Optical extinction due to intrinsic structural variations of photonic crystals

Unavoidable variations in size and position of the building blocks of photonic crystals cause light scattering and extinction of coherent beams. We present a new model for both 2 and 3-dimensional photonic crystals that relates the extinction length to the magnitude of the variations. The predicted lengths agree well with our new experiments on high-quality opals and inverse opals, and with literature data analyzed by us. As a result, control over photons is limited to distances up to 50 lattice parameters ($\sim 15 \mu$m) in state-of-the-art structures, thereby impeding large-scale applications such as integrated circuits. Conversely, scattering in photonic crystals may lead to novel physics such as Anderson localization and non-classical diffusion.Comment: 10 pages, 3 figures. Changes include: added Lagendijk as author; simplified and generalized the tex

Ferroelectric Nanotubes

We report the independent invention of ferroelectric nanotubes from groups in several countries. Devices have been made with three different materials: lead zirconate-titanate PbZr1-xTixO3 (PZT); barium titanate BaTiO3; and strontium bismuth tantalate SrBi2Ta2O9 (SBT). Several different deposition techniques have been used successfully, including misted CSD (chemical solution deposition) and pore wetting. Ferroelectric hysteresis and high optical nonlinearity have been demonstrated. The structures are analyzed via SEM, TEM, XRD, AFM (piezo-mode), and SHG. Applications to trenching in Si dynamic random access memories, ink-jet printers, and photonic devices are discussed. Ferroelectric filled pores as small as 20 nm in diameter have been studied

Atomic layer deposition of cobalt phosphide for efficient water splitting

Transition‐metal phosphides (TMP) prepared by atomic layer deposition (ALD) are reported for the first time. Ultrathin Co‐P films were deposited by using PH3 plasma as the phosphorus source and an extra H2 plasma step to remove excess P in the growing films. The optimized ALD process proceeded by self‐limited layer‐by‐layer growth, and the deposited Co‐P films were highly pure and smooth. The Co‐P films deposited via ALD exhibited better electrochemical and photoelectrochemical hydrogen evolution reaction (HER) activities than similar Co‐P films prepared by the traditional post‐phosphorization method. Moreover, the deposition of ultrathin Co‐P films on periodic trenches was demonstrated, which highlights the broad and promising potential application of this ALD process for a conformal coating of TMP films on complex three‐dimensional (3D) architectures

Numerical investigation of nanostructured silica PCFs for sensing applications.

Photonic crystal fibers (PCFs) developed using nanostructured composite materials provide special optical properties. PCF light propagation and modal characteristics can be tailored by modifying their structural and material parameters. Structuring and infusion of liquid crystal materials enhances the capabilities of all silica PCFs, facilitating their operation in different spectral regimes. The wavelength tunability feature of nanostructured PCFs can be utilized for many advanced sensing applications. This paper discusses a new approach to modify the optical properties of PCFs by periodic nanostructuring and composite material (liquid crystal-silica) infiltration. PCF characteristics like confinement wavelength, confinement loss, mode field diameter (MFD) and bandwidth are investigated by varying the structural parameters and material infiltrations. Theoretical study revealed that composite material infusion resulted in a spectral band shift accompanied by an improvement in PCF bandwidth. Moreover, nanostructured PCFs also achieved reduced confinement losses and improved MFD which is very important in long-distance remote sensing applications

Large-scale fabrication of ordered silicon nanotip arrays used for gas ionization in ion mobility spectrometers

The 9/11 events have led to an increase in the request for sensors and sensor systems that can detect rapidly, efficiently, and at moderate cost trace explosives and a whole range of toxic substances at diverse control points, e.g., at airports and inside air conditioning systems in aircraft and public buildings. To date, the security screening instruments of choice are ion mobility spectrometers (IMS), which are basically time-of-flight mass spectrometers (Sielemann, 1999 and Stach, 1997). Such instruments allow for the detection of explosives, chemical warfare agents, and illicit drugs. Widespread adoption of the IMS technology in civilian security screening applications, for instance, at airports, has been hindered due to the fact that state-of-the-art spectrometers employ radioactive ion sources. We report on fabrication and measurements of large-scale-ordered silicon nanotip arrays, used to replace the radioactive source for IMS gas ionization. Surface ionization m echanisms on the platinum-coated silicon surface can be significantly increased compared to flat structures due to the strong field enhancement at the tips. We will show measurements of the ion current of planar surfaces compared to microstructured surfaces as well as a photoelectrochemical etching process that allows to etch flat tips with a low aspect ratio as well as long tips with high aspect ratios with exact control about the tip profile

Influence of defects in opal photonic crystals on the optical transmission imaged by near-field scanning optical microscopy

The electric field intensity above the surface of opal photonic crystals (PCs) and its alteration due to 'crystallographic' defects is investigated by using nearfield scanning optical microscopy (NSOM). The photonic crystals are developed by dip coating in a liquid solution with PMMA opals. Highly regular hexagonal planes with lattice constants of about 260 nm grow on the glass substrate. During the drying process several crack lines are formed that correspond to defects in the crystal structure. The transmitted light intensity at wavelengths inside and outside of the stop band of the PC is studied with NSOM using a tapered fiber tip scanning in all three dimensions. By this technique, a 3D image of the electric field intensity can be measured with a resolution better than 100 nm. The results show that the local optical field distribution is strongly dominated by the defect states in all directions in space over a length scale of several mu m. Above the crack lines, the intensity of light is strongly reduced. Beams of light are observed emerging from the edges of the crack lines and propagate in air with heights of more than 3 mu m. In between two different crack lines, periodic repetitions of the beams are observed. These results are interpreted as light diffraction on a microscopic scale