The chemical characterisation of nanoparticles is important for innovative devices as well as environmental regulation. Secondary ion mass spectrometry is a powerful technique to measure the chemical composition of nanoparticles with depth by measuring the particles that are ejected from the surface by an incident primary ion beam in a process known as 'sputtering'. The Surface & Nanoanalysis Group at NPL has developed a fundamental understanding of the sputtering yield of nanoparticles. Due to both the dimension of nanoparticles being comparable to the size of the primary ion collision cascade, and the larger available surface area for secondary emission, the sputtering yield is expected to be significantly different for nanoparticles compared to bulk materials. For the first time, we measured a significant increase in this sputtering yield in agreement with general expectations. It is clear that under primary ion impacts, nanoparticles without an effective thermal contact with the substrate will melt very early in the depth profiling process. Nanoparticles therefore may have a much lower 'static limit' compared to bulk material and this has fundamental implications for practical analyses. This work has just been published in  the Journal of Physical Chemistry C (2012, 116, 9311) and was quoted as: "...timely and represents an important advance in understanding the process."

Illustration of a C₆₀ primary ion impacting a gold nanoparticle. The excess yields above the bulk values rises as 1/d^1.5 where d is the nanoparticle diameter.