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.

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).

September 2019 Newsletter

Recent Advance By A Nanonics Customer
Jahng et al “Photo-Induced Force Microscopy by Using Quartz Tuning-Fork Sensor” Sensors 2019, 19, 1530; doi:10.3390/s19071530

Ultrasensitivity of Tuning Forks in Photon Force Imaging (PiFM)

Photon Force is an exciting way for NSOM imaging from the UV to the mid-infrared.   The technique is generally known as PiFM.  Such photon force with a scanning probe microscope was pioneered by a Nanonics customer, Professor Aristide Dogariu of the University of Central Florida (CREOL) [Dana C. Kohlgraf-Owens, Sergey Sukhov, and Aristide Dogariu, “Mapping the mechanical action of light” PHYSICAL REVIEW A 84, 011807(R) (2011)].

Recently, Nanonics systems, both the Multivew 2000 single probe and Multiview 4000 multiple probe systems have been used to show the exceptional capabilities of tuning fork SPM probes in the measurement and analysis of imaging in PiFM mode [Junghoon Jahng , Hyuksang Kwon and Eun Seong Lee, “Photo-Induced Force Microscopy by Using Quartz Tuning-Fork Sensor  Sensors 2019, 19, 1530; doi:10.3390/s19071530 ].  

Tuning forks have multiple eigen modes which allow different parameters of both the photon momentum and the feedback that is impossible using silicon probes and beam bounce feedback technology often used in SPM imaging. 

Furthermore, both in the earlier work by Dogariu and the present study, it has been shown that the force sensitivity of a tuning fork is between 0.5 pN in the present study and 1.5 pN in the previous study by Dgariu.  The present study has shown that the fundamental eigen mode has the highest force sensitivity while the higher order of eigen mode has a sensitivity which Dogariu  reported.  

These studies highlight the great utility of Nanonics systems based on the tuning fork for photon force imaging and variety of new horizons in imaging modalities.  For example, the multiple eigen modes can be used to great advantage in such applications as nanometric visco-elasticity which can be compared to bulk DMA values for various materials.    In this application, one mode of the tuning fork can be used for feedback, while the second mode can be used for out-of-plane information related to this visco-elasticity. 

This publication highlights Nanonics tuning fork  systems.

January 2014 - In This Issue: Research Focus: Tuning fork probes and feedback User news: Detection of near-field optical forces Nanonics at Photonics West Meet our staff member Rimma Dechter

Tuning fork probe Tuning fork feedback mechanism for ultimate force sensitivity   Tuning forks offer significant advantages and increased sensitivity over conventional Si probes in large part due to their high quality factors (Q of 10x and higher.)   Tuning forks in force spectroscopy have especially begun to show exciting results that push the measurement's possibilities.  Over the last decade, Nanonics has developed instruments using a NanoToolKit of such probes that are increasingly being used with on-line force spectroscopy.  A demonstration of the force sensitivity of these probes is the measurement of 1.6 pN for the force of a single photon. [D. C. Kohlgraf-Owens et al "Mapping the mechanical action of light," Phys. Rev. A 84, 011807R (2011)]   Besides force sensitivity, tuning forks offer other advantages over optical beam deflection and conventional Si probes.  Tuning forks have much stiffer (spring constant of ~2600 N/m and greater) than standard silicon cantilevers.  As a result, the problem of "jump to contact" instability that limits the optical beam deflection based feedback methods is eliminated, and this permits the study of forces in the proximal 10-20 nm above a surface.  Smooth approach curves together with lack of adhesion ringing upon withdrawal is combined with additional advantages of no feedback laser interference; these features are important for semiconductor electrical probing and combinations of AFM with Raman spectroscopy that Nanonics has pioneered.  Furthermore, tuning forks in force spectroscopy enable the point of contact with the surface to be accurately measured for the first time.  For all these reasons and its ease of use, tuning forks are becoming an ideal choice for new horizons in experiments requiring the ultimate tip-sample control stability and force sensitivity from areas of bioimaging, to physics of devices, and to single molecule and polymer spectroscopy.

Topography color coded with ampl. measured at optical driving frequency USER NEWS - Detection of near-field optical forces   The power and sensitivity of tuning fork feedback was demonstrated in a recent groundbreaking publication in high resolution apertureless imaging by Prof. Aristide Dogariu's group at University of Central Florida.  Using a Nanonics Multiview 4000 system, his team mapped near-field optically induced forces with sub wavelength spatial resolution (Kohlgraf-Owens et al., Nanotechnology, 25, 034203 [2014]). The scientists describe a new method, multifrequency NSOM, performed with tuning forks/tuning fork feedback and cantilever probes/optical beam deflection feedback.   By exciting the probe's oscillation at two difference frequencies, they measured the amplitude and phase  at the optical modulation frequency on a gold nanosphere sample (see image on right) revealing  an amplitude that was lowest over the gold pads, moderate over the glass, and highest near the edges.  The method opens a new horizon of apertureless imaging of optical fields with very high spatial resolution over a large range of wavelengths - including far-IR and THz - and it can be accomplished without using photodetectors, a regime that to-date lacks a competitive alternative for detection!  Professor Aristide comments "We are excited about the potential of multi-frequency NSOM for using photonic forces for apertureless imaging of optical fields in a wide variety of wavelength regimes from the visible to the IR." Nanonics at Photonics West   Nanonics founder and CEO Aaron Lewis, a pioneer in near-field optics, will be at Photonics West. Please email us at info@nanonics.co.il to schedule a discussion and time to meet with him.   Professor Lewis is presenting on a variety of topics in February in San Francisco: 1) Sunday, 5:50pm, BIOS 8939-11 (ORAL) "Understanding the TERS effect with an on-line tunneling and force feedback using multiprobe AFM/NSOM with Raman integration 2) Monday, 2:50pm, OPTO 8992-24 (ORAL) "Combined far-field and multiprobe near-field imaging of hybrid photonic devices" 3) Monday, 4:20pm, OPTO 9006-16 (ORAL) "Addressing the inverse problem of imaging:  A noniterative exact solution fo rphae in imaging based on microHolography" 4) Wednesday, 6:00pm, OPTO 8988-64 (POSTER) "Piezoforce and contact resonance microscopy correlated with Raman spectroscopy applied to a non-linear optical material and to a lithium battery material" 5) Thursday, 11:30am, OPT 8999-39 (ORAL) "Ultrasensitive force detection of photonic phenomena with tunin fork based frequency modulation" Meet Nanonics staff! Welcome to our newest segment in our newsletter where we will be profiling a member of our staff.  We start this month with Dr. Rimma Dechter, a name that is familiar to many Nanonics customers. Current position at Nanonics:  Manager of Analytical Services. In this role Rimma heads the department that makes measurements on customer samples in the wide variety of characterization needs Nanonics offers from conventional scanning probe microsopy to near field and Raman measurements to multiple probe experiments. Academic Background:  PhD in Applied Physics from Hebrew University Family:  married + 3 kids Hobbies:  genealogy What I like about working at Nanonics:  The aspect I enjoy the most is the tremendous amount of innovation that goes on in our company to meet customers needs. It is exciting to interact with customers and learn about their instrumentation requirements for their research; I then work with my colleagues to develop new, out of the box solutions to meet their needs.   Where are you presenting your research? Please let us know where you are presenting your research and we will be happy to share the news! For more information, please contact us at info@nanonics.co.il or call us at +972-2-678-9573, (US toll free 1-800-289-7162)

 way to increase sensitivity in TERS experiments from complicated biological samples by providing another platform for preparing complex biological molecules that can be probed by the ultrasensitive TERS method.

Microscopy Today 2010

The Nanonics Hydra biological SPM was selected as one of the top 10 innovations by Microscopy Today. Read more about the Hydra.

R&D 100 2007

The Multiview 4000 was selected as one of the top 100 technologically significant new products in 2007 for its breakthrough multiple probe technology. See more details on the Multiview 4000.

Microscopy Today Award 2013

Presented to Nanonics for development of a novel integrated tool for the ultimate 3D characterization: the 3TB 4000. Read more about it on our website and in the November 2013 Microscopy Today (Volume 21) journal.

R and D Award 1993

Presented to Nanoptics, For the development of Glass capillary X-ray concentrator 

Selected by R&D magazine as one of the 100 Most Technologically Significant new Products of the year 

The Laser Focus World Commercial Technology Achievement Award 1996

Presented to Nanonics Ltd. Jerusalem, Israel for 3-D scanner for the optical/scanned probe microscopist.

The Laser Focus World Commercial Technology Achievement Awards recognize significant and lasting achievements in commercial electro-optical technology.

The Photonics Circle of Excellence Award 1996   Nanonics Imaging Ltd. has been cited by Photonics Spectra Magazine for developing one of the twenty-five best new products of the year.

This award is bestowed on Nanonics for the NSOM/SPM-100 Confocal™ (now called the MultiView 1000™) in recognition of excellence, innovation and achievement in the field of photonics technology.

The Rank Prize for Opto-Electronics Awarded to the President of Nanonics, Professor Aaron Lewis, 1997

The Rank Prize for Opto-Electronics Awarded to Professor Aaron Lewis for his outstanding contribution to the science and application of Opto-electronics 

Quote taken from the award given: 

"This microscope has already demonstrated its value as a reliable, relatively inexpensive tool for the optical characterisation of surfaces. It has been applied to histological specimens and biological samples which are much smaller than the diffraction limit. As a sub-wavelength emitter it extends optical lithography, making possible high density data storage and integrated circuits of the finest dimensions. The future of near-field optical microscopy seems certain to include even more far-reaching technological applications and to revolutionise our understanding of biological processes."

Chairman of the Trustees 
THE RANK PRIZE FUNDS 
London - 17th March 1997