Probing the average size of self-assembled metal nanoparticles using x-ray standing waves

We report application of x-ray standing-wave field for characterization of average vertical size of metal nanoparticles dispersed on a substrate surface with accuracies better than 1 nm. This method is applied to analyze the distribution of Fe, Co, and Au nanoparticles on Si substrate and W/C multilayer substrates. Results demonstrate that the method is a valuable tool to evaluate the surface morphology of nanoparticles over a large surface area. Unlike conventional probes such as atomic force microscopy or microinterferometry, the present method provides element-specific analysis. It also has the advantage of being able to examine nanoparticles in a liquid medium, or buried inside a coating layer. We anticipate that the proposed method has great potential to infer the internal structure of nanoparticles.