Aim

To develop techniques for SEM-based characterization and 3D visualisation of high-frequency (sub)nanoscale motion of micro-/nanostructures, to improve understanding of the physics, functionality and engineering of advanced material/device structures (e.g. opto-mechanical metamaterials, MEMS, etc.)

Details

Electron microscopy, scanning probe, and optical super-resolution imaging techniques routinely provide nanometric resolution but cannot capture the characteristically fast (MHz−GHz frequency) movements of micro-/nano-objects. Meanwhile, optical interferometric techniques can detect high-frequency picometric displacements but typically with diffraction-limited lateral (image plane) resolution. Such movements are of growing technological importance and scientific interest, in contexts including micro- and nanoelectromechanical systems (M/NEMS), and advanced materials; and in fundamental studies of dynamics, including cooperative and self-organizational effects, thermal (Brownian) motion, van der Waals and Casimir forces.

We are developing motion visualization techniques based on the spectrally resolved detection of secondary electron emission and electron-induced light emission from moving nano-objects, which combine picometric displacement sensitivity with the nanometric spatial (positional/imaging) resolution of electron microscopy. This technique has enabled the first observation of short–time scale phonon-driven ballistic thermal motion in the flexural mode of a nano-cantilever.

In recent work, we have observed and characterized electron beam-induced frequency tuning of nanomechanical oscillators – changes in effective spring constant dependent on charge at sub-nanocoulomb levels – which may be exploited in a variety of non-contact particle beam sensing applications.

References

[1] T. Thomas, et al., “Control of nanomechanical resonances by an electron beam,” arXiv:2509.10302 (2025). doi: 10.48550/arXiv.2509.10302

[2] [Invited] MacDonald, et al., “Hyperspectral visualization of picometric motion,” Microscopy Conference 2023 (Darmstadt, Germany, 2023).

[3] Liu, et al., “Ballistic dynamics of flexural thermal movements in a nanomembrane revealed with subatomic resolution,” Sci. Adv. 8 (33), eabn8007 (2022). doi: 10.1126/sciadv.abn8007

[4] Liu, et al., “Visualization of Sub-atomic Movements in Nanostructures,” Nano Lett. 21(18), 7746-7752 (2021). doi: 10.1021/acs.nanolett.1c02644