Zinc depletion at the ZnFe2O4 (1 1 1) single crystal surface: X-ray spectroscopy experiments and computer simulations

Charlotte A. Hall; David C. Grinter; Jonas Sandemann; Bo Brummerstedt Iversen; Roger A. Bennett; Georg Held; Ricardo Grau-Crespo; Pilar Ferrer

doi:10.1016/j.apsusc.2025.164253

Zinc depletion at the ZnFe₂O₄ (1 1 1) single crystal surface: X-ray spectroscopy experiments and computer simulations

Charlotte A. Hall
, David C. Grinter
, Jonas Sandemann
, Bo Brummerstedt Iversen
, Roger A. Bennett
, Georg Held
, Ricardo Grau-Crespo^*
, Pilar Ferrer

^*Corresponding author af dette arbejde

Institut for Kemi

Publikation: Bidrag til tidsskrift/Konferencebidrag i tidsskrift /Bidrag til avis › Tidsskriftartikel › Forskning › peer review

Abstract

A combination of experimental methods and computational techniques have been used to investigate the composition of the zinc ferrite (ZnFe₂O₄) (1 1 1) single crystal surface under different preparation methods. Surface-sensitive XPS and NEXAFS measurements show that upon annealing in ultra-high vacuum (UHV), Zn depletion occurs, leading to the formation of an iron-rich (1 1 1) surface, whereas annealing in the presence of O₂ gas maintains a more bulk-like ZnFe₂O₄ surface composition. Analysis of the Fe 2p photoemission (XPS) and Fe L edge X-ray absorption signals shows a clear difference in iron oxidation state and distribution between the two different preparation conditions. After annealing in UHV, a mixed Fe²⁺/Fe³⁺ oxidation state and a cation distribution like that of a magnetite (Fe₃O₄) structure is observed, whereas after annealing in oxygen gas only Fe³⁺, mostly in octahedral coordination, is observed, as expected for a ZnFe₂O₄ structure. Temperature-dependent XPS confirms significant Zn depletion in the near-surface region above 500 °C under UHV, with almost no Zn remaining at 600 °C; under an O₂ atmosphere no zinc depletion is observed up to 600 °C. A theoretical model based on DFT simulations illustrates how reduction from ZnFe₂O₄ to Fe₃O₄ with formation of O₂ and Zn gas is thermodynamically feasible under UHV conditions, whereas the same reaction is not favourable at higher oxygen partial pressures. Our findings demonstrate the strong impact that UHV treatment has on zinc ferrite surfaces, and cautions that UHV environments, routinely employed for surface analysis, can themselves induce substantial modifications to the surface, thereby complicating the interpretation of measurements in the context of catalytically relevant conditions.

Originalsprog	Engelsk
Artikelnummer	164253
Tidsskrift	Applied Surface Science
Vol/bind	713
ISSN	0169-4332
DOI	https://doi.org/10.1016/j.apsusc.2025.164253
Status	Udgivet - 15 dec. 2025

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title = "Zinc depletion at the ZnFe2O4 (1 1 1) single crystal surface: X-ray spectroscopy experiments and computer simulations",

abstract = "A combination of experimental methods and computational techniques have been used to investigate the composition of the zinc ferrite (ZnFe2O4) (1 1 1) single crystal surface under different preparation methods. Surface-sensitive XPS and NEXAFS measurements show that upon annealing in ultra-high vacuum (UHV), Zn depletion occurs, leading to the formation of an iron-rich (1 1 1) surface, whereas annealing in the presence of O2 gas maintains a more bulk-like ZnFe2O4 surface composition. Analysis of the Fe 2p photoemission (XPS) and Fe L edge X-ray absorption signals shows a clear difference in iron oxidation state and distribution between the two different preparation conditions. After annealing in UHV, a mixed Fe2+/Fe3+ oxidation state and a cation distribution like that of a magnetite (Fe3O4) structure is observed, whereas after annealing in oxygen gas only Fe3+, mostly in octahedral coordination, is observed, as expected for a ZnFe2O4 structure. Temperature-dependent XPS confirms significant Zn depletion in the near-surface region above 500 °C under UHV, with almost no Zn remaining at 600 °C; under an O2 atmosphere no zinc depletion is observed up to 600 °C. A theoretical model based on DFT simulations illustrates how reduction from ZnFe2O4 to Fe3O4 with formation of O2 and Zn gas is thermodynamically feasible under UHV conditions, whereas the same reaction is not favourable at higher oxygen partial pressures. Our findings demonstrate the strong impact that UHV treatment has on zinc ferrite surfaces, and cautions that UHV environments, routinely employed for surface analysis, can themselves induce substantial modifications to the surface, thereby complicating the interpretation of measurements in the context of catalytically relevant conditions.",

keywords = "Density functional theory, NEXAFS, Spinel, Zinc ferrite",

author = "Hall, \{Charlotte A.\} and Grinter, \{David C.\} and Jonas Sandemann and Iversen, \{Bo Brummerstedt\} and Bennett, \{Roger A.\} and Georg Held and Ricardo Grau-Crespo and Pilar Ferrer",

note = "Publisher Copyright: {\textcopyright} 2025 The Authors",

year = "2025",

month = dec,

day = "15",

doi = "10.1016/j.apsusc.2025.164253",

language = "English",

volume = "713",

journal = "Applied Surface Science",

issn = "0169-4332",

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}

Zinc depletion at the ZnFe₂O₄ (1 1 1) single crystal surface: X-ray spectroscopy experiments and computer simulations. / Hall, Charlotte A.; Grinter, David C.; Sandemann, Jonas et al.
I: Applied Surface Science, Bind 713, 164253, 15.12.2025.

Publikation: Bidrag til tidsskrift/Konferencebidrag i tidsskrift /Bidrag til avis › Tidsskriftartikel › Forskning › peer review

TY - JOUR

T1 - Zinc depletion at the ZnFe2O4 (1 1 1) single crystal surface

T2 - X-ray spectroscopy experiments and computer simulations

AU - Hall, Charlotte A.

AU - Grinter, David C.

AU - Sandemann, Jonas

AU - Iversen, Bo Brummerstedt

AU - Bennett, Roger A.

AU - Held, Georg

AU - Grau-Crespo, Ricardo

AU - Ferrer, Pilar

PY - 2025/12/15

Y1 - 2025/12/15

N2 - A combination of experimental methods and computational techniques have been used to investigate the composition of the zinc ferrite (ZnFe2O4) (1 1 1) single crystal surface under different preparation methods. Surface-sensitive XPS and NEXAFS measurements show that upon annealing in ultra-high vacuum (UHV), Zn depletion occurs, leading to the formation of an iron-rich (1 1 1) surface, whereas annealing in the presence of O2 gas maintains a more bulk-like ZnFe2O4 surface composition. Analysis of the Fe 2p photoemission (XPS) and Fe L edge X-ray absorption signals shows a clear difference in iron oxidation state and distribution between the two different preparation conditions. After annealing in UHV, a mixed Fe2+/Fe3+ oxidation state and a cation distribution like that of a magnetite (Fe3O4) structure is observed, whereas after annealing in oxygen gas only Fe3+, mostly in octahedral coordination, is observed, as expected for a ZnFe2O4 structure. Temperature-dependent XPS confirms significant Zn depletion in the near-surface region above 500 °C under UHV, with almost no Zn remaining at 600 °C; under an O2 atmosphere no zinc depletion is observed up to 600 °C. A theoretical model based on DFT simulations illustrates how reduction from ZnFe2O4 to Fe3O4 with formation of O2 and Zn gas is thermodynamically feasible under UHV conditions, whereas the same reaction is not favourable at higher oxygen partial pressures. Our findings demonstrate the strong impact that UHV treatment has on zinc ferrite surfaces, and cautions that UHV environments, routinely employed for surface analysis, can themselves induce substantial modifications to the surface, thereby complicating the interpretation of measurements in the context of catalytically relevant conditions.

AB - A combination of experimental methods and computational techniques have been used to investigate the composition of the zinc ferrite (ZnFe2O4) (1 1 1) single crystal surface under different preparation methods. Surface-sensitive XPS and NEXAFS measurements show that upon annealing in ultra-high vacuum (UHV), Zn depletion occurs, leading to the formation of an iron-rich (1 1 1) surface, whereas annealing in the presence of O2 gas maintains a more bulk-like ZnFe2O4 surface composition. Analysis of the Fe 2p photoemission (XPS) and Fe L edge X-ray absorption signals shows a clear difference in iron oxidation state and distribution between the two different preparation conditions. After annealing in UHV, a mixed Fe2+/Fe3+ oxidation state and a cation distribution like that of a magnetite (Fe3O4) structure is observed, whereas after annealing in oxygen gas only Fe3+, mostly in octahedral coordination, is observed, as expected for a ZnFe2O4 structure. Temperature-dependent XPS confirms significant Zn depletion in the near-surface region above 500 °C under UHV, with almost no Zn remaining at 600 °C; under an O2 atmosphere no zinc depletion is observed up to 600 °C. A theoretical model based on DFT simulations illustrates how reduction from ZnFe2O4 to Fe3O4 with formation of O2 and Zn gas is thermodynamically feasible under UHV conditions, whereas the same reaction is not favourable at higher oxygen partial pressures. Our findings demonstrate the strong impact that UHV treatment has on zinc ferrite surfaces, and cautions that UHV environments, routinely employed for surface analysis, can themselves induce substantial modifications to the surface, thereby complicating the interpretation of measurements in the context of catalytically relevant conditions.

KW - Density functional theory

KW - NEXAFS

KW - Spinel

KW - Zinc ferrite

UR - https://www.scopus.com/pages/publications/105012767301

U2 - 10.1016/j.apsusc.2025.164253

DO - 10.1016/j.apsusc.2025.164253

M3 - Journal article

AN - SCOPUS:105012767301

SN - 0169-4332

VL - 713

JO - Applied Surface Science

JF - Applied Surface Science

M1 - 164253

ER -