Electrical and ultraviolet characterization of 4H-SiC Schottky photodiodes

Fabrication and electrical and optical characterization of 4H-SiC Schottky UV photodetectors with nickel silicide interdigitated contacts is reported. Dark capacitance and current measurements as a function of applied voltage over the temperature range 20 °C – 120 °C are presented. The results show consistent performance among devices. Their leakage current density, at the highest investigated temperature (120 °C), is in the range of nA/cm2 at high internal electric field. Properties such as barrier height and ideality factor are also computed as a function of temperature. The responsivities of the diodes as functions of applied voltage were measured using a UV spectrophotometer in the wavelength range 200 nm - 380 nm and compared with theoretically calculated values. The devices had a mean peak responsivity of 0.093 A/W at 270 nm and −15 V reverse bias

Quartz Cherenkov Counters for Fast Timing: QUARTIC

We have developed particle detectors based on fused silica (quartz) Cherenkov radiators read out with micro-channel plate photomultipliers (MCP-PMTs) or silicon photomultipliers (SiPMs) for high precision timing (Sigma(t) about 10-15 ps). One application is to measure the times of small angle protons from exclusive reactions, e.g. p + p - p + H + p, at the Large Hadron Collider, LHC. They may also be used to measure directional particle fluxes close to external or stored beams. The detectors have small areas (square cm), but need to be active very close (a few mm) to the intense LHC beam, and so must be radiation hard and nearly edgeless. We present results of tests of detectors with quartz bars inclined at the Cherenkov angle, and with bars in the form of an "L" (with a 90 degree corner). We also describe a possible design for a fast timing hodoscope with elements of a few square mm.Comment: 24 pages, 14 figure

Aquatic polymers can drive pathogen transmission in coastal ecosystems.

Gelatinous polymers including extracellular polymeric substances (EPSs) are fundamental to biophysical processes in aquatic habitats, including mediating aggregation processes and functioning as the matrix of biofilms. Yet insight into the impact of these sticky molecules on the environmental transmission of pathogens in the ocean is limited. We used the zoonotic parasite Toxoplasma gondii as a model to evaluate polymer-mediated mechanisms that promote transmission of terrestrially derived pathogens to marine fauna and humans. We show that transparent exopolymer particles, a particulate form of EPS, enhance T. gondii association with marine aggregates, material consumed by organisms otherwise unable to access micrometre-sized particles. Adhesion to EPS biofilms on macroalgae also captures T. gondii from the water, enabling uptake of pathogens by invertebrates that feed on kelp surfaces. We demonstrate the acquisition, concentration and retention of T. gondii by kelp-grazing snails, which can transmit T. gondii to threatened California sea otters. Results highlight novel mechanisms whereby aquatic polymers facilitate incorporation of pathogens into food webs via association with particle aggregates and biofilms. Identifying the critical role of invisible polymers in transmission of pathogens in the ocean represents a fundamental advance in understanding and mitigating the health impacts of coastal habitat pollution with contaminated runoff

4H-SiC Schottky diodes with Ni2Si contacts for X-ray detection

4H-SiC Schottky photodiodes, with epitaxial layers, employing thin (20 nm) Ni2Si Schottky contacts, were investigated for high temperature photon counting X-ray spectroscopy. Important X-ray photodiode detector parameters were extracted from electrical characterization within the temperature range 160 °C to 0 °C. The devices were found to be fully depleted at an applied electric field of 20 kV/cm; a leakage current density of 33 nA cm 1 nA cm−2 at 160 °C, was measured for one of the devices. The detectors were subsequently connected to low-noise photon counting readout electronics and investigated for their spectral performance at temperatures up to 100 °C. With the charge-sensitive preamplifier operated at the same temperature as the detector the best energy resolution (Full Width at Half Maximum at 5.9 keV) obtained decreased from 2.20 keV 0.04 keV (120 e rms 2 e rms) at 100 C to 1.20 keV 0.03 keV (65 e rms 2 e rms) at 0 C. The dominant source of noise broadening the 55Fe X-ray photopeak was found to be the dielectric noise, except for the spectra accumulated at 100 °C and long shaping times (>), in those case the main source of photopeak broadening was the white parallel noise

The new generation of SPAD—Single-Photon Avalanche Diodes arrays

In the last years the single-photon detection with silicon devices has become an important goal. Here we present the performance of a new generation of single-photon avalanche diodes manufactured by ST-Microelectronics. The 5 × 5 array configuration has been also realized and the performances, in terms of crosstalk and common readout mode, have been investigated

Electrooptical Characterization of New Classes of Silicon Carbide UV Photodetectors

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Application of Silicon Photomultipliers to Positron Emission Tomography

Historically, positron emission tomography (PET) systems have been based on scintillation crystals coupled to photomultipliers tubes (PMTs). However, the limited quantum efficiency, bulkiness, and relatively high cost per unit surface area of PMTs, along with the growth of new applications for PET, offers opportunities for other photodetectors. Among these, small-animal scanners, hybrid PET/MRI systems, and incorporation of time-of-flight information are of particular interest and require low-cost, compact, fast, and magnetic field compatible photodetectors. With high quantum efficiency and compact structure, avalanche photodiodes (APDs) overcome several of the drawbacks of PMTs, but this is offset by degraded signal-to-noise and timing properties. Silicon photomultipliers (SiPMs) offer an alternative solution, combining many of the advantages of PMTs and APDs. They have high gain, excellent timing properties and are insensitive to magnetic fields. At the present time, SiPM technology is rapidly developing and therefore an investigation into optimal design and operating conditions is underway together with detailed characterization of SiPM-based PET detectors. Published data are extremely promising and show good energy and timing resolution, as well as the ability to decode small scintillator arrays. SiPMs clearly have the potential to be the photodetector of choice for some, or even perhaps most, PET systems

X-ray and electron response of 4H-SiC vertical interdigitated Schottky photodiodes

We report on the X-ray and electron performance of a low voltage reverse biased 4H-SiC vertical Schottky photodiode, based on the pinch-off surface effect, obtained by means of self-aligned Nickel Silicide (Ni2Si) interdigitated contacts. Although these photodiodes were original designed for UV detection their open Schottky contact is attractive for soft X-ray and low energy electron detection. The open electrode structure of the device allows the incident radiation to reach the active layer with minimal absorption. The photon counting spectroscopy response for soft X-rays is reported and compared to those predicted from a Monte Carlo model for SiC devices. We also show these devices can detect beta particles from 3H and 14C radioisotope sources with a combined energy range 1-156 keV. © 2012 IOP Publishing Ltd and Sissa Medialab srl

How to improve the financial conditions of local governments in a period of crisis: an explanatory case study

The context of austerity and crisis in the local governments has focused on looking for a solution to avoid the distress while also improving financial health. Therefore, a system to monitor the financial situation of local authorities is needed in order to understand what the governments’ proceeding to manage the crisis are. This paper aims to analyse the financial distress in the municipality of Rome to evaluate the processes that occur inside the “black box” of the organizational, institutional and strategic implementation of the reorganization practices and routines, also highlighting what are the indicators of the financial conditions that fall into either a positive or negative area so as to implement adequate planning. The analysis is conducted through an explanatory case study to understand and to explain the reasons for management practices in a condition of financial distress. The main finding shows that the case of Rome represents a good example of the financial resilience through a combination of capacities and reactions such as management of slack resources and income generation