Reflection properties and defect formation in photonic crystals

Cataloged from PDF version of article.We have investigated the surface reflection properties of a layer‐by‐layer photonic crystal. By using a Fabry–Perot resonant cavity analogy along with the reflection‐phase information of the photonic crystal, we predicted defect frequencies of planar defectstructures. Our predictions were in good agreement with the measureddefect frequencies. Our simple model can also predict and explain double defect formation within the photonic band gap

Ab initio study of Ru-terminated and Ru-doped armchair graphene nanoribbons

Cataloged from PDF version of article.We investigate the effects of ruthenium (Ru) termination and Ru doping on the electronic properties of armchair graphene nanoribbons (AGNRs) using first-principles methods. The electronic band structures, geometries, density of states, binding energies, band gap information, and formation energies of related structures are calculated. It is well founded that the electronic properties of the investigated AGNRs are highly influenced by Ru termination and Ru doping. With Ru termination, metallic band structures with quasi-zero-dimensional, onedimensional and quasi-one-dimensional density of states (DOS) behavior are obtained in addition to dominant one-dimensional behavior. In contrast to Ru termination, Ru doping introduces small but measurable (12.4 to 89.6 meV) direct or indirect band gaps. These results may present an additional way to produce tunable band gaps in AGNRs

Electrically small split ring resonator antennas

Cataloged from PDF version of article.We studied electrically small resonant antennas composed of split ring resonators (SRR) and monopoles. The antennas considered have the same ring radius, but slightly different geometry. The resonance frequency depends on the geometry of the SRRs. Two SRR antennas are designed. The first one, which operates at 3.62 GHz, is demonstrated theoretically and experimentally. The size of this antenna is 0.095 lambda(0)x0.100 lambda(0) and is low profile at the other dimension. The gain and directivity of the antenna was 2.38 and 5.46, respectively. The corresponding efficiency was 43.6%. The estimated radiation Q (rad Q=23.03) was much larger than the minimum radiation Q (min Q=1.78). The second one is a rather small SRR antenna in which the capacitance between the rings is increased. The size is reduced to 0.074 lambda(0)x0.079 lambda(0). This structure is called serrated SRR (SSRR). Both antennas have similar far-field patterns but the efficiency of the SSRR antenna is less. (c) 2007 American Institute of Physics

Oblique response of a split-ring-resonator-based left-handed metamaterial slab

Cataloged from PDF version of article.We experimentally studied the transmission response of a one-dimensional rectangle-prism-shaped metamaterial slab for oblique incidence angles. The electrical size of the split-ring resonators was 1 order of magnitude smaller than the operation wavelength similar to 8.5 cm. We demonstrated that the left-handed transmission peak preserved up to an angle of incidence 45 degrees. The angular measurements were performed with respect to two lateral directions. The confirmed insensitivity of split-ring-resonator-based metamaterials to the angle of incidence makes them a good candidate for superlens applications. (C) 2009 Optical Society of Americ

A new detection method for capacitive micromachined ultrasonic transducers

Cataloged from PDF version of article.Capacitive micromachined ultrasonic transducers (cMUT) have become an alternative to piezoelectric transducers in the past few years. They consist of many small circular membranes that are connected in parallel. In this work, we report; a new detection method for cMUTs. We model the membranes as capacitors and the interconnections between the membranes as inductors. This kind of LC net-work is called an artificial transmission line. The vibrations of the membranes modulate the electrical length of the transmission line, which is proportional to the frequency of the signal through it. By measuring the electrical length of the artificial line at a high RF frequency (in the gigahertz range), the vibrations of the membranes can be detected in a very sensitive manner. Far the devices we measured, we calculated the minimum detectable displacement to be in the order of 10(-5) Angstrom/root Hz with a possible improvement to 10(-7) Angstrom/root Hz

Optically thin composite resonant absorber at the near-infrared band: a polarization independent and spectrally broadband configuration

Cataloged from PDF version of article.We designed, fabricated, and experimentally characterized thin absorbers utilizing both electrical and magnetic impedance matching at the near-infrared regime. The absorbers consist of four main layers: a metal back plate, dielectric spacer, and two artificial layers. One of the artificial layers provides electrical resonance and the other one provides magnetic resonance yielding a polarization independent broadband perfect absorption. The structure response remains similar for the wide angle of incidence due to the sub-wavelength unit cell size of the constituting artificial layers. The design is useful for applications such as thermal photovoltaics, sensors, and camouflage. (C)2011 Optical Society of Americ

High-performance visible-blind GaN-based p-I-n photodetectors

Cataloged from PDF version of article.We report high performance visible-blind GaN-based p-i-n photodetectors grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The dark current of the 200 mu m diameter devices was measured to be lower than 20 pA for bias voltages up to 5 V. The breakdown voltages were higher than 120 V. The responsivity of the photodetectors was similar to 0.23 A/W at 356 nm under 5 V bias. The ultraviolet-visible rejection ratio was 6.7x10(3) for wavelengths longer than 400 nm. (C) 2008 American Institute of Physics

Solar-blind AlxGa1-xN-based avalanche photodiodes

Cataloged from PDF version of article.We report the Metalorganic Chemical Vapor Deposition (MOCVD) growth, fabrication, and characterization of solar blind AlxGa1-xN/GaN-based avalanche photodiodes. The photocurrent voltage characteristics indicate a reproducible avalanche gain higher than 25 at a 72 V applied reverse bias. Under a 25 V reverse bias voltage, the 100 mu m diameter devices had a maximum quantum efficiency of 55% and a peak responsivity of 0.11 A/W at 254 nm, and a NEP of 1.89x10(-16) W/Hz(1/2). (c) 2005 American Institute of Physics