• Schirmacher, Alfred

Abstract

The increasing use of colloidal semiconductor nanocrystals in many modern technologies demands a continuous upscaling of the production, while maintaining control over their chemical structure, the unique size-dependent optoelectronic behavior and quality. Sizing curves are based on statistical data and became a trustworthy basis for fast size determination solely by absorption spectroscopy measurements. Whereas most literature utilized transmission electron microscopy (TEM) for single particle imaging, their sizing models are questioned for applications where volume-weighted size data are preferred. Alternatively, small angle X-ray scattering (SAXS) is an integral measurement technique and a reliable tool for the precise and fast ensemble measurement of nanoparticles.We present extensive studies on the well-known cadmium selenide (CdSe) quantum dot system with band edge energies between 1.97 and 3.08 eV, especially with focus on size and polydispersity assessed by laboratory SAXS. The scattering patterns have been evaluated on the basis of an indirect Fourier transformation to derive parameters from the model free pair distance distribution function (Dmode and Dg), as well as volume (D¯v) and number (D¯n) weighted size density distributions. The results of this work reveal that D¯n is in good accordance with existing X-ray diffraction (XRD) and TEM results from the literature. Furthermore, the gyradius Dg yields similar results. The volumetric size data described by D¯v help to discuss the measurement data in dependency of the polydispersity. Dmode is influenced by occurring particle interactions or surface distortions, whereas D¯v represents the assumptions of ideal non-interacting spheres. Band edge energies were determined with absorption spectroscopy measurements to provide the correlation of the dimensional and optoelectronic properties for the comprehensive sizing curve.Metrological particle reference standards in the single-figure nanometer range are rare and the development of new standards is crucial to the promotion of novel applications in the fields of nanotechnology. The quantification of all four parameters showed great potential for CdSe to be utilized as such, and SAXS qualifies as an appropriate tool to support these metrological purposes.

Topics

• nanoparticle
• density
• impedance spectroscopy
• surface
• x-ray diffraction
• semiconductor
• transmission electron microscopy
• quantum dot
• polydispersity
• small angle x-ray scattering
• Cadmium