Photonic ring resonator filters for astronomical OH suppression.

Ring resonators provide a means of filtering specific wavelengths from a waveguide, and optionally dropping the filtered wavelengths into a second waveguide. Both of these features are potentially useful for astronomical instruments. In this paper we focus on their use as notch filters to remove the signal from atmospheric OH emission lines from astronomical spectra. We derive the design requirements for ring resonators for OH suppression from theory and finite difference time domain simulations. We find that rings with small radii (< 10 µm) are required to provide an adequate free spectral range, leading to high index contrast materials such as Si and Si3N4. Critically coupled rings with high self-coupling coefficients should provide the necessary Q factors, suppression depth, and throughput for efficient OH suppression, but will require post-inscription tuning of the coupling and the resonant wavelengths. The overall prospects for the use of ring resonators in astronomical instruments is promising, provided efficient fibre-chip coupling can be achieved.

Contrast enhancement of biological nanoporous materials with zinc oxide infiltration for electron and X-ray nanoscale microscopy.

We show that using infiltration of ZnO metal oxide can be useful for high resolution imaging of biological samples in electron and X-ray microscopy. The method is compatible with standard fixation techniques that leave the sample dry, such as finishing with super critical CO2 drying, or simple vacuum drying up to 95 °C. We demonstrate this technique can be applied on tooth and brain tissue samples. We also show that high resolution X-ray tomography can be performed on biological systems using Zn K edge (1s) absorption to enhance internal structures, and obtained the first nanoscale 10 KeV X-ray absorption images of the interior regions of a tooth.

Post-directed-self-assembly membrane fabrication for in situ analysis of block copolymer structures.

Full characterization of the three-dimensional structures resulting from the directed self-assembly (DSA) of block copolymers (BCP) remains a difficult challenge. Transmission electron microscope (TEM) tomography and resonant soft x-ray scattering have emerged as powerful and complementary methods for through-film characterization; both techniques require samples to be prepared on specialized membrane substrates. Here we report a generalizable process to implement BCP DSA with density multiplication on silicon nitride membranes. A key feature of the process developed here is that it does not introduce any artefacts or damage to the polymer assemblies as DSA is performed prior to back-etched membrane formation. Because most research and applications of BCP lithography are based on silicon substrates, process variations introduced by implementing DSA on a silicon nitride/silicon stack versus silicon were identified and mitigated. Using full-wafers, membranes were fabricated with different sizes and layouts to enable both TEM and x-ray characterization. Finally, both techniques were used to characterize structures resulting from the DSA of lamella-forming BCP with density multiplication.

Magnetoresistance anisotropy of a one-dimensional superconducting niobium strip.

We investigated confinement effects on the resistive anisotropy of a superconducting niobium strip with a rectangular cross section. When its transverse dimensions are comparable to the superconducting coherence length, the angle dependent magnetoresistances at a fixed temperature can be scaled as R(theta,H) = R(H/Hctheta) where Hctheta =Hc0(cos2theta + gamma(-2)sin2theta)(-1/2) is the angular dependent critical field, gamma is the width to thickness ratio, and Hc0 is the critical field in the thickness direction at theta=0 degrees . The results can be understood in terms of the anisotropic diamagnetic energy for a given field in a one-dimensional superconductor.