1,721,196 research outputs found
Calculation of surface x-ray diffraction patterns in total external reflection conditions
No full textThe high brilliance of the new generation of synchrotron radiation sources improves the grazing incidence x‐ray diffraction techniques and leads to great advances in the determination of crystal surface structures. The evaluation of the diffraction pattern intensity can be obtained in the distorted‐wave approximation introduced by Vineyard. In conditions of total reflection, typical penetration depths are about 50 Å and only the atoms in the near‐surface layers interact with the electric field and produce the diffraction pattern. This model is the ground for a simulation code developed in order to calculate the diffracted peaks intensity of reconstructed and/or relaxed surfaces. An example of application, the Au (110) (1×2) reconstructed surface, is given. The intensity and the position of the diffraction peaks are determined for different values of the azimuthal angle and for different diffraction orders. The program takes into account the parameters of the beamline Advanced Line for Overlayer Interface and Surface Analysis (ALOISA) which will be available at the storage ring ELETTRA in Trieste
Degradation of Image Quality Induced by Thermal Loads and Slope Errors in a XUV High Resolution Synchrotron Radiation Monochromator
Full text linkThe limiting effects to the performances of an optical device, such as an XUV monochromator inserted in a synchrotron radiation facility, are mainly manufacturing slope errors and thermal loads induced by the optical beam itself. We have performed numerical simulations on such effects in the low energy section of a high resolution, wide spectral range monochromator for the storage ring ELETTRA in Trieste. The instrument will be used in the dedicated surface physics beamline ALOISA (advanced line for overlayer interface and surface analysis). Thermal effects have been evaluated by using finite element analysis. Thermal induced deformations and slope errors have been included in a ray tracing program. The resulting aberrations at the output of the instrument have been evaluated for the extreme conditions of maximum power density and asymmetrical illumination of the second mirror. The results stress the relevance of manufacturing slope errors in limiting spatial and spectral resolution
Thermal effects on optical performances of a prefocussing mirror for high-resolution soft-x-ray beamlines
No full textHeating of grazing incidence mirror surfaces by absorbed soft X-rays from a synchrotron beamline has been studied numerically to evaluate resultant displacements of the thermally loaded surface. Subsequent ray-tracing analysis has provided the corresponding change in optical performances. This procedure has been applied in particular to a thermally loaded prefocussing ellipsoidal mirror to be used in a high-spectral-resolution soft-X-ray beamline in the U2 undulator beamline of ELETTRA, and ultrahigh brightness synchrotron radiation facility under construction in Trieste. Various cooling geometries have been investigated. A detailed analysis of the results indicates deterioration of imaging properties beyond the present fabrication tolerances only at extreme irradiation levels
The Effect of Mn Depleted Surface Layer on the Corrosion Resistance of Shape Memory Fe-Mn-Si-Cr Alloys
Full text linkIn this work, we have examined Fe-Mn-Si-Cr alloys possessing a good shape memory effect due to
a high Mn content (28 wt pct). The addition of Cr (5 wt pct) was made in order to give fairly good
corrosion resistance to the alloy. But we have verified that even in moderately corrosive environ-ments, the presence of chromium does not bear any passivation. On the other hand, we have found
that the alloy can acquire corrosion resistance by means of the formation of a Mn-depleted surface
layer obtained by heating the alloy at high temperature (.10507C) in air. This modified layer forms
since manganese is selectively oxidized with respect to the other components. The adhesion of this
layer is maintained even under severe stress if the thickness of the modified region does not exceed
20mm. Under this limit, the shape memory characteristics of the alloy are not affected, and at the
same time, the specimen acquires properties of passivity comparable with one of the most common
austenitic stainless steels at the presence of the same environmental conditions
Electrochemical and X-ray photoelectron spectroscopy investigation into anodic behaviour of electroless Ni–9·5 wt-%P in acidic chloride environment
No full textThis paper reports on the anodic behaviour of as plated (X-ray amorphous) and heat treated (crystalline) high P electroless Ni-P deposits investigated by potentiodynamic and potentiostatic methods in acidic aqueous chloride solutions. Potentiodynamic measurements show all active-passive behaviour for both structures. The valence of P dissolution was assessed by the weight loss v. charge technique; dissolution valences do not correlate clearly with potentiodynamic behaviour. This call nevertheless he clearly interpreted ill terms of ex situ X-ray photoelectron spectroscopy analyses of attacked layer composition: the layers formed at lower anodic potential within the passive range consist of NiO, the ones obtained at high anodic polarisation contain phosphate. Differences ill anodic behaviour of as plated and heat treated specimens can he explained in terms of the defectiveness of protective NiO layers as a function of grain boundaries emerging at the surface
Electrodeposition of stoichiometric polycrystalline ZnTe on n+-GaAs and Ni-P
No full textAn acid aqueous sulphate electrolyte is proposed for the low temperature direct electrochemical growth of single-phase polycrystalline ZnTe. Single-crystal n+-GaAs and amorphous electroless Ni-P were used as substrates. The relationship between electrochemical growth conditions and the crystalline structure of as-deposited ZnTe were disclosed and correlated to the cathode chemistry during the growth process. Under suitable plating conditions the removal of tellurium (Te) excess from the deposit can be achieved, resulting in stoichiometric ZnTe. The nucleation of ZnTe was assessed through morphology observations by scanning electron microscopy: an instantaneous type prevails on GaAs and a progressive one on amorphous Ni-P. Chemical depth profiles of Zn and Te were investigated by X-ray photoelectron spectrometry measurements
Soluble poly (amido-amines) useful as promoters of cell adhesion, proliferation and differentiation
No full textUse of sol. polyamidoamines having a mol. wt. comprised from about 3.000 Da to about 120.000 Da, more
preferably from about 5.000 Da to about 40.000 Da, to promote adhesion, growth and differentiation of
cultured cell lines and primary cell cultures on cell-growth supporting substrates
Quantitative Control of Protein and Cell Interaction with Nanostructured Surfaces by Cluster Assembling
Full text linkThe development of smart prosthetics, scaffolds, and biomaterials for tissue engineering and organ-on-a-chip devices heavily depends on the understanding and control of biotic/abiotic interfaces. In recent years, the nanometer scale emerged as the predominant dimension for processes impacting on protein adsorption and cellular responses on surfaces. In this context, the extracellular matrix (ECM) can be seen as the prototype for an intricate natural structure assembled by nanoscale building blocks forming highly variable nanoscale configurations, dictating cellular behavior and fate. How exactly the ECM nanotopography influences mechanotransduction, that is, the cellular capacity to convert information received from the ECM into appropriate responses, remains partially understood due to the complexity of the involved biological structures, limiting also the attempts to artificially reproduce the nanoscale complexity of the ECM. In this Account, we describe and discuss our strategies for the development of an efficient and large-scale bottom-up approach to fabricate surfaces with multiscale controlled disorder as substrates to study quantitatively the effect of nanoscale topography on biological entities. Our method is based on the use of supersonic cluster beam deposition (SCBD) to assemble, on a substrate, neutral clusters produced in the gas phase and accelerated by a supersonic expansion. The assembling of clusters in the ballistic deposition regime follows simple scaling laws, allowing the quantitative control of surface roughness and asperity layout over large areas. Due to their biocompatibility, we focused on transition metal oxide nanostructured surfaces assembled by titania and zirconia clusters. We demonstrated the engineering of structural and functional properties of the cluster-assembled surfaces with high relevance for interactions at the biotic/abiotic interface. We observed that isoelectric point and wettability, crucial parameters for the adhesion of biological entities on surfaces, are strongly influenced and controlled by the nanoscale roughness. By developing a high-throughput method (protein surface interaction microarray, PSIM), we characterized quantitatively the capacity of the nanostructured surfaces to adsorb proteins, showing that with increasing roughness the adsorption rises beyond what could be expected by the increase in specific area, paralleled by an almost linear decrease in protein binding affinity. We also determined that the spatial layout of the surface asperities effectively perceived by the cells mimics at the nanoscale the topographical ECM characteristics. The interaction with these features consequently regulates parameters significant for cell adhesion and mechanotransductive signaling, such as integrin clustering, focal adhesion maturation, and the correlated cellular mechanobiology, eventually impacting the cellular program and differentiation, as we specifically showed for neuronal cells
Cluster beam synthesis of nanostructured thin films
No full textThe use of clusters as elemental building blocks can open routes toward the fabrication of a new class of nanostructured solids and devices. We report the synthesis of nanostructured films using supersonic cluster beam deposition. A new type of cluster source based on microplasma ablation has been developed. This allows a substantial improvement in terms of deposition rate and control on cluster mass distribution. These achievements make supersonic cluster beams a useful tool in the arena of cluster assembling of materials. We have applied this technique to the growth of nanostructured carbon thin films. The structure and morphology of the films can be controlled by varying the cluster mass distribution prior to deposition. Deposition conditions affect the surface roughness and the onset of scale-invariant morphology on a dimension domain extending from the nanometer up to the micrometer. The cluster beam deposition method shows very promising features in view of the large scale growth of nanostructured films with novel functional and structural properties. The patterning of three-dimensional nanostructured objects is also demonstrated
Photoelectrochemical imaging of non-planar surfaces : the influence of geometrical and optical factors on image formation
No full textIn situ scanning photoelectrochemical (PEC) microscopy is a technique for mapping the photocurrent stimulated by a focused light at an electrode-electrolyte interface. This technique gives position-sensitive information on the nature of passivating films (composition, type and degree of crystallization, thickness, etc) that cover metal electrodes. In the analysis of PEC images, further aspects related to the surface shape and/or surface irregularities (roughness, slope errors, surface waviness, etc) have to be taken into account. In this paper we present the effects of non-planar surfaces by measuring the photoresponse of passivating oxide films on cylindrical iron rods with different diameters. The variation of the angle of incidence of the light, as the laser beam scans the surface of the rod, implies either a change in the spot size and different optical response of the oxide-metal system, such as the transmittivity of the oxide, the reflectivity of the metal and the light path inside the film. For evaluating the behaviour of the photocurrent, we have simulated these geometrical and optical effects by using a simple model in geometrical optics approximation. Images have been also acquired at various distances from the beam focus for highlighting the degradation of the spatial resolution induced by the focusing misalignment of the curved samples
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