Real-time observation on surface diffusion and molecular orientations for phthalocyanine thin films at nanometer spacial resolution

The morphology, electronic structure and ordering of the phthalocyanine thin films have been investigated at nanometer scale by photoelectron emission microscopy (PEEM) excited by polarized soft X-rays from synchrotron light source. The sample investigated was micropattern of silicon phthalocyanine deposited on gold surface. The incident angle dependences of the X-ray absorption near edge structure (XANES) spectra at the silicon K-edge revealed that the molecules of 5-layered films are lying nearly flat on the surface. Clear image of the micropattern was observed by PEEM, showing that the molecules are deposited via Volmer–Weber (VW) mode at room temperature. While, the surface diffusion was observed upon heating, and the micropattern image almost disappeared at 240 °C, representing the deposition mode changes from VW-mode to Frank–van der Merwe (FM)-one. On the basis of the photon-energy dependences of the brightnesses in the PEEM images, it was found that the molecules diffusing to the fresh gold surface rather stand-up at 240 °C. The observed changes in the molecular orientations at nanometer domains are discussed on the basis of the strengths of the molecule–molecule and molecule–surface interactions.     

Description and interpretation of the bracts epidermis of Gramineae (Poaceae) with rotated image with maximum average power spectrum (RIMAPS) technique

During the last few years, RIMAPS technique has been used to characterize the micro-relief of metallic surfaces and recently also applied to biological surfaces. RIMAPS is an image analysis technique which uses the rotation of an image and calculates its average power spectrum. Here, it is presented as a tool for describing the morphology of the trichodium net found in some grasses, which is developed on the epidermal cells of the lemma. Three different species of grasses (herbarium samples) are analyzed: Podagrostis aequivalvis (Trin.) Scribn. & Merr., Bromidium hygrometricum (Nees) Nees & Meyen and Bromidium ramboi (Parodi) Rúgolo. Simple schemes representing the real microstructure of the lemma are proposed and studied. RIMAPS spectra of both the schemes and the real microstructures are compared. These results allow inferring how similar the proposed geometrical schemes are to the real microstructures. Each geometrical pattern could be used as a reference for classifying other species. Finally, this kind of analysis is used to determine the morphology of the trichodium net of Agrostis breviculmis Hitchc. As the dried sample had shrunk and the microstructure was not clear, two kinds of morphology are proposed for the trichodium net of Agrostis L., one elliptical and the other rectilinear, the former being the most suitable.     

Theoretical calculation of surface tension and its temperature coefficient associated with liquid Cu–Ti alloys

In this work, the surface tension of Cu–Ti binary liquid alloys is calculated in the framework of Eyring theory as a function of composition and temperature. It is observed that for all investigated alloys the surface tension can be described by a linear function of the temperature with negative slope, and the temperature coefficient of surface tension decreases as Ti-content of the alloys increases linearly. The obtained theoretical results are compared to the experimental data available in the literature as well as to the theoretical results evaluated by using four models, such as the compound formation model, the quasi-chemical approximation for regular solutions, ideal solution model and Butler model treated in literature frequently.     

Secondary scintillation yield from GEM and THGEM gaseous electron multipliers for direct dark matter search

The search for alternatives to PMTs as photosensors in optical TPCs for rare event detection has significantly increased in the last few years. In particular, in view of the next generation large volume detectors, the use of photosensors with lower natural radioactivity, such as large area APDs or GM-APDs, with the additional possibility of sparse surface coverage, triggered the intense study of secondary scintillation production in micropattern electron multipliers, such as GEMs and THGEMs, as alternatives to the commonly used uniform electric field region between two parallel meshes. The much higher scintillation output obtained from the electron avalanches in such microstructures presents an advantage in those situations. The accurate knowledge of the amount of such scintillation is important for correct detector simulation and optimization. It will also serve as a benchmark for software tools developed and/or under development for the calculation of the amount of such scintillation.     

Quadric surface projection model for fish-eye cameras

The curved surface projection model in fisheye image correction algorithm is presented. To analyze the causes of distortion in existing models, we establish an ideal surface projection model and compare its surface with the surfaces of existing models. Subsequently, feature points are obtained on the ideal surface according to the relationship of coordinates of fish-eye image points and their ideal three-dimentional (3D) points. Finally, the least square method is used to obtain a quadric surface and presents a quadric surface projection model. The experiment shows that the corrected image of the new model is more similar to the actual scene than the corrected images of previous models.     

Imprinted optical pattern of low-softening phosphate glass

Thermal imprinting of transparent tin phosphate glass was performed at 250 degrees C using a fine-patterned silica mold. The glass sample was prepared by a conventional melt-quenching method and polished with a roughness of < or =10 nm for imprinting experiments. The imprinting temperature is optimized based on experimental viscosity data. Scanning electron microscope and atomic force microscope observations revealed that a square grid pattern has a surface roughness of < or =10 nm and 5 microm x 5 microm squares with ~1 microm intervals and 90-100 nm depth. Diffraction spots due to the micropattern are demonstrated by illuminating He-Ne laser light.     

Local thermal equilibrium and ideal gas Stephani universes

The Stephani universes that can be interpreted as an ideal gas evolving in local thermal equilibrium are determined. Five classes of thermodynamic schemes are admissible, which give rise to five classes of regular models and three classes of singular models. No Stephani universes exist representing an exact solution to a classical ideal gas (one for which the internal energy is proportional to the temperature). But some Stephani universes may approximate a classical ideal gas at first order in the temperature: all of them are obtained. Finally, some features about the physical behavior of the models are pointed out.This revised version was published online in April 2005. The publishing date was inserted.     

The surface composition of the silver—Gold system by Auger electron spectroscopy

The surface composition of polycrystalline AgAu alloy foils is studied by Auger electron spectroscopy. The intensities of principal Auger peaks over a wide range of electron energies are obtained as a function of alloy bulk composition for the clean equilibrated surfaces. Their ratios are compared with ratios expected for a surface showing no surface segregation, and for a surface obeying the regular solution monolayer model that predicts silver surface segregation. The experimental results give evidence for enrichment of the surface with silver, but to an extent less than predicted by the regular solution model.     

Measuring polarization in the x‐ray range: simulation for the impact gas mixture and pressure in gaseous detectors

The development of new technology in micropattern gaseous detectors makes it possible to measure x‐ray polarization for energies where the photoelectric effect is the main mechanism of interaction with matter. In a previous work, we showed that a modification of the Geant4 simulation code is a useful toolkit to simulate the photoelectric interaction of linearly polarized x‐rays with micropattern gas detectors. In particular, by properly taking into account the direction of the photoelectron, we developed a new calculation of the final state. We simulated one experimental setup found in the literature and showed that the simulation results obtained are in agreement with the experimental data. In this work, we present new results on simulation of a mixture of two gases with different pressures and study the impact in the modulation factor. The simulations were done for both low and high Z mean mixture. With these gas mixtures, we observed that the modulation factor was greater for a low Z mixture than that with a high Z, but the efficiency was opposite. We also observed that the modulation factor for high Z was influenced by the absorption edge of the photoelectric cross section. Copyright © 2009 John Wiley & Sons, Ltd.     

Relativistic fluid dynamics as a Hamiltonian system

The equations of ideal relativistic fluid dynamics in the laboratory frame form a noncanonical hamiltonian system with the same Poisson bracket as for nonrelativistic fluids, but with dynamical variables and hamiltonian obtained via a regular deformation of their nonrelativistic counterparts.     

Patterning of polypyrrole using a fluoropolymer as an adsorption-protecting molecule

Patterning of the conducting polymer polypyrrole (PPy) was achieved using perfluoropolyether (PFPE) as a mask material. The fluoropolymer PFPE has both hydrophobic and oleophobic properties that allowed the generation of passivated patterns against PPy deposition. We exploited these properties to achieve the selective micropattern deposition of PPy, by simple chemical oxidation in an aqueous solution. Using a microcontact printing method, circle patterns with exposed carboxyl groups were prepared, while other region was protected by PFPE. Chemical oxidation of PPy on the patterned substrate resulted in selective deposition of PPy onto only the carboxylate-terminated regions, with little deposition on the PFPE layer. Cross-sectional analysis of the pattern revealed that the PFPE layer would form a hole-like structure around the carboxylate-terminated surfaces, with PPy deposition only in the holes. The PFPE layer had little influence on surface smoothness, compared to other self-assembled monolayers. These results suggest that PFPE can be used as a protective material for the surface modification and patterning of various materials.     

Vavilov-Cherenkov effect in a chiral waveguide

The Vavilov-Cherenkov radiation appearing in a circular regular ideal waveguide with a chiral medium is considered. The features of the emission spectrum excited by a charge moving along the waveguide axis are investigated. Expressions for the energy loss of a moving charge are obtained. Zh. Tekh. Fiz. 69, 69–71 (March 1999)     

Highly regular nanometer-sized hexagonal pipes in 6H-SiC(0001)

An array of troughs was prepared on a 6H-SiC(0001) surface using focused ion beam (FIB) patterning. Troughs were etched with various ion doses and close-to-circular voids of increasing depths for larger ion doses were obtained. The samples were then etched in a hot-wall reactor at a hydrogen partial pressure of 13 mbar at 1800 °C. The resulting morphological reorganizations have been studied by scanning electron and atomic force microscopy. Very regular hexagonal voids with facets oriented perpendicular to the surface were obtained after hydrogen etching. The voids were surrounded by regular secondary facets of lower inclination. Whereas the depth of the voids increases with ion dose, the void diameter and facet sizes stay constant. This effect is explained by surface diffusion during hydrogen etching. The FIB technique in combination with hydrogen etching allows the preparation of very regular surface patterns and highly ordered wells and tubes for nanometer-sized sieves and photonic crystals. PACS 47.70.Fw; 68.37.-d; 68.37.Hk; 68.37.Ps; 81.65.Cf     

The amount and location of amorphous component in polyethylene single crystals

Polyethylene single crystals from dilute solutions usually have a density ρ which is less than that of the ideal crystal lattice (ρ_c = 1.000 g/cm³). This density defect can be formally assigned to an “amorphous” component (1-α) = (ρ_c-ρ)/(ρ_c-ρa) and may be caused by vacancies in the crystal lattice and/or by the surface disorder connected with chain folds. The two-phase concept of single crystal structure assumes a very nearly ideal lattice core and two amorphous layers on the fold-containing surfaces. It is supported by density and heat content data of annealed samples, by small-angle X-ray scattering, by wide-line NMR investigations, and by the results of fuming nitric acid treatment.

The maximum thickness of the amorphous surface layer as a function of temperature may be estimated from the free energy requirement of such a layer. With regular chain folds one has a high concentration of gauche conformations yielding a high surface energy. The need for such a concentration disappears in the amorphous layer with loose loops. This gain in energy may be spent for surface melting. Still more important is the gain in entropy caused by the random distribution of loop lengths.     

On the effective action of center vortices in continuum Yang-Mills theory

The effective action of sufficiently smooth center vortices in continuum Yang-Mills theory is investigated taking into account some of their basic properties observed in lattice simulations. The obtained action is given by the action of an ideal vortex configuration, which is local on the vortex worldsheet, nonlocal quantum corrections due to virtual gluon exchanges, which can be reliably calculated using perturbation theory, and the contribution of Abelian magnetic monopoles. Smooth center vortices appear to have negative rigidity. This implies that, in agreement with lattice data, in the ground state of the theory center vortices are not regular surfaces. The text was submitted by the authors in English.     

基于光切法的表面粗糙度检测的图像处理研究

介绍了表面粗糙度的检测方法，阐述了利用视频化改造后的9J型光切显微镜，基于光切法的表面粗糙度检测的数字图像处理方法，利用Canny算子进行边缘检测和保持连通的边缘细化算法进行细化处理，得到了较为理想的表面粗糙度轮廓曲线，为后续的表面粗糙度参数的计算奠定了基础。     

Ge quantum dots growth on nanopatterned Si(0 0 1) surface: Morphology and stress relaxation study

The self-organized growth of germanium quantum dots on square nanopatterned Si(0 0 1) substrates is investigated by scanning tunnelling microscopy (STM) and grazing incidence X-ray diffraction (GIXRD) techniques. A regular surface patterning in the 10-100 nm period range is obtained by etching an interface dislocation network obtained by the controlled molecular bonding of Si substrates. The depth of the silicon surface profile is increased by a double etching process. Growth experiments are performed by solid source molecular beam epitaxy (MBE), and for deep trenches, germanium growth conditions are optimized to obtain one Ge dot per Si mesa. It is shown that the trench depth and the mesa profile strongly affect the dot size and its coincidence with the initial regular surface network. Anomalous GIXRD measurements are performed to highlight the Ge elastic relaxation and intermixing during heteroepitaxial growth. We report a significant modification in the stress state of Ge dots as a function of thermal annealing after growth.     

Nanoscopic surface patterns of diblock copolymer thin films

The surface topography of thin diblock copolymer films is studied by atomic force microscopy (AFM). With AFM an island-to-ribbon transition is observed for symmetric polystyrene-b-poly (4-vinylpyridine) (PS-b-P4VP) on mica with increasing solution concentration. Our study also demonstrates how the formation of the pattern strongly depends on the copolymer composition based on the volume fraction. The substrate and solvent used both have great effects on the morphology of the thin films. Only by using highly polar substrate (mica), can we gain regular pattern. The reason why the regular islands cannot be obtained with symmetric PS-b-P4VP on graphite is also explained. On mica using nonselective and selective solvents, a rather regular pattern can be obtained. The difference is only in the solution concentration for forming regular patterns.     

On interpretation of intrinsic surface states on Si(111) surface

Extended Hückel theory is applied to the Si9111) ideal and relaxed surfaces. In addition to the results obtained by selfconsistent pseudopotential calculations of Schlütter et al., new surface states gave been found. The results are essentially independent of surface relaxation.     

Molecular dynamics study of the equilibrium flux of gas molecules to a fractal/rough surface: Effects of gas atom diameter

The frequency of collisions of ideal gas molecules (argon) with a rough surface has been studied. The rough/fractal surface was created using the random deposition technique. By applying various depositions the surface roughness was controlled and, as a measure of irregularity, the fractal dimensions of the surfaces were determined. The surfaces were next immersed in ideal gas and the numbers of collisions with these surfaces were counted. The calculations were carried out using the simplified molecular dynamics simulation technique (only hard core repulsions were assumed). The calculations were performed for various ratios of gas phase atoms diameter to the surface substrate atoms diameter. The results obtained showed that the size of a gas phase atom has crucial influence on the relation between the frequency of collision and the surface fractal dimension