Spin-wave propagation in a microstructured magnonic crystal

Transmission of microwave spin waves through a microstructured magnonic crystal in the form of a permalloy waveguide of a periodically varying width was studied experimentally and theoretically. The spin wave characteristics were measured by spatially-resolved Brillouin light scattering microscopy. A rejection frequency band was clearly observed. The band gap frequency was controlled by the applied magnetic field. The measured spin-wave intensity as a function of frequency and propagation distance is in good agreement with a model calculation.Comment: 4 pages, 3 figure

Optical and THz Galois diffusers

Binary surface reliefs with sub-wavelength features making up a pseudorandom pattern based on mathematical Galois fields GF(p^m) [1, 2] can scatter incoming waves into a large number of diffraction maxima within a huge solid angle. A one-dimensional (1D) Galois number sequence can be folded into a two-dimensional (2D) array by the sino-representation [2]. This concept was been verified for acoustic waves a long time ago [3, 4] and is investigated here for visible light and THz waves. Our Galois diffusers are designed as reflection reliefs and realised by electron beam lithography for the optical regime and UV photolithography for the THz regime. Our results show that optical and THz Galois surfaces are excellent diffusers for electromagnetic waves; they distribute the reflected intensity evenly over a large number of maxima nearly within the entire half solid angle in the backward direction

The application of the Kelvin probe in materials science

This thesis reports on the application of the Kelvin probe in materials science and in particular on the study of metal and semiconductor surfaces in both ambient and UHV environments. The concept of the work function #phi# and its importance as a parameter in materials science is discussed in the context of novel technological applications. The various methods to determine the work function are reviewed. The main measurement technique used here - the Kelvin probe - is described in detail. The Kelvin probe measures local work function differences between a conducting sample and a reference tip in a non-contact, truly non-invasive way over a wide temperature range. However, it is an inherently relative technique and does not provide an absolute work function if the work function of the tip (#phi#_t_i_p) is not known. Therefore, a novel technique has been developed to measure #phi#_t_i_p with the Kelvin probe via the photoelectric effect, thus combining the advantages of both methods to provide the absolute work function of the sample surface. High and low work function surfaces were generated as target materials for a novel ion source based on hyperthermal surface ionisation: oxidised rhenium exhibits the highest work function of 7.15eV at a temperature of #approx#900K whereas the lowest work function of #approx#2.54eV was measured on lanthanum hexaboride, LaB_6. The process of thermal and hyperthermal surface ionisation (SI, HSI) as well as the generation of hyperthermal molecular beams is discussed and a model of the surface ionisation process is developed to estimate its efficiency. Experimental data of SI and HSI are presented. The application of the Kelvin probe for the detection of defects and impurities in semiconductors, namely iron contamination, is demonstrated via two methods based on the measurement of the surface photovoltage. We find that both methods yield a lower surface potential and surface charge for iron contaminated wafers compared to a clean sample and therefore can be used as an indicator for chemical contamination on semiconductor surfaces. (author)SIGLEAvailable from British Library Document Supply Centre- DSC:DXN039059 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Optofluidic refractive index sensor based on air-suspended SU‐8 grating couplers

This work presents the design, numerical simulation, fabrication and characterization of a label-free optofluidic refractive index sensor that is based on air-suspended SU‐8 grating couplers. By exploiting a polymer-onto-polymer lamination method for thin structured SU‐8 films, waveguide grating couplers can be fabricated in a film on top of a microfluidic channel system. A capillary force valve, integrated into the microchannels, precisely positions the employed test analytes, which are different DI water based sugar solutions, below the sensing grating coupler. By performing numerical simulations, the sensing grating coupler is optimized to a center wavelength of 1550 nm in the case that pure DI water (n = 1.33) is applied to the microfluidic channel. When a supported mode, guided in the waveguide, reaches the sensing grating region, it is exposed to the test solution resulting in a change of the effective refractive index of the mode. Similar to the simulation results, the experimental characterization of the sensor structure demonstrates a refractive index sensitivity of approximately 400 nm per refractive index unit (RIU) with respect to the wavelength shift of the grating coupler response, and 17 dB RIU ‐1 with respect to the intensity decrease at the individual center wavelengths for refractive index variations between n = 1.33 and n = 1.36. Due to the combination of microfluidic channels and air-suspended grating couplers, analytes can directly be probed in-line in an integrated microfluidic channel making the presented principle suitable for low-cost, in-line polymer optofluidic and photonic sensing applications

Tunable air-suspended polymer grating couplers

We present thermal tuning of air-suspended SU-8 polymer waveguide grating couplers for TE-polarized light. Numerical simulations have been performed to estimate the wavelength shift caused by the change of temperature. Due to the small positive thermal expansion and large negative thermo-optic coefficient of SU-8, a shift toward shorter wavelengths is expected. In the experimental evaluation, a negative wavelength shift from 1542 nm at 20°C toward 1527 nm at 56°C is obtained with approximately -0.42 nm K-1 matching the theoretical considerations

Scalable fabrication and application of nanoscale IDE-arrays as multi-electrode platform for label-free biosensing

© 2018 Elsevier B.V. The continuous progress in the construction of advanced, miniaturized electrodes provides a promising route towards compact and sensitive biological and chemical sensor platforms. We present a combined micro- and nanofabrication process at wafer-scale with nanoimprint lithography and subsequent photolithography for the realization of ultra-small, interdigitated electrode arrays. Several chips of gold nanoelectrode arrays (NEA) in a 4 × 4 configuration designed as interdigitated electrodes (NEA-IDEs) with finger structures measuring 14 μm in length and 600 nm in width with 600 nm spacing were fabricated simultaneously on 4-inch wafers. Our process involved a nanoimprint lithography step, wet-etching, metal evaporation and nano lift-off followed by optical lithography for metal contact lines and passivation layers. The optimized procedure yielded high-quality NEA-IDEs with reliable electrochemical behavior as inferred from voltammetric and impedimetric analysis. The final array allows the control of all 16 NEA-IDEs in parallel, which can be beneficial for multi-analyte detection. In a proof-of-concept assay, to demonstrate the applicability of the NEA-IDEs for biosensing, the nanostructures were modified with short DNA molecules as recognition elements for the detection of hybridization via impedance spectroscopy. Stable impedance signals were found using the redox system ferri-/ferrocyanide. After hybridization with complementary target DNA the sensors showed an enhancement of the charge transfer resistance. Experiments with different target DNA concentrations demonstrated a dynamic detection range of 1–100 nM. The main advantage of these NEA-IDE structures is that they are small enough to be integrated into typical microchannel dimensions of 50–100 μm for miniaturized lab-on-a-chip biosensor devices in future.status: publishe