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The detection of biologically infectious agents, such as bacteria, in water is often a cumbersome process that can only be performed by trained personnel in a well-equipped laboratory and may require sufficient time (sometimes days) until detectable concentration levels of the pathogen are reached. Surface-based biosensors, on the other hand, have shown great promise as miniaturized devises that can provide efficient and de-centralized detection of bacteria. Their operation involves the selective capture of the target pathogen from a liquid sample to a surface (“sampling”) and their subsequent detection via signal transduction. Sampling currently presents a major bottleneck in the successful operation of these sensors as it relies on the extremely slow diffusive transport of the target particle from the bulk of the sample to the capture surface. The present work investigates how alternating current (AC) electric field effects produced by planar microelectrode arrays embedded into a solid surface can improve capture of bacteria. Specifically, numerical and experimental work is combined toward the analysis of a host of electric field generated phenomena (electrophoresis, electroosmosis, and electrothermal fluid flow) that can potentially guide and enhance the transport of K12 E. coli bacteria to the capture surface inside an electric field to find the effective frequency/voltage combination for an efficient capture. Bacteria capture at concentrations as low as 104 particles/mL was experimentally achieved. Proof of principle demonstrations on how antibody-functionalized microelectrode arrays can accelerate and selectively capture K12 E. coli bacteria (target pathogens) from samples containing debris or mixed bacteria populations are also demonstrated. / Thesis (Master, Chemical Engineering) -- Queen's University, 2014-02-28 14:53:46.437

Este trabalho segue os passos históricos, descritos na literatura, das interações normalmente consideradas nos sistemas intermetálicos de terras raras. O capítulo 2 considera o efeito do campo elétrico gerado pela distribuição de cargas no cristal, por isso denominado de campo elétrico cristalino. Já o capítulo 3 descreve o passo seguinte que é considerar uma interação entre dois íons vizinhos do cristal. Essa interação ocorre por mediação de elétrons itinerantes e é conhecida como interação de Ruderman-Kittel- Kasuya-Yosida, ou interação RKKY. Considerando-se apenas estas duas interações já é possível explicar boa parte do comportamento magnético dos compostos intermetálicos de terras raras. O PrMg2 é uma exceção para o qual a interação quadrupolar tem sido sugerida na literatura. A adição desta interação é o principal objetivo deste trabalho e tema do capítulo 4. A dependência dos parâmetros de ordem magnético e quadrupolar com a temperatura são estudados com a aproximação de campo médio. A estabilidade destes parâmetros é analisada através da energia livre na aproximação de campo médio (ao contrário da expansão de Landau, uma aproximação comum na literatura). Um diagrama de fases é obtido mostrando natureza do estado fundamental do Hamiltoniano de campo médio e o tipo de transição de fase (primeira ou segunda ordem) em função dos acoplamentos magnéticos e quadrupolares. É mostrado que o PrMg2 tem uma transição de fase de segunda ordem, como observado experimentalmente, após a inclusão de um acoplamento antiferroquadrupolar do tipo Heisenberg. Os cálculos numéricos foram feitos usando o programa Maple 5, e os códigos usados são mostrados nos apêndices A e C. / This work considers the presence of interactions in rare earth intermetallic compounds with cubic symmetry. In chapter 2 the crystalline electric field is taken into account and in chapter 3 an RKKY interaction between nearest neighbours is introduced in order to obtain magnetic order in the crystal. These interactions alone are sufficient to explain magnetic behavior of several based Pr compounds, with PrMg2 an exception for what a quadrupolar interaction has been proposed in the literature; the addition of this interaction constitutes the principal goal of this work and is developed in chapter 4. The temperature dependence of the magnetic- and quadrupolar-order parameters is studied under the mean-field approximation. The stability of those parameters are analyzed by means of an exact mean-field free energy (as opposed of a Landau expansion, an approximation common in the literature). A phase diagram is obtained relating the magnetic and quadrupolar couplings with the nature of the ground state mean-field Hamiltonian and the kind of the phase transitions (first or second). It is showed that the PrMg2 undergoes a second order phase transition, as observed experimentally, after an inclusion of a Heisenberg like antiferroquadrupolar coupling. The numerical calculations were performed using the Maple software and the codes are listed in the appendix.

Strongly correlated systems represent one of the major topics in modern solid-state physics. The rare-earth intermetallic compounds belonging to this class provide rich grounds for investigation of various phenomena. They show one of the most fascinating types of ground states in condensed-matter physics. Among them are: Kondolattice effects, heavy fermion behavior, superconductivity, magnetic order, non-Fermi liquid behavior, and quantum phase transition. Those properties occur mainly due to two competing interactions, the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida interaction. The study of unconventional superconductivity in heavy fermion systems attracted great interest over the last two decades. The exotic pairing mechanism (e.g. mediated by spin fluctuations) and the symmetry of the order parameter have been intensively discussed especially for superconducting Ce- and U-based compounds. The discovery of superconductivity below 0.65 K in the heavy-electron system CeCu2Si2 appeared unexpected as magnetic moments were known to destroy superconductivity. The pronounced anomaly of the electronic specific heat at Tc, however, strongly suggests that the unusual low temperature properties of heavy-electron systems indicate an unconventional origin of the superconducting phase. Since the discovery of superconductivity in CeCu2Si2, the question of the exact nature and origin of this phenomenon has been the subject of great interest in research. It has been postulated, that the superconductivity in these materials is not caused primarily by the usual electronphonon mechanism but rather by some magnetic interaction. CeCu2Si2 shows a rich phase diagram with different phases competing, depending on slight changes of the interactions. These properties are also strongly sample dependent. Small changes in composition eventually lead to changes in the electron interactions. These unique properties make this compound a fascinating subject of study. On the other hand it is difficult to synthesis the single crystals with defined physical properties. During the last three decades CeCu2Si2 has been an active research topic, from single crystal growth to sophisticated experiments like high-pressure measurements, neutron experiments etc. This thesis involved systematic investigations of the phase diagram, starting with the single crystal growth of different ground state and catheterized their physical properties including neutron experiments. The second part of the thesis contains, for the first time (to our knowledge), detailed investigations of the very interesting physical properties on YbRu2Ge2, which shows a quasiquartet crystalelectric-field ground state with quadrupolar ordering at 10 K. The first chapter is an overview of the underlying physics of heavy- fermion systems, including a description of the Doniach phase diagram. The second part of this chapter gives a brief introduction of crystalline-electric-field effect in rare-earth intermetallic compounds. Chapter 2. describes the experimental methods and crystal growth details. This chapter provides the main focus of this dissertation, presenting detailed experimental results for the different types of CeCu2Si2 crystals. Magnetic, thermodynamic and transport measurements on the new generation of large highquality single crystals were conducted by our research group. Furthermore, complimentary neutron investigations have been performed, which allowed to conclude that both magnetic and superconducting phases compete with each other. The effect of Ge doping on the Si site and possible coexistence of magnetic and superconducting phase is discussed in chapter 4. Chapter 5 provides a detailed investigation of the physical properties of YbRu2Ge2 single crystals. In addition, neutron experiments as well as the determination the magnetic structure and crystalline-electric-field scheme of YbRu2Ge2 are presented. The μSR experiments were also performed as a complimentary method to the neutron experiments. Chapter 6 ends the dissertation with a conclusion and summary.

Este trabalho segue os passos históricos, descritos na literatura, das interações normalmente consideradas nos sistemas intermetálicos de terras raras. O capítulo 2 considera o efeito do campo elétrico gerado pela distribuição de cargas no cristal, por isso denominado de campo elétrico cristalino. Já o capítulo 3 descreve o passo seguinte que é considerar uma interação entre dois íons vizinhos do cristal. Essa interação ocorre por mediação de elétrons itinerantes e é conhecida como interação de Ruderman-Kittel- Kasuya-Yosida, ou interação RKKY. Considerando-se apenas estas duas interações já é possível explicar boa parte do comportamento magnético dos compostos intermetálicos de terras raras. O PrMg2 é uma exceção para o qual a interação quadrupolar tem sido sugerida na literatura. A adição desta interação é o principal objetivo deste trabalho e tema do capítulo 4. A dependência dos parâmetros de ordem magnético e quadrupolar com a temperatura são estudados com a aproximação de campo médio. A estabilidade destes parâmetros é analisada através da energia livre na aproximação de campo médio (ao contrário da expansão de Landau, uma aproximação comum na literatura). Um diagrama de fases é obtido mostrando natureza do estado fundamental do Hamiltoniano de campo médio e o tipo de transição de fase (primeira ou segunda ordem) em função dos acoplamentos magnéticos e quadrupolares. É mostrado que o PrMg2 tem uma transição de fase de segunda ordem, como observado experimentalmente, após a inclusão de um acoplamento antiferroquadrupolar do tipo Heisenberg. Os cálculos numéricos foram feitos usando o programa Maple 5, e os códigos usados são mostrados nos apêndices A e C. / This work considers the presence of interactions in rare earth intermetallic compounds with cubic symmetry. In chapter 2 the crystalline electric field is taken into account and in chapter 3 an RKKY interaction between nearest neighbours is introduced in order to obtain magnetic order in the crystal. These interactions alone are sufficient to explain magnetic behavior of several based Pr compounds, with PrMg2 an exception for what a quadrupolar interaction has been proposed in the literature; the addition of this interaction constitutes the principal goal of this work and is developed in chapter 4. The temperature dependence of the magnetic- and quadrupolar-order parameters is studied under the mean-field approximation. The stability of those parameters are analyzed by means of an exact mean-field free energy (as opposed of a Landau expansion, an approximation common in the literature). A phase diagram is obtained relating the magnetic and quadrupolar couplings with the nature of the ground state mean-field Hamiltonian and the kind of the phase transitions (first or second). It is showed that the PrMg2 undergoes a second order phase transition, as observed experimentally, after an inclusion of a Heisenberg like antiferroquadrupolar coupling. The numerical calculations were performed using the Maple software and the codes are listed in the appendix.

Strongly correlated systems represent one of the major topics in modern solid-state physics. The rare-earth intermetallic compounds belonging to this class provide rich grounds for investigation of various phenomena. They show one of the most fascinating types of ground states in condensed-matter physics. Among them are: Kondolattice effects, heavy fermion behavior, superconductivity, magnetic order, non-Fermi liquid behavior, and quantum phase transition. Those properties occur mainly due to two competing interactions, the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida interaction. The study of unconventional superconductivity in heavy fermion systems attracted great interest over the last two decades. The exotic pairing mechanism (e.g. mediated by spin fluctuations) and the symmetry of the order parameter have been intensively discussed especially for superconducting Ce- and U-based compounds. The discovery of superconductivity below 0.65 K in the heavy-electron system CeCu2Si2 appeared unexpected as magnetic moments were known to destroy superconductivity. The pronounced anomaly of the electronic specific heat at Tc, however, strongly suggests that the unusual low temperature properties of heavy-electron systems indicate an unconventional origin of the superconducting phase. Since the discovery of superconductivity in CeCu2Si2, the question of the exact nature and origin of this phenomenon has been the subject of great interest in research. It has been postulated, that the superconductivity in these materials is not caused primarily by the usual electronphonon mechanism but rather by some magnetic interaction. CeCu2Si2 shows a rich phase diagram with different phases competing, depending on slight changes of the interactions. These properties are also strongly sample dependent. Small changes in composition eventually lead to changes in the electron interactions. These unique properties make this compound a fascinating subject of study. On the other hand it is difficult to synthesis the single crystals with defined physical properties. During the last three decades CeCu2Si2 has been an active research topic, from single crystal growth to sophisticated experiments like high-pressure measurements, neutron experiments etc. This thesis involved systematic investigations of the phase diagram, starting with the single crystal growth of different ground state and catheterized their physical properties including neutron experiments. The second part of the thesis contains, for the first time (to our knowledge), detailed investigations of the very interesting physical properties on YbRu2Ge2, which shows a quasiquartet crystalelectric-field ground state with quadrupolar ordering at 10 K. The first chapter is an overview of the underlying physics of heavy- fermion systems, including a description of the Doniach phase diagram. The second part of this chapter gives a brief introduction of crystalline-electric-field effect in rare-earth intermetallic compounds. Chapter 2. describes the experimental methods and crystal growth details. This chapter provides the main focus of this dissertation, presenting detailed experimental results for the different types of CeCu2Si2 crystals. Magnetic, thermodynamic and transport measurements on the new generation of large highquality single crystals were conducted by our research group. Furthermore, complimentary neutron investigations have been performed, which allowed to conclude that both magnetic and superconducting phases compete with each other. The effect of Ge doping on the Si site and possible coexistence of magnetic and superconducting phase is discussed in chapter 4. Chapter 5 provides a detailed investigation of the physical properties of YbRu2Ge2 single crystals. In addition, neutron experiments as well as the determination the magnetic structure and crystalline-electric-field scheme of YbRu2Ge2 are presented. The μSR experiments were also performed as a complimentary method to the neutron experiments. Chapter 6 ends the dissertation with a conclusion and summary.

Neste trabalho implementamos a técnica da ressonância quadrupolar nuclear (RQN) em duas dimensões. O espectro bidimensional é obtido a partir do pseudo-FID usando o estimador autoregressivo. Como o gradiente de campo-elétrico (GCE) no sítio do núcleo é produzido pelas cargas externas ao núcleo e o tensor GCE é simétrico, bastam dois parâmetros para determinar este tensor num sistema de coordenadas dos eixos principais. Estes parâmetros podem ser obtidos a partir do espectro de RQN para todos os núcleos quadrupolares, menos os núcleos com spin 3/2. Usando o espectro bidimensional é possível determinar o parâmetro de assimetria, eta, e consequentemente o outro parâmetro do tensor GCE, mesmo para as amostras policristalinas contendo núcleos com spin 3/2. A oprientação do sistema de coordenadas do tensor GCE no sistema de coordenadas do laboratório não pode ser obtida usando apenas o espectro de RQN. Há vários métodos experimentais que permitem determinar esta orientação relativa. Em todos os casos esta determinação requer um grande esforço experimental com um equipamento muito mais caro que um simples espectrômetro de RQN. Neste trabalho apresentamos um novo método para a deterrminação da orientação do tensor GCE no sistema de coordenadas do laboratório, usando apenas a RQN em duas dimensões e o método da máxima entropia para a deconvolução dos dados experimentais / In this work we implemented the nuclear quadrupole resonance (NQR) in two dimensions. The bidimensional spectrum is obtained from pseudo FID through the auto-regressive estimator. Since the electric field gradient (EFG) at the nucleus site is produced by the external charges and the EFG tensor is symmetric, we need only two parameters to determine this tensor in the coordinate system of principal axis. These parameters can be obtained from the NQR spectra for all the nucleus possessing quadrupole moment, except the one with spin 3/2. Using the bidimensional spectra, it is possible to determine the asymmetry parameter, 7], and consequently the other parameters of the EFG tensor, even in polycrystalline samples containing nucleus with spin 3/2.

Neste trabalho implementamos a técnica da ressonância quadrupolar nuclear (RQN) em duas dimensões. O espectro bidimensional é obtido a partir do pseudo-FID usando o estimador autoregressivo. Como o gradiente de campo-elétrico (GCE) no sítio do núcleo é produzido pelas cargas externas ao núcleo e o tensor GCE é simétrico, bastam dois parâmetros para determinar este tensor num sistema de coordenadas dos eixos principais. Estes parâmetros podem ser obtidos a partir do espectro de RQN para todos os núcleos quadrupolares, menos os núcleos com spin 3/2. Usando o espectro bidimensional é possível determinar o parâmetro de assimetria, eta, e consequentemente o outro parâmetro do tensor GCE, mesmo para as amostras policristalinas contendo núcleos com spin 3/2. A oprientação do sistema de coordenadas do tensor GCE no sistema de coordenadas do laboratório não pode ser obtida usando apenas o espectro de RQN. Há vários métodos experimentais que permitem determinar esta orientação relativa. Em todos os casos esta determinação requer um grande esforço experimental com um equipamento muito mais caro que um simples espectrômetro de RQN. Neste trabalho apresentamos um novo método para a deterrminação da orientação do tensor GCE no sistema de coordenadas do laboratório, usando apenas a RQN em duas dimensões e o método da máxima entropia para a deconvolução dos dados experimentais / In this work we implemented the nuclear quadrupole resonance (NQR) in two dimensions. The bidimensional spectrum is obtained from pseudo FID through the auto-regressive estimator. Since the electric field gradient (EFG) at the nucleus site is produced by the external charges and the EFG tensor is symmetric, we need only two parameters to determine this tensor in the coordinate system of principal axis. These parameters can be obtained from the NQR spectra for all the nucleus possessing quadrupole moment, except the one with spin 3/2. Using the bidimensional spectra, it is possible to determine the asymmetry parameter, 7], and consequently the other parameters of the EFG tensor, even in polycrystalline samples containing nucleus with spin 3/2.

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