Electron sampling depth and saturation effects in perovskite films investigated by soft x-ray absorption spectroscopy

Abstract

Knowledge of the electron sampling depth and related saturation effects is important for quantitative analysis of X-ray absorption spectroscopy data, yet for oxides with the perovskite structure no quantitative values are so far available. Here we study absorption saturation in films of two of the moststudied perovskites, La 0.7 Ca 0.3 MnO 3 (LCMO) and YBa 2 Cu 3 O 7 (YBCO), at the L 2,3 edge of Mn and Cu, respectively. By measuring the electron-yield intensity as a function of photon incidence angle and film thickness, the sampling depth d, photon attenuation length λ and the ratio λ/d have been independently determined between 50 and 300 K. The extracted sampling depth d LCMO ≈ 3 nm for LCMO at high temperatures in its polaronic insulator state (150 -300 K) is not much larger than values reported for pure transition metals (d Co or Ni ≈ 2 -2.5 nm) at room temperature, but is smaller than d YBCO ≈ 3.9 nm for metallic YBCO that is in turn smaller than the value reported for Fe 3 O 4 (d Fe3O4 ≈ 4.5 nm). The measured d LCMO increases to 4.5 nm when LCMO is in the metallic state at low temperatures. These results indicate that a universal rule of thumb for the sampling depth in oxides cannot be assumed, and that it can be measurably influenced by electronic phase transitions that derive from strong correlations.

Universal electronic structure of polar oxide hetero-interfaces

“…For the highest values of the retarding potentials employed in this experiment, the PEY probing depth approaches the photoemission inelastic mean free path (IMFP = 1.1 nm at hν  = 450 eV). In TEY, the probing depth is larger (≃3–4 nm)3940. The LaAlO 3 /SrTiO 3 difference spectra in Fig.…”

Formation of ultrathin cobalt ferrite films by interdiffusion ofFe3O4/CoObilayers

“…For this purpose the x-ray energy of the incoming beam was tuned in the soft x-ray regime over the Fe and Co L 2,3 edges (700-740 eV and 770-810 eV, respectively). The absorption signal was detected in surface-sensitive total electron yield (TEY) mode, which provides probing depths of 2-5 nm in transition metal oxides [24][25][26]. All presented XAS measurements have been normalized to the current from an Au-coated mesh in the incident x-ray beam.…”

Site-mixing effect on the XMCD spectrum in double perovskite Bi2FeMnO6

“…1(c)), and can cause core-level shifts which affect the X-ray absorption spectra (XAS). Since the attenuation length of the total electron yield (TEY) signal in insulating perovskite oxides is usually not more than a few nanometers, 6 the XMCD signal we measured is dominated by the bulk-like BFMO phase near the surface of the sample. Our experimentally observed XMCD signals are thus coming from the bulk-like layers in thin film BFMO, and the oscillating W-shaped peak features can be understood by considering a very simple site-mixing scenario.…”