SIMS2015 Session FS-ThP: FIB-SIMS Poster Session

FIB-based instruments become of increasing importance in materials and life sciences. They are an ideal tool for high resolution 2D and 3D imaging and for nanofabrication (nano-machining and deposition, etc.), yet their analytical capabilities are currently limited. By contrast, secondary ion mass spectrometry (SIMS) is an extremely powerful technique for surface analysis owing to its excellent sensitivity, good dynamic range, high mass resolution and its ability to differentiate between isotopes. Adding SIMS capability to FIB instruments offers not only the prospect of obtaining elemental information at much higher resolution than state-of-the-art SIMS instruments, but allows for a direct correlation of SIMS images with high resolution secondary electron images. Preliminary results show that lateral resolutions in the 10 nm range can be achieved in ion microscopy.

In this context, the influence of irradiation induced damage on FIB-based imaging must be minimized. In the current presentation the evolution of polymer samples under He⁺, Ne⁺ and Ar⁺ bombardment will be investigated. A first point of concern is the formation of roughness. An experimental study based on ion irradiation with subsequent characterization of the sample surface by AFM has shown that surface roughness can be kept well below 1 nm up to the maximum investigated fluence of 10¹⁷-10¹⁸ ions/cm². Polymer swelling is not observed, which means that the projectile atoms are not accumulated inside the irradiated sample. This is opposite to what is observed for He⁺ irradiation in metallic or semiconductor samples where the formation of bubbles is observed. A possible explanation is the higher diffusion coefficients of the gases in polymer samples. To complement the picture of the evolution of polymer topography, the results of MD/MC computer simulations are presented to show the influence of diffusion processes on phenomena like bubble formation, polymer swelling and damage formation.

Many studies have been done to understand the release of radionuclides from glass waste forms over time. For HLW glasses, the release is usually assessed through studies of kinetic dissolution behaviour. In the UK, most of the data that exists are from Soxhlet tests on simulant glasses, in deionised water at ≥ 90°C. There are two UK HLW glass compositions: (a) Magnox which arises from reprocessing of Magnox fuel (Mg- and Al- rich); and (b) Blend that arises from other reprocessing activities within the Thermal Oxide Reprocessing Plant (THORP) at Sellafield (2). UK HLW glasses are high in Mg and Al content, compared to other countries, making the properties of this glass different especially in terms of durability. Thus, there are significant uncertainties associated with extrapolating data from international programmes to represent the behaviour of UK glass products (3).

The aim of this project is to characterize the surfaces of leached UK HLW glass to help interpret the corrosion mechanism of simulated waste glass in aqueous environments using ToF-SIMS. The elemental distributions from the glass surface into the bulk for both unleached and leached simulated waste glass was examined. Conventional depth profiling of these samples can be very difficult, due to the extent of the corrosion layers and difficulty in charge compensating. In order to overcome these issues a novel FIB-ToF-SIMS approach was performed, to successfully obtain depth profiles up to a depth of ~600µm.

Refs:

(1) Jain V. and Pan Y. M., 2000. Glass Melt Chemistry and Product Qualification, Centre for Nuclear Waste Regulatory Analyses (CNWRA) San Antonio, Texas. Nuclear Regulatory Commission Contract NRC-02-97-009.

(2) Cassingham N. J., Bingham P. A.and Hand R. J., 2008. Property modification of a high level nuclear waste borosilicate glass through the addition of Fe2O3, Glass Technology, 49 (1), 21-26.

(3) Swanton S. W., Schofield J. M., Clacher A., Farahani B., Myatt B. J., Burrows S. E., Holland D., Brigden C.T. and Farnan I., Experimental studies of the chemical durability of UK HLW and ILW glasses – First interim progress report, AMEC Report, Reference Number AMEC/D.005824/IPR/01 Contractor-approved draft, Oxfordshire United Kingdom, December 2012b.

Batteries are one of the most prevalent technologies used in modern life (cellular communication, computing, electric vehicles, etc.). Improvements in the specific capacity (energy by weight or volume) and charging rates have the potential to significantly improve their efficacy. Hence, battery materials research is a critical enabling technology with direct broad economic and social impact. Most advanced battery technology is based on the transfer of lithium ions (Li⁺) between two active materials such as graphite for the anode and LiFePO₄ (LFP) for the cathode. To improve this battery technology, it is essential to determine the distribution and amount of Li present with good spatial resolution (<1µm) In terms of microstructural characterization, Li is very difficult to analyze using energy dispersive spectroscopy (EDS) because it is a very light element and emits low energy x-rays (52 eV). Optical emission spectrometry and XPS can detect Li, but with limited lateral resolution. Li has a relatively high sputtered yield and low backscattered coefficient. Mass spectrometry is used in dedicated SIMS instruments, but with a limited lateral resolution. It is now possible to combine high-resolution imaging and chemical imaging using TOF-SIMS in a FIB/SEM instrument with a resolution better than 50 nm that also has EDS, electron backscattered diffraction (EBSD), cathodoluminescence detector (CL), backscattered electron images, etc. These analytical techniques will greatly complement TOF-SIMS analysis and assist with quantification.

Battery materials are composed of organics (polymer, electrolyte) and inorganic (active material, conductive carbon, current collector) materials. Using TOF-SIMS and EDS, it will be possible to identify the various species that are essential to fully characterize battery materials. However, this effort will require considerable development. This investigation will address the present and future use of electron microscopy in advanced battery research, with a focus on the development of a specialised analytical microscope combining TOF-SIMS and other analytical detectors capable of detecting lithium.