Combined scanning probe nanotomography and optical microspectroscopy: a correlative technique for 3D characterization of nanomaterials.

Combination of 3D structural analysis with optical characterization of the same sample area on the nanoscale is a highly demanded approach in nanophotonics, materials science, and quality control of nanomaterial. We have developed a correlative microscopy technique where the 3D structure of the sample is reconstructed on the nanoscale by means of a "slice-and-view" combination of ultramicrotomy and scanning probe microscopy (scanning probe nanotomography, SPNT), and its optical characteristics are analyzed using microspectroscopy. This approach has been used to determine the direct quantitative relationship of the 3D structural characteristics of nanovolumes of materials with their microscopic optical properties. This technique has been applied to 3D structural and optical characterization of a hybrid material consisting of cholesteric liquid crystals doped with fluorescent quantum dots (QDs) that can be used for photochemical patterning and image recording through the changes in the dissymmetry factor of the circular polarization of QD emission. The differences in the polarization images and fluorescent spectra of this hybrid material have proved to be correlated with the arrangement of the areas of homogeneous distribution and heterogeneous clustering of QDs. The reconstruction of the 3D nanostructure of the liquid crystal matrix in the areas of homogeneous QDs distribution has shown that QDs do not perturb the periodic planar texture of the cholesteric liquid crystal matrix, whereas QD clusters do perturb it. The combined microspectroscopy-nanotomography technique will be important for evaluating the effects of nanoparticles on the structural organization of organic and liquid crystal matrices and biomedical materials, as well as quality control of nanotechnology fabrication processes and products.