In this dissertation I present inelastic and elastic light scattering studies of collective states emerging from interactions in electron systems confined to two dimensions. These studies span the first, second and third Landau levels. I report for the first time, high energy excitations of composite fermions in the quantum fluid at v = 1/3. The high energies discovered represent excitations across multiple composite fermion energy levels, demonstrating the topological robustness of the fractional quantum Hall state at v = 1/3. This study sets the ground work for similar measurements of states in the second Landau level, such as those at v = 5/2. I present the first light scattering studies of low energy excitations of quantum fluids in the second Landau level. The study of low energy excitations of the quantum fluid at 3 ≥ v ≥ 5/2 reveals a rapid loss of spin polarization for v ≤ 3, as monitored by the intensity of the spin wave excitation at the Zeeman energy. The emergence of a continuum of low-lying excitations for v ≤ 3 reveals competing quantum phases in the second Landau level with intriguing roles of spin degrees of freedom and phase inhomogeneity. The first light scattering studies of the electron systems in the third Landau level are reported here. Measurements of low energy excitations and their spin degrees of freedom reveal contrasting behavior of states in the second and third Landau levels. I discuss these measurements in the context of the charge density wave phases, that are believed, by some, to dominate the third Landau level, and suggest ways of verifying this belief using light scattering. Distinct behavior in the dispersion of the spin wave at v = 3 is measured for the first time. The study may highlight differences in the first and second Landau levels that are manifested through the electron wavefunctions. In addition to intra-Landau level measurements, inter-Landau level studies are also reported. The results of which reveal roles of spin degrees of freedom and many body interactions in odd denominator integer quantum Hall states.

In this thesis we initiate a systematic study of fluid dynamics using the effective field theory (EFT) program. We consider the canonical quantization of an ordinary fluid in an attempt to discover if there is some kind of quantum mechanical inconsistency with ordinary fluids at zero temperature. The system exhibits a number of peculiarities associated with the vortex degrees of freedom. We also study the dynamics of a nearly incompressible fluid via (classical) effective field theory. In the kinematical regime corresponding to near incompressibility (small fluid velocities and accelerations), compressional modes are, by definition, difficult to excite, and can be dealt with perturbatively. We systematically outline the corresponding perturbative expansion, which can be thought of as an expansion in the ratio of fluid velocity and speed of sound. This perturbation theory allows us to compute many interesting quantities associated with sound-flow interactions. Additionally, we also improve on the so-called vortex filament model, by providing a local field theory describing the dynamics of vortex-line systems and their interaction with sound, to all orders in perturbation theory. Next, we develop a cosmological model where primordial inflation is driven by a 'solid'. The low energy EFT describing such a system is just a less symmetric version of the action of a fluid---it lacks the volume preserving diffeomorphism. The symmetry breaking pattern of this system differs drastically from that of standard inflationary models: time translations are unbroken. This prevents our model from fitting into the standard effective field theory description of adiabatic perturbations, with crucial consequences for the dynamics of cosmological perturbations. And finally, we introduce dissipative effects in the effective field theory of hydrodynamics. We do this in a model-independent fashion by coupling the long-distance degrees of freedom explicitly kept in the effective field theory to a generic sector that "lives in the fluid'', which corresponds physically to the microscopic constituents of the fluid. At linear order in perturbations, the symmetries, the derivative expansion, and the assumption that this microscopic sector is thermalized, allow us to characterize the leading dissipative effects at low frequencies via three parameters only, which correspond to bulk viscosity, shear viscosity, and---in the presence of a conserved charge---heat conduction. Using our methods we re-derive the Kubo relations for these transport coefficients.

Chemical vapor deposition growth has been a popular technique to produce large-area, high-quality monolayer graphene on Cu substrates ever since its first demonstration in 2009. Pristine graphene grown in such a way owns the natures of zero charge carriers and zero band gap. As an analogy to semi-conductor studies, substitutional doping with foreign atoms is a powerful way to tailor the electronic properties of this host materials. Within such a context, this thesis focuses on growing and characterizing both pristine and chemically-doped CVD grown monolayer graphene films at microscopic scales. We first synthesized pristine graphene on Cu single crystals in ultra-high-vacuum and subsequently characterized their properties by scanning tunneling microscopy/spectroscopy (STM/S), to learn the effects of Cu substrate crystallinity on the quality of graphene growth and understand the interactions between graphene films and Cu substrates. In the subsequent chapters, we chemically doped graphene with nitrogen (N) and boron (B) atoms, and characterized their topographic and electronic structures via STM/S. We found that both N and B dopants substitionally dope graphene films, and contribute electron and hole carriers, respectively, into graphene at a rate of approximately 0.5 carrier/dopant. Apart from this, we have made comparisons between N- and B-doped graphene films in aspects of topographic features, dopant distribution and electronic perturbations. In the last part of this thesis, we used Raman spectroscopy mapping to investigate the N dopant distribution within and across structural grains. Future experiments are also brief discussed at the end of the thesis.

Enzyme immobilization has been of great industrial importance because of its use in various applications like bio-fuel cells, bio-sensors, drug delivery and bio-catalytic films. Although research on enzyme immobilization dates back to the 1970's, it has been only in the past decade that scientists have started to address the problems involved systematically. Most of the previous works on enzyme immobilization have been retrospective in nature i.e enzymes were immobilized on widely used substrates without a compatibility study between the enzyme and the substrate. Consequently, most of the enzymes lost their activity upon immobilization onto these substrates due to many governing factors like protein-surface and inter-protein interactions. These interactions also play a major role biologically in cell signaling, cell adhesion and inter-protein interactions specifically is believed to be the major cause for neurodegenerative diseases like Alzheimer's and Parkinson's disease. Therefore understanding the role of these forces on proteins is the need of the hour. In my current research, I have mainly focused on two factors a) Surface Curvature b) Surface Chemistry as both of these play a pivotal role in influencing the activity of the enzymes upon immobilization. I study the effect of these factors computationally using a stochastic method known as Monte Carlo simulations. My research work carried out in the frame work of a Hydrophobic-Polar (HP) lattice model for the protein shows that immobilizing enzymes inside moderately hydrophilic or hydrophobic pores results in an enhancement of the enzymatic activity compared to that in the bulk. Our results also indicate that there is an optimal value of surface curvature and hydrophobicity/hydrophilicity where this enhancement of enzymatic activity is highest. Further, our results also show that immobilization of enzymes inside hydrophobic pores of optimal sizes are most effective in mitigating protein-aggregation. These results provide us a rationale to understand the role of chaperonins in protein folding and disaggregation. Our results indicate that strong protein-surface interactions and confinement inducement stability inside pores makes it best suitable for enzyme immobilization.

This thesis studies electronic properties of molecular devices in the limiting cases of strong and weak electrode-molecule coupling. In these two limits, we use the complementary techniques of X-Ray spectroscopy and Scanning Tunneling Microscopy (STM) to understand the mechanisms for electrode-molecule bond formation, the energy level realignment due to metal-molecule bonds, the effect of coupling strength on single-molecule conductance in low-bias measurements, and the effect of coupling on transport under high-bias. We also introduce molecular designs with inherent asymmetries, and develop an analytical method to determine the effect of these features on high-bias conductance. This understanding of the role of electrode-molecule coupling in high-bias regimes enables us to develop a series of functional electronic devices whose properties can be predictably tuned through chemical design. First, we explore the weak electrode-molecule coupling regime by studing the interaction of two types of paracyclophane derivates that are coupled `through-space' to underlying gold substrates. The two paracyclophane derivatives differ in the strength of their intramolecular through-space coupling. X-Ray photoemission spectroscopy (XPS) and Near-Edge X-ray Absorbance Fine Structure (NEXAFS) spectroscopy allows us to determine the orientation of both molecules; Resonant Photoemission Spectroscopy (RPES) then allows us to measure charge transfer time from molecule to metal for both molecules. This study provides a quantititative measure of charge transfer time as a function of through-space coupling strength. Next we use this understanding in STM based single-molecule current-voltage measurements of a series of molecules that couple through-space to one electrode, and through-bond to the other. We find that in the high-bias regime, these molecules respond differently depending on the direction of the applied field. This asymmetric response to electric field direction results in diode-like behavior. We vary the length of these asymmetrically coupled molecules, and find that we can increase the rectifying characteristics of these molecules by increasing length. Next, we explore the strong-coupling regime with an X-Ray spectroscopy study of the formation of covalent gold-carbon bonds using benzyltrimethyltin molecules on gold surfaces in ultra high vacuum conditions. Through X-ray Photoemission Spectroscopy (XPS) and X-ray absorption measurements, we find that the molecule fragments at the Sn-Benzyl bond when exposed to gold and the resulting benzyl species only forms covalent Au-C bonds on less coordinated Au surfaces like Au(110). We also find spectroscopic evidence for a gap state localized on the Au-C bond that results from the covalent nature of the bond. Finally, we use Density Functional Theory based Nudged Elastic Band methods to find reaction pathways and energy barriers for this reaction. We use our knowledge of the electronic structure of these bonds to create single-molecule junctions containing Au-C bonds in STM-based break junction experiments. In analogy with our approach for the weakly coupled `through-space' systems, we study the high-bias current-voltage characteristics of molecules with one strong Au-C bond, and one weaker donor-acceptor bond. These experiments reveal that the `gap state' created due to the covalent nature of the Au-C bond remains essentially pinned to the Fermi level of its corresponding electrode, and that most of the electric potential drop in the junction occurs on the donor-acceptor bond; as a result, these molecules behave like rectifiers. We use this principle to create a series of three molecular rectifiers, and show that the unique properties of the Au-C bond allow us to easily tune the rectification ratio by modifying a single electronic parameter. We then explore the process of molecular self-assembly to create organic electronic structures on metal surfaces. Specifically, we study the formation of graphene nanoribbons using a brominated precursor deposited on Au(111) surface in ultra high vacuum. We find that the halogen atoms cleave from the precursors at surprisingly low temperatures of <100C, and find that the resulting radicals bind to Au, forming Au-C and Au-Br bonds. We show that the Br desorbs at relatively low temperatures of <250C, and that polymerization of the precursor molecules to form nanoribbons proceeds only after the debrominization of the surface. Finally, with Angle-Resolved Photoemission and Density Functional Theory calculations, we quantify the interaction strength of the resulting nanoribbons with the underlying gold substrate. Taken together, the results presented in this thesis offer a mechanistic understanding of the formation of electrode-molecule bonds, and also an insight into the high-bias behavior of molecular junctions as a function of electrode-molecule coupling. In addition, our work in developing tunable, functional electronic devices serves as a framework for future technological advances towards molecule-based computation.

Quantifying the statistical uncertainty in diffracted intensities was first investigated by Alexander, Klug and Kummer in 1948, who developed a formulation that estimated the relative uncertainty in the diffracted intensities from the relative uncertainty in the populations of diffracting particles within an irradiated powder. In this thesis, we show that this formulation becomes inapplicable for powder ensembles with particle sizes below 1 micron. In this size regime, the probability of diffraction cannot be formulated based on simple area ratios, and the classical multiplicity should be replaced by effective multiplicities. To properly relate the diffracted intensities collected by the detector to the grains participating in diffraction, we develop a modeling methodology which isolates the sampling and intensity spaces and links each diffracting particle to its own diffracted spot. The independent investigation of diffracted intensities and diffracting particle populations reveals that the uncertainties in the diffracted intensities are almost always greater than those in the diffracting particle populations. The only special case, where the two uncertainties are equal, occurs for 'large' particle sizes, where the full angular width of the particle's characteristic rocking curve is smaller than the angular resolution of the detector pixel. Our modeling results also show that the population of particles required to reach the ultimate average diffracted intensities predicted by the Debye equation depends on the size and crystallinity of the irradiated particles. Finally, the direct link between diffracting grains and diffracted intensities is not preserved in the formulation of the Debye scattering equation, and therefore the analysis and refinement of experimental diffraction data against the Debye model are shown to result in ambiguous structural parameters.

New torques acting on magnetization in metallic ferromagnets, accompanied by new terms to the Landau-Lifshitz-Gilbert (LLG) equation which governs GHz magnetization dynamics, are important for both the fundamental understanding of magnetism and applications in magnetoelectronic devices. In this thesis, we have carried out experimental investigations of several proposed novel torques acting on magnetization dynamics using broadband ferromagnetic resonance (FMR) between 2-26 GHz. The FMR technique is well-suited for materials studies, as it investigates unpatterned (sheet-level) films with relatively high throughput, enabling comparison of the response of several room-temperature, device-relevant ferromagnetic alloys (e.g. Ni₇₉Fe₂₁, or ‘Py’, Co, and CoFeB.) The common aspect of the torques which we have investigated by FMR is their origin in nonequilibrium spin populations, related to spin transfer torque. In Chapter 3 we have identified intrinsic “inertial” torques on magnetization, significant only at very high frequencies (up to 300 GHz), where the electron population cannot quite keep pace with the precession of magnetization. In Chapters 4 and 5 we have studied torques from “pumped” pure spin current due to the texture of precessing magnetization (intralayer spin pumping) and the precession of noncollinear magnetizations in trilayer structures (spin pumping). These three studies extend understanding of magnetism and magnetization dynamics at room temperature, and in limits of high speed and small dimension relevant for emerging applications.

Os fosfolipídios são moléculas anfifílicas que constituem o principal componente das membranas celulares. Na presença de água e para urna concentração suficientemente alta do fosfolipídio, as moléculas se auto organizam formando bicamadas separadas por água. Dentro das bicamadas, e dependendo da temperatura e a concentração, os fosfolipídios podem apresentar diferentes empacotamentos, dando origem a diferentes mesofases. Três mesofases são bem conhecidas: L IND. P IND. e L IND.. As mesofases L IND. e L IND. apresentam as bicamadas planas, porém, a diferença entre as duas está em que a fase L IND. apresenta as cadeias hidrocarbonadas ordenadas, com uma certa inclinação em relação à normal às bicamadas, e na fase L IND. as cadeias hidrocarbonadas estão completamente desordenadas. A fase P IND. conhecida como fase \"ripple\", apresenta uma ondulação periódica das bicamadas e as cadeias carbônicas com um certo grau de ordenamento. Existe na literatura urna grande discussão acerca da origem das mesofases lamelares, porém não existe um trabalho sistemático que permita caracterizar experimentalmente em forma completa as transições de fase entre as mesofases lamelares. Neste trabalho investigamos as transições de fases no sistema DMPC/água (dimiristoil-fosfatidil-colina/água), na região do diagrama de fases onde são observadas as fases L IND. P IND. e L IND.. Utilizamos as técnicas de calorimetria DSC e espalhamento de Raios X para levantar o diagrama de fases do sistema DMPC/água, e estudamos o comportamento da entalpia das diferentes transições de fase em função da concentração. Mediante microscopia de luz polarizada e espalhamento de Raios X caracterizamos o ordenamento induzido em amostras submetidas ao processo de \"shear\" . O procedimento permite observar por espalhamento de Raios X o comportamento da ordem no plano das bicamadas. Esse estudo permitiu também o acompanhamento do espaçamento entre as bicamadas nas transições de fase L IND. P IND. e P IND. L IND.. Tradicionalmente, em modelos teóricos, as transições L IND. P IND. e P IND. L IND. são tratadas corno de primeira ordem. Alguns modelos propõem que estas linhas de transição se encontram num ponto de Lifshitz. Mediante calorimetria de alta resolução estudamos o comportamento do calor específico em diferentes regiões do diagrama de fases. A transição P IND. L IND. para uma concentração de 28% em peso de água, não mostra a forma esperada para transições de primeira ordem, embora apresenta uma certa histerese. Encontramos que a primeira correção de \"scaling\" descreve bem o comportamento do calor específico a até uma temperatura onde este, claramente mostra-se arredondado. Essa região arredondada pode ser entendida no contexto das transições que envolvem ordem hexática, devido ao acoplamento entre o \"tilt\" e a ordem hexagonal. Essa observação é reforçada pela ordem bidimensional observada por espalhamento de raios-x. Finalmente investigamos a existência de fase \"ripple\" em outro fosfolipídio, DMPG (dimiristoil-fosfatidil-glicerol) que difere do DMPC apenas na cabeça polar. / Phospholipids are amphiphilic molecules that constitute the main component of the cellular membranes. In the presence of water and for concentrations sufficiently high of the lipid, the molecules self-assemble in bilayers separated by water. Inside the bilayers, and depending on the temperature and concentration, the phospholipids can present different packings, giving origin to different mesophases. Three mesophases are well-known: L´, P´ and La . The mesophases L´ and La present planar bilayers, even so, the difference between them is in the hydrocarbons chains. The L´ presents the chains orderly, with a certain tilt related to the normal of the bilayers, and in the La phase the chains are completely disordered. The P´ phase, known in the literature as ripple phase, presents periodic undulation of the bilayers and the carbonic chains with a certain degree of order. There is a great discussion in the literature concerning the origin of the lamellar phases, even though there is no systematic experimental work characterizing the phase transitions between lamellar phases. In this work we investigated the phase transitions in the DMPC/water system (dimiristoyl- phosphatidyl-choline), in the area of the phase diagram where the L´ P´, and La phases are observed. We used the calorimetric DSC technique and x-ray scattering to construct the phase diagram of DMPC/water, and we studied the behavior of the enthalpy associated to the different transitions as a function of the concentration. By means of polarized light microscopy and x-ray scattering we characterized the order induced in samples submitted to shear. The procedure allows us to observe the behavior of the in-plane order in the lamelas by means of x-ray scattering. This study also allowed to see the behavior of the lamellar spacing in the L´ -> P´, and P´, -> La phase transitions. Usually, the L´ -> P´, e P´ -> La are treated as first order transitions. Some models proposes that this transition lines encounters in a Lifshitz point. With high calorimetric resolution we study the behavior of the specific heat in different regions of the phase diagram. The P´ -> La transition for 28% of water, doesn\'t show the expected first order behavior. Instead of that we find that the first order correction to scaling succeeded to describe the specific heat near the transition, but clearly, de experimental data shows some rounding region. This rounded region can be understood in the context of the transitions involving hexatic order, where the tilt and the hexagonal ordering are coupled. This observation is reinforced by the 2D order observed by x ray scattering. We also investigated the existence of the \"ripple\" phase in another phospholipid, DMPG (dimiristoyl-phosphatidyl-glycerol) that just differs from DMPC in the polar head.

The Kibble-Zurek mechanism (KZM) was originally proposed to describe the evolution and "freezing" of defects in the early universe, but later it was generalized to study other quantum and classical systems driven by a varying parameter. The basic idea behind the KZM is that, as long as the changing rate (velocity) of the parameter is below a certain critical velocity, 𝑣_crit, the system will remain adiabatic (for isolated quantum systems) or quasi-static (for classical systems with a heat bath). The nonequilibrium finite-size scaling (FSS) method based on KZM has been exploited systematically. Through applying the scaling hypothesis, we can extract the critical exponents and study the dynamic properties of the system. In the first few chapters of this dissertation, we discuss the applications of KZM in several classical systems: first, we study the dynamics of 2D and 3D Ising model under a varying temperature as well as a varying magnetic field. Secondly, we examine the classical ℤ₂ gauge model, in which we show that KZM also works for topological phase transitions. Moreover, we also investigate the dynamics of other models with topological ordering only at T=0, where KZM cannot be applied. Lastly, we explore the 2D Ising spin glass with bimodal and gaussian couplings. With bimodal couplings, we find dual time scales associated with the order parameter and the energy correspondingly, while in the gaussian case one unique time scale is involved. The systems mentioned above are all classical and the dynamics are approached through simulated annealing (SA), in which thermal fluctuations drives systems to explore the energy landscape in finding the ground state. In the last chapter, we explore the efficiency of Quantum Annealing (QA) on a fully-connected spin glass (or Sherington-Kirkpatrick model) with a transverse field. QA is the counterpart of SA, where quantum fluctuations drive the system toward the ground state when the quantum terms are reduced. QA is currently widely explored as a paradigm for quantum computing to solve optimization problems. Here we compare the scaling of the dynamics (with system size) of the fully-connected spin glass through QA versus SA.

This dissertation presents an investigation on the effects of large scale roughness on the properties of giant magnetoresistive multilayers. The large scale roughness (sigmarms > 5 nm) is introduced into giant magnetoresistive thin films through the substrate. Current-in-plane (CIP) and current-perpendicular-to-the-plane (CPP) thin films were deposited by dc magnetron and triode sputtering. All films were characterized for roughness, magnetic and electronic behavior.;Our research on both pseudo spin valves and exchange-biased spin valves shows that long length scale roughness does not have a significant detrimental effect on GMR thin films. For the CIP films, we find that a decrease in GMR correlates to an increase in minimum film resistivity. as the minimum resistivity increased, the maximum resistivity increased linearly with a slope ∼1. This suggests that the decrease in GMR may primarily be an effect of increased spin-independent scattering resulting from the increased film roughness. The CPP films showed a similar relationship between minimum and maximum resistance. Studying the effect of such large scale substrate roughness is important for applications in which GMR multilayers are deposited on non-standard substrates and buffer layers including flexible media.