A “point” SPPs source is generated first by an NSOM probe and then a second NSOM probe detects interference patterns

 SPP Interference with MV4000 Two Probe System

The study of Surface Plasmon Polariton (SPP) interference and propagation is increasingly recognized as a very effective way to concentrate and guide light in nanometric domains. A team in the University of Science and Technology of China  demonstrated a unique approach for recording SPP interference from a "point" source on a plasmonic structure utilizing the Nanonics MultiView 4000^TM MultiProbe Scanning Probe Microscope (SPM) system.

MultiView 4000 Two Probe system setup has been used for NSOM excitation of  SPPs with a point source of a 100nm and for NSOM collection of the interference patterns with a second NSOM probe with 100nm aperture.	NSOM images of the SPPs distribution on the sample with excitation position at b, c, d,  and e along the red line shown in a. d shows the numerical calculation

The researchers used two cantilevered 100nm aperture NSOM probes with the MultiView 4000 in order to test the relation between the visibility of interference patterns and the size of the point source. They observed the SPPs interference phenomenon of a ring structure with different point source sizes by using one probe as a point source for near-field excitation of SPPs and the other for near-field collection of the interference patterns

 The patterns were generated through the interference of the propagated and reflected SPPs to and from the ring walls. The intensity distribution of SPPs was measured in tip scanning mode with the sample and the illumination source kept stationary during the measurement.

Published: Appl. Phys. Lett. 98, 201113 (2011)

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Surface plasmons excitation with STM probe and collection with apertured & apertureless NSOM photon tunneling probes

MV4000 Dual Probe function provides a flexible platform for simultanous STM and NSOM functionality. Such platform is ideal for surface plasmons (SP) excitation with an STM probe and effective imaging of the SP both in aperture NSOM and apertureless via photon tunneling process. 
The following scheme describes the dual probe setup for excitation of surface plasmons on 35nm gold coated surface. The second probe is an NSOM probe use for localized AFM/NSOM imaging of the generated surface plasmons at nanometric close proximity from the STM excitation probe.  

Left: Dual probe Setup for SPP excitation with STM probe and near-field imaging with a second NSOM probe. The multiprobe setup allows for clear optical access from above and below without any obscuration. Right: An optical microscope image from above shows dual probe STM/NSOM in during operation. Cantilevered bent probes allows for clear optical access and for multiprobe operation at close proximity. 

AFM NSOM Imaging of Surface Plasmons excited with STM Probe 

Simultaneous AFM-NSOM imaging of surface plasmons with an apertured NSOM probe. The cantilever NSOM and STM probes geometry enables bringing the NSOM probe to a close proximity from the excitation STM probe and thus allows mapping of the SP the poitn where they are generated.  In addition, the MV 4000 system incorporates sample scanning and tip scanning piezo stages and thus allows for flexible an accurate positioning of both probes until achieving "soft contact" between the probes. Such a procedure of two probe distance adjustment is performed while the two probes arekep in feedback with the sample and thus allows for safe probe manipulation

The image below shows the results of the above protocols obtained by the NSOM probes in probe scanning mode.

Ultra Sensitive Tuning Fork for AFM/STM Feedback

MV4000 multiprobe system uses ultrasensitive Tuning Fork feedback which is ideal for such combined AFM and STM feedback. The tuning fork high force sensitivity and lack of jump-to-contact allows for defined tip-sample interaction down to close proximity from the sample (<1nm) without any force discontinuity (which does occur in optical feedback AFM techniques, during to jump-to-contact and ringing adhesion effects). Such distance stability permits obtaining simultaneous AFM and Tunneling

Unique AFM-STM probes

Nanonics uniquely provides probes which are able to scan with either AFM or STM feedback using the same probe with easy switching between modes

Single and multiple atomic steps imaging with AFM and STM feedback. Line profiles of HOPG steps with AFM feedback (middle) and STM feedback (Right) performed with the same probe.

Nanonics MultiView AFM/STM system has been used for obtaining Work Function information on Q-Dot using Tunneling Feedback.  

Published:  Nano Lett. 2013, 13, 2338−2345

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One of the most powerful applications of multiprobe instrumentation for near field optical measurements is the novel capability for pump/probe experiments.  In NSOM pump/probe experiments, an optically active system is excited in the near-field (or pumped), and then mapped (or probed/detected) in the optical near fieldsimultaneously.  These optical pump-probe measurements enable the measurement of optical properties of nanostructures with the most accuracy and highest resolution.

However, now that there are two near field optical signals to measure, the complexity of interpreting these dual near-field type measurements is higher. Authors Angela Klein et al. of Institute of Applied Physics in Jena [Nano Letters, 2014]shed light specifically on exploring the polarization characteristics of the excited and detected light in dual-probe NSOM experiments using a Multiview 4000 system.  They find that the cantilever fiber probes, which are the conventional geometries of probes used in NSOM measurements, can both emit polarized light and function as polarization sensitive detectors.  Specifically, they make measurements on surface plasmon polaritons and find dipole-like SPP emission from the tips.

They conduct direct near field measurements  of dipole-like Surface Plasmon Polaritons (SPP) emission from a cantilevered aperture NSOM probe.  They study the polarization characteristics of Nanonics cantilevered single mode (SM) and multimode (MM) aperture NSOM probes in far-field and near-field.

A cantilevered SM NSOM probe with a high polarization factor was used for excitation while a MM cantilevered NSOM probe was used for collection. The experiment was done on a gold coated substrate.

This paper demonstrates that a cantilevered NSOM probe not only acts as SPP dipole, but can also be used as a polarization sensitive near–field detector.

In Brief: The MultiView 4000 Nanonics MultiProbe NSOM is the only tool that can allow for such kinds of experiments.  This microscope also assesses and confirms the polarization characteristics of cantilevered NSOM probes which leads to a better understanding of NSOM measurements.

Published: NanoLetters, 2014

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 Authors J.S. Clausen and colleagues, from the University of Denmark, report on a novel way to implement structural colors into plastic products for daily consumer use.  Structural colors offer some significant advantages over current pigment-based coloring by reducing the materials needed and new opportunities for recycling and sustainability.  The authors create structural colors here from metal disks on top of dielectric pillars that are hovering above a holey metal film composed of aluminum. They then use the dispersion of the surface plasmon polaritons (SPPs) supported by the metal-dielectric interface of the holey film to generate the colors; a schematic of the structure is shown below where the final protective coating is then added to minimize environmental contamination.  By using aluminum (instead of gold or silver), the SPPs supported by aluminum to improve the angle independence in the color observation, as well as other improvements.  The authors use a dual probe Multiview 4000 to characterize the SPP modes with excitation probe with a 100nm aperture diameter held fixed and a detection probe with a 200nm aperture diameter scanned away from the excitation.

Published:  Nano Letters 2014, 14, 4499-4504

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Near Field Scanning Microscopy has great potential in the study and characterization of 3D and 2D plasmonic metamaterials and metasurfaces.   In this paper, a Nanonics MultiView 4000 Dual probe Near-field Scanning Optical Microscope was used to investigate two phenomena in plasmonic metasurfaces (subwavelength antenna like pattern in ultrathin silver film) showing:

1. Extraordinary suppressed transmission ( EOST) in metasurfaces

2. Bright (radiative) and dark (non-radiative) plasmonic modes propagation in metasurfaces

The Nanonics MultiView 4000 Scanning Probe Microscope is ideally suited for complete characterization of the dark mode propagation.  One NSOM probe injects the light to excite the dark (non-radiative) modes, while the second NSOM probe scans in the vicinity of the illumination probe, and detects the dark modes distribution.

The NSOM results obtained demonstrate that far-field radiation resonantly excites antenna-like (bright) modes that are localized on the metal ridges. The re-radiation of these modes into far-field interferes destructively with the transmitted wave, thus almost completely suppressing transmission.  In contrast, a second type of mode, (dark) bound mode Surface Plasmon Polarities (SPPs) launched from the NSOM tip, propagate well across the metasurface, preferentially perpendicular to the grating lines.

Idea in Brief: It was shown that dark modes cannot be excited in the far-field, and instead NSOM tips are the best source for excitation and probing of the non-radiative modes, which do not interact with the far-field.  

Published:  Advanced Optical Materials, 2014, S. Dobmann et al.

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