Dimensional characterization of cadmium selenide nanocrystals via indirect Fourier transform evaluation of small-angle X-ray scattering data

The correlation of single-particle imaging and absorption spectroscopy made the development of sizing curves possible and enabled rapid size determination of semiconductor nanocrystals based solely on optical properties. The increasing demand and production of such materials has resulted in a question of comparability between existing models and adequate volume-weighted size-determining measurement techniques. Small-angle X-ray scattering (SAXS) is a well-established method for obtaining nanostructural information from particle systems while operating sample quantities up to a commercial scale with a large amount of statistically based data. This work utilizes laboratory SAXS to characterize cadmium selenide nanocrystals with band edge energies between 1.97 and 3.08 eV. The evaluation of the scattering patterns is based on an indirect Fourier transformation (IFT), while dimensional parameters are derived from the model-free pair distance distribution functions (D_mode and D_g), as well as the modeled volume (D_v) and number (D_n)-weighted size-density distributions. We find that comparable data from D_n agree well with existing X-ray diffraction (XRD) and with transmission electron microscopy (TEM) results described in literature; this qualifies SAXS as an equivalent integral characterization method. Although based on an estimate, the radius of gyration yields equivalent accurate results. Additionally, corresponding volume-weighted data are shown that can be useful when transferring information to other techniques. D_mode parametrization represents the largest estimated size of the sample and implies that particles interact and deviate from the spherical morphology, whereas D_v demonstrates results not considering such effects. A full set of the parameters discussed quantifies the quality of a sample.