Understanding the behaviour of molecules on a semiconductor surface is necessary if molecular self-assembly is going to be employed, with existing semiconductor technology, to create useful devices. Si(111)-7x7 is an invaluable surface upon which to study molecular adsorption. The surface reconstruction has been well characterized and it possesses seven symmetrically distinct dangling bonds that can serve as reaction sites. Aromatic molecules on Si(111)-7x7 have been investigated with a variety of techniques and have been shown to chemisorb at room temperature. However, it is not trivial to predict how an ensemble of aromatic molecules might distribute themselves amongst the available bonding sites on this surface. The work presented in this thesis begins with a joint STM and ab initio investigation of thiophene on 7x7 that demonstrates kinetics are necessary to describe the chemisorption sites occupied at various coverages. A kinetic Monte Carlo model, taking into account a mobile physisorbed state, is shown to accurately describe this site occupancy at room temperature. This model disregards molecule-molecule interaction because thiophene does not sterically hinder chemisorption to a neighbouring dangling bond. A larger molecule, mesitylene, was then studied on Si(111)-7x7, and shown to form an ordered molecular lattice on the Si(111)-7x7 surface. This is the first demonstration of a porous molecular lattice grown on Si(111)-7x7 at room temperature. Finally, molecular chemisorption on the related 5x5 reconstruction, grown by depositing Ge on 7x7, is studied. It is found that the presence of Ge hinders molecular chemisorption, preventing formation of the mesitylene lattice. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-09-11 10:14:10.118

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With increasing amount of user data and applications in wireless communication technology, demands are growing on performance and fabrication costs. One way to decrease cost is to integrate the building blocks in an RF system where digital blocks and high power amplifiers then are combined on one chip. This thesis presents LDMOS transistors integrated in a 65 nm CMOS process without adding extra process steps or masks. High power performance of the LDMOS is demonstrated for an integrated WLAN-PA design at 2.45 GHz with 32.8 dBm output power and measurements also showed that high output power is achievable at 5.8 GHz. For the first time, this kind of device is moreover demonstrated at X-band with over 300 mW/mm output power, targeting communication and radar systems at 8 GHz. As SOI is increasing in popularity due to better device performance and RF benefits, the buried oxide can cause thermal problems, especially for high power devices. To deal with self-heating effects and decrease the RF substrate losses further, this thesis presents a hybrid substrate consisting of silicon on top of polycrystalline silicon carbide (Si-on-poly-SiC). This hybrid substrate utilizes the high thermal conductivity of poly-SiC to reduce device self-heating and the semi-insulating properties to reduce RF losses. Hybrid substrates were successfully fabricated for the first time in 150 mm wafer size by wafer bonding and evaluation was performed in terms of both electrical and thermal measurements and compared to a SOI reference. Successful LDMOS transistors were fabricated for the first time on this type of hybrid substrate where no degradation in electrical performance was seen comparing the LDMOS to identical transistors on the SOI reference. Measurements on calibrated resistors showed that the thermal conductivity was 2.5 times better for the hybrid substrate compared to the SOI substrate. Moreover, RF performance of the hybrid substrate was investigated and the semi-insulating property of poly-SiC showed to be beneficial in achieving a high equivalent substrate parallel resistance and thereby low substrate losses. In a transistor this would be equal to better efficiency and output power. In terms of integration, the hybrid substrate also opens up the possibility of heterogeneous integration where silicon devices and GaN devices can be fabricated on the same chip.

Radiation therapy is continuously increasing in complexity due to technological innovation in delivery techniques, necessitating thorough dosimetric verification. Comparing accurately predicted portal dose images to measured images obtained during patient treatment can determine if a particular treatment was delivered correctly. The goal of this thesis was to create a method to predict portal dose images that was versatile and accurate enough to use in a clinical setting. All measured images in this work were obtained with an amorphous silicon electronic portal imaging device (a-Si EPID), but the technique is applicable to any planar imager. A detailed, physics-motivated fluence model was developed to characterize fluence exiting the linear accelerator head. The model was further refined using results from Monte Carlo simulations and schematics of the linear accelerator. The fluence incident on the EPID was converted to a portal dose image through a superposition of Monte Carlo-generated, monoenergetic dose kernels specific to the a-Si EPID. Predictions of clinical IMRT fields with no patient present agreed with measured portal dose images within 3% and 3 mm. The dose kernels were applied ignoring the geometrically divergent nature of incident fluence on the EPID. A computational investigation into this parallel dose kernel assumption determined its validity under clinically relevant situations. Introducing a patient or phantom into the beam required the portal image prediction algorithm to account for patient scatter and attenuation. Primary fluence was calculated by attenuating raylines cast through the patient CT dataset, while scatter fluence was determined through the superposition of pre-calculated scatter fluence kernels. Total dose in the EPID was calculated by convolving the total predicted incident fluence with the EPID-specific dose kernels. The algorithm was tested on water slabs with square fields, agreeing with measurement within 3% and 3 mm. The method was then applied to five prostate and six head-and-neck IMRT treatment courses (~1900 clinical images). Deviations between the predicted and measured images were quantified. The portal dose image prediction model developed in this thesis work has been shown to be accurate, and it was demonstrated to be able to verify patients’ delivered radiation treatments.

L'apparition des Systèmes d'Information ubiquitaires ou pervasifs est issue de l'émergence de nouvelles technologies fournissant au système une vision de son environnement, de l'environnement de ses utilisateurs ainsi que de leurs profils. Grâce à ces données formant le contexte de l'application, il est possible de fournir des services personnalisés, pertinents et ciblés. Mais, le problème qui se pose à ce niveau concerne le degré d'adaptation, de prise de décision à la place de l'utilisateur et de l'identification des données contextuelles nécessaires et suffisantes pour ces services. Ceci est dû à un déséquilibre entre les avancées des technologies et de leurs applications (qui reçoivent un grand intérêt de la part de la recherche et de l'industrie) et les méthodes et démarches de développement et d'ingénierie spécifiques aux systèmes ubiquitaires. Notre objectif dans ce travail de thèse est de proposer une méthode d'ingénierie des SI ubiquitaires en considérant les différentes exigences reliées à la nature mobile et grande échelle de ces systèmes. Cette méthode est basée sur une démarche de développement qui fait usage d'un ensemble de métamodèles et de langages génériques favorisant la spécification complète de ces systèmes. Cette démarche sépare les spécifications fonctionnelles, techniques et ubiquitaires. Les spécifications ubiquitaires permettent de définir des modèles structurels et événementiels du contexte respectant les exigences des utilisateurs et les contraintes de sécurité et supportant les fonctionnalités d'adaptation et de sensibilité au contexte. Cette approche orientée évènements est consolidée par l'adoption d'une architecture de traitement des évènements. Notre démarche E-CARe est une intégration des spécifications ubiquitaires dans une démarche classique de conception des SI pour garantir la couverture des spécifications fonctionnelles et techniques. Les applications d'assistance représentent un cas d'étude idéal pour cette démarche qui s'intéresse au domaine des transports, fortement dépendant de l'environnement et des évènements ambiants.

Les circuits deviennent de plus en plus intégrés pour augmenter les performances des dispositifs microélectroniques. La formation de jonctions ultra courtes (USJs) est un challenge majeur pour la réalisation de la prochaine génération de transistors à effet de champ (MOSFET) ayant une longueur de grill inférieure à 25 nm. L'implantation ionique est la technique la plus utilisée pour fabriquer des jonctions dans du Si, mais elle génère des défauts étendus, des interstitiels (Is) et des lacunes (Vs), qui introduisent des effets néfastes dans les composants, comme l'effet d'un transitoire de diffusion accélérée (TED) du bore et la formation d'agrégats de bore et d'Is (BICs). Une ingénierie de défauts par triple implantation (He, Si et B) a été utilisée pour maîtriser ces effets. Le rôle de chaque implantation d'He et de Si sur la diffusion du B est présenté dans ce mémoire. Les échantillons ont été caractérisés par SIMS, TEM, effet Hall, PAS, NRA etc. Pour fabriquer des USJs, le meilleur procédé est dans un premier temps l'introduire des cavités par implantation d'He pour créer une barrière de diffusion aux Is. Puis une implantation Si est réalisée à une énergie telle que la couche de cavités soit située entre les couches de Vs et d'Is qui sont introduites par cette même implantation. Enfin les atomes de B sont introduits à une faible énergie par implantation ionique ou par immersion plasma (PIII) pour créer les USJs. Au cours du recuit rapide d'activation (RTA), les Vs introduites par implantation Si peuvent se recombiner avec les Is introduites par implantation du B pour augmenter l'activation du dopant et limiter la diffusion du B. Une jonction ayant une épaisseur Xj de (12 ± 1) nm et une Rs de (150 ± 10) O/? a été réalisée.

Šiame darbe akcentuojami priešmokyklinio amžiaus vaikų sėkmingo ugdymo(si) veiksniai, kaip pamatas tolimesniam sėkmingam mokymuisi mokykloje. Ugdymo(si) sėkme laikoma visų vaiko fizinių ir psichinių galių puoselėjimas, pozityvios socialinės ir emocinės patirties įgijimas, pažinimo motyvacijos skatinimas. Tyrimo klausimai: Kokie atsiskleidžia vaikų ugdymąsi skatinantys ir slopinantys veiksniai? Ką pedagogai mano apie vaikų ugdymo(si) sėkmę? Atsižvelgus į tyrimo klausimų aktualumą, tyrimo objektu pasirinkta priešmokyklinio amžiaus vaikų ugdymo(si) sėkmę laiduojantys veiksniai. Tyrimo tikslas – atskleisti priešmokyklinio amžiaus vaikų sėkmingo ugdymo(si) veiksnius. Tyrimo uždaviniai: 1. Mokslinės literatūros ir švietimo dokumentų analizės pagrindu, atskleisti priešmokyklinio amžiaus vaikų sėkmingo ugdymo(si) veiksnius lemiančius ugdymo(si) sėkmę. 2. Nustatyti vidinius ir išorinius veiksnius turinčius įtakos ugdymo(si) veiklos sėkmei. 3. Atskleisti pedagogų nuomonę apie vaikų ugdymo(si) sėkmę. Tyrimo imtis: Tyrime dalyvavo 87 priešmokyklinio ugdymo grupę lankantys vaikai ir 128 priešmokyklinio ugdymo pedagogai. Tyrimas vykdytas Vilniaus miesto ir rajono ikimokyklinėse ugdymo įstaigose. Remiantis atliktu tyrimu parengtos išvados kuriose atskleidžiami vaikų sėkmingo ugdymosi veiksniai. / In this work the factors of successful education of preschool children are emphasized as the base for further successful learning at school. Educational success consists of: the nurturance of all physical and mental powers of a child, the acquisition of positive social and emotional experiences, and the encouragement of knowledge motivation. Research questions: What are the factors which stimulate and which supress children’s education? What do teachers think about the success of children’s education? Considering the urgency of research questions, factors that guarantee successful education of preschool children were chosen as the object of the research. The aim of research – to reveal factors influencing successful education of preschool children. Research objectives: 1. To reveal factors which destine successful learning of preschool children by means of scientific literature and educational document analysis. 2. To identify inner and outer elements that have influence on the success of educational activity. 3. To disclose teachers’ openion on the success of children’s education. Research sample: 87 children who attend preschool education group and 128 teachers took part in the research. The research was held in preschool institutions of Vilnius city and in the area of Vilnius. Relying on the accomplished research, the conclusion reveals factors of successful children’s education.

Radiation therapy is continuously increasing in complexity due to technological innovation in delivery techniques, necessitating thorough dosimetric verification. Comparing accurately predicted portal dose images to measured images obtained during patient treatment can determine if a particular treatment was delivered correctly. The goal of this thesis was to create a method to predict portal dose images that was versatile and accurate enough to use in a clinical setting. All measured images in this work were obtained with an amorphous silicon electronic portal imaging device (a-Si EPID), but the technique is applicable to any planar imager. A detailed, physics-motivated fluence model was developed to characterize fluence exiting the linear accelerator head. The model was further refined using results from Monte Carlo simulations and schematics of the linear accelerator. The fluence incident on the EPID was converted to a portal dose image through a superposition of Monte Carlo-generated, monoenergetic dose kernels specific to the a-Si EPID. Predictions of clinical IMRT fields with no patient present agreed with measured portal dose images within 3% and 3 mm. The dose kernels were applied ignoring the geometrically divergent nature of incident fluence on the EPID. A computational investigation into this parallel dose kernel assumption determined its validity under clinically relevant situations. Introducing a patient or phantom into the beam required the portal image prediction algorithm to account for patient scatter and attenuation. Primary fluence was calculated by attenuating raylines cast through the patient CT dataset, while scatter fluence was determined through the superposition of pre-calculated scatter fluence kernels. Total dose in the EPID was calculated by convolving the total predicted incident fluence with the EPID-specific dose kernels. The algorithm was tested on water slabs with square fields, agreeing with measurement within 3% and 3 mm. The method was then applied to five prostate and six head-and-neck IMRT treatment courses (~1900 clinical images). Deviations between the predicted and measured images were quantified. The portal dose image prediction model developed in this thesis work has been shown to be accurate, and it was demonstrated to be able to verify patients’ delivered radiation treatments.

A new one-dimensional device simulation package developed for the simulation of neutron radiatiol! effects in silicon avalanche photodiodes is described. The software uses a finite difference technique to solve the time-independent semiconductor equations across a user specified structure. Impact ionisation and illumination are included, allowing accurate simulation with minimal assumptions about the device under investigation. The effect of neutron radiation damage is incorporated via the introduction of deep acceptor levels subject to Shockley-Read-Hall statistics. Two models are presented. A reverse reach through model, based on the EG&G C30626E reverse reach through avalanche photo diode originally proposed for use in the CMS electromagnetic calorimeter, and a reach through model, based on widely available commerical devices. A short experimental study on two commercial silicon avalanche photodiodes, a C30719F reverse reach through APD and a C30916E reach through APD, is presented for comparison with the simulation data. To allow full comparison with the simulated predictions, the commercial devices were irradiated at the Rutherford Appleton Laboratory's ISIS facility. The simulated data shows good qualitative agreement with the measurements performed on the commercial devices, quantitative predictions would require exact information about the doping profile. The characteristic behaviour of the devices is predicted over a wide range of conditions both before and after neutron irradiation. The effect of ionised deep acceptors in the bulk of the devices is investigated. The simulation package provides a useful tool for the analysis of semiconductor devices, particularly in areas where a non-ionising radiation damage is prevelent e.g. high energy physics, and provides a good basis for further development.

The growth of the Si(001) surface from gas sources such as disilane is technologically important, as well as scientifically interesting. The aspects of growth covered are: the clean surface, its defects and steps; the action of bismuth, a surfactant; the diffusion behaviour of hydrogen in different environments; and the entire pathway for formation of a new layer of silicon from adsorption of fragments of disilane to nucleation of dimer strings. The theoretical methods used, density functional theory and tight binding, are described. Four linear scaling tight binding methods are compared. The construction of the tight binding parameterisations used is also explained. The structure of the most common defect on the Si(001) surface is identified by comparison of the electronic structure with scanning tunneling microscopy (STM) images. The energy and structure of steps is calculated, and their kinking behaviour is modelled, achieving good agreement with experimental results. Two unusual features which form when bismuth is placed on the surface and annealed are investigated. The first has possible applications as a quantum wire, and its structure and growth are described. The second relates to a controversial area in the field; a structure is proposed which fits all available experimental evidence. The behaviour of hydrogen is vital to understanding growth, as large amounts are deposited during disilane growth. After validating the tight binding parameterisation against DFT and experiment for the system of a single hydrogen diffusing on the clean Si(001) surface, the barriers for diffusion on the saturated surface, down a step and away from a defect are found, and prove to be in good agreement with available experimental data. The pathway for the formation of a new layer of silicon from disilane is described step by step, giving barriers and structures for all events. The interaction with experiment is highlighted, and demonstrates that great benefit accrues from such close work, and that the atomistic modelling techniques used in the thesis produce results in close agreement with reality.