Universal Work Function of Metal Oxides Exposed to Air

Rietwyk, Kevin J.; Keller, David A.; Ginsburg, Adam; Barad, Hannah‐Noa; Priel, Maayan; Majhi, Koushik; Yan, Zhi; Tirosh, Shay; Anderson, Assaf Y.; Ley, L.; Zaban, Arie

doi:10.1002/admi.201802058

Cited by 36 publications

(23 citation statements)

References 53 publications

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“…From secondary electron cutoff of the low‐intensity X‐ray photoelectron spectroscopy (LIXPS) spectra ( Figure A), the work function of the [FeFe] modified Si (Si‐[FeFe]) was determined to be approximately equal to that of an oxide‐free, freshly ion‐sputtered bare Si wafer. This result demonstrates that covalent [FeFe] modification is capable of inhibiting oxide growth maintaining the work function of Si after exposure to air for 300 h. The work function of bare Si is 0.75 eV more positive than that of the treated surface due to native oxide growth, [ 38 ] demonstrating that the modified surface possesses favorable electronic properties for more efficient charge transfer compared to the bare Si surface. In solution phase, the flat band potential can be determined by an approximation of the valence band edge potential, [ 39 ] where a shift in flat band potential reflects changes in the valance and conduction band positions.…”

Section: Resultsmentioning

confidence: 91%

Unraveling Activity and Decomposition Pathways of [FeFe] Hydrogenase Mimics Covalently Bonded to Silicon Photoelectrodes

Williams

Nash

Yamamoto

et al. 2021

Adv Materials Inter

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now generate hundreds of megawatts of electricity, [1] enabling solar energy to compete with fossil fuels in the near future. Nevertheless, one challenge facing this solar future is its intermittency. [2] Consequently, deployable systems which can store solar energy have been added to the growing lists of requirements for building ideal clean and renewable energy platforms. One promising approach is using solar energy to drive photoelectrochemical reactions for fuel production, such as generation of hydrogen (H 2 ) via water splitting. This method has been described as "artificial photosynthesis," akin to the process in nature which converts light into energy stored as sugars. [3][4][5] Thus, there remains a need to develop an economically viable water splitting cell composed of a light-absorbing semiconductor for solarto-electron conversion coupled to a viable electrocatalyst for a rapid chemical conversion process.Currently, limitations of constructing an efficient semiconductor−catalyst interface include instability, insufficient light absorptivity of the semiconductor materials, and poor charge separation efficiency at the semiconductor−catalyst interface. [6,7] It is known that functionalizing semiconductor surfaces with organic compounds can tune surface properties by adjusting charge distribution, density of surface states, surface dipole, and electric fields at the semiconductor−molecule interface. [8] However, only a handful of reports review the stability of semiconductor−molecule interfaces or their decomposition mechanisms. [7,[9][10][11] Herein, we tether organometallic catalysts onto semiconductor photoelectrodes to shed light on catalyst decomposition pathways during electrolysis. Moreover, the presence of functional molecules on the semiconductor surface can stabilize the interface by limiting growth of native oxides on unmodified surface sites. [12][13][14] Current and future applications of semiconductor devices demand higher performance systems that prevent the accumulation of insulating oxide layers which inhibit charge transport at the semiconductor−functional compound interface.The employed organometallic catalyst, Fe 2 (CO) 6 (μ-S-C 6 H 4 -p-OH) 2 , denoted herein as [FeFe], is a synthetic analog of the active site in a diiron hydrogenase

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Section: Resultsmentioning

confidence: 91%

Unraveling Activity and Decomposition Pathways of [FeFe] Hydrogenase Mimics Covalently Bonded to Silicon Photoelectrodes

Williams

Nash

Yamamoto

et al. 2021

Adv Materials Inter

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“…The results presented in Figure 8 confirm that the same applies to Fe as well, as was already suggested in Huber and Kirk. 36 The influence of exposure to air on the band energies of metal oxides was also investigated in Rietwyk et al 37 and universal reduction in the work function was observed across 18 oxides. This effect arises from charge transfer events with the ubiquitous water layer that forms on surfaces in air.…”

Section: Near-zero Landing Energies In Semmentioning

confidence: 99%

Electron reflectivity from clean and oxidized steel surface

Mikmeková¹,

Aoyama²,

Paták³

et al. 2022

Surface & Interface Analysis

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This paper aims to elucidate the effect of an air‐formed native oxide covering mild steel surface on the contrast in the scanning electron microscopy (SEM) images obtained with the landing energy from 5 keV down to 0 eV. Part of the mild steel surface was in‐situ cleaned by Ar+ ion sputtering process in order to remove native oxide from the surface. It enabled us to observe the oxide‐free and the naturally oxidized area on the mild steel surface simultaneously in the SEM micrographs. Presence of the native oxide starts to play a role in the SEM images acquired at landing energy below roughly 3 keV. Contrast between differently oriented grains situated inside the area covered by the native oxide starts to be negligible with landing energy decreasing below 3 keV, up to some ultra‐low values where the contrast increases again. Total reflectivity contrast between the clean and the oxidized area increases exponentially with landing energy decreasing below 3 keV. The reflectivity‐versus‐energy curves of the cleaned and the naturally oxidized mild steel surface are markedly different. The reflectivity of the electrons is correlated with the density of states (DOS), as is demonstrated at very low landing energies. Sensitivity of the very low‐energy electrons to the electronic structure was verified by comparison of the experimental data with the simulations of reflectivities, band structure, and DOS. The theoretical predictions are based on the density‐functional theory calculations and they have been performed in energy range corresponding to specular reflectivities of the Fe‐BCC (001) orientation. We have also observed that close to the mirror condition, that is, near‐zero landing energies, the primary electrons become sensitive to the surface potential differences caused by the work function differences of clean and native oxide‐covered steel surfaces.

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“…80,81 The oxide layer on top of the metal electrode will be hydroxyl terminated, followed by a physisorbed layer of water, hydrocarbons and other small molecules when exposure to air, which will form a dipole moment pointing away from the surface and decrease the work function significantly. 82 In the case of non-reactive metals or the reactive metals in the inert atmosphere, there will be a physisorption of heteroatoms and small molecules directly on the metal surface and the work function is reduced by the push-back effect. Even if the electrode is made in-situ, its surface may also be slightly contaminated and/or oxidized due to the higher pressure used during the deposition process (> 10 -7 mbar).…”

Section: Energy Level Alignmentmentioning

confidence: 99%

Image dipoles and polarons in organic semiconductors

Chen

2021

Linköping Studies in Science and Technology. Dissertations

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Universal Work Function of Metal Oxides Exposed to Air

Cited by 36 publications

References 53 publications

Unraveling Activity and Decomposition Pathways of [FeFe] Hydrogenase Mimics Covalently Bonded to Silicon Photoelectrodes

Unraveling Activity and Decomposition Pathways of [FeFe] Hydrogenase Mimics Covalently Bonded to Silicon Photoelectrodes

Electron reflectivity from clean and oxidized steel surface

Image dipoles and polarons in organic semiconductors

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