The transport gap of organic semiconductors studied using the combination of direct and inverse photoemission

The combination of valence band photoemission and inverse photoemission spectroscopy is applied to study the densities of occupied and unoccupied states of perylene derivative and phthalocyanine organic layers on inorganic semiconductors. The ionisation energies and electron affinities are determined and it is proposed that the transport gap of the materials can be evaluated from the distance of the HOMO and LUMO edges. The resulting values for the transport gap which are somewhat smaller than other published data are in good agreement with e.g. electrical measurements. The experimental spectra are compared with simulated ones obtained by density functional theory calculations.     

Fractal dimensions of lanthanum ferrite samples by adsorption isotherm method

Fractal dimensions of three different samples of lanthanum ferrite were computed using single adsorption method. The fractal Dubinin–Radushkevitch isotherm was used to fit directly the experimental nitrogen adsorption data. Avnir–Jaroniec method for fractal dimension determination was also used. Low and intermediate fractal dimensions were obtained according to BET specific surface areas.     

Molecular motion in solid ammonia trimethylalane

Solid state ²H NMR has been used to study molecular motion in deuterated ammonia trimethylalane (CH₃)₃AlND₃. From analysis of the ²H NMR lineshape between 123 and 298 K, reorientation of the -ND₃ group about the molecular Al-N axis is shown to occur at a rate higher than 10⁸ s^-1, and simulation of partially relaxed ²H NMR lineshapes shows that the reorientation can be described as a 3-site 120° jump motion. From the temperature dependence of the ²H spin-lattice relaxation time, the activation energy for this motion is estimated to be 9.3±0.3 kJ mol^-1. There is no evidence from either ²H or ²⁷Al NMR data for any site-exchange between the sites occupied by the -ND₃ and -CH₃ groups. The anisotropy of the dynamics of (CH₃)₃AlND₃ indicates that the orientation of the Al-N bond is highly constrained, presumably by a strong interaction between the electric dipoles of neighboring molecules.     

Hemin interaction with bare and 4,4'-thio-bis-benzene-thiolate covered n-GaAs (110) electrodes

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) investigations on the redox behavior of hemin at bare and 4,4'-thio-bis-benzene-thiolate (TBBT) covered n-GaAs (110) electrodes in dimethylsulfoxide (DMSO) revealed the high irreversibility of the electroreduction process, which appeared to be closely related to the stable adsorbed species strongly interfering with the electronic properties of the semiconducting substrate. The subsequent exploration of the hemin-modified electrodes by second harmonic generation (SHG), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements pointed to significant differences between the iron protoporphyrin species adsorbed on the bare- and TBBT-GaAs (110) electrodes. Only Fe(2+) species having a flat configuration with the porphyrin plane oriented parallel to the surface were detected on GaAs, unlike the TBBT-GaAs, where Fe(2+) and Fe(3+) species having both flat and vertical adsorption positions could be observed. These differences originate from the mutual interactions between the solvent, hemin and dithiolate molecules as well as their competition for the surface sites found to play a key role in the electrochemical process under discussion.     

Preparation, characterization and catalytic behavior of Pt-Cu nanoparticles in methane combustion

Fine and well dispersed Pt-Cu bimetallic nanoparticles stabilized by polyvinyl pyrrolidone (PVP) were synthesized by alkaline polyol method. The molar ratio of Pt to Cu was 1 : 1. Further, the Pt-Cu bimetallic nanoparticles were supported on alumina and their catalytic behavior in methane combustion was investigated. The as-prepared as well as the supported Pt-Cu nanoparticles were characterized by transmission elec-tron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fractal analysis and X-ray diffraction (XRD). The dependence of methane combustion on the morphology and surface composition of Pt-Cu nanoparticles was analyzed based on the experimental results.     

Paclitaxel-Loaded Magnetic Nanoparticles Based on Biotinylated N-Palmitoyl Chitosan: Synthesis,Characterization and Preliminary In Vitro Studies

A considerable interest in cancer research is represented by the development of magnetic nanoparticles based on biofunctionalized polymers for controlled-release systems of hydrophobic chemotherapeutic drugs targeted only to the tumor sites, without affecting normal cells. The objective of the paper is to present the synthesis and in vitro evaluation of the nanocomposites that include a magnetic core able to direct the systems to the target, a polymeric surface shell that provides stabilization and multi-functionality, a chemotherapeutic agent, Paclitaxel (PTX), and a biotin tumor recognition layer. To our best knowledge, there are no studies concerning development of magnetic nanoparticles obtained by partial oxidation, based on biotinylated N-palmitoyl chitosan loaded with PTX. The structure, external morphology, size distribution, colloidal and magnetic properties analyses confirmed the formation of well-defined crystalline magnetite conjugates, with broad distribution, relatively high saturation magnetization and irregular shape. Even if the ability of the nanoparticles to release the drug in 72 h was demonstrated, further complex in vitro and in vivo studies will be performed in order to validate the magnetic nanoparticles as PTX delivery system.     

Total oxidation of benzene using Cu-Cr mixed oxide as catalyst

Benzene total oxidation on a Cu-Cr supported catalyst was investigated using the work function method. Above 300°C, the majority of the oxygen species on the surface was O²⁻ in the absence or in the presence of hydrocarbon.     

The molecular orientation of DNA bases on H-passivated Si(1 1 1) surfaces investigated by means of near edge X-ray absorption fine structure spectroscopy

Layers of the DNA bases adenine, cytosine, and guanine were deposited onto hydrogen passivated Si(1 1 1) surfaces. The average tilt angles of these molecules with respect to the substrate surface were determined by the angular dependence of the Near Edge X-ray Absorption Fine Structure (NEXAFS) of the carbon K-edge. The interpretation of the NEXAFS spectra was assisted by a semi-empirical approach to the calculation of the π^∗-transition region which employs density functional theory calculations and core level photoemission data.     

Monte Carlo simulation of magnetic ordering in the Gd3Fe5O12 Ising ferrite with garnet structure

The simulation of magnetic properties in extended quantum spin networks can be done in good conditions with Ising models within Monte Carlo–Metropolis algorithms, as our systematic studies, employing original computer codes, proved. The present analysis provides interesting insights into the exchange interactions governing the magnetic behavior of the Gd₃Fe₅O₁₂ system, taken as a prototype for ferrites with garnet structure. Effective exchange interaction parameters are estimated by fitting the computed with experimental compensation temperature and temperature dependence of the magnetization.     

Synthesis and characterization of zinc oxide nanoparticles

The research is aimed at synthesis and characterization of nanoscaled zinc oxide particles and their application on linen fibrous supports, for thermal properties. To impart thermal activity to the fibrous nanocomposites, nanoparticles as well as fibrous nanocomposites were produced in different hydrothermal conditions of temperature (90 °C). To characterize the nanoparticles composition, their shape, size, and crystallinity, investigations technique, such as Fourier transformed infrared spectroscopy, scanning electron microscopy, and X-ray powder diffractometry were used. Differential scanning calorimetry analysis profiles were also revealed. The thermal treatment of linen fabrics with nanosized ZnO does not modify significantly their thermal stability.