Optical properties of free sub-10-nm diameter FeO nanoparticles studied by broad-band cavity enhanced absorption spectroscopy (BB-CEAS).

We present direct optical extinction measurements on free size filtered iron oxide nanoparticles in the size range between 3 nm and 10 nm diameter. The high number density of nanoparticles required for the cavity enhanced absorption spectroscopy (CEAS) measurements was achieved by combining a high intensity plasma synthesis source of iron oxide particles with an aerodynamic lens inlet into the vacuum system and radiofrequency particle guiding and storage devices. The extinction cross sections can be quantitatively explained using the bulk optical constants of hematite, which may exist in the form of nanoparticles in the mesosphere. [ABSTRACT FROM AUTHOR]