Baigiamajame magistro darbe buvo lyginama ofsetinės ir fleksografinės spaudos kokybė spausdinant spalvines kontrolines skales, spalvų sutapdinimo kryžius, skiriamosios gebos elementus. Atspaudai buvo atspausdinti ofsetine lapine spaudos mašina ir siauraritinine fleksografinės spaudos mašina su centriniu spaudos cilindru. Mikroskopu buvo matuojamas spalvų sutapdinimo tikslumas, skiriamosios gebos elementų dydis. Densitometru buvo matuojamas atskirų ir binarinių spalvų rastrinių taškų santykinis plotas bei įvertintas gradacinis tikslumas. Pagal gautus kiekybinius rezultatus nustatyta, jog fleksografinės spaudos kokybė prastesnė negu ofsetinės spaudos. Darbą sudaro šios dalys: įvadas, literatūros apžvalga, kokybės reikalavimai, problemos analizė, eksperimento eiga ir rezultatų analizė, išvados, literatūros sąrašas. Darbo apimtis – 80 p. teksto be priedų, 65 pav., 43 lentelės, 18 literatūros šaltinių. / In master thesis was compared the offset and flexographic printing quality. Printing quality was evaluated using control strips, register crosses, resolving power test elements. Jobs were printed with offset sheet-fed printing press and flexographic narrow web press with central impresion cilinder. Register accuracy and resolving power were investigated using microscope. Dot area of single and binary colors wes measured with densitometer and halftone graduation characteristics were evaluated. On the basis of quantitative results it was determined that offset printing quality in comparison with flexography is higher. Master thesis comprise of folowing chapters: literature review, quality requirements, experimental, results and discusion, conclusions, references. Amount – 80 pages, 65 figures, 43 tables, 18 references.

<p>The role of the surroundings, or <italic> environment </italic>, is essential in understanding funda- mental quantum-mechanical concepts, such as quantum measurement and quantum entanglement. It is thought that a dissipative environment may be responsible for certain types of quantum (i.e. zero-temperature) phase transitions. We observe such a quantum phase transition in a very basic system: a resonant level coupled to a dissipative environment. Specifically, the resonant level is formed by a quantized state in a carbon nanotube, and the dissipative environment is realized in resistive leads; and we study the shape of the resonant peak by measuring the nanotube electronic conductance.</p><p>In sequential tunneling regime, we find the height of the single-electron conductance peaks increases as the temperature is lowered, although it scales more weakly than the conventional T<super>-1</super>. Moreover, the observed scaling signals a close connec- tion between fluctuations that influence tunneling phenomenon and macroscopic models of the electromagnetic environment.</p><p>In the resonant tunneling regime (temperature smaller than the intrinsic level width), we characterize the resonant conductance peak, with the expectation that the width and height of the resonant peak, both dependent on the tunneling rate, will be suppressed. The observed behavior crucially depends on the ratio of the coupling between the resonant level and the two contacts. In asymmetric barriers the peak width approaches saturation, while the peak height starts to decrease.</p><p>Overall, the peak height shows a non-monotonic temperature dependence. In sym- metric barriers case, the peak width shrinks and we find a regime where the unitary conductance limit is reached in the incoherent resonant tunneling. We interpret this behavior as a manifestation of a quantum phase transition.</p><p>Finally, our setup emulates tunneling in a Luttinger liquid (LL), an interacting one-dimensional electron system, that is distinct from the conventional Fermi liquids formed by electrons in two and three dimensions. Some of the most spectacular properties of LL are revealed in the process of electron tunneling: as a function of the applied bias or temperature the tunneling current demonstrates a non-trivial power-law suppression. Our setup allows us to address many prediction of resonant tunneling in a LL, which have not been experimentally tested yet.</p> / Dissertation

The synthesis of nanocrystals is unique compared to the formation of larger micron-sizesspecies as the final crystal sizes are not much larger than the primary nuclei. As a consequencethe final outcome of a nanocrystal synthesis i.e mean crystal size, concentrationand standard deviation is almost solely determined by the end of the nucleation phase. Directingthe growth of crystals beginning from aggregates of only tens of atoms into maturemonodisperse nanocrystals requires that the governing kinetics are strictly controlled at everymoment of the reaction. To effect this task various different ligands need to be employed,each performing a particular function during both nucleation and growth. (For complete abstract open document)

O consumo excessivo de álcool é recorrente entre universitários e está associado a inúmeras conseqüências negativas. Fatores ambientais (bottom-up) podem favorecer este consumo (ex.: influência do grupo, pistas associadas à droga). Além destes, fatores individuais podem influenciar o comportamento de beber desta população, entre eles fatores cognitivos (top-down). Bebedores freqüentes tendem a apresentar um viés atencional para estímulos associados ao álcool. Com o uso repetido do álcool, pistas ambientais associadas aos efeitos desta droga tornam-se salientes, em função de suas propriedades reforçadoras, atraindo a atenção do usuário em detrimento de outros estímulos e exacerbam o desejo de beber. O uso freqüente de álcool também tem sido relacionado a um conjunto de expectativas predominantemente positivas acerca dos seus efeitos e riscos para desenvolver dependência que podem influenciar o início e a manutenção do uso. Neste contexto, o objetivo deste estudo foi: a) examinar a relação entre o padrão de consumo e expectativas em relação aos efeitos do álcool entre universitários e b) desenvolver uma tarefa para investigar o viés atencional para pistas relacionadas ao álcool em indivíduos com diferentes padrões de consumo. Participaram deste estudo graduandos da UFRGS (N=79), do sexo masculino, com 22 anos de idade em média (dp=2,81). O padrão de consumo de risco e as expectativas positivas foram acessados através do Alcohol Use Disorders Identification Test (AUDIT) e do Inventário de Expectativas e Crenças Pesssoais acerca do Álcool (IECPA), respectivamente. Participaram deste estudo graduandos da UFRGS (N=79), do sexo masculino, com 22 anos de idade em média (dp=2,81). O padrão de consumo de risco e as expectativas positivas foram acessados através do Alcohol Use Disorders Identification Test (AUDIT) e do Inventário de Expectativas e Crenças Pesssoais acerca do Álcool (IECPA), respectivamente. Examinou-se o viés atencional através de uma tarefa computadorizada. O consumo de risco de álcool, que inclui o beber problemático e o padrão binge, estava associado a altas expectativas positivas em relação aos seus efeitos. Constatou-se que 43% dos participantes eram bebedores de alto risco para desenvolver dependência, conforme o AUDIT. Além disso, 68,4% deles foram caracterizados como bebedores com padrão binge de uso de álcool e 44,3% possuíam expectativas positivas em relação aos efeitos do álcool altas. Houve correlação entre beber problemático e expectativas positivas. Quanto à avaliação do viés atencional, não foi observado nenhum efeito de grupo, de tempo de exposição, nem de interação entre grupo e tempo de exposição. Identificar os fatores top down e bottom-up envolvidos no consumo de álcool de risco é essencial para formulação de modelos teóricos que compreendam este preocupante fenômeno. A avaliação das expectativas a respeito dos efeitos do álcool contribui para o planejamento de intervenções terapêuticas e estratégias preventivas mais precisas, visando a reduzir os riscos comportamentais e de saúde associados ao álcool. Além disso, o estudo do viés atencional pode favorecer o entendimento da relação entre fissura e atenção, da transição do uso ocasional para a dependência e da recaída. / The excessive alcohol consumption is recurrent among college students and it is associated with a variety of negative consequences. Environmental factors (bottom-up) can contribute to this phenomenon (group influences, drug cues). Furthermore, individual factors can also influence drinking behavior of this population, such as cognitive factors (top-down). Drug cues become highly salient as a result of their reinforcing properties, attracting the attention of the drug user in detriment of other stimuli. The exposure to drug cues can increase the desire to drink. Thus, heavy social drinkers show an attentional bias towards alcohol cues. The frequent alcohol use has also been related to a set of positive outcome expectancies and risk to develop drug dependence. These expectancies can influence the maintenance of drug intake. The aim of this study was: to examine the association of risk pattern and alcohol expectancies among college students and b) to develop a task to investigate attentional bias for alcohol cues in individuals with different drink patterns. Participants (N=79, mean age 22, dp=2,81) were college students. The risk pattern and the positive alcohol expectancies were assessed through Alcohol Use Disorders Identification Test (AUDIT) and Inventário de Expectativas e Crenças Pessoais acerca do Álcool (IECPA). The attentional bias was examined using a computerized task. The risk pattern, which includes drinking problematic and binge drinking, was associated with high positive expectancies. Results indicated that 43% of the participants had high risk to develop alcohol dependence. Moreover, 68.4% were binge drinkers and 44.3% had high positive alcohol expectancies. Risk pattern was associated with higher levels of positive alcohol expectancies. Related to the atencional bias assessment, there was not observed any group effect, exposition time, interaction between group and exposition time. Identifying bottom-up and top-down factors associated with the risk pattern of alcohol consumption is important to understand this preoccupant phenomenon. The alcohol expectancies assessment contributes to more efficient planning for therapeutical interventions and preventing strategies to reduce behavioral and health risks associated to the alcohol consumption. Moreover, the study of atencional bias can contribute to the understanding of the relationship between craving and attention, of the transition of the occasional use for the dependence and relapse.

p. 1-38 / Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-04-23T20:37:59Z No. of bitstreams: 1 44444444.pdf: 639088 bytes, checksum: 4e30ebf9edb1a60e107b4e1461e251d6 (MD5) / Approved for entry into archive by Maria Creuza Silva(mariakreuza@yahoo.com.br) on 2013-05-04T17:32:06Z (GMT) No. of bitstreams: 1 44444444.pdf: 639088 bytes, checksum: 4e30ebf9edb1a60e107b4e1461e251d6 (MD5) / Made available in DSpace on 2013-05-04T17:32:06Z (GMT). No. of bitstreams: 1 44444444.pdf: 639088 bytes, checksum: 4e30ebf9edb1a60e107b4e1461e251d6 (MD5) Previous issue date: 2007 / OBJETIVO: Verificar a efetividade da estratégia DOTS para tuberculose e os percentuais de cura e de abandono em municípios brasileiros, além de comparar as coberturas do Programa Saúde da Família (PSF) e os percentuais de cura e de abandono nos municípios prioritários. MÉTODOS: Estudo ecológico exploratório de agregado espacial, em 114 municípios prioritários para tuberculose em 2004 e 109 em 2005 nos estados do Amazonas, Mato Grosso, Pernambuco, Rio Grande do Sul e São Paulo, utilizando-se dados da coorte de casos de tuberculose. RESULTADOS: Porto Alegre apresentou nos dois anos o menor percentual de Unidades de Saúde com Programa de Controle da Tuberculose e DOTS implantados e menor cobertura do Programa Saúde da Família, contudo não foi a capital com menores percentuais de cura no mesmo período. Da mesma forma, os municípios do Rio Grande do Sul foram os com menores coberturas DOTS, mas não necessariamente os com menores proporções de cura e de abandono quando comparados aos das outras Unidades Federadas do estudo. Cuiabá foi a capital com maiores coberturas DOTS, maiores percentuais de cura e menores de abandono. Nenhuma das capitais atingiu os 85% de cura e 5% de abandono preconizados pelo Ministério da Saúde. A mediana da cura entre os municípios selecionados no período variou em 2005, de 63,6% em Pernambuco a 81,7% no Amazonas, em 2004. O valor mediano da proporção de abandono variou de 5,7 em São Paulo, 2005 a 11,5% em Mato Grosso, 2004. As menores coberturas do Programa Saúde da Família foram no Rio Grande do Sul. CONCLUSÕES: Neste estudo, os maiores percentuais de cura e os menores de abandono não estão associados à estratégia DOTS. / Salvador

MELO, Heitor Alves de. Propriedades eletrônicas de pontos quânticos contendo muitos elétrons. 2010. 75 f. : Dissertação (mestrado) - Universidade Federal do Ceará, Centro de Ciências, Departamento de Física, Fortaleza, 2010 . / Submitted by francisco lima (admir@ufc.br) on 2012-11-27T15:20:10Z No. of bitstreams: 1 2010_hadmelo.pdf: 2475149 bytes, checksum: f2b733568c55c95683fc14e493c5ab31 (MD5) / Approved for entry into archive by Nirlange Queiroz(nirlange@gmail.com) on 2015-09-18T12:10:21Z (GMT) No. of bitstreams: 1 2010_hadmelo.pdf: 2475149 bytes, checksum: f2b733568c55c95683fc14e493c5ab31 (MD5) / Made available in DSpace on 2015-09-18T12:10:21Z (GMT). No. of bitstreams: 1 2010_hadmelo.pdf: 2475149 bytes, checksum: f2b733568c55c95683fc14e493c5ab31 (MD5) / This work investigates the eletronic properties of semiconductor quantum dots in which there are many electrons con ned. In particular, we study Si and Ge quantum dots embedded in dielectric matrices (SiO2 e HfO2). The theoretical methos used to calculate the total energy of N electrons con ned in quantum dots is based on a simpli ed version of the Hartree-Fock method. In this model, the total energy is obtained from single-particle wavefunctions and eigen-energies. The obtained results show that the total energy in Ge quantum dots are always larger than in Si ones. The reason is the smaller electron e ective mass in Ge, which raises the energies of the con ned states. As for the role of the dielectric matrix, the total energy is always larger for SiO2 than for HfO2. Physically, this e ect is caused by the fact that SiO2 has larger con nement barriers (3.2 eV) than HfO2 (1.5 eV). Smaller barriers favor larger spatial extent of the wavefunctions, decreasing the repulsion energy of the con ned electrons. The chemical potential and additional energy was also calculated as function of the number of con ned electrons. It was observed that the chemical potential of Ge quantum dots are always larger than Si ones, but the role of the dielectric matrix is inverted. The chemical potential for HfO2 is larger than for SiO2. With respect to the additional energy, we observed that this quantity strongly oscillates within the range 0 to 0.4 eV for cases. If one takes into account that the Coulomb blockade phenomena is only observed for additional energies much larger the thermal enegy (of the order of 3=2kBT), this phenomena can only be observed for the case where there are only a few electrons con ned in the quantum dots. / Este trabalho dedica-se ao estudo das propriedades eletrônicas de pontos quânticos semicondutores contendo muitos el etrons con nados. Em particular, ser~ao investigados pontos quânticos de Si e Ge imersos em matrizes diel etricas (SiO2 e HfO2). O m etodo te orico utilizado para calcular a energia total de um sistema de N el etrons con nados baseia-se numa vers~ao simpli cada do m etodo de Hartree-Fock. Neste modelo a energia total e calculada a partir das fun ções de onda e estados de energia de uma unica part cula. Os resultados obtidos mostram que a energia total em pontos quânticos de Ge s~ao em geral maiores que em pontos quânticos de Si, independentemente do n umero de el etrons con nados. Isto acontece devido a massa efetiva menor dos el etrons no Ge que aumentam as energia de con namento. Em rela ção ao papel das barreiras diel etricas, a energia total e sempre maior nos casos em que o ponto quântico est a envolvido por SiO2. Fisicamente, isto se deve ao fato de que a barreira de con namento do SiO2 (3.2 eV) e maior que a do HfO2 (1.5 eV). Barreiras mais baixas favorecem o aumento da extensão espacial das funções de onda, reduzindo a repulsão coulombiana dos el etrons con nados. Calculouse tamb em o potencial quí mico dos pontos quânticos em fun ção do n umero de el etrons con nados, e a energia adicional necess aria para aprisionar mais um el etron nos pontos quânticos. Veri cou-se que o potencial qu mico dos pontos quânticos de Ge são sempre maiores que nos de Si, por em o potencial qu mico para pontos quânticos envoltos em HfO2 são sempre maiores que no caso do SiO2. Em relação a energia adicional, observa-se que esta quantidade apresenta fortes oscilações e que varia entre 0 e 0.4 eV para todos os casos estudados. Se levarmos em conta que o fenômeno conhecido como bloqueio de Coulomb acontece quando a energia adicional e muito maior que a energia t ermica (da ordem de 3=2kBT), este fenômeno s o ser a observado quando houver poucos el etrons con nados nos pontos quânticos.

8-band k.p theory was applied to bulk GaN and InN. The optical transitionintensity was computed and results show &gt; 80-90% degree of polarization inthe direction of compression. Polarization switching is observed when strainwas reversed from compressive to tensile. 6 band k.p theory was used tostudy InGaN quantum dot/GaN elliptical pyramid structures. The opticaltransition intensity was calculated for different elongations of the pyramid.Elongation of the pyramid gives rise to a small polarization in the directionof the pyramid elongation. The optical transition intensity was calculatedfor elongated quantum dots and was strongly in uencing the polarization inthe direction of the quantum dot elongation, with a degree of polarization of &gt;90%.

O consumo excessivo de álcool é recorrente entre universitários e está associado a inúmeras conseqüências negativas. Fatores ambientais (bottom-up) podem favorecer este consumo (ex.: influência do grupo, pistas associadas à droga). Além destes, fatores individuais podem influenciar o comportamento de beber desta população, entre eles fatores cognitivos (top-down). Bebedores freqüentes tendem a apresentar um viés atencional para estímulos associados ao álcool. Com o uso repetido do álcool, pistas ambientais associadas aos efeitos desta droga tornam-se salientes, em função de suas propriedades reforçadoras, atraindo a atenção do usuário em detrimento de outros estímulos e exacerbam o desejo de beber. O uso freqüente de álcool também tem sido relacionado a um conjunto de expectativas predominantemente positivas acerca dos seus efeitos e riscos para desenvolver dependência que podem influenciar o início e a manutenção do uso. Neste contexto, o objetivo deste estudo foi: a) examinar a relação entre o padrão de consumo e expectativas em relação aos efeitos do álcool entre universitários e b) desenvolver uma tarefa para investigar o viés atencional para pistas relacionadas ao álcool em indivíduos com diferentes padrões de consumo. Participaram deste estudo graduandos da UFRGS (N=79), do sexo masculino, com 22 anos de idade em média (dp=2,81). O padrão de consumo de risco e as expectativas positivas foram acessados através do Alcohol Use Disorders Identification Test (AUDIT) e do Inventário de Expectativas e Crenças Pesssoais acerca do Álcool (IECPA), respectivamente. Participaram deste estudo graduandos da UFRGS (N=79), do sexo masculino, com 22 anos de idade em média (dp=2,81). O padrão de consumo de risco e as expectativas positivas foram acessados através do Alcohol Use Disorders Identification Test (AUDIT) e do Inventário de Expectativas e Crenças Pesssoais acerca do Álcool (IECPA), respectivamente. Examinou-se o viés atencional através de uma tarefa computadorizada. O consumo de risco de álcool, que inclui o beber problemático e o padrão binge, estava associado a altas expectativas positivas em relação aos seus efeitos. Constatou-se que 43% dos participantes eram bebedores de alto risco para desenvolver dependência, conforme o AUDIT. Além disso, 68,4% deles foram caracterizados como bebedores com padrão binge de uso de álcool e 44,3% possuíam expectativas positivas em relação aos efeitos do álcool altas. Houve correlação entre beber problemático e expectativas positivas. Quanto à avaliação do viés atencional, não foi observado nenhum efeito de grupo, de tempo de exposição, nem de interação entre grupo e tempo de exposição. Identificar os fatores top down e bottom-up envolvidos no consumo de álcool de risco é essencial para formulação de modelos teóricos que compreendam este preocupante fenômeno. A avaliação das expectativas a respeito dos efeitos do álcool contribui para o planejamento de intervenções terapêuticas e estratégias preventivas mais precisas, visando a reduzir os riscos comportamentais e de saúde associados ao álcool. Além disso, o estudo do viés atencional pode favorecer o entendimento da relação entre fissura e atenção, da transição do uso ocasional para a dependência e da recaída. / The excessive alcohol consumption is recurrent among college students and it is associated with a variety of negative consequences. Environmental factors (bottom-up) can contribute to this phenomenon (group influences, drug cues). Furthermore, individual factors can also influence drinking behavior of this population, such as cognitive factors (top-down). Drug cues become highly salient as a result of their reinforcing properties, attracting the attention of the drug user in detriment of other stimuli. The exposure to drug cues can increase the desire to drink. Thus, heavy social drinkers show an attentional bias towards alcohol cues. The frequent alcohol use has also been related to a set of positive outcome expectancies and risk to develop drug dependence. These expectancies can influence the maintenance of drug intake. The aim of this study was: to examine the association of risk pattern and alcohol expectancies among college students and b) to develop a task to investigate attentional bias for alcohol cues in individuals with different drink patterns. Participants (N=79, mean age 22, dp=2,81) were college students. The risk pattern and the positive alcohol expectancies were assessed through Alcohol Use Disorders Identification Test (AUDIT) and Inventário de Expectativas e Crenças Pessoais acerca do Álcool (IECPA). The attentional bias was examined using a computerized task. The risk pattern, which includes drinking problematic and binge drinking, was associated with high positive expectancies. Results indicated that 43% of the participants had high risk to develop alcohol dependence. Moreover, 68.4% were binge drinkers and 44.3% had high positive alcohol expectancies. Risk pattern was associated with higher levels of positive alcohol expectancies. Related to the atencional bias assessment, there was not observed any group effect, exposition time, interaction between group and exposition time. Identifying bottom-up and top-down factors associated with the risk pattern of alcohol consumption is important to understand this preoccupant phenomenon. The alcohol expectancies assessment contributes to more efficient planning for therapeutical interventions and preventing strategies to reduce behavioral and health risks associated to the alcohol consumption. Moreover, the study of atencional bias can contribute to the understanding of the relationship between craving and attention, of the transition of the occasional use for the dependence and relapse.

Light from the sun is an attractive source of energy for its renewability, supply, scalability, and cost. Silicon solar cells are the dominant technology of choice for harnessing solar energy in the form of electricity, but the designs are approaching their practical efficiency limits. New multijunction designs which use the tunable properties of the more expensive III-V semiconductors have historically been relegated to space applications where absolute power conversion efficiency, resilience to radiation, and weight are more important considerations than cost. Some of the more recent developments in the field of semiconductor materials are the so-called III-nitride materials which mainly use either indium, aluminum or gallium in combination with nitrogen. Indium gallium nitride (InGaN) is one of these III-nitride semiconductor alloys that can be tailored to span the vast majority of the solar spectrum. While InGaN growth traditionally requires expensive substrate materials such as sapphire, three-dimensional nanowire growth modes enable high quality lattice mismatched growth of InGaN directly on silicon without a metamorphic buffer layer. The absorption and electronic properties of InGaN can also be tuned by incorporating it into quantum confined regions in a GaN host material. This opens up a route towards cost-effective, high efficiency devices such as light emitted diodes and solar cells which can operate over a large range of wavelengths. The combination of the two material systems of InGaN/GaN and silicon can marry the low cost of silicon wafers with the desirable optoelectronic properties of III-nitride semiconductors. This thesis investigates the potential for highly nanostructured InGaN/GaN based devices using quantum-dot-in-nanowire designs as novel solar cells which can enable intermediate band absorption effects and multiple junctions within a single nanowire to absorb more of the solar spectrum and operating more efficiently. Such semiconductor nanostructures can in principle reach power conversion efficiencies of over 40\% on silicon, with a cost closer to conventional silicon solar cells as opposed to methods which use non-silicon substrates. In the primary strategy, the nanowires contain InGaN quantum dots which act as photon absorption/carrier generation centres to sequentially excite photons within the large band gap semiconductor. By using this intermediate band of states, large operating voltages between contacts can be maintained without sacrificing the collection of long wavelength solar photons. In this work, we characterize the properties of such nanowires and experimentally demonstrate sub-bandgap current generation in a large area InGaN/GaN dot-in-nanowire solar cell. Experimental characterization of InGaN / GaN quantum dots in nanowires as both LEDs and solar cells is performed to determine the nanowire material parameters to understand how they relate to the nanowire device performance. Multiple microscopy techniques are performed to determine the nanowire morphology and contact effectiveness. Optical characterization of bare and fabricated nanowires is used to determine the anti-reflection properties of nanowire arrays. Photoluminescence and electroluminescence spectroscopy are performed. Illuminated current-voltage characteristics and quantum efficiencies are determined. Specular and diffuse reflectivities are measured as a function of wavelength. Technology computer-aided design (TCAD) software is used to simulate the performance of the overall nanowire device. The contribution from quantum dots or quantum wells is simulated by solving for the carrier wavefunctions and density of states with the quantum structures. The discretized density of states from the quantum dots is modelled and used in a complete drift-diffusion device simulation to reproduce electroluminescence results. The carrier transport properties are modified to demonstrate effects on the overall device performance. An alternate design is also proposed which uses an InGaN nanowire subcell on top of a silicon bottom subcell. The dual-junction design allows a broader absorption of the solar spectrum, increasing the operating voltage through monolithically grown series-connected, current-matched subcells. The performance of such a cell is simulated through drift-diffusion simulations of a dual-junction InGaN/Si solar cell. The effects of switching to a nanowire subcell based on the nanowires studied in this thesis is discussed.

abstract: This dissertation presents research findings regarding the exploitation of localized surface plasmon (LSP) of epitaxial Ag islands as a means to enhance the photoluminescence (PL) of Germanium (Ge) quantum dots (QDs). The first step of this project was to investigate the growth of Ag islands on Si(100). Two distinct families of Ag islands have been observed. “Big islands” are clearly faceted and have basal dimensions in the few hundred nm to μm range with a variety of basal shapes. “Small islands” are not clearly faceted and have basal diameters in the 10s of nm range. Big islands form via a nucleation and growth mechanism, and small islands form via precipitation of Ag contained in a planar layer between the big islands that is thicker than the Stranski-Krastanov layer existing at room-temperature. The pseudodielectric functions of epitaxial Ag islands on Si(100) substrates were investigated with spectroscopic ellipsometry. Comparing the experimental pseudodielectric functions obtained for Si with and without Ag islands clearly identifies a plasmon mode with its dipole moment perpendicular to the surface. This observation is confirmed using a simulation based on the thin island film (TIF) theory. Another mode parallel to the surface may be identified by comparing the experimental pseudodielectric functions with the simulated ones from TIF theory. Additional results suggest that the LSP energy of Ag islands can be tuned from the ultra-violet to the infrared range by an amorphous Si (α-Si) cap layer. Heterostructures were grown that incorporated Ge QDs, an epitaxial Si cap layer and Ag islands grown atop the Si cap layer. Optimum growth conditions for distinct Ge dot ensembles and Si cap layers were obtained. The density of Ag islands grown on the Si cap layer depends on its thickness. Factors contributing to this effect may include the average strain and Ge concentration on the surface of the Si cap layer. The effects of the Ag LSP on the PL of Ge coherent domes were investigated for both α-Si capped and bare Ag islands. For samples with low-doped substrates, the LSPs reduce the Ge dot-related PL when the Si cap layer is below some critical thickness and have no effect on the PL when the Si cap layer is above the critical thickness. For samples grown on highly-doped wafers, the LSP of bare Ag islands enhanced the PL of Ge QDs by ~ 40%. / Dissertation/Thesis / Doctoral Dissertation Physics 2015