High energy Au+ ion implantation of polar and nonpolar ZnO—Structure modification and optical properties

The paper presents a study of 5-MeV energy Au⁺ ion implantation in polar c-plane (0001), nonpolar a-plane (11-20) and m-plane (10–10) ZnO crystallographic cuts using fluences of 5 × 10¹⁴ and 1 × 10¹⁵ cm⁻². The implanted samples were subsequently annealed in O₂ atmosphere at 600°C. It was shown that a-plane ZnO exhibited a lowest level of Zn sublattice disorder evidenced by Rutherford backscattering spectroscopy in channelling mode (RBS-C); in contrast, m-plane ZnO showed the highest disorder. The disorder in the Zn sublattice grew progressively in the subsurface as well as in the implanted layer in c-plane and m-plane ZnO, while a-plane has shown slight increase of disorder just in the implanted layer. Angular scans provided using RBS-C have shown the preservation of channelling effect in the subsurface layer in a-plane ZnO. On the contrary, the narrowed and shallow angular scan dips were seen in m-plane ZnO. Raman spectroscopy has shown significant O-sublattice disorder and O rearrangement mainly in a-plane and m-plane ZnO compared to c-plane. After ion implantation, the exciton-related luminescence band at 375 nm vanished almost completely, and the defect-related band ‘shifted’ to shorter wavelengths. Annealing has beneficial influence on near-band-edge (NBE) luminescence recovery, whereas deep-level-emission (DLE) luminesce has been shifted to lower wavelengths than appeared after implantation.     

Control of light transmission through opaque scattering media in space and time

We report the first experimental demonstration of combined spatial and temporal control of light transmission through opaque media. This control is achieved by solely manipulating spatial degrees of freedom of the incident wave front. As an application, we demonstrate that the present approach is capable of forming bandwidth-limited ultrashort pulses from the otherwise randomly transmitted light with a controllable interaction time of the pulses with the medium. Our approach provides a new tool for fundamental studies of light propagation in complex media and has the potential for applications for coherent control, sensing and imaging in nano- and biophotonics.     

Clusterized nuclear matter in the (proto-)neutron star crust and the symmetry energy

Though generally agreed that the symmetry energy plays a dramatic role in determining the structure of neutron stars and the evolution of core-collapsing supernovae, little is known in what concerns its value away from normal nuclear matter density and, even more important, the correct definition of this quantity in the case of unhomogeneous matter. Indeed, nuclear matter traditionally addressed by mean-field models is uniform while clusters are known to exist in the dilute baryonic matter which constitutes the main component of compact objects outer shells. In the present work we investigate the meaning of symmetry energy in the case of clusterized systems and the sensitivity of the proto-neutron star composition and equation of state to the effective interaction. To this aim an improved Nuclear Statistical Equilibrium (NSE) model is developed, where the same effective interaction is consistently used to determine the clusters and unbound particles energy functionals in the self-consistent mean-field approximation. In the same framework, in-medium modifications to the cluster energies due to the presence of the nuclear gas are evaluated. We show that the excluded volume effect does not exhaust the in-medium effects and an extra isospin and density-dependent energy shift has to be considered to consistently determine the composition of subsaturation stellar matter. The symmetry energy of diluted matter is seen to depend on the isovector properties of the effective interaction, but its behavior with density and its quantitative value are strongly modified by clusterization.     

Determination of Heavy Metals in Bio-Collectors as Indicator of Environmental Pollution

The heavy metal levels in bio-collector ( Fabaceae Rabinia Pseudoacacia L. sprouts) samples collected from seven sites, which had the characteristic properties of the Sivas city, Turkey, in year 2000, have been determined by atomic absorption spectrometry (AAS), after the bio-collector sprouts were prepared for analysis by bio-collector-ultrasonic leaching method (BC-ULM). The results of the analyses were used to determine major sources and magnitude of heavy metal pollution. The mean concentration levels of Pb, Cu, Ni, Zn and Cd were found to be 6.8, 5.5, 6.7, 12.4 and 0.20 µg/g fresh bio-collector, respectively, for September 2000. The highest levels of the heavy metals at the sites affected by industrial emissions and heavy traffic were noted. The heavy metal levels in urban bio-collectors were several times higher than the background levels. After heavy metal pollution factors of each site were determined, their possible major pollutant sources were discussed.     

Enthalpy and Entropy Barriers Explain the Effects of Topology on the Kinetics of Zeolite‐Catalyzed Reactions

The methylation of ethene, propene, and trans‐2‐butene on zeolites H‐ZSM‐58 (DDR), H‐ZSM‐22 (TON), and H‐ZSM‐5 (MFI) is studied to elucidate the particular influence of topology on the kinetics of zeolite‐catalyzed reactions. H‐ZSM‐58 and H‐ZSM‐22 are found to display overall lower methylation rates compared to H‐ZSM‐5 and also different trends in methylation rates with increasing alkene size. These variations may be rationalized based on a decomposition of the free‐energy barriers into enthalpic and entropic contributions, which reveals that the lower methylation rates on H‐ZSM‐58 and H‐ZSM‐22 have virtually opposite reasons. On H‐ZSM‐58, the lower methylation rates are caused by higher enthalpy barriers, owing to inefficient stabilization of the reaction intermediates in the large cage‐like pores. On the other hand, on H‐ZSM‐22, the methylation rates mostly suffer from higher entropy barriers, because excessive entropy losses are incurred inside the narrow‐channel structure. These results show that the kinetics of crucial elementary steps hinge on the balance between proper stabilization of the reaction intermediates inside the zeolite pores and the resulting entropy losses. These fundamental insights into their inner workings are indispensable for ultimately selecting or designing better zeolite catalysts.     

The Binding of Curcuma longa Extract with Bovine Serum Albumin Monitored via Time‐Resolved Fluorescence

Turmeric (Curcuma longa L.) is obtained from the rhizome of the Zingberaceae family and has a long history as an ingredient in cooking. It has been used as a dye and recently research has concentrated on its possible health benefits, specifically because of its antioxidant activity. The principal compound that is responsible for this activity is curcumin, which is present with the other curcuminoids; demethoxycurcumin and bisdemethoxycurcumin. Curcumin exhibits fluorescence and its photophysics are markedly affected by the polarity, hydrogen bonding and pH. This provides a means to examine its interaction with proteins, which is important if its potential health role is to be fully investigated. In this work, we monitor the binding kinetics using time‐resolved fluorescence measurements, enabled by the use of low dead time electronics coupled with a high repetition rate excitation source and time‐resolved emission spectra of the extracted curcuminoids upon interaction with bovine serum albumin. From these measurements the decay‐associated spectra of the different lifetime components were obtained, which is consistent with reports of more than one binding site. Monitoring changes in these spectra with increasing temperature also allows for the denaturing of the serum albumin to be inferred.     

The charge-transfer states in a stacked nucleobase dimer complex: a benchmark study

Electronic singlet excitations of stacked adenine-thymine (AT) and guanine-cytosine (GC) complexes have been investigated with respect to local excitation and charge-transfer (CT) characters. Potential energy curves for rigid displacement of the nucleobases have been computed to establish the distance dependence of the CT states. The second-order algebraic diagrammatic construction [ADC(2)] method served as reference approach for comparison to a selected set of density functionals used within the time-dependent density functional theory (TD-DFT). Particular attention was dedicated to the performance of the recently developed family of M06 functionals. The calculations for the stacked complexes show that at the ADC(2) level, the lowest CT state is S(6) for the AT and as S(4) for the GC pair. At the reference geometry, the actual charge transferred is found to be 0.73 e for AT. In case of GC, this amount is much smaller (0.17 e). With increasing separation of the two nucleobases, the CT state is strongly destabilized. The M06-2X version provides a relatively good reproduction of the ADC(2) results. It avoids the serious overstabilization and overcrowding of the spectrum found with the B3LYP functional. On the other hand, M06-HF destabilizes the CT state too strongly. TD-DFT/M06-2X calculations in solution (heptane, isoquinoline, and water) using the polarizable continuum model show a stabilization of the CT state and an increase in CT character with increasing polarity of the solvent.     

New generation decorative paint technology

The growth of waterborne paints in the higher performance decorative paint segments (like in high gloss paints, trim paints and also in stains and varnishes) has been slowed down due to a lack of open time, rheology, film build and scratch resistance. Over the years the improvement of the open time has been an intense area of research, but to date the typical paint rheology and brushing performance of a solvent based paint could not be achieved in a waterborne system. In this paper very low viscosity oligomers are presented as a solution for the open time problem. These oligomers remain liquid even after the evaporation of water and are self-crosslinking to achieve good final properties. The oligomers are combined with a dispersed polymer to reduce tack free times of the resulting coatings and to increase the rate of development of the properties. A model system is described where this effect is demonstrated.