Subbandgap photoluminescence of Si photonic crystal nanocavity at room temperature

Using a photonic crystal cavity and a hydrogen plasma treatment, we enhance the photoluminescence (PL) from optically active defects in silicon by a factor of 3000 compared to the as-bought material at room temperature. © 2011 IEEE.

Light absorption in silicon quantum dots embedded in silica

The photon absorption in Si quantum dots (QDs) embedded in SiO2 has been systematically investigated by varying several parameters of the QD synthesis. Plasma-enhanced chemical vapor deposition (PECVD) or magnetron cosputtering (MS) have been used to deposit, upon quartz substrates, single layer, or multilayer structures of Si-rich- SiO2 (SRO) with different Si content (43-46 at. %). SRO samples have been annealed for 1 h in the 450-1250 °C range and characterized by optical absorption measurements, photoluminescence analysis, Rutherford backscattering spectrometry and x-ray Photoelectron Spectroscopy. After annealing up to 900 °C SRO films grown by MS show a higher absorption coefficient and a lower optical bandgap (∼2.0 eV) in comparison with that of PECVD samples, due to the lower density of Si-Si bonds and to the presence of nitrogen in PECVD materials. By increasing the Si content a reduction in the optical bandgap has been recorded, pointing out the role of Si-Si bonds density in the absorption process in small amorphous Si QDs. Both the photon absorption probability and energy threshold in amorphous Si QDs are higher than in bulk amorphous Si, evidencing a quantum confinement effect. For temperatures higher than 900 °C both the materials show an increase in the optical bandgap due to the amorphous-crystalline transition of the Si QDs. Fixed the SRO stoichiometry, no difference in the optical bandgap trend of multilayer or single layer structures is evidenced. These data can be profitably used to better implement Si QDs for future PV technologies. © 2009 American Institute of Physics.

Thermal evolution of Er silicate thin films grown by rf magnetron sputtering

Stoichiometric Er silicate thin films, monosilicate (Er2SiO 5) and disilicate (Er2Si2O7), have been grown on c-Si substrates by rf magnetron sputtering. The influence of annealing temperature in the range 1000-1200 °C in oxidizing ambient (O 2) on the structural and optical properties has been studied. In spite of the known reactivity of rare earth silicates towards silicon, Rutherford backscattering spectrometry shows that undesired chemical reactions between the film and the substrate can be strongly limited by using rapid thermal treatments. Monosilicate and disilicate films crystallize at 1100 and 1200 °C, respectively, as shown by x-ray diffraction analysis; the crystalline structures have been identified in both cases. Moreover, photoluminescence (PL) measurements have demonstrated that the highest PL intensity is obtained for Er2Si2O7 film annealed at 1200 °C. In fact, this treatment allows us to reduce the defect density in the film, in particular by saturating oxygen vacancies, as also confirmed by the increase of the lifetime of the PL signal. © 2008 IOP Publishing Ltd.

Characterization of vertical Mo/diamond Schottky barrier diode from non-ideal I-V and C-V measurements based on MIS model

In this study, we investigated non-ideal characteristics of a diamond Schottky barrier diode with Molybdenum (Mo) Schottky metal fabricated by Microwave Plasma Chemical Vapour Deposition (MPCVD) technique. Extraction from forward bias I-V and reverse bias C- 2-V measurements yields ideality factor of 1.3, Schottky barrier height of 1.872 eV, and on-resistance of 32.63 mö·cm2. The deviation of extracted Schottky barrier height from an ideal value of 2.24 eV (considering Mo workfunction of 4.53 eV) indicates Fermi level pinning at the interface. We attributed such non-ideal behavior to the existence of thin interfacial layer and interface states between metal and diamond which forms Metal-Interfacial layer-Semiconductor (MIS) structure. Oxygen surface treatment during fabrication process might have induced them. From forward bias C-V characteristics, the minimum thickness of the interfacial layer is approximately 0.248 nm. Energy distribution profile of the interface state density is then evaluated from the forward bias I-V characteristics based on the MIS model. The interface state density is found to be uniformly distributed with values around 1013 eV - 1·cm- 2. © 2013 Elsevier B.V.

2-Scale topography dry electrode for biopotential measurements.

The design and fabrication of a novel 2-scale topography dry electrode using macro and micro needles is presented. The macro needles enable biopotential measurements on hairy skin, the function of the micro needles is to decrease the electrode impedance even further by penetrating the outer skin layer. Also, a fast and reliable impedance characterization protocol is described. Based on this impedance measurement protocol, a comparison study is made between our dry electrode, 3 other commercial dry electrodes and a standard wet gel electrode. Promising results are already obtained with our electrodes which do not have skin piercing micro needles. For the proposed electrodes, three different conductive coatings (Ag/AgCl/Au) are compared. AgCl is found to be slightly better than Ag as coating material, while our Au coated electrodes have the highest impedance.

Electrorheologic liquid crystals in microsystems: model and measurements

Fluids with a controllable viscosity gained a lot of interest throughout the last years. One of the advantages of these fluids is that they allow to fabricate hydraulic components such as valves with a very simple structure. Although the properties of these fluids are very interesting for microsystems, their applicability is limited at microscale since the particles suspended in these fluids tend to obstruct microchannels. This paper investigates the applicability of electrorheologic Liquid Crystals (LCs) in microsystems. Since LC's do not contain suspended particles, they show intrinsic advantages over classic rheologic active fluids in microapplications. As a matter of fact, LC molecules are usually only a few nanometers long, and therefore, they can probably be used in systems with sub-micrometer channels or other nanoscale applications. This paper presents a novel model describing the electrorheologic behavior of these nanoscale molecules. This model is used to simulate a microvalve controlled by LC's. By comparing measurements and simulations performed on this microvalve it is possible to prove that the model developed in this paper is very accurate. In addition, these simulations and measurements revealed other remarkable properties of LC's, such as high bandwidths and high changes in flow resistance. © 2006 IEEE.

The use of liquid crystals as electrorheological fluids in microsystems: Model and measurements

Fluids with controllable flow properties have gained considerable interest in the past few years. Some of these fluids such as magnetorheologic fluids are now widely applied to active dampers and valves. Although these fluids show promising properties for microsystems, their applicability is limited to the microscale since particles suspended in these fluids tend to obstruct microchannels. This paper investigates the applicability of electrorheologic liquid crystals (LCs) in microsystems. Since LCs do not contain suspended particles, they show intrinsic advantages over classic rheologic fluids in micro-applications. This paper presents a novel physical model that describes the static and the dynamic behaviour of electrorheologic LCs. The developed model is validated by comparing simulations and measurements performed on a rectangular microchannel. This assessment shows that the model presented in this paper is able to simulate both static and dynamic properties accurately. Therefore, this model is useful for the understanding, simulation and optimization of devices using LCs as electrorheological fluid. In addition, measurements performed in this paper reveal remarkable properties of LCs, such as high bandwidths and high changes in flow resistance. © 2006 IOP Publishing Ltd.

Flow field measurements of pulverized coal combustion using optical diagnostic techniques

This paper demonstrates the application of laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) techniques to a particle-laden reacting flow of pulverized coal. A laboratory-scale open-type annular burner is utilized to generate velocity profiles of coal particles and micrometric alumina particles. Pair-wise two-component LDV measurements and high-speed stereo PIV measurements provide three-dimensional velocity components of the flow field. A detailed comparison of velocities for alumina and coal particle seeding revealed differences attributed to the wide size distribution of coal particles. In addition, the non-spherical shape and high flame luminosity associated with coal particle combustion introduces noise to the Mie scatter images. The comparison of mean and RMS velocities measured by LDV and PIV techniques showed that PIV measurements are affected by the wide size distribution of coal particles, whereas LDV measurements become biased toward the velocity of small particles, as signals from large particles are rejected. This small-particle bias is also reflected in the spectral characteristics for both techniques, which are in good agreement within the range of frequencies accessible. PIV measurements showed an expected lack of response of large coal particles to the turbulence fluctuations. The overall good agreement between LDV and PIV measurements demonstrates the applicability of the high-speed PIV technique to a particle-laden, high luminosity coal flame while highlighting some of its limitations. © 2013 Springer-Verlag Berlin Heidelberg.

Localized tail state distribution in amorphous oxide transistors deduced from low temperature measurements

In this paper, we extract density of localized tail states from measurements of low temperature conductance in amorphous oxide transistors. At low temperatures, trap-limited conduction prevails, allowing extraction of the trapped carrier distribution with energy. Using a test device with a-InGaZnO channel layer, the extracted tail state energy and density at the conduction band minima are 20 meV and 2 × 10 19 cm -3 eV -1, respectively, which are consistent with values reported in the literature. Also, the field-effect mobility as a function of temperature from 77 K to 300 K is retrieved for different gate voltages, yielding the activation energy and the percolation threshold. © 2012 American Institute of Physics.

Turbulence length scale measurements in a motored internal combustion engine

A novel technique, using a 'flying' Hot Wire Anemometer is described; it is shown how the turbulent structure in a motored engine, using a high molecular weight gas as the working fluid, may be investigated with relative simplicity and very little engine modification. Initial results are presented for integral and micro length scales, which are within the range expected based on previous work. Copyright © 1987 Society of Automotive Engineers, Inc.

Spatially-resolved photoluminescence imaging of CdS and GaAs/AlGaAs nanowires

We use low temperature spatially resolved photoluminescence imaging to study optical properties and electronic states of single CdS and GaAs/AlGaAs core-shell nanowires. © 2007 American Institute of Physics.

Polarization and temperature dependence of photoluminescence from zincblende and wurtzite InP nanowires

We use polarization-resolved and temperature-dependent photoluminescence of single zincblende (ZB) (cubic) and wurtzite (WZ) (hexagonal) InP nanowires to probe differences in selection rules and bandgaps between these two semiconductor nanostructures. The WZ nanowires exhibit a bandgap 80 meV higher in energy than the ZB nanowires. The temperature dependence of the PL is similar but not identical for the WZ and ZB nanowires. We find that ZB nanowires exhibit strong polarization parallel to the nanowire axis, while the WZ nanowires exhibit polarized emission perpendicular to the nanowire axis. This behavior is interpreted in terms of the different selection rules for WZ and ZB crystal structures. © 2007 American Institute of Physics.