Marco Faustini

Recording study of percolated perpendicular media

We examine the magnetic recording properties of percolated perpendicular media (PPM) fabricated by depositing a Co/Pt multilayer film on top of nanoperforated templates created by self-assembly. We characterize the recording performance by examining the magnetic transition jitter in patterns written to the media using a hard disk drive write head. The transition jitter is lowest in the media created using the template with the highest perforation density, which demonstrates a route for further improving PPM-based recording media.

Role of quantum confinement in luminescence efficiency of group IV nanostructures

Experimental results obtained previously for the photoluminescence efficiency (PLeff) of Ge quantum dots (QDs) are theoretically studied. A log-log plot of PLeff versus QD diameter (D) resulted in an identical slope for each Ge QD sample only when E-G similar to (D-2 + D)(-1). We identified that above D approximate to 6.2 nm: E-G similar to D-1 due to a changing effective mass (EM), while below D approximate to 4.6 nm: E-G similar to D-2 due to electron/hole confinement. We propose that as the QD size is initially reduced, the EM is reduced, which increases the Bohr radius and interface scattering until eventually pure quantum confinement effects dominate at small D

Superamphiphobic Silicon-Nanowire-Embedded Microsystem and In-Contact Flow Performance of Gas and Liquid Streams

Gas and liquid streams are invariably separated either by a solid wall or by a membrane for heat or mass transfer between the gas and liquid streams. Without the separating wall, the gas phase is present as bubbles in liquid or, in a microsystem, as gas plugs between slugs of liquid. Continuous and direct contact between the two moving streams of gas and liquid is quite an efficient way of achieving heat or mass transfer between the two phases. Here, we report a silicon nanowire built-in microsystem in which a liquid stream flows in contact with an underlying gas stream. The upper liquid stream does not penetrate into the lower gas stream due to the superamphiphobic nature of the silicon nanowires built into the bottom wall, thereby preserving the integrity of continuous gas and liquid streams, although they are flowing in contact. Due to the superamphiphobic nature of silicon nanowires, the microsystem provides the best possible interfacial mass transfer known to date between flowing gas and liquid phases, which can achieve excellent chemical performance in two-phase organic syntheses.

Probing the energy barriers and magnetization reversal processes of nanoperforated membrane based percolated media

Magnetization reversal processes in Co/Pt multilayers prepared on nanoperforated templates are probed by magnetization relaxation measurements. The signature of pinning controlled domain wall movement as expected for percolated media is identified. This contrasts with the nucleation-type reversal mechanism of a Co/Pt reference film prepared on a smooth substrate. A zero field energy barrier of 93kBT is determined by fluctuation field measurements and is elucidated by micromagnetic calculations using the nudged elastic band method. This value is sufficiently large to qualify the material as a promising percolated medium.

Towards bottom-up nanopatterning of Prussian blue analogues

Summary Ordered nanoperforated TiO2 monolayers fabricated through sol–gel chemistry were used to grow isolated particles of Prussian blue analogues (PBA). The elaboration of the TiO2/CoFe PBA nanocomposites involves five steps. The samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) all along the synthesis process. Selected physico-chemical parameters have been varied in order to determine the key steps of the synthesis process and to optimize it. This study is an important step towards the full control of the fabrication process.

Design of cytocompatible bacteria-repellent bio-based Polyester films via an aqueous photoactivated process

Nosocomial infections are often induced by the presence of pathogenic organisms on the surface of medical devices or hospital equipment. Chemical or topographical modifications of the surface are recognized as efficient strategies to prevent bacteria adhesion but they may have negative impact on the material interaction with living tissues. Here we have developed a photoactivated method for the modification of a biocompatible polymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) under aqueous conditions. A photoinduced free-radical technique employing a grafting-from process in water media has been successfully performed to covalently anchored fluorine or PEG groups onto PHBHV surfaces. PEGylated hydrophilic surfaces showed higher bacteria-repellency performances than fluorinated hydrophobic films, achieving a >98% anti-adhesion efficiency against Escherichia coli and Staphylococcus aureus. In addition, these surfaces allowed for the adhesion and proliferation of human dermal fibroblasts without the evidence of cytotoxicity.

Sol-Gel Derived Functional Coatings for Optics

This chapter gives a focus on recent achievements on sol-gel functional optical coatings and, in particular, those dealing with reflection and antireflection phenomena, such as photonic crystals and antireflective coatings. In the first part, a historical overview will highlight the key role of optical applications in the evolution and development of sol-gel science and technology. Then some general chemical strategies to modulate the optical properties of sol-gel coatings will be described together with a critical analysis of various liquid deposition techniques. In the second part, recent examples of functional (and multifunctional) antireflective coatings and photonic crystals will be highlighted.

Photoluminescence efficiency of self-assembled germanium dots

Under the proviso that the existing tight-binding (TB) and effective mass (EM) theoretical models provide a good description of the Ge dot energy gap versus dot diameter, this work investigates the effect of nanoparticle size and the size distribution on the near infrared PL spectrum obtained from self-assembled Ge dots grown on a thin layer of TiO2 or SiO2 on Si. For the as-grown samples, the dot PL emission occupies a wide near-infrared band between 0.8 and 1 eV. The PL efficiency versus dot size for four samples was obtained in three steps. Firstly, the PL spectrum was converted to an intensity plot versus dot diameter rather than energy by taking the PL emission from each dot to occur at the dot bandgap calculated using the TB or EM model. Secondly, a numerical form for the physical size distribution of that sample was obtained by performing a least-squares fit of a Gaussian to the dot size distribution measured by atomic force microscopy or transmission electron microscopy. Finally, the PL efficiency versus dot size was calculated using the fitted Gaussian dot size distribution to normalize the PL intensity distribution obtained in the first step. Although the absolute intensities of the PL from the samples vary, the calculated curves are all well-fitted by straight lines on a log-log plot with essentially the same slope for all samples, which indicates that under weak confinement there is a universal power-law increase in PL efficiency with decreasing dot size.

Optical Properties of Germanium Dots Self-Assembled on Porous TiO2 Templates

Self-assembled Ge quantum dots were formed by in-situ thermal annealing of a thin amorphous Ge layer deposited by molecular beam epitaxy on a thin porous TiO2 layer grown on SiO2 on Si(001). For samples with dot diameters ranging from 10 to 35 nm, the dot photoluminescence (PL) appeared primarily as a wide near-infrared band peaked near 800 meV. The peak energy of the PL band reflects the average dot size and its shape depends on the dot size distribution. Using a tight binding bandgap model, we have analyzed the PL spectrum in terms of the dot size distribution. The observed size distribution determined from transmission electron and atomic force microscopy allowed the determination of the nonlinear increase in the PL efficiency with decreasing dot diameter. Knowing this generic PL efficiency, we show that it is possible to evaluate the size distribution of Ge dots from their PL energy dependence.