Mapping the excited-state bands above the vacuum level with VLEED: principles, results for Cu, and the connection to photoemission

Abstract

Experimental photoelectron spectra are usually interpreted using rather crude approximations for the upper states into which the electrons are excited. Better knowledge about these excited states could substantially improve the accuracy of valence band mapping by photoelectron spectroscopy. We here demonstrate that VLEED measurements are ideally suited for accurate determination of the desired upper states. This is illustrated by model calculations including absorption and self-energy corrections. The close correspondence between so-called irregularity points of the excited-state bands and the total electron reflectivity is established, which opens up the possibility for direct mapping of irregularity points by comparison with experimental VLEED spectra, and for fitting of the whole excited-state bands between these points. The proposed scheme is finally used to determine the excited-state bands of Cu along L from measurements on Cu(111).

Elastic scattering effects in the electron mean free path in a graphite overlayer studied by photoelectron spectroscopy and LEED

“…3 Although in this case the k ͑r͒ interference in ⌽͑r͒ means that the total T is not exactly equal to the sum of the individual T k , these figures well characterize the relative contributions of the Bloch wave constituents to the total current transmitted by the LEED state.…”

“…Its strength is expressed by a finite electron lifetime or, phenomenologically, by the imaginary part V i = ប /2 of the optical potential describing the electron absorption. 2,3 The inelastic scattering results in an energy dependence of , which is described by the well-known "universal curve" having a broad minimum around 50-100 eV. 1,4 This dependence is fairly similar for many materials.…”

High-resolution angle-resolved photoemission spectra from Ni(100): Matrix element effects and spin-resolved initial and final state bands

“…40 which are based on an analysis of the low-energy electrondiffraction data from Ni suggest ⌺ f ЉϷ3 eV. Other studies 34,[41][42][43] in Cu, including a recent one-step computation of ARPES spectra for emission from the E F in Cu͑100͒, 44 indicate smaller ⌺ f Љ values ranging from 1.8 eV to 3 eV. In this connection, we have carried out extensive simulations using different values of ⌺ f Љ .…”

Matrix element effects in angle-resolved photoemission fromBi2Sr2CaCu<

“…3. [42,43]. Incidentally, computations become more demanding as the value of Σ ′′ f decreases because the mean free path of the outgoing electron increases and an exponentially larger number of layers must be included in the calculations to obtain a converged result.…”