Объект изучения – модуль плазмохимического травления и осаждения на базе нанотехнологического комплекса Нанофаб-100. Цель работы — плазмохимический синтез тонких покрытий на основе нитридов алюминия и титана. Методы исследования: плазмостимулированное химическое осаждение из газовой фазы, электрохимическое окисление, плазменное азотирование, сканирующая электронная и атомно-силовая микроскопия, оптическая спектроскопия, наноиндентирование. В результате исследования разработана методика синтеза нитрида алюминия на установке плазмохимического синтеза. Синтезированы тонкие пленки нитрида алюминия толщиной 50-200 нм. Продемонстрирована возможность получения наноточек нитрида алюминия. С помощью плазмохимического азотирования модифицирована поверхность металлического титана с увеличением твердости в 4 раза. Показана возможность получения нанотубулярных структур нитрида титана, являющихся перспективными в целях создания электронных устройств, фотокаталитических ячеек и др. Результаты работы отражены в тезисах докладов III Международной молодежной научной конференции «Физика. Технологии. Инновации. ФТИ-2016». / The object of this study is the module of plasma chemical etching and deposition based on nanotechnology complex Nanofab-100. The goal of the current paper is the plasma-chemical synthesis of thin coatings based on aluminum and titanium nitrides. As a result of the research, a technological map for the routine of the plasma-chemical synthesis and a technique for obtaining nanomaterials on the example of aluminum nitride have been developed. There were synthesized thin films of aluminum nitride with 50-200 nm thickness. The possibility of synthesis nano-dots of AlN is demonstrated. The surface of metallic titanium has been modified with an increase in hardness by 4 times using plasma-assisted nitriding process. The possibility of obtaining nanotubular structures of titanium nitride, which are promising for microelectronic and photocatalysis, is shown. The results of the work are reported in abstracts of the III International Youth Scientific Conference «Physics. Technologies. Innovation. FTI-2016».

η (eta) nitride, Cr3Ni2SiN, is a precipitate found in high temperature austenitic stainless steel and is not yet included in Thermo-Calc steel database TCFE7. The aim of this thesis is to collect thermodynamic data to enable the addition of η nitride in the databases. Three laboratory melts with varying levels of silicon, chromium and nickel have been aged at 700-1000 °C for 75 h, 300 h and 1200 h and examined by Light Optical Microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Wavelength Dispersive Spectroscopy, Electron Backscattered Diffraction and X-ray Powder Diffraction. η nitride is in the studied alloys an equilibrium phase stabilized with nitrogen. Presence of η nitride was confirmed by Energy Dispersive Spectroscopy and X-ray Powder Diffraction. It was found to precipitate in four different ways, at primary grain boundaries, intragranularly, as a "skeleton-like" precipitate and as a border around the occurring Cr2N precipitates. The area fraction of η nitrides increases with longer aging times and is favored by silicon and nickel. The composition of η nitride is not changing regardless of material composition, aging temperature and aging time. The composition of η nitride in all three materials are 8.7-9.7 wt.% silicon, 47-54 wt.% chromium, 1.4-4.1 wt.% iron and 33-36 wt.% nickel. The nitrogen content 2 determined by Wavelength Dispersive Spectroscopy is 2.8-3.2 wt.%. No complete equilibrium was achieved and together with incomplete mixing of the alloying elements during melting, the microstructure is difficult to evaluate. Other precipitates found are Cr2N, π nitride, σ phase and two unidentified phases, M and N. Of these phases at least Cr2N is not an equilibrium phase as it dissolves during aging. Further aging to achieve complete equilibrium is necessary.

No description available.

No description available.

Metallic fuels were produced through arc-melting. As-cast phases, microstructuresand selected mechanical properties were investigated for UZr,U-Th, and U-Th-Zr systems. For each system, two compositions wereinvestigated, with approximately 5 at. % and 20 at. % solute material, for atotal of six alloys. As-cast alloy microstructures were assessed in the contextof their equilibrium systems and compared to relevant published works whereapplicable. Mechanical testing revealed increased hardness with increasingsolute concentration, compared to the reference materials. The results supportthe conclusion that solid solution strengthening is the primary mechanismenabling this change in each binary system.Additionally, (U,Zr)N fuel was synthesized. This work exemplified aprocess to produce fuel with a homogeneous distribution of zirconium in thefuel matrix, thus representing a simulated burn-up distribution of zirconium.Refinements can be made to further improve this process in future work. Thesefindings will support a broader separate effects testing campaign underway bythe SUNRISE centre / Metalliska bränslen framställdes genom bågsmältning. Som gjutna faser,mikrostrukturer och utvalda mekaniska egenskaper undersöktes för U-Zr-, UTh-och U-Th-Zr-system. För varje system undersöktes två sammansättningar,med cirka 5 at. % och 20 at. % löst material, för totalt sex legeringar.Mikrostrukturer av gjutna legeringar diskuterades i samband med derasjämviktssystem och jämfördes med literattur. Mekanisk testning visadeökad hårdhet med ökad halt lösta atomer, jämfört med råvarorna. Denprimära mekanismen som möjliggör denna förändring föreslogs vara solidlösningsförstärkning.Vidare syntetiserades (U,Zr)N-bränsle. Detta arbete exemplifierade enprocess för att producera bränsle med en homogen fördelning av zirkoniumi bränslematrisen, vilket representerar en simulerad utbränningsfördelning avzirkonium. Denna process kan förbättras. Resultaten stödjer en bredare separateffekttestningskampanj som SUNRISE-centret arbetar med.

Doctor of Philosophy / Department of Industrial & Manufacturing Systems Engineering / Shuting Lei / Laser-assisted machining (LAM) is a promising non-conventional machining technique for advanced ceramics. However, the fundamental machining mechanism which governs the LAM process is not well understood so far. Hence, the main objective of this study is to explore the machining mechanism and provide guidance for future LAM operations. In this study, laser-assisted milling (LAMill) of silicon nitride ceramics is focused. Experimental experience reveals that workpiece temperature in LAM of silicon nitride ceramics determines the surface quality of the machined workpiece. Thus, in order to know the thermal features of the workpiece in LAM, the laser-silicon nitride interaction mechanism is investigated via heating experiments. The trends of temperature affected by the key parameters (laser power, laser beam diameter, feed rate, and preheat time) are obtained through a parametric study. Experimental results show that high operating temperature leads to low cutting force, good surface finish, small edge chipping, and low residual stress. The temperature range for brittle-to-ductile transition should be avoided due to the rapid increase of fracture toughness. In order to know the temperature distribution at the cutting zone in the workpiece, a transient three-dimensional thermal model is developed using finite element analysis (FEA) and validated through experiments. Heat generation associated with machining is considered and demonstrated to have little impact on LAM. The model indicates that laser power is one critical parameter for successful operation of LAM. Feed and cutting speed can indirectly affect the operating temperatures. Furthermore, a machining model is established with the distinct element method (or discrete element method, DEM) to simulate the dynamic process of LAM. In the microstructural modeling of a β-type silicon nitride ceramic, clusters are used to simulate the rod-like grains of the silicon nitride ceramic and parallel bonds act as the intergranular glass phase between grains. The resulting temperature-dependent synthetic materials for LAM are calibrated through the numerical compression, bending and fracture toughness tests. The machining model is also validated through experiments in terms of cutting forces, chip size and depth of subsurface damage.

Doctor of Philosophy / Department of Physics / Jingyu Lin / Time-resolved deep ultraviolet (DUV) Photoluminescence (PL) spectroscopy system has been employed to systematically monitor crystalline quality, identify the defects and impurities, and investigate the light emission mechanism in III-nitride semiconducting materials and photonic structures. A time correlated single photon counting system and streak camera with corresponding time resolutions of 20 and 2 ps, respectively, were utilized to study the carrier excitation and recombination dynamics. A closed cycle He-flow cryogenic system was employed for temperature dependent measurements. This system is able to handle sample temperatures in a wide range (from 10 to 900 K). Structural, electrical, and morphological properties of the material were monitored by x-ray diffraction (XRD), Hall-effect measurement, and atomic force microscopy (AFM), respectively. Most of the samples studied here were synthesized in our laboratory by metal organic chemical vapor deposition (MOCVD). Some samples were bulk AlN synthesized by our collaborators, which were also employed as substrates for homoepilayer growth. High quality AlN epilayers with (0002) XRD linewidth as narrow as 50 arcsec and screw type dislocation density as low as 5x10[superscript]6 cm[superscript]-2 were grown on sapphire substrates. Free exciton transitions related to all valence bands (A, B, and C) were observed in AlN directly by PL, which allowed the evaluation of crystal field (Δ[subscript]CF) and spin-orbit (Δ[subscript]SO) splitting parameters exerimentally. Large negative Δ[subscript]CF and, consequently, the difficulties of light extraction from AlN and Al-rich AlGaN based emitters due to their unique optical polarization properties have been further confirmed with these new experimental data. Due to the ionic nature of III-nitrides, exciton-LO phonon Frohlich interaction is strong in these materials, which is manifested by the appearance of phonon replicas accompanying the excitonic emission lines in their PL spectra. The strength of the exciton-phonon interactions in AlN has been investigated by measuring the Huang-Rhys factor. It compares the intensity of the zero phonon (exciton emission) line relative to its phonon replica. AlN bulk single crystals, being promising native substrate for growing nitride based high quality device structures with much lower dislocation densities (<10[superscript]4 cm[superscript]-2), are also expected to be transparent in visible to UV region. However, available bulk AlN crystals always appear with an undesirable yellow or dark color. The mechanism of such undesired coloration has been investigated. MOCVD was utilized to deposit ~0.5 μm thick AlN layer on top of bulk crystal. The band gap of strain free AlN homoepilayers was 6.100 eV, which is ~30 meV lower compared to hetero-epitaxial layers on sapphire possessing compressive strain. Impurity incorporation was much lower in non-polar m-plane growth mode and the detected PL signal at 10 K was about an order of magnitude higher from a-plane homo-epilayers compared to that from polar c-plane epilayers. The feasibility of using Be as an alternate p-type dopant in AlN has been studied. Preliminary studies indicate that the Be acceptor level in AlN is ~330 meV, which is about 200 meV shallower than the Mg level in AlN. Understanding the optical and electronic properties of native point defects is the key to achieving good quality material and improving overall device performance. A more complete picture of optical transitions in AlN and GaN has been reported, which supplements the understanding of impurity transitions in AlGaN alloys described in previous reports.

Transition metal nitrides (TMNs) refractory ceramic materials are  widely employed as wear-resistant protective coatings in industrial machining as well as diffusion barriers inhibiting migration of metal impurities from the interconnects to the semiconducting region of electronic devices. TiN is the prototype of this class of materials and the most studied among TMNs. However, also for this system, a complete picture of the migration processes occurring at the atomic scale is still lacking. In this work I investigate the stability of Ti vacancy configurations and corresponding migration rates in TiN by means of density functional theory (DFT) calculations and ab-initio molecular dynamics simulations (AIMD). DFT calculations show that Ti vacancies tend to stay isolated because of repulsive interaction which decreases as the inverse of the distance between the vacancies.The equilibrium jump rate of single Ti vacancies in TiN is extrapolated temperature as a function of temperature from the results of non-equilibrium AIMD simulations accelerated by a bias force field according to the color diffusion algorithm. For each force field and, the jump occurrence times are fitted with the two parameters Gamma distribution in order to obtain the non equilibrium jump rate with the corresponding uncertainty. Extrapolated equilibrium values show an Arrhenius-like behavior, with activation energy Ea= (3.78 ± 0.28)eV and attempt frequency A = 4.45 (x3.6±1) x 1014 s-1.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The main focus of this thesis is to document the formulation, extraction and validation of nonlinear models for the on-wafer gallium nitride (GaN) high-electron mobility (HEMT) devices manufactured at the Interuniversity Microelectronics Centre (IMEC) in Leuven, Belgium. GaN semiconductor technology is fast emerging and it is expected that these devices will play an important role in RF and microwave power amplifier applications. One of the main advantages of the new GaN semiconductor technology is that it combines a very wide band-gap with high electron mobility, which amounts to higher levels of gain at very high frequencies. HEMT devices based on GaN, is a fairly new technology and not many nonlinear models have been proposed in literature. This thesis details the design of hardware and software used in the development of the nonlinear models. An intermodulation distortion (IMD) measurement setup was developed to measure the second and higher-order derivative of the nonlinear drain current. The derivatives are extracted directly from measurements and are required to improve the nonlinear model IMD predictions. Nonlinear model extraction software was developed to automate the modelling process, which was fundamental in the nonlinear model investigation. The models are implemented in Agilent’s Advanced Design System (ADS) and it is shown that the models are capable of accurately predicting the measured S-parameters, large-signal singletone and two-tone behaviour of the GaN devices. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie tesis is om die formulering, ontrekking en validasie van nie-lineêre modelle vir onverpakte gallium nitraat (GaN) hoë-elektronmobilisering transistors (HEMTs) te dokumenteer. Die transistors is vervaaardig by die Interuniversity Microelectronics Centre (IMEC) in Leuven, België. GaN-halfgeleier tegnologie is besig om vinnig veld te wen en daar word voorspel dat hierdie transistors ʼn belangrike rol gaan speel in RF en mikrogolf kragversterker toepassings. Een van die hoof voordele van die nuwe GaN-halfgeleier tegnologie is dat dit 'n baie wyd band-gaping het met hoë-elektronmobilisering, wat lei tot hoë aanwins by mikrogolf frekwensies. GaN HEMTs is 'n redelik nuwe tegnologie en nie baie nie-lineêre modelle is al voorgestel in literatuur nie. Hierdie tesis ondersoek die ontwerp van die hardeware en sagteware soos gebruik in die ontwikkeling van nie-lineêre modelle. 'n Intermodulasie distorsie-opstelling (IMD-opstelling) is ontwikkel vir die meting van die tweede en hoër orde afgeleides van die nie-lineêre stroom. Die afgeleides is direk uit die metings onttrek en moet die nie-lineêre IMD-voorspellings te verbeter. Nie-lineêre onttrekking sagteware is ontwikkel om die modellerings proses te outomatiseer. Die modelle word geïmplementeer in Agilent se Advanced Design System (ADS) en bewys dat die modelle in staat is om akkurate afgemete S-parameters, grootsein enkeltoon en tweetoon gedrag van die GaN-transistors te kan voorspel.

The development of state-of-the-art AlGaN/GaN high electron mobility transistors (HEMTs) has shown much promise for advancing future RF and microwave communication systems. These revolutionary devices demonstrate great potential and superior performance and many commercial companies have demonstrated excellent reliability results based on multiple temperature accelerated stress testing. However, a physical understanding of the various reliability limiting mechanisms is lacking and the role and relative contribution of the various intrinsic material factors, such as physical stress and strain has not been clearly explained in the literature. Part of issues that impact device reliability are the mechanical stresses induced in the devices as well as the self-heating that also limit device performance. Thus, quantification of stress and temperature in AlGaN/GaN HEMTs is of great importance. To address some of the needs for metrology to quantify stress in AlGaN/GaN HEMTs, micro-Raman spectroscopy and micro-photoluminescence (micro-PL) were utilized to quantify the residual stress in these devices. Through the use of micro-Raman and micro-PL optical characterization methods, mapping of the vertical and lateral stress distributions in the device channels was performed. Results show that stress can be influenced by the substrate material as well as patterned structures including metal electrodes and passivation layers. Previously developed and reported micro-Raman thermometry methods require an extensive calibration process for each device investigated. To improve the implementation of micro-Raman thermometry, a method was developed which offers both experimental simplicity and high accuracy in temperature results utilizing a universal calibration method that can be applied to a broad range of GaN based devices. This eliminates the need for performing calibration on different devices. By utilizing this technique, it was revealed that under identical power dissipation levels, the bias conditions (combination of Vgs and Vds) alter the heat generation profile across the conductive channel and thus influence the degree of device peak temperature. The role of stress in the degradation of AlGaN/GaN HEMTs was also explored. A combined analysis using micro-Raman spectroscopy, coupled electro-thermo-mechanical simulation, and electrical step stress tests was conducted to investigate the link between performance degradation and the evolution of total stress in devices. It was found that in addition to stresses arising from the inverse piezoelectric effect, the substrate induced residual stress and the operational themo-elastic stress in the AlGaN layer play a major role in determining the onset of mechanically driven device degradation. Overall, these experiments were the first to suggest that a critical level of stress may exist at which point device degradation will start to occur. The optical characterization methods developed in this study show the ability to reveal unprecedented relationships between temperature/stress and device performance/reliability. They can be used as effective tools for facilitating improvement of the reliability of future AlGaN/GaN HEMTs.