Speaker
Description
A huge disadvantage of conventional electron energy-loss spectroscopy (EELS) is the low scattering probability. Most of the electrons do not interact with the sample and contribute to the zero-loss peak, which is several orders of magnitude larger than the signal of interest. This is particularly limiting when probing samples that are sensitive to electron irradiation. . In contrast, when electrons interact with the near field of a nanostructure excited with a sufficiently intense laser pulse, the zero-loss peak can be strongly reduced or even completely depleted. This signal enhancement is used in a technique called electron energy-gain spectroscopy (EEGS) [1–3], where a series of electron spectra at a given positions aquired for different wavelengths of the exciting laser pulses. When the laser pulse energy approaches an optical resonance frequency of the sample, the scattering signal is increased. One can then construct the EEGS spectrum by calculating the scattering intensity integrated over a certain energy gain range as a function of the light frequency. As has been predicted theoretically [1–2] and demonstrated experimentally [3], EEGS allows us to probe a sample with a high combined energy-spatial resolution compared to EELS.
Here, we envision to further decrease the electron dose required to characterize the optical resonance by exciting the sample with a broadband laser pulse. The proposed technique that we call broadband electron energy-gain spectroscopy (BEEGS) involves the detection of a single electron energy spectrum. To demonstrate the feasibility of BEEGS for realistic experimental parameters, we first study a semianalytical model, in which we model the sample with a Lorentzian polarizability associated with purely dipolar response. We show that with a suitably chosen optical pulse intensity, more than 15 % of the electrons contribute to the signal. Thus, BEEGS allows us to obtain a much more intense spectral signal than conventional electron spectroscopies, increasing the amount of information retrieved from the sample for a fixed electron dose. We support this conclusion through an analysis of the spectral information retrieved per electron in different electron-based techniques.
References
[1] F.J. García de Abajo and M. Kociak, New J. Phys. 10, 073035, (2008).
[2] A. Asenjo-Garcia and F.J. García de Abajo, New J. Phys. 15, 103021, (2013).
[3] Y.Auad et. al., Nat. Com. 14, 4442, (2023)
Acknowledgements
This project has received funding from the European Union’s Horizon Europe research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 101081441.