Gentle quantitative measurement of helium density in nanobubbles in silicon by spectrum imaging.

We propose an original method for the determination of the physical properties of nanometer sized helium bubbles using spectrum imaging in an energy-filtered transmission electron microscope. Helium bubbles synthesized by high fluence implantation and thermal annealing in silicon are investigated. The acquisition parameters are determined to optimize both signal/noise ratio and time. The limitations to the extent of observable areas on a typical sample are explained. The necessary data correction and helium K-edge position measurement procedures are detailed and the accuracy of the method is discussed. Finally helium density maps are obtained and discussed.

Self-organized ultrathin FePt nanowires produced by glancing-angle ion-beam codeposition on rippled alumina surfaces.

Ultradense macroscopic arrays of ferromagnetic alloy nanowires exhibit unique properties that make them attractive both for basic physics studies and for prospective nanodevice applications in various areas. We report here on the production of self-organized equiatomic FePt nanowires produced by glancing-angle ion-beam codeposition on alumina nanoripple patterns at room temperature and subsequent annealing at 600 °C. This study demonstrates that periodically aligned FePt nanowires with tunable size (∼10-20 nm width and ∼0.5-10 nm height) can be successfully grown as a consequence of shadowing effects and low mobility of Fe and Pt on the rippled alumina surface. Moreover, the structure and magnetic properties of the FePt nanowires, which undergo a phase transition from a disordered A1 (soft) structure to a partially ordered L10 (hard) structure, can be modified upon annealing. We show that this behavior can be further exploited to change the effective uniaxial anisotropy of the system, which is determined by a strong interplay between the shape and magnetocrystalline anisotropies of the nanowires.

Atomic scale structure of (001) hydrogen-induced platelets in germanium.

An accurate characterization of the structure of hydrogen-induced platelets is a prerequisite for investigating both hydrogen aggregation and formation of larger defects. On the basis of quantitative high resolution transmission electron microscopy experiments combined with extensive first principles calculations, we present a model for the atomic structure of (001) hydrogen-induced platelets in germanium. It involves broken Ge-Ge bonds in the [001] direction that are dihydride passivated, vacancies, and trapped H(2) molecules, showing that the species involved in platelet formation depend on the habit plane. This model explains all previous experimental observations.

Deposit of glass fragments during femtosecond laser penetrating keratoplasty.

BACKGROUND: To evaluate femtosecond laser interaction with the applanation lens during pre-programmed penetrating keratoplasty corneal cuts. METHODS: Three different-shaped penetrating keratoplasty dissections were performed on edematous corneas from bank eyes using a clinical femtosecond laser system (Intralase FS60) with energies higher than 2 microJ, and the "depth into glass" parameter at 50 microm, which is defined as the length over which the laser interacts with the glass of the applanation cone in contact with the cornea. Additional full-thickness corneal incisions were obtained with an experimental laser source with technical characteristics similar to the clinical laser. Following cutting, tissue sections were examined by optical microscopy (OM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). After the procedure, the cones were examined by optical and scanning electron microscopy (SEM). A control was obtained by repeating the procedures and stopping the laser at the cornea-lens interface. RESULTS: OM and TEM analysis of the tissue showed the presence of solid particles of a maximum dimension of 1.5 mum on the epithelium and the anterior stroma, regardless of the laser system used to cut. The EELS technique revealed their composition as silicon dioxide. We believe that the fragments originate from the applanation cone, which is machined by the laser interacting with the glass in contact with cornea. This is consistent with the structures observed on the lens by OM and SEM. Radial and circumferential tracks on the surface of the lens are visible, corresponding to the laser path in penetrating keratoplasty protocols. No particles were found in the control samples. CONCLUSIONS: When performing penetrating keratoplasty corneal cuts by infra-red femtosecond laser, the applanation lens in contact with the cornea is machined by the laser depending on the system parameters. As a consequence, microscopic glass fragments are created, which may remain in the tissue. This unwanted effect can be avoided by stopping the procedure at the lens-cornea interface.

Improved oxygen mobility in nanosized mixed-oxide particles synthesized using a simple nanocasting route.

This work reports the synthesis of homogeneously dispersed mixed-oxide nanoparticles (<5 nm) exhibiting improved lattice oxygen mobility (ca. two times higher than on bulk samples), using a novel synthesis procedure of nanocasting in mesoporous silica host support.