Raphaëlle Dianoux, CEO at NanoScan, talks to AZoNano.com about their new VLS-80 system for surface analysis from the milli- to the nanoscale.
SM - Could you please provide a brief introduction to the industry that NanoScan works within and outline the key drivers?
RD - Our microscopes offer the highest magnetic resolution on the market. NanoScan is a Zurich-based company designing and manufacturing high-end Scanning Force Microscopes (SFMs) for both industry and academia. In the competitive SFM market, NanoScan’s strength is its deep know-how measuring the nano-magnetic properties of materials.
In addition to this core competence, we have developed a novel tool for SFM analysis of micro and nano-patterned surfaces on the millimetre range with nanometer resolution. This tool was developed in partnership with our parent company Ion-Tof with a view to analysing relatively large structures such as sputter craters. This extreme dimensional span stretching over six orders of magnitude was made possible thanks to the experience we have gained over the years in thermal drift, structural stiffness and stage motion accuracy.
SM - Could you briefly explain the basic technique of how magnetic imaging works?
RD - In Magnetic Force Microscopy (MFM), a magnetically-coated tip is scanned a few nanometers above the surface. The tip is mounted at the end of a cantilever which is excited at its resonance frequency. The interaction between the magnetic stray fields of tip and sample causes a shift in this resonance frequency. The resulting frequency shift is tracked and directly maps the magnetic landscape of the sample surface.
NanoScan’s instruments fulfil the three essential requirements for optimum MFM resolution: firstly they are mechanically stable, which means the sharp tip can be kept only nanometers away from the surface while never touching it. Secondly, very accurate electronics are required to track milli-hertz frequency shifts from a resonance ranging from a few tens of kHz up to the MHz range. Finally, a high-vacuum environment is required to increase the sensitivity of measurement by two orders of magnitude. Only when these requirements are fulfilled can a magnetic resolution of 10 nm be achieved.
SM - How does this differ from other techniques?
RD - When it comes to imaging magnetic nanostructures of surfaces, there are a handful of alternatives to MFM such as PEEM and SEMPA. However, only MFM offers a relatively low-cost solution compared to a synchrotron or a SEM. Furthermore, no special sample preparation is required. Thus, MFM is a “light” measurement mode, which can be installed in every lab. On top of this, high-vacuum provides the perfect trade-off between fast measurement (15 minutes pump-down time, no stringent requirements of Ultra-High Vacuum) and high-sensitivity (a factor 30 higher than in air).
SM - Could you please explain how your hr-MFM analytical and quantitative magnetic imaging system works?
RD - MFM can provide quantitative information of the magnetic properties of nanostructures such as hard disks or magnetic nano-dots. For this, the tip’s magnetic response is calibrated on a known magnetic sample, for example a hard disk. Then the recorded frequency shift data of an unknown sample can be converted to physical values of the stray fields below the tip. The quantitative MFM routines developed for Matlab and available online are adapted to process NanoScan’s data format.
SM - What are the major advantages of using your product?
RD - Both the VLS-80 and the PPMS-AFM are SFMs primarily developed for the investigation of magnetic properties at the nanoscale. They are the only SFMs on the market that offer high-vacuum as a trade-off between time-to-measurement (compared to UHV) and high-sensitivity (compared to air). They both can be operated under magnetic fields, for the VLS-80 using the Perpendicular Field Option (PFO) that can apply a variable field of up to ±550 mT. Most importantly, both microscopes offer unbeatable lateral magnetic resolution.
But there is more to that: NanoScan’s proprietary controller was developed to be very robust and yet very flexible to carry out any future measurement the user may think of. It comes with a lot of extras such as the Break Conditions to prevent tip damage or Kelvin Probe Force Microscopy (KPFM) operation. It also supports the optional 2nd Phase-Locked Loop (PLL) for multi-frequency operation.
Furthermore, the VLS-80 offers a large sample stage of 100 x 100mm2 that can accommodate many samples, thus reducing the time-to-measurement to a minimum. The Navigator function of the controller makes it very easy to position the tip over any area of the whole sample stage with a precision of 20 nm.
SM - What are the primary applications?
RD - Primarily all combinations of nano with magnetism! However today there is much more to this thanks to our latest developments. Whether nano-mechanical stiffness, contact potential differences with KPFM, or even long-distance profiling of craters. High-vacuum enhances sensitivity and opens the door to a diverse range of applications.
We put a great deal of effort into exhibiting the variety of applications our VLS-80 is able to achieve. The result is a series of applications notes, all available on the AZoNano website. For example, we showed how to distinguish simultaneously between topographical and magnetic structures using dual-frequency SFM, or how KPFM could allow to measure correct topography on charged surfaces.
SM - What industries primarily benefit from this?
RD - Historically, the first instrument developed at NanoScan was targeted at the hard-disk industry. For example, the first sample stage was not equipped with Cartesian coordinates (X, Y, Z) but with cylindrical ones (R, Phi, Z). The high-resolution was required as the size of the bits on a hard-disk became smaller than the resolution of existing MFMs. Over the years, NanoScan used this acquired know-how to meet the requirements of not just industry, but all research groups at the cutting-edge of magnetic materials science.
SM - What are the main differences between this product and previous versions?
RD - While we kept the focus on MFM excellence when developing the successor of the hr-MFM, the VLS-80, we also decided to emphasize our know-how on accurate positioning. As mentioned above, we changed to a Cartesian coordinate system for our sample stage so as to easily combine it with the scanner directions. The result is the possibility to perform long-distance profiling, theoretically across the whole sample plate (10 cm), while keeping sub-nanometer resolution in the vertical direction.
The heart of the VLS-80
Moreover, we figured that the effort we had put in the last years to develop a robust and precise controller could be implemented for other SFM techniques, such as KPFM or Dual-PLL AFM. These are now two features available with the VLS-80. There are also some add-ons such as top-view camera and Quiet Mode operation which complete the package.
With a lot more to offer than “just” MFM, we picked up the more generic name “VLS-80” for “Vacuum Large Stage with 80 µm scan range”.
SM - Are there any recent case studies that you are particularly proud of?
RD - In a recent request from Trinity College Dublin, we were asked if we could image the domain during magnetization reversal in an exchange biased CoFe/Pt multilayer. Using the magnetic Perpendicular Field Option of the VLS-80, we were able to image the domains at fields all around the hysteresis loop. By doing this, we identified two independent types of reversal: layer-by-layer growth and domain growth. This information could not of have been extracted otherwise from standard hysteresis loops obtained with magnetometry.
SM - Where do you currently supply to? Are there plans to expand operations in the near future?
RD - Together with our mother company Ion-Tof and its distribution network, we supply our instruments worldwide.
SM - How do you see your sector progressing over the next decade?
RD - Scanning Force Microscopy is a very competitive market with well-established key players and smaller companies like NanoScan offering niche applications. Today, practically every materials science lab has a SFM, if not several.
I see the future of SFM in two ways: on one hand in the simplification of measurement modes, with the goal to assist the user as much as possible. This is something we are actively working on at the moment. Closely related to this I see the combination with other measurement techniques as the logical step forward.
SM - How will NanoScan be a part of this change?
RD - We are already working on it! We have developed synergies with outstanding research groups from industry and academia to keep our technology developments at the forefront. In particular, we have taken part, together with our mother company, in the development of a combined SFM / ToF SIMS instrument within a FP7 EU project comprising 7 partners. The combined instrument provides 3-dimensional chemical information correlated to topographical and physical information, all this at the nanometer scale. The complexity of both techniques makes it a requirement to automate the measurement as much as possible. At this stage, the prototype already delivers very promising results so I am confident that the commercial version will be available very soon.
Altogether, being part of the Ion-Tof group of companies we benefit from the resources and support of a market leader in surface analysis and thus stay sharp on innovation.
SM - Where can our readers find out more about NanoScan?
RD - On our website www.nanoscan.ch, and naturally on the AZoNano network with news and application notes to download.
About Raphaëlle Dianoux
Raphaëlle Dianoux completed her physics studies between Grenoble, France and Karlsruhe, Germany before obtaining her PhD from the Université Joseph Fourier in Grenoble. Her thesis was already focussed on Scannning Force Microscopy, back then in air and investigating electrical properties of semiconductor nano dots. During her post-doc at Empa, Switzerland, she built a low-temperature UHV-SFM before joining the NanoScan team in 2009.
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