Metallic nanostructures are attracting growing interest because of their potential application in various devices such as batteries, solar cells, or drug delivery systems. This thesis focuses on the synthesis and characterization of three different nanostructures: (1) solid cylindrical AuAg nanowires with controlled composition and size, fabricated by electrodeposition in etched ion-track membranes with cylindrical channels, (2) porous cylindrical Au nanowires attained by selective dealloy-ing of AuAg nanowires, and (3) Au nanocones synthesized by electrodeposition in conical channels.
AuAg nanowires with controlled diameter and composition, namely Au, Au40Ag60, Au60Ag40, and Ag were synthesized and characterized. By dealloying these nanowires were converted into porous Au-based nanowires with diameters above and below 100 nm possessing an enhanced surface area. Surface morphology and com-position of the nanostructures before and after dealloying were studied by means of high spatial resolution energy-dispersive X-ray spectroscopy (EDX) in a high-resolution transmission electron microscope (TEM). The results demonstrate surface segregation effects in solid AuAg nanowires that strongly vary with the initial composition. Surface segregation occurs on a time scale of days (< 3 days) inde-pendently of the wire dimensions. After dealloying of Au40Ag60 nanowires, the porous nanowires have a silver content below 10% and ligament size from 5 to 30 nm. Solid and porous wires are particularly attractive for future applications, e.g., in sensorics. The characterization of such small nanostructures regarding, e.g. electrical transport properties, requires suitable contacts. Special designs to contact nanowires by laser lithography as well as by using pre-patterned templates were developed.
Gold nanocones with sharp tips down to 50 nm diameter and several microns large bases were fabricated. Given by this special geometry, the nanostructures exhibit a high mechanical stability and are freestanding with an aspect ratio of 500 and above. Stable gold nanocone arrays are attractive for a large range of applications including field emission and as coating for hydrophobic surfaces. In this work, the standard wire deposition process from base to tip was inverted in order to improve the electrical and thermal contact of the nanocones to the substrate. After selective removal of the template, 30 µm long gold nanocones with ~ 50 nm sharp tips were freestanding and vertically aligned. Such structures are highly tunable in terms of cone dimensions and number density. The field emission properties of patterned nanocone arrays, investigated in collaboration with the Bergische Universität Wuppertal, exhibit field enhancement factors between 200 and 1000 as well as a maximum emission current ranging from ~ 1 to 100 μA.
The results presented in this thesis emphasize the variety of possibilities that ion-track technology offers in order to tailor dimensions and characteristics of nanostructures
