Understanding variations and changes in the composition of materials is an important area of our expertise. Please contact us to discuss the most appropriate means of analysing samples to derive the required information.

 

Surface Analysis by SIMS

Secondary ion mass spectrometry (SIMS) analyses the top 1-2 nanometres of the surface by abstraction of atomic and molecular clusters and analyses the resultant positive and negative ions to provide information on surface chemical composition.

Monitoring of specific SIMS fragments can provide information on properties relevant to processing parameters, such as coating coverage / uniformity, chemical modification, surface layer enrichment / depletion, as well as ‘traditional’ contamination analysis.

For example, many metallic surfaces are protected from oxidation by appropriate surface treatment protocols. For brass, a typical treatment uses an organic triazole for passivation. Variations in treatment level can be monitored by spectral analysis, and visualised by chemical imaging.

SIMS Analysis

 

Bulk Composition by Fourier Transform Infra-red Spectroscopy

Analysis by FTIR gives bulk information relating to functional groups and molecular structure.

Samples can be compared, in order to evaluate differences between grades, impurity species can be detected and ratios of mixtures evaluated.

For example, analysis of an ethylene vinyl acetate (EVA) polymer by FTIR shows bands related to the different molecular groups within the compound.

FTIR Analysis

                                                       

Shifts in absorption band energies and relative intensities can be quantified between similar samples. As a result of these changes, composition changes, degradation processes, molecular re-orientation and migration events can be evaluated. Cure reactions and aging effects can be monitored in real time directly.


X-Ray Photoelectron Spectroscopy (XPS or ESCA)

Photoelectron peaks determine quantitatively the element and chemical state compositions of surfaces to about 7nm depth. Sub-surface and bulk analysis by XPS is achieved after ion beam etching or mechanical milling. Chemical state concentration analysis information from XPS can be used directly in many ways. For example the pollutant nitrogen dioxide at ppm levels causes measurable depletion of surface phospholipids (PC) of egg tempera used in fine art paint (Ref. 81). Hence XPS can help in degradation studies of fine art materials, as shown below:

XPS Spectra

A wealth of other information carriers is available in XPS, including the valence band (VB), and Auger peaks such as oxygen OKVV (see above spectrum). Auger transition and photoelectron peak energies are combined in ‘Wagner Auger parameters’; from which bulk properties, such as refractive index, can be predicted without the need for absolute theoretical calculations (Ref. 9).

When presented as ‘Chemical State Plots’, Auger parameters allow a wider range of processes to be investigated. For example, changes in both the physical, as well as chemical environments of elements affect Auger parameter values. This can be observed for zinc used in calcium – zinc stabilisers; before and after incorporation in UPVC (Ref. 82).

XPS Auger Params