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Journal of Physical Chemistry Letters

Ye Wang, Amine Slassi, Marc-Antoine Stoeckel, Simone Bertolazzi, Jerome Cornil, David Beljonne, Paolo Samorì
Two-dimensional (2D) transition metal dichalcogenides (TMDs) recently emerged as novel materials displaying a wide variety of physico-chemical properties that render them unique scaffolds for high-performance (opto)electronics. The controlled physisorption of molecules on the TMD surface is a viable approach to tune their optical and electronic properties. Solvents, made of small aromatic molecules, are frequently employed for the cleaning of the 2D materials or as "dispersant" for their chemical functionalization with larger (macro)molecules, without considering their potential key effect in locally modifying the characteristics of 2D materials...
January 16, 2019: Journal of Physical Chemistry Letters
Abhishek Bagusetty, J Karl Johnson
We predict that graphane functionalized with hydroxyl groups, hydroxygraphane, can conduct protons in the complete absence of water, as shown from density functional theory calculations. Hydroxygraphane's anhydrous intrinsic proton conductivity results from the self-assembling two-dimensional network of hydrogen bonds on its surface. We show that the proton conduction occurs through a Grotthuss-like mechanism, as protons hop between neighboring hydroxyl groups, aided by their rotation. Our calculations predict that hydroxygraphane has a direct bandgap of 3...
January 16, 2019: Journal of Physical Chemistry Letters
Roland Kozubek, Mukesh Tripathi, Mahdi Ghorbani-Asl, Silvan Kretschmer, Lukas Madauß, Erik Pollmann, Maria O'Brien, Niall McEvoy, Ursula Ludacka, Toma Susi, Georg S Duesberg, Richard Arthur Wilhelm, Arkady V Krasheninnikov, Jani Kotakoski, Marika Y Schleberger
Porous single layer molybdenum disulfide (MoS2 ) is a promising material for applications such as DNA sequencing and water desalination. In this work, we introduce irradiation with highly charged ions (HCIs) as a new technique to fabricate well-defined pores in MoS2 . Surprisingly, we find a linear increase of the pore creation efficiency over a broad range of potential energies. Comparison to atomistic simulations reveals the critical role of energy deposition from the ion to the material through electronic excitation in the defect creation process, and suggests an enrichment in molybdenum in the vicinity of the pore edges at least for ions with low potential energies...
January 15, 2019: Journal of Physical Chemistry Letters
Asif Equbal, Alisa Leavesley, Sheetal K Jain, Songi Han
The scope of this perspective is to analytically describe NMR hyper-polarization by the three-spin cross effect (CE) dynamic nuclear polarization (DNP) using an effectiveHamiltonian concept. We apply, for the first time, the bimodal operator-based Floquet theory in the Zeeman-interaction frame for two and three coupled spins to derive the known interaction Hamiltonian for CE-DNP. With a unified understanding of CE-DNP, and supported by empirical observation of the state of electron spin polarization under the given experimental conditions, we explain diverse manifestations of CE from oversaturation, enhanced hyper-polarization by broad-band saturation to nuclear spin depolarization under magic-angle spinning...
January 15, 2019: Journal of Physical Chemistry Letters
Xin Liang, Feihu Dai
In this work, heat and charge transport were measured in a series of deformed bulk Cu samples where dislocation density was tuned but dislocation character generally remains unchanged. We observe a notable violation of the Wiedemann-Franz law at room temperature for such a conventional metal. We show that high-density dislocations introduce strong inelastic electron scattering, which relax heat and charge currents to different extent. A reduction of Lorenz number by 15% is observed. We reveal that the contribution from elastic scattering to the incremental thermal resistivity scarcely varies with dislocation density, but the contribution due to inelastic scattering monotonically increases, and becomes overwhelmingly dominant for dislocation density above 1...
January 15, 2019: Journal of Physical Chemistry Letters
Manuel A Ortuño, Oldamur Hollóczki, Barbara Kirchner, Nuria Lopez
Increasing the activity of the nitrogen reduction reaction (NRR) while slowing down the detrimental hydrogen evolution reaction (HER) is a key challenge in current electrocatalysis to provide a sustainable route to ammonia. Recently, nanoparticles in ionic liquid (IL) environments have been found to boost the selectivity of electrochemical synthesis of ammonia from dinitrogen at room temperature. Here, we use for the first time a fully atomistic representation of metal-IL interfaces at DFT level to understand experimental evidence, with particular focus on the rate and selectivity determining formation of N2 H intermediates compared to hydrogen evolution...
January 15, 2019: Journal of Physical Chemistry Letters
Haobo Li, Chenxi Guo, Qiang Fu, Jianping Xiao
A number of experiments have demonstrated that electrochemical reactions are feasible in confined nanoscale reactors, while it is not clear what is the fundamentals of confined electrochemistry. Using first principles calculations and electrochemical modelling, we find that the capacitance in the confined nanoscale reactors can be significantly enhanced, compared to an open electrode interface, essentially promoting the electrochemical reactions and charge transfer efficiency in nanoscale reactors. More importantly, this is a general character, as found in a variety of electrochemical and thermochemical reactions...
January 14, 2019: Journal of Physical Chemistry Letters
Xiyu Li, Sai Duan, Haichun Liu, Guanying Chen, Yi Luo, Hans Ågren
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 cubic phase of inorganic perovskite, we seek to obtain an atom-level-insight into the basic mechanisms behind these observations in order to boost the further development of RE3+ doped CsPbX3 NCs for optoelectronics...
January 14, 2019: Journal of Physical Chemistry Letters
Chengmei Zhong, Vinod K Sangwan, Joohoon Kang, Jan Luxa, Zdeněk Sofer, Mark C Hersam, Emily A Weiss
Layered indium selenide (InSe) is a van der Waals solid that has emerged as a promising material for high-performance ultrathin solar cells. The optoelectronic parameters that are critical to photoconversion efficiencies, such as hot carrier lifetime and surface recombination velocity, are however largely unexplored in InSe. Here, these key photophysical properties of layered InSe are measured with femtosecond transient reflection spectroscopy. The hot carrier cooling process is found to occur through phonon scattering...
January 14, 2019: Journal of Physical Chemistry Letters
Xiaoming Wang, Weiwei Meng, Wei-Qiang Liao, Jianbo Wang, Ren-Gen Xiong, Yanfa Yan
Broadband emission is attributed to the formation of self-trapped excitons (STEs) due to the strong electron-phonon coupling. Interestingly, it has been observed in only certain three-dimensional and low-dimensional metal halide perovskites. Here, we show by density-functional theory calculation that a low electronic dimensionality is a prerequisite for the formation of STE and, therefore, broadband emission. We further show that multiple STE structures exist in each perovskite exhibiting broadband emission...
January 14, 2019: Journal of Physical Chemistry Letters
Qiuyang Li, Tianquan Lian
Two-dimensional cesium lead halide perovskite colloidal nanoplatelets show sharper excitonic absorption/emission peaks and larger absorption cross-section compared to bulk materials and quantum dots. It remains unclear how 2D exciton and charge separation properties can be utilized to further enhance the performance of perovskite materials for these applications. Herein, we report a study of exciton and interfacial charge transfer dynamics of CsPbBr3 nanoplatelets via transient absorption spectroscopy. The exciton binding energy (~260 meV) is determined via detailed spectral analysis...
January 14, 2019: Journal of Physical Chemistry Letters
Fengshuo Zu, Patrick Amsalem, David A Egger, Rongbin Wang, Christian M Wolff, Hong-Hua Fang, Maria Antonietta Loi, Dieter Neher, Leeor Kronik, Steffen Duhm, Norbert Koch
Photovoltaic cells based on halide perovskites and possessing remarkably high power conversion efficiencies have been reported. To push the development of such devices further, a comprehensive and reliable understanding of their electronic properties is essential, but presently not available. To provide a solid foundation for understanding the electronic properties of polycrystalline thin films, we employ single crystal band structure data from angle-resolved photoemission measurements. For two prototypical perovskites (CH3 NH3 PbI3 and CH3 NH3 PbBr3 ) we reveal the band dispersion in two high symmetry directions, and identify the global valence band maxima...
January 14, 2019: Journal of Physical Chemistry Letters
Ying Wang, Renmeng Zou, Jin Chang, Zewu Fu, Yu Cao, Liangdong Zhang, Yingqiang Wei, Decheng Kong, Wei Zou, Kaichuan Wen, Ning Fan, Nana Wang, Wei Huang, Jianpu Wang
Tin-based halide perovskites have attracted considerable attention for non-toxic perovskite light-emitting diodes (PeLEDs), but the easy oxidation of Sn2+ and non-uniform film morphology cause poor device stability and reproducibility. Herein, we report a facile approach to achieve efficient and stable lead-free PeLEDs by using tin-based perovskite multiple quantum wells (MQWs) for the first time. Based on various spectroscopic investigations, we find that the MQW structure not only facilitates the formation of uniform and highly emissive perovskite films, but also suppresses the oxidation of Sn2+ cations...
January 14, 2019: Journal of Physical Chemistry Letters
Borna Zandkarimi, Anastassia N Alexandrova
Scaling relationships in catalysis impose fundamental limitations on the catalyst maximal performance, and so there is a continuous hunt for ways of circumventing them. We show that, at the subnano-scale, scaling relationships can be broken through catalyst dynamics. Oxygen reduction reaction (ORR), which can be catalyzed by Pt nanoparticles, is used as our study case. Subnanometer gas phase and graphene-deposited Ptn cluster catalysts are shown to exhibit poor correlation between binding energies of molecular fragments, O, OH, and OOH, involved in the linear scaling relationships for ORR...
January 11, 2019: Journal of Physical Chemistry Letters
Andrew H Proppe, Madeline H Elkins, Oleksandr Voznyy, Ryan D Pensack, Felipe Zapata, Lucas Vazquez Besteiro, Li Na Quan, Rafael Quintero-Bermudez, Petar Todorovic, Shana O Kelley, Alexander O Govorov, Stephen K Gray, Ivan Infante, Edward H Sargent, Gregory D Scholes
Solution-processed perovskite quantum wells have been used to fabricate increasingly efficient and stable optoelectronic devices. Little is known about the dynamics of photogenerated excitons in perovskite quantum wells within the first few hundred femtoseconds - a crucial timescale on which energy and charge transfer processes may compete. Here we use ultrafast transient absorption and two-dimensional electronic spectroscopy to clarify the movement of excitons and charges in reduced-dimensional perovskite solids...
January 10, 2019: Journal of Physical Chemistry Letters
Rahul Gera, Stephen L Meloni, Jessica M Anna
Self-assembled coordination cages form host-guest complexes through weak non-covalent interactions. Knowledge of how these weak interactions affect the structure, reactivity, and dynamics of guest molecules is important to further the design principles of current systems and optimize their specific functions. In this manuscript, we apply ultrafast mid-IR polarization dependent pump-probe spectroscopy to probe the effects of two Pd6 L4 self-assembled nanocages on the properties and dynamics of fluxional group VIII metal carbonyl guest molecules...
January 10, 2019: Journal of Physical Chemistry Letters
Debbie Zhuang, Marc Riera, Gregory K Schenter, John L Fulton, Francesco Paesani
A systematic analysis of the hydration structure of Cs+ ions in solution is derived from simulations carried out using a series of molecular models built upon a hierarchy of approximate representations of many-body effects in ion-water interactions. It is found that a pairwise-additive model, commonly used in biomolecular simulations, provides poor agreement with experimental X-ray spectra, indicating an incorrect description of the underlying hydration structure. Although the agreement with experiment im- proves in simulations with a polarizable model, the predicted hydration structure is found to lack the correct sequence of water shells...
January 10, 2019: Journal of Physical Chemistry Letters
Miao-Ling Lin, Mario Miscuglio, Anatolii Polovitsyn, Yuchen Leng, Beatriz Martin-Garcia, Iwan Moreels, Ping-Heng Tan, Roman Krahne
The interaction between excitons and phonons in semiconductor nanocrystals plays a crucial role in the exciton energy spectrum and dynamics, and thus in their optical properties. We investigate the exciton-phonon coupling in giant-shell CdSe/CdS core-shell nanocrystals via resonant Raman spectroscopy. The Huang-Rhys parameter is evaluated by the intensity ratio of the longitudinal-optical (LO) phonon of CdS with its first multiscattering (2LO) replica. We used four different excitation wavelengths in the range from the onset of the CdS shell absorption to well above the CdS shell band edge to get insight into resonance effects of the CdS LO phonon with high energy excitonic transitions...
January 9, 2019: Journal of Physical Chemistry Letters
Roman Baskov, Alexander J White, Dmitry Mozyrsky
Mixed quantum-classical mechanics descriptions are critical to modeling coupled electron-nuclear dynamics, i.e. non-adiabatic molecular dynamics, relevant to photochemical and photophysical processes. We introduce an efficient description of such dynamics in terms of an effective Hamiltonian that not only properly captures electron-nuclear correlation effects but also helps developing an efficient computational method. In particular we introduce a coupled Gaussian wavepacket parameterization of the nuclear wavefunction, which generalizes the Ehrenfest approach to account for electron-nuclei correlations...
January 9, 2019: Journal of Physical Chemistry Letters
Aleksandra G Boldyreva, Azat F Akbulatov, Sergey Tsarev, Sergey Yurevich Luchkin, Ivan S Zhidkov, Ernst Zagidovich Kurmaev, Keith J Stevenson, Vladimir Petrov, Pavel A Troshin
We report on the impact of gamma radiation (0-500 Gy) on the triple cation Cs0.15MA0.10FA0.75Pb(Br0.17I0.83)3 perovskite solar cells. A set of experiments was designed to reveal the individual contributions of the hole-collecting bottom electrode, perovskite absorber and electron transport layer (ETL) to the overall solar cell degradation under the radiation exposure. We show that Glass/ITO/PEDOT:PSS hole-collecting electrode withstands 500 Gy dose without any losses in the solar cell performance. On the contrary, the perovskite absorber films and PC61BM ETL are very sensitive to gamma rays as can be concluded from the radiation-induced decay of the solar cell efficiency by ~32-41%...
January 8, 2019: Journal of Physical Chemistry Letters
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