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Journal of Physical Chemistry Letters

Jinlu He, Meng Guo, Run Long
All-inorganic perovskites have attracted intense interest as promising photovoltaic materials due to their excellent performance. Using time domain density functional theory combined with nonadiabatic (NA) molecular dynamics, we demonstrate that a photoinduced localized polaron-like hole greatly delays the nonradiative electron-hole recombination relative to the structure with delocalized free charge of the CsPbBr3 . This is because localized charge carriers diminish overlap between electron and hole wave functions and decrease the NA coupling by a factor of 6...
May 22, 2018: Journal of Physical Chemistry Letters
Rebecca L M Gieseking, Joonhee Lee, Nicholas Tallarida, Vartkess Ara Apkarian, George C Schatz
Tip-enhanced Raman spectromicroscopy (TERS) with CO-terminated plasmonic tips can probe Ångstrom-scale features of molecules on surfaces. The development of this technique requires understanding of how chemical environments affect the CO vibrational frequency and TERS intensity. At the scanning tunneling microscope junction of a CO-terminated Ag tip, we show that rather than the classical vibrational Stark effect, the large bias dependence of the CO frequency shift is due to ground-state charge transfer from the Ag tip into the CO π* orbital softening the C-O bond at more positive biases...
May 21, 2018: Journal of Physical Chemistry Letters
Maria Acebron, Juan F Galisteo-López, Cefe Lopez, Facundo C Herrera, Martin D Mizrahi, Felix G Requejo, Francisco Javier Palomares, Beatriz H Juarez
Compositional changes taking place during the synthesis of alloyed CdSeZnS nanocrystals (NCs) allow shifting the optical features to higher energy as the NCs grow. Under certain synthetic conditions, the effect of those changes on the surface/interface chemistry competes with and dominates over the conventional quantum confinement effect in growing NCs. These changes, identified by means of complementary advanced spectroscopic techniques such as XPS (X-ray Photoelectron Spectroscopy) and XAS (X-ray absorption Spectroscopy), are understood in the frame of an ion migration and exchange mechanism taking place during the synthesis...
May 21, 2018: Journal of Physical Chemistry Letters
Ilia Kaminker, Songi Han
Dynamic nuclear polarization (DNP) takes center stage in nuclear magnetic resonance (NMR) as a tool to amplify its signal by orders of magnitude through the transfer of polarization from electron to nuclear spins. In contrast to modern NMR and electron paramagnetic resonance (EPR) that extensively rely on pulses for spin manipulation in the time domain, the current mainstream DNP technology exclusively relies on monochromatic continuous wave (CW) irradiation. This study introduces arbitrary phase shaped pulses that constitute a train of coherent chirp pulses in the time domain at 200 GHz (7 Tesla) to dramatically enhance the saturation bandwidth and DNP performance compared to CW DNP, yielding up to 500-fold in NMR signal enhancements...
May 18, 2018: Journal of Physical Chemistry Letters
Viktoriia A Saveleva, Li Wang, Detre Teschner, Travis E Jones, Aldo S Gago, K Andreas Friedrich, Spyridon Zafeiratos, Robert Schloegl, Elena R Savinova
Progress in the development of the proton exchange membrane (PEM) water electrolysis technology requires decreasing the anode overpotential, where the sluggish multistep oxygen evolution reaction (OER) occurs. This calls for the understanding of the nature of the active OER sites and reaction intermediates, which are still being debated. In this work, we apply synchrotron radiation - based near ambient pressure X-ray photoelectron and absorption spectroscopies under operando conditions in order to unveil the nature of the reaction intermediates and shed light on the OER mechanism on electrocatalysts most widely used in PEM electrolyzers - electrochemical and thermal iridium oxides...
May 18, 2018: Journal of Physical Chemistry Letters
Hatice Gokcan, Eric Granville Kratz, Thomas A Darden, Jean-Philip Piquemal, Gerardo Andres Cisneros
The use of advanced polarizable potentials in Quantum Mechanical/Molecular Mechanical (QM/MM) simulations have been shown to improve the overall accuracy of the calculation. We have developed a density-based potential called the Gaussian Electrostatic Model (GEM), which has been shown to provide very accurate environments for QM wavefunctions in QM/MM. In this contribution we present a new implementation of QM/GEM that extends our implementation to include all components (Coulomb, exchange-repulsion, polarization, and dispersion) for the total inter-molecular interaction energy in QM/MM calculations, except for the charge-transfer term...
May 18, 2018: Journal of Physical Chemistry Letters
Hao Wang, Weitao Yang
We developed a novel neural network based force field for water based on training with high level ab initio theory. The force field was built based on electrostatically embedded many-body expansion method truncated at binary interactions. Many-body expansion method is a common strategy to partition the total Hamiltonian of large systems into a hierarchy of few-body terms. Neural networks were trained to represent electrostatically embedded one-body and two-body interactions, which require as input only one and two water molecule calculations at the level of ab initio electronic structure method CCSD/aug-cc-pVDZ embedded in the molecular mechanics water environment, making it efficient as a general force field construction approach...
May 18, 2018: Journal of Physical Chemistry Letters
Seiichiro Izawa, Naoto Shintaku, Masahiro Hiramoto
Open-circuit voltage ( VOC ) is a key parameter governing the power conversion efficiency of organic solar cells. We clarified the effect of band bending in organic semiconductor films on the VOC of phthalocyanine (H2 Pc)/fullerene (C60 ) planar heterojunction (PHJ) OSCs. The VOC was significantly affected by the H2 Pc layer thickness, varying from 0.20 V at 2 nm to 0.49 V at 100 nm thickness. The large VOC change is due to the band bending in the H2 Pc layer, where the difference in H2 Pc layer thickness led to significant changes in the degree of the vacuum-level shift in the C60 layer because of the Fermi level ( EF ) difference between the H2 Pc and C60 layers...
May 18, 2018: Journal of Physical Chemistry Letters
Rhokyun Kwak, Jongyoon Han
On ion selective membranes, cation/anion selective transport under electric field initiates ion concentration polarization (ICP); ion concentration increases at one side of the membrane (ion enrichment), while it decreases at the other side (ion depletion). This polarization always occurs as the pair of ion enrichment and ion depletion. Here, departing from such pair generation, we demonstrate that only half of ICP (either ion enrichment or ion depletion) can be solitary on a Nafion-coated electrode. Current-voltage-time responses and conductance measurement capture this half-cell ICP with qualitative in situ pH / ion concentration visualization...
May 17, 2018: Journal of Physical Chemistry Letters
Yuanyuan Hu, Lang Jiang, Qinjun Chen, Jing Guo, Zhuojun Chen
It is commonly accepted that gate dielectric dipoles can induce energetic disorder in organic field-effect transistors. However, convincing experimental evidence that directly demonstrate this effect are still in lack. In this work, we present a combined experimental and theoretical study to reveal this effect. We have investigated the temperature-dependent mobility of two rubrene single-crystal transistors with different polymer dielectrics. Model fittings of the data indicate there is higher energetic disorder in the device on dielectric with larger permittivity...
May 17, 2018: Journal of Physical Chemistry Letters
Joshua S Kretchmer, Garnet Kin-Lic Chan
We explore model electron dynamics of an atom scattering off a surface within the time-dependent complete active space self-consistent field (TD-CASSCF) approximation. We focus especially on the scattering of a hydrogen atom and its resulting spin dynamics starting from an initially spin-polarized state. Our results reveal competing electronic time scales that are governed by the electronic structure of the surface as well as the character of the atom. The time scales and nonadiabaticity of the dynamics are reported on by the final spin polarization of the scattered atom, which may be probed in future experiments...
May 17, 2018: Journal of Physical Chemistry Letters
Immad M Nadeem, Jon P W Treacy, Sencer Selcuk, Xavier Torrelles, Hadeel Hussain, Axel Wilson, David C Grinter, Gregory Cabailh, Oier Bikondoa, Chris Nicklin, Annabella Selloni, Jörg Zegenhagen, Robert Lindsay, Geoff Thornton
Elucidating the structure of the interface between natural (reduced) anatase TiO2 (101) and water is an essential step towards understanding the associated photo-assisted water splitting mechanism. Here we present surface X-ray diffraction results for the room temperature interface with ultra-thin and bulk water, which we explain by reference to density functional theory calculations. We find that both interfaces contain a 25:75 mixture of molecular H2 O and terminal OH bound to titanium atoms along with bridging OH species in the contact layer...
May 16, 2018: Journal of Physical Chemistry Letters
Alex P Gaiduk, Jeffrey A Gustafson, Francois Gygi, Giulia Galli
We carried out first-principles simulations of liquid water at ambient conditions using a dielectric-dependent hybrid functional, where the fraction of exact exchange is set equal to the inverse of the high-frequency dielectric constant of the liquid. We found excellent agreement with experiment for the oxygen-oxygen partial correlation function at the experimental equilibrium density and 311±3 K. Other structural and dynamical properties such as the diffusion coefficient, molecular dipole moments, and vibrational spectra, are also in good agreement with experiment...
May 16, 2018: Journal of Physical Chemistry Letters
Yongliang Shi, Boao Song, Reza Shahbazian-Yassar, Jin Zhao, Wissam A Saidi
In nanometer clusters (NCs) each atom counts. It is the specific arrangement of these atoms that determines the unique size-dependent functionalities of the NCs and hence their applications. Here we employ a self-consistent, combined theoretical and experimental approach to determine atom-by-atom the structures of supported Pt NCs on MoS2. The atomic structures are predicted using a genetic algorithm utilizing atomistic force fields and density functional theory, which are then validated using aberration-corrected scanning transmission electron microscopy...
May 16, 2018: Journal of Physical Chemistry Letters
Nikita V Tepliakov, Ilia A Vovk, Anvar S Baimuratov, Mikhail Yu Leonov, Alexander V Baranov, Anatoly V Fedorov, Ivan D Rukhlenko
We present a rigorous analysis of optical activity of chiral semiconductor gammadions whose chirality in three dimensions is caused by the nonuniformity of thickness in the transverse plane. It is shown that such gammadions not only distinguish between the two circular polarisations upon scattering and reflection of light, like all two-dimensional semiconductor nanostructures with planar chirality do, but also exhibit circular dichroism and circularly polarized luminescence. Chiral semiconductor gammadions whose charge carriers are mostly confined to the arms are found to feature both high dissymmetry of optical response and a constant-sign circular dichroism signal over a wide frequency range...
May 16, 2018: Journal of Physical Chemistry Letters
Julie Desarnaud, Hannelore Derluyn, Jan Carmeliet, Daniel Bonn, Noushine Shahidzadeh
The growth of hopper crystals is observed for many substances, but the mechanism of their formation remains ill understood. Here we investigate their growth by performing evaporation experiments on small volumes of salt solutions. We show that sodium chloride crystals that grow very fast from a highly supersaturated solution form a peculiar form of hopper crystal consisting of a series of connected miniature versions of the original cubic crystal. The transition between cubic and such hopper growth happens at a well-defined supersaturation where the growth rate of the cubic crystal reaches a maximum ( 6...
May 16, 2018: Journal of Physical Chemistry Letters
Yanan Wang, Hongli Guo, Qijing Zheng, Wissam A Saidi, Jin Zhao
Solvated electron states at oxide/aqueous interface represent the lowest energy charge transfer pathways, thereby playing an important role in photocatalysis and electronic device applications. However, their energies are usually higher than the conduction band minimum (CBM), which makes the solvated electrons difficult to utilize in charge transfer processes. Thus, it is essential to stabilize the energy of the solvated electron states. In this report, taking LaAlO3/SrTiO3 (LAO/STO) oxide heterostructure with H2O adsorbed monolayer as a prototypical system, we show using DFT and ab initio time dependent nonadiabatic molecular dynamics simulation that the energy and dynamics of solvated electrons can be tuned by the electric field in the polar-nonpolar oxide heterostructure...
May 16, 2018: Journal of Physical Chemistry Letters
Mihael Coric, Nitin Saxena, Mika Pflüger, Peter Muller-Buschbaum, Michael Krumrey, Eva M Herzig
Scattering techniques are a powerful tool for probing thin film nanomorphologies, but often require additional characterization by other methods. We applied the well-established grazing-incidence small angle X-ray scattering (GISAXS) technique for a selection of energies around the absorption edge of sulfur to exploit the resonance effect (grazing incidence resonant tender X-ray scattering - GIR-TeXS) of the sulfur atoms within a P3HT-PCBM sample to gain information about the composition of the film morphology...
May 16, 2018: Journal of Physical Chemistry Letters
Bei Ding, Lijiang Yang, Debopreeti Mukherjee, Jianxin Chen, Yi Qin Gao, Feng Gai
: We employ site-specific, linear and nonlinear infrared spectroscopic techniques as well as fluorescence spectroscopy and molecular dynamics simulations to investigate the binding interactions of urea and three of its derivatives, methylurea, 1,3-dimethylurea and tetramethylurea, with protein aromatic and polar sidechains. We find that (1) urea methylation leads to preferential interactions between the co-solvent molecules and aromatic sidechains with an affinity that increases with the number of methyl groups; (2) interactions with tetramethylurea cause significant dehydration of aromatic sidechains and the effect is most pronounced for tryptophan; and (3) while neither urea nor tetramethylurea shows preferential accumulation around a polar sidechain, the number of hydrogen-bond donors around this sidechain is significantly decreased in the presence of tetramethylurea...
May 16, 2018: Journal of Physical Chemistry Letters
Federico A Gorelli, Simone De Panfilis, Taras Bryk, Lorenzo Ulivi, Gaston Garbarino, Paraskevas Parisiades, Mario Santoro
We investigated the atomic structure of liquid Rb along an isothermal path at 573 K, up to 23 GPa, by x-ray diffraction measurements. By rising pressure, we observed a liquid-liquid transformation between a simple metallic liquid, to a complex one. The transition occurs at 7.5 ± 1 GPa which is slightly above the first maximum of the T-P melting line. This transformation is traced back to the density induced hybridization of highest electronic orbitals leading to the accumulation of valence electrons between Rb atoms and to the formation of interstitial atomic shells, a behavior that Rb shares with Cs and is likely to be common to all alkali metals...
May 15, 2018: Journal of Physical Chemistry Letters
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