While defects are known to inhibit device level performance, research shows specific spin defects resulting from silicon vacancy, carbon vacancy, or divacancy in SiC are alternative platforms to NV center in diamond for quantum sensing. Multiple 4H-SiC Schottky barrier diodes (SBD) were in-house fabricated and irradiated with 241Am alpha particles to a total accumulated fluence between 1×1013-1×1014 cm-2 over about 2-years low dose irradiation at room temperature. These irradiated devices, after annealing, were electrically characterized using I/V and C-V measurements and electron paramagnetic resonance (EPR) spectroscopy for the concentration of electronic active traps, atomic and electronic structure. The EPR spectroscopy shows that alpha irradiation induces changes in the properties of paramagnetic sites in 4H-SiC. Differences include increased line width and distorted line shape in irradiated samples, suggesting changes in relaxation behavior. Slight differences in g-values suggest possible changes in the paramagnetic sites due to irradiation. The temperature dependence studies conducted on vacancy sites, however, is inconclusive in identifying carbon and silicon vacancies or nitrogen donors in 4H-SiC, due to signal saturation at temperatures below 100 K.
Silicon carbide (SiC), particularly the 4H-SiC polytype, is a maturing wide bandgap semiconductor that has been shown to be an optimal material for high performance electronics in extreme environments. Conventional semiconductor radiation detectors have been shown to have limited performance above room temperature, with loss of sensitivity and degradation of detector resolution due to increase in electronic noise. The wide bandgap (3.27eV) of 4H-SiC and the variable active region of Schottky barrier diodes produce a device capable of maintaining a lower-level of electronic noise, even at elevated temperature. We fabricated 4H-SiC Schottky barrier diodes and evaluated their electrical parameters using current-voltage (I-V) and capacitance-voltage (C-V) measurements. The I-V and C-V measurements were performed at elevated temperatures up to 500 °C at 100 °C increments. Electrical performance was also measured at room temperature following each thermal cycle. Energy spectroscopy performance of the devices was also measured following each thermal cycle. Detector characteristics such as resolution and peak channel were compared following thermal cycles. However, at low temperatures, the TFE model does not match well with our experimental results. A model where the TFE current and the reverse saturation current (FE model) at room temperature is proposed, and proved a good fit with experimental data from room temperature to 500 C when high bais is applied.
Neutron Depth Profiling (NDP) is an analytical neutron technique that continues to grow in popularity for the quantification of Li ions in lithium-ion battery (LIB) materials. Most investigations occur at high flux neutron sources, i.e. cold or thermal neutron beam facilities, offered by high-power (10-20 MW) research reactors and employing multiple NDP energy and concentration standards. This work aims to develop a feasible method using NDP facilities with less intense neutron flux at lower power research reactors to quantitatively determine the Li concentration in LIB materials, while also applying a “thick” energy and concentration standard. Here, we describe a methodology for processing and calibrating NDP data collected using a multi-detector (i.e., 7-detector setup), which is essential to increase the detection efficiency. The Li concentration of a Li6PS5Cl0.5Br0.5 solid-state electrolyte was determined to be 2.2×1022 Li atoms cm−3. This value deviated by less than 3% of the expected Li atom concentration using a “thick” LiF single crystal wafer as a concentration standard. The method described in this work can be applied to other low-power reactors and other NDP-sensitive isotopes to further increase the application and availability of user-based NDP facilities.
The alpha emitting actinide 241Am is electrodeposited on the surface of the Pt electrode of in-house fabricated SiC Schottky diodes. With 17 nCi 241Am directly coated on the top of a device, the 2-pi geometry yields a high energy (5.486 MeV) and a long-term irradiation accumulating to a high fluence (1.6 × 109 alpha particles’ infusion/month). The forward, reverse I/V, and dark current, are periodically measured to monitor key characteristics of device durability for any sign of degradation over time. The direct deposition of actinides on the surface of the device also enables the evaluation of radiation damage through alpha particles’ energy spectroscopic performance, which shows a clear spectrum degradation that can be reversed by optical excitation of the device prior to spectrum acquisition. As an analytical aide, the device performance is also simulated by Allpix2 . This study provides an insight into the durability of 4H-SiC as an energy converter option for alpha-voltaic batteries and the survivability in the other harsh environment found in nuclear fuel cycle, high energy physics, fission, fusion, and space exploration where rad-hard sensors are required.
Perovskites are a family of semiconductor materials with molecular formula ABX3 [where A+ = Cesium (Cs), methylammonium (MA or CH3NH3) or formamidinium (FA or CH(NH2)2), B-site is metal, and X− = chlorine (Cl), bromine (Br) or iodine (I)] that have recently seen a surged interest for X-ray and gamma-ray detection. The all inorganic version, CsPbBr3, grown by high temperature melt method has been demonstrated with an impressive gamma-ray energy resolution of 1.4%@662 keV, while the solution grown CsPbBr3 showed the best achievable resolution of 5.5% at the same energy from a 137Cs source. This paper gives an overview of the development of perovskite in both X-ray detection and gamma spectroscopy, including the most recent advancement with perovskite single crystal grown by low temperature inverse temperature method for solid-state X-ray detector. The crystal shows a decent long carrier diffusion length that is ideal for charge collection, while their mobilities are still not on par with CdZnTe. We also reported our most recent development on clarifying the concepts around X-ray detection limits. The X-ray sensitivity and the lowest detectable dose rate (i.e., X-ray detection limits) of several MAPbI3 detectors made of single crystal were experimentally measured. The best achieved X-ray sensitivity is ~2.5E4 μC/Gyair/cm2 under 15.4 V/mm, which is comparable to the current state-of-the-art MAPbI3 based X-ray detectors (~ 2.3E4 μC/Gyair/cm2 under 4.2 V/mm for GAMAPbI3 (GA=guanidinium) single crystal detector). The best achieved lowest detectable X-ray dose rate for the same MAPbI3 detector is ~61 nGyair/s under 15.4 V/mm, and decreased to ~24 nGyair/s under 3.8 V/mm. The good performance of the MAPbI3 detectors further proves their great potential as the next generation low-cost X-ray detector.
The Ohio State University Research Reactor's (OSURR) fast neutron beamline is aimed to meet the growing demand for high flux and well-collimated neutron sources for fast neutron radiography and tomography applications. The beam facility consists of two collimators, separated by a neutron-gamma shutter, and a movable beam stop, sitting on a rail system for back/forth and up/down motion to provide an adjustable working space. The beam facility provides a beam diameter of 3.2-cm and has a calculated geometric L/D ratio of ~62. The collimator closer to reactor core includes a 10.16-cm thick polycrystalline Bismuth for filtering gamma-rays, which provides ~2 orders of magnitude reduction in gamma flux at 2-MeV, and a 15.24-cm thick graphite with a 3.2-cm diameter aperture. Various Monte Carlo N-Particle (MCNP) simulations were performed to obtain neutron energy spectrum, neutron and gamma flux distributions, and dose rate values. Simulations showed a fast neutron (@1.6 MeV) flux ~5.4 × 107 n·cm-2·s-1 at the collimator exit. While the simulations of neutron and gamma flux distributions have verified that the beam shutter and beam stop provide a decent neutron and gamma shielding, a neutron radiograph of the beam was experimentally obtained using a Polyvinyl Toluene (PVT) based plastic scintillator and a lens-based imaging setup which has further validated the simulated radiographs of the beam. Simulations also provided neutron dose rates around the beam stop with a close agreement with experimental values. However, disagreements were found between experimental and simulated gamma flux dose rates, which needs further validation.
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