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showing 10 items of 2224 documents
Qualitative Models for the Photoresponse and Capacitance of Annealed Titania Nanotubes
2015
Physicochemical characterization of annealed TiO2 nanotubes (TNTs) was conducted by using photocurrent spectroscopy and differential capacitance techniques. It has been shown that the geometry and architecture of nanotubes determine how photogenerated electrons and holes are separated and transferred. Photocurrent generation in TNTs is a consequence of two phenomena; drifting of holes into the electrolyte and diffusion of electrons toward the substrate. These two processes have been shown to be independent of the anodic polarization. The capacitance of TiO2 nanotubes is also affected by their geometry. In anodic potentials, with respect to the flat band potential of the underlying barrier l…
Transient photoresponse and incident power dependence of high-efficiency germanium quantum dot photodetectors
2012
We report a systematic study of time-resolved and power-dependent photoresponse in high-efficiency germanium quantum dot photodetectors (Ge-QD PDs), with internal quantum efficiencies greater than 100 over a broad wavelength, reverse bias, and incident power range. Turn-on and turn-off response times (τ on and τ off) are shown to depend on series resistance, bias, optical power, and thickness (W QD) of the Ge-QD layer, with measured τ off values down to ∼40 ns. Two different photoconduction regimes are observed at low and high reverse bias, with a transition around -3 V. A transient current overshoot phenomenon is also observed, which depends on bias and illumination power. © 2012 American …
Characterization of soft breakdown in thin oxide NMOSFETs based on the analysis of the substrate current
2001
We have investigated the properties of soft breakdown (SBO) in thin oxide (4.5 nm) nMOSFETs with measurements of the gate and substrate leakage currents using the carrier separation technique. We have observed that, at lower gate voltages, the level of the substrate current exhibits a plateau. We propose that the observed plateau is due to the Shockley-Hall-Read (SHR) generation of hole-electron pairs in the space charge region and at the Si-SiO/sub 2/ interface. At higher voltages, the substrate current steeply increases with voltage, due to a tunneling mechanism, trap-assisted or due to a localized effective thinning of the oxide, from the substrate valence band to the gate conduction ban…
Profiling of traps in SiO2/Al2O3 gate stack by the charge pumping technique
2006
In this paper, we present our results on the distribution and generation of traps in a SiO 2 /A1 2 O 3 transistor. The investigation has been carried out by using charge pumping measurements, both variable voltage and frequency techniques, and constant voltage stress. By increasing the amplitude of the gate pulse we observe an increase of the charge recombined per cycle closely related to the contribution of shallow traps near the SiO 2 /Al 2 O 3 interface. By reducing the pulse frequency we measure an increase in the charge pumping current due to traps located deeper in the Al 2 O 3 . By combining charge pumping and constant voltage stress measurements, we found that the traps are mostly g…
CMOS Photodiode Design for Gamma Camera Application
2008
We designed new photodiodes sensors including current mirror amplifiers. These photodiodes have been fabricated using a CMOS 0.6 micrometers process from Austria Micro System (AMS). The photodiode areas are respectively 1 mm × 1 mm and 0.4 mm × 0.4 mm with fill factor 98% and total chip area is 2 square millimetres. The sensor pixels show a logarithmic response in illumination and are capable of detecting very low blue light (less than 0.5 lux) . These results allow to use our sensor in new gamma camera solid-state concept.
Surface characterization of functional poly(diacetylene) and poly(butadiene) mono- and multilayers
1982
The surface properties of Langmuir-Blodgett mono- and multilayers of a variety of amphiphilic poly(diacetylene)s and poly(butadiene)s were investigated by contact angle, streaming potentialζ, ellipsometry, and X-ray photoelectron spectroscopic (XPS) measurements. Captive air and octane angles varied between approximately 60° and 105° for hydrophobicx-layers and 31° to 46° for hydrophilic surfaces depending on the particular head group, whereas advancing angles determined via the vertical plate method are considerably higher. Negative streaming potentials were obtained for all surfaces. Positively charged monolayers yielded less negativeζ- potential values (−28 mV) than negatively charged (−…
Electrochemical Characterization of Polyelectrolyte/Gold Nanoparticle Multilayers Self-Assembled on Gold Electrodes
2006
Polyelectrolyte/gold nanoparticle multilayers composed of poly(l-lysine) (pLys) and mercaptosuccinic acid (MSA) stabilized gold nanoparticles (Au NPs) were built up using the electrostatic layer-by-layer self-assembly technique upon a gold electrode modified with a first layer of MSA. The assemblies were characterized using UV-vis absorption spectroscopy, cyclic and square-wave voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. Charge transport through the multilayer was studied experimentally as well as theoretically by using two different redox pairs [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+/2+). This paper reports a large sensitivity to the charge of the out…
Review of acoustic methods for space charge measurement
2015
In the last decade, due to the increased use of direct current, the space charge accumulation phenomenon has reached more interest. In this regard, several non-destructive measurement systems were used. In particular, for solid dielectrics, the acoustic methods have had greater success. This review presents a brief historical evolution of the Pulse Electro- Acoustic (PEA) method, describing the working operation, the thicknesses analyzed and the spatial resolution for the different configurations of the PEA cell. The Pressure Wave Propagation (PWP) method in both configurations Piezo-PWP and Laser Induced Pressure Pulse (LIPP) is also described.
Photoelectrochemical and XPS characterisation of oxide layers on 316L stainless steel grown in high-temperature water
2015
Passive films on AISI 316L stainless steel were grown by exposure in high temperature (300 °C and 150 bar) water. X-ray photoelectron spectroscopy was employed to study their composition as a function of immersion time. A photoelectrochemical investigation, supported by electrochemical and impedance measurements, allowed to get information on the solid-state properties of the investigated layers. The experimental results suggest the formation of a stratified layer with an outer iron-rich layer and an inner Cr-rich oxide layer, whose relative thickness and composition are dependent on the immersion time.
Heat and mass transfer analysis in single cell of PEFC using different PEM and GDL at higher temperature
2019
Abstract According to the H2 and fuel cell road map in Japan, the target operating temperature of polymer electrolyte fuel cell (PEFC) should be 90 °C from 2020 to 2025. In this study, the impact of polymer electrolyte membrane (PEM) and gas diffusion layer (GDL)'s thickness on heat and mass transfer characteristics as well as power generation performance of PEFC is investigated at operating temperature of 90 °C. The in-plane temperature distributions on anode and cathode separator are also measured using thermograph. As a result, it is observed that the increase in power from 1 W to 5 W at the current density of 0.80 A/cm2 as well as even temperature distribution within 1 °C can be obtaine…