Abstract
Understanding the chemistry of nanoparticles is crucial in many applications. Their synthesis in a controlled manner and their characterization at the single particle level is essential to gain deeper insight into chemical mechanisms. In this work, single nanoparticle spectro-microscopy with top-down nanofabrication is demonstrated to study individual iron nanoparticles of nine different lateral dimensions from 80 nm down to 6 nm. The particles are probed simultaneously, under same conditions, during in-situ redox reaction using X-ray photoemission electron microscopy elucidating the size effect during the early stage of oxidation, yielding time-dependent evolution of iron oxides and the mechanism for the inter-conversion of oxides in nanoparticles. Fabrication of well-defined system followed by visualization and investigation of singled-out particles eliminates the ambiguities emerging from dispersed nanoparticles and reveals a significant increase in the initial rate of oxidation with decreasing size, but the reactivity per active site basis and the intrinsic chemical properties in the particles remain the same in the scale of interest. This advance of nanopatterning together with spatially-resolved single nanoparticle X-ray absorption spectroscopy will guide future discourse in understanding the impact of confinement of metal nanoparticles and pave way to solve fundamental questions in material science, chemical physics, magnetism, nanomedicine and nanocatalysis.
Highlights
Understanding the chemistry of nanoparticles is crucial in many applications
Combining the precision of top-down lithography[43,44] to obtain single iron nanoparticles and the elemental sensitivity of the photoemission electron microscopy (PEEM) (Fig. 1a)[45,46], we demonstrated single particle spectroscopy and performed in-situ studies simultaneously on a well-defined model systems consisting of ordered iron nanoparticles
Since the PEEM is a surface-sensitive technique probing about 3 nm of the surface, the thickness of the particles was optimized to 2.5 nm so that the whole particle is probed by X-rays, which is an advantage over earlier studies performed at similar particle sizes
Summary
Understanding the chemistry of nanoparticles is crucial in many applications. Their synthesis in a controlled manner and their characterization at the single particle level is essential to gain deeper insight into chemical mechanisms. Fabrication of well-defined system followed by visualization and investigation of singled-out particles eliminates the ambiguities emerging from dispersed nanoparticles and reveals a significant increase in the initial rate of oxidation with decreasing size, but the reactivity per active site basis and the intrinsic chemical properties in the particles remain the same in the scale of interest This advance of nanopatterning together with spatially-resolved single nanoparticle X-ray absorption spectroscopy will guide future discourse in understanding the impact of confinement of metal nanoparticles and pave way to solve fundamental questions in material science, chemical physics, magnetism, nanomedicine and nanocatalysis. We achieved the deposition of nanoparticles of controlled sizes and subsequently the synchronous spectroscopic characterization of individual nanoparticles of different sizes during reduction and oxidation These developments open up new opportunities in design and synthesis of surfaces with controlled functionality and in applications of in-situ single particle spectro-microscopy for metallic nanocatalysis
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