Electron-Donor Dye Molecule on ZnO(101̅0), (0001), and (0001̅) Studied by Photoelectron Spectroscopy and X-ray Absorption Spectroscopy

Ozawa, K.; Suzuki, Masahiro; Tochikubo, Ryo; Kato, Hidemi; Sugizaki, Yuichi; Edamoto, K.; Mase, Kenji

doi:10.1021/acs.jpcc.6b00454

Cited by 8 publications

(10 citation statements)

References 42 publications

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“…Using highresolution soft X-ray, PES measurements, and NEXAFS measurements of the Sn M 4,5 -edge and O K-edge were performed at the 13B beamline of the Photon Factory, High Energy Accelerator Research Organization (KEK). 15,16 The NEXAFS spectra were acquired in the partial electron yield mode. Clean surfaces were prepared by fracturing the singlecrystal samples in an ultrahigh vacuum (UHV) preparation chamber at a pressure of 10 −8 Pa. 17 The cleanliness of the surfaces was checked by the core-level PES measurement (see section 1 of Supporting Information).…”

Section: Experimental Methodsmentioning

confidence: 99%

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇

et al. 2017

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The electronic structure of ternary tin oxide with pyrochlore structure, Sn 2 Nb 2 O 7 , which has the contribution of the Sn 5s orbitals in the valence band, is examined by synchrotron-radiation-excited photoelectron spectroscopy and X-ray absorption spectroscopy together with ab initio calculations. The empirical spectra are qualitatively consistent with the calculated density of states with the exception of a striking discrepancy in the electronic structure around the valence band maximum (VBM). The band calculation suggests the presence of a sharp peak around the VBM, mainly due to dispersionless bands that are derived from hybridization of Sn 5s orbitals and O 2p orbitals close to the Sn atom. However, the photoelectron spectra show no such characteristic spectral feature. From the theoretical prediction about the orbital origin of the localized VBM and the experimental estimation of the elemental composition by chemical analysis, it seems reasonable to conclude that the discrepancy of the electronic structure around the VBM is caused by the off-stoichiometric effect due to the point defects such as oxygen vacancies close to Sn 2+ , Sn 2+ vacancies, and Sn 4+ -on-Nb 5+ substitutional defects. Oxides with such localized VBM are not considered to be suitable for practical p-type oxide semiconductors. Therefore, the disappearance of the theoretically predicted localized VBM suggests the possibility to improve the mobility of hole carriers, and is considered to be closely related to our success in the development of the p-type oxide semiconductor Sn 2 Nb 2 O 7 .

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Section: Experimental Methodsmentioning

confidence: 99%

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇

et al. 2017

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“…Using this approach, Ozawa et al showed that tetrathiafulvalene (TTF) acts as an electron acceptor on the Zn-polar (0001) face and as a donor on the O-polar (0001̅) and m-plane (1010̅) faces because of different levels of decomposition of the TTF molecule. In contrast, acridine orange base acted as an electron donor on all of these ZnO surfaces . Schlesinger et al .…”

Section: Introductionmentioning

confidence: 96%

Synchrotron X-ray Photoelectron Spectroscopy Study of Electronic Changes at the ZnO Surface Following Aryldiazonium Ion Grafting: A Metal-to-Insulator Transition

et al. 2018

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ZnO is a member of a small class of semiconductors that includes In2O3, SnO2, CdO, and InN, whose surfaces are highly unusual because their electronic bands bend downward to form a quantized potential well in which a two-dimensional electron gas is confined. At the O-polar ZnO(0001̅) surface, this effect arises from the adsorption of H adatoms which produces a hydroxyl-terminated surface. In this work, we investigate the effect of covalently anchored organic layers on the band bending at ZnO(0001̅) surfaces. We use aryldiazonium salt electrochemistry to deposit 4–5 nm thick layers of 4-nitrophenyl (NP) and 4-(trifluoromethyl)phenyl (TFMP) groups. Synchrotron X-ray photoelectron spectroscopy (XPS) showed that both NP and TFMP modifications permanently removed the downward band bending at the ZnO surface. This behavior can be explained by the direct covalent bonding of the aryl groups to the surface, also revealed by XPS analysis, and the electron-withdrawing character of both modifiers. Surprisingly, the in situ irradiation-induced reduction of the grafted NP groups to aminophenyl-like moieties resulted in a further band bending shift in the upward direction, producing a combined change of more than 1.0 eV, corresponding to strong near-surface electron depletion. This phenomenon can be explained by the participation of electrons from the ZnO surface and possibly hydrogen from subsurface donors in the reduction process. Our study shows that electrochemically grafted aryl layers can alter the fundamental nature of ZnO surfaces by producing a “metal-to-insulator transition” in its unusual surface conductivity.

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“…They also showed that only a relatively small electron transfer between the adsorbate and the semiconductor surface was required to significantly influence the surface band bending. 18 Most recently, Ozawa et al 19 used X-ray spectroscopy to investigate the deposition of acridine orange base (AOB) on ZnO surfaces and found that AOB behaved as an electron donor inducing downward bending of the ZnO bands (up to 0.74 eV on the O-polar face), although without the formation of a potential well as the resulting bands were effectively flat.…”

Section: Introductionmentioning

confidence: 99%

Tuning the Band Bending and Controlling the Surface Reactivity at Polar and Nonpolar Surfaces of ZnO through Phosphonic Acid Binding

McNeill

Hyndman

Reeves

et al. 2016

ACS Appl. Mater. Interfaces

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ZnO is a prime candidate for future use in transparent electronics; however, development of practical materials requires attention to factors including control of its unusual surface band bending and surface reactivity. In this work, we have modified the O-polar (0001̅), Zn-polar (0001), and m-plane (101̅0) surfaces of ZnO with phosphonic acid (PA) derivatives and measured the effect on the surface band bending and surface sensitivity to atmospheric oxygen. Core level and valence band synchrotron X-ray photoemission spectroscopy was used to measure the surface band bending introduced by PA modifiers with substituents of opposite polarity dipole moment: octadecylphosphonic acid (ODPA) and 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctylphosphonic acid (FOPA). Both PAs act as surface electron donors, increasing the downward band bending and the strength of the two-dimensional surface electron accumulation layer on all of the ZnO surfaces investigated. On the O-polar (0001̅) and m-plane (101̅0) surfaces, the ODPA modifier produced the largest increase in downward band bending relative to the hydroxyl-terminated unmodified surface of 0.55 and 0.35 eV, respectively. On the Zn-polar (0001) face, the FOPA modifier gave the largest increase (by 0.50 eV) producing a total downward band bending of 1.00 eV, representing ∼30% of the ZnO band gap. Ultraviolet (UV) photoinduced surface wettability and photoconductivity measurements demonstrated that the PA modifiers are effective at decreasing the sensitivity of the surface toward atmospheric oxygen. Modification with PA derivatives produced a large increase in the persistence of UV-induced photoconductivity and a large reduction in UV-induced changes in surface wettability.

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Electron-Donor Dye Molecule on ZnO(101̅0), (0001), and (0001̅) Studied by Photoelectron Spectroscopy and X-ray Absorption Spectroscopy

Cited by 8 publications

References 42 publications

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇

Synchrotron X-ray Photoelectron Spectroscopy Study of Electronic Changes at the ZnO Surface Following Aryldiazonium Ion Grafting: A Metal-to-Insulator Transition

Tuning the Band Bending and Controlling the Surface Reactivity at Polar and Nonpolar Surfaces of ZnO through Phosphonic Acid Binding

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Electron-Donor Dye Molecule on ZnO(101̅0), (0001), and (0001̅) Studied by Photoelectron Spectroscopy and X-ray Absorption Spectroscopy

Cited by 8 publications

References 42 publications

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn2Nb2O7

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn2Nb2O7

Synchrotron X-ray Photoelectron Spectroscopy Study of Electronic Changes at the ZnO Surface Following Aryldiazonium Ion Grafting: A Metal-to-Insulator Transition

Tuning the Band Bending and Controlling the Surface Reactivity at Polar and Nonpolar Surfaces of ZnO through Phosphonic Acid Binding

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Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇

Disappearance of Localized Valence Band Maximum of Ternary Tin Oxide with Pyrochlore Structure, Sn₂Nb₂O₇