XPS study of the Sc/SiO<sub><i>x</i></sub> interface at room temperature

Reichl, R.; Gaukler, K. H.

doi:10.1002/sia.740171010

Cited by 2 publications

(3 citation statements)

References 7 publications

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“…Clear trends with photon energy and acid treatment are seen in the Y 3d core levels in Figure . For both samples (as‐deposited and after acid treatment) there are three contributions to the overall signal: bulk metallic yttrium (Y 0 ) around 155.9 eV (3d 5/2 ), yttrium oxide (Y 3+ ) around 158 eV , . There is a third peak that we assign to substochiometric Pt 3 Y oxide (Y–O) around 157 eV; where the material composition and oxidation is different to Y 2 O 3 , .…”

Section: Resultssupporting

confidence: 90%

Surface Composition of a Highly Active Pt₃Y Alloy Catalyst for Application in Low Temperature Fuel Cells

et al. 2020

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Currently, platinum is the most widely used catalyst for low temperature proton exchange membrane fuel cells (PEMFC). However, the kinetics at the cathode are slow, and the price of platinum is high. To improve oxygen reduction reaction (ORR) kinetics at the cathode, platinum can be alloyed with rare earth elements, such as yttrium. We report that Pt3Y has the potential to be over 2 times more active for the ORR compared with Pt inside a real fuel cell. We present detailed photoemission analysis into the nature of the sputtered catalyst surface, using synchrotron radiation photoelectron spectroscopy (SRPES) to examine if surface adsorbates or impurities are present and can be removed. Pretreatment removes most of the yttrium oxide in the surface leaving behind a Pt overlayer which is only a few monolayers thick. Evidence of a substochiometric oxide peak in the Y 3d core level is presented, this oxide extends into the surface even after Ar+ sputter cleaning in‐situ. This information will aid the development of new highly active nanocatalysts for employment in real fuel cell electrodes.

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Section: Resultssupporting

confidence: 90%

Surface Composition of a Highly Active Pt₃Y Alloy Catalyst for Application in Low Temperature Fuel Cells

et al. 2020

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“…Losses are observed in the SiO 2 phonon modes that attenuate before the 10th exposure of 1 , proving that the passivating interface layer grows during the first 7–10 exposures of 1 at 275 °C, regardless of the thickness of the initial SiO 2 layer (Figure S15). For comparison, a previous study evaluated a Sc/SiO x /Si system by XPS after evaporating scandium metal onto a 1.5 nm thick SiO x layer maintained at room temperature . A redox reaction was confirmed at the Sc/SiO x interface following the deposition of a 3.1 nm thick scandium film.…”

Section: Results and Discussionmentioning

confidence: 99%

“…For comparison, a previous study evaluated a Sc/SiO x /Si system by XPS after evaporating scandium metal onto a 1.5 nm thick SiO x layer maintained at room temperature. 68 A redox reaction was confirmed at the Sc/SiO x interface following the deposition of a 3.1 nm thick scandium film. Analysis of the Si 2p core level showed a small new peak, corresponding to silicon atoms in a local environment that is different from that inside bulk silicon.…”

Section: And Figures S12−s14)mentioning

confidence: 92%

Selective Growth of Interface Layers from Reactions of Sc(MeCp)₂(Me₂pz) with Oxide Substrates

Rahman

Klesko

Dangerfield

et al. 2018

ACS Appl. Mater. Interfaces

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The transformation of an oxide substrate by its reaction with a chemical precursor during atomic layer deposition (ALD) has not attracted much attention, as films are typically deposited on top of the oxide substrate. However, any modification to the substrate surface can impact the electrical and optical properties of the device. We demonstrate herein the ability of a precursor to react deep within an oxide substrate to form an interfacial layer that is distinct from both the substrate and deposited film. This phenomenon is studied using a scandium precursor, Sc(MeCp)(Mepz) (1, MeCp = methylcyclopentadienyl, Mepz = 3,5-dimethylpyrazolate), and five oxide substrates (SiO, ZnO, AlO, TiO, and HfO). In situ Fourier transform infrared (FTIR) spectroscopy shows that at moderate temperatures (∼150 °C) the pyrazolate group of 1 reacts with the surface hydroxyl groups of OH-terminated SiO substrates. However, at slightly higher temperatures (≥225 °C) typically used for the ALD of ScO, there is a direct reaction between 1 and the SiO layer, in addition to chemisorption at the surface hydroxyl groups. This reaction is sustained by sequential exposures of 1 until an ∼2 nm thick passivating interface layer is formed, indicating that 1 reacts with oxygen derived from SiO. A shift of the Si 2p core level position, measured by ex situ X-ray photoelectron spectroscopy, is consistent with the formation of a ScSi O layer. Similar observations are made following the exposure of a ZnO substrate to 1 at 275 °C. In contrast, AlO, TiO, and HfO substrates remain resistant to reaction with 1 under similar conditions, except for a surface reaction occurring in the case of TiO. These striking observations are attributed to the differences in the electrochemical potentials of the elements comprising the oxide substrates to that of scandium. Precursor 1 can react with SiO or ZnO substrates, since the constituent elements of these oxides have less-negative electrochemical potentials than do aluminum, titanium, and hafnium. Additionally, ScO and surface carbonates are deposited on all substrates by gas-phase reactions between 1 and residual water vapor in the reactor. The extent of gas-phase reactions contributing to film growth is governed by the relative pressure of water vapor in the presence of 1. These results suggest caution when using very reactive, oxophilic precursors such as 1 to avoid misinterpreting unconventional film deposition as that resulting from a standard ALD process.

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XPS study of the Sc/SiO_x interface at room temperature

Cited by 2 publications

References 7 publications

Surface Composition of a Highly Active Pt₃Y Alloy Catalyst for Application in Low Temperature Fuel Cells

Surface Composition of a Highly Active Pt₃Y Alloy Catalyst for Application in Low Temperature Fuel Cells

Selective Growth of Interface Layers from Reactions of Sc(MeCp)₂(Me₂pz) with Oxide Substrates

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XPS study of the Sc/SiOx interface at room temperature

Cited by 2 publications

References 7 publications

Surface Composition of a Highly Active Pt3Y Alloy Catalyst for Application in Low Temperature Fuel Cells

Surface Composition of a Highly Active Pt3Y Alloy Catalyst for Application in Low Temperature Fuel Cells

Selective Growth of Interface Layers from Reactions of Sc(MeCp)2(Me2pz) with Oxide Substrates

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XPS study of the Sc/SiO_x interface at room temperature

Surface Composition of a Highly Active Pt₃Y Alloy Catalyst for Application in Low Temperature Fuel Cells

Surface Composition of a Highly Active Pt₃Y Alloy Catalyst for Application in Low Temperature Fuel Cells

Selective Growth of Interface Layers from Reactions of Sc(MeCp)₂(Me₂pz) with Oxide Substrates