Berlin 2024 – scientific programme

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DS: Fachverband Dünne Schichten

DS 6: Thin Film Properties I

DS 6.8: Talk

Tuesday, March 19, 2024, 12:00–12:15, A 060

Determination of Material Compositions from Strain Measurements in Scanning Transmission Electron Microscopy — •Frederik Otto, Laura Niermann, Tore Niermann, and Michael Lehmann — Technische Universität Berlin, Germany

Scanning Transmission Electron Microscopy (STEM) offers atomic-scale resolution for strain analysis by scanning a focused electron probe across a sample and evaluating the spacing between Bragg discs of the resulting electron diffraction patterns at each beam position. These Bragg discs contain features of multiple electron scattering, manifesting as patterns within the diffraction disc. While these patterns contain 3D scattering information, they can compromise the precise detection of diffraction discs’ positions. To address this, a common strategy for achieving high-precision strain measurements involves utilizing a precessing electron beam, effectively averaging over multiple patterns.

In this study, rather than disregarding the effects of multiple electron scattering, we focus on carefully evaluating variations in the patterns. A comparative analysis of measured diffraction discs and simulations reveal that these variations originate from deformations appearing at the TEM lamella’s surface. These deformations arise as a consequence of stress relaxation in a strained sample during the preparation process. Therefore, this effect is indicative of the strain in the sample (here: the (Al,Ga)N/GaN interface) and thus provides insights into the material’s composition. Consequently, we demonstrate a novel method for deducing the composition of layered structures through a single STEM measurement of the strain at the interfaces.

Keywords: Strain; (Scanning) Transmission Electron Microscopy; Composition Determination; Electron Diffraction; Heterointerfaces