Successes and Challenges for Atom Probe Tomography of Small-Molecule Organic Materials

We will highlight several successes using atom probe tomography (APT) to analyze small-molecule organic materials and discuss challenges and opportunities for APT of these materials. Organic small molecule materials are used in a variety of applications, such as organic light emitting diodes (OLEDs); OLEDs are widely used in displays, yet there are many open questions about how molecular design ultimately impacts device properties. The light-emitting layer of an OLED is comprised of a co-deposited layer of two or more molecules, but little is known about how well these dissimilar molecules mix. A primary challenge with APT of organic molecules is that they are very sensitive to both electron-beam and ion-beam damage during conventional FIB-based tip preparation. We will review techniques to prepare and analyze these organic molecular materials,¹ including the development of large-radius APT tip coupons that enable fast sample preparation through thermal evaporation of materials onto the tips, entirely avoiding damage associated with FIB preparation and a quantitative model for understanding and predicting fragmentation of small molecules during APT measurement.² We will also address challenges associated with these materials, including low detector efficiencies, which can limit the sensitivity of APT measurements. This research expands the capabilities of APT, enabling additional materials science of organic small molecule materials research.<br/> <br/>¹ A. P. Proudian, M. B. Jaskot, D. R. Diercks, B. P. Gorman, and J. D. Zimmerman, “<i>Atom Probe Tomography of Molecular Organic Materials: Sub-Dalton Nanometer-Scale Quantification</i>” Chem. Mater. <b>31</b> (7), 2241 (2019).<br/>² Jacob T. Bingham, Andrew P. Proudian, Shubham Vyas, and Jeramy D. Zimmerman, “<i>Understanding Fragmentation of Organic Small Molecules in Atom Probe Tomography</i>” The Journal of Physical Chemistry Letters <b>12</b> (42), 10437 (2021).