Abstract text (incl. figure legends and references)

Motivated by the discovery of a highly non-linear optical response, occurring as directional white-light emission (WLE) in tin-sulfide-clusters [1], we investigate structurally similar organic functionalized diamondoids as well as inorganic cluster molecules.

The goal of our TEM (transmission electron microscopy) study is to identify the structure as well as chemical bonding by analyzing the pair distribution functions (PDF) and the electron energy loss spectra (EELS) of these materials in the low and high loss regime. These shall be correlated to the optoelectronic properties of the materials to discover structural prerequisites for the WLE mechanism.

In order to achieve high quality samples for TEM that have a suitable thickness, we embed the specimens in epoxy and cut them into 50 nm thick slices using a LEICA ULTRACUT UCT ultramicrotome (UMT).

The electron scattering measurements to derive the pair distribution function (PDF) are carried out with a JEOL JEM-3010 TEM equipped with a TVIPS-XF416 ES camera. The EELS measurements are done with a double-aberration corrected JEOL JEM-2200FS (S)TEM that is additionally equipped with a PNDetector pnCCD direct electron camera with full frame rate of 2000 fps. An additional precession electron diffraction (PED) unit (Nanomegas) is used on both microscopes.

By using conventional and precession diffraction we derive pair distribution functions (PDFs) of the typically amorphous materials providing the inter- and intramolecular arrangements of these molecules (Fig. 1). These properties are considered to play a fundamental role in the process of white light emission since the inclusion of nanometer scale crystallites can suppress the WLE [2]. By using diffraction experiments the PDFs can be used to investigated molecules in a dose efficient manner which is shown to be critical for some of the organic clusters [3].

In conjunction with a scanning unit we acquire spatially resolved diffraction patterns in 4-dimensional datasets. We investigate the limits of scanned PDF measurements with and without precession in terms of accuracy and dose requirements aiming for a spatial resolution down to a few nanometers.

Finally, we consolidate our findings with X-ray scattering experiments, scattering simulations and density functional theory calculations.

References:

[1] N. W. Rosemann et al., Science 352, 1301 (2016).

[2] J. Haust et al., ChemPhotoChem 6 (2022).

[3] J. Belz et al., The Journal of Physical Chemistry C 126, 9843 (2022).

Fig 1: Electron diffraction and the derived PDF of an amorphous WLE showing a characteristic ring pattern which relates to molecular and atomic arrangements.