In-situ X-ray diffraction studies during growth of Ni-Ti shape memory alloy films and their complementary ex-situ characterization

Shape Memory Alloy (SMA) Ni-Ti films have attracted much interest as functional and smart materials due to their unique properties. However, there are still important issues unresolved like formation of film texture and its control as well as substrate effects. Thus, the main challenge is not only the control of the microstructure, including stoichiometry and precipitates, but also the identification and control of the preferential orientation since it is a crucial factor in determining the shape memory behaviour. The aim of this PhD thesis is to study the optimisation of the deposition conditions of films of Ni-Ti in order to obtain the material fully crystallized at the end of the deposition, and to establish a clear relationship between the substrates and texture development. In order to achieve this objective, a two-magnetron sputter deposition chamber has been used allowing to heat and to apply a bias voltage to the substrate. It can be mounted into the six-circle diffractometer of the Rossendorf Beamline (ROBL) at the European Synchrotron Radiation Facility (ESRF), Grenoble, France, enabling an in-situ characterization by X-ray diffraction(XRD) of the films during their growth and annealing. The in-situ studies enable us to identify the different steps of the structural evolution during deposition with a set of parameters as well as to evaluate the effect of changing parameters on the structural characteristics of the deposited film. Besides the in-situ studies, other complementary ex-situ characterization techniques such as XRD at a laboratory source, Rutherford backscattering spectroscopy(RBS), Auger electron spectroscopy (AES), cross-sectional transmission electron microscopy (X-TEM), scanning electron microscopy (SEM), and electrical resistivity (ER) measurements during temperature cycling have been used for a fine structural characterization. In this study, mainly naturally and thermally oxidized Si(100) substrates, TiN buffer layers with different thicknesses (i.e. the TiN topmost layer crystallographic orientation is thickness dependent) and MgO(100) single crystals were used as substrates. The chosen experimental procedure led to a controlled composition and preferential orientation of the films. The type of substrate plays an important role for the texture of the sputtered Ni-Ti films and according to the ER results, the distinct crystallographic orientations of the Ni-Ti films influence their phase transformation characteristics.

Laser-induced diffusion decomposition in Fe-V thin-film alloys

We investigate the origin of ferromagnetism induced in thin-film (similar to 20 nm) Fe-V alloys by their irradiation with subpicosecond laser pulses. We find with Rutherford backscattering that the magnetic modifications follow a thermally stimulated process of diffusion decomposition, with formation of a-few-nm-thick Fe enriched layer inside the film. Surprisingly, similar transformations in the samples were also found after their long-time (similar to 10(3) s) thermal annealing. However, the laser action provides much higher diffusion coefficients (similar to 4 orders of magnitude) than those obtained under standard heat treatments. We get a hint that this ultrafast diffusion decomposition occurs in the metallic glassy state achievable in laser-quenched samples. This vitrification is thought to be a prerequisite for the laser-induced onset of ferromagnetism that we observe. 2014 Elsevier B.V. All rights reserved.

Velocity estimation of moving ships using C-band SLC SAR data

A new algorithm for the velocity vector estimation of moving ships using Single Look Complex (SLC) SAR data in strip map acquisition mode is proposed. The algorithm exploits both amplitude and phase information of the Doppler decompressed data spectrum, with the aim to estimate both the azimuth antenna pattern and the backscattering coefficient as function of the look angle. The antenna pattern estimation provides information about the target velocity; the backscattering coefficient can be used for vessel classification. The range velocity is retrieved in the slow time frequency domain by estimating the antenna pattern effects induced by the target motion, while the azimuth velocity is calculated by the estimated range velocity and the ship orientation. Finally, the algorithm is tested on simulated SAR SLC data.

A technical investigation of an oil painting on copper support, including a study on consolidants for treatment

Paper submitted to e-conservation Journal: Maria Leonor Oliveira, Leslie Carlyle, Sara Fragoso, Isabel Pombo Cardoso and João Coroado, “Investigations into paint delamination and consolidation of an oil painting on copper support”.

Tailored deposition of coloured coatings: on the widening of the available colour range

Dissertação de mestrado integrado em Engenharia de Materiais

Improvement of the specificity of cancer detection by autofluorescence imaging in the tracheo-bronchial tree using backscattered violet light.

BACKGROUND: Autofluorescence bronchoscopy (AFB) is a highly sensitive tool for the detection of early bronchial cancers. However, its specificity remains limited due to primarily false positive results induced by hyperplasia, metaplasia and inflammation. We have investigated the potential of blue-violet backscattered light to eliminate false positive results during AFB in a clinical pilot study. METHODS: The diagnostic autofluorescence endoscopy (DAFE) system was equipped with a variable band pass filter in the imaging detection path. The backscattering properties of normal and abnormal bronchial mucosae were assessed by computing the contrast between the two tissue types for blue-violet wavelengths ranging between 410 and 490 nm in 12 patients undergoing routine DAFE examination. In a second study including 6 patients we used a variable long pass (LP) filter to determine the spectral design of the emission filter dedicated to the detection of this blue-violet light with the DAFE system. RESULTS: (Pre-)neoplastic mucosa showed a clear wavelength dependence of the backscattering properties of blue-violet light while the reflectivity of normal, metaplastic and hyperplastic autofluorescence positive mucosa was wavelength independent. CONCLUSIONS: Our results showed that the detection of blue-violet light has the potential to reduce the number of false positive results in AFB. In addition we determined the spectral design of the emission filter dedicated to the detection of this blue-violet light with the DAFE system.

Estimation of surface roughness in a semiarid region from C-band ERS-1 synthetic aperture radar data

In this study, we investigated the feasibility of using the C-band European Remote Sensing Satellite (ERS-1) synthetic aperture radar (SAR) data to estimate surface soil roughness in a semiarid rangeland. Radar backscattering coefficients were extracted from a dry and a wet season SAR image and were compared with 47 in situ soil roughness measurements obtained in the rocky soils of the Walnut Gulch Experimental Watershed, southeastern Arizona, USA. Both the dry and the wet season SAR data showed exponential relationships with root mean square (RMS) height measurements. The dry C-band ERS-1 SAR data were strongly correlated (R² = 0.80), while the wet season SAR data have somewhat higher secondary variation (R² = 0.59). This lower correlation was probably provoked by the stronger influence of soil moisture, which may not be negligible in the wet season SAR data. We concluded that the single configuration C-band SAR data is useful to estimate surface roughness of rocky soils in a semiarid rangeland.

Threshold effects on heavy quark production in gamma gamma interactions

The exchange of gluons between heavy quarks produced in e+e- interactions results in an enhancement of their production near threshold. We study QCD threshold effects in collisions. The results are relevant to heavy quark production by beamstrahlung and laser backscattering in future linear collider experiments. Detailed predictions for top-, bottom-, and charm-quark production are presented.

Monte Carlo simulation of kilovolt electron transport in solids

A Monte Carlo procedure to simulate the penetration and energy loss of low¿energy electron beams through solids is presented. Elastic collisions are described by using the method of partial waves for the screened Coulomb field of the nucleus. The atomic charge density is approximated by an analytical expression with parameters determined from the Dirac¿Hartree¿Fock¿Slater self¿consistent density obtained under Wigner¿Seitz boundary conditions in order to account for solid¿state effects; exchange effects are also accounted for by an energy¿dependent local correction. Elastic differential cross sections are then easily computed by combining the WKB and Born approximations to evaluate the phase shifts. Inelastic collisions are treated on the basis of a generalized oscillator strength model which gives inelastic mean free paths and stopping powers in good agreement with experimental data. This scattering model is accurate in the energy range from a few hundred eV up to about 50 keV. The reliability of the simulation method is analyzed by comparing simulation results and experimental data from backscattering and transmission measurements.

Epitaxial growth of Y-doped SrZrO3 films on MgO by pulsed laser deposition

Epitaxial thin films of Y¿doped SrZrO3 have been grown on MgO(001) by pulsed laser deposition. The deposition process has been performed at temperatures of 1000¿1200¿°C and at an oxygen pressure of 1.5×10¿1 mbar. The samples are characterized by Rutherford backscattering spectrometry/channeling (RBS/C) and x¿ray diffraction (XRD). We found an epitaxial relationship of SrZrO3 (0k0) [101]¿MgO (001) [100]. Good crystalline quality is confirmed by RBS/C minimum yield values of 9% and a FWHM of 0.35° of the XRD rocking curve.

Composition, nanostructure, and optical properties of silver and silver-copper lusters

Lusters are composite thin layers of coinage metal nanoparticles in glass displaying peculiar optical properties and obtained by a process involving ionic exchange, diffusion, and crystallization. In particular, the origin of the high reflectance (golden-shine) shown by those layers has been subject of some discussion. It has been attributed to either the presence of larger particles, thinner multiple layers or higher volume fraction of nanoparticles. The object of this paper is to clarify this for which a set of laboratory designed lusters are analysed by Rutherford backscattering spectroscopy, transmission electron microscopy, x-ray diffraction, and ultraviolet-visible spectroscopy. Model calculations and numerical simulations using the finite difference time domain method were also performed to evaluate the optical properties. Finally, the correlation between synthesis conditions, nanostructure, and optical properties is obtained for these materials.

Estabilização do ácido lipoico via encapsulação em nanocápsulas poliméricas planejadas para aplicação cutânea

This work reports the development of polymeric nanocapsules containing lipoic acid prepared by interfacial deposition of poli(ε-caprolactona). The suspensions showed acid pH and encapsulation efficiencies from 77 to 90%. Zeta potential values were from -7.42 to -5.43 mV and particle sizes were lower than 340 nm with polidispersion lower than 0.3. The stability of nanocapsules within 28 days was evaluated in terms of pH, lipoic acid content, diameter, size distribution, zeta potential and measurements of relative light backscattering. The stability of formulations containing free lipoic acid was also evaluated. Nanoencapsulation drastically improved the physico-chemical stability of lipoic acid.

Influence of data acquisition geometry on soybean spectral response simulated by the prosail model

View angle and directional effects significantly affect reflectance and vegetation indices, especially when daily images collected by large field-of-view (FOV) sensors like the Moderate Resolution Imaging Spectroradiometer (MODIS) are used. In this study, the PROSAIL radiative transfer model was chosen to evaluate the impact of the geometry of data acquisition on soybean reflectance and two vegetation indices (Normalized Difference Vegetation Index - NDVI and Enhanced Vegetation Index -EVI) by varying biochemical and biophysical parameters of the crop. Input values for PROSAIL simulation were based on the literature and were adjusted by the comparison between simulated and real satellite soybean spectra acquired by the MODIS/Terra and hyperspectral Hyperion/Earth Observing-One (EO-1). Results showed that the influence of the view angle and view direction on reflectance was stronger with decreasing leaf area index (LAI) and chlorophyll concentration. Because of the greater dependence on the near-infrared reflectance, the EVI was much more sensitive to viewing geometry than NDVI presenting larger values in the backscattering direction. The contrary was observed for NDVI in the forward scattering direction. In relation to the LAI, NDVI was much more isotropic for closed soybean canopies than for incomplete canopies and a contrary behavior was verified for EVI.

Sensory acceptability and physical stability evaluation of a prebiotic soy-based dessert developed with passion fruit juice

The aim of this study was to use a factorial design approach for developing a palatable and stable soy-based dessert with the addition of Soy Protein (SP), oligofructose, and Passion Fruit Juice (PFJ). Panelists (n = 50) used a seven-point hedonic scale to assess the overall liking, degree of liking of creaminess, taste, and color of the desserts. In addition, the samples were submitted to a preference ranking test in order to evaluate the products' preference. Water Holding Capacity (WHC) and backscattering (BS) measures were also determined to assess the physical stability of the trials. Sample F3 (35% PFJ and 2% SP) was the only one that presented a WHC index of 94.8%; moreover, none of the developed samples had synerisis after 72 hours of storage indicating adequate physical stability of the emulsion process. Samples F2 (25% PFJ, and 3.0% SP), F4 (35% PFJ, and 3.0% SP), and F5 (30% PFJ, and 2.5% SP) presented mean hedonic scores above 'slightly liked' for all sensory attributes. The acceptance index of samples varied from 62.50 to 88% showing the great sensory potential of such products.

Dechanneling of 2 Mev Heâ ½ in gold

Thick gold single crystals of high quality were prepared for Rutherford Backscattering Dechanneling studies by electropolishing and annealing. The variation.; with temperature of the Random Fraction versus Depth spectrtnn for 2 MeV He+ on < 110> gold was extracted from measured Aligned and Random (Energy) Spectra. The measured dechanneling rate showed a sixfold increase in going from 4loK to 293°K and is in reasonable agreement with calculations made using the Steady Increase in Transverse Energy (SITE) approximation.