This thesis presents an atomic-scale study of nanoindentation, with carbon materials and both bcc and fcc metals as test specimens. Classical molecular dynamics (MD) simulations using Newtonian mechanics and many-body potentials, are employed to investigate the elastic-plastic deformation behaviour of the work materials during nanometresized indentations. In a preliminary model, the indenter is represented solely by a non-deformable interface with pyramidal and axisymmetric geometries. An atomistic description of a blunted 90° pyramidal indenter is also used to study deformation of the tip, adhesive tip-substrate interactions and atom transfer, together with damage after adhesive rupture and mechanisms of tip-induced structural transformations and surface nanotopograpghy. To alleviate finite-size effects and to facilitate the simulation of over one million atoms, a parallel MD code using the MPI paradigm has also been developed to run on multiple processor machines. The work materials show a diverse range of deformation behaviour, ranging from purely elastic deformation with graphite, to appreciable plastic deformation with metals. Some qualitative comparisons are made to experiment, but available computer power constrains feasible indentation depths to an order of magnitude smaller than experiment, and over indentation times several orders of magnitude smaller. The simulations give a good description of nanoindentation and support many of the experimental features.

For numerous technical applications, condensed materials must be specifically produced and manipulated on the nanometre scale. This frequently means the creation of an order with characteristic lengths in the range of extension of single atoms. Besides the possibility of constructing a solid "atom by atom" with suitable procedures, specific local transformations driven by energy input can also produce modified structures which display new and technically utilisable properties. / Für zahlreiche technische Anwendungen müssen kondensierte Materialien auf der Nanometerskala gezielt hergestellt und manipuliert werden. Dies bedeutet häufig die Schaffung einer Ordnung mit charakteristischen Längen in der Größenordnung der Ausdehnung einzelner Atome. Neben der Möglichkeit, den Festkörper „Atom für Atom“ mit geeigneten Verfahren aufzubauen, können auch gezielte lokale Umwandlungen durch Energieeintrag modifizierte Strukturen, welche neuartige und technisch nutzbare Eigenschaften aufweisen, hervorbringen.

For numerous technical applications, condensed materials must be specifically produced and manipulated on the nanometre scale. This frequently means the creation of an order with characteristic lengths in the range of extension of single atoms. Besides the possibility of constructing a solid "atom by atom" with suitable procedures, specific local transformations driven by energy input can also produce modified structures which display new and technically utilisable properties. / Für zahlreiche technische Anwendungen müssen kondensierte Materialien auf der Nanometerskala gezielt hergestellt und manipuliert werden. Dies bedeutet häufig die Schaffung einer Ordnung mit charakteristischen Längen in der Größenordnung der Ausdehnung einzelner Atome. Neben der Möglichkeit, den Festkörper „Atom für Atom“ mit geeigneten Verfahren aufzubauen, können auch gezielte lokale Umwandlungen durch Energieeintrag modifizierte Strukturen, welche neuartige und technisch nutzbare Eigenschaften aufweisen, hervorbringen.

Au cours des dernières années, les matériaux optiques non linéaires ont attiré beaucoup d'attention en raison de leur application dans les télécommunications optiques. Les vitro-céramiques pour l’optique non-linéaire, ayant une microstructure alignée, présentent des propriétés physiques anisotropes. Il est donc intéressant de maîtriser la cristallisation dans ce genre de verre. Nous avons étudié ici la distribution, la taille et l'orientation sous un champ supplémentaire, en particulier par l’irradiation femtoseconde, de verres silicatés. Ce travail est important pour la conception et la production de nouveaux matériaux optiques non linéaires multi- fonction. Dans cette thèse, le champ thermique a été utilisé pour produire des cristaux dans un verre SrO-TiO₂-SiO₂. L’analyse a été menée à l’aide de la méthode des franges de Maker et de de diffraction des rayons X pour étudier la cristallisation et les propriétés optiques non-linéaires. Il a montré que les cristaux non linéaires Sr₂TiSi₂O₈ peut être obtenue dans la couche de surface par traitement thermique. L'axe polaire de cristaux orientés est perpendiculaire à la surface du verre. En augmentant la température ou en prolongeant la durée de traitement thermique, l’apparition d’une intensité non-nulle de génération de second harmonique (GSH) en incidence perpendiculaire indique la présence de cristaux orientés de manière aléatoire dans le volume du verre. Etant donné la cristallisation, spatialement difficile à contrôler par traitement thermique, l’irradiation laser femtoseconde pour contrôler la cristallisation dans le verre sont proposée en raison de son contrôle précis du dépôt d'énergie dans le temps et dans l'espace. Il ouvre des possibilités fantastiques pour la fabrication de matériaux multifonctionnels par maîtrisant la cristallization des cristaux non linéaires dans le verre. Nous avons précipité des cristaux orientés de LiNbO₃ et de Sr₂TiSi₂O₈ en volume par irradiation laser femtoseconde à haute cadence (typ. 300 kHz). Dans le verre Li₂O-Nb₂O₅-SiO₂, les micro-/nano-cristaux en variant l'énergie d'impulsion et la direction de polarisation ont obtenu. En particulier, lors de l'application à basse énergie et de la polarisation parallèle à la direction d'inscription du laser, la cristallization orientée en nanomètre a été démontrée par EBSD (Electron diffraction rétro-diffusée). Le mesure microscopique de SH a prouvé l’orientation préférentielle de cristallisation parallèlement à la direction de déplacement du faisceau laser. Afin de comprendre l'orientation exacte des cristaux par rapport à la direction d'écriture, une série de mesurer les signaux cohérent de SH ont été réalisés dans des paires de lignes de laser avec des orientations de déplacement opposées. EDS (spectromètre à dispersion d'énergie) et la micro-sonde nucléaire ont été utilisées pour réaliser l'analyse chimique dans les lignes de laser. Nous discutons aussi le mécanisme de cristallisation orientée en mode statique et en mode dynamique en illustrant la distribution des gradients différents. Pour le système SrO-TiO₂-SiO₂, l'irradiation du laser a été appliquée dans les verres stoechiométrique et non-stoechiométrique. Dans le premier cas, non seulement la taille et la distribution peuvent être contrôlées en variant les paramètres du laser, mais aussi la phase peuvent être choisis dans l'échantillon. La mesure de SH a montré que l'axe polaire de cristaux est toujours dans le sens de l'écriture. Pour le verre non-stoechiométrique, des purs cristaux de Sr₂TiSi₂O₈ ont été obtenus seulement. En utilisant EBSD, l'écriture asymétrique ont été étudiés en variant l’orientation de la polarisation et de l'écriture. On a montré ainsi que le mécanisme d'orientation est probablement dû à l'action combinée du front « tilté » de l’impulsion et à l’orientation du plan de polarisation qui conduit à une photosensibilité anisotrope. En conséquence, cela induit une distribution asymétrique des gradients thermiques et chimiques. / In the past few years, nonlinear optical materials have attracted much attention due to their application in optical telecommunications. Nonlinear optical glass-related materials have been widely studied according to their advantages. Glass ceramics having an aligned microstructure would exhibit an anisotropy of physical properties. This dissertation mainly contributes to the control of micro/nano-crystallization in silicate glass in crystalline phase, distribution, size and orientation under additional field, particularly by femtosecond irradiation, to master the nonlinear optical properties of glass further. This work is significant for the design and production of novel nonlinear optical material with multi-function in future. In this thesis, thermal field was used to induce crystals in SrO-TiO₂-SiO₂ glass. The crystallization behavior of glasses in different heat-treated condition and their second-order nonlinear optical properties have been analyzed by Maker fringes method and X-ray diffraction measurement, respectively. It showed that the oriented crystallization of nonlinear Sr₂TiSi₂O₈ crystals can be obtained in the surface layer by heat treatment. The polar axis of oriented crystals was perpendicular to the sample surface. Moreover, by applying higher temperature or prolonging the time duration of heat treatment, the maximum intensity of second harmonic generation shifting toward 0º is likely due to the presence of randomly distributed crystals in glass and surface crystallization turns to be volume at this moment. However, since it is hard to control crystallization by heat treatment and time-consuming, femtosecond laser irradiation was proposed to realize the control of crystallization in glass owing to the accessible control of energy deposition in time and in space. It opens fantastic opportunities to manufacture novel multifunctional materials by manipulating the crystallization of nonlinear crystals embedded in glasses. Therefore, we achieved to precipitate preferential oriented LiNbO₃ and Sr₂TiSi₂O₈ crystals in glass with femtosecond laser irradiation at high repetition rate (typ. 300 kHz). In Li₂O-Nb₂O₅-SiO₂ glass, we obtained micro-/nano-crystals in glass sample by varying pulse energy and polarization direction. Specifically, when applying low pulse energy and polarization parallel to laser writing direction, the oriented nano-crystallization has been obtained as shown by EBSD (Electron back-scattered diffraction). Second harmonic (SH) microscopy measurement illustrated preferred orientation of crystallization in laser lines. In order to understand the exact orientation of crystals with respect to the writing direction, a series of coherent SH measurement has been achieved in pairs of laser lines written in opposite orientation. EDS (Energy Dispersive Spectrometer) and nuclear micro-probe has been used to realize the chemical analysis in laser lines. The mechanism of oriented crystallization was discussed both in static mode and in dynamic mode through illustrating the distribution of different gradients. In SrO-TiO₂-SiO₂ system， laser irradiation was applied both in stoichiometric and non-stoichiometric glasses. In the former case, not only the size and distribution can be controlled by varying laser parameters, but also the crystalline phase can be chosen in samples. SH microscopy measurement was used to characterize the nonlinear properties of glass and it implied that the polar axis of crystals is always along the writing direction. In non-stoichiometric glass, only pure Sr₂TiSi₂O₈ crystals were obtained. The asymmetric writing involving oriented crystallization has been studied by varying polarization and writing orientation. The orientational dependent is likely due to the combined action of oblique pulse front tilt affected by the polarization orientation plane leading to different anisotropic photosensitivity and its aftereffects to induce asymmetric distribution of thermal and chemical gradients.

To investigate quantum confinement effects on silicon (Si) light source electroluminescence (EL) properties like quantum efficiency, external power efficiency and spectral emission, thin Si finger junctions with nanometre-scale dimensions were designed and manufactured in a fully customized silicon-on-insulator (SOI) semiconductor production technology. Since commonly available photolithography is unusable to consistently define and align nanometre-scale line-widths accurately and electron-beam lithography (EBL) by itself is too time-expensive to expose complete wafers, the wafer manufacturing process employed a selective combination of photolithography and EBL. The SOI wafers were manufactured in the clean-rooms of both the Carl and Emily Fuchs Institute for Microelectronics (CEFIM) at the University of Pretoria (UP) and the Georgia Institute of Technology’s Microelectronic Research Centre (MiRC), which made a JEOL JBX-9300FS electron-beam pattern generator (EPG) available. As far as is known this was the first project in South Africa (and possibly at the MiRC) that employed EBL to define functional nanometre-scale semiconductor devices. Since no standard process recipe could be employed, the complete design and manufacturing process was based on self-obtained equipment characterization data and material properties. The manufacturing process was unprecedented in both the CEFIM and MiRC clean-rooms. The manufacture of nanometre-scale Si finger junctions not only approached the manufacturing limits of the employed processing machinery, but also had to overcome undesirable physical effects that in larger-scale semiconductor manufacture usually are negligible. The device design, mask layout and manufacturing process therefore had to incorporate various material, equipment limitation and physical phenomena like impurity redistribution occurring during the physical manufacturing process. Although the complicated manufacturing process allowed many unexpected problems to occur, it was expected that at least the simple junction breakdown devices be functional and capable of delivering data regarding quantum confinement effects. Although due to design and processing oversights only 29 out of 505 measured SOI light sources were useful light emitters, the design and manufacture of the SOI light sources was successful in the sense that enough SOI light sources were available to conduct useful optical characterization measurements. In spite of the fact that the functional light sources did not achieve the desired horizontal (width) confinement, measured optical spectra of certain devices indicate that vertical (thickness) confinement had been achieved. All spectrometer-measured thickness-confined SOI light sources displayed a pronounced optical power for 600 nm < λ < 1 μm. The SOI light source with the highest optical power output emitted about 8 times more optical power around λ = 850 nm than a 0.35 μm bulk-CMOS avalanche light-source operating at the same current. Possible explanations for this effect are given. It was shown that the buried oxide (BOX) layer in a SOI process could be used to reflect about 25 % of the light that would usually be lost to downward radiation back up, thereby increasing the external power efficiency of SOI light sources. This document elaborates on the technical objectives, approach, chip and process design, physical wafer manufacture, production process control and measurement of the nanometre-scale SOI light sources. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted