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Dissertations / Theses on the topic 'High vacuum'

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Published: 4 June 2021
Last updated: 12 February 2022

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1

Gieseler, Jan. "Dynamics of optically levitated nanoparticles in high vacuum." Doctoral thesis, Universitat Politècnica de Catalunya, 2014. http://hdl.handle.net/10803/144555.

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Nanotechnology was named one of the key enabling technologies by the European Commission and its tremendous impact was envisioned early by 20th century physicist R.Feynman in his now oft-quoted talk "Plenty of Room at the bottom". Nanotechnology and nanoscience deal with structures barely visible with an optical microscope, yet much bigger than simple molecules. Matter at this mesoscale is often awkward to explore as it contains too many atoms to be easily understood by straightforward application of quantum mechanics (although the fundamental laws still apply). Yet, these systems are not so large as to be completely free of quantum effects; thus, they do not simply obey the classical physics governing the macroworld. It is precisely in this intermediate regime, the mesoworld, that unforeseen properties of collective systems emerge. To fully exploit the potential of nanotechnology, a thorough understanding of these properties is paramount. The objective of the present thesis is to investigate and to control the dynamics of an optically levitated particle in high vacuum, a system which belongs to the broader class of nanomechanical oscillators. Nanomechanical oscillators exhibit high resonance frequencies, diminished active masses, low power consumption and high quality factors - significantly higher than those of electrical circuits. These attributes make them suitable for sensing, transduction and signal processing. Furthermore, nanomechanical systems are expected to open up investigations of the quantum behavior of mesoscopic systems. Testing the predictions of quantum theory on macroscopic scales is one of today's outstanding challenges of modern physics and addresses fundamental questions on our understanding of the world. The state-of-the-art in nanomechanics itself has exploded in recent years, driven by a combination of interesting new systems and vastly improved fabrication capabilities. Despite major break-throughs, including ground state cooling, observation of radiation pressure shot noise, squeezing and demonstrated ultra-high force and mass sensitivity, difficulties in reaching ultra-high mechanical quality (Q) factors still pose a major limitation for many of the envisioned applications and significant improvements in mechanical quality (Q) factors are generally needed to facilitate quantum coherent manipulation. This is difficult given that many mechanical systems are approaching fundamental limits of dissipation. To overcome the limitations set by dissipation, I developed an experiment to trap and cool nanoparticles in high vacuum. The combination of nanoparticles and vacuum trapping results in a very light and ultra-high-Q mechanical oscillator. In fact, the Q-factor achieved with this setup is the highest observed so far in any nano- or micromechanical system. The scope of the thesis ranges from a detailed description of the experimental apparatus and proof-of-principle experiments (parametric feedback cooling) to the first observation of phenomena owing to the unique parameters of this novel optomechanical system (thermal nonlinearities). Aside from optomechanics and optical trapping, the topics covered include the dynamics of complex (nonlinear) systems and the study of fluctuation theorems, the latter playing a pivotal role in statistical physics. Optically trapped nanoparticles are just beginning to emerge as a new class of optomechanical systems. Owing to their unique mechanical properties, there is clearly a vast and untapped potential for further research. Primary examples of how levitated particles in high vacuum can impact other fields and inspire new research avenues have been the first observation of thermal nonlinearities in a mechanical oscillator and the study of fluctuation relations with a high-Q nanomechanical resonator. Based on recent progress in the field, a plethora of fundamental research opportunities and novel applications are expected to emerge as this still young field matures.
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2

Coaker, Brian M. "Mechanisms for triggering high-voltage breakdown in vacuum." Thesis, Aston University, 1995. http://publications.aston.ac.uk/8236/.

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The electrical and optical characteristics of a cylindrical alumina insulator (94% Al203) have been measured under ultra-high vacuum (P < 10-8 mBar) conditions. A high-resolution CCD camera was used to make real-time optical recordings of DC prebreakdown luminescence from the ceramic, under conditions where DC current magnitudes were limited to less than 50μA. Two concentric metallized rings formed a pair of co-axial electrodes, on the end-face of the alumina tube; a third 'transparent' electrode was employed to study the effect of an orthogonal electric field upon the radial conduction processes within the metallized alumina specimen. The wavelength-spectra of the emitted light was quantified using a high-speed scanning monochromator and photo-multiplier tube detector. Concurrent electrical measurements were made alongside the recording of optical-emission images. An observed time-dependence of the photon-emission is correlated with a time-variation observed in the DC current-voltage characteristics of the alumina. Optical images were also recorded of pulsed-field surface-flashover events on the alumina ceramic. An intensified high-speed video technique provided 1ms frames of surface-flashover events, whilst 100ns frames were achieved using an ultra high-speed fast-framing camera. By coupling this fast-frame camera to a digital storage oscilloscope, it was possible to establish a temporal correlation between the application of a voltage-pulse to the ceramic and the evolution of photonic emissions from the subsequent surface-flashover event. The electro-optical DC prebreakdown characteristics of the alumina are discussed in terms of solid-state photon-emission processes, that are believed to arise from radiative electron-recombination at vacancy-defects and substitutional impurity centres within the surface-layers of the ceramic. The physical nature of vacancy-defects within an alumina dielectric is extensively explored, with a particular focus placed upon the trapped electron energy-levels that may be present at these defect centres. Finally, consideration is given to the practical application of alumina in the trigger-ceramic of a sealed triggered vacuum gap (TVG) switch. For this purpose, a physical model describing the initiation of electrical breakdown within the TVG regime is proposed, and is based upon the explosive destabilisation of trapped charge within the alumina ceramic, triggering the onset of surface-flashover along the insulator. In the main-gap prebreakdown phase, it is suggested that the electrical-breakdown of the TVG is initiated by the low-field 'stripping' of prebreakdown electrons from vacancy-defects in the ceramic under the influence of an orthogonal main-gap electric field.
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3

Barreto, Suzana Maria. "Towards autonomous sample positioning for ultra high vacuum chambers." Thesis, Aberystwyth University, 2018. http://hdl.handle.net/2160/77e7f40d-eb63-4062-bc1f-e5e4e7d102a9.

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Materials Science has in recent years become a high priority research area, having been identified as a growth sector for the UK economy over the next decade. Breakthroughs in this field are likely to have a significant impact on every area of our lives. There has recently been a trend toward automation at beamlines which is driven by rapid technology advancement. This technology advancement has improved the quality of experiment data and has allowed data collection times to improve exponentially. The Materials Science Research Group in the Institute of Mathematics, Physics and Computer Science, at Aberystwyth University have achieved international recognition for their research on materials under extreme conditions. They have a rich history in the development and use of specialist instruments to conduct real time surface analysis. Their custom made instrumentation has allowed them to greatly improve experiment throughput. Automation of the group's ultra high vacuum chambers is therefore a further enhancement that is advantageous, important, necessary and inevitable. This thesis presents the research undertaken to study what is required to provide automated sample positioning inside vacuum chambers that are operated under ultra high vacuum conditions, as the first step towards automation. As part of the research, a prototype automated positioning system that employs state of the art model based visual tracking techniques was developed to gain an understanding of the challenges the ultra high vacuum environment presents. Experimentation was carried out to assess the effects of different lighting conditions on tracking, evaluate the tracking library, extract suitable extrinsic parameters for tracker initialisation, and evaluate both monocular and stereo mode tracking. Key findings were that the model based tracking is a suitable approach for an automated positioning system but that performance depends on having suitable port placement for the cameras. Stereo tracking provided the best performance but was still prone to divergence at certain relative positions of the manipulator. On linear runs the average error was 0.06mm. On rotational runs, anti-clockwise runs proved better with an average error of 2o to 3o. The high errors of mixed rotational and linear tracking runs did not match the visual outputs indicating that there were inherent errors in the data evaluation. Tracking output video footage is available at [8]. More work is needed to take the system forward and close the tracking loop. Recommendations for improvements were provided.
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4

Beyer, Vivien. "A study of laser-induced incandescence under high vacuum conditions." Thesis, Cranfield University, 2006. http://hdl.handle.net/1826/1786.

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Laser-Induced Incandescence (LII) occurs when a high-energy pulsed laser beam encounters graphitic particulate matter particles like soot or carbon black. The particles absorb laser energy from the beam and see an increase in their internal energy, resulting in an increase of temperature. At the same time, the particles loose energy through heat transfer mechanisms. If the energy absorption rate is sufficiently high, particle temperature will rise to levels where significant incandescence (blackbody emission) can occur .Typically, Laser-Induced Incandescence produces 50ns to 1μs long light pulses at atmospheric pressure. So far, LII measurements had been restrained to conduction-dominated conditions, whereby signals are short-lived (less than one microsecond) and require sensitive nanosecond resolution instrumentation. This thesis introduces a novel LII – based measurement method performed under high vacuum conditions. The novelty of LII under vacuum resided in the fact that heat conduction away from the soot particle becomes negligible below 10-2 mbar and this constituted a step away from the typical situation, whereby laser absorption is followed by heat conduction from the particles to the surrounding medium. Instead, sublimation and radiative heat transfer would follow laser absorption. The consequence was the obtention of long-lived LII signals (up to 100 microseconds) and a large gain of photons (ranging between 50 to 300) emitted per primary soot particle during LII temperature decays. Furthermore, the refractive index function E(m) value could be determined directly from measured radiative temperature decays, with potentially an uncertainty of circa 7%, which outperformed current soot extinction measurements. In addition, for laser fluences below 0.06 J/cm2, a regime where only laser energy absorption and radiative heat transfer apply would be reached and LII signals became independent of particle size. Throughout this project, Laser-Induced Incandescence under vacuum was applied to a sample of carbon powder (agglomerated soot particles) sealed in a glass vessel and held below 10-3 mbar. Initial spectral measurements performed at a laser fluence of 0.3 J/cm2 confirmed the obtention of long-lived (60 microseconds long) blackbody spectra, which confirmed the feasibility of the technique and yielded an E(m) measurement of between 0.35 and 0.45. A second study was performed with a dualwavelength pyrometric system specifically designed for recording live LII temperatures and signal intensities coupled to an absolute light intensity calibrated intensified imaging system. Experimental results unveiled the thermo-physical behaviours of agglomerates enduring LII. The most remarkable outcomes of the results concerning carbon nanoparticles agglomerates were that: clusterous particulate matter absorbs and radiates light in a very similarly to single isolated carbon nanoparticles and therefore obey largely the Rayleigh limit; soot agglomerates also dissociate during LII in an explosive mode and ejecta were measured to reach up to 400 m/s following chain dissociations; complete agglomerate dissociations can be obtained and measurements performed on individual aggregates of primary soot nanoparticles. In parallel, LII measurements revealed that optical shielding is largely present within agglomerates, and therefore clusters dissociations exposed large quantities of particulate matter and increased greatly LII signal levels. Overall, radiative heat transfer measurements yielded E(m) = 0.4 to 0.6 and time-integrated ICCD measurements resolved signal levels as low as groups of 6 carbon nanoparticles. This sensitivity clearly was the highest recorded to date for Laser Induced Incandescence and the sensitivity boundary of the technique was increased to nearly resolving single nanoparticles. Further measurements were performed in collaboration with the National Research Council (NRC) of Ottawa, Canada, at the Combustion Research Group facility. The results obtained validated the obtention of repeatable temperature profiles for Laser- Induced Incandescence under vacuum. In addition, comparison between results obtained on a controlled source of agglomerates at atmospheric pressure established that the increase for LII signals with laser fluence for both atmospheric and vacuum conditions could be directly associated with agglomerates dissociations. Indeed, net diminutions in optical shielding were measured in both conditions and could be coupled with diminutions in thermal shielding at atmospheric pressures. Highresolution temperature measurements established that laser absorption, annealing, sublimation and radiative heat transfer rates could be unprecedently and directly measured by laser-induced incandescence under vacuum. Annealing and sublimation of soot primary particles could also reasonably be assumed to be the phenomena at the heart of agglomerate dissociations. It was also established that agglomerate dissociation was dependent not only on laser fluence but also on the instantaneous laser power absorbed by the carbon agglomerates: indeed measurements performed at NRC were effected with a instantaneous laser powers four times lower than previously and radiative heat transfer measurements attested incomplete agglomerate dissociations with E(m) values measured between 0.8 and 1. Overall, the present work introduces LII under vacuum as a high sensitivity measurement method for particulate matter. The sensitivities obtained approached nanoparticles resolution and constitutes one of the most sensitive particulate matter measurement technique to date with real-time measurements capability. Because of the sample studied, agglomerate dynamics during LII were unveiled for the first time and explained the increase of LII signals with laser fluence as a diminution of both thermal and optical shielding. The LII under vacuum technique also proved its ability to resolve and isolate some of the key phenomena occurring during LII: laser absorption, annealing, sublimation and heat radiation.
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5

Schambach, Philip [Verfasser]. "Tip-enhanced Raman spectroscopy in ultra-high vacuum / Philip Schambach." Berlin : Freie Universität Berlin, 2013. http://d-nb.info/104348079X/34.

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6

Benwell, Andrew L. "Flashover prevention on polystyrene high voltage insulators in a vacuum." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/5018.

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Thesis (M.S.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 18, 2008) Includes bibliographical references.
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7

Gieseler, Jan [Verfasser]. "Dynamics of optically levitated nanoparticles in high vacuum / Jan Gieseler." München : GRIN Verlag, 2015. http://d-nb.info/1175809705/34.

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8

Pires, Ellis John. "Electrical conductivity of single organic molecules in ultra high vacuum." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/56796/.

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Measurement of the I(V ) characteristics of single molecules is the first step towards the realisation of molecular electronic devices. In this thesis, the electronic transport properties of alkanedithiol (ADT) and alkylthiol-terminated oligothiophene molecules are investigated under ultra high vacuum (UHV) using a scanning tunnelling microscope (STM). Two techniques are employed that rely upon stochastic molecular bridge formation between gold STM tip and substrate; a novel I(V; s) method is proven to be a powerful alternative to the well-known I(s) method. For ADTs, three temperature-independent (180 - 390 K) conduction groups are identified, which arise from different contact-substrate coordination geometries. The anomalous reduction of conductance at small chain lengths reported by other groups for non-UHV conditions is far less pronounced here; all groups closely follow the anticipated exponential decay with chain length, β = (0.80 ± 0.01) Å ¹, until a small deviation occurs for the shortest molecule. Thus, the likely explanation for the anomalous effect is hydration of thiol groups. The I(V ) curves were fitted using a rectangular tunnel barrier model, with parameters in agreement with literature values; m = (0.32 ± 0.02) m, φ = 2 eV. For the oligothiophene molecules, one common temperature-independent (295-390 K) conduction group was identified; the conductance decays exponentially with molecular length, with different factors of β = (0.78 ± 0.15) Å ¹ and β = (0.16 ± 0:04) Å ¹ for length changes to the alkylthiol chains and thiophene backbone, respectively. An indented tunnel barrier model, anticipated from the physical and electronic structure of the molecules, was applied to fit the measured I(V ) curves; φ1 = φ3 = 2 eV, φ2 = 1.3 to 1.6 eV, m = 0.17 to 0.24 m. These UHV measurements provide an important baseline from which to better understand recent reports indicating hydration-dependent, and hydration-induced temperature-dependent, transport properties.
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9

Woodburn, Charles N. "Development of low-temperature, ultra high vacuum, scanning tunnelling microscope." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264506.

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10

Nick, Schwartz Nick (Nick Raoul). "Design and construction of high-temperature, high-vacuum tensile tester for fusion reactor materials." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119939.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 24-25).
Fusion energy is a promising carbon-free, limitless source of energy that could contribute to mitigating global climate change. One of the critical challenges in realizing fusion energy is the survival of structural materials in the extreme environment of a fusion device. Specifically, materials that surround the 100 million °C plasma must survive high temperatures (>500 °C), intense thermal cycling, transient high heat loads, large structural forces during off-normal plasma events, and exposure to high energy neutrons. Neutron exposure leads to high levels of radiation damage, which results in changes to critical material properties such as ductility and strength. In order to facilitate a better understanding of the effect of radiation on fusion material properties at high temperatures, a novel high-vacuum (<106 torr), high-temperature (<1000°C), tensile testing stand for irradiated specimens was designed and constructed. The test stand was designed to perform tensile testing of structural materials that have been irradiated by 12 MeV protons, which emulate the material response to high-energy neutrons produced in a deuterium-tritium burning fusion device. The specimen will then be heated to 500-1000 °C and tensile tested in high vacuum to eliminate sample oxidation and provide clean measurements. The design and fabrication of the test stand are given in this thesis, and first results from its commissioning are presented.
by Nick Schwartz.
S.B.
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11

Schiappacasse, Enrico D. "Beyond Semiclassical Gravity| Quantum Stress Tensor Fluctuations in the Vacuum." Thesis, Tufts University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10812605.

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Large vacuum fluctuations of a quantum stress tensor can be described by the asymptotic behavior of its probability distribution. Here we focus on stress tensor operators which have been averaged with a sampling function in time. The Minkowski vacuum state is not an eigenstate of the time-averaged operator, but can be expanded in terms of its eigenstates. We calculate the probability distribution and the cumulative probability distribution for obtaining a given value in a measurement of the time-averaged operator taken in the vacuum state. In these calculations, we use the normal ordered square of the time derivative of a massless scalar field in Minkowski spacetime as an example of a stress tensor operator. We analyze the rate of decrease of the tail of the probability distribution for different temporal sampling functions, such as compactly supported functions and the Lorentzian function. We find that the tails decrease relatively slowly, as exponentials of fractional powers, in agreement with previous work using the moments of the distribution. Our results lead additional support to the conclusion that large vacuum stress tensor fluctuations are more probable than large thermal fluctuations, and may have observable effects.

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12

Baily, Christopher John. "UHV studies of the adsorption of small adsorbate molecules on low index platinum single crystals." Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288413.

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13

Multone, Xavier. "High vacuum chemical vapor deposition (HV-CVD) of alumina thin films /." [S.l.] : [s.n.], 2009. http://library.epfl.ch/theses/?nr=4485.

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14

Welsh, David S. "Current density limitations in a fast-pulsed high-voltage vacuum diode." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23850.

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Approved for public release: distribution is unlimited.
An investigation into the limitations on the enhanced field-emitted current density in a fast-pulsed (rise-time = ns), high voltage (> 106 V), 1-inch vacuum diode was conducted using a computer simulation based on the Fowler-Nordheim equation. Oscillations in the emitted current density (due to the change in the amount of space charge within the gap) were found to quickly decay into a final steady-state for the voltages applied. Steady-state values for a wide variety of work functions, electric field enhancement factors (based on the theory that "whiskers" on the cathode surface experience varying degrees of enhancement), and applied potentials were compared to two benchmarks: the amount of current density required to explode a whisker in < 10 ns by joule heating (J E = 109 A/cm2 ); and the Child-Langmuir (C-L) spacecharge- limited current density. Steady-state values were found to be less than J E . One model of the formation process of a plasma at the cathode surface requires that J E be met or exceeded by the steady-state value. Thus, such a model is not supported by this project's findings. The C-L limit is based on a thermionic-type emission process. As only pure field emission (i.e., no thermionic emission included) was considered, the steady-state values were, in all conclusive cases, less than the corresponding C-L limited values.
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15

Kiefer, Florian [Verfasser]. "Multi-Effect Vacuum Membrane Distillation for High-Recovery Desalination / Florian Kiefer." München : Verlag Dr. Hut, 2020. http://d-nb.info/1219470961/34.

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16

Jang, Yuseong. "High resolution time-resolved imaging system in the vacuum ultraviolet region." Master's thesis, University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6293.

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High-power debris-free vacuum ultraviolet (VUV) light sources have applications in several scientific and engineering areas, such as high volume manufacturing lithography and inspection tools in the semiconductor industry, as well as other applications in material processing and photochemistry. For the past decades, the semiconductor industry has been driven by what is called "Moore's Law". The entire semiconductor industry relies on this rule, which requires chip makers to pack transistors more tightly with every new generation of chips, shrinking the size of transistors. The ability to solve roadmap challenges is, at least partly, proportional to our ability to measure them. The focus of this thesis is on imaging transient VUV laser plasma sources with specialized reflective imaging optics for metrology applications. The plasma dynamics in novel laser-based Zinc and Tin plasma sources will be discussed. The Schwarzschild optical system was installed to investigate the time evolution of the plasma size in the VUV region at wavelengths of 172 nm and 194 nm. The outcomes are valuable for interpreting the dynamics of low-temperature plasma and to optimize laser-based VUV light sources.
M.S.
Masters
Optics and Photonics
Optics and Photonics
Optics and Photonics
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17

Al-Rawi, S. A. N. "Silicon sublimation at ultra high vacuum with microprocessor monitoring and measurements." Thesis, University of Kent, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382189.

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18

ZHOU, CAIXIA. "HIGH THROUGHPUT pKa DETERMINATION BY VACUUM-ASSISTED MULTIPLEXED CAPILLARY ELECTROPHORESIS (VAMCE)." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1078413797.

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19

Callahan, Michael O. "X-ray pulse considerations and electron flow in high voltage vacuum diodes." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA277301.

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Thesis (M.S. in Physics) Naval Postgraduate School, December 1993.
Thesis advisor(s): Fred R. Schwirzke, Xavier K. Maruyama. "December 1993." Cover title: X-ray ... voltage diodes. Includes bibliographical references. Also available online.
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20

Hoefer, Ulrike Martina. "Design and development of a high-speed motor for a vacuum pump." Thesis, University of Newcastle Upon Tyne, 2008. http://hdl.handle.net/10443/758.

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Turbomolecular pumps require a motor to drive them at speeds of up to 90,000 rpm. These high-speed motors are typically brushless permanent magnet motors that are specifically designed for the application. Intellectual property rights over the design lock the company into one single supplier. Also low manufacturing volumes make the motor expensive to produce. To stay competitive continuous cost reductions or product improvements are necessary. This can only be achieved by looking at new materials, alternative manufacturing methods and simplified assembly processes. The aim of this project is to replace an existing laminated, high-speed (60,000rpm) motor with a new low-cost design. Special considerations need to be given to the motor design with regards to minimising losses due to the high operating speed and the fact that the motor operates in a vacuum. A machine design employing a simple, 3-tooth segmented stator made from soft magnetic composites (SMC) and using non-overlapping coils, and a `deep' plastic bonded magnet on the rotor is proposed to deliver low rotor losses and low manufacturing costs. Four SMC prototype motors have been built, which have led to the following discoveries: (1) Bulk eddy currents in the SMC material cannot be neglected and need to be taken into account separately as a function of the actual component size and shape. (2) A process is suggested to improve the iron loss calculation in SMC, which is evaluated against the prototypes built. (3) SMC material properties are adversely affected by prototype machining, leading to higher iron losses than initially expected. (4) The segmented SMC design has proven to be commercially very attractive. During testing a large sensitivity of the magnetically supported pump shaft to the inherent unbalanced magnetic pull (UMP) force of the 3-tooth, 2-pole design was discovered. This led to a practical and theoretical study into the effects of UMP in this application. An alternative design that avoided the inherent UMP was required, and a 6- tooth, 4-pole motor has been designed and built. For reasons of minimising risks laminations were chosen as the stator material rather than SMC. Test results of this motor in the pump have been successful and the motor has been selected to go into the next generation of turbomolecular pumps.
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Ebert, Helen Diane. "The study of adsorbed species using electrochemical and ultra high vacuum techniques." Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255669.

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22

ʿAẓīm, Muḥammad. "Ultra high vacuum-scanning electron microscope studies of Cs/Si(100)-2x1." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385984.

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23

MENDONZA, CESAR AUGUSTO DIAZ. "PHOSPHORUS INCORPORATION IN SINGLE WALL CARBON NANOTUBES PRODUCED BY HIGH VACUUM CVD." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2014. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=24237@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
Neste trabalho estudamos a síntese e caracterização de nanotubos de carbono de paredes simples com incorporação de fósforo. Os nanotubos foram produzidos em duas diferentes temperaturas (800 e 850 Graus Celsius), usando um precursor em pó (fase sólida) sem diluição em nenhum liquido. O sistema utilizado na síntese foi o CVD em alto vácuo. Para a caracterização comparamos as amostras incorporadas com SWNTs crescidos com etanol. Usamos a espectroscopia Raman, espectroscopia de fotoelétrons induzida por raios x (XPS) e microscopia eletrônica de transmissão (TEM) para caracterizar as amostras. A espectroscopia Raman e a microscopia eletrônica de transmissão foram usadas para confirmar a presença de SWNTs na amostra. Encontramos evidencia de que o fósforo foi incorporado nas amostras ao compararmos os espectros Raman dos SWNTs com amostra de referência. A partir dos resultados de XPS, observamos a presença de fósforo ligado a átomos de carbono que nós faz concluir que houve incorporação de fósforo nos nanotubos.
In this work was studied the synthesis and characterization of single wall carbon nanotubes (SWCN) with phosphorus incorporation. The nanotubes were produced in two different temperatures (800 and 850 Degrees Celsius), using a powder precursor (solid phase) without liquid dilution. The system used for the synthesis was High Vacuum Chemical Vapor Deposition (HVCVD). The samples were characterized comparing the samples with phosphorus with SWNT synthetized with ethanol. Raman spectroscopy, x-ray photoelectron spectroscopy (XPS) on transmission electron microscopy (TEM) were employed to characterize the samples. The Raman spectroscopy and TEM were employed to confirm the presence of SWNT in the samples. We found evidences that phosphorus were incorporated comparing the Raman spectra with the reference sample. The XPS results showed the presence of phosphorus atoms bonded to carbon atoms which make us conclude that the phosphorus were incorporated to the nanotubes.
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au, E. Mohamed@murdoch edu, and Eman Mohamed. "Microcrystalline Silicon Thin Films Prepared by Hot-Wire Chemical Vapour Deposition." Murdoch University, 2004. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20050421.133523.

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Silicon is widely used in optoelectronic devices, including solar cells. In recent years new forms of silicon have become available, including amorphous, microcrystalline and nano-crystalline material. These new forms have great promise for low cost, thin film solar cells and the purpose of this work is to investigate their preparation and properties with a view to their future use in solar cells. A Hot Wire-Deposition Chemical Vapour Deposition CVD (HW-CVD) system was constructed to create a multi-chamber high vacuum system in combination with an existing Plasma Enhanced Chemical Vapour Deposition (PECVD) system; to study the amorphous to crystalline transition in silicon thin films. As the two chambers were linked by a common airlock, it was essential to construct a transfer mechanism to allow the transfer of the sample holder between the two systems. This was accomplished by the incorporation of two gate valves between the two chambers and the common airlock as well as a rail system and a magnetic drive that were designed to support the weight of, and to guide the sample holder through the system. The effect of different deposition conditions on the properties and structure of the material deposited in the combined HW-CVD:PECVD system were investigated. The conditions needed to obtain a range of materials, including amorphous, nano- and microcrystalline silicon films were determined and then successfully replicated. The structure of each material was analysed using Transmission Electron Microscopy (TEM). The presence of crystallites in the material was confirmed and the structure of the material detected by TEM was compared to the results obtained by Raman spectroscopy. The Raman spectrum of each sample was decoupled into three components representing the amorphous, intermediate and crystalline phases. The Raman analysis revealed that the amorphous silicon thin film had a dominant amorphous phase with smaller contribution from the intermediate and crystalline phase. This result supported the findings of the TEM studies which showed some medium range order. Analysis of the Raman spectrum for samples deposited at increasing filament temperatures showed that the degree of order within the samples increased, with the evolution of the crystalline phase and decline of the amorphous phase. The Selected Area Diffraction (SAD) patterns obtained from the TEM were analysed to gain qualitative information regarding the change in crystallite size. These findings have been confirmed by the TEM micrograph measurements. The deposition regime where the transition from amorphous to microcrystalline silicon took place was examined by varying the deposition parameters of filament temperature, total pressure in the chamber, gas flow rate, deposition time and substrate temperature. The IR absorption spectrum for ƒÝc-Si showed the typical peaks at 2100cm-1 and 626cm-1, of the stretching and wagging modes, respectively. The increase in the crystallinity of the thin films was consistent with the evolution of the 2100cm-1 band in IR, and the decreasing hydrogen content, as well as the shift of the wagging mode to lower wavenumber. IR spectroscopy has proven to be a sensitive technique for detecting the crystalline phase in the deposited material. Several devices were also constructed by depositing the ƒÝc-Si thin films as the intrinsic layer in a solar cell, to obtain information on their characteristics. The p- layer (amorphous silicon) was deposited in the PECVD chamber, and the sample was then transferred under vacuum using the transport system to the HW-CVD chamber where the i-layer (microcrystalline silicon) was deposited. The sample holder was transferred back to the PECVD chamber where the n-layer (amorphous silicon) was deposited. The research presented in this thesis represents a preliminary investigation of the properties of ƒÝc-Si thin films. Once the properties and optimum deposition characteristics for thin films are established, this research can form the basis for the optimization of a solar cell consisting of the most efficient combination of amorphous, nano- and microcrystalline materials.
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25

Newton, Mark A. "Alloy effects in catalysis : the structure and reactivity of the CuPd[85:15]{110}p(2x1) surface." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240235.

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26

Gedik, Abdullah. "Energy threshold for laser induced breakdown on a metal surface under high and ultra high vacuum conditions." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28165.

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27

Lain, amador Lucia. "Production of ultra-high-vacuum chambers with integrated getter thin-film coatings by electroforming." Thesis, Bourgogne Franche-Comté, 2019. http://www.theses.fr/2019UBFCD006/document.

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Des couches minces co-deposées de Titanium Zirconium Vanadium (TiZrV) sont utilisés dans les accélérateurs de particules et les sources de lumière synchrotron pour maintenir les conditions d’ultravide. Elles sont pulvérisés sur les parois internes des chambres à vides, transformant celles-ci en « pompe chimique de gaz ». La tendance dans la conception d’accélérateurs d’électrons consiste à approcher les pôles des aimants de direction au plus près du faisceau d’électrons. Cela implique la réduction du diamètre des tubes hébergeant le vide et nécessite l’utilisation de très petits diamètres pour les chambres à vide. L’application du dépôt par vaporisation physique (PVD) dans un aussi faible diamètre devient alors très difficile. Le but de ce projet est de développer une nouvelle procédure de dépôt couplé à l’assemblage, en utilisant un mandrin sacrificiel en aluminium comme substrat de la couche mince en même temps que la création autour de lui de la chambre à vide elle-même par électroformage de cuivre. La première partie de l’étude concerne la production et la caractérisation de chambre de cuivre électroformées. La robustesse mécanique de l’assemblage complet a été validée, et les caractéristiques du film lui-même sont etudièes par microscopie électronique à balayage (MEB), diffraction des rayons X (DRX), spectrométrie de fluorescence-X (XRF) et spectrométrie de photoélectrons X (XPS). De plus, les performances de « pompage chimique des gaz » des nouvelles chambres à vide ainsi élaborées sont mesurées et comparées avec des valeurs de références de revêtements déposés par des procédures classiques dans des tubes de plus grand diamètres. La deuxième partie de l‘étude concerne l’évaluation des impuretés incluses lors des différentes étapes du procédé : le revêtement PVD, l’électroformage et l’étape de dissolution chimique du mandrin. La spectrométrie de désorption thermique et les profils de composition en épaisseur par XPS permettent de quantifier les impuretés dans le cuivre électroformé et dans le film de TiZrV. De plus, la présence d’hydrogène emprisonné dans le cuivre électroformé est étudiée à partir de différents bains à base de sulfate de cuivre. L’un d’entre eux, sans additifs, nécessite l’utilisation de courants pulsés. Le comportement électrochimique du bain permet la sélection de différents paramètres de séquences de pulses, dérivées de situations typiques des courbes transitoires. Finalement, le développement de prototypes de taille réelle a été atteint avec la création de chambres à vide revêtues de TiZrV de 2 mètres de long et 4mm de diamètre, ce qui n’a pas d’équivalent à ce jour
Titanium Zirconium Vanadium (TiZrV) thin film coatings are used in particle accelerators and synchrotron light sources to maintain ultra-high vacuum conditions. They are deposited on the internal walls of the vacuum chambers, transforming them from a gas source into a chemical pump. The trend in electron accelerators design consists in approaching the poles of the steering magnets close to the electron beam. This implies reducing the bore hosting the vacuum chamber and using very small diameter vacuum pipes. The application of physical vapor deposition (PVD) in such small diameter chambers becomes then very difficult. The aim of this project is to develop a novel procedure of coating/assembly, using a sacrificial aluminium mandrel as substrate of the thin film together with the creation of a surrounding copper chamber by electroforming. The first part of the study deals with the production and characterization of the electroformed chambers. The mechanical robustness of the assembly is checked, and the film characterization is performed by secondary electron microscopy (SEM), X-ray diffraction analysis (XRD), X-ray Fluorescence Spectroscopy (XRF) and X-Ray Photoelectron Spectroscopy (XPS). Moreover, the pumping performance is measured and compared with reference values of coatings produced by the standard PVD technique. The second part of the study evaluates the impurities included during the different steps of the process: PVD coating, electroforming and chemical etching of the mandrel. Thermal desorption spectroscopy and XPS depth profiling allow to quantify the impurities in the electroformed copper and the TiZrV thin film. Furthermore, the presence of hydrogen trapped in the electroformed copper is studied for different copper sulphate baths. One of them, without additives, require the use of pulse currents. The electrochemical behaviour of the bath allows the selection of different pulse parameters, derived from typical situations on the transient curves. Finally, the development of real-scale prototypes was achieved with the creation of a 4 mm diameter, 2 meters TiZrV coated vacuum chamber, which is unrivalled up to date
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28

Grimes, Mikal Keola. "Vacuum heating absorption and expansion of solid surfaces induced by intense femtosecond laser irradiation /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.

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29

Talib, Zeeshan. "Investigation of Fast High Voltage PDC Measurement based on a Vacuum Reed-switch." Thesis, KTH, Elektroteknisk teori och konstruktion, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91924.

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The diagnostic technique, polarization and depolarization current (PDC) is useful for insulation testing. It requires applying a DC step voltage to the test sample and measuring the current. To measure fast PDC phenomena a fast step is needed. One way of applying a fast high voltage step is to use power electronic switches. Series connection can be used to increase the voltage limit, but this result in unequal voltage sharing unless equipped with voltage balancing. In this work a high voltage vacuum reed switch is investigated as a simple and low-cost alternative to power electronic switches, handling up to 10 kV with a single device. The switch turn on and off behavior was studied. It was found that the initial turn-on is good, in the range of nanoseconds, but there is a problem with the vacuum recovering its insulating properties at low currents before the contacts fully close. The required output voltage level is therefore obtained only after a further settling time that increases with increased input voltage and is much longer than the initial breakdown, e.g. 20 µs for the case of 4.5 kV input voltage. Other limitations of the fast high voltage PDC were also studied. The output voltage was measured across the test sample without adding an intentional resistor in the circuit. There were large oscillations for 1 µs but these oscillations are damped due to inherent resistance of the connecting leads, series resistance of the capacitors and resistance of the reed switch. A comparison is made between the measured and the simulated results using MATLAB to see the effect of parasitic inductance. A damping resistor was added in the circuit and the output results were again compared. With the addition of the damping resistor, the number of oscillations were reduced and their time scale was limited to 0.1 µs . An analysis is made at the end which describes the limitation occurring in determining the high frequency component of PDC. The current during the step is many orders of magnitude higher than the polarization current even at 1 µs , so measurement of the current and protection of the apparatus is not trivial.
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30

Lee, King Hung. "Ellipsometric studies of the nucleation of zinc sulphide films in ultra-high vacuum." Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335519.

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31

Squires, Matthew B. "High repetition rate Bose-Einstein condensate production in a compact, transportable vacuum system." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3303829.

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32

Schmid, Nehir. "High Magnetic Field in Low Temperature Vacuum Conditions : Magnet Design, Modeling and Testing." Thesis, Luleå tekniska universitet, Rymdteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-82093.

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The Swiss Free Electron Laser (SwissFEL) at the Paul Scherrer Institute is a national prestige project that will enable ground breaking new x-ray scattering experiments in areas such as biology, chemistry and physics. A plannedactivity is to generate possibility for x-ray diffraction under high pulsed magnetic fields to explore quantum mattermaterials. In fact, an entire beam line (CristallinaQ), dedicated to extreme sample environment (vacuum, electro-magnetic field, low temperature).This Master’s thesis project concerns the development of a magnet system for pulsed magnetic fields to be synchronised with the free electron laser pulses. The system is based on small-sized coils. This makes the systemtransportable and avoids the huge financial challenges and power requirements of the magnets at pulsed fields laboratories at Toulouse, Dresden or Tallahassee. Ultimately the magnet shall provide large pulsed fields of more than 30 T under conditions very similar to space, i.e. vacuum, low-temperature.The thesis presents the development of a complete coil manufacture and testing setup including a capacitor bank topower the magnet. With planned upgrades of the equipment, the coil manufacturing process is reaching reproduceable levels. I produce a first iteration of magnet coils. They follow a classical copper conductor design reinforcedwith an epoxy-Zylon matrix. During testing we produced 15 Tesla fields without degradation of the coils. At lastI analyse the observations from the tests and propose improvements and future steps for the further developmentof the magnet.
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33

Höfer, Katharina. "All in situ ultra-high vacuum study of Bi2Te3 topological insulator thin films." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-220737.

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The term "topological insulator" (TI) represents a novel class of compounds which are insulating in the bulk, but simultaneously and unavoidably have a metallic surface. The reason for this is the non-trivial band topology, arising from particular band inversions and the spin-orbit interaction, of the bulk. These topologically protected metallic surface states are characterized by massless Dirac dispersion and locked helical spin polarization, leading to forbidden back-scattering with robustness against disorder. Based on the extraordinary features of the topological insulators an abundance of new phenomena and many exciting experiments have been proposed by theoreticians, but still await their experimental verification, not to mention their implementation into applications, e.g. the creation of Majorana fermions, advanced spintronics, or the realization of quantum computers. In this perspective, the 3D TIs Bi2Te3 and Bi2Se3 gained a lot of interest due to their relatively simple electronic band structure, having only a single Dirac cone at the surface. Furthermore, they exhibit an appreciable bulk band gap of up to ~ 0.3 eV, making room temperature applications feasible. Yet, the execution of these proposals remains an enormous experimental challenge. The main obstacle, which thus far hampered the electrical characterization of topological surface states via transport experiments, is the residual extrinsic conductivity arising from the presence of defects and impurities in their bulk, as well as the contamination of the surface due to exposure to air. This thesis is part of the actual effort in improving sample quality to achieve bulk-insulating Bi2Te3 films and study of their electrical properties under controlled conditions. Furthermore, appropriate capping materials preserving the electronic features under ambient atmosphere shall be identified to facilitate more sophisticated ex-situ experiments. Bi2Te3 thin films were fabricated by molecular beam epitaxy (MBE). It could be shown that, by optimizing the growth conditions, it is indeed possible to obtain consistently bulk-insulating and single-domain TI films. Hereby, the key factor is to supply the elements with a Te/Bi ratio of ~8, while achieving a full distillation of the Te, and the usage of substrates with negligible lattice mismatch. The optimal MBE conditions for Bi2Te3 were found in a two-step growth procedure at substrate temperatures of 220°C and 250°C, respectively, and a Bi flux rate of 1 Å/min. Subsequently, the structural characterization by high- and low-energy electron diffraction, photoelectron spectroscopy, and, in particular, the temperature-dependent conductivity measurements were entirely done inside the same ultra-high vacuum (UHV) system, ensuring a reliable record of the intrinsic properties of the topological surface states. Bi2Te3 films with thicknesses ranging from 10 to 50 quintuple layers (QL; 1QL~1 nm) were fabricated to examine, whether the conductivity is solely arising from the surface states. Angle resolved photoemission spectroscopy (ARPES) demonstrates that the chemical potential for all these samples is located well within the bulk band gap, and is only intersected by the topological surface states, displaying the characteristic linear dispersion. A metallic-like temperature dependency of the sheet resistance is observed from the in-situ transport experiments. Upon going from 10 to 50QL the sheet resistance displays a variation by a factor 1.3 at 14K and of 1.5 at room temperature, evidencing that the conductivity is indeed dominated by the surface. Low charge carrier concentrations in the range of 2–4*10^12 cm^−2 with high mobility values up to 4600 cm2/Vs could be achieved. Furthermore, the degradation effect of air exposure on the conductance of the Bi2Te3 films was quantified, emphasizing the necessity to protect the surface from ambient conditions. Since the films behave inert to pure oxygen, water/moisture is the most probable source of degeneration. Moreover, epitaxially grown elemental tellurium was identified as a suitable capping material preserving the properties of the intrinsically insulating Bi2Te3 films and protecting from alterations during air exposure, facilitating well-defined and reliable ex-situ experiments. These findings serve as an ideal platform for further investigations and open the way to prepare devices that can exploit the intrinsic features of the topological surface states
Der Begriff "Topologischer Isolator" (TI) beschreibt eine neuartige Klasse von Verbindungen deren Inneres (engl. Bulk) isolierend ist, dieses Innere aber gleichzeitig und zwangsläufig eine metallisch leitende Oberfläche aufweist. Dies ist begründet in der nicht-trivialen Topologie dieser Materialien, welche durch eine spezielle Invertierung einzelner Bänder in der Bandstruktur und der Spin-Bahn-Kopplung im Materialinneren hervorgerufen ist. Diese topologisch geschützten, metallischen Oberflächenzustände sind gekennzeichnet durch eine masselose Dirac Dispersionsrelation und gekoppelte Helizität der Spinpolarisation, welche die Rückstreuung der Ladungsträger verbietet und somit zur Stabilisierung der Zustände gegenüber Störungen beiträgt. Auf Grundlage dieser außergewöhnlichen Merkmale haben Theoretiker eine Fülle neuer Phänomene und spannender Experimente vorhergesagt. Deren experimentelle Überprüfung steht jedoch noch aus, geschweige denn deren Umsetzung in Anwendungen, wie zum Beispiel die Erzeugung von Majorana Teilchen, fortgeschrittene Spintronik, oder die Realisierung von Quantencomputern. Aufgrund ihrer relativ einfachen Bandstruktur, welche nur einen Dirac-Kegel an der Oberfläche aufweist, haben die 3D TI Bi2Te3 und Bi2Se3 in den letzten Jahren großes Interesse erlangt. Weiterhin besitzen diese Materialien eine merkliche Bandlücke von bis zu ~0,3 eV, welche sogar Anwendungen bei Raumtemperatur ermöglichen könnten. Dennoch ist deren experimentelle Umsetzung nachwievor eine enorme Herausforderung. Das Haupthindernis, welches bis jetzt insbesondere die elektrische Charakterisierung the topologischen Oberflächenzustände behindert hat, ist die zusätzliche Leitfähigkeit des Materialinneren, welche durch Kristalldefekte und Beimischungen, sowie die Verunreinigung der Probenoberfläche durch Luftexposition bedingt wird. Die vorliegende Arbeit liefert einen Beitrag zu aktuellen den Anstrengungen in der Verbesserung der Probenqualität der TI um die Leitfähigkeit des Materialinneren zu unterdrücken, sowie die anschließende Untersuchung der elektrischen Eigenschaften unter kontrollierten Bedingungen durchzuführen. Weiterhin sollen geeignete Deckschichten identifiziert werden, welche die besonderen elektronischen Merkmale der TI nicht beeinflussen sowie diese gegen äußere Einflüsse schützen, und somit die Durchführung anspruchsvoller ex situ Experimente ermöglichen können. Die untersuchten Bi2Te3 Schichten wurden mittels Molekularstrahlepitaxie (MBE) hergestellt. Es konnte gezeigt werden, dass es allein durch Optimierung der Wachstumsbedingungen möglich ist Proben herzustellen, die gleichbleibend isolierende Eigenschaften des TI Inneren aufweisen und Eindomänen-Ausrichtung besitzen. Die zentralen Faktoren sind hierbei die Aufrechterhaltung eines Flussratenverhältnisses von Te/Bi ~8 der einzelnen Elemente, sowie die Wahl einer ausreichend hohen Substrattemperatur, um ein vollständiges Abdampfen (Destillation) des überschüssigen Tellur zu erreichen. Weiterhin müssen Substrate mit gut angepassten Gitterparametern verwendet werden, welches bei BaF2 (111) gegeben ist. Optimales MBE Wachstum konnte durch ein Zwei-Stufen Prozess bei Substrattemperaturen von 220°C und 250°C und einer Bi-Verdampfungsrate von 1 Å/min erreicht werden. Die nachfolgende Charakterisierung der strukturellen Eigenschaften, Photoelektronenspektroskopie, sowie temperaturabhängige Leitfähigkeitsmessungen wurden alle in einem zusammenhängenden Ultrahochvakuum-System durchgeführt. Auf diese Weise wird eine zuverlässige Erfassung der intrinsischen Eigenschaften der TI sichergestellt. Zur Überprüfung, ob die Leitfähigkeit der Proben tatsächlich nur durch die Oberflächenzustände hervorgerufen wird, wurden Filme mit Schichtdicken im Bereich von 10 bis 50 Quintupel-Lagen (QL; 1QL~ 1 nm) hergestellt und charakterisiert. Winkelaufgelöste Photoelektronenspektroskopie (ARPES) belegt, dass das chemische Potential (Fermi-Niveau) in allen Proben innerhalb der Bandlücke der Bandstruktur des Materialinneren liegt und nur von den topologisch geschützten Oberflächenzuständen gekreuzt wird, welche die charakteristische lineare Dirac Dispersionsrelation aufweisen. Die temperaturabhängigen Widerstandsmessungen zeigen ein metallisches Verhalten aller Proben. Bei der Variation der Schichtdicke von 10 zu 50QL wird eine Streuung des Flächenwiderstandes vom Faktor 1,3 bei 14K und 1,5 bei Raumtemperatur beobachtet. Dies beweist, dass die gemessene Leitfähigkeit vorrangig durch die topologisch geschützten Oberflächenzustände hervorgerufen wird. Eine geringe Oberflächenladungsträgerkonzentration im Bereich von 2–4*10^12 cm^−2 und hohe Mobilitätswerte von bis zu 4600 cm2/Vs wurden erreicht. Weiterhin wurden die negativen Auswirkungen auf die Eigenschaften der TI durch Luftexposition quantifiziert, welches die Notwendigkeit belegt, die Oberfläche der TI vor Umgebungseinflüssen zu schützen. Die Proben verhalten sich inert gegenüber reinem Sauerstoff, daher ist Wasser aus der Luftfeuchte höchstwahrscheinlich der Hauptgrund für die beobachtbare Verschlechterung. Darüber hinaus konnte epitaktisch gewachsenes Tellur als geeignete Deckschicht ausfindig gemacht werden, welches die Eigenschaften der Bi2Te3 Filme nicht beeinflusst, sowie gegen Veränderungen durch Luftexposition schützt. Die gewonnenen Erkenntnisse stellen eine ideale Grundlage für weiterführende Untersuchungen dar und ebnen den Weg zur Entwicklung von Bauelementen welche die spezifischen Besonderheiten der topologischen Oberflächenzustände
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34

Mayhew, Christopher Anthony. "The high resolution vacuum ultraviolet absorption spectra of group VI dihydrides and deuterides." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37778.

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35

Chew, Andrew David. "A rotating disc gauge for absolute total pressure measurement in a high vacuum." Thesis, University of York, 1993. http://etheses.whiterose.ac.uk/10874/.

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36

Hann, Raiford Eugene. "Phase equilibria of the high-baria portion of the BaO-CaO-Al[subscript]2O[subscript]3 system." Diss., Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/19105.

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37

Hamann, Christian [Verfasser]. "An Electrospray Ion Source for Ultra-High Vacuum Deposition of Organic Molecules / Christian Hamann." Kiel : Universitätsbibliothek Kiel, 2011. http://d-nb.info/104859226X/34.

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38

Fostner, Shawn. "Ultra high vacuum fabrication of metallic contacts for molecular devices on an insulating surface." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=95011.

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The preparation and characterization of metallic wires on insulating substrates by a variety of mechanisms has been explored. A multi-scale approach utilizing microfabricated silicon stencil masks, feedback controlled electromigration, and field induced metal cluster deposition in a novel geometry has been explored on potassium bromide (KBr), indium phosphide (InP), and silicon oxide substrates in an ultra-high vacuum environment (UHV). The initial deposition of gold, and tantalum wires between one hundred nanometers and micrometers in size was performed using reinforced silicon nanostencils. The stencil fabrication was discussed, and an examination of the deformation of the integrated structures under the deposition of highly stressed tantalum films was shown to be significantly smaller than typical structures. Metallic wires deposited using these stencils as well as electron beam lithography were electrically stressed and the breaking characteristics analyzed. Typical nanometer scale gaps were observed, as well as larger features more commonly found in the breaking of bamboo-like structures in gold wires 100 nm in size or less, particularly with a significant series resistance. These larger gaps are expected to be more applicable for the deposition of subsequent metallic clusters and preparation of molecular devices. As a step towards connecting the initially deposited wires as well as localized molecules in an a fashion allowing atomic scale imaging by AFM, modelling and experiments of field induced deposition of gold clusters on KBr and InP substrates was carried out. Deposition on InP substrates with a backside 2D electron gas as a counter-electrode demonstrated the feability of this deposition technique in UHV. Subsequent depositions on or adjacent to metallic pads on the bulk insulating KBr provided a proof of principle of the technique, though some experimental limitations such as large current pulses with the tip in close proximity to the surface are d
La préparation et la caractérisation de fils métalliques sur des substrats isolants par une variété de mécanismes a été explorée. Une approche multi-échelle utilisant des masques-stencils microfabriqués de silicium, l'électromigration contrôlée par rétroaction, et le dépôt induit par champ en nouvelle géométrie d'agrégats métalliques, a été explorée sur des substrats de bromure de potassium (KBr), de phosphure d'indium (InP) et d'oxyde de silicium sous Ultra Haut Vide (UHV). Le dépôt initial de fils d'or et de tantale entre cent nanomètres et quelques micromètres a été réalisé en utilisant des nanostencils au silicium renforcé. La fabrication des stencils a été discutée, et un examen de la déformation des structures intégrées dans le cas du dépôt de couches de tantale sous hautes contraintes a montré qu'elle était significativement plus petite que pour les structures typiques. Les fils métalliques déposés à l'aide de ces stencils, ainsi que la lithographie par faisceau électronique ont été mis sous contrainte électriquement et les caractéristiques de rupture analysées. Des vides typiques à l'échelle du nanomètre ont été observés, ainsi que des structures communément retrouvées dans la rupture de structure de type bambou dans les fils d'or de 100nm et moins, en particulier avec une résistance en série importante. Ces vides plus grands devraient être plus applicables pour le dépôt par la suite d'agrégats métalliques et la préparation de dispositifs moléculaires. Une étape a été franchie vers la connexion des fils déposés initialement ainsi que de molécules localisées de façon imageable, en réalisant un modèle et des expériences de dépôt induit par champ d'agrégats d'or sur KBr et InP. Le dépôt sur des substrats InP avec derrière un gaz d'électrons 2D comme contre-électrode a démontré la faisabilité de cette technique de dépôt sous UHV. Des dépôts ultérieurs sur ou
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39

Manzoor, Tahir. "Ellipsometric studies of the nucleation and growth of thin films in ultra high vacuum." Thesis, Queen's University Belfast, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335428.

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40

Ludwick, Jonathan. "Physics of High-Power Vacuum Electronic Systems Based on Carbon Nanotube Fiber Field Emitters." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613745398331048.

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41

Luhman, Xavier D. "Sulfurizing and selenizing metal films in ultra-high vacuum by hydride gas kinetic control." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122393.

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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (page 30).
Molecular beam epitaxy (MBE) is an important, well-established method for creation of thin films. The addition of gaseous sources of hydrogen sulfide and hydrogen selenide is not currently a well-documented or common modification to such systems. While the thermodynamics of using such sources for the production of various chalcogenide thin films are favorable, the actual results thus far do not demonstrate the desired outcome. This indicates that the kinetics of the desired reactions are inhibiting the process. Compared to oxygen, reactions involving sulfur and selenium are slow. In order to ensure that the hydride gases have the opportunity to react as desired, it is necessary to keep the system free of oxygen and to maximize the collisions of gas molecules with the substrate. The first requirement should be achieved simply by using MBE for the process. The second requirement is not provided for in a typical MBE system. Thus, modifications are necessary to increase the reaction rate of the gases, namely by extending the source lines to be closer to the substrate. This thesis addresses the design process for tubing inserts in an existing MBE system.
by Xavier D. Luhman.
S.B.
S.B. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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42

Blanden, Zachary F. "Process development for high powered amplifier Au/Sn eutectic die attach via vacuum furnace." Thesis, State University of New York at Binghamton, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10250174.

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This research was conducted to develop and qualify a vacuum GaAs semiconductor monolithic microwave integrated circuit die attach process. Research was done to understand the causes and effects of voiding levels on device performance and reliability. Simultaneous investigation was done to qualify vacuum-attach as a successful methodology by which minimal voiding levels were achieved. After an initial vacuum-attach trial was completed to verify the methodology, internal accept/reject criteria were developed to qualify die attach interfaces. A dual phase attachment methodology was created to minimize tolerance stacking resulting in more consistent component placement. MATLAB image processing code was developed to quantify the voiding levels against the accept/reject criteria. Statistical methodologies were employed to troubleshoot root causes for special cause variation of initial attachment failures. A design of experiment was conducted testing three factors each at two levels (process gas [Gas A, Gas B], leaking chamber [yes, no], and carrier supplier [Supplier A, Supplier B]). The DOE identified process gas and its interaction with the carrier supplier to be significant. Further investigation of the carriers identified plating contamination, resulting in the process gas the primary factor of interest. A secondary experiment focusing on process gas identified no statistical difference between Gas A? and Gas B (Gas A? indicating a high purity form of Gas A). With this information, Gas A? was selected as the process gas. A total of 56 attachment interfaces were then produced yielding 0.7485% voiding, on average, following a Weibull distribution (?= 1.04171, ? = 0.75967) with zero rejections. The process?s consistency of minimal voiding levels were deemed a success and the process was released to production.

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43

Qin, Feili. "Metal Oxide Reactions in Complex Environments: High Electric Fields and Pressures above Ultrahigh Vacuum." Thesis, University of North Texas, 2005. https://digital.library.unt.edu/ark:/67531/metadc4843/.

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Metal oxide reactions at metal oxide surfaces or at metal-metal oxide interfaces are of exceptional significance in areas such as catalysis, micro- and nanoelectronics, chemical sensors, and catalysis. Such reactions are frequently complicated by the presence of high electric fields and/or H2O-containing environments. The focus of this research was to understand (1) the iron oxide growth mechanism on Fe(111) at 300 K and 500 K together with the effect of high electric fields on these iron oxide films, and (2) the growth of alumina films on two faces of Ni3Al single crystal and the interaction of the resulting films with water vapor under non-UHV conditions. These studies were conducted with AES, LEED, and STM. XPS was also employed in the second study. Oxidation of Fe(111) at 300 K resulted in the formation of Fe2O3 and Fe3O4. The substrate is uniformly covered with an oxide film with relatively small oxide islands, i.e. 5-15 nm in width. At 500 K, Fe3O4 is the predominant oxide phase formed, and the growth of oxide is not uniform, but occurs as large islands (100 - 300 nm in width) interspersed with patches of uncovered substrate. Under the stress of STM induced high electric fields, dielectric breakdown of the iron oxide films formed at 300 K occurs at a critical bias voltage of 3.8 ± 0.5 V at varying field strengths. No reproducible result was obtained from the high field stress studies of the iron oxide formed at 500 K. Ni3Al(110) and Ni3Al(111) were oxidized at 900 K and 300 K, respectively. Annealing at 1100 K was required to order the alumina films in both cases. The results demonstrate that the structure of the 7 Å alumina films on Ni3Al(110) is k-like, which is in good agreement with the DFT calculations. Al2O3/Ni3Al(111) (γ'-phase) and Al2O3/Ni3Al(110) (κ-phase) films undergo drastic reorganization and reconstruction, and the eventual loss of all long-range order upon exposure to H2O pressure > 10-5 Torr. Al2O3/Ni3Al(110) film is significantly more sensitive to H2O vapor than the Al2O3/Ni3Al(111) film, and this may be due to the incommensurate nature of the oxide/Ni3Al(110) interface. STM measurements indicate that this effect is pressure- rather than exposure- dependent, and that the oxide instability is initiated at the oxide surface, rather than at the oxide/metal interface. The effect is not associated with formation of a surface hydroxide, yet is specific to H2O (similar O2 exposures have no effect).
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44

Shipman, Nicholas Christopher. "Experimental study of DC vacuum breakdown and application to high-gradient accelerating structures for CLIC." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/experimental-study-of-dc-vacuum-breakdown-and-application-to-highgradient-accelerating-structures-for-clic(b6eae72f-72d2-42da-87a6-cab7c30f1bda).html.

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The compact linear collider (CLIC) is a leading candidate for the next generation high energy linear collider. As any breakdown would result in a partial or full loss of luminosity for the pulse in which it occurs, obtaining a low breakdown rate in CLIC accelerating structures is a critical requirement for the successful operation of the proposed collider. This thesis presents investigations into the breakdown phenomenon primarily in the low breakdown rate regime of interest to CLIC, performed using the CERN DC spark systems between 2011 and 2014.The design, construction and commissioning of several new pieces of hardware, as well as the development of improved techniques to measuring the inter-electrode gap distance are detailed. These hardware improvements were fundamental in enabling the exciting new experiments mentioned below, which in turn have provided significant additional insight into the phenomenon of breakdown. Experiments were performed o measure fundamental parameters of individual breakdowns, including, the turn-on time and the delay before breakdown in order to gain an improved understanding of how breakdowns are triggered and the underlying process behind them. The turn-on time measurements are the highest bandwidth measurements made to date with the CERN DC systems and are closer than ever before to the value which is expected from the present understanding of breakdown simulations. Another key measurement was that of the breakdown rate scaling with electric field. Previous investigations of this relationship in the DC systems were unable to investigate breakdown rates below 10^3 breakdowns per pulse. These new results are able to investigate this relationship down to a breakdown rate of 10^-8 and are hence a considerable improvement. Thanks to these improved results a remarkable similarity to the scaling of the breakdown rate with electric field in RF cavities was discovered. The conditioning, or change in breakdown rate over time was also studied for the first time in the CERN DC spark systems as well as the newly built fixed gap system. The qualitative conditioning behaviour of the Fixed Gap System again showed interesting similarities to that observed in RF structures. Preliminary studies into the effect of pulse length and magnetic field on the breakdown rate were conducted as well. This is the first time the effect of a DC magnetic field was studied in a DC spark system and in contrast to experiments in RF cavities no statistically significant effect was observed. The dependence of the breakdown rate on pulse length, again the first measurement of its kind in a DC system also revealed a similar scaling law to that observed in RF accelerating structures. Both of these preliminary measurements would need to be repeated to confirm the results.
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45

Tabatabaei, SeyedAli. "Design and Analysis of "High Vacuum Densification Method" for Saturated and Partially Saturated Soft Soil Improvement." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1398187554.

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46

Lautenschlager, Eric J. "Silicon nanoclusters : ultra high vacuum laser ablation fabrication and in situ scanning tunneling microscopy characterization /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.

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47

Day, Brian Scott. "The Dynamics of Gas-Surface Energy Transfer in Collisions of Rare Gases with Organic Thin Films." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29860.

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Understanding mechanisms at the molecular level is essential for interpreting and predicting the outcome of processes in all fields of chemistry. Insight into gas-surface reaction dynamics can be gained through molecular beam scattering experiments combined with classical trajectory simulations. In particular, energy exchange and thermal accommodation in the initial collision, the first step in most chemical reactions, can be probed with these experimental and computational tools. There are many questions regarding the dynamic details that occur during the interaction time between gas molecules and organic surfaces. For example, how does interfacial structure and density affect energy transfer? What roles do intramonolayer forces and chemical identity play in the dynamics? We have approached these questions by scattering high-energy, rare gas atoms from functionalized self-assembled monolayers. We used classical trajectory simulations to investigate the atomic-level details of the scattering dynamics. We find that approximately six to ten carbon atoms are involved in impulsive collision events, which is dependent on the packing density of the alkyl chains. Moreover, the higher the packing density of the alkyl chains, the less energy is transferred to the surface on average and the less often the incident atoms come into thermal equilibrium with the surface. In addition to the purely hydrocarbon monolayers, organic surfaces with lateral hydrogen-bonding networks create more rigid collision partners than surfaces with smaller inter-chain forces, such as van der Waals forces. Finally, we find some interesting properties for organic surfaces that possess fluorinated groups. For argon scattering, energy transfer decreases with an increasing amount of surface fluorination, whereas krypton and xenon scattering transfer most energy to monolayers terminated in CF3 groups, followed by purely hydrocarbon surfaces, and then perfluorinated surfaces.
Ph. D.
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48

Willis, Gregory. "Investigation of onset of plasma formation at anode of fast-pulsed high-voltage vacuum diode." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA267214.

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49

Leffler, Jens, and Christoffer Sörmark. "Beating the carpet : Developing an active vacuum cleaner nozzlefor high carpet performance using less energy." Thesis, KTH, Maskinkonstruktion (Inst.), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-156891.

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The power use of vacuum cleaners accounts for a substantial share of the total energy demand in the European Union. This partly due to the common notion associating good vacuum cleaner performance to high input power. To regulate this European Commission will introduce a energy labeling standard from September 2014 that will enforce a power cap for vacuum cleaners and classify them according to energy efficiency, cleaning performance, dust-emission and sound power level. One company currently trying to adapt their products to this label is Electrolux. The one performance criterion that is currently the furthest from being reached is the level of dust pick up on carpet ( dpuc). Traditionally, motorized vacuum cleaner nozzles with agitators, so called active nozzles, pick up more dust on carpet than other (passive) nozzles. The aim of this thesis has been to investigate whether it is possible for an Electrolux canister vacuum cleaner system to achieve the highest energy efficiency class – A to A+++ – while maintaining a good cleaning performance – class C or better – on carpet. This was done by constructing an active nozzle which performed well on carpet on low input power. An Electrolux active nozzle was adapted to function better with lower airflows and less vacuum. Several prototypes of different agitators were developed and tested in the nozzle according to industry standard testing methods. It was concluded from testing that it was possible to reach the higher classes – A to A+++ – in energy efficiency while maintaining a good cleaning performance class.
Dammsugare står för en stor del av energikonsumtionen inom EU. Detta dels på grund av att höga ineffekter i dammsugare traditionellt har blivit felaktigt sammankopplat med en bra prestanda hos produkten. För att reglera detta kommer Europakommissionen introducera en ny energietikett för dammsugare från och med september 2014. Med den kommer maxgränser för ineffekt att införas och produkter att klassificeras efter energieffektivitet, städprestanda, återutsläpp av damm och ljudnivå. Ett företag som just nu håller på att anpassa sina produkter till den nya märkningen är Electrolux. Ett av de kriterier som är svårast att nå med en lägre ineffekt är dammupptagning på matta ( dpuc). Generellt är munstycken med motordrivna roterande borstar eller lameller, så kallade aktiva munstycken, bättre på att ta upp damm på matta än andra, så kallade passiva, munstycken. Målet med denna uppsats har varit att undersöka möjligheten för ett dammsugarsystem att uppnå de högsta klasserna i energieffektivitet – A till A+++ – men samtidigt behålla en god dammupptagning – klass C eller bättre – på matta. Detta gjordes genom att anpassa ett aktivt munstycke från Electrolux till ett lägre luftflöde och lägre undertryck. Ett flertal motordrivna borstvalsar togs fram och testades i detta munstycke enligt industristandarden för prestandatester. Det kunde konstateras genom testning att det var möjligt att nå de högre klasserna i energieffektivitet och samtidigt behålla en god dammupptagning.
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50

Morse, Michael Ty. "Growth of erbium-doped Si/SiGe double heterostructures by ultra-high vacuum chemical vapor deposition." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10380.

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