F. Pérez-Willard

Nanostructuring the graphite basal plane by focused ion beam patterning and oxygen etching

Ga+ focused ion beam (FIB) patterning was used to structure highly oriented pyrolytic graphite surfaces with square, periodic arrays of amorphous carbon defects (mesh sizes: 300 nm–2 µm). Controlled oxygen etching of these arrays leads to matrices of uniform, orientationally aligned, nm-sized, hexagonal holes. The properties of the resulting hole assembly (hole depths and lateral hole dimensions) have been investigated by means of atomic force microscopy, scanning electron microscopy and FIB sectioning. The hole dimensions and uniformity both depend on the FIB parameters and etching conditions. Etching temperatures from 500 to 700 °C were applied. Initial etch rates of up to 106 C s−1 per individual hole were observed when using oxygen pressures of 200 mbar. For an etch temperature of 590 °C the rate of etching of individual holes was found to depend measurably on the inter-hole separation. This confirms that the associated reaction kinetics is mediated by the finite diffusion length of reactive oxygen species along the graphite basal plane. Prolonged etching results in hole–hole contact and generation of mesa arrays of controllable size and shape.

Fully ultrahigh-vacuum-compatible fabrication of submicrometer-spaced electrical contacts

We present an approach by which submicrometer-spaced electrical contacts can be fabricated on virtually any surface under ultrahigh-vacuum conditions. The metallic contacts are formed by subsequent deposition through a macroscopic mask and a nanostructured stencil mask. The stencil mask with a high aspect ratio was obtained by nanopatterning of suspended low-stress Si 3 + x N 4 − x membranes with a focused ion-beam system. The fabricated contacts can be electrically connected in situ by simply exchanging the mask carrier by a second, spring-loaded, carrier.

Optimizing the design parameters for split-ring resonators at telecommunication wavelengths

We discuss the influence of different sample parameters on the magnetic-resonance wavelength of split-ring resonators. Samples based on an optimized design are prepared via focused-ion-beam writing and show a resonance wavelength of 1.45 mum

Specific-heat study of the triangular-lattice antiferromagnet RbCuCl \(\)

Abstract:We report on the magnetic phase diagram of the distorted triangular-lattice antiferromagnet RbCuCl3 for a magnetic field applied parallel to the basal plane (). High-resolution measurements of the specific heat and of the magnetocaloric effect have been performed in magnetic fields up to 14 T. The high-field specific-heat data reveal the existence of an intermediate phase between the paramagnetic and the frustrated antiferromagnetic phase.

Spintronics in metallic superconductor/ferromagnet hybrid structures

Abstract Metallic hybrid structures comprizing superconducting and ferromagnetic materials are interesting objects for studying the mutual influence between superconductivity and ferromagnetic order. We focus on two particular systems that have been studied during the last few years. In superconducting spin-valves the transition temperature of a superconductor squeezed between two ferromagnetic layers depends on the relative orientation of the two magnetization directions. Results have been obtained for systems with in-plane and out-of-plane magnetizations. Furthermore, we report on the electronic transport through superconductor/ferromagnet nanocontacts that allow a determination of the current spin-polarization which is related to the bulk spin polarization.

Colloidal quantum dots in high-Q pillar microcavities

In summary, we have fabricated high-Q micropillar cavities with circular and elliptical cross section containing CdSe/ZnS quantum dots or rods in the spacer layer. We find a systematically higher Q-factor along the short axis of the elliptical pillar compared to circular ones. The spectral position of the cavity resonances have been calculated by modeling the pillar cavity as a waveguide with an effective refractive index.

Colloidal Quantum Dots in High-Q Pillar Microcavities

We have fabricated high-Q pillar resonators with colloidal CdSe/ZnS quantum dots or rods as light emitters by focused ion beam milling. Cavities with elliptical cross section show higher Q-values compared to circular resonators.

Recent progress in silicon double inversion of three-dimensional polymer templates

We present recent progress in converting polymer templates into three-dimensional silicon photonic crystals by using a silicon-double-inversion procedure. This has led to woodpiles with both improved structural and optical quality.

Three-Dimensional Silicon Photonic Crystals from Polymer Templates: Single versus Double Inversion

We present recent progress in converting polymer templates into three-dimensional silicon photonic crystals by using double (single) inversion. This has led to woodpiles (inverse woodpiles) with improved structural and optical quality.

Silicon double inversion of polymeric templates: a new route towards three-dimensional photonic bandgap materials

We present the successful silicon double inversion of direct laser written polymer templates for three-dimensional (3D) photonic crystals. Combined with plasma pre-treatment it allows for the fabrication of 3D photonic bandgap materials for telecommunication wavelengths.