Advancing Time-Resolved Photoemission Electron Microscopy for Imaging Ultrafast Dynamics
(2025)- Abstract
- By combining ultrashort laser pulses with PEEM, time-resolved photoemission electron microscopy (TRPEEM) provides a powerful approach for investigating ultrafast charge carrier dynamics with simultaneous femtosecond temporal resolution and nanometer spatial precision. It has evolved into a versatile method
to study a wide range of phenomena, including charge carrier dynamics, surface plasmons, scattering by defects, and related processes in diverse material systems such as 2D materials, semiconductor nanowires, metals, and halide perovskites. Thus, TR-PEEM enables direct imaging of processes that are inaccessible to conventional optical or electrical measurement techniques.
In this thesis, we develop and implement advanced... (More) - By combining ultrashort laser pulses with PEEM, time-resolved photoemission electron microscopy (TRPEEM) provides a powerful approach for investigating ultrafast charge carrier dynamics with simultaneous femtosecond temporal resolution and nanometer spatial precision. It has evolved into a versatile method
to study a wide range of phenomena, including charge carrier dynamics, surface plasmons, scattering by defects, and related processes in diverse material systems such as 2D materials, semiconductor nanowires, metals, and halide perovskites. Thus, TR-PEEM enables direct imaging of processes that are inaccessible to conventional optical or electrical measurement techniques.
In this thesis, we develop and implement advanced TR-PEEM techniques to extend the capabilities of the method. These techniques are then applied to study semiconductor systems, including 2D materials, semiconductor nanostructures, and surfaces. In monolayer WS2, sub-100 fs formation of dark K–Λ excitons and subsequent picosecond decay dynamics were observed, revealing the interplay of intervalley scattering, defect states, and trion formation. A transient grating PEEM method was developed to directly image carrier diffusion, which was demonstrated in wurtzite InP platelets, allowing extraction of diffusion coefficients and mobilities with high spatiotemporal resolution. Finally, TR-PEEM combined with Fourier transform excitation spectroscopy enabled excitation-frequency–resolved studies, illustrated in a study of GaAs substrates and nanowires. The influence of excitation energy on the evolution of excited charge carriers is demonstrated, identifying contributions from defect states at sub-bandgap energies, and highlighting the role of surface-mediated dynamics in electron transport. (Less)
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https://lup.lub.lu.se/record/1bc88b6d-9f6e-424c-b999-7f62037a7298
- author
- Babu, Chandni LU
- supervisor
- opponent
-
- Professor Speller, Sylvia, Institute for Physics, University of Rostock, Germany
- organization
- publishing date
- 2025
- type
- Thesis
- publication status
- published
- subject
- keywords
- Photoemission Electron Microscopy (PEEM), Time-resolved PEEM, Ultrashort laser pulses, two-dimensional materials, Semiconductor nanowires, Excitons, charge carrier dynamics, Diffusion
- pages
- 148 pages
- publisher
- Lund University
- defense location
- Lecture hall KC:A
- defense date
- 2025-11-21 09:00:00
- ISBN
- 978-91-8096-126-4
- 978-91-8096-127-1
- language
- English
- LU publication?
- yes
- id
- 1bc88b6d-9f6e-424c-b999-7f62037a7298
- date added to LUP
- 2025-10-26 18:40:03
- date last changed
- 2025-10-28 09:39:22
@phdthesis{1bc88b6d-9f6e-424c-b999-7f62037a7298,
abstract = {{By combining ultrashort laser pulses with PEEM, time-resolved photoemission electron microscopy (TRPEEM) provides a powerful approach for investigating ultrafast charge carrier dynamics with simultaneous femtosecond temporal resolution and nanometer spatial precision. It has evolved into a versatile method<br/>to study a wide range of phenomena, including charge carrier dynamics, surface plasmons, scattering by defects, and related processes in diverse material systems such as 2D materials, semiconductor nanowires, metals, and halide perovskites. Thus, TR-PEEM enables direct imaging of processes that are inaccessible to conventional optical or electrical measurement techniques.<br/><br/>In this thesis, we develop and implement advanced TR-PEEM techniques to extend the capabilities of the method. These techniques are then applied to study semiconductor systems, including 2D materials, semiconductor nanostructures, and surfaces. In monolayer WS2, sub-100 fs formation of dark K–Λ excitons and subsequent picosecond decay dynamics were observed, revealing the interplay of intervalley scattering, defect states, and trion formation. A transient grating PEEM method was developed to directly image carrier diffusion, which was demonstrated in wurtzite InP platelets, allowing extraction of diffusion coefficients and mobilities with high spatiotemporal resolution. Finally, TR-PEEM combined with Fourier transform excitation spectroscopy enabled excitation-frequency–resolved studies, illustrated in a study of GaAs substrates and nanowires. The influence of excitation energy on the evolution of excited charge carriers is demonstrated, identifying contributions from defect states at sub-bandgap energies, and highlighting the role of surface-mediated dynamics in electron transport.}},
author = {{Babu, Chandni}},
isbn = {{978-91-8096-126-4}},
keywords = {{Photoemission Electron Microscopy (PEEM); Time-resolved PEEM; Ultrashort laser pulses; two-dimensional materials; Semiconductor nanowires; Excitons; charge carrier dynamics; Diffusion}},
language = {{eng}},
publisher = {{Lund University}},
school = {{Lund University}},
title = {{Advancing Time-Resolved Photoemission Electron Microscopy for Imaging Ultrafast Dynamics}},
year = {{2025}},
}