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Thursday, 30 April 2015 18:31

NSOM Key Features

Cantilevered probes for the best NSOM performance

Nanonics is the global pioneer in glass probe manufacturing and has developed a whole suite of probes for all your NSOM applications for both apertured and apertureless NSOM, fiber probes with metallic nanoparticles embedded in the tip, metallized probes for STM, and straight probes for shear force feedback.

All modes of NSOM

True reflection mode NSOM

True Reflection mode NSOM is possible due to the use of transparent, cantilever probes. Furthermore, our design separates the excitation and collection paths so that they don't affect each other, thus enabling true reflection mode NSOM measurements to be conducted. Other designs that take advantage of straight probes or apertured Si probes are significantly more challenging for true reflection mode.

Transmission mode NSOM

Transmission mode NSOM is suitable for transparent or semi-transparent samples where light is introduced through the optical fiber and collected by a detector underneath the sample.

True Collection Mode

True collection mode enabled by systems with both tip scanning and a sample scanning stage. A sample scanning stage enables easy and rapid alignment of the sample relative to the illumination source and ensures that the microscope optics are independent of the AFM scanner.

Multiple probe capability

Near-field excitation and collection are possible with instrumentation accomodating up to 4 independent probes for simulatneous operation.  Each probe can be configured in apertured or apertureless configurations for applications like plasmon injection, dark plasmons studies, and generation and distribution of SPPs and other photonic waveguides.

Any optical configuration

This enables total flexibility in your NSOM setup by integration with any optical microscope. Additionally, total optical access to sample and probe position from above is possible since the cantilever probe/scanner assembly does not obscure access.

Largest commercially available Z range 

The large, 85 μm X, Y and Z-range of the Nanonics 3D FlatscanTM makes it ideal for optical sectioning in confocal imaging. Used in this way, you can integrate conventional far-field imaging, confocal microscopy, AFM, and near-field optics in a single system

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Thursday, 30 April 2015 18:23

Raman Key Features

Effortless AFM and Raman integration 

The design results in a natural and straightforward Raman path for integration without the need for tilting or bending the Raman path to accomodate the scanning probe microscope. Both reflection Raman and transmission Raman are standard with unhindered access to the sample and probe from both above and below.  Additionally, advanced SPM modes including MFM and EFM are available; these measurements can be done on their own or in conjunction with simultaneous Raman imaging.

Optically transparent probes for best Raman quality

Nanonics is the pioneering manufacturer of bent glass, optically transparent probes with no obstruction

of the optical axis and the sample surface, which are provided exclusively to Nanonics customers.

Designed for TERS operation

Quick and easy TERS hotspot detection.

Combined tip and sample scanning stage provides accurate positioning of the probe at the ideal location with respect to the focused laser spot.  Tip can be positioned within the center of the Raman hotspot for optical Raman signal detection.

Sample can be scanned without losing the Raman hotspot position.

    All modes of TERS including STM and AFM-TERS with easy interchangeability. Thus the same probe (either conducting or with a conductive coating for STM-based feedback) can be operated as an AFM probe using tuning fork based feedback, and then it can be switched to tunneling based feedback for TERS operation.

   TERS on non-conducting surfaces.

   3 point TERS measurementsfor comparing the difference between enhanced and non-enhanced spectra and extracting new information.

 

Tuning fork feedback without Raman laser interference 

Laser-free feedback method called normal force tuning fork feedback is provided on the MV2000 and MV 4000. For example, many SPM laser-based feedback systems employ red lasers, which would then interfere with the Raman emission in the red from the sample.

Autofocus for superior Raman resolution 

Our systems provides autofocusing onto the sample at every pixel point. Thus for rough samples, tilted samples, or samples with unusual Z variation, these systems provides the best Raman resolution as it makes sure to have the sample in focus at every point a Raman spectrum is collected.

Ideal for biological applications

The MV 2000 and MV 4000 combine the ability to scan large z ranges (upto 170um), suitable for Raman imaging of most biological species.  In addition, they can image biological species in situ in aqueous environments with the ability to work with a water immersion objective.  In addition, the tuning fork feedback provides the ultimate force sensitivity to conduct AFM-based measurements on soft samples.

 

Best TERS probes on the  market (exclusively for Nanonics users)

Including: transparent TERS probes with gold ball grown inside the glass, STM and non-STM TERS probes, and gold-coated AFM probes.  Nanonics glass probes are supplied bent at 60 degree angle, the ideal angle for TERS excitation.

Multiprobe MV 4000 Raman application - graphene bridge

A dual probe MV4000 system integrated with a Raman spectromer studied the electrical and chemical properties of a graphene bridge that was connected between electrical pads.  Two cantilever electrical probes (Nanonics) were brought down to the electrical pads. The variable electrical voltage was applied to the substrate and the current between the electrical probes through the graphene was measured. The Raman signal was collected from the graphene simultaneously with the electrical measurements.

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Role of Contacts in graphene transistors: A scanning Photocurrent study

T. Mueller,F. Xia, M. Freitag, J. Tsang, and Ph. Avouris

IBM Thomas J. Watson Reserch Center, Yorktown Heights, New York 10598, USA

 

PHYSICAL REVIEW B 79, 245430 (2009)

Graphene is a 2D material with extraordinary electrical and optical properties, high electron and hole mobility, high thermal conductivity, temperature stability and tensile strength. All of these properties make graphene a very attractive material for nanoelectronics.

In most experiments and simulations for evaluating the transport properties of graphene transistors, the graphene channels are treated as being homogeneous. However, recent experimental work provided evidence that the metal contacts induce strong charge inhomogeneity and should be taken in the account especially near the Dirac point. Most recent experiments that assessed the transport properties of graphene were done in the far-field.  Scanning probe techniques that can measure on the nanoscale are required for an improved understanding of the role of metal contacts in graphene nanodevices.

Scanning the photocurrent (PC) is an effective tool to study the potential profiles as a function of the photoresponse on the nanoscale. In 

this paper, high resolution photoconductivity was studied with Near-field Scanning Probe Microscopy (NSOM). A Nanonics Multiview 2000 was used for the measurements, which provided three key advantages for photoconductivity measurements:

1)  tuning fork based actuation so there is no laser for feedback that can cause artifacts during PC imaging

2) scanning head with both tip and sample scanning.  With this hardware setup, the probe can be moved to the specific location on the sample with high accuracy and then scanned there locally, without moving the sample which is electrically connected.

3) completely open optical axis from the top and from the bottom. This open optical axis and the cantilevered NSOM probe with extended tip enables locating the NSOM probe relative to the sample features from on the opaque sample, such as graphene transistor on Si substrate with high accuracy.

A modulated Ar-ion laser (514 nm) was coupled into cantilevered NSOM probe (aperture diameter of 100 nm) to excite the photoconductivity on the graphene device.  An NSOM probe scanned across the graphene transistor, while the photocurrent was recorded simultaneously with topography. The pho

1) The presence of a strong PC voltage near the metal contact electrodes, at the point on the local electrical field near the graphene/metal interfacetocurrent was measured versus gate voltage under short-circuit conditions where the gate voltage was sweeping between -60 and 100V.   The PC results showed:

  1. 2) PC polarity switching at gate bias 20 V. This behavior of the PC can be described with the theoretical model that treats bending of the graphene bands as the result of the charge transfer between the graphene sheet and the metal electrodes.
  2. 3) Same band bending occurs when the single graphene layer contacts with multilayer graphene.

 

Thus near field photocurrent microscopy is a powerful technique to study the electrical properties of graphene nanodevices with nanoscale resolution.  This method showed modification of the electronic structure of the graphene device near the metal contacts and inhomogenity of the charge transfer. The obtained results provide further understanding of the asymmetric behavior of the electrons and holes in the graphene transistors. Photocurrent imaging can be also used to probe single-layer/multilayer graphene interfaces.

 

Published:  PHYSICAL REVIEW B 79, 245430 (2009)

 

 

In a beautiful example of work that approaches the ultimate limits of nano-fabrication, a TERS tip has been used to reversibly tailor a graphene surface by inducing defects.  Graphene is 2D hexagonal lattice of carbon atoms with unique electronic transport properties, high mobility and stability with applications for novel extraordinary fast microelectronic devices. Despite the fact that  graphene is fabricated by mechanical methods, it has a very low density of lattice defects.  The  crystal deformations, corrugations, and extrinsic rippled can produce structure distortion as lattice defects.    Defects in graphene can break its hexagonal symmetry and affect its properties, so any ability to control them is important to improving graphene properties.  Also, controlling graphene defects has application potential in phase transformation, recording information, and nanoscale switching.  Thus the ability to control and even reverse defects in graphene has important practical applications.  

In this paper Ag particles were deposited on the exfoliated graphene prepared on SiO2/Si substrate. The obtained Raman results show that the metal nanoparticles strongly interact with graphene and induce artificial defects (through appearance of D band). In spite of the advantages of the SERS, this process was irreversible and uncontrolled.  Tip enhanced Raman spectroscopy (TERS) is an excellent alternative to SERS where the Au or Ag metallized  probes approach the sample and create enhancement near the tip apex due to surface plasmons excitation near the metal apex.  The proces is reversible and controllable by careful approach and retract of the TERS probe.

In this work exploring the origin of graphene defects, the TERS tip performed a double function both by artificially inducing the defect and detecting it by enhancing the Raman signal.  A MultiView 4000 equipped with nanoparticle-tipped TERS and AFM-TERS feedback induce a reversible defect in the graphene through interaction with the TERS tip; the defect went away when the TERS tip was retracted.  The Nanonics instrumentation has several distinct advantages for these kinds of experimental setups:

 

1. Open optical axis to scanning head, enabling integration with up-right and inverted optical microscopes for TERS measurements on the opaque and transparent samples.   

2. Laser-free, tuning fork based feedback resulting in no optical interference between the feedback and Raman signal.

3. Tip and sample scanning in the one scanning head. Tip scanner enables the accurate positioning of the TERS probe relatively to the focused laser for the maximum Raman enhancement.

 

TERS spectra are shown below of the tip on (red) and off (black) the graphene surface show new bands (D,D+G) induced by the TERS probe.  These bands are associated with the creation of the extrinsic deformation on the graphene surface.
 

                           

 
These results show that TERS is an effective, non invasive, reversible and controllable technique to study 2D nanomaterial on the nanoscale.

Access full publication here  [P. Wang et al, Plasmonics, vol 7, p. 555, 2012]
Friday, 27 February 2015 16:15

February 2015 Newsletter

APS, ImagineNano, Image Contest, and Graphene

Graphene Transistor

 

A unique protocol of near-field excitation for generating photocurrent with strong impact in solar cell applications is demonstrated here. A near-field scanning optical microscope has been used to locally induce photocurrent in a graphene transistor with high spatial resolution. By analyzing the spatially resolved photoresponse, it is shown that in the n-type conduction regime a p-n-p structure forms along the graphene device due to the doping of the graphene by the metal contacts.

The left picture shows the SEM image of a graphene transistor and the electrical setup for PC measurements. On the right seven PC images taken at gate biases between -60 and +100 V are shown. The dashed lines indicate the edges of the source and drain electrodes. The two scale bars on the bottom of the very right image are both 1 nm long.

Schematic illustration of the experimental setup and sample structure.

 

Mueller et al. PHYSICAL REVIEW B 79, 245430 2009

Sunday, 22 February 2015 20:09

Nanonics at SPIE Photonics West

Nanonics will be attending and exhibiting at SPIE Photonics West February 2015 in San Francisco

Sunday, 22 February 2015 20:09

2015 Nanonics Image Contest

2015 Image Contest

Sunday, 22 February 2015 20:09

Nanonics Receives New Economy Award

 

Sunday, 22 February 2015 20:07

Holiday Discount

End of year holiday discount

 

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