<p> This thesis investigates the fundamental nanoscale near-field light matter interaction between a probe tip and plasmonic antenna nanostructures. The thesis is focused on polarization control of metallic plasmon modes using scattering-type scanning near-field optical microscopy (s-SNOM). Part of the thesis is dedicated to spectroscopic near-field comparison of coated and bare single plasmonic particles in the infrared wavelength range (&lambda;= 9&ndash;11 &micro;m) using s-SNOM. By tuning the wavelength of the incident light, we have acquired information on the spectral polarization dependence plasmon modes and plasmon/phonon&ndash;polariton resonant near-field interactions. The enhanced near-field coupling between the probe tip and high index Au nanostructures and Au-core thin silica coating (thickness &ap;10 nm) is described and quantified. </p>

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 1018. Adviser: Richard L. Weaver. Includes bibliographical references (leaves ) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--Lehigh University, 2007.

Thesis (Ph.D.)--Lehigh University, 2008.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6871. Adviser: Eduardo Fradkin. Includes bibliographical references (leaves 180-191) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1058. Includes bibliographical references (leaves 78-81) Available on microfilm from Pro Quest Information and Learning.

The three key areas of this thesis are crystal synthesis strategies, growth mechanisms, and new types of quantum materials nanowires. The highlights are introduction of a new catalyst (TiO2) for nanowire growth and application to Bi2Se3, Bi2Te3, SnO2, and Ge nanowires; demonstration of step-flow growth, a new growth mechanism, for Bi2Te3 sub-micron belts; and the characterisation of the first quasi-one dimensional topological insulator (orthorhombic Sb-doped Bi2Se3) and topological Dirac semimetal nanowires (Cd3As2). Research into new materials has been one of the driving forces that have contributed to the progress of civilisation from the Bronze Age four thousand years ago to the age of the semiconductor in the 20^th century. At the turn to the 21^st century novel materials, so-called quantum materials, started to emerge. The fundamental theories for the description of their properties were established at the beginning of the 20^th century but expanded significantly during the last three decades based, for example, on a new interpretation of electronic states by topological invariants. Hence, topological insulator (TI) materials such as mercury-telluride are one manifestation of a quantum material. In theory, TIs are characterised by an insulating interior and a surface with spin-momentum locked conduction. In real crystals, however, the bulk can be conducting due to crystal imperfections. Nanowires suppress this bulk contribution inherently by their high surface-to-volume ratio. Additionally, trace impurity elements can be inserted into the crystal to decrease the conductance further. These optimised TI nanowires could provide building blocks for future electronic nanodevices such as transistors and sensors. Initial synthesis efforts using vapour transport techniques and electronic transport studies showed that TI nanowires hold the promise of reduced bulk contribution. This thesis expands the current knowledge on synthesis strategies, crystal growth mechanisms, and new types of quantum materials nanowires. Traditionally, gold catalyst nanoparticles were used to grow TI nanowires. We demonstrate that they are suitable to produce large amounts of nanowires but have undesired side-effects. If a metaloxide catalyst nanoparticle is used instead, quality and even quantity are significantly improved. This synthesis strategy was used to produce a new TI which is built from chains of atoms and not from atomic layers as in case of previously known TIs. The growth of large nanowires with a layered crystal structure leads to step-flowgrowth, an intriguing phenomenon in the growth mechanism: New layers grow on top of previous layers with a single growth frontmoving fromthe root to the tip. These wires are ideal for further electronic characterisation that requires large samples. The nanowire growth of tin-oxide will also be discussed, a side project that arose from my growth studies, which is useful for sensor applications. Under certain conditions it forms tree-like structures in a single synthesis step. All of the aforementioned growth studies are carried out at atmospheric pressure. A separate growth study is carried out in ultra-high vacuum to assess the transferability of the growth process towards the cleanliness requirements of the semiconductor industry. If two quantum materials are joined together, exotic physics may emerge at the interface. One of the goals of TI research is the experimental observation of Majorana fermions, exotic particles which are their ownantiparticles with potential applications in quantum computing that may appear in superconductor/TI hybrid structures. We have synthesised such structures and initial characterisation suggests that the resistivity increases when they are cooled below the critical temperature of the superconductor. Beyond TIs, a new type of quantum material, called a topological Dirac semimetal, opens new realms of exotic physics to be discovered. Nanowires are grownfroma material which has recently been discovered to be a topological Dirac semimetal. Their growth mechanism is characterised and an extremely high electron mobility at room temperature is measured. The contribution of this thesis to the field is summarised in Fig. 1. Its core is the study of the growth mechanism of quantum materials which will be vital for future development of applications and fundamental research.

<p> I discuss the design and operation of a system for levitating a charged, &mu;m-scale, multilayer graphene nanoplatelet in a quadrupole electric field trap in high vacuum. Levitation decouples the platelet from its environment and enables sensitive mechanical and magnetic measurements. </p><p> First, I describe a method of generating and trapping the nanoplatelets. The platelets are generated via liquid exfoliation of graphite pellets and charged via electrospray ionization. Individual platelets are trapped at a pressure of several hundred mTorr and transferred to a trap in a second chamber, which is pumped to UHV pressures for further study. All measurements of the trapped platelet's motion are performed via optical scattering. </p><p> Second, I present a method of gyroscopically stabilizing the levitated platelet. The rotation frequency of the platelet is locked to an applied radio frequency (rf) electric field <i><b>E</b></i>_rf. Over time, frequency-locking stabilizes the platelet so that its axis of rotation is normal to the platelet and perpendicular to <i><b>E</b></i>_rf. </p><p> Finally, I present optical data on the interaction of a multilayer graphene platelet with an applied magnetic field. The stabilized nanoplatelet is extremely sensitive to external torques, and its low-frequency dynamics are determined by an applied magnetic field. Two mechanisms of interaction are observed: a diamagnetic polarizability and a magnetic moment proportional to the frequency of rotation. A model is constructed to describe this data, and experimental values are compared to theory.</p><p>

<p>The macroscopic quantum phenomenology of superconductivity has attracted broad interest from both scientific research and applications. Many exotic physics found in the first high $T_C$ superconductor family cuprate remain unsolved even after 30 years of intense study. Angle-Resolved Photoemission Spectroscopy (ARPES) provides the direct probe to the major information of the electronic interactions, which plays the key role in these exotic physics including high $T_C$ superconductivity. ARPES is also the best tool to study the electronic structure in materials that potentially hold high $T_C$ superconductivity, providing insight for materials research and design. In this thesis, we present the ARPES study of the cuprate high $T_C$ superconductor Pb doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, and potential high $T_C$ superconductors K doped \textit{p}-terphenyl, and trilayer nickelate La$_4$Ni$_3$O$_{10}$. For Pb doped Bi2212, our study focuses on the key part of the electronic interactions---the self-energies. With the development of a novel 2-dimensional analysis technique, we present the first quantitative extraction of the fully causal complex self-energies. The extracted information reveals a conversion of the diffusive strange-metal correlations into a coherent highly renormalized state at low temperature followed by the enhancement of the number of states for pairing. We then further show how this can lead to a strong positive feedback effect that can stabilize and strengthen superconducting pairing. In K doped \textit{p}-terphenyl, we discover low energy spectral gaps that persist up to 120 K, consistent with potential Meissner effect signal from previous studies. Among a few potential origins for these gaps, we argue that the electron pairing scenario is most likely. For La$_4$Ni$_3$O$_{10}$, we present the Fermiology and electron dynamics of this material, and they show certain similarities to the cuprate electronic structure, as well as a few unique features.

<p> Due to high specific capacity for lithiation, molybdenum dichalcogenides such as MoO₂ and MoS₂ are potential replacements for graphite anodes in Li-ion batteries. However, in bulk form these materials exhibit poor rate capability and lose capacity with each cycle. While the performance can be improved by changes to morphology, the details of the lithium intercalation mechanism are not fully understood. </p><p> In this work, X-ray absorption spectroscopy (XAS) is employed to investigate this mechanism, including X-ray absorption near-edge spectroscopy (XANES) and X-ray absorption fine-structure spectroscopy (XAFS). For MoS₂, modeling of the local structure supports the metallic conversion reaction model by the second lithiation.</p><p>