Table of ContentsIntroduction Simultaneous Confocal-AFM Imaging and TERS Integration Package Solution Parallel Imaging
Conventional Confocal Raman Mapping Raman
Mapping with Z-Control Examples of the Integrated
Raman/AFM Nanoindentation Correlated with Material
Local Stress of MEMs Devices
Intermittent Contact Mode in Liquids About
Nanoscale imaging is a rapidly evolving field. Nowadays there are several
techniques available for sample characterisation, but each of them is targeted
to extract specific information. It would therefore be ideal to have several of
these analysis tools all integrated into the same measuring system to achieve
full characterisation of the specimen.
Simultaneous Confocal-AFM Imaging and TERS
Nanonics Imaging pioneered the field of AFM-Raman/Tip Enhance Raman
Spectroscopy (TERS) with the MultiviewTM series. Its hallmark free
optical axis allows for seamless integration with any Raman system, whether
upright or inverted. Figure 1 shows the Multiview
4000TM two probe head mounted on the HORIBA Jobin Yvon Raman
Spectrometer (Left) and the Multiview 1000TM head mounted on the Renishaw Raman
Figure 1. Multiview
4000TM two probe head, mounted on the HORIBA Jobin Yvon Raman
Spectrometer (left) and Multiview
1000TM head, mounted on the Renishaw Raman Spectrometer (right).
Packages are available for a variety of Raman
manufactures including Renishaw PLC and HORIBA Jobin Yvon. These
state-of-the-art integrations mark the beginning of a new era in high-resolution
Raman spectroscopy. Such Integration Package allow for complete
isolation of the AFM from Raman and laser sources and provides the ultimate in
AFM performance and optical/confocal Raman/TERS throughput for various samples
such as carbon nanotube, graphene flakes, monolayers, bio-surfaces, etc.
Integration Package Solutions
The Integration Package is an optical connection package which can connect
either to the Raman microscope or directly to the Raman spectrometer. The
advantage is that the AFM sits on its own microscope which is completely
isolated from vibrations from the Raman's laser, spectrometer or CCD. This
allows both the AFM and the Raman to work under the best operating conditions.
Three configurations for the Integration Package are available:
- Inverted microscope
- Dual microscope (a combination of an Upright
and an Inverted microscope).
The Nanonics MultiviewTM series is designed to be transparently
optically integrated (Fig. 2). The same head can work with either an upright or
an inverted microscope and with a dual microscope system where either
backscattered or transmission operation is presented.
Figure 2. Integration Package scheme of a
Dual Microscope system with an efficient optical connection to external devices
such as Raman spectrometers and Raman microscopes (Left). Multiview
4000TM SPM system mounted on a Dual microscope and a vibration
isolation platform of the Integration Package (Right). The Integration Package contains
an enclosure for acoustic shielding.
With the combined system, it is possible to record in parallel with Raman, a
wide variety of scanned probe imaging modalities. For instance, while the Si
Raman peak of a microcircuit is being monitored to detect stress in the silicon,
the micro-topography of the circuit can simultaneously be measured by AFM, as
well as its NSOM reflectivity or its electrical properties, such as the dopant
concentration (Fig. 3).
In addition, Nanonics provides a software displaying all these images at
once, for direct and simultaneous comparison and analysis.
Figure 3. Parallel imaging of a Silicon Semiconductor.
9x7 μm2 AFM image (left) and Raman Intensity of the
same region at 520nm/cm (right).
Conventional Confocal Raman Mapping
There is a serious drawback to Raman Spectroscopy when studying non-smooth
surfaces. As with all lens-based microscopy techniques, Raman suffers from the
problem of out-of-focus light.
When a sample is scanned conventionally under the illuminating beam of a
Raman microscope, the uneven sample surface will scan in and out of the focal
plane. As a result the resolution of the Raman mapping is limited by the large
area of the unfocussed beam on the sample.
In addition, the point spread function is significantly broader where there
are contributions from the out-of-focus light. As a result the Raman spectra of
non-flat surfaces can be very misleading, and tends to misrepresent the true
information that can be gained by using Raman.
Raman Mapping with Z-Control
The problem of out-of focus light can be solved by using a Z-feedback
mechanism. With this feedback in place, the surface of the sample can be kept in
the focal plane throughout the scan. All the Nanonics MultiviewTM AFM platforms have a completely free
optical axis. This makes them the ideal add-on to any Raman system to provide
the Z-control necessary for true high resolution Raman mapping.
Examples of the Power of Integrated Raman/AFM
The difference between Raman mapping with and without Z-control can be seen
clearly in the examples below. Here the vibrational mode of diamond at 1334
cm-1 is represented (Fig. 4).
Figure 4. The pair of images on the top shows
the same area mapped with and without Z-control (Top). The advantage of Z-control is
made apparent by the differences between the two. The images on
the bottom are collages of AFM topography and Raman intensity of the same sample
at two different wavelengths (Bottom). Note the differences in the intensity of the two
images: the bright spots at the top of the image at 1334 cm-1 are
absent from the image at 1525 cm-1.
Specialized AFM/Raman/TERS Functional NanoImaging and NanoManipulation of
Carbon NanoMaterials protocols are available for a variety of materials such as
carbon nanotubes, Graphene, diamonds, etc. No other Raman system has sufficient control of Z position to pick out
Nanoindentation Correlated with Material Properties
To illustrate the combination of the worlds of AFM and Raman spectroscopy,
actual data has been obtained on the Si stress problem mentioned above (Fig.
Figure 5. (a) 14 x 14 μm2 AFM height image of a
nanoindentation in Si, (b) a line scan through a region of the AFM image
The points on the AFM cross section are points at which Raman microscope
spectra were collected. As a result of the nanoindentation, the silicon has been
displaced. The question is whether or not these regions correspond to different
phases of the silicon that can be correlated with the AFM measurements.
Only Raman microprobe spectroscopy can give this information. The Raman
spectra were obtained at the same time as the topography was measured.
Local Stress of MEMs Devices
Raman spectroscopy is a very important technique for measuring silicon
strain. On-line AFM can impose finely controlled and well-defined strain on
silicon with pressures exceeding megapascals since the area of a probe tip is
nanometric. NanoRaman technology is ideal for super-resolution silicon stress
measurements in floating structures such as combs and forks.
The on-line AFM
allows for defined forces to be imposed on a MEMs cantilever while the on-line
Raman measures the shift in the silicon vibrational frequency and silicon strain
at the cross (Figs. 6 and 7). No other AFM is capable of such a combination.
Figure 6. AFM imposing forces on a MEMs cantilever with
the Raman measuring simultaneously the silicon vibrational frequency and
silicon strain at the cross.
Figure 7. Raman shift as a function of local stress
Intermittent Contact Mode in Liquids
In addition, the Nanonics SPM/Raman systems can operate in intermittent
contact mode even in liquids. Thus, the whole world of NSOM/SPM imaging of
biological materials in physiological media can now be directly correlated with
About Nanonics Imaging
Nanonics Imaging is
the premier innovator of AFM and NSOM systems in the SPM market. Since its
inception in 1997 and throughout the last ten years Nanonics have introduced
to the SPM market new concepts in system functionality which in turn have
supported the pursuit of new areas of scientific application.
contributions span from the revolutionary approach to NSOM imaging with
cantilevered NSOM probes, to the introduction of dual tip/sample scanning AFM
systems and from the introduction of the first ever NSOM/AFM cryogenic systems
to the first ever, Raman/AFM, Multiprobe AFM and SEM/AFM systems.
This information has been sourced, reviewed and adapted from
materials provided by Nanonics Imaging.
For more information on this source, please visit Nanonics