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Laser-driven shock experiments were conducted at a synchrotron facility to investigate the dynamic response of polyurethane foam. These experiments were coupled to in situ x-ray imaging to radiograph foam deformations and to determine the propagation velocity of stress waves. To increase the amplitude and the duration of the pressure load generated by the laser–matter interaction, the front surface of the target was covered with a confining layer (water and BK7 glass). Preliminary calibration tests involving time-resolved velocity measurements were performed to calculate the ablation pressure on the front surface of foam samples. The calculated pressure loads were used as input data for hydrodynamic simulations, in which the foam is modeled using a homogeneous porous macroscopic model, and model predictions were compared with experimental results. A fair consistency was found for most experiments, while for the others, an overestimation of the applied pressure is suspected, likely due to a laser breakdown within the confining medium. Finally, post-shot x-ray tomography of the recovered samples showed permanent deformation of the foam, unlike what was observed under quasi-static compression, and revealed heavy damage in the vicinity of the loaded zone. [ABSTRACT FROM AUTHOR]

The last missing piece of the puzzle for the full functionalization of group IV optoelectronic devices is a direct bandgap semiconductor made by CMOS compatible technology. Here, we report on the fabrication of GeSn alloys with Sn concentrations up to 4.5% using ion implantation followed by millisecond-range explosive solid phase epitaxy. The n-type single crystalline GeSn alloys are realized by co-implantation of Sn and P into Ge. Both the activation of P and the formation of GeSn are performed during a single-step flash lamp annealing for 3 ms. The bandgap engineering in GeSn as a function of the doping level and Sn concentration is theoretically predicted by density functional theory and experimentally verified using ellipsometric spectroscopy. We demonstrate that both the diffusion and the segregation of Sn and P atoms in Ge are fully suppressed by millisecond-range nonequilibrium thermal processing. [ABSTRACT FROM AUTHOR]

Holographic inscription of surface grating, a well controlled process used in formation of polymer surface gratings with optical properties is described. The erasing process studied on different length scales as a function of temperature and time is also presented.

X-ray Absorption Fine Structure (XAFS) techniques, namely, X-ray Near Edge Structure (XANES), Extended XAFS (EXAFS), and Anomalous X-ray Diffraction (AXRD) were used to investigate the local atomic and electronic structure of (Ga, Mn)N magnetic layers with Mn concentrations of up to 10% grown by Molecular Beam Epitaxy. The XANES and AXRD analysis prove the Mn incorporation on substitutional GaN lattice sites. EXAFS results indicate the good quality of the structure under examination, although 0.5 nitride atom vacancies were found. The Wien2k code was applied to interpret the XANES spectra quantitatively, i.e., to determine the electronic structure of the Mn atoms. It was shown that accounting for the core-hole effect is necessary to reconstruct effectively the XANES spectra. Conducted charge density analysis based on DFT calculations identified the valency of Mn atom to be of 2.4+. [ABSTRACT FROM AUTHOR]

It is demonstrated that both the nucleation field and the irreversible switching field of Sm2Co7/Fe exchange spring bilayers is decreased by means of 10 keV He ion irradiation. The reduction is attributed to interfacial mixing and irradiation induced softening of the hard magnetic layer. By lowering the energy to 0.8 keV the ions do not penetrate the hard magnetic layer and, consequently, no softening is observed. However, although irradiation induced interfacial mixing is still present it is not large enough to create a graded interface layer and the nucleation field decreases. In contrast, conventional annealing under appropriate conditions leads to an increase in the nucleation field. This distinct discrepancy can be explained by detailed investigation of the layer structure by x-ray reflectivity measurements. [ABSTRACT FROM AUTHOR]

A comprehensive characterization of the structural and magnetic properties of Fe-implanted rutile TiO2(110) is presented. Fe and FeTiO3 (ilmenite) nanocrystals (NCs) are identified by synchrotron-radiation x-ray diffraction. The majority of Fe NCs are crystallographically oriented with respect to the matrix following the relation Fe(001)[010]∥TiO2(110)[11_0]. Postannealing induced the out-diffusion of Fe and the growth of FeTiO3 at the cost of Fe NCs. Mössbauer spectroscopy and superconducting quantum interference device (SQUID) magnetometry reveal the corresponding evolution of magnetic properties, i.e., magnetization, and superparamagnetic blocking temperature. We unambiguously identify Fe NCs as the origin of the ferromagnetism. These Fe NCs possess a uniaxial in-plane magnetic anisotropy, such that the two Fe[100] axes are inequivalent. [ABSTRACT FROM AUTHOR]

We show that metallic secondary phase formation inside ZnO(0001) single crystals implant-doped with Ni at an atomic concentration of 5% can be suppressed. All the Ni ions are in the 2+ valence state after mild postannealing. The suppression is achieved by means of annealing of the crystals in high vacuum prior to implantation and is correlated with the introduction of structural disorder. The observed ferromagnetic properties of the preannealed crystals are evidently induced by defects and not primarily by the Ni doping. They degrade at ambient temperature within several days. [ABSTRACT FROM AUTHOR]

A method to study temperature dependent thickness variation of thin films has been developed based on angle and energy dispersive x-ray reflectivity (EDR) techniques. The data analysis scheme developed for this method combines both energy and angle dispersive x-ray reflectivity (ADR) profiles. The ADR technique provides the electron density profile on an absolute scale and the EDR technique facilitates rapid collection of reflectivity data as a function of temperature. We demonstrate the utility of the developed method with results of a study of thermal expansion of single and bilayer polymer films. We could detect a change of the thickness of the film in angstroms and could demonstrate interplay of negative and positive thermal expansions of dissimilar polymer layers in determining density profiles of polymer–polymer interface as a function of temperature. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of the sputtering gases, Ar and Xe, on FePt clusters formation by magnetron sputtering deposition at high working pressures is studied. Ar assisted growths have led to FePt clusters in the [L1.sub.0] phase only if the sequential layer deposition is used, whereas for Xe no differences in the deposition methods are seen.

A correlation between structure and ferromagnetism in transition-metal-implanted Ti[O.sub.2] is described. Fe nanocrystals (NCs) are identified as the origin of the ferromagnetism and these Fe NCs possess a uniaxial in-plane magnetic anisotropy, such that the two Fe[100] axes are inequivalent.

The studies related to possible origin of the nanoparticle suppression and the ferromagnetic signal observed for the postannealed Ni:Zn[O.sub.vac], are discussed. The suppression is obtained via annealing of the crystals in high vacuum prior to implantation and is correlated with the introduction of structural disorder.

The transition from the paramagnetic NiMn phase to the chemically ordered, antiferromagnetic [L1.sub.0] phase of MiMn/[Fe.sub.1][Nisub.81] thin films deposited on a Si/Si[O.sub.2] substrate as a function of the annealing temperature is studied using synchroton x-ray diffraction and reflectivity. The transformation to a dominating [L1.sub.0] -ordered NiMn film takes place between 300 and 400 degree Celsius irrespective of the irradiation.

A comprehensive characterization of the structural and magnetic properties of Fe-implanted rutile TiO2(110) is presented. Fe and FeTiO3 (ilmenite) nanocrystals (NCs) are identified by synchrotron-radiation x-ray diffraction. The majority of Fe NCs are crystallographically oriented with respect to the matrix following the relation Fe(001)[010]∥TiO2(110)[11_0]. Postannealing induced the out-diffusion of Fe and the growth of FeTiO3 at the cost of Fe NCs. Mössbauer spectroscopy and superconducting quantum interference device (SQUID) magnetometry reveal the corresponding evolution of magnetic properties, i.e., magnetization, and superparamagnetic blocking temperature. We unambiguously identify Fe NCs as the origin of the ferromagnetism. These Fe NCs possess a uniaxial in-plane magnetic anisotropy, such that the two Fe[100] axes are inequivalent. [ABSTRACT FROM AUTHOR]