Scanning near-field optical microscopy with aperture probes: Fundamentals and applications

Abstract

In this review we describe fundamentals of scanning near-field optical microscopy with aperture probes. After the discussion of instrumentation and probe fabrication, aspects of light propagation in metal-coated, tapered optical fibers are considered. This includes transmission properties and field distributions in the vicinity of subwavelength apertures. Furthermore, the near-field optical image formation mechanism is analyzed with special emphasis on potential sources of artifacts. To underline the prospects of the technique, selected applications including amplitude and phase contrast imaging, fluorescence imaging, and Raman spectroscopy, as well as near-field optical desorption, are presented. These examples demonstrate that scanning near-field optical microscopy is no longer an exotic method but has matured into a valuable tool.

High-speed atomic force microscopy and its future prospects

“…To obtain a clear correlation, it is probably best to use near-field scanning optical microscopy (NSOM) for the hybrid system. NSOM breaks the diffraction limit of light, and a cantilever (metal-coated) tip can also be used as an aperture or aperture-less probe for NSOM (Hecht et al 2000). The simultaneous, pixel-by-pixel acquisition of the fluorescence and AFM signals at nearly identical sample positions facilitates finding correlations between the two overlaid images.…”

Microfluidic and bio-applications of optical microfibres

“…At the moment, the apex size is limited by the tip transmission efficiency. For tips smaller than 50nm, T ε <10 -6 have been recorded [7]. A way to increase T ε by orders of magnitude relies on the exploitation of surface plasmons: by converting light into surface plasmons and then back into light, confinements to spot sizes smaller than 10nm should be possible [28], with extraordinary benefits for the sensor size.…”

“…This limitation has been overcome by using coated tapers (generally with Al), which exploit the evanescent field along the longitudinal direction. In metal coated tapers [7], when r is smaller than ~λ/6, an evanescent field exists in the longitudinal direction of decreasing sections; this has been exploited to produce highly divergent light beams over extremely small apertures at the tip apex. Although this technique provided ω<100nm, the device transmission efficiency T ε was poor; indeed the field of the fundamental mode decays exponentially along the longitudinal direction: for a 20nm aperture, T ε~1 0 -8 [7].…”

Antenna-Based Optical Imaging of Single Ca2+ Transmembrane Proteins in Liquids

“…[20][21][22] However, so far, all of the reported biological applications in liquid environments are exclusively based on the use of circular aperture probes. The limitations of aperture probes (low transmission, low reproducibility, large physical size) 23 restrict the achievable optical resolution as well as the ability to simultaneously measure the membrane topology. To overcome these barriers, so-called "tip-enhanced near-fieldopticalmicroscopy"(TENOM)hasbeenintroduced.…”