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.

PublishedNanoLetters, 2014

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Published in Publication Highlights
Tuesday, 03 February 2015 19:42

Dual probe NSOM on plasmonic metasurfaces

 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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Published in Publication Highlights
Tuesday, 03 February 2015 19:41

Multiprobe Nanoindentation

Novel Approach to Nanoindentation Using a Multiprobe System

Authors Eyup Cinar and Ferat Sahin  describe a unique approach to nanoindentation that utilizes a MultiView 4000 multiprobe setup with tuning fork technology to conduct AFM-based nanoindentation with power advantages for measurements on soft and compliant materials.  Their method relies on tuning fork actuation and a frequency-based feedback (instead of the classical amplitude based feedback), which enables a very precise measurement of tip-sample interactions that avoids instabilities such as adhesion ringing and jump to contact that plague conventional measurements.

In this novel and exciting method, a dual-probe setup (schematic shown below followed by actual setup) is implemented where one probe is a diamond-tipped indentation probe while the second AFM probe measures the displacement of the indentation probe.  The tuning fork actuation controls the motion of the diamond-tip probe, thereby bring unprecedented stability to this measurement.

                                                

The authors demonstrate initial results showing proof-of-concept of this approach to nanoindentation with indents on a silicon sample where the stage positions of the 2 probes is successfully monitored and force vs. displacement curves are collected as shown below.  They further simulate their results with finite element analysis that shows good agreement from the simulated level of force and experimentally obtained force for a given penetration depth.  These preliminary results demonstrate the exciting potential of this approach to nanoindentation, and further experiments are already underway to try this method on a variety of samples.  

Published:  IEEE Nano, Sahin and Cinar 2014

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Published in Publication Highlights

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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Published in Publication Highlights
Page 2 of 2

 

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