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Spatiotemporal Microscopy

Spatiotemporal Microscopy (SPTM) is an ultrafast pump–probe microscopy technique that directly images the diffusion of energy, charge, excitons, and heat through a material with femtosecond temporal resolution and sub-micron spatial accuracy. The setup scans a probe pulse over a fixed pump pulse in both time and space; the resulting space–time map of transient reflectivity (or photoluminescence) is a direct measurement of how excitations spread, with no need for assumed material parameters. The Tielrooij group at TU/e Applied Physics develops and operates several custom-built SPTM setups specialised for thin films, 2D materials, and nanoribbons.

Capabilities

  • Heat diffusion in opaque thin films via pre-time-zero transient reflectivity — uses the ~13 ns gap between successive pump pulses (76 MHz repetition rate) to access slow thermal diffusion without a long delay stage. Demonstrated on ~15 nm TMD films (MoSe₂, WSe₂, MoS₂, WS₂), giving in-plane thermal diffusivities of order 0.2–0.6 cm²/s.
  • Charge and exciton diffusion with femtosecond resolution. Typical pump: visible (~600 nm), ~150 fs, sub-µm spot. Charge mobilities up to several hundred cm² V⁻¹ s⁻¹ have been resolved on 1D systems such as graphene nanoribbons.
  • Transient and negative diffusion of carriers in 2D semiconductors — measured in suspended MoSe₂ from monolayer to multilayer.
  • Quantitative diffusivity extraction without requiring thermal-conductivity input or strong heating.
  • Sample classes: 2D materials (graphene, TMDs), graphene nanoribbons, semiconductors, perovskites, layered heterostructures, and other thin films.

What makes it distinctive

Unlike commercial pump–probe systems and time-resolved photoluminescence, SPTM resolves transport in space and time simultaneously rather than at a single point. The pre-time-zero variant accesses nanosecond-scale heat dynamics with no mechanical delay-line extension, and the same setup can separate fast electronic transport from slow phononic heat in the same sample, or distinguish charge from exciton diffusion in the same time series.

Status

Operational. The SPTM setups are hosted and managed by the group of Klaas-Jan Tielrooij (Applied Physics, TU/e). Access and project scoping go through Klaas-Jan and his team.

Key references

  • Tutorial review — G. D. Brinatti Vazquez, G. Lo Gerfo Morganti, A. Block, N. F. van Hulst, M. Liebel, K.-J. Tielrooij. Spatiotemporal Microscopy: Shining Light on Transport Phenomena. Adv. Electron. Mater. 10, 2300584 (2024). https://doi.org/10.1002/aelm.202300584
  • Heat-diffusion setup (pre-time-zero) — S. Varghese et al. A pre-time-zero spatiotemporal microscopy technique for the ultrasensitive determination of the thermal diffusivity of thin films. Rev. Sci. Instrum. 94, 034903 (2023). https://doi.org/10.1063/5.0142623
  • Charge / exciton diffusion in graphene nanoribbons — S. Varghese et al. Ultrafast Charge and Exciton Diffusion in Monolayer Films of 9-Armchair Graphene Nanoribbons. Adv. Mater. 2407796 (2024). https://doi.org/10.1002/adma.202407796
  • Transient and negative diffusion in MoSe₂ — G. Lo Gerfo Morganti et al. Transient ultrafast and negative diffusion of charge carriers in suspended MoSe₂ from multilayer to monolayer. Nat. Commun. 16, 5184 (2025). https://doi.org/10.1038/s41467-025-60197-3