Electronic excitations of α- Fe2 O3 heteroepitaxial films measured by resonant inelastic x-ray scattering at the Fe L edge

Journal Article · 31 January 2022 · Physical Review. B

DOI: https://doi.org/10.1103/physrevb.105.075101 · OSTI ID:1855216

Ellis, David S.  ^[1]; Wang, Ru-Pan  ^[2]; Wong, Deniz  ^[3]; Cooper, Jason K.  ^[4]; Schulz, Christian  ^[3]; Chuang, Yi-De  ^[4]; Piekner, Yifat  ^[1]; Grave, Daniel A.  ^[5]; Schleuning, Markus  ^[6]; Friedrich, Dennis  ^[6]; de Groot, Frank F.  ^[7]; Rothschild, Avner  ^[1]

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1. Technion-Israel Inst. of Technology, Haifa (Israel)
2. Univ. of Hamburg (Germany)
3. Helmholtz-Zentrum Berlin für Materialen und Energie, Berlin (Germany)
4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
5. Technion-Israel Inst. of Technology, Haifa (Israel); Ben Gurion Univ. of the Negev, Be'er Sheva (Israel)
6. Ben Gurion Univ. of the Negev, Be'er Sheva (Israel)
7. Utrecht Univ. (Netherlands)

Resonant inelastic x-ray scattering (RIXS) spectra of hematite (α-Fe₂O₃) were measured at the Fe L₃ edge for heteroepitaxial thin films which were undoped and doped with 1% Ti, Sn, or Zn, in the energy-loss range in excess of 1 eV to study electronic transitions. The spectra were measured for several momentum transfers q, conducted at both low temperature (T=14 K) and room temperature. While we cannot rule out dispersive features possibly owing to propagating excitations, the coarse envelopes of the general spectra did not appreciably change shape with q, implying that the bulk of the observed L-edge RIXS intensity originates from (mostly) nondispersive ligand field excitations. Summing the RIXS spectra over q and comparing the results at T=14 K to those at T=300 K revealed pronounced temperature effects, including an intensity change and energy shift of the ≈1.4 eV peak, a broadband intensity increase of the 3-4 eV range, and higher energy features. The q-summed spectra and their temperature dependencies are virtually identical for nearly all of the samples with different dopants, save for the temperature dependence of the Ti-doped sample's spectrum, which we attribute to being affected by a large number of free charge carriers. Comparing with magnetization measurements for different temperatures and dopings likewise did not show a clear correlation between the RIXS spectra and the magnetic ordering states. To clarify the excited states, we performed spin multiplet calculations which were in excellent agreement with the RIXS spectra over a wide energy range and provide detailed electronic descriptions of the excited states. Furthermore, the implications of these findings to the photoconversion efficiency of hematite photoanodes is discussed.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1855216
• Journal Information: Physical Review. B, Journal Name: Physical Review. B Journal Issue: 7 Vol. 105; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English