Nanoantennas for visible and infrared radiation

Nanoantennas for visible and infrared radiation can strongly enhance the interaction of light with nanoscale matter by their ability to efficiently link propagating and spatially localized optical fields. This ability unlocks an enormous potential for applications ranging from nanoscale optical microscopy and spectroscopy over solar energy conversion, integrated optical nanocircuitry, opto-electronics and density-ofstates engineering to ultra-sensing as well as enhancement of optical nonlinearities. Here we review the current understanding of optical antennas based on the background of both well-developed radiowave antenna engineering and the emerging field of plasmonics. In particular, we address the plasmonic behavior that emerges due to the very high optical frequencies involved and the limitations in the choice of antenna materials and geometrical parameters imposed by nanofabrication. Finally, we give a brief account of the current status of the field and the major established and emerging lines of investigation in this vivid area of research.Comment: Review article with 76 pages, 21 figure

Synthesis and Characterization of Functional One Dimensional Nanostructures

One- dimensional (1D) nanostructures have received growing interest due to their unique physical and chemical properties and promising nanodevice applications, as compared with their bulk counterparts. Complex 1D nanostructures with tunable properties and functionalities have been successfully fabricated and characterized in this thesis. I will show our recent efforts on precise controlled 1D nanostructures by template- assisted electrochemical synthesis as well as fundamental understanding of their physical behavior and growth mechanism of as-synthesized nanostructures. Particularly, three topics are presented: Firstly, a constant current (CC) based anodization technique is newly demonstrated to fabricate and control the structure of an anodic aluminum oxide (AAO) template. This technique has enabled the formation of long- range self- ordered hexagonal nanopore patterns with broad range of tunability of interpore distance (Dint). In addition, the combination of CC based anodization and conventional CV anodization can offer a fast, simple, and flexible methodology to achieve new degrees of freedom for engineering planar nanopore structures. This work also facilitates our understanding of the self- ordering mechanism of alumina membranes and complex nanoporous structure. Secondly, functional 1D nanostructures including pure metallic, magnetic and semiconducting nanowires and their heterostructure are demonstrated by versatile template- based electrochemical deposition under feasible control. This study has enabled the creation of high quality and well- controlled 1D nanostructures that can be applied as a model system for understanding unique 1D physics. Some preliminary investigations including exciton confinement, anisotropic magnetism and surface plasmon resonance are also presented. Lastly, a novel and universal non-epitaxial growth of metal-semiconductor core-shell lattice-mismatched hybrid heterostructures is presented. Importantly, a new mechanical stress driven crystalline growth mechanism is developed to account for non-epitaxial shape and monocrystalline evolution kinetics

Copolymer template control of gold nanoparticle synthesis via thermal annealing

We present here an original process combining top-down and bottom-up approaches by annealing a thin gold film evaporated onto a hole template made by etching a PS-PMMA copolymer film. Such process allows a better control of the gold nanoparticle size distribution which provides a sharper localized surface plasmon resonance. This makes such route appealing for sensing applications since the figure of merit of the Au nanoparticles obtained after thermal evaporation is more than doubled. Such process could besides allow tuning the localized surface plasmon resonance by using copolymer with various molecular weights and thus be attractive for surface enhanced raman spectroscopy

EXPLORING THE STRUCTURE AND PROPERTIES OF NANOMATERIALS USING ADVANCED ELECTRON MICROSCOPY TECHNIQUES

Nowadays people are relying on all kinds of electronic devices in their daily life. All these devices are getting smaller and lighter with longer battery life due to the improvement of nanotechnology and materials sciences. Electron microscopy (EM) plays a vital role in the evolution of materials characterization which shapes the technology in today’s life. In electron microscopy, electron beam is used as the illumination source instead of visible light used in traditional optical microscopy, the wavelength of an electron is about 105 times shorter than visible light. By taking this advantage, the resolving power and magnification are greatly improved which gives us the ability to understand the morphology and the structure of smaller materials. Besides high resolution and high magnifications, the electron-matter interactions in electron microscopy are also very interesting and provide useful information. Typically, there are three types of post electron-matter interaction electrons, and they are: secondary electrons, backscattered electrons and transmitted electrons. Different signals are carried out with these electron-matter interactions, the most common techniques including electron dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS) and selected area electron diffraction (SAED). In this dissertation, I will discuss how electron microscopy techniques approach complicated nanostructures, such as MnSb2Se4 nanorods to reveal the composition, structure, surfactant controlled size, and relative magnetic properties. Other important features such as mapping localized surface plasmon resonance (LSPR) using EELS and newly developed liquid cell scanning mode transmission electron microscopy (STEM) in situ observation are also presented

On the role of 4-methoxypyridine in the electrochemical formation of plasmonic gold nanoparticles

This thesis details an electrochemical approach to generate homogenous and densely populated films of anisotropic gold nanoparticles. The electrochemistry of coinage metals in the presence of the ligand 4-methoxypyridine (MOP) is described in detail and the role of the ligand in the formation of nanoparticle films on conductive substrates is discussed. The thesis demonstrates application of Stopped-flow UV-Vis spectroscopy to evaluate and study the kinetics of the homogenous chemistry of MOP with the gold salt precursor. It discusses the role of Au(I) ions, and the different species involved in the complex Au-MOP system by thermodynamic and kinetic analysis. The thesis illustrates the excellent suitability of these nanoparticle films for surface-enhanced Raman scattering (SERS) applications utilizing near-IR excitation sources. The chronoamperometric study described in the thesis demonstrates the nucleation and growth mechanism of the electrodeposited gold nanostructures. Overall, the work described in this thesis outlines the advancement of electrochemical platforms that pertains to the potential applications of anisotropic gold nanostructures by tuning the shapes and size of the nanostructures