Metal-dielectric-metal plasmonic resonators for active beam steering in the infrared

Cataloged from PDF version of article.Active beam-steering devices near the optical frequencies have long been sought after due to their applications in communication, defense, and display technologies; however, the challenge lies in achieving actively tunable structures near these frequencies. An array of metal-dielectric-metal plasmonic resonators is demonstrated as a dynamic beam-steering device to operate at midinfrared wavelengths. We numerically demonstrate continuous-angle beam steering of 8.75° by making use of tunable properties of silicon as the active dielectric. The proposed device achieves a refractive index insensitive divergence angle and it operates in a 650 nm wide spectral window around 10 μm wavelength. The results of this Letter pave the way to exploiting active beam steering in various applications at midinfrared wavelengths. © 2013 Optical Society of Americ

Silicon Nano-Particles with High Resistance to Harsh Ambient Conditions

Cataloged from PDF version of article.Silicon nanoparticles which have an average size of 1 nm are synthesized using electrochemical methods and their stability under high temperature and humidity conditions have been investigated. These types of Silicon nanoparticles exhibit strong blue emission (centered around 420 nm) upon excitation with ultraviolet illumination. Standard heating procedures showed that, these nanoparticles in a liquid suspension (de-ionized water) are stable to heating and they retain characteristic emissions even at elevated temperatures. Thin solid films of such Silicon nanocrystals also show good stability under plasma and oxidizing environments at high temperatures. © 2012 Springer Science+Business Media, LL

Resistive Switching based Electro-Optical Modulation

Cataloged from PDF version of article.Resistive switching enables optical modulation via atomic scale modifications that induce change in the refractive index of active device materials. The formation of filaments and migration of atoms around these filaments between high resistance and low resistance states results in the modulation of the free carrier concentration and, hence, the optical constants of the material

Synthesis of ultra-small Si/Ge semiconductor nano-particles using electrochemistry

Cataloged from PDF version of article.In this paper, we describe the formation of colloidal Si/Ge semiconductor nano-particles by electrochemical etching of Ge quantum dots (GEDOT), SiliconeGermanium graded layers (GRADE) and SiliconeGermanium multi-quantum well (MQW) structures which are prepared on Silicon wafers using low pressure chemical vapor deposition (LPCVD) technique. The formation of Si/Ge nano-particles is verified by transmission electron microscope (TEM) images and photoluminescence (PL) measurements. The Si/Ge nano-particles obtained from GEDOT and GRADE structures, gave blue emissions, upon 250 nm, and 300 nm UV excitations. However, the nano-particles obtained from the MQW structure did exhibit various color emissions (orange, blue, green and red) upon excitation with 250 nm, 360 nm, 380 nm and 400 nm wavelength light. (C) 2012 Elsevier B.V. All rights reserve

Complementary spiral resonators for ultrawideband suppression of simultaneous switching noise in high-speed circuits

Cataloged from PDF version of article.In this paper, a novel concept for ultra-wideband simultaneous switching noise (SSN) mitigation in high-speed printed circuit boards (PCBs) is proposed. Using complementary spiral resonators (CSRs) etched on only a single layer of the power plane and cascaded co-centrically around the noise port, ultra-wideband SSN suppression by 30 dB is achieved in a frequency span ranging from 340 MHz to beyond 10 GHz. By placing a slit in the co-centric rings, lower cut-off frequency is reduced to 150 MHz, keeping the rest of the structure unaltered. Finally, the power plane structure with modified complementary spiral resonators (MCSRs) is designed, fabricated, and evaluated experimentally. Measurement and simulation results are in well-agreement

Atomic layer deposited HfO2 based metal insulator semiconductor GaN ultraviolet photodetectors

Cataloged from PDF version of article.A report on GaN based metal insulator semiconductor (MIS) ultraviolet (UV) photodetectors (PDs) with atomic layer deposited (ALD) 5-nm-thick HfO2 insulating layer is presented. Very low dark current of 2.24 x 10(-11) A and increased photo to dark current contrast ratio was achieved at 10 V. It was found that the dark current was drastically reduced by seven orders of magnitude at 10 V compared to samples without HfO2 insulating layer. The observed decrease in dark current is attributed to the large barrier height which is due to introduction of HfO2 insulating layer and the calculated barrier height was obtained as 0.95 eV. The peak responsivity of HfO2 inserted device was 0.44 mA/W at bias voltage of 15 V. (C) 2014 Elsevier B.V. All rights reserved

Post-Treatment od Silicon Nanocrystals Produced by Ultra-Short Pulsed Laser Ablation in Liquid: Toward Blue Luminescent Nanocrystal Generation

Cataloged from PDF version of article.Blue luminescent colloidal silicon nanocrystals (Si-NCs) were produced in a two-stage process. In the first step, synthesis of Si-NCs was achieved by femtosecond pulsed laser ablation of a silicon wafer, which was immersed in deionized water. The size and the structural and the chemical characteristics of colloidal Si-NCs were investigated by TEM and EDAX analyses, and it is found out that the Si-NCs are in spherical shape and the particle diameters are in the range of 5-100 nm. In the second step, ultrasonic waves and filtering chemical-free post-treatment of colloidal Si-NCs solution was performed to reduce the particle size. High-resolution TEM (HRTEM) studies on post-treated colloidal solution clearly show that small (1-5.5 nm in diameter) Si-NCs were successfully produced. Raman spectroscopy results clearly confirms the generation of Si nanoparticles in the crystalline nature, and the Raman scattering study of post-treated Si-NCs confirms the reduction of the particle size. The UV-vis absorption and photoluminescence (PL) spectroscopy studies elucidate the quantum confinement effect of Si-NCs on the optical properties. The colloidal Si-NCs and post-treated Si-NCs solutions present strong absorption edge shifts toward UV region. Broadband PL emission behavior is observed for the initial colloidal Si-NCs, and the PL spectrum of post-treated Si-NCs presents a blue-shifted broadband PL emission behavior due to the particle size reduction effect. © 2012 American Chemical Societ

Surface Engineered Angstrom Thick ZnO-sheathed TiO2 Nanowires as Photoanode for Performance Enhanced Dye-sensitized Solar Cells

Cataloged from PDF version of article.This paper presents a systematic study on the effects of angstrom-thick atomic layer deposited (ALD) ZnO sheaths on hydrothermally-grown TiO2 nanowires (NWs) used as photoanodes in dye-sensitized solar cells (DSSCs). We designed, synthesized and characterized the samples prepared using different numbers of ZnO cycles and compared their photovoltaic (PV) performances. The device consisting of TiO2 NWs coated with the optimum thickness (two cycles) of ZnO shell exhibits a three-fold increase in efficiency compared to a control reference device. This paper reports results and features that demonstrate the passivation of surface state traps upon deposition of ZnO shells. While this passivation of surface traps provides a reduction in the back-reactions of the surface state mediated electrons (KET trap), it is speculated that ZnO-induced surface band bending (SBB) substantially reduces the recombination rate of the device by reducing the recombination rate of the conduction band (CB) electrons (KET CB). Moreover, an enhancement in the amount of dye uptake for ZnO-coated TiO2 samples is observed and explained with the isoelectric point (IEP) concept. In spite of the excellent PV power conversion efficiencies achieved by the first ZnO cycles, thicker layers impede the electron injection rate, reducing the efficiency of the device by capturing the photogenerated dye electrons in ZnO quantum wells. Here, we investigate the mechanisms contributing to this unprecedented change and correlate them with the enhancement in device efficiency. © The Royal Society of Chemistry 2014

Ultrahigh contrast one-way optical transmission through a subwavelength slit

Cataloged from PDF version of article.We computationally demonstrate one-way optical transmission characteristics of a subwavelength slit. We comparatively study the effect in single layer and double layer metallic corrugations. We also investigate the effect of a dielectric spacer layer between double corrugations to control the volumetric coupling of plasmon and optical modes. We computationally show unidirectional transmission behavior with an ultrahigh contrast ratio of 53.4 dB at λ01.56 μm. Volumetric coupling efficiency through the nanoslit strongly depends on the efficient excitation of both the surface plasmon resonance and metal–insulator–metal waveguide modes. We show that the behavior is tunable in a wide spectral range (C) Springer Science+Business Media, LLC 201