A high-energy electron scattering study of the electronic structure and elemental composition of O-implanted Ta films used for the fabrication of memristor devices

Abstract

High-energy electron scattering is used to investigate Ta films implanted with 10 keV O ions. These films are of interest as they have been used for the fabrication of memristors. High-energy electron scattering is used with incoming electron energies ranging from 5 to 40 keV. The inelastic mean free path, and hence the probing depth, is at these energies of the same order as the range of the implanted ions. At the same time, we can distinguish the mass of the atom that scattered the electron elastically, due to the dependence of the recoil energy on the mass of the scatterer. This allows us to determine quantitatively the atomic composition near the surface from the signal of electrons that have scattered elastically but not inelastically. Electrons that have scattered inelastically as well as elastically provide us with information on the possible electronic excitations. Their signal is used to monitor the presence of the Ta 2 O 5 phase near the surface (characterised by a significant band gap of ' 4:5 eV), and estimate at what depth below the surface pure Ta metal is present. In this way, we obtain a fairly detailed picture of the elemental composition and electronic properties of these films.

Advanced techniques for characterization of ion beam modified materials

“…One example of an eRBS application is a study of the electronic structure and elemental composition of O-implanted Ta films [33] used for the fabrication of memristor devices [35]. Memristors based on tantalum oxides rely on the facts that Ta 2 O 5 is highly resistive due to its large band gap ($4.5 eV), and sub-stoichiometric tantalum oxides are much more conductive due to much smaller or no band gaps.…”

“…A recently developed technique, electron Rutherford backscattering spectrometry [32][33][34], has demonstrated its analytical power that is complementary to other surface analysis techniques, including RBS, medium energy ion scattering (MEIS), X-ray photoemission spectroscopy (XPS), and secondary ion mass spectrometry (SIMS).…”

“…Uranium dioxide (UO 2 ) is currently the standard fuel used in light water reactors, and its response to ion Detailed scattering geometry and data analysis can be found in Ref. [33]. irradiation is of great interest for the nuclear industry.…”

“…The eRBS technique, based on high-energy (from 5 to 40 keV) electron scattering, can be used to probe depth profile of a sample surface region from very thin (a few nm) to relative thick layers (a few tens of nm, depending on the incoming energy and geometry), and provide information on the electronic structure of the layer [32,33]. The main features of the eRBS technique are the use of elastic cross-sections and kinematic factors as in RBS and inelastic electron mean free paths (IMFP) as in photoemission.…”

“…Memristors based on tantalum oxides rely on the facts that Ta 2 O 5 is highly resistive due to its large band gap ($4.5 eV), and sub-stoichiometric tantalum oxides are much more conductive due to much smaller or no band gaps. eRBS with electron energies ranging from 5 to 40 keV was utilized to investigate Ta films implanted with 10 keV O ions to different ion fluences [33]. The inelastic mean free path and hence the probing depth at these electron energies are of the same order as the range of the implanted ions.…”