Study of Graphene by Scanning Low Energy Electron Microscopy and Time-of-Flight Spectroscopy

0575427 - ÚPT 2024 RIV GB eng A - Abstract
Müllerová, Ilona - Konvalina, Ivo - Zouhar, Martin - Paták, Aleš - Daniel, Benjamin - Průcha, Lukáš - Piňos, Jakub - Materna Mikmeková, Eliška
Study of Graphene by Scanning Low Energy Electron Microscopy and Time-of-Flight Spectroscopy.
Microscopy and Microanalysis. Cambridge University Press. Roč. 29, S1 (2023), s. 1861-1862. ISSN 1431-9276. E-ISSN 1435-8115.
[Microscopy & Microanalysis 2023. 23.07.2023-27.07.2023, Minneapolis]
R&D Projects: GA ČR(CZ) GA22-34286S
Grant - others:AV ČR(CZ) StrategieAV21/26
Program: StrategieAV
Institutional support: RVO:68081731
Keywords : scanning low energy electron microscopy (SLEEM) * time-of-flight spectroscopy * graphene
OECD category: Electrical and electronic engineering
https://academic.oup.com/mam/article/29/Supplement_1/1861/7229038

Müllerová, I., Konvalina, I., Zouhar, M., Paták, A., Daniel, B., Průcha, L., Piňos, J., Materna Mikmeková, E. Study of Graphene by Scanning Low Energy Electron Microscopy and Time-of-Flight Spectroscopy. Microscopy and Microanalysis. 2023, 29, S1, 1861-1862. ISSN 1431-9276. E-ISSN 1435-8115. The scanning low energy electron microscopy (SLEEM) and the time-of-flight (ToF) spectroscopy are appropriate methods to study advanced 2D materials and thin foils. There has been rapid progress in the technological development of advanced 2D materials in recent years. This places high demands on analytical techniques for study and analysis of such materials. Theoretical and experimental studies of low energy electron transport near solid surfaces are important for surface sensitive electron spectroscopy and microscopy. In particular, it is necessary to have reliable knowledge of electron transport in the sample and across its interface in order to obtain quantitative information. For our experiments, we use the Ultra High Vacuum (UHV) SLEEM, equipped with a ToF spectrometer that was developed at our institute. It is a unique device that operates in transmission mode. We performed several experiments for monolayer, bilayer and multilayer graphene commercial samples to obtain electron energy-loss spectra (EELS). The experimental data are displayed in Fig. 1 with the zero-loss peak (ZLP) region not displayed in the EELS spectra. Both plasmons peaks are present, the π-plasmon is more pronounced and we see that its position shifts to higher losses with increasing number of layers. This dispersion is less obvious between the 2-layer and few-layer graphene, partially due to the peak of the latter being too close to the ZLP. Let us note that position of these plasmon peaks is also sensitive to the collected momentum transfer (MT). Fig. 2 shows simulated momentum-resolved EELS spectra using many-body perturbation theory (MBPT), Yambo code, on top of the density-functional theory, Quantum Espresso. We employ MBPT with random-phase approximation using Hartree kernel (details with the related parameters will be published elsewhere). A real experiment uses a primary electron beam with a possible slight divergence and finite size of aperture, meaning we collect an interval of MT, corresponding to an interval of polar angle θ. This means that typical measured EELS are a weighted sum over different values of MT. Any comparison with simulations has to take said properties of the electron microscope into account, even in the case of normal incidence. This alone is a strong motivation to calculate momentum-resolved EELS instead of the “single” point in the reciprocal space. Nevertheless, the simulated EELS for a single value of MT in Fig. 2 show that the π-plasmon peak shifts to higher losses with increasing layer count. We expect this dispersion will be preserved even after the aforementioned weighted sum not performed here. The experimental EELS data will be used to derive inelastic mean free path (IMFP) values using the so-called log-ratio method already successfully applied to our earlier monolayer EELS. IMFP is widely used for the quantification of electron microscopic and spectroscopic data, for example for image contrast interpretation, film thickness determination, and chemical composition analysis. The IMFP depends on the kinetic energy of the electrons.
Permanent Link: https://hdl.handle.net/11104/0345212