Space Charge and Statistical Coulomb Effects

Kruit, P.; Jansen, G. H.

doi:10.1201/9781420045550-7

Cited by 12 publications

(9 citation statements)

References 49 publications

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“…The excess electric charge due to electrons and ions dispersed in vacuum (or in a dielectric where screening processes are prevented) is known as space charge and the results of the mutual interactions among particles are denoted space-charge effects. These effects must be taken in very careful account in designing devices operating with electron beams like cathode tubes, electron guns and electron microscopes [34]. The most usual effect of the mutual interaction of electrons in vacuum is the reduction of the thermionic and photoemission currents known as the space-charge limit (SCL), which is fundamental in the operation of the vacuum tubes [35].…”

Section: Introductionmentioning

confidence: 99%

Space-charge effects in high-energy photoemission

Verna

Greco

Lollobrigida

et al. 2016

Journal of Electron Spectroscopy and Related Phenomena

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Pump-and-probe photoelectron spectroscopy (PES) with femtosecond pulsed sources opens new perspectives in the investigation of the ultrafast dynamics of physical and chemical processes at the surfaces and interfaces of solids. Nevertheless, for very intense photon pulses a large number of photoelectrons are simultaneously emitted and their mutual Coulomb repulsion is sufficiently strong to significantly modify their trajectory and kinetic energy. This phenomenon, referred as space-charge effect, determines a broadening and shift in energy for the typical PES structures and a dramatic loss of energy resolution. In this article we examine the effects of space charge in PES with a particular focus on time-resolved hard X-ray (∼10 keV) experiments. The trajectory of the electrons photoemitted from pure Cu in a hard X-ray PES experiment has been reproduced through N-body simulations and the broadening of the photoemission core-level peaks has been monitored as a function of various parameters (photons per pulse, linear dimension of the photon spot, photon energy). The energy broadening results directly proportional to the number N of electrons emitted per pulse (mainly represented by secondary electrons) and inversely proportional to the linear dimension a of the photon spot on the sample surface, in agreement with the literature data about ultraviolet and soft X-ray experiments. The evolution in time of the energy broadening during the flight of the photoelectrons is also studied. Despite its detrimental consequences on the energy spectra, we found that space charge has negligible effects on the momentum distribution of photoelectrons and a momentum broadening is not expected to affect angle-resolved experiments. Strategy to reduce the energy broadening and the feasibility of hard X-ray PES experiments at the new free-electron laser facilities are discussed

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Section: Introductionmentioning

confidence: 99%

Space-charge effects in high-energy photoemission

Verna

Greco

Lollobrigida

et al. 2016

Journal of Electron Spectroscopy and Related Phenomena

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“…Typically these approximations yield a simple algebraic dependence on experimental parameters such as beam energy, system length, beam current, and numerical aper ture. The reader is referred to two excellent reviews by Kruit and Jansen [55] and by Jansen [49] for details.…”

Section: Analytical Approximation By Markov's Methods Of Random Flightsmentioning

confidence: 99%

Charged Particle Optics Theory

Groves¹

2017

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Cover picture: A monatomically thick graphene layer, viewed in a Nion UltraSTEM200 aberration-corrected scanning transmission electron microscope (STEM) located at the Oak Ridge National Laboratory. The microscope was operated at 60 KV in annular dark field (ADF) mode. The red regions represent individual carbon atoms with nearest-neighbor spacing of 0.14 nm. The red regions represent the highest scattered intensity, and the blue regions represent the lowest scattered intensity. The image is a sum of intensities of 350 separate areas of a single graphene specimen, each having 128×128 pixels. Each individual scan is translated so as to maximize the cross-correlation function between separate scans. This greatly reduces noise in the composite image. The original image and specimen were prepared by Dr. Florence Nelson, and the correlation analysis was performed by Jennifer Passage.

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“…The space-charge effect is reduced at higher electron energy levels because the electrostatic repulsion is largely compensated for by magnetic attraction of the moving electrons. Ideally, the space charge can be compensated by refocusing (Kruit & Jansen, 1997), but solenoid focusing appears to be limited to several μm for 2.5-MeV electrons. If negligible damage occurs within 100 fs and if 10 electrons must be diffracted from a single particle of diameter d ¼ 10 nm, then 10 ¼ (d/D) 2 (10 5 )(d/λ e ) and the beam diameter D needs to be no more than 100 nm.…”

Section: Dose-limited Resolutionmentioning

confidence: 99%