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Nanonics congratulates 2014 Chemistry Nobel laureates!

Transmission, reflection, and collection mode

Plant dry matter or lignocellulosic biomass is a feedstock of bioenergy, biofuel production and novel biomaterials. Understanding the cell wall structure is important for effective utilization of the lignocellulosic biomass.

Structure, chemistry and mechanics of the polymer assembly of the secondary cell walls have been studied for decades on the macrolevel. However, characterization of the chemical components of the cell walls on the nanolevel are still unknown due to the limitation in spatial resolution of spectral techniques such as FTIR and Raman, which are used  for chemical analysis.  

Most secondary cell walls of xylem cells are made up of three dominating polymers: cellulose, lignin and hemicelluloses. Cellulose fibrils with diameter 3-4 nm are arranged in larger agglomerates with size of 20-25 nm and are embedded in a matrix consisting of lignin and hemicelluloses. Different theoretical models of special arrangement of the polymers in the cell walls have been suggested. Most of these models are based on the SEM or AFM study but not on the chemical information.

In this work, a Nanonics MultiView 2000 with Near-field Scanning Optical Microscopy (NSOM) was used  for the first time to study the photo-optical and thus chemical properties of cell walls at the nanoscale. This technique enables scientists to overcome the optical diffraction limit and to reach the spatial resolution of 50nm (limited to size of the NSOM aperture)

The cell walls of three different plants-beeches (hard-wood), spruce (soft wood) and bamboo (grass) were studied with NSOM.

Since the samples are semi-transparent, the NSOM measurements were conducted in reflection mode. In this mode the light coming out from the probe aperture interacts with the sample, is reflected and then collected from the top with an optical objective of an upright microscope. The NSOM measurements were performed with a Nanonics MultiView 2000 and Nanonics cantilevered NSOM probes. The MV-2000 scanning head has a completely open optical axis from the top and from the bottom and can be easily integrated with almost any kind of optical microscopes. MV-2000 together with cantilevered NSOM probes, which have extended tip and special geometry, enable true reflection NSOM measurements.

Three images were acquired simultaneously: height, phase and NSOM. The obtained NSOM images showed curls- like structures with dimensions about 125 nm and more, which are not seen in the height and phase images. It is most likely that lignin contributes a stronger NSOM signal than cellulose and hemicelluloses due to its interaction with light (autofluorescence and resonance effect). NSOM results obtained on the three different plants species (hard wood, soft wood and grasses) point to the universal principle of the special cellulose and lignin assembly in secondary cell walls. For the first time, NSOM images provide sub diffraction limited chemical information about the spatial distribution of the secondary cell wall components. This contributes to the understanding of the cell wall structure and its enzymatic degradation for energy conversion from ligninocellulosic raw material in general.  

Published:  Keplinger et al. Plant Methods 2014, 10:1 

Click here for more information on this Nanonics MV 2000 system

The need for periodic metallic nanoparticle arrays is driven by a wide variety of applications including plasmonic waveguides, nanoscale lenses, and catalyzing the growth of ordered carbon nanotubes.  Current methods to form such organized, periodic structures usually suffer from high cost or poor quality structures.  Researchers Yadavali et al. from Oak Ridge National Labs and Univ of Tennessee reveal a new way to spontaneously make low cost, high quality periodic arrangements of gold nanoparticles.   

Laser interferences processes are known to induce periodic surface structures where a pattern forms due to the interference phenomenon between incident light and scattered light. The interference pattern produces periodic thermal gradients that induces mass transport and rearrangement. However, these types of patters often poor quality with defects. 

This work describes a new method involving irradiation of the surface by a single laser beam while apply a DC electric field to the underlying substrate.   When an electric field parallel to the laser polarization is applied, single-crystal like periodic ordering was formed covering a large area and with very low defect density.  In addition to high resolution studies by SEM, a Nanonics Multiview 1000 was used to analyze the topography and quality of the resulting patterns.  The resulting AFM images below show the gold periodic structures at difference conditions of a) no E field  b) E field perpendicular to the polarization and c) E field parallel to the polarization.

Published: Yadavali et al., Nanotechnology 25 (2014) p. 465301

Click here for more information on this Nanonics MultiView system

Nanonics Probes for Tough to Reach Places

Unique capabilities of Nanonics custom-made optical fiber probes continue to be developed.  In this paper, the specialized geometry of these probes to successfully measure various parameters in semiconductor devices is shown.  The area of critical dimension (CD) metrology is a well-known area in the semiconductor field where accurate measurement of critical dimensions such as deep trench depths, line edge roughness, linewidth, sidewall roughness and sidewall angles are critical and increasingly challenging as these dimensions continue to decrease. In the past decade, AFM has become a popular method to make these measurements of irregular features not possible with other common methods like SEM and TEM.

The sharp optical fiber probes with a tip length of upto 400um and an aspect ratio of 10:1 are uniquely suited to image sidewalls and deep trenches.  A schematic is shown below, left where the probe can easily fit into a deep trench and image along its bottom or its edges (right.) 

Using a Nanonics optical fiber probe, these challenging features were successfully measured, as shown in the image below.  These probes far surpass the ability of silicon probes, which cannot successfully measure steep sidewall angles, deep trenches, or bottom of trenches due to the geometry and shape of the silicon probe which skews the resulting image with artifacts.

Nanonics has an in-house probe fabrication facility with decades of experience between our scientists and engineers.  Our probes are provided exclusively to our customers, and we are always willing to help customize the probes to your research needs.

Published: H. Xie et al., Review of Scientific Instruments, 85, p. 123704 2014 

Click here for more information on these sidewall probes

Unique apertured and apertureless NSOM protocols with low background

MultiProbe Apertureless NSOM ANSOM 

Link to pdf version of app note

 In standard approaches to apertureless NSOM (ANSOM) the probe is simply a modulated scatterer with gross far-field optical illumination using elements such as lenses or mirrors, which cause large spot sizes of radiation around the scattering probe. 

It has been very chellenging to develop ways to reduce the artifacts that arise from the background that is created by these far-field optical elements; this background can interfere with the desired signal from the nanometric tip of an atomic force sensor capturing the near-field surface component in a large far-field radiation background.

The MultiView 4000 with its unique multiprobe capability enables the reduction of both the optical and mechanical background and thus increase the overall S/N.

One probe can be used as a limited illumination spot onto a second scattering probe.  This both reduces the optical background and generates the correct k vectors to excite the scattering probe.  In addition, since the feedback employs tuning forks, the scattering probe can be kept with an oscillation amplitude of 1 nm.  This has been shown to be critical due to the fact that the probe tip has to be modulated close to the surface without a jump to contact and without variation in z which adds additional background to the signal from mechanical sources.  Furthermore, the rigid tuning fork frequency significantly enhances heterodyne and homodyne lock-in detection schemes to further reduce background.

	This scheme diagrammatically describes the two probe configuration where the illuminating probe excites the scattering probe and this probe can even be a single gold nanoparticle with high scattering contrast at the exposed tip of the AFM probe for increased signal from the very tip of the probe.  These probes have been developed by Nanonics for Tip Enhanced Raman Spectroscopy

Near-Field Plasmon Excitation & Apertureless Scattering and Collection  Apertureless NSOM ANSOM

A Multiview 4000 with a two Probe SPM setup has been used for effective localized illumination of a plasmonic structure with an apertured NSOM probe which produces all k-vectors, and so it is most efficient for such plasmonic propagation. The propagating plasmons are scattered and then collected with a second probe, which has a very low dielectric constant and minimal perturbation of the plasmonic propagation

Two Probe Setup Scheme: An apertured probe to produce an evanescent field with a spectrum of k vectors to effectively excite SPP (Left Probe). Right probe is a very low dielectric contrast, highly exposed, non-interfering scanning and work in Photon Tunneling mode to scatter SPP and directly collect the photons produced by such scattering	MV4000 picture of two probes in close nanometric proximity. MV4000 provides flexible probe and sample piezo scanning stages for fine and coarse probe positioning and scanning. The image above shows two probe attached to Tuning Forks for the ultimate in AFM force sensitivity.	A microscope picture (100x objective) top view shows two tips of apertured (Left) NSOM fiber probe providing 532nm near-field illumination and an Apertureless NSOM probe (Right). Surface plasmons are generated on top of an Au strip and scattered by the scanning ANSOM tip.

Left: AFM Height image of the Au strip performed with the ANSOM scanning tip. The circle at the bottom shows the effect of the illumination apertured tip when scanning in its close proximity. Middle: ANSOM image performed with the scanning tip.  Rich contrast is seen by the apertureless probe doing the AFM and ANSOM imaging. Right: 3D ANSOM image shows sustained plasmon propagation and then rapid decay

 Apertureless Probes  

Standard probes that need to be used in order to effectively scatter the plasmonic signal have significant perturbation on the plasmonic propagation because of the need to use probes with high dielectric constant to obtain effective signal to noise in such scattering experiments. 
Nanonics exclusively provides Apertureless probes of glass with plasmonic or Non-Plasmonic Scattering Particles.  Nanonics ANSOM probes are low dielectric constant, provide non-interfering scanning, highly exposed and work in Photon Tunneling Mode to scatter SPP. For such plasmonic probes, glass provides for high dielectric contrast for exceptional antenna effects at the tip of the probe.  Such probes can be provided with a nanoparticle as small as 10 nm or simple 5nm diameter glass probes.

Apertureless IR NSOM, nanoIR  

In the IR ANSOM regime standard far-field optical elements give large spot sizes of microns to tens of microns which seriously compromise the nature of the signal detected by the nanometric tip of an atomic force sensor.  Applying a Dual Probe system allows for ultra low background with minimal spot illumination size through an infrared fiber probe, which is nanometrically held in close proximity using the dual probe geometry to a scattering low dielectric glass probe or a single  gold nanoparticle probe or a silicon exposed tip probe.  Such a tip is generally modulated in close proximity to a surface in order to delineate the near-field interactions.

NanoIR Probe: Unique methods for IR illumination with a 100 nm point heat source for broad band IR irradiation of a scattering probe tip using multiple probe capabilities and with subsequent interfero-metric IR spectral resolution.  Overcome tens of micron spot sizes with lens based IR optical illumination.

Nanonics MultiProbe Apertureless NSOM: 

• Multiprobe systems are singularly capable of exceptional apertureless and scattering NSOM imaging.

• Ideal Apertureless solution with minimum stray light & maximum plasmonic excitation

• MultiProbe ANSOM appears to have significant potential to reduce background and maximizing signal at the highest resolution

FPN Nanolithography deposition of BSA protein with simultanous AFM imaging 

MultiProbe Nanolithography Writing and Reading

Link to pdf version of this app note

 The images and movie below show deposition of BSA protein lines onto a silicon surface with an MV4000 Two Probe system for simultaneous "writing" and "reading". The size of the deposited protein feature is controlled by the applied forces, which are defined by the setpoint of the AFM tip-sample interaction. The movie shows a fountain pen nanopipette probe delivering the protein to the surface and then retracting from the surface. The lines are then immediately imaged with the second on-line AFM probe of the MultiProbe AFM system

 AFM images of the deposited structure is seen at the end of the movie and in the right image below. The MultiProbe system allows for improved online imaging of the deposited structures without switching to a "writing" probe from an imaging probe, and thus it provides a quick and accurate solution for finding and imaging lithographic patterns.

(Left) BSA protein deposition with FPN capillary nanopipette probe where pipette's tip is indicated by a blue circle. (Middle) AFM imaging with a second online probe where tip is indicated by blue circle. (Right) 3D AFM Height image performed with the AFM probe showing BSA printed lines

 See more information about Nanonics FPN Nanolithography: http://nn.taktiko.co.il/products/chemical-writing

Reading and Writing Movie: