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Communication Dans Un Congrès Année : 2022

Oxide thin film depth profiling: interest and limitations of argon sputtering for photoemission spectroscopy

Résumé

Active research is currently conducted to find alternatives to the silicon-based CMOS semiconductor technologies. Among the materials classes considered, thin films of oxides are promising candidates for emerging electronic applications. In this context, perovskite oxide heterostructures are valuable since their interfaces are not only conducting but can also present functional properties: ferroelectricity, superconductivity or thermoelectricity. For characterization purpose, argon ion beam is traditionally employed for thin film depth-profiling analysis. This gives trends on the reactions involved in the initial and final steps of the deposition processes. In this presentation, we will focus on different aspects of this ion interaction with oxide surfaces grown by Pulse Laser Deposition (PLD) and Atomic Layer Deposition (ALD): from cleaning with large Gas Cluster Ion Beam (GCIB) at low energies[1] to etching with energetic monoatomic ions (Ar+ ). The access to unmodified buried interfaces in heterostructures will be discussed. One of the most promising materials for emerging electronic applications is SrVO3 (SVO). This versatile transparent conductive perovskite oxide can be considered as a metal, i.e. presenting an excellent electronic conductivity with low work function. However, its high sensitivity to external stimuli remains a burning issue. For instance, reconstructed thin layers are generally observed due to Sr migration under soft stress as oxygen environment or temperature exposure. We showed using XPS depth profiling that the upper layer strongly differs from the rest of the film. Indeed, Sr-enrichment at the extreme surface was measured whereas stoichiometric SVO oxide was evidenced through the bulk[2]. However, information about the different chemical environments involved was no longer accessible. Sputtering sources are known to induce disorder (atomic implantation inside the matrix, amorphization, elemental dissociation, and/or chemical reduction). A clear modification of the Sr3d, and O1s-V2p spectral regions induced by Ar+ ion bombardment was observed during the depth profiling making the data not suitable for fine determination of the constituting element chemical environments. Experiments at TEMPO beamline (SOLEIL synchrotron) were conducted to overcome this issue. Indeed, tuning the excitation energy (probed depth) as well as gas exposure during photoemission experiments (NAP-XPS) successfully revealed the “effective” SVO spectral signature. Otherwise, the very sensitive surface reactivity of SVO has also been studied. We particularly obtained valuable results after treatments in liquid water which remove the Sr-rich layer on top of SVO thin films and provide new surface termination for the uppermost vanadium atoms[2]. Complementary angle resolved XPS and Low Energy Ion Scattering (LEIS) experiments confirmed the vertical arrangement and the formation of V-rich surface after water exposure. Finally, we have monitored by XPS the influence of ion beam irradiations on the famous LaAlO3/SrTiO3 (LAO/STO) heterostructure. We demonstrated that a short-time cluster ion irradiation of the LAO surface induces significant modifications in the chemical and electronic properties of the buried STO substrate[3]: i) a lowering of Ti atoms oxidation states (from Ti4+ to Ti3+ and Ti2+) correlated to the formation of oxygen vacancies at the LAO surface and ii) creation of new surface states for Sr atoms after atom migration through the covering layer.

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Chimie
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Dates et versions

hal-04404647 , version 1 (19-01-2024)

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  • HAL Id : hal-04404647 , version 1

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Mathieu Frégnaux, Yoan Bourlier, Bruno Berini, Yves Dumont, Damien Aureau. Oxide thin film depth profiling: interest and limitations of argon sputtering for photoemission spectroscopy. ECASIA 22, May 2022, Limerick (Ireland),, Ireland. ⟨hal-04404647⟩
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