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Wednesday, 16 April 2014 12:53

MultiProbe NanoHeating and Thermal Imaging

 

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

Tuesday, 15 April 2014 10:56

Two Probes Distance Monitoring

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

Thursday, 10 April 2014 09:23

Energy Transfer in Phycocyanin Nanowires

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

Unique apertured and apertureless NSOM protocols with low background

Tuesday, 08 April 2014 11:44

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

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

Thursday, 03 April 2014 02:02

Glossary of AFM-Raman-TERS Terminology

 

AFM-Raman-TERS

Glossary of Key Terminology

 

AFM Raman
Co-located confocal Raman microscope with an AFM tip enabling simultaneous acquisition of AFM and Raman spectroscopy images from the same location on the surface.
AFM Raman TERS
Collective name for high resolution Raman measurements including Raman confocal microscope integrated with SPM microscope and metalized TERS probe.
Graphene TERS
TERS has been successful in measuring the spectral characteristics of graphene with very high spatial resolution.
SERS
Surface enhanced Raman scattering (SERS).  A well-known Raman enhancing effect where a roughened metal surface can provide orders of magnitude increase in Raman signal intensity.
Conventional TERS probes
Typically Au or Ag metalized AFM probes or STM probes.
Strained Silicon TERS
ERS measurements on strained silicon substrate for TERS probes characterization in terms of the enhancement efficiency.
TERS AFM
Same as AFM Raman TERS
TERS
Tip enhanced Raman scattering (see TERS effect)
TERS Effect
enhancement of the Raman signal using the metalized AFM tip as the source for enhancement. By using such a small dia
meter tip, enhancement occurs only in the immediate vicinity of the tip providing a high spatial resolution for the Raman measurement.  TERS provides significant improvement in resolution over conventional AFM-Raman methods.
TERS Microscope
A microscope fitted with TERS equipment, including a lens (optical microscope), AFM head, TERS probes, Raman spectrometer, and CCD camera.
TERS Probes
Specialized probes suitable for AFM/TERS measurements.  A gold or silver ball at a variety of diameters is embedded at the end of a glass cantilevered probe to generate the enhancement of the Raman signal near the probe

Nanonics probes are extended and transparent allowing for all modes of TERS operation: Reflection, transmission and side illumination.

TERS Raman
As TERS stands for “Tip-Enhanced Raman Spectroscopy”, this term is redundant on its own, but used by searchers to specify this particular meaning of the term “TERS”.- It is the same as “TERS” or “TERS effect”
TERS Tips
same as TERS probes.
Reflection TERS
TERS measurements on opaque sample, when the SPM integrated with upright confocal Raman microscope. 
Transmission TERS
TERS measurements on transparent or half transparent  samples, when the SPM integrated with inverted confocal Raman microscope. 
Side illumination TERS
TERS measurements on opaque sample, when the SPM integrated with upright confocal Raman microscope, when the laser for Raman excitation  illuminates the sample by the 45˚-60˚ relatively to the axis of the TERS probe.    
 

 

 

Raman measurements are also possible in liquids, but they require the specialized liquid immersion objectives available on our systems.  Below is a Raman image of a Si/SiO2 grid immersed in liquid collected at 532nm.  The image on the right was collected using a 50x objective with an NA of 0.45, a typical optical objective used in an air environment.  The periodic grid features are poorly resolved.  On the left, the same grid was imaged with the water immersion optical objective clearly showing the grid features with excellent resolution.

 

Below is a short 15 minute video explaining the basics of AFM technology and feedback mechanisms:

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Nanonics held a very successful workshop with our expert customers giving excellent talks.  The talks, including the plenary lecture by Prof. Federico Capasso of Harvard, are now posted online on the Nanonics Youtube Channel or see individual links to the various talks here.
 

 

 

Thursday, 27 March 2014 21:44

Barak Raman system

MicroRaman system with excellent performance, total flexibility

Laser Focus World has highlighted a recent paper showing how multi-frequency NSOM maps optical forces without a photodetector.  This groundbreaking research was conducted by researchers at University of Central Florida and CNRS in Paris with a Nanonics Multiview system and was able to map optical forces using a tuning fork architecture without a photodetector.  This paper was published in Nanotechnology, 2014 (vol 25, p. 035203) and was highlighted in our January newsletter.

 

MICROSCOPY: Multi-frequency NSOM maps optical forces without a photodetector

03/03/2014

By Gail Overton
Senior Editor

 

Near-field scanning optical microscopy (NSOM) uses a sharp probe tip or a small aperture to scatter the electromagnetic field near the surface of a sample to gather high-spatial-resolution information present in the surrounding evanescent field. The subwavelength field information is then converted to a propagating far-field and measured with a photodetector to image the sample.

In a new technique called multifrequency NSOM, researchers at the College of Optics and Photonics (CREOL) at the University of Central Florida (UCF; Orlando, FL) and CNRS Institute Langevin (Paris, France) apply both an electrical signal and an optical signal to the tuning-fork architecture to map both surface topography and the spatial distribution of optically induced forces acting on the probe.1 Because the method does not require a photodetector for radiation-distribution mapping, broadband detection of light is possible using a single probe.

Optically induced force measurement
In the experimental setup, an oscillating quartz tuning fork with a sharp probe tip (a conventional gold-coated, pulled-fiber 100-nm-diameter aperture) affixed to one arm is piezoelectrically driven just above the sample surface and the probe position is maintained through a feedback mechanism for the first resonance signal to enable surface topography mapping as in standard atomic force microscopy (AFM). When a second oscillation is applied to the probe tip on one arm of the tuning fork, an additional higher-order resonance can be monitored that yields information on the forces acting upon the tip.

The probe is situated above the sample surface and is illuminated by 635 nm laser light coupled out of a single-mode fiber and maintained at an intensity of 0.36 mW/μm2. While the electrical signal enables topography mapping, the amplitude and phase of the optically induced resonance signal depend directly on the optical force acting on the tip.

 

Oscillating a scanning near-field optical probe at two different frequencies—one driven electrically to provide positional feedback and the other one by modulating the electromagnetic fields acting on it—allows simultaneous mapping of the topography (a) and optical forces (b) across the surface of a gold nanosphere lithography sample. (Courtesy of CREOL)

Using standard coupled equations of motion for the damped, driven NSOM harmonic oscillator that include both the electrical and optical frequency parameters, the amplitude and phase of the optical signal can be obtained. From variations in these two values, the magnitude of the optical force acting on the probe and its gradient can be extracted, yielding information on optical forces occurring spatially within the sample under test.

In an experiment, the force distribution was measured across a gold nanosphere lithography sample consisting of 0.453-μm-diameter gold spheres placed against a glass substrate and separated with 260 nm center-to-center spacing. Using both a tuning fork and a cantilevered-probe NSOM, near-field optical forces were measured with better than wavelength/50 resolution.

In the context of NSOM practice, CREOL professor of optics Aristide Dogariu says, “This multifrequency approach permits measuring—simultaneously—multiple aspects of the near field in the proximity of a sample and it also provides means to decouple the effects of different forces acting on the probe. Most importantly, it allows to separate the possible influence of thermal effects induced by the electromagnetic radiation. Without sacrificing spatial resolution, this technique not only circumvents the need for photon detectors but it also complements traditional approaches for optical characterization of metamaterials, plasmonic nanostructures, and biological structures.”

REFERENCE
1. D. C. Kohlgraf-Owens et al., Nanotechnol., 25, 035203 (2014).

 

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