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<p>The crystalline surface of NiFe<sub>2</sub>O<sub>4</sub>(111) is highly dielectric at room temperature, as is evident in the photovoltaic charging seen in X-ray photoelectron spectroscopy (XPS) binding energy shifts for the Ni 2p<sub>3/2</sub>, Fe 2p<sub>3/2</sub>, and O 1s core levels at room temperature. These apparent XPS core level binding energy shifts are roughly 5 eV under the experimental&#xa0;conditions used in this work.&#xa0;The NiFe<sub>2</sub>O<sub>4</sub> XPS core level binding energies decreased to the expected binding energy values at elevated temperatures. While the dielectric phase is reversible, excess oxygen vacancies at the surface affect reversibility of the phase transition with temperature. Effective bulk Debye temperatures of 629 ± 58&#xa0;K and 787 ± 53&#xa0;K were estimated using temperature dependent Fe 2p<sub>3/2</sub> and Ni 2p<sub>3/2</sub> XPS intensities respectively. An unusually low effective surface Debye temperature of 250 ± 11&#xa0;K was&#xa0;estimated from temperature dependent low energy electron diffraction (LEED).&#xa0;The very low surface Debye temperature is&#xa0;consistent with the very small carrier generation activation energy extracted from the temperature dependent XPS.</p> Graphical Abstract <p></p>

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A reversible dielectric phase transition with temperature for highly crystalline NiFe2O4 thin films

  • 期刊论文

  • 发表日期：

    2025年3月30日

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  • Arjun Subedi,
  • Detian Yang,
  • Takashi Komesu,
  • Peace Adegbite,
  • Xiaoshan Xu,
  • Peter A. Dowben

摘要

The crystalline surface of NiFe2O4(111) is highly dielectric at room temperature, as is evident in the photovoltaic charging seen in X-ray photoelectron spectroscopy (XPS) binding energy shifts for the Ni 2p3/2, Fe 2p3/2, and O 1s core levels at room temperature. These apparent XPS core level binding energy shifts are roughly 5 eV under the experimental conditions used in this work. The NiFe2O4 XPS core level binding energies decreased to the expected binding energy values at elevated temperatures. While the dielectric phase is reversible, excess oxygen vacancies at the surface affect reversibility of the phase transition with temperature. Effective bulk Debye temperatures of 629 ± 58 K and 787 ± 53 K were estimated using temperature dependent Fe 2p3/2 and Ni 2p3/2 XPS intensities respectively. An unusually low effective surface Debye temperature of 250 ± 11 K was estimated from temperature dependent low energy electron diffraction (LEED). The very low surface Debye temperature is consistent with the very small carrier generation activation energy extracted from the temperature dependent XPS.

Graphical Abstract