Chemical Physics Letters (v.495, #4-6)

Contents (iii-x).

Singlet–triplet quenching in high intensity fluorescent organic light emitting diodes by Yifan Zhang; Matthew Whited; Mark E. Thompson; Stephen R. Forrest (161-165).
Display Omitted► Doped fluorescent OLEDs exhibit significant intensity overshoot at the beginning of a current pulse when driven at very high brightnesses. ► The effect is due to interaction of dopant singlets with host triplets and polarons. ► Rate equations are developed to describe all aspects of the overshoot. ► A means to reduce this effect, and to achieve potentially higher quantum efficiency in ultrabright fluorescent OLEDs is to co-dope the emission layer with a fast phosphor molecule that acts as a triplet sink.Electroluminescence (EL) transient turn-on peaks with more than twice the brightness of the steady-state EL are observed in fluorescent organic light emitting diodes with a doped emission layer. By modeling both the singlet and triplet population dynamics, we identify the EL drop after the peak as due to singlet–triplet (ST) quenching. The peak recovery following a double voltage pulse sequence is explained in terms of triplet population relaxation through triplet–triplet quenching. A mechanism of using phosphors in the emission region is proposed for reducing ST quenching.

Ab initio potential energy surface and bound states of the Xe–HF complex by Chunzao Zhang; Zhongquan Wang; Haijun Yu; Jianming Du; Jianguo Ma (166-169).
Display Omitted► The two-dimensional interaction potential energy surface of the Xe–HF complex is developed by CCSD(T) method.The two-dimensional potential energy surface for the Xe–HF van der Waals interaction is calculated by the single and double excitation coupled-cluster theory with noniterative treatment of triple excitations [CCSD(T)]. Mixed basis sets, aug-cc-pVQZ for the H and F atom and aug-cc-pVQZ-PP for the Xe atom, with an additional (3s3p2d2f1g) set of midbond functions are used. There are two minima on the potential. The global minimum at R e = 7.05 a 0 and θ e = 180 ° with well depth −309.2906 cm−1. The shallower minimum is located at R = 7.00 a 0 and θ = 0 ° . Based on the potential, the predicted transition frequencies are in good agreement with the experimental results.

The HOCO + N reaction makes a chemically activated HOC(=O)N intermediate, which dissociates in ∼50 ps by two competing pathways.Display Omitted► The N + HOCO reaction produces a chemically activated HOC(=O)N intermediate that dissociates via two competing pathways. ► The ultimate product of the N + HOCO reaction is mostly OH + NCO rather than the energetically favored 3NH + CO2. ► While the barrier leading from the HOC(=O)N intermediate to 3NH + CO2 is lower than that leading to OH + NCO, the chemically activated HOC(=O)N intermediate reacts more rapidly to form OH + NCO. ► The chemically activated HC(=O)OH (formic acid) intermediate formed from H + HOCO forms mostly CO + H2O, not CO2  + H2.This work presents ab initio calculations on the triplet potential energy surface for the N + HOCO reaction and RRKM/Master Equation calculations of the fates of chemically activated species formed in that reaction and in the reaction H + HOCO. Ab initio calculations were carried out at CCSD(T)/aug-cc-pVTZ//CCSD/aug-cc-pVDZ. The fates of chemically activated intermediates are determined for a range of temperatures and pressures. We have shown that the reaction N + HOCO produces OH + NCO as the dominant product (about two-thirds yield). We also show that the major product of the H + HOCO reaction is CO + H2O.

Direct evidence for weak intramolecular O–H⋯π hydrogen bonding in 1-hydroxytetralin by Tasuku Isozaki; Yu-ichiro Tsutsumi; Tadashi Suzuki; Teijiro Ichimura (175-178).
Hydroxyl hydrogen pointing toward the benzene ring indicates the existence of weak intramolecular O–H ⋯ π hydrogen bonding.Laser-induced fluorescence (LIF) excitation and single vibronic level fluorescence (SVLF) spectra of jet-cooled 1-hydroxytetralin (1HT) have been measured to investigate the nature of weak intramolecular hydrogen bonding. The vibronic bands observed in the LIF excitation spectrum were responsible for two conformers resulting from different configurations of the saturated six-membered ring with the orientation of the hydroxyl group. The hydroxyl hydrogen in the stable conformers was directed toward the benzene π-electrons. The conformational preferences in 1HT clearly indicate the weak intramolecular O–H ⋯ π hydrogen bonding.

OH yields for C2H5CO + O2 at low pressure: Experiment and theory by Gábor L. Zügner; István Szilágyi; Judit Zádor; Emese Szabó; Sándor Dóbé; Xinli Song; Baoshan Wang (179-181).
Display Omitted► The OH yields of the reaction of C2H5CO radicals with O2 are close to unity at ∼1 mbar pressure of helium at room temperature. ► The OH yields decrease rapidly with increasing pressure, down to ∼0.3 at 13 mbar, and become by far negligible compared with the combination product propionyl-peroxyl radical, C2H5C(O)O2, at atmospheric pressure. ► The experimental OH yields can be reproduced well by using multichannel variational RRKM theory.Kinetics of OH formation for the reaction of C2H5CO radicals with O2 have been studied using the low-pressure discharge flow technique coupled with resonance fluorescence monitoring of OH radicals at room temperature in He buffer gas. The OH yields are close to unity at the lowest pressures studied, but decrease rapidly with increasing pressure. The experimental OH yields are reproduced well using multichannel variational RRKM theory.

Conformational energies of C 4 F 9 OC 2 H 5 (HFE-7200) by G.S. Grubbs; S.A. Cooke (182-186).
Display Omitted► We have studied a large, conformationally complex molecule C4F9OC2H5, using chirped pulse Fourier transform microwave spectroscopy. ► The rapid spectral measurements and reliable, relative transition intensities have enabled four species to be identified amongst the very dense spectra. ► Calculations have assisted in the identification of these species.A chirp Fourier transform microwave spectrometer has been used to record the rotational spectra of two isomers of the hydrofluoroether C 4 F 9 OC 2 H 5 (ethoxynonafluorobutane also known as HFE-7200) between 7.8 and 16.2 GHz. The target compound was spectroscopically examined as it participated in a supersonic expansion of argon. Four separate rotational spectra have been identified amongst the congested data. Spectroscopic parameters are presented for each species. The structures of all four species have been identified by exploring the multi-dimensional potential energy surfaces using quantum chemical calculations.

Resonance-enhanced multiphoton ionization spectroscopy of jet-cooled hexafluorobenzene and sym-trifluorobenzene provides vibronic spectra of the gerade 3dxz,yz A1g Rydberg state.Display Omitted► Two-photon spectra of jet-cooled hexafluorobenzene and sym-trifluorobenzene ► Rydberg states ► Vibrational structure, Jahn–Teller effect(2+1) Resonance-enhanced multiphoton ionization (REMPI) spectra were recorded for hexafluorobenzene (HFBz) and 1,3,5-trifluorobenzene (TRFBz) using UV laser light. Vibronic structure of the Rydberg series converging to the first ionization threshold are resolved. While only one Rydberg series is observed for HFBz (region 67 500–70 820 cm−1), two of them are detected for TRFBz (region 66 000–69 100 cm−1). The resolved vibronic structures are assigned with the aid of theoretical predictions.

Display Omitted► G3 computations provide new thermochemical data for C7H6O molecules and C7H7O+ ions.Quantum chemistry calculations using composite G3B3, G3MP2B3 and CBS-QB3 methods were performed for benzaldehyde, 1, tropone, 2, ortho-quinone methide, 3, para-quinone methide, 4, their protonated forms 1H +4H + and the isomeric meta-hydroxybenzyl cation 5H +. The G3B3 298 K heats of formation values obtained in this work are: −39, 61, 52, 39, 661, 679, 699, 680 and 733 kJ mol−1 for 14, 1H +5H +, respectively. At the same level of theory, computed proton affinities are equal to 834, 916, 887 and 892 kJ mol−1 for molecules 14. These results allow to correct discrepancies on the previously reported thermochemistry of molecules 24 and cations 2H +5H +.

How many intramolecular hydrogen bonds does the oxalic acid dimer have? by Shamus A. Blair; Ajit J. Thakkar (198-202).
Display Omitted► 69 MP2/6–31+G (d, p) local minima located on the oxalic acid dimer potential energy surface. ► Lowest-energy oxalic acid dimer contains a monomer in a higher-energy form. ► π – π stacking is not favorable for the oxalic acid dimer.Second-order Møller–Plesset (MP2) calculations are used to locate 69 unique minima on the potential energy surface of the oxalic acid dimer. Additional MP2 calculations, with and without scaling of the spin components of the correlation energy, are performed for 24 selected minima using larger basis sets. The global minimum is a dimer in which one of the monomers is not in its lowest-energy rotameric form. The dimer has two intermolecular and three intramolecular hydrogen bonds.

Pressure induced structural changes in the potential hydrogen storage compound ammonia borane: A combined X-ray, neutron and theoretical investigation by Ravhi S. Kumar; Xuezhi Ke; Jianzhong Zhang; Zhijun Lin; Sven C. Vogel; Monika Hartl; Stanislav Sinogeikin; Luke Daemen; Andrew L. Cornelius; Changfeng Chen; Yusheng Zhao (203-207).
Display Omitted► Structural phase transition in the important hydrogen storage material ammonia borane under compression. ► Neutron and X-ray diffraction experiments for structural identification of high pressure phases. ► Density functional theoretical calculation results support the transition.The crystal structure of NH3BH3 was investigated using synchrotron high pressure X-ray diffraction (HPXRD) up to 27 GPa and neutron diffraction up to 5 GPa. Density functional theoretical (DFT) calculations were carried out simultaneously for comparison. The results confirm a pressure induced phase transition from the tetragonal I 4 mm phase to a high pressure orthorhombic Cmc21 phase around 1.22 GPa. Further increase of pressure above 8 GPa, we observed a second structural transition from Cmc21 to a triclinic P1 phase which are reversible with small hysteresis. The transition pressures and the bulk modulus obtained experimentally are in good agreement with theory.

Modulation of fluorescence properties of MMeAQ in micelles and cyclodextrins by Tarak Nath Burai; Nirmalya Bag; Shipra Agarwal; E. Siva Subramaniam Iyer; Anindya Datta (208-211).
Display Omitted► Cationic form of MMeAQ: low fluorescence quantum yield. ► Enhancement of fluorescence with surfactants. ► Specific interaction with β-cyclodextrin.The interactions of the N-methylquinoline-3-amine (MMeAQ) with three cyclodextrins and micelles have been investigated using fluorescence spectroscopic techniques. It is shown that cationic and neutral surfactants enhance the fluorescence quantum yield of the MMeAQ in water by breakup of aggregates of MMeAQ and incorporation into the micelles. However such enhancement is not observed in SDS micelle. The fluorescence enhancement of MMeAQ in β-cyclodextrin host is rationalized in the light of the stoichiometry of the inclusion complexes. There is no such interaction is observed for α-CD and γ-CD. Quantum chemical calculation has also been performed in order to support the experimental findings of cationic species.

.Display Omitted►Tetrafluoro-tetracyanoquinodimethane effectively p-dopes pentacene. ►Donated holes are localized by ionized acceptor molecules. ►STM images of localized holes can be modeled by Coulomb potential. ►Fitting line profiles of localized holes to Coulomb potential yields ϵ, Hubbard U. Temperature-dependent IV measurements determine that pentacene is effectively p-doped by tetrafluoro-tetracyanoquinodimethane (F4-TCNQ). It has been shown by scanning tunneling microscopy (STM) that the donated hole is localized by the ionized dopant counter potential, and that the hole can be visualized . Here, it is argued that the effect of the localized hole on STM images should depend on distance as 1/ϵr, as per the Coulomb potential. By fitting line profiles of localized hole features to the Coulomb potential, it is shown that approximate values for the relative permittivity and Hubbard U of pentacene can be extracted.

Schematic illustration of the ground state and the excited state free energy landscapes of the isomer interacting with surrounding molecules.Non-exponential kinetics showing the induction period is observed for photoisomerization in solid phase. A possible source of the induction period is local minima along the pathway to the product which arises from the interaction of the isomerizing molecule with the surrounding molecules. In this case, multiple photoexcitations are required to complete photoisomerization. We show that product formation by photoisomerization in solid states can be analyzed by a simple equation (Eq. ). By fitting experimental data to this equation the number of local minima can be estimated.

The significantly different intensity patterns between the 299.1 and 245.9 nm resonance Raman spectra provide us an evident that the primary photoreduction reactions of Cu(II)-bisacetylacetone in alcohol solutions are wavelength dependent. The excited state structural dynamics upon 245.9 nm excitation (orbitals 66 → 69) is predominantly along the photochemically important Cu–O stretch (ν 11) reaction coordinate, which correlates to the CuL2  → CuL + L photodissociation reaction, while the structural dynamics upon 299.1 nm excitation (orbitals 65 → 68) is along both the photophysically important CγCβ/CβCα symmetric stretch (ν 7) and the photochemically important Cu–O stretch (ν 11) reaction coordinates.Display Omitted► Most of the A-band (∼290 nm band) resonance Raman spectra of Cu(AA)2 are assigned to the fundamentals, overtones and combination bands of about 9 Ag totally symmetry and 2 B1g symmetry vibrations, while most of the B-band (∼240 nm band) resonance Raman spectra are assigned to the fundamentals, overtones and combination bands of about 9 Ag totally symmetry vibrations. ► The A- and B-bands structural dynamics of Cu(AA)2 in methanol solution were revealed to be significantly different. The A-band structural dynamics is along both the photophysically important CγCβ/CβCα symmetric stretch (ν 7) reaction coordinate and the photochemically important Cu–O stretch (ν 11) reaction coordinate, while the B-band structural dynamics is mainly along the photochemically important Cu–O stretch (ν 11) reaction coordinate, which correlates to the CuL2  → CuL + L photodissociation reaction mechanism. ► The appearances of ν 23 (B1g) and ν 20 (B1g) vibrational modes in the A-band resonance Raman spectra indicate that the 1 2B3u excited state is certainly coupled to some nearby 2B2u states that is within or not far away from the Franck–Condon region.The A- and B-band resonance Raman spectra of Cu(II)-bisacetylacetone in methanol solution were obtained and their intensity patterns were found to be significantly different. It appears that the A-band structural dynamics is mostly along the photophysically and photochemically important CγCβ/CβCα and Cu–O stretch reaction coordinates, while the B-band structural dynamics is mainly along photochemically important Cu–O stretch reaction coordinate. The significantly different structural dynamics provide an evident that the primary photoreduction reactions of Cu(II)-bisacetylacetone are wavelength dependence.

Optical absorption spectrum of pentacene cation radicals measured by charge-modulation spectroscopy by Yutaka Harima; Yasushi Ishiguro; Kenji Komaguchi; Ichiro Imae; Yousuke Ooyama (228-231).
Display Omitted► Optical absorption spectrum of monocation radical of pentacene is measured by charge-modulation spectroscopy. ► Charge-modulation spectroscopy was applied to vacuum-sublimed films of pentacene in the MIS diode configuration. ► The spectrum exhibited several peaks in the wavelength range of 300–800 nm. ► The signal in the visible was ascribed to the field-modulation effect of a neutral pentacene film, while the three broad peaks in the UV were ascribed to the optical absorption due to a monocation radical of pentacene. ► This assignment was supported by the theoretical calculations reported earlier.Charge-modulation spectroscopy was applied to vacuum-sublimed films of pentacene in the metal–insulator–semiconductor configuration with Parylene-C or cross-linked polymer as insulator. The spectrum exhibited several peaks in the wavelength range of 300–800 nm. The signal in the visible was ascribed to the field-modulation effect of a neutral pentacene film, while the three broad peaks in the UV exhibited field and frequency dependences different from those in the visible and were ascribed to the optical absorption due to a monocation radical of pentacene. This assignment was supported by the calculation reported earlier on the basis of the time-dependent density functional theory.

Structural and chemical properties of highly oriented cadmium sulfide (CdS) cauliflower films by R.S. Vemuri; S.K. Gullapalli; D. Zubia; J.C. McClure; C.V. Ramana (232-235).
Fabrication of the highly oriented, single phase hexagonal-CdS films with a cauliflower morphology using sputter-deposition under controlled sputtering-power has been demonstrated.Display Omitted►CdS is an important material with a potential for a wide range of scientific and technological applications. A wide and direct band gap (∼2.42 eV) coupled with n-type conductivity makes CdS suitable for application in large area optoelectronic devices such as such as solid state lasers and detectors, window layer in hetero-junction solar cells, field-effect transistors, and photoconductors. ► Significant research efforts were directed involving higher temperatures, chemical treatments, intense pulsed-lasers to grow the single phase, oriented CdS films. In this communication, we demonstrate the room-temperature growth of high-quality H-phase CdS thin films with a very high degree of orientation along c-axis. The present work has been performed on CdS films deposited using RF magnetron sputtering, which offers the advantage in simplicity of the process, cost effectiveness, industrial scalability. Interestingly, we found that the high-structural and chemical quality H-CdS layers can be stabilized by carefully controlling the sputtering-power. The results and their implications for technology are presented and discussed in this Letter.Cadmium sulfide (CdS) films have been produced by sputter-deposition varying the sputtering-power (P) in the range of 60–120 W. The crystal structure, morphology and chemical quality of the CdS films has been investigated employing X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray spectrometry (EDS). Structural characterization indicates that all the CdS layers exhibit cauliflower morphology. Highly oriented, single phase hexagonal-CdS films can be produced at P  = 75–105 W while the films at other power contain mixed phases. Characterization using XPS and EDS indicate that the CdS layers are nearly stoichiometric at P  = 75–105 W, at which point S-deficiency is induced resulting in Cd-rich-CdS layers.

Influence of ZnS quantum dots on optical and photovoltaic properties of poly(3-hexylthiophene) by Monika Mall; Pankaj Kumar; S. Chand; Lokendra Kumar (236-240).
.Display Omitted► Effects of ZnS nanoparticles inclusion on the properties of P3HT were investigated. ► Absorption and Raman spectra show the reduction in conjugation length and inter-chain interaction of the polymer. ► Significantly quenched luminescence confirms the occurrence of charge transfer between the constituents. ► Small amount of ZnS incorporation leads the significant enhancement in V oc.The influence of ZnS quantum dots (QDs) on the photo-physical and electrical properties of poly(3-hexylthiophene) (P3HT) conjugated polymer, has been investigated. Composite material has been prepared by blending P3HT with low concentration of chemically synthesized ZnS nanocrystals. Absorption spectra of conjugated polymer exhibit a small blue shift of about 3 nm, with the incorporation of ZnS nanocrystals. We observed the charge transfer between conjugated polymer molecules and ZnS nanoparticles which is discussed with the energy levels of the materials. Current density–voltage measurement of the hybrid device showed a significant improvement in V oc in comparison to P3HT only device.

The ripples and nanoparticles are formed on silicon irradiated by femtosecond laser. The period of the ripples decreases with the increasing pulse number, while the diameter of the visible structured region increases with the increasing pulse number. The interference of laser with surface plasmons is proposed to explain the formation of the ripple. The decreasing of the spatial period for surface ripples is due to the decrease of the surface plasmon wavelength with the decreasing electron number density in the plasma.Display Omitted► The ripples and nanoparticles are formed on silicon irradiated by femtosecond laser. ► The interference of laser with surface plasmons is the possible mechanism to form the ripple. ► The decreasing electron number density result to the decreasing of the ripples’ period.The surface configuration evolvement of silicon with the increasing pulse number irradiated by femtosecond laser has been studied. The ripples and nanoparticles are formed in the irradiated region. The period of the ripples decreases with the increasing pulse number, while the diameter of the visible structured region increases with the increasing pulse number. The interference of laser with surface plasmons is proposed to explain the formation of the ripple. The decreasing of the spatial period for surface ripples is due to the decrease of the surface plasmon wavelength with the decreasing electron number density in the plasma.

Transient nonlinear optical response of some symmetrical nickel dithiolene complexes by Panagiotis Aloukos; George Chatzikyriakos; Irini Papagiannouli; Nikos Liaros; Stelios Couris (245-250).
Display Omitted► Ni-dithiolenes. ► Dithiolenes. ► Nonlinear optical properties. ► Third-order susceptibility. ► Second hyperpolarizability.The transient nonlinear optical response of some recently synthesized symmetric nickel dithiolene complexes, namely the Ni(etodddt)2 (etodddt = 4,5-(1,4-oxathiane-2,3-diyldithio)-1,3-dithiole), the Ni(pddt)2 (i.e., bis(6,7-dihydro-5H-[1,4]dithiepine-2,3-ddithiole) nickel)) and the Ni(dddt)2 (bis(5,6-dihydro-1,4-dithiine-2,3-dithiole) nickel), is studied using Z-scan technique employing 1064 and 532 nm, nanosecond laser pulses. The absorptive and the refractive parts of the third-order susceptibility χ (3) were determined and the second hyperpolarizability γ of each dithiolene complex was deduced at both excitation wavelengths, while strong resonance enhancement was found to occur under 1064 nm excitation. The present results are discussed and compared with other literature results obtained on similar symmetric and unsymmetric dithiolene complexes.

Adsorption and diffusion of atomic hydrogen on a curved surface of microporous carbon: A theoretical study by Megumi Kayanuma; Umpei Nagashima; Hirotomo Nishihara; Takashi Kyotani; Hiroshi Ogawa (251-255).
Adsorption and diffusion of atomic hydrogen (blue circle) on flat and curved graphene fragments are compared using DFT calculation.Display Omitted►Evaluation of chemisorption energies of a hydrogen atom on four graphene-like fragments with different curvature showed that hydrogen atoms adsorb strongly at the edge site and convex surface. ►We showed that hydrogen chemisorption at edge sites enhances the adsorption energy at the inner site. ►The results suggest that the hydrogen dissociation from the carbon surface is more likely to occur than the hydrogen migration along the C–C bond keeping a weak C–H bond in flat surface. ►It was suggested that diffusion path of chemisorbed hydrogen might be modified by introducing curvature. ►These results suggest that hydrogen uptake caused by spillover on carbon-based hydrogen storage materials will be enhanced by controlling the structure of the carbon surfaces.The interaction between atomic hydrogen and microporous carbon is investigated by density functional theory (DFT) calculations. To reveal how the nanographene structures affect the atomic hydrogen uptake, which is caused by hydrogen spillover, chemisorption energies of a hydrogen atom on four graphene-like fragments are compared: a condensed hexagonal plane, two buckybowls, and a heptagon-containing curved structure. It is shown that hydrogen atoms adsorb strongly at the edge sites and on convex surfaces. Two hydrogen diffusion paths on the carbon surface are examined: hydrogen migration along the C–C bond and hydrogen desorption. The results suggest that a probable path depends on the nanographene structure.

The quasi-Landau levels and Landau wave functions of the nanographene ribbons are modified by the external electric field.Our study reveals that the magneto-electronic properties of the zigzag nanographene ribbons are tuned by the external electric fields. The spatially modulated electric field (the uniform transverse electric field) converts the dispersionless Landau levels into subbands with the sinusoidal (linear) energy dispersions. The energies of the band-edge states are affected by the electric potentials. The localization positions and the spatial symmetry of the Landau wave functions are altered. The modulated electric potential with shorter periodic length has stronger influence on the quasi-Landau levels. The magneto-optical absorption spectra are expected to be changed by the external electric fields.

Spatial confinement of carriers and tunable band structures in InAs/InP-core–shell nanowires by Haibo Shu; Xiaoshuang Chen; Xiaohao Zhou; Wei Lu (261-265).
The nature of spatial confinement of carriers in InAs/InP-core–shell nanowires is revealed based on the subband charge density distributions.Display Omitted►In this work, we performed the study of the first-principles density-functional theory by focusing on the nature of spatial confinement of carriers and the size and composition dependence of the band gaps in InAs/InP-core–shell nanowires.By means of first-principles calculations, we investigate the structural and electronic properties in a series of InAs/InP-core–shell nanowires with different sizes and compositions. Analysis of the subband charge density distributions reveals that both electrons and holes are spatially localized at the InAs-region of the core–shell nanowires, in consistent with a type-I band alignment. The size and composition effects on the confinement energies of electron carriers and the band gaps in the core–shell nanowires are investigated detailedly. These results provide an important guidance for the fabrication and applications of the core–shell nanowires.

Correlation between the saturation of emission current and defect co-ordination number for irradiated aligned multiwalled carbon nanotubes by Brahmananda Chakraborty; Padmnabh Rai; Kiran Shankar Hazra; Dipti R. Mohapatra; D.S. Misra; S. Banerjee (266-269).
At low Ar+ ion energies the defects production increases quickly with incident energy, as all the ion energy is deposited in the CNT. However, at higher energies the damage increases more slowly and finally starts to saturate at the energy 0.6 keV. The saturation in the emission current density and defect co-ordination number occurs at exactly same energy of Ar+ ions.Display Omitted► This letter establishes a correlation between the saturation of field emission current density and defect co-ordination number for low energy Ar+ ion irradiation of aligned multiwalled carbon nanotubes. ► Under high dose irradiation field emission current density, as obtained by in situ ion irradiation and field emission measurement decreases with the energy of the incident ion and finally saturates. ► Defect co-ordination number, calculated through Molecular Dynamics simulations increases for the low energy and finally saturates. ► Interestingly, the saturation in the emission current density and defect co-ordination number occurs at exactly same energy of Ar+ ions.Low energy Ar+ ion irradiation of aligned multiwalled carbon nanotube and in situ field emission measurement revealed deterioration of field emission current density with the energy of incident ions for high dose irradiation. Defect co-ordination number, calculated through Molecular Dynamics simulations increases for the low energy and finally saturates. The saturation of emission current density follows the same pattern as the defect co-ordination number varies with the energy of the incident ion. Interestingly, both the curves saturate at exactly same energy of Ar+ ions which establishes a correlation between the saturation of emission current density and defect co-ordination number.

For the calcium oscillations in mean-field coupling hepatocytes, synchronization may be improved or destroyed by external signal and noise, the complete synchronization is achieved above the critical coupling strength and the novel phenomenon of synchronization without tuning is found.Display Omitted► The critical coupling strength for the complete synchronization, the optimal frequency and the critical amplitude of external signal for the best synchronization and the novel phenomenon of synchronization without tuning in mean-field coupling hepatocytes.The synchronization of calcium oscillations in coupled hepatocytes has been investigated by the mean-field approach. Results show that, below the critical noise intensity, the synchronization is improved with increasing the noise intensity, while above it, the synchronization disappears. Meanwhile, a critical coupling strength is found, which is a threshold of occurrence of the complete synchronization, and the phenomenon of synchronization without tuning might be exhibited. Furthermore, when external signal is introduced into the coupled system, there exist an optimal frequency and a critical amplitude of external signal, which makes the system display the best synchronization.

New fluorescent probes for detection and characterization of amyloid fibrils by Galyna Gorbenko; Valeriya Trusova; Elena Kirilova; Georgiy Kirilov; Inta Kalnina; Aleksey Vasilev; Stefka Kaloyanova; Todor Deligeorgiev (275-279).
New benzanthrone derivative displays high sensitivity to amyloid aggregates of lysozyme.Display Omitted► The present study revealed an important new feature of the fluorescent benzanthrone dye ABM, viz. its amyloid specificity. ► As judged from the analysis of ABM interaction with lysozyme fibrils, this dye displays: (i) greater extent of fluorescence increase, (ii) higher affinity for fibrillar structures, (iii) weaker binding to the native protein, (iv) larger Stokes shift, being compared to classical amyloid marker ThT. ► Resonance energy transfer measurements involving ABM, squaraine dye SQ-1 and polymethine dye V2 demonstrated principal possibility of determining fractal dimension of fibrillar aggregates through analyzing the RET data from several donor–acceptor pairs.The applicability of the novel fluorescent probes, aminoderivative of benzanthrone ABM, squaraine dye SQ-1 and polymethine dye V2 to identification and structural analysis of amyloid fibrils has been evaluated using the lysozyme model system in which fibrillar aggregates have been formed in concentrated ethanol solution. The association constant, binding stoichiometry and molar fluorescence of the bound dye have been determined. ABM was found to surpass classical amyloid marker ThT in the sensitivity to the presence of fibrillar aggregates. Resonance energy transfer measurements involving ABM–SQ-1 and SQ-1–V2 donor–acceptor pairs yielded the limits for fractal-like dimension of lysozyme fibrils.

A spray drying system for synthesis of rare-earth doped cerium oxide nanoparticles by Vaneet Sharma; Kathryn M. Eberhardt; Renu Sharma; James B. Adams; Peter A. Crozier (280-286).
Display Omitted►A simple and inexpensive spray dryer to synthesize Pr-doped CeO2 nanoparticles. ► XRD confirmed the fluorite-type cubic crystal structure of the nanopowders. ► Nanopowders showed nanoscale compositional heterogeneity. ► The lattice parameter of Pr-doped CeO2 depends on the type of heat treatment process.We have constructed a spray dryer to synthesize doped ceria nanoparticles. The system was employed to synthesize mixed oxide nanoparticles of praseodymium doped CeO2 (Ce0.97Pr0.03O2, Ce0.90Pr0.10O2, and Ce0.80Pr0.20O2). X-ray diffraction confirmed the fluorite-like cubic crystal structure of the synthesized materials after heat treatment at 700 °C for 2 h. As-dried CeO2 samples were found to have an average particle size of (6.0 ± 0.2) nm which increased to (17.0 ± 0.4) nm after heat treatment with an improvement in crystallinity. The particle size increased steadily with Pr content. The lattice parameter of Pr-doped CeO2 was found to increase or decrease with Pr content depending on the heat treatment process.

NMR relaxometry: Spin lattice relaxation times in the laboratory frame versus spin lattice relaxation times in the rotating frame by Emilie Steiner; Mehdi Yemloul; Laouès Guendouz; Sébastien Leclerc; Anthony Robert; Daniel Canet (287-291).
Display Omitted► Extension of dispersion curves (NMR relaxometry) toward very low frequencies. ► Connection between relaxation times in the laboratory and in the rotating frames. ► Possibility to access dynamics involved at very low frequencies.Relaxometry dispersion curves display the spin lattice relaxation rate as a function of the measurement frequency. However, as far as proton NMR is considered, dispersion curves usually start around 5 kHz and thus miss the very low frequency region. This gap can be filled by the measurement of the spin–lattice relaxation rate in the rotating frame. The issue of connecting both relaxation rates is considered for two relaxation mechanisms: (i) randomly varying magnetic fields, (ii) dipolar interaction within a system of two equivalent spins. Appropriate data processing is presented and the random field mechanism turns out to be adequate.

Author Index (292-296).