Sputtering yields of PMMA films bombarded by keV C60 ions

A quartz crystal microbalance (QCM) has been used to determine total-mass sputtering yields of PMMA films by 1-16 keV C₆₀^+,2+ ion beams. Quantitative sputtering yields for PMMA are presented as mass loss per incident ion Y_m. Mass-lost rate QCM data show that a 13 keV C₆₀ cluster leads to emission equivalent to 800 PMMA molecules per ion. The power law obtained for the increase in sputtering yield with primary ion energy is in good agreement those predicted by “thermal spike” regime and MD models, when crater sizes are used to estimate sputtering.     

Fundamental studies of the cluster ion bombardment of water ice

The fundamental sputtering properties of water ice are of interest for molecular depth profiling of biological samples in their native environment. We report on a method of studying amorphous water ice films of precise thicknesses in which pure water vapor is condensed onto a pre-cooled, silver-coated quartz crystal microbalance (QCM). This scheme allows for the determination of water ice sputter yields for any primary projectile as well as providing a means for studying escape depths of atoms and molecules beneath the deposited water ice layer. Specifically, we find a removal of approximately 2500 water molecule equivalents/20 keV C₆₀⁺ projectile with an underlying silver ion escape depth of 7.0 Å.     

Element-selective mapping of magnetic moments in ultrathin magnetic films using a photoemission microscope

We combine X-ray magnetic circular dichroism (XMCD) and photoelectron emission microscopy to obtain locally resolved magnetic information on a microscopic scale. Scanning the photon energy across elemental absorption edges and recording microscopic images of the local secondary electron intensity for both photon helicities at each photon energy step allows to analyze local XMCD spectra at any position of the imaged area of the sample. With the help of magnetic sum-rules local quantitative information about magnetic moments can be extracted from such microspectroscopic measurements. The full power of XMCD as a spectroscopic tool is so maintained, while microscopic spatial resolution is added.     

Generalized Newtonian and Herschel-Bulkley yield stress fluids pressure behavior near the tip of a sharp edge in thin film flows

The Letter deals with two-dimensional symmetric and antisymmetric flows of generalized Newtonian and Herschel-Bulkley yield stress fluids close to a sharp edge which, for modeling purposes, is taken to be a geometric singularity. The pressure field is approximated using an asymptotic expansion valid in the tip neighborhood, and its dependence upon the edge angle is studied. For these special flows, the methodology used to obtain the pressure behavior does not require explicit knowledge of the viscosity dependence upon shear rate. Moreover, we prove that whenever the tip angle is such that the edge is hollow shaped, the yield stress fluid behaves solid-like in a neighborhood domain of the tip.     

8位取代吡咯甲川-BF_2化合物的光物理行为

90年代以来 ,人们先后发现了吡咯甲川- BF2化合物在许多领域的重要应用价值 ,如染料激光领域 ,与传统的香豆素、罗丹明及多甲川菁类化合物相比 ,它们具有激光效率高、光稳定性好、溶解度合适等无可比拟的优点 [1～ 3],目前已有数种商品染料问世 .在有机固体激光领域 ,将它们和以 PMMA等为基质的高分子材料掺杂后，得到的固体激光材料拥有相当高的能量转换效率和使用寿命 [4～ 6]，经过合理的结构改造 ,在激光医学领域也获得了一类极具开发潜力的用于肿瘤的激光光动力疗法（ photodynamic therapy）的吡咯甲川- BF2型新型光敏药物 ,据…     

A new distyrylbenzene derivative with Weinreb amide functionality: An efficient laser dye and nonlinear optical material

We report here the synthesis of a distyrylbenzene derivative with end substituent as Weinreb amide. This Weinreb amide-based distyrylbenzene (WADSB) gives indications of highly efficient laser dye as well as a nonlinear optical medium. The photophysical parameters of the dye are given here. The lasing spectra of the dye have been measured in a cuvette configuration. The third-order nonlinear susceptibility has been measured by laser-induced transient grating technique (LITG). A comparison with the existing standard molecules shows that it is a comparably an efficient lasing material as well as an efficient nonlinear optical material at the pump wavelength of 355 nm.     

Dependence of equilibrium properties of channeled particles on the transverse quasitemperature

We use methods of nonequilibrium thermodynamics to investigate the quasiequilibrium and kinetic characteristics of channeled particles regarded as a separate thermodynamic subsystem. For the channeled particles, we derive the energy—momentum balance equation in the moving coordinate system and show that the solution of the balance equation provides an expression for the main thermodynamic parameter, the transverse quasitemperature of the channeled-particle subsystem. We study the quasiequilibrium angular distribution of particles after their passage through a thin single crystal, the quasiequilibrium distribution over the particle exit angles under backscattering conditions, and also the rate constant for the nonequilibrium (dechanneling) process at large deviations of the system as a whole from the thermodynamic equilibrium. We discuss a measurement method for the particle beam transverse temperature over the peak height of the angular particle distribution found in the framework of a “shoot-through” experiment. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 146, No. 3, pp. 509–524, March, 2006.     

Structural Modeling of the Mechanical Behavior of Periodic Cellular Solids: Open-Cell Structures

The numerical simulation of random cellular metals, e.g., metal foams, is still connected with many unsolved problems due to their stochastic structure. Therefore, a periodic model of cellular metals is developed and its mechanical behavior is investigated numerically under uniaxial and multiaxial stress states. The main advantage of the model is that a wide range of relative densities can be covered and that test specimens of the same geometry are possible to manufacture without oversimplifying their shape. The influence of different hardening behavior and different boundary conditions on the characteristics of the material is investigated. Furthermore, the effect of internal pore pressure on its uniaxial behavior and on the shape of yield surface are determined.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 3, pp. 405–422, May–June, 2005.     

Spectroscopic properties and electronic structure of uranyl complex compounds (Review)

Fundamental problems of the photophysics of uranyl complex compounds are considered. Works on the spectroscopy of uranyl compunds in a wide spectral range from the visible to the vacuum UV region of the spectrum are reviewed. The characteristics of their electronic structure are discussed. It is shown that the optical properties of uranyl compounds are determined by electronic transitions from three occupied molecular orbitals. The highest occupied orbital of the uranyl complex is predominantly ligand in character; the lower-lying occupied orbitals have a significant contribution from uranyl orbitals. Intiation of electronic transitions from shielded valent orbitals increases the probability of nonradiative deactivation of electronic excitation of the uranyl complex. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 818–831, November–December, 1998     

Improving Matrix Corrections

 Except in the idealized case where the unknown and the standard are essentially identical obtaining accurate matrix corrections requires a knowledge of the absolute value and functional behavior of a number of quantities such the mass absorption coefficient, the electron stopping power, ionization cross sections and fluorescent yields. This talk examines the accuracy of the data available in each category, and the range of elements and compounds for which values have been published. It is found that the quality and quantity of data available varies greatly and that, with only a few exceptions, much more work is required to produce the reliable and inclusive data base required for accurate matrix corrections.