The uniqueness of nanoparticles, NPs, due to their functionalities not present in bulk size is well documented [1]. A nuanced understanding of their functionalities depends on their accurate characterization.  Generally the analysis is done on an ensemble of NPs.  However there is likely some variation in the NP population and ensemble averaging can limit insight into the relationships between size, composition and chemical reactivity of NPs. This is especially the case for very small NPs where minor changes in size, shape, composition can significantly affect chemical reactivity [2]. We present here an innovative methodology for analyzing individual NPs, in particular objects of 2-20 nm in size. Our approach is based on an original Secondary Ion Mass Spectrometry, SIMS, technique where NPs dispersed on a substrate are probed one by one. They are bombarded with a sequence of individual �nanoprojectiles�, specifically Au4004+(a NP of ~2 nm in diameter). The impact of a single nanoprojectile at hypervelocity (~30 km/s) generates abundant ion emission from an area of ~10 nm in diameter. The ejecta from each impact are mass-analyzed and recorded individually. The approach avoids problems due to ensemble averaging. From the pool of individual NP records (typically ~1M) we extract subsets of data from alike NPs; specifically we can identify molecules co-located within ~10 nm.   The presentation will describe the custom-built instrumentation, the methodology for data acquisition-processing and critical aspects of nanoprojectile-NP interactions for accurate characterization.  The analysis of outer shell vs. core composition will be shown on metallic and hybrid NPs in sizes >10 nm. The examination of objects <10 nm will be illustrated with mass spectra obtained in transmission on NPs deposited on graphene.[1] G.M. Whitesides, Small 2005 , 1, 172-179.[2] D.R. Baer, D.J. Gaspar, P. Nachimuthu, S.D. Techane, D.G. Castner, Anal. Bioanal. Chem. 2010 , 396, 983-1002.

Characterization of individual nanoparticles with nanoprojectile-SIMS

247th National Meeting (2014)

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