Characterization and fabrication of fully metal‐coated scanning near‐field optical microscopy SiO₂ tips

Abstract

SummaryThe fabrication of silicon cantilever-based scanning near-field optical microscope probes with fully aluminium-coated quartz tips was optimized to increase production yield. Different cantilever designs for dynamic-and contact-mode force feedback were implemented. Light transmission through the tips was investigated experimentally in terms of the metal coating and the tip cone-angle. We found that transmittance varies with the skin depth of the metal coating and is inverse to the cone angle, meaning that slender tips showed higher transmission. Near-field optical images of individual fluorescing molecules showed a resolution < 100 nm. Scanning electron microscopy images of tips before and after scanning near-field optical microscope imaging, and transmission electron microscopy analysis of tips before and after illumination, together with measurements performed with a miniaturized thermocouple showed no evidence of mechanical defect or orifice formation by thermal effects.

A virtual optical probe based on localized Surface Plasmon Polaritons

“…For example, it is possible to obtain a localized field by tightly focusing higher-order Hermite-Gaussian beams on metal tips, which can be employed as nano-sources [1]. Another possibility is to use metal-coated tapered monomode optical fibers having a subwavelength hole at the apex [2] or microfabricated fully metal-coated probes [3]. Some investigations based on numerical calculations (see, for example, Ref.…”

Propagation of the electromagnetic field in fully coated near-field optical probes

“…Transmission electron microscopy reveals a 60-nm-thick polycrystalline iridium layer, that completely covers the quartz tip. 6 Iridium coated cantilever probes present interesting mechanical and optical features: the hardness of the material guarantees high mechanical damage threshold, potentially increasing the lifetime of the probes. Optically, this metal has also a satisfying behavior.…”

Analysis of mode coupling due to spherical defects in ideal fully metal-coated scanning near-field optical microscopy probes

“…2 To better understand the operating characteristics of this class of probes, a considerable amount of work has been performed to optimize their fabrication, as well as to experimentally measure their performance characteristics. [3][4][5][6][7][8] In particular, the properties of the metal coating 9,10 and the polarization state of the light transiting the probe [11][12][13] have been found to play an important role in the optical properties and performance capabilities of the probe. However, as fabricating and testing large numbers of probes with varying configurations is presently impractical, rigorous electromagnetic modeling of such probes has proven to be a useful complement to experimental work in gaining insight into the propagation of light inside and near such probes.…”

“…We focus on defects in the metal layer as they most closely correspond to the observed characteristics of real manufactured probes. 2,6 Because of restrictions based on an unambiguous interpretation of results as well as computational load limitations, we focus on studying an ensemble of simple but insightful defect configurations in a simplified model of the probe. Although these simplified models do not accurately reflect the characteristics of real probes in their entirety, they do facilitate understanding the fundamental mechanisms of optical coupling between the polarization modes in the probe.…”