Characterization of the native Cr2O3 oxide surface of CrO2

Abstract

Using photoemission and inverse photoemission, we have been able to characterize the Cr2O3 oxide surface of CrO2 thin films. The Cr2O3 surface oxide exhibits a band gap of about 3 eV, although the bulk CrO2 is conducting. The thickness of this insulating Cr2O3 layer is twice the photoelectron escape depth which is about 2 nm thick. The effective Cr2O3 surface layer Debye temperature, describing motion normal to the surface, is about 370 K. From a comparison of CrO2 films grown by different techniques, with different Cr2O3 content, evidence is provided that the CrO2 may polarize the Cr2O3.

Double Percolation Transition in Superconductor-Ferromagnet Nanocomposites

“…2. In the inset we show the resistance of the samples prepared in the same fashion from pure MgB 2 (which has a superconducting transition of around 37 K), and pure CrO 2 whose resistance is fairly ‡at except for the lowest temperatures, where the activation type behavior is observed, due to the presence of a nm thick Cr 2 O 3 insulating layer at the surface of CrO 2 [18] . The resistance of the composite samples is low for pure ate composition range 0:35 < x < 0:5, with the low-temperature peak value of the resistance about three orders of magnitude higher than that of pure CrO 2 sample.…”

Oxidation of metals at the chromium oxide interface

“…For a clean Cr 2 O 3 /CrO 2 surface ͑zero monolayers Co coverage͒, the spectrum is the typical Cr 2 O 3 /CrO 2 valence-band spectrum. 5,18 With increasing Co coverage, the bands at 4 to 8 eV from Cr-O 2p hybridization bands, and the band at 2 eV binding energy dominated by the Cr 3d orbitals, are suppressed while a strong feature at about 1 eV becomes very prominent and the density of states at Fermi energy is increasingly well established. At Co coverages above 15 ML, the overlapping Co 3d bands around 1 eV binding energy are dominant and show the sharp Fermi edge characteristic of a metal.…”

“…5,18,20 From the outset, i.e., from the initial stages of surface preparation, the core-level binding energies indicated that the stable surfaces were Cr 2 O 3 . X-ray photoemission ͑XPS͒ measurements were obtained using the Mg K␣ line radiation ͑1253.6 eV͒.…”

“…Before Co growth, the binding energy of Cr 2p 3/2 is 576.3Ϯ0.2 eV but with a large FWHM, indicative of a thin layer of Cr 2 O 3 residing ontop of CrO 2 . 18 After deposition of the equivalent of 3 monolayers ͑ML͒ of Co, the Cr 2p 3 23 and the binding energy of the accompanying shoulder is 136.7 Ϯ0.2 eV, which is the core-level binding energy expected for metallic Pb. 24 Evidence of CoO formation at the Co/Cr 2 O 3 interface, for CrO 2 epitaxial samples, is found after the deposition of 3 monolayer Co.…”

“…17 The insulator ''I'' in their junctions was also fabricated by oxidation of a Cr film, and the anomaly attributed to the presence of magnetic CrO 2 and Cr 2 O 3 . Angle-resolved x-ray photoemission ͑ARXPS͒ investigations of these films, 18 allowed us to differentiate between CrO 2 and Cr 2 O 3 . We find a mixture of these two oxides, being phase separated after longer annealing times, and becoming a superposition of CrO 2 and Cr 2 O 3 thin films after even longer annealing.…”