Determination and correction of distortions and systematic errors in low-energy electron diffraction

Abstract

We developed and implemented an algorithm to determine and correct systematic distortions in low-energy electron diffraction (LEED) images. The procedure is in principle independent of the design of the apparatus (spherical or planar phosphorescent screen vs. channeltron detector) and is therefore applicable to all device variants, known as conventional LEED, micro-channel plate LEED, and spot profile analysis LEED. The essential prerequisite is a calibration image of a sample with a well-known structure and a suitably high number of diffraction spots, e.g., a Si(111)-7×7 reconstructed surface. The algorithm provides a formalism which can be used to rectify all further measurements generated with the same device. In detail, one needs to distinguish between radial and asymmetric distortion. Additionally, it is necessary to know the primary energy of the electrons precisely to derive accurate lattice constants. Often, there will be a deviation between the true kinetic energy and the value set in the LEED control. Here, we introduce a method to determine this energy error more accurately than in previous studies. Following the correction of the systematic errors, a relative accuracy of better than 1% can be achieved for the determination of the lattice parameters of unknown samples.

Band Dispersion and Hole Effective Mass of Methylammonium Lead Iodide Perovskite

“…LEED patterns measured at three sample temperatures between 350 and 250 K are presented in Figure . All LEED images are distortion‐corrected, calibrated using LEEDCal and analyzed using LEEDLab (overlayed simulations) . The uniformity and sufficient quality of the crystal surfaces for ARUPS measurements were confirmed in advance by varying the sample position and beam‐energy of LEED (Figure S2, Supporting Information).…”

Adsorption heights and bonding strength of organic molecules on a Pb-Ag surface alloy

“…In order to determine the vertical positions of all chemically different species, we recorded core data for C 1s, N 1s, O 1s, Cu 2p, and Pb 4f . Using sophisticated fitting [37]. models for the C 1s and O 1s spectra, we were able to disentangle different contributions of chemically different atomic species of PTCDA as well as of structurally inequivalent PTCDA molecules.…”

“…1(a). All systematic distortions of the LEED data due to the flat screen of the microchannel plate (MCP) LEED optics were corrected by means of the software LEEDCAL [37].…”

Growth of coronene on (100)- and (111)-surfaces of fcc-crystals

“…The inherent distortions and systematic errors of the recorded diffraction images were corrected using the recently introduced commercially available software LEEDCal [17,18]. Following this procedure, the reciprocal space dimensions were calibrated with well-known Si(111)-(7 × 7) and commensurate PTCDA/Ag(111) superstructures as reference samples [19,20], yielding highly precise results for the unit cell parameters and epitaxial relations.…”