The thesis examines the prospects of using the superconductor NbN as the gatemetal for an InP HEMT. A HEMT or High Electron Mobility Transistor is aheterostructure transistor engineered to reach very high electron mobility. InPHEMTs are used as cryogenic Low Noise Amplifiers (LNAs), which have increasedin demand as quantum computing is scaling up. A superconducting NbN gate isof interest as it has the potential to decrease the amount of noise generated by theHEMT LNAs.A gate width dependence for both the transconductance (gm) and the large-signal HEMT channel resistance (RON ) of the NbN HEMTs at room temperaturehas been observed, and the first goal pf the thesis is to determine the originof the dependence. Moreover, the measured RF characteristics of the NbNdevices tend to deviate from the norm of a standard HEMT, and the secondgoal is to understand why. The third goal is to determine if the NbN gate stayssuperconducting at cryogenic temperatures or if self-heating from the channelduring DC operations will break superconductivity.In the thesis, it was possible to recreate the observed gate width dependence withnew devices, and additionally, a gate width dependence in the threshold voltageis observed. The origin of width dependence is most likely related to the straincreated by the NbN gate. At DC, extremely high peaks in the transconductanceare observed, which is most likely related to impact ionization and a subsequentincrease in hole trapping caused by the introduction of the NbN gate.Using simulations, it was possible to accurately recreate the observed deviantbehaviour, likely associated with the NbN gate’s high capacitance, inductance andresistance at room temperature. The high capacitance is likely partly related tosome NbN gates of the HEMTs being broken. Finally, the HEMT can operatein DC at 2 K with VG = 0.3 V and a maximum VD = 0.1 V before self-heatingfrom the channel will break the NbN superconductivity of the gate. This is oneof the critical conclusions of the work because it shows that a superconductinggate electrode can be implemented and functional in a high-performance HEMTdevice structure and under realistic operating bias conditions. As long as it can bedemonstrated that the superconductivity does not break when operating in RF, aNbN gate is a promising avenue to increase the noise performance of the cryogenicHEMT. / Detta arbete utforskar möjligheterna att använda supraledaren NbN som metallför gaten av en InP HEMT. En HEMT eller High Electron Mobility Transistor är entyp av transistor som är designad för väldigt hög elektron mobilitet. InP HEMTsanvänds som lågbrusförstärkare eller på engelska Low Noise Amplifiers (LNAs),vilket har ökat i efterfrågan när kvantdatorer nu skalar upp. En supraledande gateär av intresse för att den har potentialen att minska mängden brus som skapas ien HEMT LNA.Ett gatebredd beroende för både transkonduktans och RON har observerats och ettmål i arbetet är försöka fastställa dess ursprung. Utöver detta tenderar beteendet,av HEMTs med en NbN gate, att avvika från normen av en standard HEMT närden drivs i RF, och det andra målet är att förstå varför. Det tredje målet äratt fastställa om en NbN gate kommer supraleda i kryogen temperatur eller omsjälvuppvärmning från kanalen i HEMTen kommer bryta supraledningen.I arbetet var det möjligt att återskapa beroendet av gatebredden för nyaHEMTs och ett gatebredd beroende för HEMTens tröskelström observeradesockså. Gatebredd beroendet kommer troligtvis från spänning i HEMTen skapatav introduktionen av NbN gaten. I DC observerades väldigt höga toppar itranskonduktansen, vilket troligt är relaterat till processen ”impact ionization”och en efterföljande ökning i infångningen av hål som skapats på grund av NbNgaten.Genom simulationer är det möjligt att återskapa det observerade avvikandebeteendet i RF, vilket troligtvis är relaterat till NbN gatens höga resistans,kapacitans och induktans i rumstemperatur. Den höga kapacitansen är möjligtvisrelaterad till att vissa gates är trasiga. Slutligen fastställer vi att HEMTen kanvara i funktion under DC med T = 2 K, VG = 0.3 V och en max source-drainpotential av VD = 0.1 V, innan självuppvärmning bryter supraledningen. Dettaär den viktigaste slutsatsen i arbetet, eftersom den visar att en supraledandegateelektrod kan implementeras i en högpresterande HEMT och fungera underrimliga driftförhållanden. Så länge det går att visa att supraledningen inte brytsunder RF, är en HEMT med en supraledande NbN gate en lovande väg framåt föratt förbättra brusprestandan för en kryogenisk HEMT.

This thesis focuses on simulating, designing, and characterizing a narrow-linewidth continuous-wave (CW) Ytterbium (Yb) master oscillator fiber amplifier (MOFA) system. The primary goal was to achieve a watt-level output at 1087 nm with a narrow 1 GHz linewidth, making the MOFA well-suited for serving as a pump source in Terahertz (THz) generation experiments. This system can essentially be divided into two main parts: a narrow-linewidth Yb fiber seed laser (master oscillator), responsible for delivering a stable and narrow-linewidth signal power, and a Yb fiber amplifier for scaling this signal power.The all-fiber Yb seed laser produced a maximum output power of 11.31 mW at 1087.39 nm with a narrow linewidth of approximately 1.86 GHz. The narrow-linewidth operation was achieved by incorporating a fiber Bragg grating (FBG) as a resonator mirror and an intracavity FBG based Fabry-Perot interferometer as a bandpass filter, allowing only specific portion of the FBG reflected spectrum to pass through. A simulation was subsequently developed to identify the optimal Yb gain fiber lengths and pump powers required to realize an efficient Yb fiber amplifier with high gains. Finally, by employing a 10-meter Yb fiber amplifier, seed laser’s output power was boosted to 0.86 W, resulting in a 23.1 dB gain, achieved with a notable power conversion efficiency of 33 %. The final amplified spectrum exhibited a Gaussian-like profile centered at 1087.12 nm, with a bandwidth of less than 12.7 GHz. By further scaling the output power to watt-level range, this Yb MOFA system has the potential to be utilized as a pump source in Terahertz (THz) generation research. / I detta examensarbete presenteras simuleringar, konstruktion och karaktärisering av en kontinuerlig smalbandig Ytterbium (Yb) fiberlaser och förstärkare. Målet med arbetet är att uppnå en effekt runt en watt med en centervåglängd på 1087 nm och en bandbredd på 1 GHz som kan användas vid generation av terahertzstrålning (THz-strålning). Systemet kan delas in i två delar: en Yb fiberlaser som levererar en stabil och smalbandig signal och den andra är en Yb fiber baserad förstärkare för amplifikation av signalen. Yb fiberlasern hade en maxeffekt på 11.31 mW med en centervåglängd på 1087.39 nm och en bandbredd på 1.86 GHz. Den smalbandiga operationen var uppnådd genom att inkorporera en fiber bragg-gitter (FBG) som formade en resonator, med två ytterligare FBG element som agerade som en intra-kavitär Fabry-Perot interferometer vilket begränsar vilka våglängder som kan propagera. Ett program för att simulera den optimala längden på Yb fiberförstärkaren samt vilken pumpeffekt som maximerade den förstärkta signalen togs fram för projektet. Det resulterade i en förstärkare med en 10 m lång Yb fiber som kunde förstärka fiberlasern till 0.86 W, vilket motsvarade till en 23.1 dB förstärkning med en effektivitet på 33%. Den slutgiltiga signalen hade ett spektrum med gaussisk profil och en bandbredd under 12.7 GHz. Med ytterligare skalning på effekten genom fler förstärkare kan system som helhet användas vid generation av THz strålning.

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC), necessitates that the ATLAS experiment replace their current Inner Detector (ID) system. The new Inner Tracker (ITk) will be an all silicon detector, utilising both pixel and strip sensors, with the aim of performing as well, or better than the current system - but in a much more challenging environment. The ITk Strip detector will consist of 17888 modules, ∼ 700 of which will be produced in the Scandinavian ITk Cluster - a collaboration of Copenhagen, Lund, Oslo and Uppsala university and our industrial partner NOTE. This work encompasses the journey from individual components through industrial scale module assembly and on to performance evaluation studies at the DESY II testbeam facility. Optimisation studies were performed of the correlated multi-variable calibration necessary for a glue robot to precisely and reliably dispense the two component epoxy used in the bonding of front-end electronics to the silicon sensor. Procedures and tools were developed for integrating this process into an industrial workflow, and to account for future fundamental changes, such as a switch in the epoxy utilised. To demonstrate sufficient tracking performance of ITk strip modules, even at end-of-life, testbeam campaigns of pre-irradiated modules are conducted. These campaign serve as vi-tal feasibility studies for the ITk as a whole. Reconstruction of end-cap type modules have been historically tricky, due to their complex geometry. This work presents the full integration of semi-automated end-cap type module reconstruction in the Corryvreckan testbeam analysis framework. This represent a major improvement in turnover time from raw data to final result, making the previously impossible concept of live reconstruction during testbeam campaigns within reach.

Wavefront sensors for measurements on human eyes are usually large, expensive and difficult to move. A compact wavefront sensor would be more cost-effective and versatile as is could be used in multiple systems. The aim of this thesis was to produce a more compact and portable wavefront sensor. A shorter telescope design for the wavefront sensor was proposed and checked theoretically and with computer simulations. An experimental arrangement comparing the proposed telescope design with a conventional telescope design was constructed. A compact wavefront sensor was built using off-the-shelf components and a few modified components. Tests with the compact wavefront sensor were made both on eye models and on human eyes. The compact wavefront sensor correctly measured the refractive errors of two eye models. It was also possible to perform measurements on human eyes, both in the central and peripheral visual fields, and higher order aberrations were confirmed. For positioning human eyes at the correct distance from the wavefront sensor an additional pupil camera was needed, which was not included in the system. Future improvements for the compact wavefront sensor are discussed. / Vågfrontssensorer för mätningar på ögon är ofta mycket stora, dyra och svåra att transportera. En kompakt vågfrontssensor skulle vara kostnadseffektiv och flexibel eftersom den skulle kunna användas i flera olika system. Målet med detta examensarbete var att producera en mer kompakt och transportabel vågfrontssensor. En kortare teleskopvariant föreslogs och analyserades både teoretiskt och med datorsimuleringar. En experimentell uppsättning gjordes också för att jämföra den kortare teleskopdesignen med ett sedvanligt vågfrontssensorteleskop. En kompakt vågfrontssensor byggdes med standardkomponenter samt med några modifierade standardkomponenter. Tester med den kompakta vågfrontssensorn gjordes både på ögonmodeller och mänskliga ögon. Den kompakta vågfrontssensorn gav korrekta mätvärden på brytningsfelen på ögonmodellerna. Det gick bra att genomföra mätningar på mänskliga ögon, både i centrala och perifera synfältet, och högre ordningens aberrationer bekräftades. För att placera mänskliga ögon på korrekt avstånd från vågfrontssensorn krävdes en extra pupillkamera, som inte var inkluderad i den kompakta vågfrontssensorn. Framtida förbättringar för den kompakta vågfrontssensorn diskuteras.

We have investigated the Faraday effect of bismuth-doped rare-earth iron-garnets with varying doping levels of gallium from z = 1.0 to 1.35. We used lutetium to control the film's in-plane magnetic properties and found that gallium doping levels above the compensation point caused a loss of anisotropy control, a canted out-of-plane magnetization in the film, and an extremely weak but linear coercivity above 10 micro-Tesla fields. Using these results we focused on in-plane films to create 8 layer stacks of 500 um thick films to achieve a minimum detectable field of 50 pT at 1 kHz. Unlike previous Magneto-Optic (MO) studies that typically used thin films of approximately 1um thickness, we used approximately 400um thick films to allow experimentation with the final, robust, ideal form the MO sensor would take. We measured what most other MO studies with garnets neglected: the magnetic anisotropy axis or structure within the film. Knowledge of this structure is essential in improving the sensitivity of a stacked MO probe. Studying thick films proved to be key to understanding the magnetic anisotropy and domain properties that can degrade or enhance the sensitivity of the Faraday rotation in bismuth doped rare-earth iron-garnets to an applied magnetic field and to pointing the direction of future research to develop the conditions for rugged magnetometer sensors. / Physics

<p> Nuclear waste management and nonproliferation are among the critical tasks to be addressed for the advancement of nuclear energy in the United States. In this regard, monitoring spent nuclear fuel (SNF) and special nuclear materials (SNM) is important to continue reliable stewardship of SNF management and prevent SNM proliferation. Cosmic ray muons have been used for imaging large and dense objects, e.g., SNF dry casks, the Fukushima Daiichi unit-1 reactor, and the great pyramid of Giza. Despite their potential and success, the wide application of cosmic ray muons is limited by the naturally low intensity at sea level, approximately 10⁴ m^-2min^-1. For example, when imaging large objects, time consuming measurements typically in the order of several days or even weeks, are frequently needed to collect a statistically significant amount of muon samples to reconstruct images using muon tomography. However, when scanning time is of essence, e.g., treaty verification, low resolution imaging can result in potentially undetected diversion of nuclear materials.</p> <p>To maximize the utilizability of cosmic ray muons in engineering and physics applications, two important quantities–scattering angle and momentum–must be measured. Although many studies have demonstrated that there are significant benefits when measuring momentum in muon applications, measuring both the muon scattering angle and muon momentum in the field remains a challenge. To fill this critical gap, a novel concept using multi-layer pressurized gas Cherenkov radiators that is fieldable to allow muon momentum measurement in the field is presented in this dissertation. The proposed Cherenkov muon spectrometer is: (i) accurate (~90%) in classifying muon momentum, (ii) lightweight (< 10 kg) for easy transport and deployment in the field, (iii) compact (< 1 m³), and (iv) easily coupled with existing muon tomographic systems. Although muon momentum measurement resolution of spectrometers used in high energy physics laboratories, such as CMS or ATLAS of LHC at CERN, is less than 5% for low energy muons, these spectrometers typically (i) use bulky and large solenoidal or toroidal magnets and (ii) interfere with muon trajectories to measure momentum. These characteristics make them unsuitable for field deployment.</p> <p>In this work, the feasibility of using the proposed Cherenkov muon spectrometer coupled with current muon tomographic systems is explored and evaluated using Monte Carlo simulations and reconstruction algorithms. It is shown the use of the proposed Cherenkov muon spectrometer has the potential to improve muon tomographic imaging resolution or reduce measurement time by a factor of 10 or more when used to identify a missing fuel assembly from a SNF dry cask. In addition, a new imaging algorithm is developed that integrates muon momentum and muon scattering without significantly increasing computational cost. Advances in momentum-integrated muon tomography have the potential to improve monitoring and imaging efficiency in various nuclear engineering applications. For example, it can expand current capabilities to continue reliable stewardship in nuclear material management, i.e., Continuity of Knowledge, and prevent SNM proliferation to unauthorized states and parties. The benefit of such an approach is a compact, lightweight, and portable spectrometer that can be deployed in the field to improve existing or explore new engineering applications: muon tomography, geological studies, and cosmic radiation measurement in space.</p>

abstract: Mathematical models are important tools for addressing problems that exceed experimental capabilities. In this work, I present ordinary and partial differential equation (ODE, PDE) models for two problems: Vicodin abuse and impact cratering. The prescription opioid Vicodin is the nation's most widely prescribed pain reliever. The majority of Vicodin abusers are first introduced via prescription, distinguishing it from other drugs in which the most common path to abuse begins with experimentation. I develop and analyze two mathematical models of Vicodin use and abuse, considering only those patients with an initial Vicodin prescription. Through adjoint sensitivity analysis, I show that focusing efforts on prevention rather than treatment has greater success at reducing the total population of abusers. I prove that solutions to each model exist, are unique, and are non-negative. I also derive conditions for which these solutions are asymptotically stable. Verification and Validation (V&V) are necessary processes to ensure accuracy of computational methods. Simulations are essential for addressing impact cratering problems, because these problems often exceed experimental capabilities. I show that the Free Lagrange (FLAG) hydrocode, developed and maintained by Los Alamos National Laboratory, can be used for impact cratering simulations by verifying FLAG against two analytical models of aluminum-on-aluminum impacts at different impact velocities and validating FLAG against a glass-into-water laboratory impact experiment. My verification results show good agreement with the theoretical maximum pressures, and my mesh resolution study shows that FLAG converges at resolutions low enough to reduce the required computation time from about 28 hours to about 25 minutes. Asteroid 16 Psyche is the largest M-type (metallic) asteroid in the Main Asteroid Belt. Radar albedo data indicate Psyche's surface is rich in metallic content, but estimates for Psyche's composition vary widely. Psyche has two large impact structures in its Southern hemisphere, with estimated diameters from 50 km to 70 km and estimated depths up to 6.4 km. I use the FLAG hydrocode to model the formation of the largest of these impact structures. My results indicate an oblique angle of impact rather than a vertical impact. These results also support previous claims that Psyche is metallic and porous. / Dissertation/Thesis / Psyche asteroid impact simulation initialization / Psyche asteroid impact simulation video / Doctoral Dissertation Applied Mathematics 2019

With increase in the number of three dimensional (3-D) nanometer-scale objects that are being either fabricated or studied, there is a need to accurately characterize their geometry. While the Atomic force microscope (AFM) is a versatile tool for performing nano-metrology, it suffers from issues of poor accessibility of 3-D features and inability to measure 3-D forces that limit its applicability in 3-D nano-metrology. This thesis investigates the design and development of a novel probing system based on AFM that improves accessibility and enables direct measurement of 3-D forces acting on the AFM tip. Two approaches are investigated to address the issue of poor accessibility. The first is to develop a novel system that enables in-situ replacement and reuse of specialized AFM tips that improve accessibility, and the second is to design a special AFM tip that can actively re-orient about two independent axes. In order to perform in-situ tip replacement, a liquid meniscus based micro-gripper is developed and integrated on to a conventional AFM probe. The stiffness of the gripper is analyzed and shown to be adequately high along all three axes for AFM imaging to be performed. Tip replacement and re-use are both experimentally demonstrated by employing a novel tip-exchange station. The replaced tips are employed to show artifact-free AFM imaging of a standard calibration grating in both tapping-mode and contact-mode. To actively re-orient a conventional tip, a novel magnetically-actuated micro-scale ball-and-socket joint is integrated onto an AFM probe. The quasi-static behavior of the joint is experimentally characterized, and the ability of the tip to independently re-orient about two axes is demonstrated. The achieved range is about +/- 90 degrees about both X- and Y-axes. In order to realize the potential of the proposed probes for 3-D nano-metrology, an AFM is developed in-house that possesses the capability to make direct measurement of 3-D forces. Optimization of the measurement system to achieve identical sensitivities and resolution along all three axes is studied. Subsequently, the necessary electronics for measurement, actuation and control are developed. All the subsystems are experimentally calibrated and integrated. The overall AFM is shown to have a resolution of about 0.2 nm when operated in tapping-mode. The developed AFM is employed to showcase the following applications: characterization of the coefficient of kinetic friction of Muscovite mica, force controlled nano-scribing on polymethyl methacrylate (PMMA) and tapping-mode imaging of a calibration grating with the developed re-orientable AFM probe. Finally, the unique ability of the re-orientable AFM probe to control its tip-orientation is employed to develop a nanometer-scale coordinate measurement machine (CMM). The developed nano-CMM is shown to access the vertical wall of a sample and obtain its topography.

Orientador: Alexandre Mesquita / Banca: Luis Fernando Silva / Banca: Fabio Simões de Vicente / Resumo: O óxido de zinco (ZnO) é um semicondutor de tipo n com um largo intervalo de banda proibida que é utilizado devido às suas excelentes propriedades de luminescência. Diferentes métodos de preparação de amostras, assim como a incorporação de átomos de magnésio, modifica a banda proibida do ZnO, alterando a intensidade da luminescência, sem grandes alterações em sua estrutura cristalina. Neste estudo, foram preparadas amostras nanoestruturadas de ZnO por três diferentes métodos de preparação (Precursores Poliméricos, Solvotermal e Co-precipitação) e amostras dopadas com diferentes quantidades de magnésio (Zn1-xMgxO). Os resultados de difração de raios-X mostram que as amostras de Zn1-xMgxO cristalizaram completamente sem a presença de fases secundárias (até 20% de magnésio) e os padrões de difração correspondem à estrutura espacial wurtzita hexagonal P63mc. Com o uso do Microscópio eletrônico de varredura comprovamos o aumento do tamanho das partículas relacionado com o aumento da temperatura de calcinação. Espectroscopia de Fotoluminescência exibe uma emissão na região do verde para amostras com magnésio. À medida que a concentração de Mg aumenta, observa-se um aumento desta emissão, o que está associado com o aumento das vacâncias de oxigênio em função da concentração de Mg. Esta técnica ainda mostrou uma emissão na região do laranja em ~ 600 nm para as amostras preparadas por co-precipitação e solvotermal, devido a defeitos do tipo Zn intersticial e a formação de Zn(OH)2 na... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Zinc oxide (ZnO) is a n-type semiconductor with a large band gap which has received considerable attention because of its optical properties and technological applications. Different methods of sample preparation, as well as the incorporation of magnesium atoms, modify the ZnO band gap, changing the intensity of the luminescence, without major changes in its crystalline structure. In this study, nanostructured ZnO samples were prepared by three different preparation methods (polymeric precursors, solvotermal and co-precipitation) and with the incorporation of different amounts of magnesium (Zn1-xMgxO). The X-ray diffraction results show that Zn1-xMgxO samples crystallized completely without the presence of secondary phases (up to 20% of magnesium) and the diffraction patterns correspond to the hexagonal wurtzite structure with space group P63mc. The characterization by scanning electron microscopy showed that the prepared samples have nanometric dimensions and that the increase of the calcination temperature causes an increase in the particle size. Results obtained with photoluminescence spectroscopy show an emission centered in the green region for all samples, which is caused by defects in the crystalline structure associated with oxygen vacancies. As the concentration of Mg increases, an increase of this emission is observed. This technique also showed an emission in the orange region at ~ 600 nm for samples prepared by co-precipitation and solvotermal due to interstitial Zn-type defects and Zn(OH)2 formation on the surface of ZnO nanoparticles, whose existence is confirmed with Raman spectroscopy measurements. Results obtained with the X-ray absorption spectroscopy technique (XANES and EXAFS) at the Zn K-edge exhibit the occurrence of oxygen vacancies and these vacancies may be related to the emission in the green region of the photoluminescence ... (Complete abstract click electronic access below) / Mestre

abstract: The inductance of a conductor expresses its tendency to oppose a change in current flowing through it. For superconductors, in addition to the familiar magnetic inductance due to energy stored in the magnetic field generated by this current, kinetic inductance due to inertia of charge carriers is a significant and often dominant contribution to total inductance. Devices based on modifying the kinetic inductance of thin film superconductors have widespread application to millimeter-wave astronomy. Lithographically patterning such a film into a high quality factor resonator produces a high sensitivity photodetector known as a kinetic inductance detector (KID), which is sensitive to frequencies above the superconducting energy gap of the chosen material. Inherently multiplexable in the frequency domain and relatively simple to fabricate, KIDs pave the way to the large format focal plane array instruments necessary to conduct the next generation of cosmic microwave background (CMB), star formation, and galaxy evolution studies. In addition, non-linear kinetic inductance can be exploited to develop traveling wave kinetic inductance parametric amplifiers (TKIPs) based on superconducting delay lines to read out these instruments. I present my contributions to both large and small scale collaborative efforts to develop KID arrays, spectrometers integrated with KIDs, and TKIPs. I optimize a dual polarization TiN KID absorber for the next generation Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry, which is designed to investigate the role magnetic fields play in star formation. As part of an effort to demonstrate aluminum KIDs on sky for CMB polarimetry, I fabricate devices for three design variants. SuperSpec and WSpec are respectively the on-chip and waveguide implementations of a filter bank spectrometer concept designed for survey spectroscopy of high redshift galaxies. I provide a robust tool for characterizing the performance of all SuperSpec devices and demonstrate basic functionality of the first WSpec prototype. As part of an effort to develop the first W-Band (75-110 GHz) TKIP, I construct a cryogenic waveguide feedthrough, which enhances the Astronomical Instrumentation Laboratory’s capability to test W-Band devices in general. These efforts contribute to the continued maturation of these kinetic inductance technologies, which will usher in a new era of millimeter-wave astronomy. / Dissertation/Thesis / Doctoral Dissertation Astrophysics and Astronomy 2018