Tip-enhanced Raman spectroscopy (TERS) is a scanning probe technique that utiHscs a confined, ovanescent field at the tip apex to conduct optical characterisation of a surface at length-scales below the diffraction limit. This thesis details the development of a new TER.S system based upon a shear-force scanning probe microscope (SPM) which sits atop an inverted microscope configured for bottom illumination geometry and coupled to a Raman spectrometer. The system has been optimised for use with solid silver probes and 532 nm illumination. Measurement procedures, automated scripts and data analysis software have been developed that allow reliable alignment of the tip; complex automated mapped measurements; and post processing which produces visual summary sheets to facilitate rapid review of a TERS experiment. Enhanced TERS spectra have been demonstrated on ultra-thin Rhodamine 6G films, self assembled monolayers (SAM) of thiophenole molecules, ultra-thin graphitic films and on multilayered graphene. Improvements in fabrication and alignment procedures have reduced the setup time between fabrication and approach to 20 minutes and improved the reliability of TERS tips with ~ 50% of tips demonstrating TERS activity. Using TERS, heightened defect sensitivity was observed on graphene edges, folds and overlapping regions. The TERS contrast of the defect induced D band was ~ 7.5 times the contrast of the graphene G band. Calculations show that the phonons correlating to the D and G bands interact differently with the enhanced TERS field and that the for certain defect types the D band experiences greater enhancement. Defects play an important role in tailoring the electronic and chemical properties of graphene which is key to the development of graphene based devices. The localised structural and spectral information makes TERS a highly promising tool for the characterisation of defects in graphene. This work demonstrates the potential of TERS for this exciting and important application.

<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>

Frequency multiplication is an effect that arises in electronic components that exhibit a non-linear response to electromagnetic stimuli. Barriers to achieving very high frequency response from electronic devices are the device capacitance and other parasitic effects such as resistances that arise from the device geometry and are in general a function of the size of the device. In general, smaller device geometries and features lead to a faster response to electromagnetic stimuli. It was posited that the small size of the silicon nanowires (SiNWs) would lead to small device capacitance and spreading resistance, thus making the silicon nanowires useful in generating microwave and terahertz radiation by frequency multiplication. To verify this hypothesis, silicon nanowires based devices were fabricated and investigated using two experimental setups. The setups were designed to allow the investigation of the nanowire based devices at low frequencies and at high frequencies. Both setups consisted of an RF/microwave source, filters, waveguide, and a spectrum analyzer. They also allowed the characterization of the samples with a semiconductor parameter analyzer. The first step in the investigation of the SiNW devices was to install them in the waveguides and perform Current-Voltage (I-V) sweeps using the semiconductor parameter analyzer. The devices that exhibited the non-linear I-V characteristics typical of diodes were further investigated by first exposing them to 70MHz and 500MHz frequencies in the low frequency setup and then to 50GHz microwaves in the high frequency setup. The response of the devices was captured with a spectrum analyzer. The results demonstrate that the non-linear effect of frequency multiplication is present in nanowire devices from DC to 100GHz. The HF setup provides a platform that with an appropriate detector can be used to detect harmonics of the SiNWs in sub-millimeter/THz region of the electromagnetic spectrum.

<p> In light of their escalating exposure to possible environmental toxicants, there are many biological systems that need to be evaluated in a resource and time efficient manner. Understanding how toxicants behave in relation to their physicochemical properties and within complex biological media is especially important toward developing a stronger scientific foundation of these systems so that adequate regulatory decisions may be made. While there are many emerging methods available for the detection and characterization of these chemicals, nanotechnology has presented itself as a promising alternative toward creating more efficient assays. In particular, metallic nanoparticles and thin films exhibit unique optical properties that allow for highly sensitive and multiplexed studies to be performed. These plasmonic materials often preclude the use of molecular tags and labels, enabling direct characterizations and enhancing the throughput of biomolecular studies. However, their lack of specificity toward certain targets and potential toxicity has thus far precluded their widespread use in toxicity testing.</p><p> The cell membrane, a natural signal transducer, represents one of the fundamental structures for biological recognition and communication. These interfaces principally function as a selective barrier to exogenous materials, including ions, signaling molecules, growth factors, and toxins; therefore, understanding interactions at membrane interfaces is a vital step in elucidating how biological responses are effected. Supported lipid bilayers, which may easily be tailored in composition and complexity, are ideal interfaces for coupling to plasmonic assays since they may be supported in close proximity to metallic nanoparticles and thin films, where measurements are most sensitive. This research will focus on the coupling of plasmonic materials and biomimetic interfaces to increase the sensitivity, efficiency, and throughput of conventional toxicity assays. The fabrication of new plasmonic materials for membrane-based assays is presented, as well as method developments in membrane array formation and opportunities for hyphenation with complementary analytical techniques. </p><p>

<p> Ferromagnetic nanostructures are under considerable interest for producing larger capacity magnetic storage devices. Denser magnetic storage leads to finer magnetic grains and smaller bit size, however, as bit size shrinks it approaches a limit, such that, a single magnetic grain is only capable of holding a single bit of information. Therefore, changes in nanoscale morphology can produce different magnetic properties, so characterizing nanostructures is crucial. Atomic force microscopy (AFM) is a common way to model the morphology of ferromagnetic thin films atop of nanosphere templates. In our research, we used AFM images of polystyrene nanospheres on top of silicon substrates to define the morphology of the AFM tip geometry. We calculated &thetas;L to be approximately 4.30 &plusmn; 1.07&deg;, &thetas;R to be approximately 21.14 &plusmn; 0.33&deg;, the tip apex radius r to be 37.87 &plusmn; 2.43 nm, and a total angle of 25.44&deg; with an error of 15.2% from manufacture specifications. After analyzing the same sample scanned at 4 different angles, 0&deg;, 45&deg;, 90&deg;, and 135&deg;, relative to the cantilever, we determined the optimal scan direction for our samples was 0&deg; relative to the cantilever, due to the geometry of the AFM tip. After scanning several samples containing 600 nm nanospheres with 20 nm and 40 nm of Permalloy thin film deposited on top, the AFM images were obtained. Further research is needed, such as, modification of the geometrical relationship between the tip and the layers atop of the nanospheres to clearly model the structure of Py atop of nanospheres.</p><p>

<p> Our need to reduce global energy use is well known and without question, not just from an economic standpoint but also to decrease human impact on climate change. Emerging advances in this area result from the ability to tailor-make materials and energy-saving devices using solution&ndash;phase chemistry and deposition techniques. Colloidally synthesized nanocrystals, with their tunable size, shape, and composition, and unusual optical and electronic properties, are leading candidates in these efforts. Because of recent advances in colloidal chemistries, the inventory of monodisperse nanocrystals has expanded to now include metals, semiconductors, magnetic materials, and dielectric materials. For a variety of applications, an active layer composed of a thin film of randomly close-packed nanocrystals is not ideal for optimized device performance; here, the ability to arrange these nano building units into mesoporous (2 nm &lt; d &lt; 50 nm) architectures is highly desirable. Given this, the goal of the work in this dissertation is to determine and understand the design rules that govern the interactions between ligand-stripped nanocrystals and polymeric materials, leading to their hierarchical assembly into colloidal nanocrystal frameworks. I also include the development of quantitative, and novel, characterization techniques, and the application of such frameworks in energy efficiency devices such as electrochromic windows.</p><p> Understanding the local environment of nanocrystal surfaces and their interaction with surrounding media is vital to their controlled assembly into higher-order structures. Though work has continued in this field for over a decade, researchers have yet to provide a simple and straightforward procedure to scale across nanoscale material systems and applications allowing for synthetic and structural tunability and quantitative characterization. In this dissertation, I have synthesized a new class of amphiphilic block copolymer architecture-directing agents based upon poly(dimethylacrylamide)-b-poly( styrene) (PDMA-b-PS), which are strategically designed to enhance the interaction between the hydrophilic PDMA block and ligand-stripped nanocrystals. As a result, stable assemblies are produced which, following solution deposition and removal of the block copolymer template, renders a mesoporous framework. Leveraging the use of this sacrificial block copolymer allows for the formation of highly tunable structures, where control over multiple length scales (e.g., pore size, film thickness) is achieved through the judicious selection of the two building blocks. I also combine X-ray scattering, electron imaging, and image analysis as novel quantitative analysis techniques for the physical characterization of the frameworks. </p><p> Last, I demonstrate the applicability of these porous frameworks as platforms for chemical transformation and energy efficiency devices. Examining the active layer in an electrochromic window, I show a direct comparison between, and improved performance for, devices built from both randomly close-packed nanocrystals and those arranged in mesoporous framework architectures. I show that the framework also serves as a scaffold for in-filling with a second active material, rendering a dual&ndash;mode electrochromic device. These results imply that there may exist a broad application space for these techniques in the development of ordered composite architectures.</p><p>

Microphase separated block copolymers (BCPs) are emerging as promising templates and scaffolds for the fabrication of nanostructured materials. To achieve the desired nanostructures, it is necessary to establish convenient approaches to control the morphology of BCPs. It remains challenging to induce morphological transitions of BCPs via external fields. Click chemistry, especially alkyne/azide click chemistry, has been widely used to synthesize novel functionalized materials. Here, we demonstrate that alkyne/azide click chemistry can be used as an efficient approach to chemically modify BCPs and therefore induce morphological transitions. Alkyne-functionalized diblock copolymers (di-BCPs) poly(ethylene oxide)- block-poly(n-butyl methacrylate-random-propargyl methacrylate) (PEO-b-P(nBMA-r-PgMA)) have been successfully synthesized. When the di-BCP is blended with an azide additive Rhodamine B azide and annealed at elevated temperatures, click reaction occurs between the two components. With the Rhodamine B structure attached to the polymer backbone, the di-BCP shows dramatic change in the interactions between the two blocks and the volume fraction of each block. As a result, morphological transitions, such as disorder-to-order transitions (DOTs) and order-to-order transitions (OOTs), are observed. The reaction kinetics and morphology evolution during the click chemistry induced DOTs have been investigated by in-situ and ex-situ characterizations, and fast kinetics properties are observed. Microphase separated morphologies after the DOTs or OOTs are dictated by the composition of neat di-BCPs and the mole ratio between the alkyne and azide groups. The DOTs of PEO-b-P(nBMA-r-PgMA) di-BCPs induced by alkyne/azide click chemistry have also been achieved in thin film geometries, with comparable kinetics to bulk samples. The orientation of the microdomains is dependent on the grafting density of Rhodamine B structure as well as film thickness. At higher grafting densities, a perpendicular orientation of the microdomains can be obtained. For di-BCPs with certain compositions, the microphase separated morphologies in thin films deviate from the corresponding bulk morphologies, which is probably due to the interfacial interactions and confined geometries arising from film thickness.

Magnetic mesoscopic and nano-sized structures have promising applications such as high-density data storage, magnetic field sensors, and microwave devices. Patterned magnetic structures are especially interesting because their constitutive material, sizes and geometry are easily adjustable in fabrication. This makes manipulation of electromagnetic properties possible and creates many novel features never discovered in conventional bulk materials. The artificial magnetic structures that can be engineered to meet specific application purposes are called magnetic metamaterials. This thesis aims to investigate magnetic materials nanostructured to produce high permeability and low loss performance at gigahertz (GHz) frequency region. Such property is highly desired for communication devices with miniaturized size, reduced energy consumption and enhanced signal detection sensitivity. Antennas, microwave field sensors are the examples of applications. We first analyze the single domain model for ac magnetization to get theoretical understanding and prediction. Then we evaluate all free energy terms for a magnetic dipole to know which energies (or fields) are contributing to the effective magnetic field in our real experiments. Secondly experiment work including fabrication, dc characterization and ac characterization of Permalloy and cobalt nanoscale magnetic structures, as well as FePt nanoparticles are covered. Different microwave techniques regarding sensitive magnetic permeability measurements are discussed in detail for comparison. In the last chapter, micromagnetic simulations are performed to obtain broadband ac magnetization response spectrum for a single Permalloy nanowire and two interacting Permalloy nanowires.

Self-assembly of nanoparticles presents an excellent tool in the development of novel nanoscale structures and materials for creating high sensitive sensors, electronic and diagnostic devices, ultrahigh-density magnetic storage devices and many more. In these systems, the nanoparticle core imparts exceptional physical properties while their organic coatings regulate the assembly process. Moreover, organic coatings improve particle stability and solubility, as well as regulate charge and hydrophobicity. This thesis has focused on the engineering of nanoparticles’ surfaces using organic molecules and assembly of these particles through supramolecular interactions for various applications. Morphology of the nanoparticle assembly was tuned simply by varying the degree of fluorinated coating on particles’ surfaces and thus controlling their hydrophobicity. Surface engineered particles were also assembled at oil-water interfaces alone and with enzymes creating colloidal microcapsules for controlled release and catalysis respectively. The combination of the unique attributes of the nanoparticle cores and the function of the organic coating provides ample opportunities in the creation of multi-functional nano-materials that are useful in biological and materials applications.

Nanoparticles as novel materials have unique properties due to their incredibly small sizes. Ensembles of nanoparticles not only collect their intrinsic properties but also generate new ones when nanoparticles are sufficiently close. One important way of forming nanostructures entails the assembly of nanoparticle monolayers at liquid interfaces. It is important to understand how the iron oxide nanoparticles transport in a liquid phase and on a liquid/liquid interface and self-assemble into nanostructures over time. As a preliminary research topic before the comprehensive small angle X-ray scattering (SAXS) study, real-time optical reflection of incident p-polarized light near Brewster’s angle shows that after drop-casting iron oxide nanoparticle heptane dispersion on top of a diethylene glycol (DEG) liquid substrate, an iron oxide nanoparticle layer forms at the DEG/heptane interface, and it self-limits to one monolayer even when there are excess nanoparticles dispersed in the upper heptane phase. As is needed for the high time resolution and X-ray exposure minimization requirements of kinetics studies, a new cell with walls at angles is designed to significantly reduce the size of the meniscus, which enables the collection of much larger signals in the SAXS images of ordered arrays of nanoparticles at liquid/air interfaces, along with the observation of extremely high degrees of order. Spatial and temporal SAXS scans show that 8.6 and 11.8 nm iron oxide nanoparticles in heptane drop-cast on top of a heptane layer atop a DEG layer are trapped at the DEG/heptane interface to generally form a single ordered, hexagonally close-packed monolayer, and this occurs long before the heptane evaporates. The morphology of the monolayer is independent of the number of nanoparticles used in the formation process. Many nanoparticles remain dispersed in the heptane after this nanoparticle assembly. Assembly occurs faster than expected from considering only the diffusion of nanoparticles from the drop-cast site to this liquid/liquid interface. And, on the same time scale there is a concomitant decrease in the SAXS form factor from disordered nanoparticles. X-ray beam transmission at different vertical heights characterizes the heptane and DEG bulk and interfacial regions, while monitoring the time dependence of SAXS at and near the DEG/heptane interface gives a clear picture of the evolution of nanoparticle assembly at this liquid/liquid interface. These SAXS observations of self-limited nanoparticle monolayer formation at the DEG/heptane interface are consistent with those using the less direct method of real-time optical reflection monitoring of that interface.