Electron Compton scattering and the measurement of electron momentum distributions in solids

Abstract

Summary Electron Compton scattering is a technique that gives information on the electron momentum density of states and is used to characterize the ground state electronic structure in solids. Extracting the momentum density of states requires us to assume the so‐called ‘impulse approximation’, which is valid for large energy losses. Here, the robustness of the impulse approximation in the low energy transfer regime is tested and confirmed on amorphous carbon films. Compared to traditional Compton measurements, this provides additional benefits of more efficient data collection and a simplified way to probe valence electrons, which govern solid state bonding. However, a potential complication is the increased background from the plasmon signal. To overcome this, a novel plasmon background subtraction routine is proposed for samples that are resistant to beam damage. Lay Description Properties of solids depend on their electronic structure which can be studied using electron Compton scattering technique. Here, an electron beam is used to penetrate a very thin sample. During the interaction between the electrons in the beam and electrons in the sample, the former transfer a part of their energy to the latter, resulting in a measurable energy loss of the transmitted beam. The amount of the energy transfer depends on the angle of incidence between the beam and the sample. Typically, the experiments are carried out using high tilt angles and high energy transfer; however, in this work, we show that even smaller angles of incidence are suitable, which improve the signal quality and ease data processing procedures.

Towards Electron Energy Loss Compton Spectra Free From Dynamical Diffraction Artifacts

“…The q 4 factor is derived from the Compton scattering cross-section (Williams et al, 1987;Schattschneider et al, 1990). The Compton profile shape is given by J( p z ), where p z is the magnitude along the scattering vector q. p z can be converted to energy loss, ΔE, according to (Talmantaite et al 2020):…”

“…The Compton profile shape is given by J ( p z ), where p z is the magnitude along the scattering vector q . p z can be converted to energy loss, Δ E , according to (Talmantaite et al 2020):where T is the primary electron energy, m 0 c 2 is the rest mass energy of the electron, Δ E p is the Compton peak energy at p z = 0, and φ is the Compton scattering angle, which, at small angles, is related to the magnitude of the primary electron momentum p inc by . The above equations are derived within the impulse approximation.…”

“…A limited number of electron Compton measurements have been performed, such as on carbon-based materials (Williams et al, 1984; Exner et al, 1996; Feng et al, 2013, 2019; Talmantaite et al, 2020) and silicon (Jonas & Schattschneider, 1993; Exner & Schattschneider, 1996). Although the Compton intensity is comparable to phonon scattering in low atomic number solids (Eaglesham & Berger, 1994), its analysis using EELS has not been as widespread as X-ray and γ-ray photon-based methods.…”

“…However, this can now largely be mitigated by advances in instrumentation, such as EELS spectrometers with direct electron detection capability (Cheng et al, 2020; Plotkin-Swing et al, 2020) and/or low-kV microscopy performed below the knock-on damage threshold for specimens undergoing sputter damage (Krivanek et al, 2010). Talmantaite et al (2020) have also shown that accurate Compton data can be acquired from only a subset of the atomic electrons, e.g. the lower binding energy valence and semi-core electrons.…”

Characterization of some stone samples of archaeological interest via Compton profile analysis

“…Hence, obviously, over the years, there have been several theoretical and experimental Compton profile studies on materials such as elements [4,5], compounds [6], 1D and 2D materials [7,8], solids [9], ceramics [10,11], alkali metals [12] etc. It must also be noted here that in order to calculate the momentum distribution and hence to obtain the normalized Compton profiles usually one needs to know the composition of the sample of interest.…”