Nanoscale spatial limitations of large-area substrate conformal imprint lithography.

We demonstrate a soft-imprint nanofabrication technique offering nanometer resolution over an area as large as a 150 mm diameter wafer. It makes use of a composite imprint stamp composed of a quaternary siloxane-modified poly-di-methyl-siloxane patterned rubber layer with a relatively high Young's modulus that is laminated on a thin glass support. The in-plane stiffness of the stamp avoids pattern deformation over large areas, while out-of-plane flexibility allows conformal contact to be made over the entire substrate area. The stamp is used in conjunction with a novel tetra-methyl-ortho-siloxane/methyl-tri-methoxy-siloxane sol-gel imprint resist material developed to replicate nanoscale features in rigid silica at room temperature. We demonstrate better than 10 nm resolution in imprinted line gratings and individual pillars with aspect ratio as high as 5:1. Gaps as small as 6 nm can be reproduced. The patterns can be used as an etch mask to pattern 150 mm diameter silicon and quartz substrates while maintaining sub-10 nm resolution.

Design Considerations for CMOS-Integrated Hall-Effect Magnetic Bead Detectors for Biosensor Applications.

We describe a design methodology for on-chip magnetic bead label detectors based on Hall-effect sensors. Signal errors caused by the label-binding process and other factors that limit the minimum detection area are quantified and adjusted to meet typical assay accuracy standards. The methodology is demonstrated by designing an 8192 element Hall sensor array, implemented in a commercial 0.18 µm CMOS process with single-mask postprocessing. The array can quantify a 1% surface coverage of 2.8 µm beads in 30 seconds with a coefficient of variation of 7.4%. This combination of accuracy and speed makes this technology a suitable detection platform for biological assays based on magnetic bead labels.

Comparing photonic band structure calculation methods for diamond and pyrochlore crystals.

The photonic band diagrams of close-packed colloidal diamond and pyrochlore structures, have been studied using Korringa-Kohn-Rostoker (KKR) and plane-wave calculations. In addition, the occurrence of a band gap has been investigated for the binary Laves structures and their constituent large- and small-sphere substructures. It was recently shown that these Laves structures give the possibility to fabricate the diamond and pyrochlore structures by self-organization. The comparison of the two calculation methods opens the possibility to study the validity and the convergence of the results, which have been an issue for diamond-related structures in the past. The KKR calculations systematically give a lower value for the gap width than the plane-wave calculations. This difference can partly be ascribed to a convergence issue in the plane-wave code when a contact point of two spheres coincides with the grid.

[No relationship between so-called 'haemopyrrollactamuria' and fatigue in secondary-school students]. / Geen verband tussen zogeheten 'hemopyrrollactamurie' en vermoeidheid bij gymnasiasten.

OBJECTIVE: To determine the relationship between urinary haemopyrrollactam (HPL) and subjective fatigue in secondary-school students. DESIGN: Cross-sectional and descriptive. METHOD: Urine samples were collected from 75 secondary-school students (43 boys and 32 girls, aged 16-18 years) in Nijmegen, the Netherlands. The samples were tested for HPL complex at the Centre for Environmental Medicine (Klinisch Ecologisch Allergie Centrum; KEAC) in Weert. Students also completed the 'Abbreviated fatigue questionnaire'. A score of 21 points was considered the threshold for fatigue. RESULTS: Of the 75 participants, 22 (29%) had increased HPL complex excretion, including 15 boys (35%) and 7 girls (22%). Overall, 19 (25%) had a fatigue score > 21: 16 boys (37%) and 3 girls (9%). There was no statistical relationship between increased HPL complex excretion and fatigue score. CONCLUSION: These findings do not support a relationship between fatigue and increased urinary HPL complex excretion.

Electro-optic response and switchable Bragg diffraction for liquid crystals in colloid-templated materials.

We report optical switching studies on nematic liquid crystal incorporated into structures based on self-assembled colloids. We compare the electro-optic responses of liquid crystal imbibed into colloid-templated polymers, liquid crystal imbibed in the interstitial space of colloid crystals, and conventional polymer-dispersed liquid crystals. We characterize the Bragg diffraction of our templated liquid-crystal/polymer composites as a function of electric field and measure switching times. The response of liquid crystal in connected networks differs qualitatively from that of liquid crystal in isolated cavities.

Particle excursions in colloidal crystals.

We have performed synchrotron small-angle x-ray diffraction experiments on charge-stabilized colloidal crystals. The mean squared displacements, obtained from Debye-Waller factors, decrease with increasing density beyond freezing. Irrespective of the range of the repulsion, our data and previous results lie on a common curve, linearly scaled between the melting and close-packed densities. Surprisingly, the excursions are smaller than predicted by theory.