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Journal of Physical Chemistry Letters

X D Wang, J Zhang, T D Xu, Q Yu, Q P Cao, D X Zhang, J Z Jiang
The secondary β-relaxation is an intrinsic feature in glassy materials. However, its structural origin is still not well understood. Here we report that the β-relaxations in La50 Al15 Ni35 and La50 Al15 Cu35 metallic glasses (MGs) mainly depend on the vibration of small Ni and Cu atoms in local cages. By using advanced synchrotron X-ray techniques and theoretical calculations, we elucidate that the tricapped-trigonal-prism-like polyhedra with more large La atoms in shells favor the local vibration of center Ni atoms, leading to the pronounced β-relaxation event...
July 18, 2018: Journal of Physical Chemistry Letters
Yedilfana Setarge Mekonnen, Rune Christensen, Juan María García-Lastra, Tejs Vegge
The Na-O2 system holds great potential as a low cost, high energy density battery, but under normal operating conditions, the discharge is limited to sodium superoxide (Na-O2 ), whereas the high capacity peroxide state (Na2 O2 ) remains elusive. Here, we apply density functional theory calculations with an improved error-correction scheme to determine equilibrium potentials and free energies as a function of temperature for the different phases of Na-O2 and Na2O2, identifying Na-O2 as the thermodynamically preferred discharge product up to ~120 K, after which Na2 O2 is thermodynamically preferred...
July 17, 2018: Journal of Physical Chemistry Letters
Xue Qiu, Jiajia Guo, Jingyue Xu, Niko Hildebrandt
Photoluminescence (PL) multiplexing usually relies on spectral or temporal separation. Their combination into higher-order multiplexing for biosensing is extremely challenging because the PL intensity is required for target quantification at very low concentrations and the interplay of color, lifetime, and intensity must be carefully adapted. Here, we demonstrate time-gated Förster resonance energy transfer (TG-FRET) from a long-lifetime Tb-complex to Cy3.5 and Cy5.5 dyes for spectrotemporal multiplexing of four different DNA targets in the same sample by single-color excitation and two-color detection...
July 17, 2018: Journal of Physical Chemistry Letters
Katherine Reece Phillips, Yu Katayama, Jonathan Hwang, Yang Shao-Horn
The electrochemical CO2 reduction reaction (CO2RR) has gained attention recently due to rising concern over atmospheric carbon levels, but catalyst selectivity and efficiency remain a challenge, particularly for products other than CO. Here, we report the selective formation of formate using a sulfide-derived copper (SD-Cu) catalyst for CO2RR. Based on in situ and post-electrolysis spectroscopy, we propose that this selectivity is due to stronger binding of the CO intermediate originating from remaining sub-surface sulfur atoms...
July 17, 2018: Journal of Physical Chemistry Letters
Samantha M Harvey, Brian T Phelan, Daniel C Hannah, Kristen E Brown, Ryan M Young, Matthew S Kirschner, Michael R Wasielewski, Richard D Schaller
We report femtosecond stimulated Raman spectroscopy (FSRS) measurements on dispersions of CdSe semiconductor nanocrystals (NCs) as a function of particle size and pump fluence. Upon photoexcitation we observe depletion of stimulated Raman gain corresponding to generation of longitudinal optical (LO) phonons followed by recovery on picosecond timescales. At higher fluences, production of multiple excitons slows recovery of FSRS signals, which we attribute to sustained increases of LO phonon populations due to multiexcitonic Auger heating...
July 16, 2018: Journal of Physical Chemistry Letters
Jing Qiu, Xin Bai, Linjun Wang
In the traditional fewest switches surface hopping (FSSH), trivial crossings between uncoupled or weakly-coupled states have highly peaked nonadiabatic couplings and thus are difficult to deal with in the preferred, adiabatic representation. Here, we classify surface crossings into four general types and propose a parameter-free crossing corrected FSSH (CC-FSSH) algorithm, which could treat multiple trivial crossings within a time interval. As examples, Holstein Hamiltonians with different parameters are adopted to mimic electron dynamics in tens to hundreds of molecules, which suffer from severe trivial crossing problems...
July 16, 2018: Journal of Physical Chemistry Letters
Lopa Paul, Ambar Banerjee, Ankan Paul, Kenneth Ruud, Swapan Chakrabarti
We present a heuristic mechanism for the origin of the unusual triplet lasing from (E)-3-(((4-nitrophenyl)imino)methyl)-2H-thiochroman-4-olate.BF2.We demonstrate that whereas the moderate lifetime (1.03µs) of the first triplet state(T1) prohibits triplet-triplet annihilation, the relatively faster S1 →T1 intersystem crossing and the 104 times smaller reverse intersystem crossing effectively help achieve population inversion in theT1 state. Furthermore, the triplet lasing wavelength (675 nm) for the tetramer does not overlap with the triplet-triplet absorptions wavelength, indicating that the spin-forbidden emission cross section is very large...
July 16, 2018: Journal of Physical Chemistry Letters
David S Bull, Nathaniel Nelson, Danielle Konetski, Christopher N Bowman, Daniel K Schwartz, Andrew P Goodwin
Whereas nanobubble stability on solid surfaces is thought to be based on local surface structure, in this work, we show that nanobubble stability on polymer brushes does not appear to require contact-line pinning. Glass surfaces were functionalized with copolymer brushes containing mixtures of hydrophobic and hydrophilic segments, exhibiting water contact angles ranging from 10 to 75°. On unmodified glass, dissolution and redeposition of nanobubbles resulted in reformation in mostly the same locations, consistent with the contact line pinning hypothesis...
July 16, 2018: Journal of Physical Chemistry Letters
Yulun Han, Kenneth J Anderson, Erik K Hobbie, Philip Boudjouk, Dmitri S Kilin
Photoinduced reactions of a pair of cyclohexasilane (CHS) monomers are explored by time-dependent excited-state molecular dynamics (TDESMD) calculations. In TDESMD trajectories, one observes vivid reaction events including dimerization and fragmentation. A general reaction pathway is identified as (i) ring-opening formation of a dimer, (ii) rearrangement induced by bond breaking, and (iii) decomposition through the elimination of small fragments. The identi-fied pathway supports the chemistry proposed for the fabrication of silicon-based materials us-ing CHS as a precursor...
July 13, 2018: Journal of Physical Chemistry Letters
Stefan Bötschi, Ashwin Kumar Rajagopalan, Manfred Morari, Marco Mazzotti
The solute concentration in crystallization processes is generally estimated by observing properties of the liquid phase. Here, a novel method for online estimation of the change in the solute concentration caused by seeded batch crystallization or dissolution of a population of crystals in suspension is presented. The method is based on multiprojection imaging to track variations in the total solid volume of the population, thus enabling inference of the solute concentration through the mass conservation constraint...
July 13, 2018: Journal of Physical Chemistry Letters
Alice Judith Gillen, Justyna Kupis-Rozmyslowicz, Carlo Gigli, Nils Schürgers, Ardemis Anoush Boghossian
The omnipresence of salts in biofluids creates a pervasive challenge in designing sensors suitable for in vivo applications. Fluctuations in ion concentrations have been shown to affect the sensitivity and selectivity of optical sensors based on single-walled carbon nanotubes wrapped with single-stranded DNA (ssDNA-SWCNTs). We herein observe fluorescence wavelength shifting for ssDNA-SWCNT-based optical sensors in the presence of divalent cations at concentrations above 3.5 mM. In contrast, no shifting was observed for concentrations up to 350 mM for sensors bioengineered with increased rigidity using xeno nucleic acids (XNAs)...
July 13, 2018: Journal of Physical Chemistry Letters
Thomas Gibaud, Doru Constantin
Using synchrotron-based small angle x-ray scattering, we study rigid \textit{fd} viruses assembled into isolated monolayers from mixtures with a non-absorbing polymer, which acts as osmotic agent. As the polymer concentration increases we observe a direct liquid to crystal transition, without an intermediate hexatic phase, in contrast with many other similar systems, such as concentrated DNA phases or packings of surfactant micelles. We tentatively attribute this effect to the difference in stiffness.The liquid phase can be well described by a hard-disk fluid, while we model the crystalline one as a hexagonal harmonic lattice and we evaluate its elastic constants...
July 13, 2018: Journal of Physical Chemistry Letters
Qisheng Wu, Yehui Zhang, Qionghua Zhou, Jinlan Wang, Xiao Cheng Zeng
Two-dimensional (2D) ferromagnetic materials with intrinsic half-metallicity are highly desirable for nanoscale spintronic applications. Here, we predict a new and stable family of 2D transition metal dihydride (MH2 ; M=Sc, Ti, V, Cr, Fe, Co, Ni) monolayers with novel properties. Our density-functional-theory computation shows that CoH2 and ScH2 monolayers are ferromagnetic metals, while the others are antiferromagnetic semiconductors. In particular, CoH2 monolayer is perfect half-metal with a wide spin gap of 3...
July 13, 2018: Journal of Physical Chemistry Letters
Youngwook Park, Sunghwan Shin, Heon Kang
Chemical reactions are extremely difficult to occur in ice at low temperature, where atoms and molecules are frozen in position with minimal thermal energy and entropy. Contrary to this general behavior, certain weak acids including fluoroacetic acids dissociate spontaneously and more efficiently in cryogenic ice than in aqueous solution at room temperaure. The enhanced reactivity of weak acids is an unexpected consequence of proton transfer equilibrium in ice. The configurational entropy of protons in ice shifts the acid dissociation equilibrium forward...
July 12, 2018: Journal of Physical Chemistry Letters
Lu Wei, Wei Min
Optical microscopy has generated great impact for modern research. While fluorescence microscopy provides the ultimate sensitivity, it generally lacks chemical information. Complementarily, vibrational imaging methods provide rich chemical-bond specific contrasts. Nonetheless, they usually suffer from unsatisfying sensitivity or compromised biocompatibility. Recently an electronic pre-resonance stimulated Raman scattering (epr-SRS) microscopy was reported, achieving simultaneous high detection sensitivity and superb vibrational specificity of chromophores...
July 12, 2018: Journal of Physical Chemistry Letters
Orion Shih, Yi-Qi Yeh, Kuei-Fen Liao, Chun-Jen Su, Pei-Hao Wu, Richard K Heenan, Tsyr-Yan Yu, U-Ser Jeng
Direct binding of calcium ions (Ca2+) to phospholipid membranes is an unclarified yet critical signaling pathway in diverse Ca2+-regulated cellular phenomena. Here, high-pressure-liquid-chromatography, small-angle X-ray scattering (SAXS), UV-Vis absorption, and differential refractive index detections are integrated to probe Ca2+-binding to the zwitterionic lipid membranes in nanodiscs. The responses of the membranes upon Ca2+-binding, in composition and conformation, are quantified through integrated data analysis...
July 12, 2018: Journal of Physical Chemistry Letters
Zhuoran Kuang, Qianjin Guo, Xian Wang, Hongwei Song, Mark Maroncelli, Andong Xia
4'- N, N-Diethylamino-3-hydroxyflavone (DEAHF), due to excited-state intramolecular proton transfer (ESIPT) reaction, exhibits two solvent-dependent emission bands. Because of the slow formation and fast decay of the ground-state tautomer, its population does not accumulate enough for its detection during the normal photocycle. As a result, the details of the ground-state intramolecular proton-transfer (GSIPT) reaction have remained unknown. The present work uses femtosecond pump-dump-probe spectroscopy to prepare the short-lived ground-state tautomer and track this GSIPT process in solution...
July 12, 2018: Journal of Physical Chemistry Letters
Hua Wang, Ning Sui, Xue Bai, Yu Zhang, Quinton Rice, Felix Jaetae Seo, Qingbo Zhang, Vicki L Colvin, William W Yu
Inorganic lead halide perovskite quantum dots (PQDs), especially red emission PQDs, are well-known to easily lose their luminescence emission with time, which shows from strong emission of fresh PQDs to no emission of aged PQDs. Here, we demonstrate that trioctylphosphine (TOP) can effectively and instantly recover the luminescence emission of aged red PQDs, making the "dead" PQDs "reborn". Furthermore, TOP also works to improve the emission intensity of freshly synthesized PQDs. In this process, TOP does not make any detectable structural changes to PQDs...
July 12, 2018: Journal of Physical Chemistry Letters
Wei Gan, Bolei Xu, Hai-Lung Dai
It is found that, by curing the surface defects that quench photoexcited carriers, luminescence efficiency of metallic nanoparticles can be dramatically increased. For Ag nanoparticles, as much as 300 times increase in photoexcitation induced luminescence is observed upon surface adsorption of ethanethiol. The same treatment increases Au nanoparticle luminescence efficiency by a factor of 3. A model based on the elimination of surface defects by the sulfur-metal bond formed upon thiol adsorption can quantitatively account for the observations, which also indicate that nanoparticles without proper surface treatment typically have low luminescence quantum yields...
July 12, 2018: Journal of Physical Chemistry Letters
David Morgan, David F Kelley
Transient absorption (TA) and time-resolved photoluminescence (PL) spectroscopies have been used to provide direct spectroscopic evidence for the recently reported phenomenon of thermal "surface charging" in II-VI quantum dots (QDs). In these studies, zincblende CdSe cores are synthesized by standard methods, and a thin CdS shell deposited by the decomposition of Cd(DDTC)2 , resulting in core/shell QDs with chalcogenide-rich surfaces. Following ligand exchange with oleylamine, these QDs have empty low-lying surface states that can be thermally populated from the valence band...
July 12, 2018: Journal of Physical Chemistry Letters
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