IMPROVED SPATIAL RESOLUTION FOR DOUBLE-SIDED STRIP DETECTORS USING LITHIUM INDIUM DISELENIDE SEMICONDUCTORS

This research focuses on the evaluation of lithium indium diselenide (LISe) semiconductors in double-sided strip detector (DSSDs) designs as an example for the potential to achieve unparalleled neutron detection efficiency, spatial resolution, and timing resolution detection. LISe semiconductors offer high neutron detection efficiency due to the ~25% atomic ratio of Lithium-6, maximizing its efficiency of ~75% with 1 mm thickness at 2.8 angstroms. Furthermore, the 4.78 MeV -value enables high intrinsic gamma discrimination in a pixelated design (electron range). These characteristics make LISe an alternative option for neutron radiography, energy-resolved imaging, and other neutron interrogation techniques. This dissertation summarizes my current efforts to enhance LISe-based neutron imaging systems to achieve an end goal of sub-5 μm spatial resolution and sub-1 μs timing resolution. My research focuses on using MATLAB and Silvaco to simulate the expected response of a LISe DSSD. These various datasets are then trained to Machine Learning models in order to predict the neutron interaction location based upon the induced signal across multiple strip electrodes. In addition, various DSSD designs were simulated to determine the strip electrode width/pitch that optimizes the tradeoff between signal integrity and reconstruction of the neutron absorption location. The addition of electronic and statistical noise to the signal as well as varying the charge collection efficiency was also explored. The improvement upon current neutron imaging systems has the opportunity to open new avenues of research that are not possible today

Physics and Technology of Silicon Carbide Devices

Recently, some SiC power devices such as Schottky-barrier diodes (SBDs), metal-oxide-semiconductor field-effect-transistors (MOSFETs), junction FETs (JFETs), and their integrated modules have come onto the market. However, to stably supply them and reduce their cost, further improvements for material characterizations and those for device processing are still necessary. This book abundantly describes recent technologies on manufacturing, processing, characterization, modeling, and so on for SiC devices. In particular, for explanation of technologies, I was always careful to argue physics underlying the technologies as much as possible. If this book could be a little helpful to progress of SiC devices, it will be my unexpected happiness

Characterisation of ScN and ScGaN alloys grown by Molecular Beam Epitaxy

The wurtzite III-nitrides AlN, GaN and InN are currently widely used in optoelectronic applications such as light-emitting diodes and this success is owed in large part to the possibility of band gap engineering by alloying between the constituent nitrides. Unfortunately, the restricted material properties currently limit the performance of such devices, and efficiencies of emitters in the green and ultraviolet spectral regions remain low. These challenges have motivated the search for alloying additions offering greater degrees of freedom for tuning the material properties. ScN is of particular interest in this regard, and ScGaN alloys have been predicted to remain stable in the wurtzite structure with direct band gaps for Sc contents of up to 27%. Of further interest is the predicted deviation from wurtzite symmetry towards a non-polar structure at higher Sc contents, which could lead to additional device functionalities such as ferroelectric switching. However, experimental data regarding the properties of ScGaN alloys are very limited, and further investigations of the growth are required if these materials are to be integrated into the existing III-nitride technology. This thesis is an in-depth characterisation of ScN and dilute ScGaN films grown by molecular beam epitaxy (MBE), with special emphasis on the microstructure, surface topography and local bonding environment of Sc in these materials. The results are based on a broad range of characterisation techniques including transmission electron microscopy, scanning probe microscopy, high-resolution X-ray diffraction and X-ray absorption spectroscopy (XAS). The effects of varying growth conditions on the properties of ScN and ScGaN films are discussed, including observed growth rates and defect densities. The introduction of Sc into the GaN system was found to decrease growth rates due to the likely presence of a ‘floating layer’, as has also been observed for other transition metal doped nitrides. Microstructural investigations found that at low Sc contents the formation of I1-type basal-plane stacking faults is promoted, while at higher contents lamellar inclusions of the cubic phase of up to 4 stacking repeats were observed. The local flattening of the wurtzite unit cell around substitutional Sc atoms was directly observed by XAS measurements, confirming theoretical predictions and giving confidence that related predictions for higher Sc content films are also correct

Selected problems of materials science. Vol. 2. Nano-dielectrics metals in electronics. Mеtamaterials. Multiferroics. Nano-magnetics

The textbook examines physical foundations and practical application of current electronics materials. Modern theories are presented, more important experimental data and specifications of basic materials necessary for practical application are given. Contemporary research in the field of microelectronics and nanophysics is taken into account, while special attention is paid to the influence of the internal structure on the physical properties of materials and the prospects for their use. English-language lectures and other classes on the subject of the book are held at Igor Sikorsky Kyiv Polytechnic Institute at the departments of “Applied Physics” and “Microelectronics” on the subject of materials science, which is necessary for students of higher educational institutions when performing scientific works. For master’s degree applicants in specialty 105 “Applied physics and nanomaterials”.Розглянуто фізичні основи та практичне застосування актуальних матеріалів електроніки. Подано сучасні теорії, наведено найважливіші експериментальні дані та специфікації основних матеріалів, які потрібні для практичного застосування. Враховано сучасні дослідження у галузі мікроелектроніки та нанофізики, при цьому особливу увагу приділено впливу внутрішньої структури на фізичні властивості матеріалів і на перспективи їх використання. Англомовні лекції та інші види занять за тематикою книги проводяться в КПІ ім. Ігоря Сікорського на кафедрах «Прикладна фізика» та «Мікро-електроніка» за напрямом матеріалознавство, що необхідно студентам вищих навчальних закладів при виконанні наукових робіт. Для здобувачів магістратури за спеціальністю 105 «Прикладна фізика та наноматеріали»

Permeability and Flammability Study of Composite Sandwich Structures for Cryogenic Applications

Fiber reinforced plastics offer advantageous specific strength and stiffness compared to metals and has been identified as candidates for the reusable space transportation systems primary structures including cryogenic tanks. A number of carbon and aramid fiber reinforced plastics have been considered for the liquid hydrogen tanks. Materials selection is based upon mechanical properties and containment performance (long and short term) and upon manufacturing considerations. The liquid hydrogen tank carries shear, torque, end load, and bending moment due to gusts, maneuver, take-off, landing, lift, drag, and fuel sloshing. The tank is pressurized to about 1.5 atmosphere (14.6psi or 0.1MPa) differential pressure and on ascent maintains the liquid hydrogen at a temperature of 20K. The objective of the research effort is to lay the foundation for developing the technology required for reliable prediction of the effects of various design, manufacturing, and service parameters on the susceptibility of composite tanks to develop excessive permeability to cryogenic fuels. Efforts will be expended on developing the materials and structural concepts for the cryogenic tanks that can meet the functional requirements. This will include consideration for double wall composite sandwich structures, with inner wall to meet the cryogenic requirements. The structure will incorporate nanoparticles for properties modifications and developing barriers. The main effort will be extended to tank wall’s internal skin design. The main requirements for internal composite stack are: • introduction of barrier film (e.g. honeycomb material paper sheet) to reduce the wall permeability to hydrogen, • introduction of nanoparticles into laminate resin to prevent micro-cracking or crack propagation. There is a need to characterize and analyze composite sandwich structural damage due to burning and explosion. Better understanding of the flammability and blast resistance of the composite structures needs to be evaluated