Dark-field transmission electron microscopy (DF-TEM) images a sample using only electrons diffracted into a chosen Bragg reflection, selected by an aperture in the diffraction plane. For bilayers it provides direct, large-area maps of stacking domains and domain walls with nanometre resolution [1; 2].
How it distinguishes domains. For Bernal bilayer graphene, the first-order $\{10\bar10\}$ reflections have intensities that differ between AB and BA when the sample is tilted, so AB and BA appear light and dark. Second-order $\{2\bar1\bar10\}$ reflections are insensitive to AB vs BA but darken where the stacking deviates — at walls — and each of the three reflections highlights walls with a particular Burgers-vector direction (the wall is invisible when $\mathbf g\cdot\Delta\mathbf u=0$ modulo $2\pi$) [1, Fig. 1c-d].
What it revealed. Triangular networks of AB/BA domains in CVD bilayer graphene, the shear/tensile character of walls, topological nodes, and — through in-situ heating to 1000–1200 °C and beam exposure — soliton motion, straightening and pairwise annihilation [1, Fig. 4].
Successors. DF-TEM of twisted bilayers established the angle-dependent reconstruction crossover [3]; atomic-resolution STEM resolves wall structure; 4D-STEM Bragg interferometry quantifies local stacking, rotation and strain [4; 5]. Complementary probes include conductive and piezoresponse AFM [6] and STM.
Limits. Contrast is influenced by out-of-plane corrugation and by additional layers; samples must be suspended and electron-transparent, and high beam doses can move walls.
Also known as: DF-TEM, dark-field electron microscopy
References
Alden et al. (2013). Strain solitons and topological defects in bilayer graphene. PNAS 110, 11256. https://arxiv.org/abs/1304.7549
Yoo et al. (2019). Atomic and electronic reconstruction at the van der Waals interface in twisted bilayer graphene. Nat. Mater. 18, 448. https://arxiv.org/abs/1804.03806
Van Winkle et al. (2023). Rotational and dilational reconstruction in transition metal dichalcogenide moiré bilayers. Nat. Commun. 14, 2989. https://arxiv.org/abs/2212.07006
Explanation-DAG node dftem · from: alden2013, yoo2019, weston2022 · Alden et al. 2013, Methods; Article copied from v05_woods2014 (dftem); Article copied from v18_wang2022fe (dftem)
**Dark-field transmission electron microscopy (DF-TEM)** images a sample using only electrons diffracted into a chosen Bragg reflection, selected by an aperture in the diffraction plane. For bilayers it provides direct, large-area maps of stacking domains and domain walls with nanometre resolution [1; 2].
*How it distinguishes domains.* For Bernal bilayer graphene, the first-order $\{10\bar10\}$ reflections have intensities that differ between AB and BA when the sample is tilted, so AB and BA appear light and dark. Second-order $\{2\bar1\bar10\}$ reflections are insensitive to AB vs BA but darken where the stacking deviates — at walls — and each of the three reflections highlights walls with a particular Burgers-vector direction (the wall is invisible when $\mathbf g\cdot\Delta\mathbf u=0$ modulo $2\pi$) [1, Fig. 1c-d].
*What it revealed.* Triangular networks of AB/BA domains in CVD bilayer graphene, the shear/tensile character of walls, topological nodes, and — through in-situ heating to 1000–1200 °C and beam exposure — soliton motion, straightening and pairwise annihilation [1, Fig. 4].
*Successors.* DF-TEM of twisted bilayers established the angle-dependent reconstruction crossover [3]; atomic-resolution STEM resolves wall structure; 4D-STEM Bragg interferometry quantifies local stacking, rotation and strain [4; 5]. Complementary probes include conductive and piezoresponse AFM [6] and STM.
*Limits.* Contrast is influenced by out-of-plane corrugation and by additional layers; samples must be suspended and electron-transparent, and high beam doses can move walls.
**Also known as:** DF-TEM, dark-field electron microscopy
**References**
1. Alden et al. (2013). *Strain solitons and topological defects in bilayer graphene*. PNAS 110, 11256. [https://arxiv.org/abs/1304.7549](https://arxiv.org/abs/1304.7549)
2. Brown et al. (2012). *Twinning and twisting of tri- and bilayer graphene*. Nano Lett. 12, 1609. [https://doi.org/10.1021/nl204547v](https://doi.org/10.1021/nl204547v)
3. Yoo et al. (2019). *Atomic and electronic reconstruction at the van der Waals interface in twisted bilayer graphene*. Nat. Mater. 18, 448. [https://arxiv.org/abs/1804.03806](https://arxiv.org/abs/1804.03806)
4. Kazmierczak et al. (2021). *Strain fields in twisted bilayer graphene*. Nat. Mater. 20, 956. [https://arxiv.org/abs/2008.09761](https://arxiv.org/abs/2008.09761)
5. Van Winkle et al. (2023). *Rotational and dilational reconstruction in transition metal dichalcogenide moiré bilayers*. Nat. Commun. 14, 2989. [https://arxiv.org/abs/2212.07006](https://arxiv.org/abs/2212.07006)
6. McGilly et al. (2020). *Visualization of moiré superlattices*. Nat. Nanotechnol. 15, 580. [https://doi.org/10.1038/s41565-020-0708-3](https://doi.org/10.1038/s41565-020-0708-3)
<sub>Explanation-DAG node `dftem` · from: alden2013, yoo2019, weston2022 · Alden et al. 2013, Methods; Article copied from v05_woods2014 (dftem); Article copied from v18_wang2022fe (dftem)</sub>
