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Nanocoax ( metal- dielectric- metal) structures are potential devices for nanoscale photonics systems such as polarization- preserving optical waveguides for optical communication. It is very important to know the propagating properties of such structure for different excitation wavelengths.

NSOM is the best tool for study of such plasmonic nanodevices since the nSOM measurement is not diffraction-limited, and it provides both topographic and optical data with high resolution.

A Nanonics MV-4000 system was used for the AFM/NSOM measurements. This system enables scanning with probe as well as with the sample. The tip scanning capability is absolutely necessary for the study of objects requiring any form of constant optical alignment. The feedback in this system is based on the tuning fork, hence there no interference between the beam bounce laser and the light propagating through the sample.

The sample with the nanocoax array was specially prepared. The sample was illuminated from the bottom with different light sources: 473 nm, 532 nm, 660nm 850 nm. The light was transmitted through the nanocoax structures, collected via cantilevered NSOM probe (aperture diameter 100 nm), and detected with an avalanche photodiode.

Experimental results together with numerical calculations showed that the propagated modes have a different nature depending on the excitation wavelength, i.e, plasmonic TE11 and TE21 modes in the near infrared and photonic TE31, TE41 and TM11 modes in the visible. Far field transmission out of the nanocoaxes is dominated by the superposition of Fabry-Perot cavity modes resonating in the structures, consistent with theory. 

In summary, propagation of the plasmonic and photonic modes in nanocoax structures was experimentally observed for the first time in this work.

Fig. 1    NSOM-measured (a - d) and calculated (f - i) images of the propagated modes in the nanocoax structure. The wavelengths were 850 nm (a, f), 660 nm (b, g), 532 nm (c, h) and 473 nm (d, i). In all cases, the polarization is in the vertical direction, the scale bars represent 200 nm and circles represent the inner and outer radii of the coax annuli. (e) Three-dimensional representation of the nanocoax topography (lower, via AFM) and the corresponding near-field intensity (upper) for 532 nm wavelength. 

Published:  Optics Express June 16, 2014 Vol 22, No. 12

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This paper demonstrates the detection of whispering–gallery mode (WGM) distribution in a fused silica micro disk resonator with a highly sensitive Nanonics Imaging cantilevered Pt/Au micro thermocouple probe and a Nanonics Imaging MultiView 4000 Scanning Probe Microscope.

Whispering gallery modes were excited by an evanescent tapered fiber with wavelengths in the 1550nm-1560nm range.  The thermocouple probe enabled detection of thermal distribution simultaneously with the topographic data.  As the tip penetrates the evanescence field, the light absorption leads to heating measured by the thermal tip, giving a thermal image of the light intensity distribution.  The thermal distribution was compared with NSOM results on the sample in transmission, reflection and collection modes.

Schematic of the experimental setup for thermal

mapping of  WGM in microdisk resonator

 

 

Thermal map of WGM in microdisk resonator

 

In Brief: This paper elegantly shows that the thermocouple probe has great potential for detection in the near field in visible and near-IR optical ranges and can be used as a tool to study different photonics devices.  

Published:  March 1, 2014/Vol.29, No.5/Optics Letters

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Near-field excitation and near-field detection of propagating surface plasmon polaritons (SPPs) on Au waveguide structures  

MultiProbe Apertured NSOM Plasmonic Charactarization

Near-field excitation and near-field detection of propagating surface plasmon polaritons on Au waveguide structures has been perfomed with Nanonics Multiview 4000 Dual Probe system

 Schematic of the MV4000 experimental setup for near-field excitation and near-field collection of SPP on gold waveguide structure (SEM shown inset)   AFM and NSOM 3D images of the Au Waveguide and the SPP distribution. The arrow shows the position of the illumination probe. The NSOM image shows exponential SPP decay with a propagation length of 550nm

Published: Appl. Phys. Lett. 94, 243118 (2009)

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Tuesday, 03 February 2015 19:55

SPP interference from a point source

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 4000TM 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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Tuesday, 03 February 2015 19:53

Energy transfer in phycocyanin nanowires

Observing energy transfer and wave guiding in phycocyanin nanowires using a MV4000 Two Probe system

Near-field Luminescence Mapping 

Energy transfer via phycocyanin nanowires has been shown by measuring near-field luminescence with a MV4000 two probe system. One NSOM probe has been used for localized excitation (532 nm light, 150 nm diameter aperture) and a second NSOM tip (150nm diameter aperture) has been used simultaneously to map AFM and Luminescence along the nanowire.
The MV4000 allows for accurate placement of the NSOM illumination probe on top of the nanowire and also allows for simultaneous tip-scanning in close proximity to the illumination tip.

Energy transfer measurement with a two probe MV4000 system.  (a) Optical microscope image of Phycocyanin nanowire. This sample was scanned by a two probe NSOM system for measuring energy transfer. Excitation was done by a 532 nm wavelength laser through a 150 nm diameter NSOM tip and detection was done with a multimode fiber with a 250 nm diameter tip. Excitation was done at the green circle in a)and collecting was done within the black frame. When comparing the excitation distribution (b) and the luminescence distribution (c) clear broadening is obtained. (d) Cross-section of these two graphs at y = 9.7 um shows that the luminescence (red) Full-Width-Half-Maximum (FWHM) is wider than the excitation (green) FWHM in more than 2 um

 PublishedPhys. Chem. Chem. Phys., 2014. DOI: 10.1039/c4cp00345d  

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Tuesday, 03 February 2015 19:53

Two probes distance monitoring

Avoiding collisions in a multiprobe setup:  Investigation of mechanical interactions between two tips using a MV4000 Two Probe NSOM microscope 

A method to monitor the distance between two tips of tuning fork-based AFM/NSOM systems is described. The distance monitoring is performed by recording the crosstalk signal which characterizes the interaction strength between the two oscillating tuning forks and tips.

 ( a) Two Probes Schematic setup. (b) and (c) are images of topographic and Crosstalk (respectively) interactions of the two probes with one scanning probe and a second stationary probe. (d) and (e) are line profiles represent topography and crosstalk signal along the dashed line (d). (e) is integrated signal values along the fast scanning axis.  

The measurements are based on aerodynamic and shear force interactions between the tips.  Both interactions increase with decreasing distance between the tips. The shear force interaction is a short-range effect and it is observed within a region of several tens of nanometers. This interaction leads to a sharp increase in the crosstalk signal once the scanning tip comes into the immediate vicinity of the stationary one. This effect is a reliable tool to detect the mechanical interactions between two tips and thus prevent them from colliding during scanning. (Klein et al)

  

Published: Appl. Phys. B. DOI 10.1007/s00340-012-5182-7(2012)

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Tuesday, 03 February 2015 19:52

Multiprobe nanoheating and thermal imaging

Multiprobe setup to heat and probe a nanowire's thermal expansion

A MultiProbe setup is used to heat and then thermally probe a nanowire, revealing the thermal distribution within the wire

  • MV 4000 Dual Probe Nano-Heater using Thermo-couple probes

  • Nanoheater (below, left ) probe was used to locally heat a Nanowire on Nickel pads.

  • Thermocouple probe (below, right) was used for AFM/Thermal scanning of the Nanowire and observe local coldspots in the wire

Upright microscope's top View (100x objective) of the Dual probe setup showing a nanoheating tip (below, left) & nanothermocouple tip (below, right) for AFM-thermal imaging on nanowire

Left: AFM Topographic Image showing the Nanowire on Nickel pads obtained with the scanning thermocouple probe. Middle: Simultanous Thermal image of the same area of the left image. The nanoheater probe was placed on the nanowire  at the lower left side of this scanned area. Right: Thermal image after “Plane Removal” filter showing “cold (blue) NanoWire”. 

See here for a video showing an example of a multiple nanoheating experiment. 

For Information about Thermal Imaging see: http://www.nanonics.co.il/thermal-spreading-resistance-electrical.html

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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.

 

Simultanous AFM Height (Left) and NSOM (Right) images performed with the aperture NSOM probe starting from the STM tip position (placed at a stationary position at the bottom side of the above image)

 

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

Ultrasensitive tuning fork AFM-STM feedback with Normal Force AFM/NSOM cantilevered and exposed probes.

 

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

AFM STM Probe acting in Normal Force with tuning fork feedback

 

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.

PublishedNanoLetters, 2014

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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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