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Kast, Matthew. "Towards Tunable and Multifunctional Interfaces: Multicomponent Amorphous Alloys and Bilayer Stacks." Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22288.
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Controlling the electronic structure and requisite charge transfer at and across interfaces is a grand challenge of materials science. Despite decades of research and numerous successes in the fields microelectronics and photovoltaics much work remains to be done. In many applications, whether they be in microelectronics, photovoltaics or display technology there is a demand for multiple functions at a single interface. Historically, existent materials were either discarded as an option due to known properties or tested with some application based figure of merit in mind. Following this, the quality of the material and/or the preparation of the surface/interface to which the material would be deposited was optimized. As the microelectronics and photovoltaics industries have matured, continued progress (faster, lower power transistors and more efficient, cheaper, abundant solar cells) will require new materials (possibly not previously existent) that are fundamentally better for their application than their highly optimized existent counter parts. The manifestation of this has been seen in the microelectronics field with introduction of hafnium silicates to replace silica (which had previously been monumentally successful) as the gate dielectrics for the most advanced transistors. Continued progress in efficient, cheap, abundant photovoltaics will require similar advances. Advances will be needed in the area of new abundant absorbers that can be deposited cheaply which result in materials with high efficiencies. In addition, selective contacts capable of extracting charge from efficient absorbers with low ohmic losses and low recombination rates will be needed. Presented here are two approaches to the multifunctional interface problem, first the use of amorphous alloys that open up the accessible composition space of thin films significantly and second the use of bilayers that loosen the requirements of a single film at an interface.
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Hassanali, Ali. "WATER AT MOLECULAR INTERFACES: STRUCTURE AND DYNAMICS NEAR BIOMOLECULES AND AMORPHOUS SILICA." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1275314943.
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Mews, Mathias [Verfasser], Bernd [Gutachter] Rech, i. Cabarrocas Pere [Gutachter] Roca, and Bernd [Gutachter] Szyszka. "Interfaces in amorphous/crystalline silicon heterojunction solar cells / Mathias Mews ; Gutachter: Bernd Rech, Pere Roca i Cabarrocas, Bernd Szyszka." Berlin : Technische Universität Berlin, 2016. http://d-nb.info/1156181437/34.
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Ross, Nick. "Interfacial Electrochemistry of Cu/Al Alloys for IC Packaging and Chemical Bonding Characterization of Boron Doped Hydrogenated Amorphous Silicon Films for Infrared Cameras." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849696/.
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We focused on a non-cooling room temperature microbolometer infrared imaging array device which includes a sensing layer of p-type a-Si:H component layers doped with boron. Boron incorporation and bonding configuration were investigated for a-Si:H films grown by plasma enhanced chemical deposition (PECVD) at varying substrate temperatures, hydrogen dilution of the silane precursor, and dopant to silane ratio using multiple internal reflection infrared spectroscopy (MIR-IR). This study was then confirmed from collaborators via Raman spectroscopy. MIR-IR analyses reveal an interesting counter-balance relationship between boron-doping and hydrogen-dilution growth parameters in PECVD-grown a-Si:H. Specifically, an increase in the hydrogen dilution ratio (H2/SiH4) or substrate temperature was found to increase organization of the silicon lattice in the amorphous films. It resulted in the decrease of the most stable SiH bonding configuration and thus decrease the organization of the film. The new chemical bonding information of a-Si:H thin film was correlated with the various boron doping mechanisms proposed by theoretical calculations. The study revealed the corrosion morphology progression on aluminum alloy (Al, 0.5% Cu) under acidic chloride solution. This is due to defects and a higher copper content at the grain boundary. Direct galvanic current measurement, linear sweep voltammetry (LSV), and Tafel plots are used to measure corrosion current and potential. Hydrogen gas evolution was also observed (for the first time) in Cu/Al bimetallic interface in areas of active corrosion. Mechanistic insight that leads to effective prevention of aluminum bond pad corrosion is explored and discussed.
(Chapter 4) Aluminum bond pad corrosion activity and mechanistic insight at a Cu/Al bimetallic interface typically used in microelectronic packages for automotive applications were investigated by means of optical and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and electrochemistry. Screening of corrosion variables (temperature, moisture, chloride ion concentration, pH) have been investigated to find their effect on corrosion rate and to better understand the Al/Cu bimetallic corrosion mechanism. The study revealed the corrosion morphology progression on aluminum alloy (Al, 0.5% Cu) under acidic chloride solution. The corrosion starts as surface roughening which evolves into a dendrite structure and later continues to grow into a mud-crack type corrosion. SEM showed the early stage of corrosion with dendritic formation usually occurs at the grain boundary. This is due to defects and a higher copper content at the grain boundary. The impact of copper bimetallic contact on aluminum corrosion was explored by sputtering copper microdots on aluminum substrate. Copper micropattern screening revealed that the corrosion is activated on the Al/Cu interface area and driven by the large potential difference; it was also seen to proceed at much higher rates than those observed with bare aluminum. Direct galvanic current measurement, linear sweep voltammetry (LSV), and Tafel plots are used to measure corrosion current and potential. Hydrogen gas evolution was also observed (for the first time) in Cu/Al bimetallic interface in areas of active corrosion. Mechanistic insight that leads to effective prevention of aluminum bond pad corrosion is explored and discussed. Micropattern corrosion screening identified hydrogen evolution and bimetallic interface as the root cause of Al pad corrosion that leads to Cu ball lift-off, a fatal defect, in Cu wire bonded device. Complete corrosion inhibition can be achieved by strategically disabling the mutually coupled cathodic and anodic reaction cycles.
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Lidbaum, Hans. "Transmission Electron Microscopy for Characterization of Structures, Interfaces and Magnetic Moments in Magnetic Thin Films and Multilayers." Doctoral thesis, Uppsala universitet, Experimentell fysik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-107941.
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Structural characterization is essential for the understanding of the magnetic properties of thin films and multilayers. In this thesis, both crystalline and amorphous thin films and multilayers were analyzed utilizing transmission electron microscopy (TEM). High resolution TEM and electron diffraction studies emphasize on the growth of amorphous Fe91Zr9 and Co68Fe24Zr8 on both Al2O3 and Al70Zr30 in multilayer structures by magnetron sputtering. The properties of the growth surfaces were found to strongly influence the formation of nano-crystallites of the magnetic material at interfaces. Field induced uniaxial magnetic anisotropy was found to be possible to imprint into both fully amorphous and partially crystallized Co68Fe24Zr8 layers, yielding similar magnetic characteristics regardless of the structure. These findings are important for the understanding of both growth and magnetic properties of these amorphous thin films. As magnetic systems become smaller, new analysis techniques need to be developed. One such important step was the realization of electron energy-loss magnetic circular dichroism (EMCD) in the TEM, where information about the ratio of the orbital to spin magnetic moment (mL/mS) of a sample can be obtained. EMCD makes use of angular dependent inelastic scattering, which is characterized using electron energy-loss spectroscopy. The work of this thesis contributes to the development of EMCD by performing quantitative measurements of the mL/mS ratio. Especially, methods for obtaining energy filtered diffraction patterns in the TEM together with analysis tools of the data were developed. It was found that plural inelastic scattering events modify the determination of the mL/mS ratio, wherefore a procedure to compensate for it was derived. Additionally, utilizing special settings of the electron gun it was shown that EMCD measurements becomes feasible on the nanometer level through real space maps of the EMCD signal.
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Fagas, Georgios. "Vibrational properties of complex solids." Thesis, Lancaster University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321898.
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Varache, Renaud. "Development, characterization and modeling of interfaces for high efficiency silicon heterojunction solar cells." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112279/document.
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L’interface entre le silicium amorphe (a-Si:H) et le silicium cristallin (c-Si) est un constituent clés de cellules solaires à haut rendement reposant sur des procédés à basse température. Trois propriétés de l’interface déterminent le rendement des cellules solaires à hétérojonction de silicium: les décalages de bandes entre a-Si:H et c-Si, les défauts d’interface et la courbure de bande dans c-Si. Ces trois aspects sont traités dans ces travaux de thèse.Dans un premier un temps, un calcul analytique de la courbure de bande dans c-Si est développé. Il repose sur l’approximation d’une densité d’état (DE) constante dans la bande interdite de a-Si:H. L’influence des principaux paramètres de la structure sur la courbure de bande est étudiée : décalage de bande, densité d’état dans a-Si:H, défaut d’interface, etc. La présence d’un effet de confinement quantique est discutée. Grâce à une comparaison entre ces calculs et des mesures de conductance planaire en fonction de la température sur des structures (p)a-Si:H/(n)c-Si et (n)a-Si:H/(p)c-Si, les décalages de bande de valence et de conduction ont pu être estimés à 0.36 eV et 0.15 eV respectivement. En outre, il est montré que le décalage de la bande de valence est indépendant de la température, alors que le décalage de la bande de conduction suit les évolutions des bandes interdites de c-Si et a-Si:H. Ces mesures tendent à prouver que le ‘branch point’ dans a-Si:H est indépendant du dopage.Ensuite, les calculs analytiques sont approfondis pour prendre en compte différents aspects de la structure complète incorporée dans les cellules : contact avec un oxyde transparent conducteur, présence d’une couche de a-Si:H non-dopée à l’interface. A l’aide de simulations numériques et à la lumière de mesures de conductance planaire conjuguées à des mesures de la qualité de passivation de l’interface, des pistes pour optimiser les cellules à hétérojonction sont commentées. En particulier, il est montré qu’un optimum doit être trouvé entre une bonne passivation et une courbure de bande suffisante. Ceci peut être accompli par un réglage fin des propriétés de la couche tampon (épaisseur, dopage), du contact (travail de sortie élevé) et de l’émetteur (p)a-Si:H (densité de défauts et épaisseur). En particulier, un émetteur avec une DE importante conduit paradoxalement à de meilleures performances.Enfin, un nouveau type d’interface a été développé. La surface de c-Si a été oxydée volontairement dans de l’eau pure dé-ionisée à 80 °C avant le dépôt de (p)a-Si:H afin d’obtenir une structure (p)a-Si:H/SiO2/(n)c-Si. A l’aide d’un modèle de courant par effet tunnel implémenté dans le logiciel de simulation numérique AFORS-HET, l’effet d’une couche à grande bande interdite (comme c’est le cas pour SiO2) sur les performances de cellules est étudié : le facteur de forme et le courant de court-circuit sont extrêmement réduits. En revanche, une couche de SiO2 n’a que peu d’impact sur les propriétés optiques de la structure. Expérimentalement, les échantillons réalisés montrent une qualité de passivation à mi-chemin entre le cas sans couche tampon et le cas avec (i)a-Si:H : ceci est expliqué par la présence d’une charge fixe négative dans l’oxyde. La courbure de bande dans c-Si est moins affectée par la présence d’une couche d’oxyde que d’une couche de (i)a-Si:H. Les cellules solaires réalisées démontrent que le concept a le potentiel d’aboutir à de hauts rendements : sur des structures non-optimisées, une tension de court-circuit supérieure à 650 mV a été démontrée, alors que l’oxyde ne semble pas limiter le transport de charge<br>The interface between amorphous silicon (a-Si:H) and crystalline silicon (c-Si) is the building block of high efficiency solar cells based on low temperature fabrication processes. Three properties of the interface determine the performance of silicon heterojunction solar cells: band offsets between a-Si:H and c-Si, interface defects and band bending in c-Si. These three points are addressed in this thesis.First, an analytical model for the calculation of the band bending in c-Si is developed. It assumes a constant density of states (DOS) in the a-Si:H band gap. The influence of most parameters of the structure on the band bending is studied: band offsets, DOS in a-Si:H, interface defects, etc. The presence of quantum confinement at the interface is discussed. Analytical calculations and temperature dependent planar conductance measurements are compared such that the band offsets on both (p)a-Si:H/(n)c-Si and (n)a-Si:H/(p)c-Si can be estimated: the valence band offset amounts 0.36 eV while the conduction band offset is 0.15 eV. In addition, it is shown that the valence band offset is independent of temperature whereas the conduction band offset follows the evolutions of c-Si and a-Si:H band gaps with temperature. A discussion of these results in the frame of the branch point theory for band line-up leads to the conclusion that the branch point in a-Si:H is independent of the doping.Then, analytical calculations are developed further to take into account the real solar cell structure where the a-Si:H/c-Si structure is in contact with a transparent conductive oxide and an undoped buffer layer is present at the interface. Measurements of the planar conductance and of the interface passivation quality are interpreted in the light of analytical calculations and numerical simulations to open a way towards a method for the optimization of silicon heterojunction solar cells. It is particularly shown that a trade-off has to be found between a good passivation quality and a significant band bending. This can be realized by tuning the buffer layer properties (thickness, doping), the TCO-contact (high work function) and the emitter (defect density and thickness). Interestingly, an emitter with a high DOS leads to better cell performances.Finally, a new type of interface has been developed, that was not applied to heterojunction solar cells so far. The c-Si surface has been oxidized in deionized water at 80 °C before the (p)a-Si:H emitter deposition such that (p)a-Si:H/SiO2/(n)c-Si structures were obtained. A tunneling current model has been developed, implemented in the 1D numerical device simulator AFORS-HET and used to study the effect of a wide band gap interfacial layer (as it is the case for SiO2) on cell performance: the fill-factor and the short-circuit current are dramatically reduced for thick and high barriers. However, a SiO2 layer has only little impact on optical properties. Fabricated samples show a passivation quality halfway between samples with no buffer layer and with an (i)a-Si:H buffer layer: this is explained by the presence of a negative fixed charge in the oxide. The band bending in (n)c-Si is higher with an oxide layer than with an (i)a-Si:H buffer layer. Solar cells demonstrate that this new concept has the potential to achieve high power conversion efficiencies: for non-optimized structures, an open-circuit voltage higher than 650 mV has been demonstrated, while the oxide does not seem to create a barrier to charge transport
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Luo, Haoming. "High frequency thermomechanical study of heterogeneous materials with interfaces." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI130.
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Le transfert de chaleur est intimement lié à la propagation du son (transfert acoustique) dans les matériaux, par exemple dans les isolants et les semi-conducteurs, les principaux vecteurs d’énergie sont des phonons acoustiques. Le concept de présence d’interfaces a été largement exploité pour manipuler efficacement les phonons des longueurs d’onde macroscopiques aux longueurs d’onde nanométriques. Les derniers correspondent aux fréquences en régime THz, qui sont responsables du transport thermique à température ambiante. Dans cette thèse, la méthode des éléments finis est utilisée pour effectuer des analyses transitoires de la propagation des paquets d’ondes dans différents milieux à 2D. Elle est commencée par une étude paramétrique de l’atténuation des paquets d’ondes dans un système élastique semi-infini avec des interfaces circulaires périodiques. Trois paramètres clés sont étudiés, notamment le contraste de rigidité, la densité d’interface et la longueur d’onde des phonons. Différents régimes de transfert (propagatif, diffusif et localisé) sont identifiés, qui permettent d’identifier la contribution des phonons à la conductivité thermique. Outre les interfaces circulaires, la réponse mécanique et l’atténuation acoustique pour différents types d’interfaces sont également étudiées, telles que l’inclusion de forme dendritique, l’inclusion d’Eshelby, et les matériaux poreux avec des pores ordonnés / désordonnés. Afin d’étendre l’étude aux matériaux amorphes, j’ai également considéré un milieu hétérogène avec des rigidités aléatoires réparties dans l’espace selon une distribution gaussienne basée sur la théorie de l’élasticité de cisaillement hétérogène des verres. Enfin et surtout, deux versions de lois de comportement viscoélastiques sont proposées pour prendre en compte l’atténuation intrinsèque des phonons dépendant de la fréquence dans les verres, dans le but qu’un milieu visqueux homogène puisse reproduire cette atténuation intrinsèque. La simulation par éléments finis confirme qu’un modèle continu peut suivre strictement l’atténuation atomistique (G) avec une loi de comportement viscoélastique linéaire macroscopique bien calibrée. Par rapport aux données expérimentales de a-SiO2, notre deuxième loi de comportement reproduit qualitativement et quantitativement les trois régimes d’atténuation acoustique en fonction de la fréquence : successivement Γ ∝ ω^2,ω^4,ω^2<br>Heat transfer is actually intimately related to the sound propagation (acoustic transfer) in materials, as in insulators and semi-conductors the main heat carriers are acoustic phonons. The concept of the presence of interfaces has been largely exploited for efficiently manipulating phonons from long-wavelength to nanometric wavelengths, i.e., frequencies in THz regime, responsible for thermal transport at room temperature. In this thesis, the finite element method is used to perform transient analysis of wavepacket propagation in different mediums. I started with a parametric study of attenuation of acoustic wave-packets in a 2D semi-infinite elastic system with periodic circular interfaces. Three key parameters are investigated, including rigidity contrast, interface density and phonon wavelength. Different energy transfer regimes (propagative, diffusive, and localized) are identified allowing to understand the phonon contribution to thermal transport. Besides the circular interfaces, mechanical response and acoustic attenuation for different types of interfaces are also investigated, such as Eshelby’s inclusion, dendritic shape inclusion and porous materials with ordered/disordered holes. In order to extend the study to amorphous materials, I also considered a heterogeneous medium with random rigidities distributed in space according to a Gaussian distribution based on the theory of heterogeneous shear elasticity of glasses. Finally yet importantly, viscoelastic constitutive laws are proposed to take into account the frequency-dependent intrinsic phonon attenuation in glasses, with the aim of reproducing such intrinsic attenuation using a homogeneous viscous medium. Finite element simulation confirms that a continuum model may strictly follow the atomistic attenuation (G) for a well-calibrated macroscopic linear viscoelastic constitutive law. Compared with the experimental data in a-SiO2, our second constitutive law reproduces qualitatively and quantitatively the three regimes of acoustic attenuation versus frequency : successively Γ∝ω^2,ω^4,ω^2
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Zhu, Kai Schiff Eric A. "Interface modulation spectroscopy and doping physics in amorphous silicon." Related Electronic Resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2003. http://wwwlib.umi.com/cr/syr/main.
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Gandy, Amy S. "A Transmission Electron Microscopy study of the Interaction between Defects in Amorphous Silicon and a Moving Crystalline/Amorphous Interface." Thesis, University of Salford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502784.
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Gandy, Amy Sarah. "A Transmission electron microscopy study of the interaction betweeen defects in amorphous silicon and a moving crystalline amorphous interface." Poitiers, 2008. http://theses.edel.univ-poitiers.fr/theses/2008/Gandy-Amy/2008-Gandy-Amy-These.pdf.
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Transmission electron microscopy (TEM) has been used to investigate the damage produced following high temperature (350˚C) Xe implantation into [100] Si at fluencies (>1x1016 Xe ions/cm2) and energy (250keV) which produce a buried amorphous layer; and the defect structures produced following thermal anneals of 400˚C, 600˚C or 800˚C for 30 minutes. Analysis of these samples yielded results which suggested that the Xe gas contained within the amorphous layers was swept by the amorphous/crystalline interfaces during solid phase epitaxial re-crystallisation (SPEG) into large bubbles elongated along a direction perpendicular to the interfaces. In order to further investigate this sweeping effect, buried amorphous layers were produced in Si by implanting Li at liquid nitrogen temperature and post implanting the layers with 1x1016 He ions/cm2. Contrary to the spherical bubbles produced under similar conditions in crystalline Si, irregular shaped bubbles were formed in the amorphous layer. Results from in-situ TEM studies showed that these bubbles are mobile at temperatures lower than expected in crystalline Si. Thus, upon reaching the moving interfaces between amorphous and crystalline Si, the bubbles are forced back into the amorphous material which ultimately results in coalescence of the gas into larger bubbles once the two interfaces combine. In addition, microtwins have been shown to form in regions of the re-crystallising layer where there exists an excess of interstitial-type defects. This is contrary to previous microtwin nucleation models which suggested that microtwins are either formed on [111] planes or on bubbles<br>L'endommagement induit par implantation de xénon dans le silicium a été étudié par microscopie électronique à transmission (MET). Les implantations réalisées à 350°C, à une énergie de 250keV et pour des fluences supérieures à >1x1016 Xe ions/cm2 conduisent à la formation d'une couche amorphe enterrée. Les observations effectuées sur les échantillons recuits montrent la présence d'une rangée de grandes cavités allongées dans la direction perpendiculaire à l'interface. Ceci suggère que, lors de la recristallisation du silicium, le déplacement simultané des deux interfaces entraîne le déplacement du gaz jusqu'à son confinement dans de larges bulles. Afin de mieux appréhender les mécanismes qui conduisent au mouvement des bulles, de l'hélium à faible dose a été implanté dans du silicium préalablement amorphisé par implantation de Li à basse température. L'implantation d'hélium dans le silicium amorphe conduit à la formation de bulles de forme irrégulière. Ce résultat diffère du silicium cristallin où des bulles sphériques sont obtenues pour des conditions d'implantation identiques. Les expériences réalisées ‘in situ’ dans le MET montrent clairement d'une part que les bulles sont poussées par l'interface, et d'autre part la nucléation de micromacles. Il a été mis en évidence au cours de cette étude que les bulles sont mobiles à plus basse température dans le silicium amorphe que dans la phase cristalline. Lors de la recristallisation, les bulles se trouvent alors confinées dans le matériel amorphe, ce qui résulte en leur coalescence et à la formation de larges bulles une fois que les deux fronts de recristallisation se sont rejoints. De plus, il a été établi que la formation de micromacles dans la région recristallisée est liée à un excès de défauts de type interstitiels dans la zone amorphe. Ce résultat est contraire aux modèles de la littérature qui suggèrent que les micromacles se forment soit sur des plans {111} soit sur les bulles
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Gilchrist, Valerie A. "The adsorption of surfactant at the amorphous polymer-solution interface." Thesis, University of Surrey, 2002. http://epubs.surrey.ac.uk/844324/.
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Adsorption of surfactants onto amorphous polymers at the solid-solution interface is of direct relevance to many industrial sectors ranging from food, pharmaceuticals, paints, paper and photographic colour films. Although it is widely accepted that surfactants play the underpinning role in these applications, little is currently understood about the interactions between surfactants and polymeric materials at the molecular level. This lack of progress is mainly due to the inability of most existing techniques in probing this type of structural information at the wet interface. Specular neutron reflection (SNR) is a recently developed technique capable of detecting structural information with resolution down to a few angstroms (A). When combined with deuterium labelling, it is possible to distinguish the surfactant from the polymeric species at the interface. The aim of this work is to explore the appropriate experimental approach that utilizes the potential of neutron reflection to unravel molecular information about the actions of surfactants. A major progress that was made in the project was the development of experimental protocols for the formation of smooth polymeric thin films onto neutron transparent substrates. This experimental process was substantially supported by spectroscopic ellipsometry (SE), a home-based laboratory optical system that was also highly sensitive to film thickness and composition. This exploratory work has mainly used model polymeric samples that are of broader implications to various technological applications. A nonionic alkyl ethoxylate surfactant, such as C12E5 was chosen because its interfacial behaviour has been widely examined. Measurements were made over a wide concentration range around the critical micellar concentration (cmc), using specially designed cells. In the case of PMMA (poly(methylmethacrylate)), adsorption of C12E5 was found to be completely reversible with no observable penetration of the surfactant into the polymer. The area per surfactant at the cmc (Acmc) was found to be around 50A2. Good agreement was obtained between SE and SNR, but the latter revealed additional information about the in-situ conformational structure of the surfactant. It was found that at the cmc, the dodecyl chain layer was only 4-SA thick, indicating that the alkyl chains lay virtually flat on PMMA surface. The ethoxylate headgroup layer was however some 16A thick, indicating the projection of the headgroups into the aqueous solution. In contrast, when anionic SDS (sodium dodecyl sulphate) and cationic C12TAB (dodecyl trimethyl ammonium bromide) were used, a much reduced adsorption was observed. While these results highlight the role of the type of surfactant headgroups, it shows the power of SNR and the effectiveness of the experimental approach adopted in unravelling molecular information at the interface. This experimental approach was subsequently extended to PBMA and PS for the assessment of different polymeric substrates. The varying extent of surfactant adsorption and the ingress of the surfactant associated with film swelling have clearly shown that with careful control of experimental conditions, detailed structural information can be reliably revealed from the experimental procedures that I have developed.
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Djurberg, Viktor. "Tailoring the Magnetic Properties of Amorphous TbCo Nano Films." Thesis, Uppsala universitet, Materialfysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-348209.
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The possibility to change magnetic anisotropy of amorphous TbCo films from out-of-plane to in-plane has been investigated. The effects of TbCo film's thickness and composition on the magnetic anisotropy were investigated together with the effects of growing the TbCo films on a SmCo seed layer. This was studied by sputtering TbCo films of composition Tb_xCo_(100-x) x=16,18,20,22 and 24, with thickness ranging between 2-20 nm, with and without the presence of a 20 nmSm_15Co_85 seed layer. All films were grown in a 130 mT magnetic in-plain field to imprint an in-plane anisotropy. The structure and composition of the films were examined with Rutherford backscattering spectrometry, X-ray reflectivity, and Grazing incidence X-ray diffraction. The magnetic properties of the films were studied with magneto-optic Kerr effect measurement, vibrating sample magnetometer, Kerr microscopy and magnetic force microscopy. The magneto-optic Kerr effect measurement showed that it was possible to change TbCo film's preferred magnetization direction from out-of-plane to in-plane by reducing the film thickness. The SmCo layer made it easier for theTbCo films to change preferred magnetization direction from out-of-plane to in-plane.
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Walczak, Malgorzata. "Role and properties of the confined amorphous phase of polymers." Phd thesis, Paris, ENSAM, 2012. http://pastel.archives-ouvertes.fr/pastel-00839174.
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The aim of the thesis was to elucidate the effect of confinement of amorphous phase of apolymer above its glass transition temperature being in contact with another polymer in a rigid state.Confinement is unavoidably connected with surfaces enforcing confinement. It is very difficult to separate theeffect of confinement from the effect of interfaces because both effects arise parallel and coincide. Multilayeredfilms were chosen as the base material for the studies because they contain multifold number of confined layerand response from confinement and interfaces is multifold increased. Hoping that some of experimentaltechniques are more sensitive to interfaces while others to confinement we selected the following:microcalorimetry, SSNMR, direlectrical spectroscopy and dynamic shear rheology. We have searched for theinfluence of PS on dynamics of phenyl rings of PC for PC/PS film with ratio 70/30 in the temperature rangefrom 296 K to 393 K employing PILGRIM pulse sequence. .We show that above the glass transition temperatureof PS, the PC component became more flexible. It is at the first glance the effect of the interface because there isno significant confinement of thicker PC layers. Dielectric relaxation spectroscopy measurements in our studyclearly provide evidence for deviations from a simple 2-phase structure in multilayered films PC/PS that is worthto be analyzed more in the future. The dielectric response of the multilayer samples was also modeled andcompared with experimental results. We obtained again discrepancies between the simulated spectra and themeasured spectra for multilayer films. Knowing the exact composition and viscoelastic behaviour of eachcomponent, the theoretical viscoelastic behavior of composites has been predicted numerically. Then,rheological tests have been made, and confronted with numerical predictions, to detect the confinement effect.The upper limit of thickness beyond which PS in confined layers at rubbery state becomes stiffer than in bulk isabout 150/200 nm. It appeared that the shear modulus of the thinnest PS layers (10 nm) is nearly 2.5 times largerthan that for bulk PS sample. We can note that Tg of PS layers also begins to increase beyond this upper limit ofthickness.. None of the experiment could clearly deliver the information about the effect of confinement orinterface on the behavior of PS layers alone. The results obtained here point out that separation of the effects ofconfinement and interfaces remains very difficult.
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Liu, Richard Yufeng. "Oxygen Transport as a Structure Probe for Amorphous Polymeric Systems." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1103694304.
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Eggers, Tatiana M. "Surface and Interface Effects of Magnetoimpedance Materials at High Frequency." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7282.
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Amorphous and nanocrystalline transition metal magnetic alloys (TMMAs) have been the subjects of fundamental and applied study due to their unique structure. The lack of long-range order in these materials sets the stage for their soft magnetic properties to be tuned for a variety of technological applications, such as sensitive magnetic field sensors, high frequency transformers, and stress sensors. Fundamental investigation of the magnetic and structural properties of these materials is also motivated by their unique amorphous or nanocrystalline-embedded amorphous matrix morphology, which has consequences on both the magnetism seen from both the atomic and macro-scale. The surfaces of these materials become important to their high frequency applications, where the skin depth of the excitation field is distributed near the surface. In conjunction with high frequency magnetoimpedance measurements, surface sensitive probes of magnetism and structure must be employed to provide a complete picture of the relationship between the surface and dynamic magnetism. This dissertation focuses on the surface impact of chemical composition, annealing conditions, and coatings on TMMAs on their magnetoimpedance response through multiple surface sensitive techniques such as atomic/magnetic force microscopy, magneto-optical Kerr effect, and scanning/transmission electron microscopy. These tools provide a view into the relationship between the nanostructure, microstructure and soft magnetic properties that make these materials highly desired for fundamental study and technological application.
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Favre, Wilfried. "Silicium de type n pour cellules à hétérojonctions : caractérisations et modélisations." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00635222.
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Les cellules à hétérojonctions de silicium fabriquées par croissance de couches minces de silicium amorphe hydrogéné (a-Si :H) à basse température sur des substrats de silicium cristallin (c-Si) peuvent atteindre des rendements de conversion photovoltaïque élevés (η=23 % démontré). Les efforts de recherche ayant principalement été orientés vers le cristallin de type p jusqu'à présent en France, ce travail s'attache à l'étude du type n pour d'une part déterminer les performances auxquelles s'attendre avec cette nouvelle filière et d'autre part les améliorer. Pour cela, nous avons mis en œuvre des techniques de caractérisation des matériaux composant la structure et de l'interface (a-Si :H/c-Si) couplées à des outils de simulations numériques afin mieux comprendre les phénomènes de transport électronique. Nous nous sommes également intéressés aux cellules à hétérojonctions avec substrats de silicium multicristallin de type n, le silicium multicristallin étant le matériau le plus répandu actuellement dans la fabrication des cellules photovoltaïques.
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Shin, Yun Kyung. "The water-amorphous silica interface: electrokinetic phenomena in a complex geometry, and treatment of interactions with biomolecules." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1299587783.
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Koishi, Ayumi. "Mécanismes de nucléation des carbonates." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAU032/document.
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La précipitation et la dissolution du carbonate de calcium (CaCO3) sont des processus clés dans les systèmes naturels en raison de leur association intime avec le cycle du carbone terrestre. La précipitation se produit généralement sur des substrats étrangers en abaissant les barrières énergétiques qui contrôlent la nucléation. Ce processus appelé nucléation hétérogène résulte d'une interaction entre la sursaturation du fluide et les différentes énergies d’interface entre substrat-noyau-fluide. Malgré l’importance des énergies d’interface sur le devenir de la nucléation hétérogène, la littérature actuelle reste rare dans leurs valeurs absolues, limitant la précision de la modélisation du transport réactif. La formation des biominéraux constitue un réservoir majeur des carbonates dans la lithosphère. Des études récentes ont révélé des nucléations par multi-étapes impliquant la formation du carbonate de calcium amorphe (ACC), un intermédiaire métastable durant les premiers stades de la formation des biominéraux. De tels précurseurs amorphes permettent de réaliser les formes complexes des biominéraux, tandis que leur stabilité et leur cinétique de cristallisation sont contrôlées par de multiples facteurs. L'élucidation des mécanismes sous-jacents est bénéfique pour le développement de matériaux biomimétiques.Le premier objectif est de développer une compréhension prédictive des valeurs d'énergie d’interface régissant la nucléation hétérogène du CaCO3 en fonction des propriétés physico-chimiques spécifiques des substrats, comme l'hydrophobicité. Cette dernière est étudiée en utilisant de la phlogopite avec et sans substitution par le fluor produisant des substrats hydrophobes et hydrophiles. La technique de diffusion des rayons X aux petits angles en incidence rasante a été employée in situ pour obtenir des valeurs d’énergie effective d’interface. Il est intéressant de noter que les valeurs extraites pour les deux substrats sont similaires, et thermodynamiquement les deux fournissent un bon modèle pour la nucléation, alors que leurs mécanismes sont différents. La caractérisation ex situ par microscopie à force atomique a montré que le substrat hydrophile favorise la formation et la stabilisation d’ACC, tandis que le substrat hydrophobe favorise la formation de calcite. Ces résultats soulignent la flexibilité structurelle intrinsèque du CaCO3 et son avantage dans les processus de nucléation hétérogènes.Le deuxième objectif est de fournir une description atomistique de l'hydrophobicité du substrat. L'adsorption d'eau sur la phlogopite a été réalisée in situ par spectroscopie de photoélectrons à pression ambiante pour étudier l'effet de la substitution par le fluor et de différents types de contre-ions (K+, Na+ vs. Cs+). Ces résultats ont été interprétés par des simulations de dynamique moléculaire et la théorie de bond-valence. La combinaison de ces techniques montre que l'hydrophobicité du substrat provient d'une compétition entre deux facteurs: l'hydratation des contre-ions par rapport à celle du substrat.Le but final est d'étudier les mécanismes moléculaires par lesquels Mg2+, une impureté chez les précurseurs amorphes biogéniques, augmente la persistance cinétique d’ACC. La technique de diffusion inélastique incohérente des neutrons a été combinée avec la spectroscopie de corrélation de photons X pour élucider la dynamique à l'échelle nanométrique de l'eau et des ions dans les ACC. Les résultats montrent que la présence de Mg2+ augmente la diffusion atomique dans le solide tout en amplifiant la rigidité du réseau des liaisons hydrogène. Ces résultats contre-intuitifs sont abordés en considérant différents facteurs cinétiques inclus dans l’équation décrivant le taux de nucléation au sein de la théorie classique de la nucléation. Dans l'ensemble, ces résultats indiquent l'importance de l'eau comme stabilisant cinétique de la structure amorphe et de l'existence de barrières stériques qui abaissent le taux de cristallisation<br>Precipitation and dissolution of calcium carbonate (CaCO3) are key processes in both natural and engineered systems due to their intimate association with the Earth’s carbon cycle. Precipitation usually occurs on foreign substrates since they lower the energetic barriers controlling nucleation events. This so-called heterogeneous nucleation results from the interplay between the fluid supersaturation and the interfacial free energies present at the substrate-nucleus-fluid interfaces. Despite the relevance of interfacial energies for the fate of heterogeneous nucleation, the current literature remains scarce in their absolute values, which limits the accuracy of reactive transport modelling. Of particular relevance to the carbon cycle, the formation of biominerals accounts for a major reservoir of the carbonate minerals in the lithosphere. Recent studies have revealed the existence of multistep nucleation pathways that involve formation of amorphous calcium carbonate (ACC), a metastable intermediate during the early stages of biomineral formation. Such amorphous precursors allow molding of the intricate shapes of biominerals, while their stability and crystallization kinetics are effectively controlled by multiple factors. Elucidating the underlying mechanisms is beneficial for the development of biomimetic materials.The first goal of this dissertation is to develop a predictive understanding of interfacial energy values governing CaCO3 heterogeneous nucleation as a function of specific physico-chemical properties of the substrates, such as hydrophobicity. This last was investigated using phlogopite, a common mica, with and without fluorine substitution yielding hydrophobic and hydrophilic substrates. In situ time-resolved Grazing-Incidence Small Angle X-ray Scattering experiments were performed to obtain effective interfacial energy values. Interestingly, the extracted values for both substrates were similar, and thermodynamically these substrates provide a good template for nucleation, but the pathways differ. By ex situ Atomic Force Microscopy characterization, the hydrophilic substrate was shown to promote the formation and stabilization of ACC, whereas the hydrophobic one favored the formation of calcite. These results point to the intrinsic structural flexibility of CaCO3 and its advantage in heterogeneous nucleation processes.The second goal is to provide an atomistic description of the substrate hydrophobicity/hydrophilicity. Water adsorption on phlogopite was studied in situ using Near-Ambient Pressure X-ray Photoelectron Spectroscopy to investigate the effect of fluorine substitution and the influence of different types of counterions (K+, Na+ vs. Cs+). The results of the spectroscopy experiments were further interpreted using molecular dynamics simulations and bond-valence theory. The combination of these techniques shows that the substrate hydrophobicity stems from a competition between two factors: hydration of counterions vs. that of substrate.The final goal is to study the molecular mechanisms by which Mg2+, a common impurity in biogenic amorphous precursors, increases the kinetic persistence of ACC. Inelastic Incoherent Neutron Scattering and X-ray Photon Correlation Spectroscopy were combined to elucidate the nanoscale dynamics of water and ions within ACC. The presence of Mg2+ was shown to enhance the atomic diffusion within the solid while simultaneously increasing the stiffness of the hydrogen bond network. These counter-intuitive results are addressed by considering the different factors included in the pre-exponential term of the nucleation rate equation within the framework of the classical nucleation theory. Overall, the results point to the importance of water as a kinetic stabilizer, and to the existence of steric barriers that lower the crystallization rate
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Desmond, Jasmine L. "Investigating the adsorption of select polar functionalities with the aqueous electrolyte/amorphous silica interface to understand the 'low salinity' effect." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/78792/.
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Low-salinity enhanced oil recovery (EOR) uses low-salinity seawater in the water flooding of sandstone reservoirs to maximise oil yields. Because oil is strongly adsorbed onto mineral surfaces, understanding the interactions involved at the oil/mineral interface, and how to weaken them, is crucial to design more efficient, low-cost EOR. This thesis focuses on the influence of electrolyte concentration on the interaction of alkylammonium (R-NH+3) and alkylcarboxylic acid/carboxylate (R-COOH/COO- functionalities, present in crude-oil, with the amorphous silica (mimic for quartz grains in sandstone)/aqueous electrolyte interface. Both computational (molecular dynamics, MD) and experimental (chemical force mapping atomic force microscopy, CFM-AFM) techniques were used. Firstly (Chapter 3), we tested the inter-operability of the new SPC/Fw water force-field with CHARMM. No significant differences were found between the data generated from SPC/Fw-CHARMM and TIPS3P-CHARMM, therefore the latter, computationally more efficient, was used in Chapters 4-6. The behaviour of the four electrolyte solutions at two concentrations was tested in Chapters 4-5 (NaCl, KCl, CaCl2 and MgCl2 at 0.1 and 0.3 M); interfacial ion and water structuring has been investigated in Chapter 4, while the effect of the electrolytes on the adsorption of R-NH+3) and alkylcarboxylic acid/carboxylate (R-COOH/COO-) was explored in Chapter 5. Interfacial ion concentration was greatest in the CaCl2 case, with various long-lived surface-site types involving different combinations of ions identified. CFM-AFM showed a substantial concentration-dependent difference in adhesion for R-NH+3 in CaCl2 and R-COOH/COO- in the divalent ion solutions. The free energy of adsorption for NH+3 CH3 was investigated using metadynamics. Force curves were calculated from the generated free energy profiles. The greatest force is, indeed, observed for one particular surface-site type in CaCl2 solution, prevalent in more concentrated solutions. Finally, a more sophisticated computational model for the experimental AFM tip, a small array of S(CH211NH3+) is presented in Chapter 6, laying the basis for future work.
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Defresne, Alice. "Amélioration de la passivation de cellules solaires de silicium à hétérojonction grâce à l’implantation ionique et aux recuits thermiques." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS533/document.
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Les cellules solaires à hétérojonction a-Si:H/c-Si atteignent un rendement record de 24.7% en laboratoire. La passivation de la surface du c-Si est la clé pour obtenir de hauts rendements. En effet, la brusque discontinuité de la structure cristalline à l'interface amorphe/cristal induit une forte densité de liaisons pendantes créant une grande densité de défauts dans la bande interdite. Ces défauts sont des centres de recombinaison pour les paires électron-trou photogénérées dans le c-Si. Différentes couches diélectriques peuvent être utilisées pour passiver les wafers dopés n et dopés p : (i) le SiO₂ réalisé par croissance thermique, (ii) l’Al₂O₃ déposé par ALD, (iii) le a-SiNₓ:H et l’a-Si:H déposés par PECVD. La couche de passivation la plus polyvalente est a Si:H puisqu’elle peut passiver aussi bien les wafers dopés n que ceux dopés p. De plus sa production est peu coûteuse en énergie car sa croissance est réalisée à une température d’environ 200°C. L’inconvénient de cette couche de passivation est que lorsqu’elle est dopée p elle ne supporte pas des températures supérieures à 200°C, en raison de l’exodiffusion des atomes d’hydrogène qu’elle contient. Cependant, afin d'avoir un bon contact électrique, TCO et électrodes métalliques, il est souhaitable de recuire à plus haute température (entre 300°C et 500°C). Nous avons implanté des ions Argon de façon contrôlée dans des précurseurs de cellules solaires à des énergies comprises entre 1 et 30 keV, pour contrôler la profondeur à laquelle nous créons les défauts. En variant la fluence entre 10¹² Ar.cm⁻² et 10¹⁵ Ar.cm⁻² nous contrôlons la concentration de défauts créés. Nous montrons qu’une implantation à une énergie de 5 keV avec une fluence de 10¹⁵ Ar.cm⁻² n’est pas suffisante pour endommager l’interface a-Si:H/c-Si. La durée de vie effective des porteurs minoritaires mesurée par photoconductance (temps de décroissance de la photoconductivité) passe de 3 ms à 2,9 ms après implantation. En revanche les implantations à 10 keV, 10¹⁴ Ar.cm⁻² ou à 17 keV, 10¹² Ar.cm⁻² sont suffisantes pour dégrader la durée de vie effective de plus de 85%. Suite aux implantations les cellules solaires ont subi des recuits sous atmosphère contrôlée à différentes températures et ce jusqu’à 420°C. Nous avons découvert que le recuit permet de guérir les défauts introduits par l’implantation. Mais surtout, dans certains cas, d’obtenir des durées de vie après implantation et recuit supérieures aux durées de vies initiales. En combinant l’implantation ionique et les recuits, nous conservons de bonnes durées de vies effectives des porteurs de charges (supérieures à 2 ms) même avec des recuits jusqu’à 380°C. Nous avons utilisé une grande variété de techniques telles que la photoconductance, la photoluminescence, l’ellipsométrie spectroscopique, la microscopie électronique en transmission, la Spectroscopie de Masse d’Ions Secondaires, la spectroscopie Raman et l’exodiffusion de l’hydrogène pour caractériser et analyser l’ensemble des résultats et phénomènes physico-chimique intervenant dans la modification des précurseur de cellules solaires. Nous discutons ici de plusieurs effets tels que l’augmentation de la durée de vie et la tenue en température par la conservation de l’hydrogène dans la couche de silicium amorphe et ceci même après les recuits. Cette conservation peut s’expliquer par l’augmentation du nombre de liaisons Si-H au sein du silicium amorphe et par la formation de cavités lors de l’implantation. Durant les recuits l’hydrogène qui diffuse est piégé puis libéré par les cavités et/ou les liaisons pendantes, ce qui limite son exo-diffusion et le rend de nouveau disponible pour la passivation des liaisons pendantes<br>A-Si:H/c-Si heterojunction solar cells have reached record efficiencies of 24.7%. The passivation of c-Si is the key to achieve a high-efficiency. Indeed, the abrupt discontinuity in the crystal structure at the amorphous/crystal interface induces a high density of dangling bonds creating a high density of defects in the band gap. These defects act as recombination centers for electron-hole pairs photogenerated in c-Si. Several dielectric layers can be used to passivate n-type and p-type wafers: (i) SiO₂ produced by thermal growth, (ii) Al₂O₃ deposited by ALD, (iii) a-SiNₓ:H and a-Si:H deposited by PECVD. The most versatile passivation layer is a-Si: H because it is effective for both p-type and n-type wafers. In addition, this process has a low thermal budget since the deposition is made at 200°C. The drawback of this passivation layer, in particular when p-type doped, is that it does not withstand temperatures above 200°C. However, in order to have a good electrical contact, TCO and metal electrodes require high temperature annealing (between 300°C and 500°C).We implanted Argon ions in solar cell precursors with energies between 1 and 30 keV, which allows to control the depth to which we are creating defects. By varying the fluence between 10¹² Ar.cm⁻² and 10¹⁵ Ar.cm⁻² we control the concentration of defects. We show that implantation with an energy of 5 keV and a fluence of 10¹⁵ Ar.cm⁻² is not sufficient to damage the a-Si:H/c-Si interface. The effective lifetime of the minority charge carriers, measured using a photoconductance technique (decay time of photoconductivity), decreases only from 3 ms to 2.9 ms after implantation. On the other hand the implantations at 10 keV, 10¹⁴ Ar.cm⁻² or at 17 keV, 10¹² Ar.cm⁻² are sufficient to degrade the effective lifetime by more than 85%.Following implantation the solar cells have been annealed in a controlled atmosphere at different temperatures and this up to 420°C. We show that annealing can heal the implantation defects. Moreover, under certain conditions, we obtain lifetimes after implantation and annealing greater than the initial effective lifetime. Combining ion implantation and annealing leads to robust passivation with effective carrier lifetimes above 2 ms even after annealing our solar cell precursors at 380°C. We used a large variety of techniques such as photoconductance, photoluminescence, spectroscopic ellipsometry, Transmission Electron Microscopy, Secondary Ion Mass Spectrometry, Raman spectroscopy and hydrogen exodiffusion to characterize and analyze the physico-chemical phenomena involved in the modification of solar cells precursors. We discuss here several effects such as the increase of the effective lifetime and the temperature robustness by the preservation of hydrogen in amorphous silicon layer and this even after annealing. This hydrogen preservation can be explained by the increase of the number of Si–H bonds in amorphous silicon and the formation of cavities during implantation. In the course of annealing the hydrogen which diffuses is trapped and then released by cavities and dangling bonds, which limits its exodiffusion and makes it available for dangling bonds passivation
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ANTOINE, ANNE-MARIE. "Mecanismes de croissance et de constitution d'interfaces dans les couches minces de semiconducteurs amorphes hydrogenes etudies par ellipsometrie spectroscopique in situ." Paris 7, 1987. http://www.theses.fr/1987PA077179.
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Etude de la croissance de couches minces de silicium, germanium et d'alliages silicium-germanium amorphes hydrogenes deposees par decomposition radiofrequence de silane, germane et d'hydrogene. Etude des mecanismes d'initiation de la couche en fonction des conditions de preparation. Analyse de l'influence de la nature du support sur le depot des premieres couches monomoleculaires
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Awad, Yousef Odeh. "Characterization of amorphous silicon carbide and silicon carbonitride thin films synthesized by polymer-source chemical vapor deposition mechanical structural and metal-interface properties." Thèse, Université de Sherbrooke, 2006. http://savoirs.usherbrooke.ca/handle/11143/1821.
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Amorphous silicon carbide (a-SiC) and silicon carbonitride thin films have been deposited onto a variety of substrates by Polymer-Source Chemical Vapor Deposition (PS-CVD). The interfacial interaction between the a-SiC films and several substrates including silicon, SiO[subscript 2], Si[subscript 3]N[subscript 4], Cr, Ti and refractory metal-coated silicon has been studied. The effect of thermal annealing on the structural and mechanical properties of the prepared films has been discussed in detail. The composition and bonding states are uniquely characterized with respect to the nitrogen atomic percentage introduced into the a-SiCN:H films. Capacitance-voltage (C-V) measurements were systematically used to evaluate the impurity level of the deposited a-SiC films. The chemical bonding of the films was systematically examined by means of Fourier transform infrared spectroscopy (FTIR). In addition, elastic recoil detection (ERD) and X-ray photoelectron spectroscopy (XPS) techniques were used to determine the elemental composition of the films and of their interface with substrates, while X-ray reflectivity measurements (XRR) were used to account for the film density. Spectral deconvolution was used to extract the individual components of the FTIR and XPS spectra. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were also employed to characterize the surface morphology of the films. In addition, their mechanical properties [(hardness (H) and Young's modulus (E)] were investigated by using the nanoindentation technique. The impurity levels of the a-SiC films were found to be clearly correlated with the nature of the underlying substrates. The Pt-Rh and TiN-coated Si substrates were shown to lead to the lowest impurity level (~ 1×10[superscript 13] cm[superscript -3]) in the PS-CVD grown a-SiC films, while Cr and Ti-coated Si substrates induced much higher impurity concentrations. Such high impurity levels were shown to be a consequence of a strong metallic diffusion of the metallic species (Cr or Ti). In contrast, no diffusion was observed at the interface of a-SiC with either Pt-Rh or TiN. Our results pinpointed TiN-coated Si as the electrode material of choice that satisfied best all criteria required for the integration of a-SiC into opto-electronic devices. FTIR measurements revealed that not only the intensity of a-SiC absorption band linearly increased, but also its position is found to shift to a higher wave number as a result of annealing. In addition, the bond density of Si-C is found to increase from (101.6-224.5)×10[superscript 21] bond[dot]cm[superscript -3] accompanied by a decrease of Si-H bond density from (2.58-0.46)× 10[superscript 21] bond[dot]cm[superscript -3] as a result of increasing the annealing temperature (T[subscript a]) from 750 to 1200 [degrees]C. Annealing-induced film densification is confirmed by the XRR measurements, as the a-SiC film density is found to increase from 2.36 to ~ 2.75 g/cm[superscript -3] when T[subscript a] is raised from 750 to 1200 [degrees]C. In addition, as annealing temperature T[subscript a] is increased from 750 to 1200 [degrees]C, both hardness and Young's modulus are found to increase from 15.5 to 17.6 GPa and 155 to 178 GPa, respectively. On the microstructural level, the increase incorporation of N in the a-SiCN:H films is found not only to lead to C atoms substitution by N atoms in the local Si-C-N environment but also to the formation of a complex structure between Si, C and N. For instance, the FTIR spectra show a remarkable drop in the intensity of Si-C vibration accompanied by the formation of further bonds including Si-N, C-N, C=N, C[identical to]N and N-H with increasing NH[subscript 3]/Ar ratio. Moreover, the XPS spectra showed the existence of different chemical bonds in the a-SiCN:H films such as Si-C, Si-N, C-N, C=N and C=C. Both FTIR and XPS data demonstrate that the chemical bonding in the amorphous matrix is more complicated than a collection of single Si-C, Si-N, or Si-H bonds. Furthermore, the increase incorporation of N in the a-SiCN:H films resulted in an increase of the average R[subcsript rms] surface roughness from 4 to 12 nm. Moreover, the films became porous with pore size and density increase as a result of increasing N at.%. Ultimately, both H and E of the a-SiCN:H films were found to be sensitive to their N content, as they decreased (from ~17 GPa and 160 GPa to ~13 GPa and 136 GPa, respectively) when the N content was increased from 0 to 27 at.%. The formation of Si-N, Si-H, and N-H bonds at the detriment of the more stiffer Si-C bonds are thought to account for the observed lowering of the mechanical properties of the a-SiCN:H films such as their N content increased. Our results confirmed the previously-established constant-plus-linear correlation between the mechanical properties of the a-SiC films and their bond densities.
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Pan, Jie. "UNDERSTANDING ELECTRICAL CONDUCTION IN LITHIUM ION BATTERIES THROUGH MULTI-SCALE MODELING." UKnowledge, 2016. http://uknowledge.uky.edu/cme_etds/62.
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Silicon (Si) has been considered as a promising negative electrode material for lithium ion batteries (LIBs) because of its high theoretical capacity, low discharge voltage, and low cost. However, the utilization of Si electrode has been hampered by problems such as slow ionic transport, large stress/strain generation, and unstable solid electrolyte interphase (SEI). These problems severely influence the performance and cycle life of Si electrodes. In general, ionic conduction determines the rate performance of the electrode, while electron leakage through the SEI causes electrolyte decomposition and, thus, causes capacity loss. The goal of this thesis research is to design Si electrodes with high current efficiency and durability through a fundamental understanding of the ionic and electronic conduction in Si and its SEI.
Multi-scale physical and chemical processes occur in the electrode during charging and discharging. This thesis, thus, focuses on multi-scale modeling, including developing new methods, to help understand these coupled physical and chemical processes. For example, we developed a new method based on ab initio molecular dynamics to study the effects of stress/strain on Li ion transport in amorphous lithiated Si electrodes. This method not only quantitatively shows the effect of stress on ionic transport in amorphous materials, but also uncovers the underlying atomistic mechanisms. However, the origin of ionic conduction in the inorganic components in SEI is different from that in the amorphous Si electrode. To tackle this problem, we developed a model by separating the problem into two scales: 1) atomistic scale: defect physics and transport in individual SEI components with consideration of the environment, e.g., LiF in equilibrium with Si electrode; 2) mesoscopic scale: defect distribution near the heterogeneous interface based on a space charge model. In addition, to help design better artificial SEI, we further demonstrated a theoretical design of multicomponent SEIs by utilizing the synergetic effect found in the natural SEI. We show that the electrical conduction can be optimized by varying the grain size and volume fraction of two phases in the artificial multicomponent SEI.
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Messaadi, Saci. "Modélisation électrique de couches ou de fils minces métalliques : Effet thermique d'interface verre-couche amorphe." Nancy 1, 1987. http://www.theses.fr/1987NAN10048.
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En utilisant l'expression de la conductivité électrique donnant l'équivalence entre le modèle de Fuchs-Sondheimer et le modèle de Cottey étendu, des expressions simples de la conductivité sont substituées à celle du modèle de Mayadas-Shatzkcs. De nouvelles formulations simplifiées relatives à la conductivité électrique des doubles couches métalliques, des fils fins métalliques en l'absence de champ magnétique et la magnétorésistance longitudinale de ces derniers sont obtenues dans le cadre du modèle de conduction multidimensionnel
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Ocampo, Juan. "Etude des phénomènes d'interface dans la glace : adsorption, croissance des clathrates et désordre protonique : [thèse en partie soutenue sur un ensemble de travaux]." Grenoble 1, 1988. http://www.theses.fr/1988GRE10087.
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Etude depuis l'etat amorphe a 77 k jusqu'a l'etat hexagonal pres du point de fusion de l'evolution structurale et dynamique de la surface de la glace en contact ou non avec des gaz (he, kr, ar, n::(2), co::(2), nc::(4)h::(10)) ou des solides (sio::(2), pvc, h::(2)so::(4)). Approche thermodynamique (adsorption de gaz), cinetique (frittage et croissance de clathrates) et spectroscopique (rmn des protons). Mecanisme de reconstruction de la surface depuis l'adsorption jusqu'a la clathration, en tenant compte des coefficients de diffusion et des energies d'activation mesurees. Existence d'une couche quasi-liquide sur la surface de la glace pour des temperatures superieures a 238 k, et dans le cas des interfaces avec d'autres corps solides
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Labdi, Yamina. "Caracterisation des structures n+in+ minces, a base de sillicium amorphe hydrogene par la methode des courants limites par charge d'espace : prise en compte des effets d'interface." Paris 7, 1988. http://www.theses.fr/1988PA077091.
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Cette these est principalement consacree a l'etude experimentale et theorique des structures minces du type metal/n**(+)in**(+)/metal a base de silicium amorphe hydrogene. Dans un premier temps, nous nous affranchissons des problemes des resistances parasites dues a la presence des jonctions metal/n**(+), en etudiant ces jonctions de facon detaillee lorsque le metal utilise est de l'oxyde d'etain, du chrome ou de l'aluminium. Nous serons amenes a corriger de facon empirique et si necessaire, les caracteristiques j(v) mesurees afin que celles ci decrivent le comportement de la couche centrale intrinseque. Nous presentons ensuite une nouvelle modelisation du transport des electrons injectes dans de telles structures. Cette modelisation prend en compte la contribution des courants dus a la diffusion des electrons a la densite de courant totale, ce qui permet de tenir compte de facon explicite du comportement des bandes aux interfaces n**(+)/i. L'ensemble des resultats obtenus sur nos echantillons nous mene a conclure que dans le cas de nos mesures, il n'y a pas de signe d'augmentation de la densite d'etats pres des interfaces n**(+)/i. Ces interfaces ne sont pas du tout abrupts mais entierement decrits par la densite des electrons pieges au voisinage du niveau de fermi. Quelques resultats concernant l'alliage si-ge depose au sein de notre laboratoire sont presentes a la fin de ce travail
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Sahli, Salah. "Etude du comportement electrique de films minces de gaas amorphes ou polycristallins elabores par depots en phase vapeur ou par plasma a partir d'organometalliques." Toulouse 3, 1986. http://www.theses.fr/1986TOU30049.
Full textAbstract:
Des films de gaas polycristallin ont ete realises par depot en phase vapeur, a partir de molecules organometalliques. L'auteur a montre que les proprietes electriques de ce materiau semiconducteur sont controlees par les joints de grains. Une densite d'etats de surface uniforme entre les grains a ete mise en evidence. L'introduction entre les grains d'une phase amorphe de type si::(y)c::(1-y) modifie le mode de conduction. La resistivite des films augmente ou diminue suivant la valeur de la concentration de si::(y)c::(1-y). Un depot par plasma froid a partir des memes molecules que celles utilisees precedemment, conduit a un materiau amorphe polymerique. Celui-ci est compose d'atomes de gallium et d'arsenic. Ses proprietes electriques sont plutot celles d'un isolant que celles d'un semiconducteur. Enfin, il a ete montre qu'un film contenant des atomes de ga et d'as peut etre utilise pour la passivation de la surface de substrats de gaas monocristallin
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Knutson, Christopher C. "The chemistry and device applications of amorphous thin-film interfaces." Thesis, 2011. http://hdl.handle.net/1957/26076.
Full textAbstract:
Solid-state amorphous materials show amazing promise in thin-film electronics. The interface-to-bulk ratio of thin films makes interfacial chemistries of these systems of utmost importance. Thin films of amorphous metals, dielectrics and semiconductors have novel chemistries that are not only based upon their elemental constituent makeup, but also based upon the method with which the amorphous material is deposited and treated after deposition. The chemical attributes unique to amorphous, thin-film systems are defined primarily through the utilization of solution-processed aluminum oxide phosphate dielectric material and Zr������Cu������Al������Ni������ metal. the chemical findings wrought via the observation of interactions between amorphous metal-dielectric systems are applied to semiconductor/insulator systems to illustrate the use of the same general chemical principles applying to diverse problems. Finally in the appendices, the systems are utilized to create extremely-thin tunneling electronic devices and optical metamaterials as well as innovative classroom material.<br>Graduation date: 2012<br>Access restricted to the OSU Community at author's request from Dec. 13, 2011 - Dec. 13, 2012
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Divya, G. "Structural signatures of relaxation mechanisms in glass forming and devitrifying colloidal suspensions." Thesis, 2023. https://etd.iisc.ac.in/handle/2005/6105.
Full textAbstract:
Connecting macroscopic behavior of matter to the microscopic interactions is the central goal of condensed matter physics. Yet, achieving such a challenging goal in atomic and molecular systems would require tracking all particles in the system up to the length scale of atomic resolution (≈ nm) and timescales of picoseconds. A typical workaround through this daunting challenge is to instead model the system with colloidal suspensions, where length scales (≈ μm)
and timescales(≈ ms) are more accessible to experiments. Over the last two decades, colloidal systems have been used to mimic atomic systems as they exhibit various phases such as liquids, crystals, gases, and glasses which have enabled study of various processes such as nucleation and growth of crystals, solid-solid phase transition, liquid crystals, liquid-liquid phase transitions and many more. In this thesis, we utilize colloids to gain insights into the phenomenon of glass formation as well as relaxation of a metastable glass into a crystal. Unlike crystals which have unique structural signatures that defines their macroscopic properties, glasses possess structure that are akin to liquids. Nevertheless, they exhibit rigidity similar to solids. Physicists have tried to link the properties of glasses to the underlying aperiodic structure over the past three decades but the studies have remained inconclusive. This is attributed to the fact that standard correlation functions that could easily identify ordered structures cannot distinguish between distinct amorphous configurations. This thesis is aimed at gaining insights into the mechanisms of glass formation from experiments on colloidal glasses. It is done by designing analytical tools towards recognizing patterns in amorphous configurations which aid in understanding structure and its relation to dynamics in glassy systems. We identify distinct signatures for these disordered structures in two different ways. We designed a protocol to determine amorphous-amorphous interfaces by defining self-induced pins to critically evaluate the assumptions of Random First Order Transition (RFOT) theory, which is a prominent thermodynamic approach to glass transition. Second, we exploited machine learning algorithms to identify distinct structural features that are responsible for relaxation to predict
where crystallization occurs in glass. The method also helped unveil possible structural connections for another prominent theory for glass transition i.e, Dynamic Facilitation which is a kinetic approach. The thesis is organized into two preliminary chapters followed by work chapters which describe in detail the above findings and a concluding chapter at the end.
In Chapter 1 we introduce colloidal suspensions that are typically used as model systems to study phase behavior in condensed matter systems, which in our case was exploited to study glass transition and devitrification. Further, we
present the formulations behind relevant theories of glass formation and briefly explain the theoretical and simulation developments involving devitrification. In addition, we discuss the principle behind machine learning and describe concisely algorithms used to achieve diverse goals. In particular, we discuss supervised learning approach in detail which we utilize to develop connections between structure and dynamics of glasses.
In Chapter 2 we describe the experimental methods utilized to perform the work presented in this thesis. Experimental systems in chapters 4 and 5 utilize polystyrene particles. We describe the synthesis protocols used to develop such systems in chapter 2. Details of experimental system used to realize devitrification in chapter 3 are described in chapter 2. The chapter also describes confocal microscopy, the instrument used for performing devitrification experiments.
Chapter 3 unravels how glasses transform into crystals, a process known as devitrification. Glasses are inherently unstable to crystallization. However, the transformation remains poorly understood as it occurs whilst the dynamics in the glass stay frozen at the particle scale. In Chapter 3, through single-particle-resolved imaging experiments, we show that due to frozen-in density inhomogeneities, a soft colloidal glass crystallizes via two distinct pathways. In the poorly packed regions of the glass, crystallinity grew smoothly due to local particle shuffles, whereas in the well-packed regions, we observed abrupt jumps in crystallinity that were triggered by avalanches - cooperative rearrangements involving many tens of particles. Importantly, we show that softness - a structural order parameter determined through
machine learning methods - not only predicts where crystallization initiates in a glass but is also sensitive to the crystallization pathway. Such a causal connection between the structure and stability of a glass has so far remained elusive. Devising strategies to manipulate softness may thus prove invaluable in realizing long-lived glassy states.
Chapter 4 deals with measurement of surface tension of amorphous-amorphous interfaces which is one of the basic ingredients for Random First Order Transition (RFOT) theory - a prominent thermodynamic approach to glass transition. The relaxation dynamics in liquids on approaching their glass transition was found to become increasingly cooperative and the relaxing regions also become more compact in shape. Of the many theories of the glass transition, only RFOT anticipates the surface tension of relaxing regions to play a role in deciding both their size and morphology. However, owing to the amorphous nature of the relaxing regions, even the identification of their interfaces has not been possible in experiments hitherto.
In Chapter 4, we devise an analytical method to directly quantify the dynamics of amorphous-amorphous interfaces in bulk supercooled colloidal liquids. Our procedure also helped unveil a non-monotonic evolution in dynamical correlations with supercooling in bulk liquids. We measure the surface tension of the interfaces and show that it increases rapidly across the mode-coupling area fraction. Our experiments support a thermodynamic origin of the glass transition.
Chapter 5 explores the possible structural connections to Dynamic Facilitation theory (DF) - which is a purely kinetic approach to glass transition. Despite decades of intense research, whether the transformation of supercooled liquids into glass is a kinetic phenomenon or a thermodynamic phase transition remains unknown.
In Chapter 5, we analyzed optical microscopy experiments on 2D binary colloidal glass-forming liquids and examined a potential structural origin for localized excitations, which are building blocks of DF. To accomplish this, we utilize machine learning methods to identify a structural order parameter termed softness that has been found to be correlated with reorganization events in supercooled liquids. Both excitations and softness qualitatively capture the dynamical slowdown on approaching the glass transition and motivated us to explore spatial and temporal correlations between them. Our results show that excitations predominantly occur in regions with high softness and the appearance of these high softness regions precedes excitations, thus suggesting a causal connection between them. Thus, unifying dynamical and thermodynamical theories into a single structure-based framework may provide a route to understand the glass transition.
In Chapter6 we discuss our findings and suggest possible future directions.
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Lin, Yang-You, and 林沇佑. "The Impact on Photovoltaic Efficiency with Regards to Defect Densities of Amorphous Silicon Layers and Carrier Recombination Velocity at Interfaces in a Heterojunction Solar Cell Using Silvaco ATLAS." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/15593378593498140236.
Full textAbstract:
碩士<br>大葉大學<br>電機工程學系<br>98<br>This study involves the novel heterojunction with intrinsic thin layer (HIT) solar cell structure. Combining the advantages of both crystalline silicon and amorphous silicon, a new structure of silicon-based solar cell was proposed - the heterojunction with an intrinsic thin layer (HIT) solar cell. It has high stability and large light absorption coefficient. It is manufactured under low temperature deposit process, which results in a low cost thin film HIT solar cell with high conversion efficiency. The influence of various layer materials and interfaces on the performance of n-type c-Si based bifacial HIT solar cell has been investigated by using the Silvaco TCAD simulation software. Accordingly, the design optimization of HIT solar cell was proven.
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Lien, Wei-Kuang, and 連偉光. "The influence of p/i interface on hydrogenated amorphous silicon solar cells." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/13566522814091809944.
Full textAbstract:
碩士<br>國立中興大學<br>電機工程學系所<br>99<br>In this thesis, 13.56 MHz plasma-enhanced chemical vapor deposition (PECVD) with pulse-wave modulation of RF plasma is used to fabricate the hydrogenated amorphous silicon (a-Si:H) solar cells. The initial gas concentration is adjusted to control the dissociation of the gases in the plasma and its influence on the performance of solar cells is investigated.
The p-layer deposition is controlled by adjusted B2H6 initial-growth gas concentration. The results show that B2H6 flowed into the chamber before the plasma excitation 8 seconds can reduce excessive dissociation of boron atoms on the film surface.
The i-layer deposition is controlled by adjusted SiH4 initial-growth gas concentration to increase the dissociation of hydrogen molecules to passivate the dangling bond on the surface of p-layer, which can increase the density of silicon films and reduce the defects on p/i interface.
Adjust the initial-growth hydrogen gas concentration can reduce the defects due to oxygen atoms on the p/i interface. Reducing the initial-growth SiH4 gas concentration for i-layer deposition can increase the absorption of short-wavelength photons, but decrease the fill factor and conversion efficiency of solar cells.
The initial-growth of i-layer can significantly influence the structure of p/i interface, thus results in the variation of fill factor and conversion efficiency of the a-Si:H solar cells. Control the dissociation of B2H6 of p-layer on the interface between TCO and p-layer and the initial-growth SiH4 of i-layer on p/i interface can effectively improve the fill factor and conversion efficiency.
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Yeh, Chun-Cheng, and 葉雋正. "Back Interface Engineering of Amorphous In-Ga-Zn-O Thin Film Transistor." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/70049527206321314667.
Full textAbstract:
碩士<br>國立交通大學<br>光電工程學系<br>99<br>With a high mobility (>10 cm2/Vs) and a low threshold voltage (&lt; 5 V) under a low temperature process, transparent amorphous oxide semiconductor thin-film transistors (AOS TFTs) draw considerable attention due to their applications on flexible displays. Beside, a-IGZO is very stable in atmosphere, which makes it an ideal material in sensor technology.
In this study, the sensor structure is based on a-IGZO TFT with an additional sensing layer capped above it. a-IGZO active layer is act as electrical transport layer, and the sensing layer can improve sensitivity significantly to diverse bio-chemical molecules. The sensing mechanism might be due to carrier transfer or field effect interaction between sensing layer and a-IGZO active layer under sensing process and influenced by the concentration of specific molecules. This work opens a route to develop low-cost large-area bio/chemical sensor array based on the commercialized a-IGZO TFT technology.
Furthermore, we proposed a structure with capping metal layer onto the active layer of bottom-gate a-IGZO TFT to provide a solution to enhance device performance and threshold voltage modulation, which does not cause leakage current degradation. In addition, the device mobility increases significantly after introducing the metal capping layer, and easily oxidized material caused higher mobility in comparison. It is possibly due to variation of oxygen concentration in a-IGZO film causing higher conductivity and carrier concentration in region near the edge and under capping layer assisting carrier transportation. We also propose a defect reduction effect based on reducing weak-bonded oxygen in a-IGZO film. The results enable the development of a-IGZO TFT for the applications like RFID and display driving.
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Yi, Yang Chun, and 楊俊儀. "A Study of Interface Between Metal/Amorphous Semiconductor/ Compound Semiconductor and Its Applications for MESFET." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/95373515315744947343.
Full textAbstract:
碩士<br>國立成功大學<br>電機工程研究所<br>81<br>The direct coupled field-effect transistor logic (DCFL) which
consist of MESFET is widely used for large scale integrated
circuit because of its simple circuit and low power
dissipation. In addition, MESFET is also an important structure
for opto-electrical applications. Unfortunately,the Schottky
barrier height between metal and Ⅲ-Ⅴ material is low owing to
Fermi-level pinning, this results in low logic swing and makes
circuit easily disturbed by noise which limit the work
characteristics of MESFET. Recently, the Schottky barrier
height is improved by depositing an amorphous material layer
which has high energy gap between metal and Ⅲ-Ⅴcompound
semiconductor to bring about slow interface state at interface.
In this thesis, we deposit three different amorphous materials
(a-Si:H, a-SiC:H, a-SiGe:H) between metal (we use Al, Au, Pt)
and Ⅲ-Ⅴ smeiconductor and observe the change of Schottky
barrier height, reverse leakage current, and breakdown voltage.
From experiment,we found that the Schottky barrier height
between Au/SiC(200A) is the highest in GaAs and Pt/Si(80A) in
InP. In these three amorphous materials, SiC has the least
reverse leakage current and the largest breakdown voltage. We
use Au/SiC( 500A) as the gate to fabricate field-effect
transistor and the transconductance(gm) is 1.5 ms/mm.
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Kuo, Jui-Lin, and 郭睿麟. "Interface Improvement Thin-Film Transistors with Amorphous Mg-InGaZnO/InGaZnO AP-PECVD Fabricated Channel Structure." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/2h8m8x.
Full textAbstract:
碩士<br>國立交通大學<br>電子研究所<br>107<br>Nowadays, Active-matrix organic light-emitting diode (AMOLED) display applications are toward large size, low power consumption, flexible substrate, high speed and high resolution. Amorphous oxide thin film transistor (AOS) has good electron mobility, process uniformity, low process temperature and high optical transmittance to meet the specifications of next-generation displays. Among many amorphous oxide thin film transistors, IGZO TFT is also competitive with better electron mobility (>10cm2/V-s), small subthreshold swing, large switching ratio (>106) and good reliability.
In this paper, the channel layers are all prepared by atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD). Because the process is in a non-vacuum system, the cost can greatly decrease, and it is beneficial to large-area manufacturing. Our active layer is double channel structure, 30nm IGZO and 10nm Mg-doped IGZO (Mg-IGZO). The atomic percentage of Mg is 5% of Zn. With subsequent XPS and AFM analysis, this structure can reduce the oxygen vacancy and enhance the metal-oxide bonds strength and the defects between channel with dielectric layer are greatly reduced due to the addition of Mg, which effectively improve the device performance, such as electron mobility, subthreshold swing and switch ratio. Through the comparison of electrical analysis, it was found that using rapid thermal annealing (RTA) is superior to the using furnace annealing in the annealing process and the rapid thermal annealing is a low thermal budget annealing, which is suitable for the application of flexible application. In addition, the faster process time and cost savings of the RTA combined with atmospheric pressure plasma enhanced chemical vapor deposition system can help increase production.
In this experiment, the AP-PECVD fabricated amorphous Mg-InGaZnO/InGaZnO channel structure thin-film transistors was successfully fabricated, and the channel layer treated by rapid thermal annealing at 500°C for 30 seconds in O2 ambient was significantly improved. The electron mobility is 16.66 cm2/V·s, the low sub-threshold swing is 83.91 mV/dec, the high switching current ratio is 6.47×107 and the small off current is maintained at about 10-12pA level.
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Schuhmann, Henning. "Hochauflösende mikroskopische und spektroskopische Untersuchungen zur strukturellen Ordnung an MgO-CoFeB-Grenzflächen." Doctoral thesis, 2014. http://hdl.handle.net/11858/00-1735-0000-0023-9929-2.
Full textAbstract:
Tunnelmagnetowiderstandselemente (MTJ) mit einer kristallinen MgO Tunnelbarriere zwischen amorphen CoFeB-Elektroden haben Aufgrund ihres hohen Tunnelmagnetowiderstandes (TMR) und der guten Integrationsmöglichkeit in bestehende Prozesse viel Aufmerksamkeit bekommen. Dabei zeigten vorherige Berechnungen, dass die strukturellen und chemischen Eigenschaften der Grenzfläche einen signifikanten Einfluss auf den TMR aufweisen, weshalb diese Grenzfläche im Rahmen dieser Arbeit mittels quantitativer, hochauflösender und analytischer Transmissionselektronenmikroskopie analysiert wurde.
Um einen hohen TMR in die diesen Systemen zu erzielen ist ein kristalliner Übergang zwischen der Tunnelbarriere und den Elektroden notwendig. Berechnungen zeigten, dass bereits wenige Monolagen kristallinen Materials an der Grenzfläche ausreichen, um einen hohen TMR in diesen Systemen zu erzielen. Ausgehend von diesen Berechnungen wurde die Mikrostruktur auf der Subnanometer-Skala an der kristallin/amorphen Grenzfläche von MgO-CoFeB in dieser Arbeit untersucht. Die experimentellen Daten wurden hierfür mittels aberrationskorrigierter, hochauflösender Transmissionselektronenmikroskopie (HRTEM) an Modellsystemproben erstellt und die vom MgO induzierte kristalline Ordnung an der Grenzfläche zum CoFeB mittels iterativen Bildserienvergleichs mit simulierten Daten quantifiziert. Zur Simulation der HRTEM-Grenzflächenabbildungen wurde die „Averaged-Projected-Potential“-Näherung genutzt, welche im Rahmen dieser Arbeit um die Berücksichtigung von monoatomaren Stufen entlang der Strahlrichtung des Mikroskops erweitert wurde. Es zeigte sich, dass mit dieser Methode die Ordnung an der MgO-CoFeB-Grenzfläche von nicht ausgelagerten Systemen gut beschrieben werden kann.
In ausgelagerten Systemen kommt es dagegen zu einer Bor-diffusion aus dem a-CoFeB heraus um damit eine Kristallisation am MgO zu ermöglichen. Im zweiten Teil dieser Arbeit werden die Bordiffusion und die Kristallisation in Abhängigkeit von der Deckschicht als auch der MgO-Depositionsmethode sowohl an Modellsystemproben als auch an funktionsfähigen MTJs untersucht. Elektronen-Energie-Verlustspektroskopie (EELS) an diesen Proben konnten zeigen, dass sowohl die Deckschicht also auch die MgO-Depositionsmethode einen entscheidenden Einfluss auf die Bor-Diffusion in diesen Systemen ausüben.
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Feng, Yu-ting, and 馮宇廷. "The investigation of mechanical properties of ZrCu/Zr/ZrCu amorphous－crystalline nanolaminates with inclined interface by molecular statics simulation." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/90556427491033621712.
Full textAbstract:
碩士<br>國立中山大學<br>機械與機電工程學系研究所<br>100<br>In this study, the mechanical properties of Cu-Zr binary bulk metallic glasses (BMG) were investigated at the nano-scale. The stable amorphous structures and corresponding energies of BMG structures are performed by density functional theory (DFT) calculation as reference data. This study will combine the Force-Matching (FM) method and Basin-Hopping (BH) method to develop a new method for fitting the Cu-Zr Tight-binding (TB) potential parameters. Moreover, the Bulk modulus, Shear modulus, Young''s modulus and Poisson ratio of Cu46Zr54, Cu50Zr50 and Cu64Zr36 structures are calculated with the fitting TB parameters. In addition, the compression process of BMG materials is simulated by the Molecular Statics. The stress and strain are obtained to investigate the deformation mechanism of CuZr/Zr/CuZr nanolaminates at 0 and 45 inclined degree.
Finally, we investigate the angle in the deformation process under different strain in the shear band, shear transformation zones (STZs) and force caused by the slip of the atomic distribution of TFMGs layer.
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Eilers, Gerrit. "Korrelationen zwischen struktureller Ordnung und elektrischen Transporteigenschaften in CoFeB|MgO|CoFeB Tunnelmagnetowiderstandselementen." Doctoral thesis, 2010. http://hdl.handle.net/11858/00-1735-0000-0006-B4D9-2.
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Thiel, Karsten. "Strukturelle Untersuchung der amorph/kristallinen Grenzfläche mittels quantitativer hochauflösender Transmissionselektronenmikroskopie an den Systemen a-Si/c-Si und a-Ge/c-Si." Doctoral thesis, 2006. http://hdl.handle.net/11858/00-1735-0000-0006-B448-6.
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Weisemöller, Thomas. "X-ray analysis of praseodymia." Doctoral thesis, 2009. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2009111311.
Full textAbstract:
In this thesis, it was shown that thin films of hexagonal praseodymium sesquioxide on Si(111) can be transformed to B-oriented twin free films of cubic praseodymium dioxide with oxygen vacancies by post deposition annealing in 1 atm. oxygen at temperatures from 300°C up to 700°C for 30 minutes. Films annealed at 100°C and 200°C are still purely hexagonal praseodymium sesquioxide after the annealing process. In the transformed films, two stoichiometric phases coexist laterally. The lateral lattice constant of both species is almost identical to the one of the originally deposited hexagonal praseodymium sesquioxide. Therefore, we assume that the lateral lattice constant is pinned throughout the oxidation process.The species are hence strained and show different vertical lattice constants, depending on the amount of oxygen vacancies. In some samples, those vacancies were partly ordered vertically, leading to a unit cell twice as large as expected for stoichiometric praseodymium dioxide.During the annealing process, an amorphous interfacial layer between substrate and oxide was detected. While the existence of this layer was known before, it was possible for the first time to quantify the thickness of the praseodymium rich part of this interface for epitaxially grown films. It was shown that this layer starts to grow significantly only during post deposition annealing at 500°C or more.These and other results for thin films were connected to previously published data for bulk praseodymia. The multi column model mentioned above for laterally coexisting praseodymia species in thin films was backed up by powder data. As a matter of fact, it was shown that this coexistence of several praseodymia species can be expected to be the rule rather than the exception.Strong evidence was found that results interpreted previously as stoichiometric cubic praseodymium sesquioxide contain more oxygen than originally thought...