014In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 5, no 23, p. 4095-4099Article in journal (Refereed)
    Abstract [en]

    The remarkable physical properties of ionic liquids (ILs) make them potentially excellent lubricants. One of the challenges for using ILs as lubricants is their high cost. In this article, atomic force microscopy (AFM) nanotribology measurements reveal that a 1 mol % solution of IL dissolved in an oil lubricates the silica surface as effectively as the pure IL. The adsorption isotherm shows that the IL surface excess need only be approximately half of the saturation value to prevent surface contact and effectively lubricate the sliding surfaces. Using Its in this way makes them viable for large-scale applications.

  • 15.
    Li, Xin
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Leck, Caroline
    Sun, Lu
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hede, Thomas
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Cross-Linked Polysaccharide Assemblies in Marine Gels: An Atomistic Simulation2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 16, p. 2637-2642Article in journal (Refereed)
    Abstract [en]

    Marine polymeric gels or colloidal nano- and microgels have been shown to contribute significantly to the primary marine aerosol and cloud condensation nuclei over remote marine areas. A microscopic understanding of such biologically derived matter at the sea air interface is important for future development of global climate models, but unfortunately cannot be obtained from modern characterization techniques. In this contribution, we employ molecular dynamics simulations to reveal the atomistic details of marine polymeric gels represented by anionic polysaccharide assemblies. The ionic bonds formed between polysaccharides and metal ions in seawater as well as the hydrophobic contribution to surface area are investigated in detail, and destabilization of the assemblies upon removal of Ca2+ or acidification is explained. These results provide insight into physicochemical properties of polysaccharide-Ca2+ structures and enable future studies of their roles of in the wetting process of cloud droplet activation.

  • 16.
    Li, Xiyu
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Duan, Sai
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Liu, Haichun
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Chen, Guanying
    Harbin Inst Technol, Sch Chem Engn & Technol, Harbin 150001, Heilongjiang, Peoples R China.
    Luo, Yi
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China ; Federal Siberian Research Clinical Centre under FMBA of Russia, 26 Kolomenskaya, Krasnoyarsk 660037, Russia.
    On the Mechanism for the Extremely Efficient Sensitization of Yb3+ Luminescence in CsPbCl3 Nanocrystals2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 3, p. 487-492Article in journal (Refereed)
    Abstract [en]

    Rare earth ion (RE3+)-doped inorganic CsPbX3 (X = Cl or Cl/Br) nanocrystals have been presented as promising materials for applications in solar-energy conversion technology. An extremely efficient sensitization of Yb3+ luminescence in CsPbCl3 nanoparticles (NCs) was very recently demonstrated where quantum cutting is responsible for the performance of photoluminescence quantum yields over 100% (T. J. Milstein, et al. Nano Letters 2018, 18, 3792). In the present work, based on the cubic phase of inorganic perovskite, we seek to obtain atom-level insight into the basic mechanisms behind these observations in order to boost the further development of RE3+-doped CsPbX3 NCs for optoelectronics. In our calculations of cubic crystal structure, we do not find any energy level formed in the middle of the band gap, which disfavors a mechanism of stepwise energy transfer from the perovskite host to two Yb3+ ions. Our work indicates that the configuration with "right-angle" Yb3+-V-Pb-Yb3+ couple is most likely to form in Yb3+-doped CsPbCl3. Associated with this "right-angle" couple, the "right-angle" Pb atom with trapped excited states would localize the photogenerated electrons and act as the energy donor in a quantum cutting process, which achieves simultaneous sensitization of two neighboring Yb3+ ions.

  • 17.
    Liu, Lige
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. Beijing Inst Technol, Sch Phys, Beijing Key Lab, Nanophoton & Ultrafine Optoelect Syst, 5 South St Zhongguancun, Beijing 100081, Peoples R China.
    Deng, Luogen
    Beijing Inst Technol, Sch Phys, Beijing Key Lab, Nanophoton & Ultrafine Optoelect Syst, 5 South St Zhongguancun, Beijing 100081, Peoples R China..
    Huang, Sheng
    Beijing Inst Technol, Sch Mat Sci & Engn, 5 South St Zhongguancun, Beijing 100081, Peoples R China..
    Zhang, Pei
    KTH, School of Engineering Sciences (SCI), Applied Physics. Zhengzhou Univ Light Ind, Sch Elect & Informat Engn, Henan Key Lab Informat Based Elect Appliances, Zhengzhou 450002, Henan, Peoples R China.
    Linnros, Jan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Zhong, Haizheng
    Beijing Inst Technol, Sch Mat Sci & Engn, 5 South St Zhongguancun, Beijing 100081, Peoples R China..
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Photodegradation of Organometal Hybrid Perovskite Nanocrystals: Clarifying the Role of Oxygen by Single-Dot Photoluminescence2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 4, p. 864-869Article in journal (Refereed)
    Abstract [en]

    Photostability has been a major issue for perovskite materials. Understanding the photodegradation mechanism and suppressing it are of central importance for applications. By investigating single-dot photoluminescence spectra and the lifetime of MAPbX(3) (MA = CH3NH3+, X = Br, I) nanocrystals with quantum confinement under different conditions, we identified two separate pathways in the photodegradation process. The first is the oxygen-assisted light-induced etching process (photochemistry). The second is the light-driven slow charge-trapping process (photophysics), taking place even in oxygen-free environment. We clarified the role of oxygen in the photodegradation process and show how the photoinduced etching can be successfully suppressed by OSTE polymer, preventing an oxygen-assisted reaction.

  • 18.
    Liu, Lige
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics. State Key Laboratory for Mesoscopic Physics, Collaborative Innovation Center of Quantum Matter, School of Physics, Peking University, Beijing, 100871, China.
    Zhao, R.
    Xiao, C.
    Zhang, F.
    Pevere, Federico
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Shi, K.
    Huang, H.
    Zhong, H.
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Size-Dependent Phase Transition in Perovskite Nanocrystals2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 18, p. 5451-5457Article in journal (Refereed)
    Abstract [en]

    The complex structure of halide and oxide perovskites strongly affects their physical properties. Here, the effect of dimensions reduced to the nanoscale has been investigated by a combination of single-dot optical experiments with a phase transition theory. Methylammonium lead bromide (CH3NH3PbBr3) nanocrystals with two average particle sizes of ∼2 and ∼4 nm with blue and green photoluminescence, respectively, were spectrally and temporally probed on a single-particle level from 5 to 295 K. The results show that the abrupt blue shift of the photoluminescence spectra and lifetimes at ∼150 K can be attributed to the cubic-to-tetragonal phase transition in the large 4 nm nanocrystals, while this phase transition is completely absent for the small 2 nm particles in the investigated temperature range. Theoretical calculations based on Landau theory reveal a strong size-dependent effect on temperature-induced phase transitions in individual CH3NH3PbBr3 nanocrystals, corroborating experimental observations. This effect should be considered in structure-property analysis of ultrasmall perovskite crystals.

  • 19.
    Liu, Lige
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics. Peking Univ, Sch Phys, Collaborat Innovat Ctr Quantum Matter, State Key Lab Mesoscop Phys, Beijing 100871, Peoples R China..
    Zhao, Ru
    Beijing Inst Technol, Sch Mat Sci & Engn, 5 South St Zhongguancun, Beijing 100081, Peoples R China.;Beijing Inst Technol, Adv Res Inst Multidisciplinary Sci, 5 South St Zhongguancun, Beijing 100081, Peoples R China..
    Xiao, Changtao
    Beijing Inst Technol, Sch Mat Sci & Engn, 5 South St Zhongguancun, Beijing 100081, Peoples R China.;Yangtze River Storage Technol Co Ltd, Gaoxin Fourth Rd, Wuhan 430000, Hubei, Peoples R China..
    Zhang, Feng
    Beijing Inst Technol, Sch Mat Sci & Engn, 5 South St Zhongguancun, Beijing 100081, Peoples R China.;Tsinghua Univ, Dept Chem, Beijing 100084, Peoples R China..
    Pevere, Federico
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Shi, Kebin
    Peking Univ, Sch Phys, Collaborat Innovat Ctr Quantum Matter, State Key Lab Mesoscop Phys, Beijing 100871, Peoples R China..
    Huang, Houbing
    Beijing Inst Technol, Sch Mat Sci & Engn, 5 South St Zhongguancun, Beijing 100081, Peoples R China.;Beijing Inst Technol, Adv Res Inst Multidisciplinary Sci, 5 South St Zhongguancun, Beijing 100081, Peoples R China..
    Zhong, Haizheng
    Beijing Inst Technol, Sch Mat Sci & Engn, 5 South St Zhongguancun, Beijing 100081, Peoples R China..
    Sychugov, Ilya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Using Mechanical Stress to Investigate the Rashba Effect in Organic-Inorganic Hybrid Perovskites2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 18, p. 5451-5457Article in journal (Refereed)
    Abstract [en]

    Organic-inorganic hybrid perovskites simultaneously possess strong spin- orbit coupling (SOC) and structure inversion asymmetry, establishing a Rashba effect to influence light emission and photovoltaics. Here, we use mechanical bending as a convenient approach to investigate the Rashba effect through SOC in perovskite (MAPbI(3-x)Cl(x)) films by elastically deforming grains. It is observed that applying a concave bending can broaden the line shape of the magnetophotocurrent, increasing the internal magnetic parameter B-0 from 121 to 205 mT, which indicates an enhancement on SOC. Interestingly, the PL lifetime is found to be enlarged from 9.9 to 14.8 ns under this bending, which suggests that introducing compressive strain can essentially increase the Rashba effect through SOC, leading to an increase upon indirect band transition. Furthermore, the PL peak associated with the Rashba effect is shifted from 776 to 780 nm under this mechanical bending. Therefore, mechanical bending provides a convenient experimental method to approach the Rashba effect in hybrid perovskites.

  • 20. Ma, S.
    et al.
    Li, H.
    Tian, K.
    Ye, S.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    In situ and real-time sfg measurements revealing organization and transport of cholesterol analogue 6-ketocholestanol in a cell membrane2014In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 5, no 3, p. 419-424Article in journal (Refereed)
    Abstract [en]

    Cholesterol organization and transport within a cell membrane are essential for human health and many cellular functions yet remain elusive so far. Using cholesterol analogue 6-ketocholestanol (6-KC) as a model, we have successfully exploited sum frequency generation vibrational spectroscopy (SFG-VS) to track the organization and transport of cholesterol in a membrane by combining achiral-sensitive ssp (ppp) and chiral-sensitive psp polarization measurements. It is found that 6-KC molecules are aligned at the outer leaflet of the DMPC lipid bilayer with a tilt angle of about 10. 6-KC organizes itself by forming an α-β structure at low 6-KC concentration and most likely a β-β structure at high 6-KC concentration. Among all proposed models, our results favor the so-called umbrella model with formation of a 6-KC cluster. Moreover, we have found that the long anticipated flip-flop motion of 6-KC in the membrane takes time to occur, at least much longer than previously thought. All of these interesting findings indicate that it is critical to explore in situ, real-time, and label-free methodologies to obtain a precise molecular description of cholesterol's behavior in membranes. This study represents the first application of SFG to reveal the cholesterol-lipid interaction mechanism at the molecular level.

  • 21. McFarland, Hannah L.
    et al.
    Ahmed, Towfiq
    Zhu, Jian-Xin
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Los Alamos Natl Lab, Inst Mat Sci, Los Alamos, NM 87545 USA.
    Haradsen, Jason T.
    First-Principles Investigation of Nanopore Sequencing Using Variable Voltage Bias on Graphene-Based Nanoribbons2015In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 13, p. 2616-2621Article in journal (Refereed)
    Abstract [en]

    In this study, we examine the mechanism of nanopore-based DNA sequencing using a voltage bias across a graphene nanoribbon. Using density function theory and a nonequilibrium Green's function approach, we determine the transmission spectra and current profile for adenine, guanine, cytosine, thymine, and uracil as a function of bias voltage in an energy minimized configuration. Utilizing the transmission current, we provide a general methodology for the development of a three nanopore graphene-based device that can be used to distinguish between the various nucleobases for DNA/RNA sequencing. From our analysis, we deduce that it is possible to use different transverse currents across a multinanopore device to differentiate between nucleobases using various voltages of 0.5, 1.3, and 1.6 V. Overall, our goal is to improve nanopore design to further DNA/RNA nucleobase sequencing and biomolecule identification techniques.

  • 22.
    Miao, Quan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Shandong University of Science and Technology, China.
    Travnikova, Oksana
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Synchrotron SOLEIL, L'Orme des Merisiers, France.
    Kimberg, Victor
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Synchrotron SOLEIL, L'Orme des Merisiers, France.
    Sun, Yu-Ping
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Shandong University of Technology, China.
    Thomas, T. Darrah
    Nicolas, Christophe
    Patanen, Minna
    Miron, Catalin
    Rotational Doppler Effect: A Probe for Molecular Orbitals Anisotropy2015In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 9, p. 1568-1572Article in journal (Refereed)
    Abstract [en]

    The vibrationally resolved X-ray photoelectron spectra of X-2 Sigma(+)(g)(3 sigma(-1)(g)) and B-2 Sigma(+)(u)(2 sigma(-1)(u)) states of N-2(+) were recorded for different photon energies and orientations of the polarization vector. Clear dependencies of the spectral line widths on the X-ray polarization as well as on the symmetry of the final electronic states are observed. Contrary to the translational Doppler, the rotational Doppler broadening is sensitive to the photoelectron emission anisotropy. On the basis of theoretical modeling, we suggest that the different rotational Doppler broadenings observed for gerade and ungerade final states result from a Young's double-slit interference phenomenon.

  • 23.
    Monti, Susanna
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Carravetta, Vincenzo
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Simulation of Gold Functionalization with Cysteine by Reactive Molecular Dynamics2016In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 2, p. 272-276Article in journal (Refereed)
    Abstract [en]

    The anchoring mechanism of cysteine to gold in water solution is characterized in detail by means of a combination of quantum chemistry (QC) and reactive classical molecular dynamics (RC-MD) calculations. A possible adsorption-reaction route is proposed, through RC-MD simulations based on a modified version of the protein reactive force field (ReaxFF), in which gold-protein interactions have been included after accurate parametrization at the QC level. The computational results confirm recent experimental findings regarding the mechanism as a two-step binding, namely, a slow physisorption followed by a fast chemisorption. The reaction barriers are estimated through the nudged elastic band approach and checked by QC calculations. Surface reconstructions, induced by the strong adsorption of the molecule, are identified, and their role, as further adsorbate stabilizers, is properly disclosed. The satisfactory agreement with QC data and experiments confirm the reliability of the simulations and the unique opportunity they provide to follow locally molecule adsorption on selected materials.

  • 24.
    Murugan, N. Arul
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Halldin, Christer
    Nordberg, Agneta
    Langstrom, Bengt
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    The Culprit Is in the Cave: The Core Sites Explain the Binding Profiles of Amyloid-Specific Tracers2016In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 7, no 17, p. 3313-3321Article in journal (Refereed)
    Abstract [en]

    The design of molecular probes and tracer molecules with specificity toward amyloid beta (A beta) fibrils is of paramount importance for the selective diagnosis of Alzheimer's disease. This requires a detailed understanding of the binding sites in amyloid targets, their number, and their binding mechanism for various tracer molecules. We adopt an integrated approach including molecular docking, molecular dynamics, and generalized Born-based free energy calculations to investigate site-specific interactions of different amyloid binding molecules. Our study reproduces the experimental results on the relative binding affinity of the tracers and amyloid binders and explains the feature of "multiple binding sites" in amyloid targets as probed by competition binding experiments. A major outcome of this study is that it is the core sites of the Afi fibrils that are responsible for the experimentally reported binding profiles of tracers in amyloid targets rather than the surface sites that received much focus in earlier investigations.

  • 25.
    Natarajan Arul, Murugan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Olsen, Jogvan Magnus Haugaard
    Kongsted, Jacob
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Aidas, Kestutis
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Amyloid Fibril-Induced Structural and Spectral Modifications in the Thioflavin-T Optical Probe2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 1, p. 70-77Article in journal (Refereed)
    Abstract [en]

    Motivated by future possibilities to design target molecules for fibrils with diagnostic or therapeutic capability related to amyloidosis diseases, we investigate in this work the dielectric nature of amyloid fibril microenvironments in different binding sites using an optical probe, thioflavin-T (THT), which has been used extensively to stain such fibrils. We study the fibril-environment-induced structural and spectral changes of THT at each binding site and compare the results to the fibril-free situation in aqueous solution. All binding sites are found to show a similar effect with respect to the conformational changes of THT; in the presence of the fibril, its molecular geometry tends to become planarized. However, depending on the dielectric nature of the specific binding site, a red shift, blue shift, or no shift in the absorption spectra of THT is predicted. Interestingly, the experimentally measured red shift in the spectra is seen only when THT binds to one of the core or surface-binding sites. It is found that the dielectric nature of the microenvironment in the fibril is strongly nonhomogeneous.

  • 26. Ni, Wenjun
    et al.
    Gurzadyan, Gagik G.
    Zhao, Jianzhang
    Che, Yuanyuan
    Li, Xiaoxin
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Organic chemistry.
    Singlet Fission from Upper Excited Electronic States of Cofacial Perylene Dimer2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 10, p. 2428-2433Article in journal (Refereed)
    Abstract [en]

    Singlet fission directly from the upper excited vibrational and electronic states of cofacial perylene dimers, bypassing the relaxed state S-1, was detected within 50 fs. This process competes well with vibrational cooling in S-1 (4.7-7.0 ps) and S-2 -> S-1 internal conversion (380 fs). The singlet fission has the energy threshold E = 3.06 eV. Other competitive relaxation processes are excimer and dimer cation formation on an ultrafast time scale. Excitation to higher energy levels (4.96 eV) leads to a higher efficiency of singlet fission.

  • 27.
    Okur, Halil I.
    et al.
    Ecole Polytech Fed Lausanne, Inst Bioengn IBI, Sch Engn STI, Lab Fundamental BioPhoton LBP, CH-1015 Lausanne, Switzerland.;Ecole Polytech Fed Lausanne, Inst Mat Sci IMX, Sch Engn STI, CH-1015 Lausanne, Switzerland.;Ecole Polytech Fed Lausanne, Lausanne Ctr Ultrafast Sci LACUS, CH-1015 Lausanne, Switzerland..
    Drexler, Chad I.
    Penn State Univ, Dept Chem, University Pk, PA 16802 USA..
    Tyrode, Eric
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry. Ecole Polytech Fed Lausanne, Inst Bioengn IBI, Sch Engn STI, Lab Fundamental BioPhoton LBP, CH-1015 Lausanne, Switzerland.;Ecole Polytech Fed Lausanne, Inst Mat Sci IMX, Sch Engn STI, CH-1015 Lausanne, Switzerland.;Ecole Polytech Fed Lausanne, Lausanne Ctr Ultrafast Sci LACUS, CH-1015 Lausanne, Switzerland..
    Cremer, Paul S.
    Penn State Univ, Dept Chem, University Pk, PA 16802 USA.;Penn State Univ, Biochem & Mol Biol, University Pk, PA 16802 USA..
    Roke, Sylvie
    Ecole Polytech Fed Lausanne, Inst Bioengn IBI, Sch Engn STI, Lab Fundamental BioPhoton LBP, CH-1015 Lausanne, Switzerland.;Ecole Polytech Fed Lausanne, Inst Mat Sci IMX, Sch Engn STI, CH-1015 Lausanne, Switzerland.;Ecole Polytech Fed Lausanne, Lausanne Ctr Ultrafast Sci LACUS, CH-1015 Lausanne, Switzerland..
    The Jones-Ray Effect Is Not Caused by Surface-Active Impurities2018In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 9, no 23, p. 6739-6743Article in journal (Refereed)
    Abstract [en]

    Pure aqueous electrolyte solutions display a minimum in surface tension at concentrations of 2 +/- 1 mM. This effect has been a source of controversy since it was first reported by Jones and Ray in the 1930s. The Jones Ray effect has frequently been dismissed as an artifact linked to the presence of surface-active impurities. Herein we systematically consider the effect of surface-active impurities by purposely adding nanomolar concentrations of surfactants to dilute electrolyte solutions. Trace amounts of surfactant are indeed found to decrease the surface tension and influence the surface chemistry. However, surfactants can be removed by repeated aspiration and stirring cycles, which eventually deplete the surfactant from solution, creating a pristine surface. Upon following this cleaning procedure, a reduction in the surface tension by millimolar concentrations of salt is still observed. Consequently, we demonstrate that the Jones Ray effect is not caused by surface-active impurities.

  • 28. Santoro, F.
    et al.
    Improta, R.
    Fahleson, T.
    Kauczor, J.
    Norman, Patrick
    Linköping University, Sweden.
    Coriani, S.
    Relative stability of the La and Lb excited states in adenine and guanine: Direct evidence from TD-DFT calculations of MCD spectra2014In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 5, no 11, p. 1806-1811Article in journal (Refereed)
    Abstract [en]

    The relative position of La and Lb ππ* electronic states in purine nucleobases is a much debated topic, since it can strongly affect our understanding of their photoexcited dynamics. To assess this point, we calculated the absorption and magnetic circular dichroism (MCD) spectra of adenine, guanine, and their nucleosides in gas-phase and aqueous solution, exploiting recent developments in MCD computational technology within time-dependent density functional theory. MCD spectroscopy allows us to resolve the intense S0 La transition from the weak S 0Lb transition. The spectra obtained in water solution, by using B3LYP and CAM-B3LYP functionals and describing solvent effect by cluster models and by the polarizable continuum model (PCM), are in very good agreement with the experimental counterparts, thus providing direct and unambiguous evidence that the energy ordering predicted by TD-DFT, La < L b, is the correct one.

  • 29.
    Sengupta, Sanghamitra
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    Moberg, Daniel R.
    Univ Calif San Diego, Dept Chem & Biochem, Mat Sci & Engn, La Jolla, CA 92093 USA..
    Paesani, Francesco
    Univ Calif San Diego, Dept Chem & Biochem, Mat Sci & Engn, La Jolla, CA 92093 USA.;Univ Calif San Diego, San Diego Supercomp Ctr, La Jolla, CA 92093 USA..
    Tyrode, Eric
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    Neat Water-Vapor Interface: Proton Continuum and the Nonresonant Background2018In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 9, no 23, p. 6744-6749Article in journal (Refereed)
    Abstract [en]

    Whether the surface of neat water is "acidic" or "basic" remains an active and controversial field of research. Most of the experimental evidence supporting the preferential adsorption of H3O+ ions stems from nonlinear optical spectroscopy methods typically carried out at extreme pH conditions (pH < 1). Here, we use vibrational sum frequency spectroscopy (VSFS) to target the "proton continuum", an unexplored frequency range characteristic of hydrated protons and hydroxide ions. The VSFS spectra of neat water show a broad and nonzero signal intensity between 1700 and 3000 cm-' in the three different polarization combinations examined. By comparing the SF response of water with that from dilute HCl and NaOH aqueous solutions, we conclude the intensity does not originate from either adsorbed H3O+ or OH- ions. Contributions from the nonresonant background are then critically considered by comparing the experimental results with many-body molecular dynamics (MB-MD) simulated spectra.

  • 30. Travnikova, Oksana
    et al.
    Kimberg, Victor
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Flammini, Roberto
    Liu, Xiao-Jing
    Patanen, Minna
    Nicolas, Christophe
    Svensson, Svante
    Miron, Catalin
    On Routes to Ultrafast Dissociation of Polyatomic Molecules2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 14, p. 2361-2366Article in journal (Refereed)
    Abstract [en]

    Dissociation pathways for complex polyatomic molecules can sometimes be obscure due to the multitude of degrees of freedom involved. Here, we suggest the description of a dissociation mechanism implying multimode dynamics on the barrierless potential energy surface. The mechanism is elaborated from the X-ray spectroscopic analysis of the ultrafast nuclear motion in core?shell excited molecules. We infer that in large molecules, dissociation pathways are observed to deviate from the two-body dissociation coordinate due to the internal motion of light linkages, which alters dissociation rates and may yield heavy products on very short time scales. The mechanism is exemplified with the case of 1-bromo-2-chloroethane, where the rotation of the C2H4-moiety leads to the dissociation of C?Cl or C?Br bonds in Cl2p or Br3d core-excited states, whose lifetimes last only ?7 fs. Dissociation pathways for complex polyatomic molecules can sometimes be obscure due to the multitude of degrees of freedom involved. Here, we suggest the description of a dissociation mechanism implying multimode dynamics on the barrierless potential energy surface. The mechanism is elaborated from the X-ray spectroscopic analysis of the ultrafast nuclear motion in core?shell excited molecules. We infer that in large molecules, dissociation pathways are observed to deviate from the two-body dissociation coordinate due to the internal motion of light linkages, which alters dissociation rates and may yield heavy products on very short time scales. The mechanism is exemplified with the case of 1-bromo-2-chloroethane, where the rotation of the C2H4-moiety leads to the dissociation of C?Cl or C?Br bonds in Cl2p or Br3d core-excited states, whose lifetimes last only ?7 fs.

  • 31.
    Wu, Yan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Zhan, Yiqiang
    Fahlman, Mats
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    'In-situ' Solution Processed Room Temperature Ferromagnetic MgO Thin Films Printed by Inkjet TechniqueIn: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185Article in journal (Other academic)
  • 32. Yang, Lei
    et al.
    Zhang, Jinbao
    Shen, Yang
    Park, Byung-Wook
    Bi, Dongqin
    Häggman, Leif
    Johansson, Erik M. J.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Vlachopoulos, Nick
    Snedden, Alan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jarboui, Adel
    Chams, Amani
    Perruchot, Christian
    Jouini, Mohamed
    New Approach for Preparation of Efficient Solid-State Dye-Sensitized Solar Cells by Photoelectrochemical Polymerization in Aqueous Micellar Solution2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 23, p. 4026-4031Article in journal (Refereed)
    Abstract [en]

    Hereby, we present a new, cost-effective, and environmentally friendly method of preparing an efficient solid-state dye-sensitized solar cell (sDSC) using a PEDOT conducting polymer as the hole conductor and a recently developed organic sensitizer. PEDOT is generated and deposited on the dye-sensitized TiO2 electrode by in situ photoelectropolymerization of bis-EDOT in aqueous micellar solution. The advantages of this approach are the use of water as the solvent and the obtainment of a sDSC simply by adding a silver layer on the as-obtained polymer film deposited on dye/TiO2 without the need for electrolytic solution. The sDSC containing the film prepared as above is compared to those where the organic dye is used to generate the same polymer film but in organic solvent. The energy conversion efficiency values of the two cells appear comparable, 4.8% for sDSC prepared in the aqueous-phase polymerized PEDOT and 6% for the sDSC prepared with in organic-phase polymerized PEDOT.

  • 33. Yu, Shun
    et al.
    Santoro, Gonzalo
    Sarkar, Kuhu
    Dicke, Benjamin
    Wessels, Philipp
    Bommel, Sebastian
    Döhrmann, Ralph
    Perlich, Jan
    Kuhlmann, Marion
    Metwalli, Ezzeldin
    Risch, Johannes F.H.
    Schwartzkopf, Matthias
    Müller-Buschbaum, Peter
    Roth, Stephan V.
    Formation of Al Nanostructure on Alq3: An in Situ Grazing Incidence Small Angle X-Ray Scattering Study during Sputtering Deposition2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 18, p. 3170-3175Article in journal (Refereed)
  • 34. Zhang, Zhisen
    et al.
    Shen, Jiawei
    Wang, Hongbo
    Wang, Qi
    Zhang, Junqiao
    Liang, Lijun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tu, Yaoquan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Effects of Graphene Nanopore Geometry on DNA Sequencing2014In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 5, no 9, p. 1602-1607Article in journal (Refereed)
    Abstract [en]

    In this Letter we assess the effect of graphene nanopore geometries on DNA sequencing by considering DNA fragments including A, T, C, G, and 5-methylcytosine (MC) pulled out of graphene nanopores of different geometries with diameters down to similar to 1 nm. Using steered molecular dynamics simulations it is demonstrated that the bases (A, T, C, G, and MC) can be indentified at single-base resolution through the characteristic peaks on the force profile in a circular graphene nanopore but not in nanopores with other asymmetric geometries. Our study suggests that the graphene nanopore surface should be modified as symmetrically as possible in order to sequence DNA by atomic force microscopy or optical tweezers.

1 - 34 of 34
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