| AVS 62nd International Symposium & Exhibition | |
| Applied Surface Science | Wednesday Sessions |
| Session AS-WeM |
| Session: | Practical Surface Analysis II: Influence of Sample Preparation and Novel Sample Prep Techniques |
| Presenter: | David Cant, National Physical Laboratory, UK |
| Authors: | D.J.H. Cant, National Physical Laboratory, UK N.A. Belsey, National Physical Laboratory, UK C. Minelli, National Physical Laboratory, UK A. Shard, National Physical Laboratory, UK |
| Correspondent: | Click to Email |
Nanoparticles with a coating or shell are widely studied in both academic and industrial research. X-ray Photoelectron Spectroscopy (XPS) and Low/Medium Energy Ion Scattering (LEIS/MEIS) have potential for accurate measurement of chemistry and thickness of nanoparticle coatings, but the accuracy of these measurements is dependent upon correct modelling for analysis and reproducibility of sample preparation. There is as yet no uniform approach to these issues; to address this, VAMAS project A19 – an interlaboratory study involving 24 participants in 12 countries – has been undertaken with the following objectives:
• Assessment of inter-laboratory variability in measuring nanoparticle coating thickness
• Comparison of sample preparation techniques.
• Testing variability of procedures for quantitative analysis.
Samples were prepared from commercial gold colloid and incubated with a short peptide. Each participant received one pre-deposited sample on Si wafer, and one solution (and Si wafer) for their own in-house deposition. Participants were requested to return their samples to help identify the effect of differences in sample deposition between pre-deposited and in-house samples.
Thickness values reported by participants performing XPS were compared to values calculated from reported atomic concentrations using the T(NP) method [1,2]. A significant difference was observed between thicknesses determined for the pre-prepared sample and those determined for samples deposited by the participants in-house. Thicknesses determined for the in-house samples were larger than those determined for the pre-deposited samples. This was attributed to increased hydrocarbon presence observed in the C 1s spectra – likely caused by uneven sample deposition allowing detection of substrate contamination. In some cases, both pre-deposited and in-house samples exhibited abnormally low calculated thicknesses, potentially due to damaging of the coating by the x-ray beam.
The results of this study will assist in the development of a new ISO standard on the measurement of surface chemistry and thickness of nanoparticle coatings. The study will also provide information relevant to the ISO standard for reporting information related to the history, preparation, handling and mounting of nanomaterials prior to analysis, currently in development under ISO TC201. The production of guidelines for the measurement of nanoparticle coatings and sample preparation will be of great use in commercial applications of coated nanoparticles.
References[1] Shard, A.G., Journal of Physical Chemistry C, 2012. 116(31): 16806-16813
[2] Belsey, N. A., Shard, A. G., Minelli, C. Biointerphases, 2015. 10, 019012