SI-Ontario will benefit from a $1.36 million investment by the Canadian Foundation for Innovation (CFI), as announced last November. The proposal, which was submitted to the Leading Edge Fund, was entitled “An Integrated Centre for Surface and Interfacial Analysis of Advanced Materials” and spear-headed by Prof. Charles Mims. The total budget, with in-kind and matching contribution, will come to $3.4 million. The award will not only allow SI-Ontario to upgrade its equipment but will greatly expand the scope of work it can currently undertake. The new infrastructure will allow Canadian researchers continued access to state-of-the-art surface analysis equipment and the related expertise, as well as comprehensive surface preparation facilities, thereby ensuring their position at the leading edge for years to come. See article on "Enhancing the capabilities of SI-Ontario".

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The research supported by SI-Ontario is as diverse as its client base and is of high impact. A common thread is the need for the best available surface and interface chemical information. While the current facilities have provided a critical component to the supported research, advances in technology have necessitated further investment in the infrastructure to allow leading edge quality and fulfill needs currently unmet both regionally and nationally. The new CFI funding allows us to now meet these goals.

Four main categories have been highlighted for enhancement.

• ToF-SIMS upgrade: This is to include the new Bi cluster ion source, which will replace the present Ga source; a third ion gun column to house a new C60 ion source; pulsed secondary electron detection and associated data systems; and improvement to the sample-cooling system to -150°C.
  
  
• Imaging XPS/AES system: A small spot (~ 10 µm), monochromatic (angle-resolved) XPS with imaging capabilities, a sample treatment chamber, heating-cooling (-150°C - 600°C), and Auger imaging with 100 nm spatial resolution.
  
  
• Specialised sample treatment/preparation facilities: This will include a cryomicrotoming/freeze fracture, custom stand-alone preparation chamber; a vacuum suitcase and other (cryo and inert gas) transfer devices; a surface profilometer; polishing equipment; and a glovebox.
  
  
• Expanded laboratory/user facility: To house the expanded facility, lab space will have to be doubled. The new space will house the old XPS - for use on dedicated projects, preparation chamber/equipment, glovebox and space for visitors. In addition to more data stations in-house, the proposal also includes networking capabilities with other institutions.

Further details will be posted on our website - www.si-ontario.utoronto.ca.

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In order to help decide which XPS fits SI-Ontario's user base the best, Rana Sodhi, Peter Brodersen and Chuck Mims visited both Thermo Electron (E. Grinstead, UK) and Kratos (Manchester, UK) in early February. Thermo offers 2 instruments of interest: the Thetaprobe and the Escalab 250, while Kratos’ flagship - the Ultra, is also a leading contender.

The advantage of the Thetaprobe is its ability to do parallel angleresolved XPS, negating the need to tilt the sample. By focusing its X-ray down to 15 µm, it is able to do small spot analysis, achieving good count-rate, while stage-rastering allows imaging capabilities.

Visiting the team at Thermo Electron.
Thetaprobe is in the foreground, Escalab 250 is in the background.

Both the Ultra and the Escalab use a parallel imaging mode. By decreasing the aperture in the lens system, small areas of analysis can be defined. Scanning the plates allows both systems to generate a map. Both systems claim a spatial resolution of better than 3 µm. Angle-resolve XPS is done by tilting the sample.

The team at Kratos busy demonstrating the performance of the Ultra.

A final instrument, Ulvac-Phi’s Versaprobe, has just come onto the market. Unlike the instruments above, it images by scanning a small spot X-ray.

All in all, it is going to be a tough decision! A comprehensive set of real samples was taken over to compare performance. Also, the ability to integrate sample preparation chambers is of importance. The good thing is that whatever our decision, we can’t really make a mistake.

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Perhaps one of the more esoteric applications of SIMS presented at SIMS XV in Manchester in 2005 was entitled “ToFSIMS applied to historical archaeology in the Alps” [1].

According to literature, there are 3 possible invasion routes followed by Hannibal during the second Punic War (see map). While proof exists that he used the Col de le Traversette, ancient literature suggests that there should be burnt rock on the Italian side of the Alps due to his “firing” of the rocks. The Col du Clapier is the only pass where “fired” rock has been found.

The question is, is this due to timber being used as related to Hannibal, or is it more recent, say to a modern day road crew?

SIMS images for a cross-section of the burnt rock are shown here.

Of interest is the presence of K on the burnt crust and within the fissures. The presence of K has been attributed directly to the firing, resulting from the ash residue that would remain after firing with timber. This would not be expected if gasoline had been used for the firing.

Thus the SIMS results are in broad agreement with the historical literature which states that Hannibal did use timber to fire the rocks and clear his route. This alone is not positive proof that he indeed did this and used the Col du Clapier, however, it does confirm that timber was used in this case.

[1] R.N.S. Sodhi, W.C. Mahaney and M.W. Milner, Applied Surface Science 252 (2006), p7140.

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Results from SI-Ontario’s collaborative work with University of Houston (Chemistry & Physics) on solid oxide fuel cells (SOFCs) were reported at SIMS XV in Manchester (UK) in the fall of 2005. The presentation highlighted the ability of SI-Ontario’s ToFSIMS instrument to study the oxygen transport kinetics of newly developed mixed ionic electronic conductor cathode materials. SOFCs are highly efficient, non-polluting electrochemical energy converters, directly transforming chemical energy into electrical energy.
For commercialization, operation of SOFCs at intermediate temperatures (500–700°C) is desirable in order to reduce costs and enhance cell stability. At lower temperatures, cathode resistance becomes the limiting factor in overall cell performance. Current efforts focus on finding oxides that are electrolyte compatible and which have the high oxygen diffusion and surface exchange kinetics necessary for low electrode resistance.

Figure 1. Dual beam depth profile of 18O/(18O+16O) and other cathode ions

Isotope exchange and depth profiling (IEDP) has been used to evaluate oxygen transport kinetics. Samples (both thin films and bulk) are equilibrated in oxygen (0.2 atm) with normal isotopic abundance and then exposed to 18O (99% isotopic abundance) and rapidly quenched. The resulting 18O profiles are determined via ToF-SIMS using either dual beam sputter analysis (thin film cathode - Fig. 1) or imaging of cross sections (bulk cathode - Fig. 2). The extracted profiles are used to determine oxygen surface exchange and oxygen bulk diffusion coefficients.

Figure 2. Depth profile (bottom) extracted from image (center)
of area of interest (top)

In this project, the imaging capability of our TOF-SIMS IV instrument has also proven useful for investigating profile phenomena, including lateral heterogeneities as a function of depth in thin films and gross distortions in 18O profiles of cross-sections caused by e.g. cracks in the material (Fig. 3).

Figure 3. 18O map (l) and secondary electron image (r) of coincident area

For further information on this project, see Journal of Materials Chemistry, DOI:10.1039/B618345J (2007).

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Being able to heat or cool a sample in situ can be very important. For example, certain polymers can restructure, showing different orientations between the wet and dry states. The ToF-SIMS has a special heating-cooling stage (below), which allows the temperature to varied between -130°C - 600°C in both the preparation and analytical chambers.

In a recent study, Sosnik [1] has looked at collagen/poloxamine hydrogels by a ‘deep freezing’ ToF-SIMS approach in order to study the availability of the collagen molecules at the surface of the hydrated polymer structure and consequently their ability to induce the attachment of cells on the designed matrices. Three matrices considered: collagen, poloxamine and poloxamine + collagen. The samples were cast in a special Cu holder which was attached to the cooling stage and placed in the transfer chamber. This was flushed with dry N2 and cooled down to -120°C at which point the vacuum was started. After placing in the analytical position, the sample was heated in 5°C increments until the H2O sublimed off.

The figure above shows the positive spectrum at -95°C and it can be seen from the marked (*) series of peaks due to H(H2O)n+ fragments that the water has not totally sublimed off. Heating the sample drives this remaining H2O. The figure below shows the positive ion spectrum of a collagen/poloxaminemethacrylate hydrogel heated to –65°C, which shows peaks characteristic of both the collagen and the pure hydrogel.

The work confirms the presence of collagen at the surface which is evenly distibuted as seen in positive ion image shown below.

[1] A. Sosnik, R.N.S. Sodhi, P.M. Brodersen and M.V. Sefton, Biomaterials 27 (2006), p2340.

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