Magnetic and structural investigation of Mn(2+)-doped ZnSe semiconductor nanoparticles.

X-ray magnetic circular dichroism (XMCD) experiments on diluted magnetic semiconductor nanocrystals were carried out to study the local electronic structure and magnetic properties of Mn(2+) embedded in the lattice of ZnSe nanoparticles. It is shown that Mn(2+) is exclusively present in the bulk of ZnSe nanoparticles. Neither Mn-Mn coupling nor traces of oxidation to higher Mn oxidation states was observed. This result, which is consistent with EPR spectroscopic data, provides clear proof of the location of Mn(2+) in semiconductor nanoparticles. Further, it is shown that the magnetic ions are highly polarised inside the nanocrystals, where they reach about 50 % of the theoretical value of a pure d(5) state under identical conditions.     

Multiphase Field Modeling Chemical Vapor Infiltration of SiC/SiC Composite

A novel multiphase field model is formulated to describe the complex microstructure evolution during Chemical Vapor Infiltration(CVI), which is one of the important method to produce the SiC matrix composites reinforced by SiC fibers in ceramic engineer. The model is composed of a set of nonlinear partial differential equations by coupling Ginzburg-Landau type phase field equations with mass balance equation. Mathematically, the codeposition of SiC, Si and C during CVI process is a typical free boundary problem. When this problem is handled by multiphase field method, it's greatly facilitated because of the implicitly boundary-tracking technique by phase field order parameters. This typical multiphysic field problem is solved by finite element software COMSOL. The numerical results show good agreement with experimental research. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Elastic light scattering from nanoparticles by monochromatic vacuum-ultraviolet radiation

Elastic light scattering is reported using monochromatic vacuum-ultraviolet radiation to study free, spherical silica nanoparticles prepared by approaches from colloidal chemistry, with diameters between 100 and 240 nm. The colloidal nanoparticles of defined size are transferred from an aqueous solution into the gas phase using a particle beam experiment. After focusing of the particle beam by an aerodynamic lens, the scattered light from monochromatic synchrotron radiation is measured. Angle-resolved elastically scattered light is detected, showing a strong forward-scattering component. Additional evidence for the detection of elastically scattered light comes from plotting the scattered light intensity as a function of the dimensionless parameter qR, where q is the magnitude of the scattering wave vector and R is the particle radius. This yields different power-law regimes that are assigned to scattering from the surface and the bulk of the nanoparticles. Furthermore, there is evidence for modulations in the scattered light intensity as a function of scattering angle, which is clearly distinguished from the forward-scattering component. The experimental results are compared to Mie scattering simulations for isolated particles, yielding general agreement with the experimental results. Deviations from Mie simulations are observed for samples consisting of significant amounts of aggregates. The present results indicate that the optical properties of free nanoparticles are sensitively probed by vacuum-ultraviolet radiation.     

Characterization of quenched-in vacancies in Fe–Al alloys

Physical and mechanical properties of Fe–Al alloys are strongly influenced by atomic ordering and point defects. In the present work positron lifetime (LT) measurements combined with slow positron implantation spectroscopy (SPIS) were employed for an investigation of quenched-in vacancies in Fe–Al alloys with the Al content ranging from 18 to 49 at.%. The interpretation of positron annihilation data was performed using ab-initio   theoretical calculations of positron parameters. Quenched-in defects were identified as Fe-vacancies. It was found that the lifetime of positrons trapped at quenched-in defects increases with increasing Al content due to an increasing number of Al atoms surrounding the Fe vacancies. The concentration of quenched-in vacancies strongly increases with increasing Al content from ≈10⁻⁵$\approx {10}^{-5}$ in Fe₈₂Al₁₈${\mathrm{Fe}}_{82}{\mathrm{Al}}_{18}$ (i.e. the alloy with the lowest Al content studied) up to ≈10⁻¹$\approx {10}^{-1}$ in Fe₅₁Al₄₉${\mathrm{Fe}}_{51}{\mathrm{Al}}_{49}$ (i.e. the alloy with the highest Al content studied in this work).     

Surface functionalization of silica nanoparticles supports colloidal stability in physiological media and facilitates internalization in cells

The influence of the surface functionalization of silica particles on their colloidal stability in physiological media is studied and correlated with their uptake in cells. The surface of 55 ± 2 nm diameter silica particles is functionalized by amino acids or amino- or poly(ethylene glycol) (PEG)-terminated alkoxysilanes to adjust the zeta potential from highly negative to positive values in ethanol. A transfer of the particles into water, physiological buffers, and cell culture media reduces the absolute value of the zeta potential and changes the colloidal stability. Particles stabilized by L-arginine, L-lysine, and amino silanes with short alkyl chains are only moderately stable in water and partially in PBS or TRIS buffer, but aggregate in cell culture media. Nonfunctionalized, N-(6-aminohexyl)-3-aminopropyltrimethoxy silane (AHAPS), and PEG-functionalized particles are stable in all media under study. The high colloidal stability of positively charged AHAPS-functionalized particles scales with the ionic strength of the media, indicating a mainly electrostatical stabilization. PEG-functionalized particles show, independently from the ionic strength, no or only minor aggregation due to additional steric stabilization. AHAPS stabilized particles are readily taken up by HeLa cells, likely as the positive zeta potential enhances the association with the negatively charged cell membrane. Positively charged particles stabilized by short alkyl chain aminosilanes adsorb on the cell membrane, but are weakly taken up, since aggregation inhibits their transport. Nonfunctionalized particles are barely taken up and PEG-stabilized particles are not taken up at all into HeLa cells, despite their high colloidal stability. The results indicate that a high colloidal stability of nanoparticles combined with an initial charge-driven adsorption on the cell membrane is essential for efficient cellular uptake.     

Mid-infrared spectroscopy of molecular ions in helium nanodroplets

High resolution IR spectra of aniline, styrene, and 1,1-diphenylethylene cations embedded in superfluid helium nanodroplets have been recorded in the 300-1700 cm(-1) range using a free-electron laser as radiation source. Comparison of the spectra with available gas phase data reveals that the helium environment induces no significant matrix shift nor leads to an observable line broadening of the resonances. In addition, the IR spectra have provided new and improved vibrational transition frequencies for the cations investigated, as well as for neutral aniline and styrene. Indications have been found that the ions desolvate from the droplets after excitation by a non-evaporative process in which they are ejected from the helium droplets. The kinetic energy of the ejected ions is found to be ion specific and to depend only weakly on the excitation energy.     

Zur Bestimmung der Mikrohärte von Baryt-Einkristallen bei hohem hydrostatischen Druck

An apparatus to generate high pressure up to 12000 kp · cm⁻² and a microhardness device to be put in it are described. The pyramid identations originate from the moving force of the falling indenter. To compare microhardnesses at normal and high pressure the viscosities of the pressure fluids are assimilated. For that purpose the microhardness device served as viscosimeter. With extrapolated falling height zero of the idennter and a load of 36 g the (001)-surface of Baryt single crystals have a microhardness of about 210 kp · mm⁻² at a hydrostatic pressure of 10000 kp · cm⁻². The corresponding microhardness at normal pressure is 90 kp · mm⁻²     

涡场中黏附性颗粒团聚体粒径分布的预测

黏附性颗粒团聚现象在自然界和工业界普遍存在,扰动流场中黏附性颗粒间的碰撞、摩擦和吸附等动力学行为,导致团聚体形态不断演化,准确预测黏附性颗粒团聚体的粒径分布是调控颗粒团聚过程的重要前提。本文通过二维泰勒格林涡场中黏附性颗粒团聚的数值模拟研究,明确了利用Monte Carlo模型预测团聚体粒径分布的可行性及其适用范围,发现当黏附性颗粒间内聚数小于3.5×10^?4时,Monte Carlo模型可较好的预测团聚体粒径分布,且相对误差小于±30%;而当内聚数大于3.5×10^?4后,Monte Carlo模型不再适用。