Cryo-ePDF: Overcoming Electron Beam Damage to Study the Local Atomic Structure of Amorphous ALD Aluminum Oxide Thin Films within a TEM

Ahmed M Jasim; Xiaoqing He; Yangchuan Xing; Tommi A White; Matthias J Young

doi:10.1021/acsomega.0c06124

Cryo-ePDF: Overcoming Electron Beam Damage to Study the Local Atomic Structure of Amorphous ALD Aluminum Oxide Thin Films within a TEM

ACS Omega. 2021 Mar 25;6(13):8986-9000. doi: 10.1021/acsomega.0c06124. eCollection 2021 Apr 6.

Authors

Ahmed M Jasim¹, Xiaoqing He^{2

3}, Yangchuan Xing^{1

3}, Tommi A White^{2

4}, Matthias J Young^{1

5}

Affiliations

¹ Department of Biomedical, Biological and Chemical Engineering, University of Missouri, Columbia, Missouri 65211, United States.
² Electron Microscopy Core, University of Missouri, Columbia, Missouri 65211, United States.
³ Department of Mechanical & Aerospace Engineering, University of Missouri, Columbia, Missouri 65211, United States.
⁴ Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, United States.
⁵ Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States.

Abstract

Atomic layer deposition (ALD) provides uniform and conformal thin films that are of interest for a range of applications. To better understand the properties of amorphous ALD films, we need an improved understanding of their local atomic structure. Previous work demonstrated measurement of how the local atomic structure of ALD-grown aluminum oxide (AlO _x ) evolves in operando during growth by employing synchrotron high-energy X-ray diffraction (HE-XRD). In this work, we report on efforts to employ electron diffraction pair distribution function (ePDF) measurements using more broadly available transmission electron microscope (TEM) instrumentation to study the atomic structure of amorphous ALD-AlO _x . We observe electron beam damage in the ALD-coated samples during ePDF at ambient temperature and successfully mitigate this beam damage using ePDF at cryogenic temperatures (cryo-ePDF). We employ cryo-ePDF and reverse Monte Carlo (RMC) modeling to obtain structural models of ALD-AlO _x coatings formed at a range of deposition temperatures from 150 to 332 °C. From these model structures, we derive structural metrics including stoichiometry, pair distances, and coordination environments in the ALD-AlO _x films as a function of deposition temperature. The structural variations we observe with growth temperature are consistent with temperature-dependent changes in the surface hydroxyl density on the growth surface. The sample preparation and cryo-ePDF procedures we report here can be used for the routine measurement of ALD-grown amorphous thin films to improve our understanding of the atomic structure of these materials, establish structure-property relationships, and help accelerate the timescale for the application of ALD to address technological needs.