To see the other types of publications on this topic, follow the link: Czochralski single crystal growth.
Dissertations / Theses on the topic 'Czochralski single crystal growth'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Czochralski single crystal growth.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Kearns, Joel K. "Origin Of Growth Twins During Czochralski Growth Of Heavily Doped, Dislocation-Free Single Crystal Silicon." Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-dissertations/514.
Full textAbstract:
Low voltage power electronics are made from dislocation free silicon heavily doped with arsenic or antimony to provide low electrical resistivity. Attempts to grow crystals with decreased resistivity have led to a higher probability of twinning during growth, so that the crystal no longer possesses the required crystallographic orientation for device fabrication. The source of the twins must be identified so that crystal growth process conditions can be designed to eliminate this defect mechanism, allowing lower resistivity crystals to be grown reliably. In lightly doped crystals, twinning was ascribed to presence of carbon impurity or a low probability atomic stacking accident, neither of which should be affected by increased concentration of arsenic or antimony. Crystals that twinned during growth were characterized by resistivity, Laue back-reflection x-ray diffraction, optical and scanning electron microscopy, energy dispersive x-ray spectroscopy, spreading resistance, x-ray computed tomography and electron backscatter diffraction. The twin nucleation site of silicon crystals that were grown heavily doped with arsenic or antimony were compared to lightly doped crystals which twinned, and crystals that exhibited other defects. The initial twinning in the <100> orientation heavily doped crystals occurred from small gas bubbles bursting at a {111} facet at the three phase boundary, and forming a twin orientation domain on that facet. The gas bubbles likely consist of argon, the process gas used during solidification to remove silicon monoxide gas from the growth system. The higher levels of arsenic or antimony dopant may have changed the silicon surface tension, or provided additional impurities into the liquid silicon. Either effect may have changed the number or size of argon bubbles in the liquid silicon, leading to a higher incidence of gas bubbles near the {111} facet during solidification. Similar but smaller crater features were observed on two lightly boron-doped silicon crystals that twinned. Two other lightly doped crystals formed twins from carbon inclusions, consistent with carbon as a cause. Some heavily-doped twinned samples also show high concentrations of metals at the twin nucleation site, which could affect surface energy. Measurement of the geometry of crystal surface-to-facet radius eliminated a recently-proposed twin nucleation theory from consideration. Constitutional supercooling was demonstrated to not be a major contributing factor to twin nucleation. It was shown that deliberately introducing additional arsenic dopant during solidification would nucleate twins, but twins did not occur if only elemental carbon was introduced.
2
Möckel, Robert. "Growth and properties of GdCa4O(BO3)3 single crystals." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2012. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-90095.
Full textAbstract:
In der vorliegenden Arbeit wird die Einkristallzüchtung nach dem Czochralskiverfahren von GdCa4O(BO3)3 (GdCOB) beschrieben. Aus insgesamt 18 Zuchtversuchen, bei denen auch die Ziehgeschwindigkeit zwischen 1 und 3mm/h variiert wurde, wurden erfolgreich nahezu perfekte Einkristalle gewonnen. In einigen Kristallen traten jedoch auch Risse oder Einschlüsse auf. Diese enthielten neben Iridium vom Tiegelmaterial auch andere Phasen des Gd2O3–B2O3–CaO-Systems, sowie P und Yb, deren Herkunft unklar ist. Als Hauptziehrichtung wurde die kristallographische b-Achse gewählt, ergänzt durch einige Experimente in der c-Richtung. In den drei kristallographischen Hauptrichtungen wurden die thermischen Ausdehnungskoeffizienten von GdCOB bestimmt. Diese können in zwei nahezu lineare Bereiche unterteilt werden: von Zimmertemperatur bis etwa 850° C und von 850 bis 1200° C, wobei die Koeffizienten im Hochtemperaturbereich deutlich höher sind (unter 850° C: alpha_a=11.1, alpha_b=8.6, alpha_c=13.3 10^-6/K, oberhalb 850° C: alpha_a=14.1, alpha_b=11.7, alpha_c=17.8 10^-6/K). Daraus ergibt sich, dass ein Phasenübergang höherer Ordnung vorliegen muss. Als mögliche Ursache wurde mittels HT-Raman Spektroskopie ein Ordnungs-Unordnungs-Übergang identifiziert, während dessen die BO3-Gruppen in der Struktur leicht rotieren. Weitere Untersuchungen mittels thermodynamischer Methoden führten zu schwachen, aber eindeutigen Signalen, die diesem Effekt ebenfalls zuzuordnen sind. Obwohl das Material ein vielversprechender Kandidat für piezoelektrische Anwendungen im Hochtemperaturbereich ist, wurde dieser Effekt bisher unzureichend beschrieben. Dieses Verhalten, kombiniert mit den anisotropen thermischen Ausdehnungskoeffizienten, könnte eine der Ursachen für das Vorkommen von Rissen in den Kristallen während der Synthese darstellen. Spektroskopische Untersuchungen ergaben einen großen Transparenzbereich von 340 bis 2500nm (29 400–4000 cm^-1), was für optische Anwendungen von großer Bedeutung ist<br>In a series of 18 growth experiments, GdCa4O(BO3)3 (GdCOB) single crystals were successfully grown by the Czochralski method. They have a well-ordered structure, as revealed by single crystal structure analysis. Although the main growth direction was along the crystallographic b-axis, some experiments were conducted using the cdirection. Pulling velocities were varied between 1 and 3mm/h. Except for a few crystals with cracks or elongated "silk-like" inclusions consisting of multiphase impurities, most of the obtained crystals are of good quality. Those inclusions contain iridium, deriving from the crucible, P and Yb with unclear source, and other phases from the system Gd2O3–B2O3–CaO. Thermal expansion coefficients of GdCOB were determined in the directions of the crystallographic axes and found to be approximately linear in two temperature ranges: from 25° C to around 850° C, and from 850 to 1200° C, with the latter range showing significantly higher coefficients (below 850° C: alpha_a=11.1, alpha_b=8.6, alpha_c=13.3 10^-6/K, and above 850° C: alpha_a=14.1, alpha_b=11.7, alpha_c=17.8 x10^-6/K). This sudden increase of thermal expansion coefficients indicates a phase transition of higher order. An order-disorder transition in form of the rotation of BO3-triangles in the structure was made tentatively responsible for this transition, as revealed by HT-Raman spectroscopy. This transition was also detected by DSC-methods but appeared to result in very weak effects. Although the material is thought to represent a promising candidate for high temperature piezoelectric applications (noncentrosymmetric space group Cm), this effect of change in specification has not been described and it is unknown whether it has influence on the piezoelectric properties. Furthermore, this characteristic behaviour in combination with anisotropic coefficients may be the reason for the development of cracks during cooling of crystals, making the growth difficult. Spectroscopic investigation revealed a wide transparency range from 340 to 2500nm (29 400–4000 cm^-1) of GdCOB, which is a very important property for optical applications
3
Tavakoli, Mohammad Hossein. "Numerical analysis of seeding process during Czochralski growth of oxide single crystals." [S.l.] : [s.n.], 2006. http://se6.kobv.de:8000/btu/volltexte/2006/14.
Full text
4
Reuther, Christoph. "Züchtung und Charakterisierung von Sr3Gd2[BO3]4-Einkristallen." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2013. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-115924.
Full textAbstract:
Polykristallines Sr3Gd2[BO3]4 (SGB) konnte mithilfe einer stöchiometrischen Mischung aus SrCO3, Gd2O3 und B2O3 durch zweimaliges Sintern bis 1.350 °C phasenrein erzeugt werden. Ein Exzess von 3 Ma% B2O3 musste der Mischung beigesetzt werden, um das an B2O3 gebundene Wasser auszugleichen [125].
Kristalle des SGB ließen sich mit verschiedenen Orientierungen erfolgreich mit dem Czochralski-Verfaren synthetisieren. Unter Einsatz eines arteigenen, b-orientierten Keimes, einer Translation von 1 mm/h und einer Rotation von 4 /min konnten Kristalle mit guter Qualität bei hoher Erfolgsrate produziert werden. Bei den gezüchteten Kristallen waren keine Segregationserscheinungen zwischen Gadolinium und Strontium feststellbar. Jedoch weist das Auftreten von Fremdphasen (vor allem Gd2O3) in wenigen Kristallen auf eine mögliche, geringfügige Bevorzugung des Sr in der Struktur hin.
Die Härte des Materials ist mit ca. 5,5 nach Mohs bestimmt, die Dichte mit 5,15(1) g/cm3. SGB ist nicht hygroskopisch, lässt sich aber in mineralischen Säuren lösen. Die Schmelztemperatur konnte mit 1.461+/-5 °C bestimmt werden.
Einkristallines SGB besitzt ein Transmissionsfenster zwischen 215-3.450 nm. Das entspricht einer Bandlücke von 5,4 eV. In diesem Bereich werden über 80% des eingestrahlten Lichtes transmittiert. Im ultravioletten Spektrum finden sich für Gd charakteristische Absorptionsbanden, die durch Elektronenübergänge erzeugt werden. Im mittleren Infrarotbereich lassen sich um die Absorptionskante mehrere Absorptionsbanden, deren Ursache ungeklärt ist, feststellen. Sie stehen offensichtlich im Zusammenhang mit dem Auftreten von [BO3]3- -Gruppen, da sie auch bei anderen Boraten, wie dem Ca4Gd[O|(BO3)3] [99], vorkommen. Gepulvertes SGB weist im Bereich von 550-1.600 cm-1 zahlreiche Absorptionsbanden, die auf verschiedene Schwingungen innerhalb der [BO3]3- -Gruppe zurückgeführt werden können, auf. Es folgen zu kleineren Wellenzahlen hin vermutlich Sr-O- und Gd-O-Schwingungen.
Die thermische Ausdehnung von SGB-Kristallen ist anisotrop sowohl zwischen den kristallographischen Richtungen a, b und c als auch über die Temperatur innerhalb einer Richtung. Sie kann im Mittel zwischen 150-830 °C mit alpha11=18,1(2)*10-6/K, alpha22=8,9(3)*10-6/K und alpha33=20,3(4)*10-6/K angenommen werden. Die Ausdehnungskurven deuten mehrere Effekte an, wobei ein Effekt im Bereich von 450-700 °C und vermutlich zwei weitere im Bereich von 800-1.000 °C zu beobachten sind. Aufgrund der Stetigkeit der Kurve ist wahrscheinlich von Phasenübergängen höherer Ordnung auszugehen.
Zur Struktur des SGB konnten wichtige Grundverständnisse gewonnen werden. So lässt sich die Struktur bei Raumtemperatur nicht durch eine orthorhombisch zentrische Metrik beschreiben, da die Einzelreflexe bei Einkristallmessungen eine Aufspaltung im Bereich von 0,1 ° zeigen. Dies deutet auf das Vorhandensein von Zwillingen und auch auf eine mögliche monokline Metrik hin. Es fällt dabei besonders auf, dass die Aufspaltung mit zunehmendem Theta-Winkel nicht größer wird, so dass auch andere Phänomene für die Reflexaufspaltung verantwortlich sein könnten. Dennoch ergeben die ermittelte Raumgruppe Pnam, die zugehörigen Gitterparameter (a0=0,7408 nm, b0=0,8757 nm, c0=1,6057 nm) und Atomkoordinaten ein vereinfachtes Modell zur Veranschaulichung der Struktur. Hoch- und Raumtemperaturstruktur sind bis 700 °C unter Annahme des vereinfachten Modells isomorph, wobei die Gitterparameter entsprechend der Ausdehnung vergrößert sind. Die Gd- und Sr-Positionen sind untereinander mischbesetzt. Außerdem deutet sich eine Positionsfehlordnung einer Sauerstoff-Position an, der Ligand eines Borions auf spezieller Lage ist. Hinweise auf die korrekte Struktur liefern die entdeckten Phasenübergänge und Hochtemperatur-Einkristalldaten. Der in der Dilatometrie entdeckte Effekt zwischen 450-700 °C korreliert mit dem Rückgang der Reflexaufspaltung, die bei ca. 700 °C nicht mehr sichtbar ist, wobei sich dieser Rückgang vermutlich von Raumtemperatur bis 700 °C erstreckt. Damit bestätigt sich, dass der erst genannte Effekt als Phasenübergang höherer Ordnung aufgefasst werden kann. Die festgestellte Positionsfehlordnung von Sauerstoff verringert sich mit steigender Temperatur. Die Mischbesetzung ändert sich ebenfalls bis ca. 500 °C. Beide Effekte sowie auch größeren Schwingungsellipsoide der Sauerstopositionen um die allgemeine Borlage sind vermutlich Ausdruck für den stattfindenden Phasenübergang und verstärken die Annahme einer Zwillingsbildung.
5
Koubaa, Taoufik. "Métrologie thermique en vue de la régulation d'un four de tirage de monocristaux d'AsGa." Grenoble 1, 1986. http://www.theses.fr/1986GRE10135.
Full textAbstract:
Mise au point et automatisation d'un four czochralski pour la croissance de monocristaux gaas. La regulation du diametre des cristaux et l'amelioration de leur qualite ne peuvent etre atteintes qu'en maitrisant la distribution de temperature dans le four, car elle conditionne la forme de l'interface de solidification. Mise au point de deux instrumentations de mesure de temperature. La premiere permet de faire une cartographie des temperatures dans le bain fondu. La deuxieme permet de determiner la temperature sous le creuset, indispensable pour la regulation de la machine de tirage. Description de quelques experiences
6
Hicks, T. W. "Hydrodynamics of liquid encapsulation Czochralski crystal growth." Thesis, University of Bristol, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233905.
Full text
7
Brakel, Thomas W. "Mathematical modelling of the Czochralski crystal growth process." Doctoral thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/4868.
Full textAbstract:
Includes bibliographical references (leaves 142-149).<br>In this document a mathematical model for the Czochralski crystal growth process is developed. The trend in current research involves developing cumbersome numerical simulations that provide little or no understanding of the underlying physics. We attempt to review previous research methods, mainly devoted to silicon, and develop a novel analytical tool for indium antimonide (lnSb) crystal growth. This process can be subdivided into two categories: solidification and fluid mechanics. Thus far, crystal solidification of the Czochralski process has been described in the literature mainly qualitatively. There has been little work in calculating actual solidification dynamics. Czochralski crystal growth is a very sensitive process, particularly for lnSb, so it is crucial to describe the system as accurately as possible. A novel ID quasi-steady method is proposed for the shape and temperature field of an lnSb crystal, incorporating the effects of the melt. The fluid mechanics of the Czochralski melt have been modelled by numerous researchers,with calculations performed using commercial software. However, a descriptionof the buoyancy and rotation interaction in the melt has not been adequatelyperformed. Many authors have presented flow patterns but none have indicated either: melt conditions preferential for crystal growth or at least a description of a typical melt structure. In this work, a scale analysis is performed that implies an idealized flow structure. An asymptotic model is then derived based on this order of magnitude analysis, resulting in a fast and efficient fluid flow calculation. The asymptotic model is validated against a numerical solution to ensure that the macroscopic features of the flow structure are present. The asymptotic model does not show exact agreement, but does provide an estimate of the melt heat flux that is necessary for the solidification calculation. The asymptotic model is also used to predict macroscopic changes in the melt due to rotation.
8
Nawash, Jalal Mohammad. "A study of the crystal growth of select II-VI oxides by Czochralski and Bridgman techniques." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Dissertations/Fall2006/J_Nawash_121406.pdf.
Full text
9
Henderson, M. B. "Fatigue crack growth in single crystal superalloys." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314993.
Full text
10
McComber, Kevin A. "Single-crystal germanium growth on amorphous silicon." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/69792.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 130-136).<br>The integration of photonics with electronics has emerged as a leading platform for microprocessor technology and the continuation of Moore's Law. As electronic device dimensions shrink, electronic signals encounter crippling delays and heating issues such that signal transduction across large on-chip distances becomes increasingly more difficult. However, these issues may be mitigated by the use of photonic interconnects combined with electronic devices in electronic-photonic integrated circuits (EPICs). The electronics in proposed EPIC designs perform the logic operations and short-distance signal transmission, while photonic devices serve to transmit signals over longer lengths. However, the photonic devices are large compared to electronic devices, and thus the two types of devices would ideally exist on separate levels of the microprocessor stack in order to maximize the amount of silicon substrate available for electronic device fabrication. A CMOS-compatible back-end process for the fabrication of photonic devices is necessary to realize such a three-dimensional EPIC. Back-end processing is limited in thermal budget and does not present a single-crystal substrate for epitaxial growth, however, so high-quality crystal fabrication methods currently used for photonic device fabrication are not possible in back-end processing. This thesis presents a method for the fabrication of high-quality germanium single crystals using CMOS-compatible back-end processing. Initial work on the ultra-high vacuum chemical vapor deposition of polycrystalline germanium on amorphous silicon is presented. The deposition can be successfully performed by using a pre-growth hydrofluoric acid dip and by limiting the thickness of the amorphous silicon layer to less than 120 nm. Films deposited at temperatures of 350° C, 450° C, and 550° C show (110) texture, though the texture is most prevalent in growths at 450° C. Poly-Ge grown at 4500 C is successfully doped n-type in situ, and the grain size of as-grown material is enhanced by lateral growth over a barrier. Structures are fabricated for the growth of Ge confined in one dimension. The growths show faceting across large areas, in contrast to as-deposited poly-Ge, corresponding to enhanced grain sizes. Growth confinement is shown to reduce the defect density as the poly-Ge grows. When coalesced into a continuous film, the material grown from 1 D confinement exhibits a lower carrier density and lower trap density than as-deposited poly-Ge, indicating improved material quality. We measure an increased grain size from as-deposited poly-Ge to Ge grown from ID confinement. Single-crystal germanium is grown at 450° C from confinement in two dimensions. Such growths exhibit faceting across the entire crystal as well as the presence of E3 boundaries ({111} twins), with many growths showing no other boundaries. These twins mediate the growth of the crystal, as they serve as the points for heterogeneous surface nucleation of adatom clusters. The twins can form after the crystal nucleates and are strongly preferred in order to obtain appreciable crystal growth rates. We model the growths from the confining channels in order to find the optimum channel geometry for large, uniform, single-crystal growths that consistently emerge from the channel. The growths from 2D confinement show lower trap density than those from 1 D confinement, indicating a further enhancement of the crystal quality due to the increased confinement. This method of single-crystal growth from an amorphous substrate is extensible to any materials system in which selective non-epitaxial deposition is possible.<br>by Kevin A. McComber.<br>Ph.D.
11
Lin, Chenting. "Single crystal growth and characterization of BSO (Bi12SiO20)." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/11647.
Full text
12
SIBILIA, MIRTA. "Organic semiconducting single crystal growth on naostructured matrices." Doctoral thesis, Università degli Studi di Trieste, 2017. http://hdl.handle.net/11368/2908140.
Full textAbstract:
In recent years, the development of the organic electronics has led to the employment of organic materials as the basis for many electronic devices, such as organic light emitting diodes, organic field effect transistors, organic solar cells and radiation sensors. As regards radiation sensors, the studies reported in literature mainly refer to devices based on thin film organic semiconductors, which, however, present problems due to instability, degradation and low reproducibility. Organic single crystals overcame most of the major limitations inherent to thin film-based detectors.
In this experimental work, a starting plethora of commercially available compounds has been crystallized and evaluated in terms of both overall crystallizability and applicability as direct X-ray detectors. This first step of work allow to select only those structures capable to provide single-crystals with good morphological properties and electronic properties suitable for X-ray detections.
A careful screening of some thermodynamic variables affecting the growth has been carried out and the obtained results suggest applicability of the present approach to achieve the control of size, quality and crystal habit. Indeed, single crystals with dimensional and morphological properties suitable to the application as X-ray detector have been prepared.
Single-crystals have been physically attached to Au electrodes deposited on a thin film of polyethylennaphthalate – via the functionalization of the electrode with different self-assembled monolayers (SAMs), chemically and structurally similar to the molecule constituting the selected crystal. In particular, two of the explored SAMs showed very promising results in the first qualitative adhesion tests.
13
Srivastava, Ankit. "Void Growth and Collapse in a Creeping Single Crystal." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc84281/.
Full textAbstract:
Aircraft engine components can be subjected to a large number of thermo-mechanical loading cycles and to long dwell times at high temperatures. In particular, the understanding of creep in single crystal superalloy turbine blades is of importance for designing more reliable and fuel efficient aircraft engines. Creep tests on single crystal superalloy specimens have shown greater creep strain rates for thinner specimens than predicted by current theories. Therefore, it is necessary to develop a more predictive description of creep processes in these materials for them to be used effectively. Experimental observations have shown that the crystals have an initial porosity and that the progressive growth of these voids plays a major role in limiting creep life. In order to understand void growth under creep in single crystals, we have analyzed the creep response of three dimensional unit cells with a single spherical void under different types of isothermal creep loading. The growth behavior of the void is simulated using a three dimensional rate dependent crystal plasticity constitutive relation in a quasi-static finite element analysis. The aim of the present work is to analyze the effect of stress traixiality and Lode parameter on void growth under both constant true stress and constant engineering stress isothermal creep loading.
14
Nunes, Benjamin P. (Benjamin Paul) 1976. "Edge-defined film-fed growth of single-crystal piezoelectrics." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/17530.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001.<br>Includes bibliographical references (leaves 97-99).<br>Many transducer technologies would benefit tremendously from the development of shaped, oriented single-crystals, of a high-strain, piezoelectric material. Recently, unusually high electrostrictive and piezoelectric actuation has been observed in polycrystals and flux-grown <100> single-crystals of ... Using seeded, Edgedefined Film-fed Growth (EFG) and the related Stepanov Technique (ST), low-hysteresis, highstrain, <100> and <111> oriented, single-crystals of BNBZT can be grown in rod and fiber form, with direct applications in active fiber composites and related devices. For this work, <100> and <111> oriented, single-crystal rods and fibers were grown via ST and EFG. Fibers, 260-700[mu]m in diameter and over 1.0 meter long, were grown using a custom built EFG machine and a capillary-shaper; rods, 2-3mm in diameter, up to 110mm long were grown using a floating-shaper. In all cases, strontium titanate (STO) was found to be an effective seed crystal. <111> oriented tetragonal crystals generated low hysteresis actuation consistent with a polarization rotation mechanism [14], but with only modest strains: ... <100> oriented tetragonal BNBZT generated high strains up to ... with hysteresis consistent with 90° domain switching. Electromechanical actuation and crystal structure in this system appear to be strongly affected by deviations from stoichiometry (B-site vacancies). Barium segregation and bismuth vaporization can also compromise electromechanical performance. Hypotheses are posed to explain the low actuation seen from <111> oriented ferroelectrics, and the effects of cation deficiencies on phase-stability. Cracks, pores, and other growth challenges encountered in ST and EFG growth of BNBZT are described.<br>by Benjamin P. Nunes.<br>S.M.
15
Rittenhouse, Tilghman L. (Tilghman Lee) 1972. "Single crystal growth and characterization of silicon germanium alloys." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85267.
Full text
16
Constantinidis, G. "Growth and characterisation of single CuInSe2̲ crystals." Thesis, University of Salford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381646.
Full text
17
Rutkowska, Agnieszka. "Growth and electrochemical characterisation of single-walled carbon nanotubes on single crystal quartz." Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/3923/.
Full textAbstract:
Single walled carbon nanotubes (SWNTs) have unique structural and electronic properties which drive their use in many different fields of modern technology. In electrochemistry, SWNTs have been shown to have outstanding electrochemical characteristic enabling their application in trace level electroanalysis amongst other areas. The SWNT electrochemical activity has been described as originating solely from sidewall structural defects, oxidised open ends and post-growth metal nanoparticles (NPs). However, recent studies have demonstrated the electrochemical activity of pristine and defect-free SWNTs, grown on insulating substrates using catalysed chemical vapour deposition (cCVD) method, suggesting sidewalls support electron transfer (ET). In this thesis cCVD is employed to grow SWNTs of different geometrical arrangements on single crystal stable temperature (ST)-cut quartz substrates for the development of novel nanoelectrodes (NEs) and optically transparent electrodes (OTE). Majority of the work concentrates on cCVD and electrochemical studies of horizontally aligned SWNTs on ST-cut quartz. The quality of SWNT horizontal arrangement is shown to strongly depend on the crystallographic structure of the ST-cut quartz substrate. Perfectly aligned SWNTs are utilised as (i) one dimensional (1D) templates for electrodeposition of silver NPs, and (ii) NEs for the fundamental assessment of SWNT electrochemical behaviour. Formation of uniform silver nanowires (NWs) on most of the SWNTs is possible at high deposition overpotentials and times. Uniformity of the NWs indicates high structural quality of the horizontally aligned SWNTs. Nernstian behaviour of SWNT NEs for simple outer-sphere redox couples is shown in localised voltammetric measurements with microcapillaries, 25 - 50 μm in diameter serving as probes, filled with the redox active electrolyte solution and the reference electrode (RE). For the first time measurements at single SWNTs in the positive and negative potential window are performed, revealing a strong dependence of SWNT electrochemical activity on SWNT structural and electronic properties. Finally, careful tuning of the cCVD parameters enables growth of interconnected SWNT networks on ST-cut quartz, with complete surface coverage and no sign of alignment. These ultrathin mats are utilised as novel OT disk ultramicroelectrodes (OT-UMEs) with complete transparency in the ultraviolet and visible (UV-Vis) range, metallic behaviour and improved electrochemical usability in comparison to conventional solid UMEs.
18
Mori, Tatsuo 1961. "Modeling the linkages between heat transfer and microdefect formation in crystal growth : examples of Czochralski growth of silicon and vertical Bridgman growth of bismuth germanate." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/9113.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2000.<br>Includes bibliographical references (p. 367-387).<br>Microdefect formation in crystalline material is strongly correlated to the processing conditions for growth of crystals important in microelectronic processing. The geometry and operation conditions for crystal growth systems affect the temperature profile in the crystal and melt, which influences microdefect formation. The objectives of this thesis are to formulate the computational framework to establish the linkage between microdefect formation in crystal and proce5sing conditions of crystal growth system. The research focuses on two industrially important crystal growth problems: Czochralski (CZ) growth of single-crystal silicon and growth of bismuth germanium oxide (Bi4Ge30 12:BGO) by the vertical Bridgman method. A sequential, two-step approach is taken for linking mathematical modeling between processing conditions and microdefect formation in crystals. An accurate model of heat transfer in CZ growth of silicon is developed by including all the components in the system. Microdefoct formation in the crystal is then modEled by imposing the temperature profile obtained by the global heat transfer simulation. The integrated hydrodynamics thermal-capillary model (IHTCM) of CZ crystal growth includes radiative and conductive heat transfer between all components of the system. An important component of this simulation is the incorporation of a model of turbulence in the melt. A low Reynolds number k-c model is incorporated into the IHTCM for CZ system. The coupled k-c/IHTCM is applicable to any CZ system geometry and operating conditions because of the self-consistency of the model. Also a robust numerical solution method is developed to solve numerically unstable k-c equations by a finite-element approximation. The comparison between simulations and experiments for CZ growth of an 8" diameter crystal shows semi-quantitative agreement in melt/crystal interface, oxygen concentration in the crystal, and the location of a neutral zone, where the concentrations of two intrinsic point defects balance, in the crystal. Microdefect formation in CZ silicon is modeled with intrinsic point defects (vacancies and self-interstitials) and their agglomerates. The model is two-dimensional in space and predicts the radial profiles of point defects, which are determined near the melt/crystal interface, and the axial development of size distribution of voids and self-interstitial agglomerates, which is a function of point defect supersaturation and the temperature profile. The model provides quantitative links between operating conditions and microdefect distribution in the entire crystal. An effective numerical method with parallel processing is developed using a mixed local discontinuous Galerkin method. The predicted agglomeration temperatures and densities for vacancy and self-interstitial clusters are within the ranges of experimental data. The predictions also include the location for ring-like oxidation-induced stacking fault (OSF) formation, assuming the OSF-ring is formed at the radial location with the peak in residual vacancy concentration after the onset of vacancy agglomeration. The simulations clearly reproduce the radial distribution of microdefects observed by experiments. Starting from the crystal center and moving to the edge, the simulations predict a void region, the OSF-ring as a region of locally high vacancy concentration, a defect free region, a region dominated by self-interstitial clusters, and finally a defect free region near the crystal edge. The defect free region at the crystal edge results from the radial diffusion of point defects caused by reactions at the crystal surface. The heat transfer model in the vertical Bridgman system for BGO crystal growth incorporates internal radiation in the semi-transparent BGO crystal and conduction and radiation for all components of the heat transfer system. A band approximation is used to model internal radiation in the crystal. The global heat transfer model provides quantitative understanding of the heat transfer within the semi-transparent BGO crystal as well as in the entire system. Comparison of the temperature profile at the crucible wall between simulations and experiments for the large 11 cm diameter BGO crystal growth shows good agreement. The detailed analysis of heat transfer near the solidification interface gives insight for the control of bubble defects in BGO crystal formed by constitutional supercooling. The framework for numerical simulations developed in this thesis quantitatively demonstrates the linkage between processing conditions and microdefect formation in crystalline material. The linkage is established by the coupling of self-consistent modeling of global heat transfer in the crystal growth systems and microdefect formation in crystals.<br>by Tatsuo Mori.<br>Ph.D.
19
Lempidaki, Dimitra. "An investigation of crack growth phenomena in single crystal superalloys." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430750.
Full text
20
Seat, Han Cheng. "Growth and characterisation of single-crystal fibres for sensing applications." Thesis, University of Glasgow, 2001. http://theses.gla.ac.uk/6926/.
Full textAbstract:
The laser heated pedestal growth technique has been successfully employed to grow pure and doped sapphire crystal fibres for characterisation as suitable sensor materials. Source materials used were polycrystalline and crystalline sapphire rods while fibres with typical diameters in the range 80 - 170 mm were grown. Pure sapphire fibres, both a- and c-axis, were found to grow easily with no complications such as melt instability. C-axis fibre growth was readily initiated while a-axis fibres required an appropriate a-axis oriented seed crystal. Dip-coating has been used to prepare suitably coated sapphire source rods for growth into doped fibres. Doped fibres grown included Cr3+:, Er3+:, Er3+:Yb3+: and Yb3+:Er3+:Al2O3. Er3+:Yb3+:Al2O3 fibres have been prepared with approximately equal concentration of both dopants while a 10:1 Yb3+ to Er3+ concentration ratio was used for preparing Yb3+:Er3+:Al2O3 fibres. Ruby fibres were also found to grow easily although brownish-green deposits have been observed on some of these fibres. Large transmission losses have been found in fibres with these deposits. Acid cleaning was not effective in removing these deposits, suggesting that they have diffused beneath the surface of the fibres. This was attributed to the condensation of chromium oxide on the fibre surface during growth. Growth of rare earth-doped fibres was initially problematic due to the constant breaking-off of the crystallising fibres from the melt. This was thought to be due to the flexibility of the small diameter source fibres used as well as the high concentration levels of doping. Replacing these small fibres with larger source rods thus permitted RE-doped fibres with relatively good optical quality to be grown. Fibres were grown with typical growth rates of 0.5 - 1 mm/min.
21
Busse, Christian. "Aspects of Crack Growth in Single-Crystal Nickel-Base Superalloys." Licentiate thesis, Linköpings universitet, Mekanik och hållfasthetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-143058.
Full textAbstract:
This Licentiate of Engineering thesis is a product of the results generated in the research project KME-702, which comprises modelling, microstructure investigations and material testing of cast nickel-base superalloys. The main objective of this work is to model the fatigue crack propagation behaviour in single-crystal nickel-base superalloys. To achieve this, the influence of the crystal orientations on the cracking behaviour is assessed. The results show that the crystal orientation is strongly affecting the material response and must be accounted for. Furthermore, a linear elastic crack driving force parameter suitable for describing crystallographic cracking has been developed. This parameter is based on resolved anisotropic stress intensity factors and is able to predict the correct crystallographic cracking plane after a transition from a Mode I crack. Finally, a method to account for inelastic deformations in a linear elastic fracture mechanics context was investigated. A residual stress field is extracted from an uncracked finite-element model with a perfectly plastic material model and superimposed on the stress field from the cracked model with a linear elastic material model to account for the inelastic deformations during the determination of the crack driving force. The modelling work is validated by material testing on two different specimen geometries at different temperatures. This Licentiate of Engineering thesis consists of two parts, where Part I gives an introduction and background to the research area, while Part II consists of three papers.<br>Denna licentiatavhandling är en produkt av resultat som genererats i forskningsprojektet KME-702, och omfattar modellering, mikrostrukturundersökningar och materialprovning av gjutna nickelbaserade superlegeringar. Huvudsyftet med detta arbete är att modellera sprickförloppet under utmattning i enkristallina nickelbaserade superlegeringar. För att uppnå detta har kristallorienteringens inverkan på sprickbeteendet utvärderats. Resultaten visar att kristallorienteringen har en stark inverkan på materialbeteendet, således måste hänsyn till denna tas. Dessutom har en linjär-elastisk sprickdrivkraftsparameter lämplig att beskriva kristallografisk sprickbildning utvecklats. Denna parameter är baserad på anisotropa spänningsintensitetsfaktorer på kristallplan och kan prediktera det korrekta kristallografiska sprickplanet efter övergång från Modus I spricka. Slutligen har undersökts en metod för att ta hand om inelastiska deformationer i en linjär-elastisk brottmekanikskontext. Ett restspänningsfält extraherades från en osprucken finita element modell med en ideal plastisk materialmodell. Denna överlagrades på spänningsfältet från den spruckna modellen, som analyserades med en linjär-elastisk materialmodell, för att ta hänsyn till de inelastiska deformationerna vid bestämning av sprickdrivkraften. Modelleringsarbetet validerades genom materialprovning på två olika provgeometrier vid olika temperaturer. Licentiatavhandlingen består av två delar, där del I ger en introduktion och bakgrund till forskningsområdet medan del II består av tre papper.<br>Dieses Lizentiat der Ingenieurwissenschaften ist im Rahmen des Forschungsprojekts KME-702 entstanden, welches Modellierung, Mikrostrukturuntersuchungen und Materialtests von gegossenen nickelbasierten Superlegierungen umfasst. Das Hauptziel dieser Arbeit ist die Modellierung der Ermüdungsrissausbreitung in einkristallinen nickelbasierten Superlegierungen. Um dieses zu erreichen, wurde der Einfluss der Kristallorientierungen auf das Rissverhalten untersucht. Die Ergebnisse zeigen, dass die Kristallorientierung das Materialverhalten stark beeinflusst und daher berücksichtigt werden muss. Darüber hinaus wurde ein linear elastischer Rissantriebskraftparameter entwickelt, der zum Beschreiben von kristallographischen Rissen geeignet ist. Dieser Parameter basiert auf aufgelösten anisotropen Spannungsintensitätsfaktoren und ist in der Lage, die korrekte kristallographische Rissebene nach einem Übergang von einem Modus I Riss vorherzusagen. Abschließend wird in einem linear-elastisch bruchmechanischen Kontext eine Methode untersucht, die nichtelastischen Deformationen bei der Bestimmung der Rissantriebskraft zu berücksichtigen. Dazu wird aus einem Finite-Elemente Modell, welches keinen Riss aufweist und mit einem perfekt plastischen Materialmodell beschrieben wird, das Restspannungsfeld extrahiert und dem Spannungsfeld überlagert, welches aus dem Modell mit Riss unter Verwendung eines linear elastischen Materialmodells erzeugt wurde. Die Modellierung wird durch Materialtests an zwei verschiedenen Probengeometrien bei unterschiedlichen Temperaturen validiert. Dieses Lizentiat der Ingenieurwissenschaften besteht aus zwei Teilen, wobei Teil I eine Einführung und einen Hintergrund in das Forschungsgebiet gibt, während Teil II aus drei Forschungsartikeln besteht.
22
Lauque, Olivier. "Effects of abrasive waterjet erosion on single crystal silicon." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/16782.
Full text
23
SANTOS, IVANILDO A. dos. "Estudo das soluções sólidas de LiGdsub(1-x)Lusub(x)Fsub(4) visando o crescimento de cristais." reponame:Repositório Institucional do IPEN, 2008. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11656.
Full textAbstract:
Made available in DSpace on 2014-10-09T12:54:23Z (GMT). No. of bitstreams: 0<br>Made available in DSpace on 2014-10-09T14:09:15Z (GMT). No. of bitstreams: 0<br>Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)<br>Dissertação (Mestrado)<br>IPEN/D<br>Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP<br>FAPESP:05/57580-2
24
Beckett, Douglas J. S. "The exchange interaction and single crystal growth of selected semimagnetic semiconductors." Thesis, University of Ottawa (Canada), 1986. http://hdl.handle.net/10393/4797.
Full text
25
BALDOCHI, SONIA L. "Sintese e crescimento de cristais de BaLiFsub3 puros e dopados com Pb." reponame:Repositório Institucional do IPEN, 1993. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10336.
Full textAbstract:
Made available in DSpace on 2014-10-09T12:37:29Z (GMT). No. of bitstreams: 0<br>Made available in DSpace on 2014-10-09T14:03:27Z (GMT). No. of bitstreams: 1
02033.pdf: 7170847 bytes, checksum: 0f6482c59ed081703c64e988f898b301 (MD5)<br>Tese (Doutoramento)<br>IPEN/T<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
26
VIDAL, AUGUSTO T. "Sintese e crescimento de cristais fluoretos dopados com terras raras: LiCAF:Er e BLF:TR (TR = Yb sup(3+), Ce sup(3+), Nd sup(3+))." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10970.
Full textAbstract:
Made available in DSpace on 2014-10-09T12:46:16Z (GMT). No. of bitstreams: 0<br>Made available in DSpace on 2014-10-09T14:01:47Z (GMT). No. of bitstreams: 1
07973.pdf: 3168450 bytes, checksum: 8bf87743d796e20893798cadfbfad208 (MD5)<br>Dissertacao (Mestrado)<br>IPEN/D<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
27
Aslan, Ozgur. "Numerical modeling of fatigue crack growth in single crystal nickel based superalloys." Paris, ENMP, 2010. http://pastel.archives-ouvertes.fr/pastel-00540893.
Full textAbstract:
Les composants monocristallins fonctionnant à des températures élevées sont soumis à des conditions de chargement thermo-mécanique sévères. La géométrie et le comportement de ces composants sont très complexes. Un défi majeur est de développer des modèles mathématiques afin de prévoir l'initiation et la propagation de fissures en présence de contraintes importantes et de forts gradients de température. Dans ce cas, le comportement élastoviscoplastique fortement anisotrope du matériau étudié (superalliage à base Ni) doit être pris en compte. Le modèle correspondant doit être en mesure de rendre compte de la croissance anisotrope des fissures et de leur bifurcation dans des champs de contrainte complexes. De plus, le modèle doit être capable de prédire non seulement le taux de croissance des fissures mais aussi les chemins de fissuration. La mécanique de l'endommagement anisotrope est un cadre théorique bien adapté au développement de modèles de croissance de fissures dans les monocristaux. Au cours d'études précédentes, une loi de comportement couplant plasticité cristalline et endommagement cyclique a été développée, démontrant l'intérêt de cette approche, mais aussi ses limites, notamment du fait de la dépendance au maillage des résultats. Le développement récent de modèles non-locaux dans le cadre de la mécanique des milieux continus pourrait ainsi aider à surmonter ces difficultés. Une grande base expérimentale existe concernant l'initiation et la propagation de fissures dans les superalliages monocristallins à base de nickel. Les simulations thermomécaniques par éléments finis des aubes de turbine fournissent des informations détaillées sur la distribution des contraintes et des déformations plastiques, en particulier près de singularités géométriques comme les trous et les fentes de refroidissement. Tout d'abord, sur la base de la théorie de la plasticité cristalline qui établit un lien solide entre les contraintes et les déformations plastiques, un modèle découplé en mécanique de l'endommagement basé sur l'historique des calculs par éléments finis sera présenté. Ensuite, un modèle d'endommagement incrémental basé sur les milieux généralisés sera proposé et enfin, les prédictions du modèle pour l'initiation et la croissance de micro-fissures en résolvant le problème de dépendance au maillage seront discutés<br>Single crystal components operating at elevated temperatures are subjected to severe thermomechanical loading conditions. The geometry and behaviour of these components are now very complex. A major issue is to develop models to predict crack initiation and crack growth in the presence of strong stress and temperature gradients. The strongly anisotropic elastoviscoplastic behaviour of the material which is a single crystal nickel base superalloy, must be taken into account. The corresponding model should be able to account for anisotropic crack growth and crack bifurcation in complex stress elds. Moreoever the model must be capable of predicting not only the crack growth rate but also the non-straight crack paths. Anisotropic damage mechanics is a well-suited theoretical framework for the development of crack growth models in single crystals. A model coupling crystal plasticity and cyclic damage has been developed in a previous project, that shows the interest of the approach, but also its current limits, in particular the strong mesh dependence of the results. Recent development of nonlocal models within the framework of the mechanics of generalized continua could help overcoming these difficulties. A large experimental basis exists concerning initiation and crack growth in single crystal nickel base superalloys. Finite element simulations of the thermomechanics of turbine blades provide detailed information about stress and plastic strain distribution, in particular near geometrical singularities like cooling holes and slits. First of all, on the basis of crystal plasticity theory which provides a solid link between stress and plastic strains, an uncoupled damage mechanics model based on the history of FE calculations will be presented. Afterwards, an incremental damage model based on generalized continua will be proposed and model predictions for the initiation and growth of microcracks by solving the mesh dependency, will be discussed
28
Joshi, Madhura A. "Growth and Characterization of Magnesium Single Crystal for Biodegradable Implant Material Application." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1448275234.
Full text
29
Yao, Yao. "Growth, Characterization and Contacts to Ga2O3 Single Crystal Substrates and Epitaxial Layers." Research Showcase @ CMU, 2017. http://repository.cmu.edu/dissertations/921.
Full textAbstract:
Gallium Oxide (Ga2O3) has emerged over the last decade as a new up-and-coming alternative to traditional wide bandgap semiconductors. It exists as five polymorphs (α-, β-, γ-, δ-, and ε-Ga2O3), of which β-Ga2O3 is the thermodynamically stable form, and the most extensively studied phase. β-Ga2O3 has a wide bandgap of ~4.8 eV and exhibits a superior figure-of-merit for power devices compared to other wide bandgap materials, such as SiC and GaN. These make β-Ga2O3 a promising candidate in a host of electronic and optoelectronic applications. Recent advances in β-Ga2O3 single crystals growth have also made inexpensive β-Ga2O3 single crystal grown from the melt a possibility in the near future. Despite the plethora of literature on β-Ga2O3-based devices, understanding of contacts to this material --- a device component that fundamentally determines device characteristics — remained lacking. For this research, ohmic and Schottky metal contacts to Sn-doped β-Ga2O3 (-201) single crystal substrates, unintentionally doped (UID) homoepitaxial β-Ga2O3 (010) on Sn-doped β-Ga2O3 grown by molecular beam epitaxy (MBE), and UID heteroepitaxial β-Ga2O3 (-201) epitaxial layers on c-plane sapphire by metal-organic chemical vapor deposition (MOCVD) were investigated. Each of the substrates was characterized for their structural, morphological, electrical, and optical properties, the results will be presented in the following document. Nine metals (Ti, In, Ag, Sn, W, Mo, Sc, Zn, and Zr) with low to moderate work functions were studied as possible ohmic contacts to β-Ga2O3. It was found that select metals displayed either ohmic (Ti and In) or pseudo-ohmic (Ag, Sn and Zr) behavior under certain conditions. However, the morphology was often a problem as many thin film metal contacts dewetted the substrate surface. Ti with a Au capping layer with post-metallization annealing treatment was the only consistently reliable ohmic contact to β-Ga2O3. It was concluded that metal work function is not a dominant factor in forming an ohmic contact to β-Ga2O3 and that limited interfacial reactions appear to play an important role. Prior to a systematic study of Schottky contacts to β-Ga2O3, a comparison of the effects of five different wet chemical surface treatments on the β-Ga2O3 Schottky diodes was made. It was established that a treatment with an organic solvent clean followed by HCl, H2O2 and a deionized water rinse following each step yielded the best results. Schottky diodes based on (-201) β-Ga2O3 substrates and (010) β-Ga2O3 homoepitaxial layers were formed using five different Schottky metals with moderate to high work functions: W, Cu, Ni, Ir, and Pt. Schottky barrier heights (SBHs) calculated from current-voltage (I-V) and capacitance-voltage (C-V) measurements of the five selected metals were typically in the range of 1.0 – 1.3 eV and 1.6 – 2.0 eV, respectively, and showed little dependence on the metal work function. Several diodes also displayed inhomogeneous Schottky barrier behavior at room temperature. The results indicate that bulk or near-surface defects and/or unpassivated surface states may have a more dominant effect on the electrical behavior of these diodes compared to the choice of Schottky metal and its work function. Lastly, working with collaborators at Structured Materials Industries (SMI) Inc., heteroepitaxial films of Ga2O3 were grown on c-plane sapphire (001) using a variety of vapor phase epitaxy methods, including MOVPE, and halide vapor phase epitaxy (HVPE). The stable phase β-Ga2O3 was observed when grown using MOVPE technique, regardless of precursor flow rates, at temperatures ranging between 500 – 850 °C. With HVPE growth techniques, instead of the stable β-phase, we observed the growth of the metastable α- and ε-phases, often a combination of the two. Cross-sectional transmission electron microscopy (TEM) shows the better lattice matched α-phase first growing semi-coherently on the c-plane sapphire substrate, followed by domain matched epitaxy of ε-Ga2O3 on top. Secondary ion mass spectrometry (SIMS) revealed that epilayers forming the ε-phase contain higher concentrations of chlorine, which suggests that compressive stress due to Cl- impurities may play a role in the growth of ε-Ga2O3 despite it being less than thermodynamically favorable.
30
Brown, Stephen James. "The Czochrlaski growth and characterisation of single crystals of lead molybdate." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364392.
Full text
31
Wu, Shyang-Chi, and 吳祥祺. "Thermal stress analysis of bulk single crystal during Czochralski growth." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/38663276210331986615.
Full textAbstract:
碩士<br>國立成功大學<br>機械工程研究所<br>81<br>Most of Single crystals is produced by the Czochralski(cz)
procress. The dislocations are frist introduced during
the Czochralski growth of GaAs that is crystallographic glid
caused by the excessive thermal stress. The dislocations formed
in bulk single crystals during Czochralski growth have adverse
effect on the performance of electronic and optical devices.
Most of studies have used the elastically isotropic model
characterized by the young''s modulus and the Poisson
ratio, which enables an axisymmetric thermal stress analysis.
This model is not correct. Strictly speaking, a three-
dimensional analysis, which takes account of elastic
anisotropic, should be conducted. Experimental evidence
indicates that in reality the solid-liquid interface is curved
during the Czochralski growth. Therefore, a parobolic-shape
interface is considered in this article. Moreover, in
order to accurately reflect the nature of material, the
physical properties are taken as function of temperature. A
powerful numerical method, consisting of discretizing the
space domain by F.E.M. , and treating the time domain by
Laplace and inverse Laplace transform,is adopted in this
article . The magnitude of stress and dislocation density
parameter are compared between anisotropic and isotroic
analyses.Numerical results indicate that the thermal stress
analyzed anisotropic theory is generally larger than
that by isotropic theory. Furthermore, significant
differences can be found in their distribution patterns
between both analyses. It is also observed that higher stress
level is concenrated around the bottom and top of interface.
Moreover,the larger the curvature of interface , the higher
the stress level concentrated in the top of interface.
32
Chiang, Chen Jeng, and 陳正強. "Growth of Lanthanum Galliun Silicate Single Crystals by Czochralski and Measurements." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/15336971890623766032.
Full textAbstract:
碩士<br>中華技術學院<br>電子工程研究所碩士班<br>96<br>ABSTRACT
This study uses the Czochralski Pulling Method to grow high quality langasite (Langasite, LGS) crystal. The method for growing LGS includes of placing a fixed weight LGS materials into a crucible. After that, insulating ceramics and then long seed crystal are placed inside in sequence into the furnace, before the internal cavity is vacuumed to a pressure of -6.5 × 10-3Pa. 90V heating is used to melt the LGS material uniformly. After that, a LGS crystal seed is placed in contact with the surface of the melted liquid LGS material and it is pulled for crystal growing. The pulling is stopped when the crystal growth reached a saturation stage. Subsequently, a cooling speed of 3v/hr is used. The LGS crystal solidified after around 20hrs. Internal cooling is done for 24 hours before the crystal inner temperature reached room temperature. The crystal can then be removed. The LGS crystal is then exposured under bright light test to study its macro-structure, and to detect any bubbles or inclusions defects.
After repeated experiments, a 3.5cm thick, 12.5 cm tall LGS crystal is grown successfully in this study. This study uses a semi-automated process. The control of the crystallization process is done by computer where parameters are setted. On the other hand, observation of weight and voltage change during crystal growth, seeding, cooling and vacuuming are done manually. This study is very dependent on manual operation. Very precise judgment in seeding time is needed to prevent the seed from being melted during seeding. Experience and experiment control are very important to keep the noises from manual operation which influences the experiment to a minimum, and to improve the stability of crystal growing
Keywords: Czochralski Pulling Method, Langasite, single crystal
33
Tsao, Pai-chun, and 曹百君. "Study on the Czochralski growth and phase inversion of LiAlO2 single crystals." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/45728595268657166874.
Full textAbstract:
碩士<br>國立中山大學<br>材料科學研究所<br>94<br>Three LiAlO2 single crystals were grown by the conventional Czochralski method under the ambient pressure with pull rate with 2.0~3.0 mm/min, rotation rate with 20~30 rpm, and at a certain growth temperature with a home-made furnace. The total lengths of the the LiAlO2 bulks are between 13.3~20 cm, including its cone and the root. The relation between the configuration of LiAlO2 bulk and the ways of the heat transport on the Czochralski method was addressed. In order to identify the inversion properties of the LiAlO2 specimen, 90°C water was utilized to etch both sides of the LAO specimen, (100) and (-100) surfaces, and we analyzed them with an optical microscopy (OM). The experimental results showed that there are certain different etching characteristics on the both sides of the specimen. The density of etch pits revealed 1.4~2.8 × 104 cm-2 on the (-100) surface, and no phase transition had been found in the specimen which was annealed for 24 hours at 800℃.
34
Huang, Jung-heng, and 黃中亨. "Study on the Czochralski Growth and characterization of (La,Sr)(Al,Ta)O3 single crystals." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/75691491002931501763.
Full textAbstract:
碩士<br>國立中山大學<br>材料科學研究所<br>94<br>In this work, two (La,Sr)(Al,Ta) O3 single crystals were grown by the conventional Czochralski pulling method by using different rotation rates and pull rates to find out the optimal growth conditions. The total length of the first (La,Sr)(Al,Ta) O3 crystal is about 8.5cm, and the shape is not symmetrical. The small thermal conductivity of the crystal would lead to small temperature gradient, so the growth rate was slow. The shape of the second crystal was improved by adjusting the thermal field. But, the bottom of the residual has blue color. The blue residual was analysed by x-ray and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Besides, the crystal structure was analyzed and the second phase had been found in crystals by high angle x-ray spectrum and polarizer microscope.
35
Tavakoli, Mohammad Hossein [Verfasser]. "Numerical analysis of seeding process during Czochralski growth of oxide single crystals / vorgelegt von Mohammad Hossein Tavakoli." 2006. http://d-nb.info/982851812/34.
Full text
36
Ying, Pan Hong, and 潘宏穎. "Numerical Simulation of Czochralski Crystal Growth." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/07071767800199926626.
Full text
37
He, Jiajie. "Segregation control in Czochralski crystal growth." 2002. http://www.library.wisc.edu/databases/connect/dissertations.html.
Full text
38
yhwang and 王裕鑫. "Growing YAG Single Crystal with Czochralski Method." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/97545470215350201566.
Full textAbstract:
碩士<br>中華技術學院<br>機電光工程研究所在職專班<br>97<br>This study investigated the single crystal growing process of Ytterbium doped Yttrium Aluminum Garnet (Yb:YAG) with the Czochralski method. An automatic control program was developed to control the process during the crystal growing. In this work, the computer program along with the weighting system and the automatic controller were integrated to control the power of the crystal growth system through a communication interface. This system was able to control the temperature of the process automatically. Therefore, the size and quality of the finished crystal can be achieved during the crystal growing process.
The results showed that the automatic control system could be successfully in conjunction with the crystal growth system. The stability and reliability of this system have been demonstrated by the experimental measurements. It is noted that the automatic temperature control was achieved and the high-quality Yb:YAG crystal was obtained effectively. This results provided an explicit parameter and distinct experience for progressed growing the Yb:YAG crystal, as well as for further industry application and development.
39
Chen, Chih-Yung, and 陳智勇. "Lithium Noibate crystal growth by the Czochralski method." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/22510190790770854790.
Full text
40
Lin, Ming-Hsien. "Segregation and shape control in Czochralski crystal growth." 1995. http://catalog.hathitrust.org/api/volumes/oclc/32875638.html.
Full text
41
hochunhsien and 何俊賢. "crystal growth of lithium niobate by Zone-Leveling Czochralski Method." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/93885318419782719953.
Full textAbstract:
碩士<br>國立臺灣大學<br>化學工程學研究所<br>91<br>Lithium niobate(LN) is one of the most important opto-electronic in applications including optical communication, optical storage, surface
-acoustic-wave etc. By using traditional Czochralski method, it can not get good diameter control in crystal growth process. And with segregation effect. It can not grow single crystal homogeneous in composition. We have grown Bismuth Silicate(BSO) crystal by using Zone-Leveling Czochralski(ZLCz) method, and have a good diameter control. We attempt to grow LN by using ZLCz method.
In this research project, we will discuss the mechanism of diameter control. Nevertheless. Bubble inclusion problem is always found in the process. We are able to solve this problem by using an inner crucible. In order to improve compositional uniformity and reduce the segregation effect, the feeding material has been directional solidified this material has been subsequently used for growth.
42
Chen, Hung Jen, and 陳煌仁. "Crystal Growth of Bismuth Silicate by Zone Leveling Czochralski Method." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/30502923516452390582.
Full textAbstract:
碩士<br>國立臺灣大學<br>化學工程學研究所<br>90<br>Nonlinear optical (NLO) crystals are important components in optoelectronic devices, and their growth is also a critical technology in the industry. Particularly, with the fast development of the optical information processing, computing, and storage, the need of photorefractive materials increases dramatically. Extensive research has been focused in this field. However, the quality of the crystals is often a bottleneck in its applications. By traditional Czochralski method, it is difficult to get good diameter control during growth. And with segregation effect, it can not grow single crystal with compositional uniformity. Therefore, we attempt to develop a non-traditional crystal growth technique, the so-called Zone-Leveling Czochralski (ZLCz) method. The ZLCz growth technique is a combination of the zone-melting (or leveling) and the Czochralski methods having the advantages of both methods. With the developed set up we have grown the important photorefractive single crystals, such as Bismuth Silicate (BSO).
In this research project, we discuss the mechanism of diameter control and established the stable crystal growth condition. Nevertheless, bubble inclusion problem is always found in the process. By using an inner crucible, we are able to solve this problem.
43
Chu, Hsin-chi, and 朱信旗. "Numerical simulation during an inductively heated Czochralski sapphire crystal growth system." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/99169550844455278658.
Full textAbstract:
碩士<br>國立中央大學<br>機械工程研究所<br>96<br>Sapphire single crystals are widely used in variety of modern high- tech applications. Among crystal growth methods, the Czochralski single crystal growth method is a good commercial method for growing the larger, high-optical-quality sapphire crystal. The finite element software COMSOL Multiphysics is employed to simulate the melt temperature and velocity distribution during an inductively heated of sapphire crystal growth process using CZ.
Temperature and velocity field in an inductively heated Czochralski crystal growth furnace is investigated numerically during the different crystal growth stage (from 25 to 125mm). The temperature and flow field inside the furnace was calculated coupled with the heat generation of the Ir crucible that was induced by the electromagnetic field (supported by the RF coil). The heat loss from the free surface and the crystal are due to thermal radiations which are calculated by the emissivity, the Gebhart factor and temperature of the furnace surface.
The results show that the temperature distributions of the melt and crystal are affected by the relative position between crucible and induction coil due to the modification of the electromagnetic field in the CZ furnace. The shape of solid-melt interface is also affected by the radiation of the crystal surface. Therefore, the growth parameters such as the position of RF coil, the growth length of crystal and the surface tension etc.; will be investigated in the present study.
44
Nguyen, Tran-Phu, and 阮陳富. "Numerical simulation for large size sapphire crystal growth during Czochralski method." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/e987d3.
Full textAbstract:
博士<br>國立中央大學<br>機械工程學系<br>107<br>Sapphire has become an important material for applications in modern optic-electronic technology because of its special optical, mechanical properties and the demand for sapphire substrates has increased significantly been enlarged in recent years. The Czochralski (CZ) technique plays an important role in the industrial growth of sapphire nowadays. However, the primary challenges faced in the manufacturing of sapphire substrates are to produce large size, low bubble defect and low thermal stress crystal. In this study, the thermal and flow transport and the solute concentration in the melt during the growth process in a large size (8 inch) sapphire crystal have been numerically investigated. From this study, it is expected to find the optimal crucible and crystal rotation for growing c-axis oriented large size sapphire crystal with lower convexity at the interface and lower thermal stress. The optimal crucible and crystal rotation rates in order to obtain the lower solute concentration, especially along the crystal-melt interface region is also obtained. This could lead to an improvement of crystal quality and make it possible to obtain better utilization of the material.
The computational results show that the convexity of the crystal is strongly dependent on the crucible and crystal rotation rates. Counter rotation between the crucible and the crystal results in a flatter crystal-melt interface and lower convexity, compared to the case with no crucible rotation or crystal rotation. Besides, high concentrations of von Mises stress are found close to the crystal-melt interface and are associated with higher curvature of the crystal surface. Applying counter rotation results in a lower temperature gradient in the radial direction along the crystal-melt interface as well as a lower thermal stress inside crystal. For the solute field, the magnitude and distribution of the solute concentration in the melt are strongly influenced by the convective flow and the thermal distribution. The lowest and most uniform solute distribution along the crystal-melt interface is obtained when the crucible rotation rate fixed at 1 rpm and there is no crystal rotation.
45
Shu-ShaoWang and 王書邵. "Numerical Analysis of Thermo-Fluid Flow and Crystal/Melt Interface Shape in Czochralski Crystal Growth." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/24220859661215267918.
Full textAbstract:
碩士<br>國立成功大學<br>工程科學系<br>102<br>Nowadays, the Czochralski (CZ) method is the most commonly used scheme for the single crystal growth of silicon, which is good for growing a large and high-quality crystal. The study is to simulate the furnace temperature and argon velocity distributions at different stages of silicon single-crystal growth, utilizing the Czochralski method. The numerical simulation is made by employing the finite element software COMSOL Multiphysics. Heat shields can prevent the heat loss in the upper portion of the furnace and guide the argon flow to make the SiO2 deposition decrease on the upper furnace wall. With the optimized hot zone, the increase of temperature gradient near the crystal/melt interface has the crystal grow faster. Accordingly, the heat shields and pulling rate are the primary factors affecting the heat transfer and crystal growth. Through analyses of the temperature distributions in the crystal and melt, it can be found that different heat transfer conditions and melt flow patterns lead to the formation of convex, concave or W shape interfaces. The results show that the temperature field affected by buoyant force causes the distortion of isothermals in melt. As the solid fraction is raised, the temperature and velocity fields of melt become eased and the increase of ingot surface enhances the heat dissipation, which makes the interface shape more convex. The crucible rotation creates three vortex in the melt, which results in the stable melt. Before adding the heat shield and changing pulling rate, the crystal/melt interface is W-shaped. After adding the heat shield, the interface becomes concave. With the increase of the pulling rate, the shape of the interface becomes flatter than before.
46
Hsieh, Yao-Te, and 謝耀德. "Numerical Simulation of Large-Size Sapphire Crystal Growth with the Czochralski Process." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/49419244343293617669.
Full textAbstract:
碩士<br>國立中央大學<br>機械工程學系<br>103<br>The Czochralski method is one of the major technologies used for high quality single crystal growth. Recently, this technology has been applied for industrial larger size sapphire crystal growth. In order to ensure the quality of the crystal growth, we must gain further insight into the flow behavior of the molten melt and heat transfer mechanisms in Czochralski furnace.
During the large size sapphire crystal growth, the temperature of furnace is too high to be observed in experiments directly. Therefore, numerical simulation is necessary in order to reduce the cost and time of experiments. The purpose of this thesis is to numerically investigate on thermal flow field, shape of the crystal-melt interface and thermal stress for larger sapphire crystal growth using the COMSOL Multiphysics software base on the finite element method.
The results show that the flow field is dominated by a buoyant vortex and the isotherms are distorted by the strong buoyancy force. The intensity of the vortex decreases when the power supply reduces. The crystal-melt interface would be more convex to the molten melt when the crystal grows. The crucible rotation increase the transfer of heat convection due to the enhancement of the buoyant vortex. The crystal rotation results in a forced vortex below crystal-melt interface caused by centrifugal force, more heat is transferred to crystallization front. The counter rotation between the crucible and the crystal results in the flatter crystal-melt interface and the lower crystal’s convexity. There is an optimal combination of the crystal and crucible rotation rates for each crystal growth length. The thermal stress would increase when the size of the crystal growth increase. Moreover, the thermal stress significantly decreases for the lower convexity of the crystal-melt interface due to the reduction of temperature gradient in the radial direction along the interface.
47
Thu, Nguyen Thi Hoai, and 阮氏懷秋. "Numerical Study of Impurity Transport during Czochralski Arsenic-doped Silicon Crystal Growth." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/53528976148509821912.
Full textAbstract:
碩士<br>國立中央大學<br>機械工程學系<br>102<br>Nowadays the Czochralski (Cz) technique has become a main method to grow large single silicon crystal. In order to enhance the quality of crystal, the level of oxygen concentration in the ingot as well as its electric properties has to be controlled. The optimal resistivity for the silicon epitaxial wafers can be obtained by adding directly some common dopants (boron, arsenic, phosphorus, antimony …) into the liquid silicon during the growth process.
In this study, the effect of doping arsenic on the oxygen concentration along the freezing interface is numerically investigated by finite volume method (FVM). In order to compare with the experimental resistivity provided by SAS Company, the conversion of crystal resistivity from arsenic concentration is made by using the standard transformation formulation. It is clear that the simulation predictions have similar tendency with the experimental ones in crystal resistivity.
The computational results show the mechanism of oxygen content reduction in heavily arsenic-doped Cz silicon melt as compared with non-doped melt. This is because arsenic doping decreases the thermodynamic activity coefficient of oxygen dissolved into the bulk melt from silica. Arsenic content also increases along the length of crystal due to its small segregation coefficient (k0=0.3). The arsenic atoms concentrated in the ingot center are much more than their concentration in the region of crystal edge.
Furthermore, the increase in doping level causes a decrease of oxygen content in the growth direction while this increases the radial segregation of arsenic. There is an inverse relationship between dopant concentration and crystal resistivity.
Last but not least, the effect of pulling rate and rotation rate on the resistivity is also predicted numerically. The results indicate that the radial resistivity variation of ingot increases with increasing the growth rate as well as crucible rotation rate while this trend is reversed as the crystal rotation rate is accelerated.
48
Jyun-HaoHuang and 黃俊豪. "COMSOL Analysis on Heat and Mass Transfer and Crystal/Melt Interface Shape in Czochralski Crystal Growth." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/3d4579.
Full textAbstract:
碩士<br>國立成功大學<br>工程科學系<br>103<br>Czochralski method is the most commonly used to grow large single crystals of silicon. In the growth process of silicon single crystal, due to the furnace body of very high temperature, the thermal flow within the melt pool cannot be observed directly. Consequently, the numerical simulation is employed to control the situation in the furnace, which could help to reduce the cost and time of crystal-growth experiments.
The study is to use COMSOL Multiphysics software to simulate the thermal flow in the furnace of Czochralski method during the crystal growth. It is expected to obtain the temperature and velocity fields and the relevant data in the furnace. It is mainly based on the different growth stages of the silicon ingot to simulate the temperature, velocity and concentration fields and the shape variation of the crystal/melt interface. In the simulation, the crucible and crystal rotations and the radiation shield are considered to analyse their effects on the heat flow and concentration fields and the interface shape.
From the simulation results of the silicon crystal growth, the natural convection, caused by the coupled effect of temperature and flow fields, could make the temperature distribution of the melt pool uneven. By using the rotation of the crucible and the crystal, the natural convection could be suppressed and the thermal flow field would be modified. Consequently, the impact of pulling rate could not make the crystal/melt interface produce different shapes and affect the internal defects. The installation of the radiation shield could effectively guide the gas flow and reduce the input heater power.
49
Chen, Chu-Su, and 陳鏡宇. "Growth of Solar Graded Single Crystalline Silicon by Crystalline Czochralski Method." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/um4g4r.
Full textAbstract:
碩士<br>國立虎尾科技大學<br>光電與材料科技研究所<br>98<br>This study investigates the influence of temperature, seed pulling rate, diameter control, and rising speeds and rotating rate of crucible on the solid - liquid interface quality during the growth of single crystal by Czochralski method.。
In this study, regarding the heat flow field in the furnace body and the diameter control of ingot, increasing the rotation speed of pillar crystal will lead to more intensive isotherm lines below the pillar crystal region. In this region the temperature changes very violently, where the cover bowl symptoms occur when ingot rod is formed. Meanwhile the melt re-flowing field in the crucible will gradually decrease, which will affect the dopant distribution becoming not uniform. When the rotation speed of crucible increases, the internal center temperature distribution of the melt inside the crucible will become non- uniform and form a cold region then resulting in crystal rods stick out during crystal pulling process. This will damage the ingot rod formation. In the flow field the generation of forced convection results in a non-uniformity for dopant distribution which will also affect the quality of pillar crystals. When the crucible has a relative rotation with ingot rod, if the ingot rod and crucible rotation speed decrease, the vortex at the bottom of crucible symmetry axis will become smaller, and the dopant distribution non-uniform situation will reduce. The results verify the equations of silicon ingot solidified rate (dm/dt) and temperature gradient (dt/dx). And growing 8” silicon ingot succeeded in 16 hours by AST silicon ingot puller. Optimized growth parameters can also control the silicon ingot diameter and quality accurately.
50
Chen, Bing-Jung, and 陳炳忠. "Numerical Simulation of thermal and microdefect distributions during the Czochralski Si-Crystal Growth." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/32204214799386084375.
Full textAbstract:
碩士<br>國立中央大學<br>機械工程研究所<br>92<br>To clear the characteristics of the Czochralski (Cz) furnace for the single-crystal growth of silicon, a set of global analyses of momentum, heat and mass transfer in small Cz furnaces is carried out using the finite-element method. Consider the global system to be a steady state, axisymmetric system with laminar flow, and ideal gas condition. Convective and conductive heat transfers, radiative heat transfer between diffuse surfaces and the Navier–Stokes equations for gas are all combined and solved together.
In this work, heat shield is installed in the Czochralski furnace. Heat shield refers from the reference papers and U.S. patent. Heat shield will effect the thermal and microdefect distributions. In this work will analysis the heat shield effects by numerical simulation.