Partielle Dissoziation von Wasser führt zu stabilen Überstrukturen auf der Oberfläche von Zinkoxid

Meyer, Bernd; Marx, Dominik; Dulub, Olga; Diebold, Ulrike; Kunat, M.; Langenberg, Deler; Wöll, Christof

doi:10.1002/ange.200461696

Cited by 71 publications

(136 citation statements)

References 33 publications

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“…Further exposure to water at 113 K resulted in the formation of amorphous 3D-islands. These results differ substantially from results on the mixed termi- nated ZnO , where a more complex scenario for ZnO(10-10) has been found in which every second water molecule of a full monolayer dissociated while the remaining water molecules were strongly bound by a "key-lock" type structural arrangement [23]. The resulting water adlayer formed a well-defined (2 × 1) superlattice of intact water molecules which is stable up to 360 K. The comparison of these results indicates that the ZnO(10-10) surface should exhibit a more pronounced ability to participate in hydrogen bridging with adsorbed SDA or sensitizers and that the two studied surfaces show significantly different interaction with OH and hence different optimum adsorption geometries and preferred binding sites for the studied SDA and sensitizers leading to the different film morphologies observed in electrodeposition.…”

Section: Model Reactions At Zno Surfaces Under Uhv Conditionscontrasting

confidence: 99%

“…Furthermore layer growth of water on ZnO is also a good model to mimic the formation of hydrogen bonds which are also of importance for interaction of ZnO with dyes containing carboxylic, sulphonic, phosphoric, OH, NH 2 or related functional groups. While water adsorption on ZnO(10-10) was already reported in the literature [23], multilayer adsorption of water on the polar ZnO(000-1) had not been studied. Exposure of a clean ZnO(000-1) surface to water vapour at room temperature led to the formation of a sharp, welldefined hexagonal low energy diffraction (LEED) pattern revealing the presence of a (1 × 1) surface structure.…”

Section: Model Reactions At Zno Surfaces Under Uhv Conditionsmentioning

confidence: 99%

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Nanoparticulate Dye-Semiconductor Hybrid Materials Formed by Electrochemical Self-Assembly as Electrodes in Photoelectrochemical Cells

Nonomura

Loewenstein

Michaelis

et al. 2009

Zeitschrift Für Naturforschung A

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Dye-sensitized zinc oxide thin films were prepared, characterized and optimized for applications as photoelectrochemically active electrodes. Conditions were established under which crystalline thin films of ZnO with a porous texture were formed by electrochemically induced crystallization controlled by structure-directing agents (SDA). Dye molecules were adsorbed either directly as SDA during this preparation step or, preferably, following desorption of a SDA. The external quantum efficiency (IPCE) could thereby be increased significantly. Particular emphasis was laid on dye molecules that absorb in the red part of the visible spectrum. Model experiments under ultrahigh vacuum (UHV) conditions with dye molecules adsorbed on defined crystal planes of single crystals aimed at a deeper understanding of the coupling of the chromophore electronic π-system within molecular aggregates and to the semiconductor surface. Detailed photoelectrochemical kinetic measurements were used to characterize and optimize the electrochemically prepared dye-sensitized ZnO films. Parallel electrical characterization in vacuum served to distinguish between contributions of charge transport within the ZnO semiconductor matrix and the ions of the electrolyte in the pore system of the electrode.

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Section: Model Reactions At Zno Surfaces Under Uhv Conditionscontrasting

confidence: 99%

Section: Model Reactions At Zno Surfaces Under Uhv Conditionsmentioning

confidence: 99%

Nanoparticulate Dye-Semiconductor Hybrid Materials Formed by Electrochemical Self-Assembly as Electrodes in Photoelectrochemical Cells

Nonomura

Loewenstein

Michaelis

et al. 2009

Zeitschrift Für Naturforschung A

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“…For the clean surfaces typical (1 1) diffraction patterns were recorded as reported elsewhere. [15,18] Exposure of the sample to CO 2 was carried out by backfilling the UHV chamber through a leak valve. Exposures are given in units of langmuir (1 L = 1.33 10 À6 mbar s).…”

Section: Methodsmentioning

confidence: 99%

“…HAS is a highly sensitive surface-analysis method, [12][13][14] and has been successfully used to determine the phase diagram of H 2 O on the same surface. [15] The HAS data show that exposure of the sample to very small amounts of CO 2 in two steps (first with 4 L at 260 K and then 8 L at 120 K; exposures are given in units of langmuir (1 L = 1.33 10 À6 mbar s)) results in the formation of a well-ordered (2 1) phase ( Figure 1 b; the arrows indicate half-order diffraction peaks). Upon saturation with CO 2 the (2 1) structure disappears and a (1 1) phase forms.…”

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confidence: 98%

CO₂ Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

et al. 2007

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The activation of CO 2 is one of the most important topics in catalysis.[1] For example, one of the simple Zn-enzymecatalyzed processes, the hydration of CO 2 by carbonic anhydrase, has led to extensive mechanistic and theoretical studies of the interaction of CO 2 with Zn-OH. [2][3][4][5] Also, in heterogeneous catalysis, a detailed understanding of the surface chemistry of CO 2 is an important issue; interest in this topic ranges from developing new processes for an emplacement of this greenhouse gas to the synthesis of methanol from syngas (CO/CO 2 /H 2 ) over Cu/ZnO catalysts. [6] Numerous studies have been reported on CO 2 adsorption on clean metal surfaces, where frequently activation is found to occur via the formation of a bent CO 2 dÀ species. [7][8][9] For oxide surfaces much less information is available. This deficit is in part due to the poor electric conductivity of many oxides which severely complicates the application of electron-based spectroscopic methods. In particular, there is a lack of information concerning molecular vibrations from highresolution electron energy loss spectroscopy (HREELS).The application of HREELS on oxide surfaces is-in addition to the electric conductivity problem-severely limited by the presence of intense substrate lattice excitations (FuchsKliewer phonons [10] ) which obscure the relatively weak vibrational modes of adsorbed species.Herein we present the results of a systematic multitechnique experimental and theoretical study on the interaction of CO 2 with the mixed-terminated ZnO(101 0) surface. In contrast to other oxides, ZnO is sufficiently conductive that electron-based methods can be applied without significant difficulties. The results from HREELS, thermal desorption spectroscopy (TDS), low-energy electron diffraction (LEED), He-atom scattering (HAS), and X-ray photoelectron spectroscopy (XPS) reveal a complicated scenario, comprising the presence of two different ordered phases. By employing accurate periodic density-functional theory (DFT) and wave-function-based quantum-chemical cluster calculations it could be shown that the previously proposed bidentate bonding of CO 2 to this ZnO surface [11] has to be revised. Exposure to CO 2 leads-even at temperatures below 100 Kto the formation of an unusual tridentate carbonate species with the two O atoms of the CO 2 molecule being almost equivalently bound to two different Zn surface atoms.In a first set of experiments, the phase diagram of CO 2 adlayers on this ZnO substrate was determined using HAS. This technique uses neutral He atoms with thermal energy so charging problems are avoided. HAS is a highly sensitive surface-analysis method, [12][13][14] and has been successfully used to determine the phase diagram of H 2 O on the same surface.[15] The HAS data show that exposure of the sample to very small amounts of CO 2 in two steps (first with 4 L at 260 K and then 8 L at 120 K; exposures are given in units of langmuir (1 L = 1.33 10 À6 mbar s)) results in the formation of a well-ordered (2 1) phase (Figure 1 ...

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“…[11,12] This attention has given rise to several surprising findings, especially for the nonpolar ZnO-(101 0) surface, such as surface metallization upon hydrogen adsorption [13] and partial dissociation of water layers on defect-free surfaces. [14] It will be shown that not F centers but missing ZnO dimers are the most characteristic atomic defects on the ZnO(101 0) surface, not only in typical ultrahigh vacuum (UHV) experiments but also at catalytic (T, p) conditions. This result convincingly explains recent experimental findings of the different catalytic activities and properties between the polar and nonpolar ZnO terminations, as discussed in the outlook below.…”

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confidence: 99%

F Centers versus Dimer Vacancies on ZnO Surfaces: Characterization by STM and STS Calculations

2007

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Not what you'd expect: Contrary to what is usually believed for oxide surfaces, density functional calculations show that not F centers but missing ZnO dimers are the thermodynamically most favorable type of atomic defect on the nonpolar ZnO surface. Simulated STM data may serve as a fingerprint for experimental identification of the different surface defect types. The picture shows a tunneling tip over ZnO (Zn gray, O red, W blue) with the corresponding STM image in between.

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Partielle Dissoziation von Wasser führt zu stabilen Überstrukturen auf der Oberfläche von Zinkoxid

Cited by 71 publications

References 33 publications

Nanoparticulate Dye-Semiconductor Hybrid Materials Formed by Electrochemical Self-Assembly as Electrodes in Photoelectrochemical Cells

Nanoparticulate Dye-Semiconductor Hybrid Materials Formed by Electrochemical Self-Assembly as Electrodes in Photoelectrochemical Cells

CO₂ Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

F Centers versus Dimer Vacancies on ZnO Surfaces: Characterization by STM and STS Calculations

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Partielle Dissoziation von Wasser führt zu stabilen Überstrukturen auf der Oberfläche von Zinkoxid

Cited by 71 publications

References 33 publications

Nanoparticulate Dye-Semiconductor Hybrid Materials Formed by Electrochemical Self-Assembly as Electrodes in Photoelectrochemical Cells

Nanoparticulate Dye-Semiconductor Hybrid Materials Formed by Electrochemical Self-Assembly as Electrodes in Photoelectrochemical Cells

CO2 Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate

F Centers versus Dimer Vacancies on ZnO Surfaces: Characterization by STM and STS Calculations

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CO₂ Activation by ZnO through the Formation of an Unusual Tridentate Surface Carbonate