Cathodoluminescence of near-surface centres in Cr-doped MgO(001) thin films probed by scanning tunnelling microscopy

Stavale, Fernando; Nilius, Niklas; Freund, Hans‐Joachim

doi:10.1088/1367-2630/14/3/033006

Cited by 41 publications

(52 citation statements)

References 58 publications

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“…Local measure ments of the phonon density of solids are still scarce [10], One example are IET spectra taken on HOPG, which revealed a complex peak structure coinciding with the symmetry points of phonon bands in graphite [11], In NaCl thin films, phonon excitations via inelastic electrons were made responsible for the surprisingly large width of gap states induced by Cl vacancies [12], The broadening was explained with a dressing of electronic resonances by longitudinal optical (LO) phonons in the halide lattice. In ZnO, the LO excitations could be identified directly upon charging or discharging of individual donors with the STM tip [13], Comparable results were obtained for Cr-doped MgO films, only that the phonon sidebands appeared in the STM-luminescence response in that case and not in the tunneling spectra [14].…”

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confidence: 80%

Phonon-Mediated Electron Transport through CaO Thin Films

et al. 2015

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Scanning tunneling microscopy has developed into a powerful tool for the characterization of conductive surfaces, for which the overlap of tip and sample wave functions determines the image contrast. On insulating layers, as the CaO thin film grown on Mo(001) investigated here, direct overlap between initial and final states is not enabled anymore and electrons are transported via hopping through the conduction-band states of the oxide. Carrier transport is accompanied by strong phonon excitations in this case, imprinting an oscillatory signature on the differential conductance spectra of the system. The phonons show a characteristic spatial dependence and become softer around lattice irregularities in the oxide film, such as dislocation lines.

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confidence: 80%

Phonon-Mediated Electron Transport through CaO Thin Films

et al. 2015

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“…The presence of suitable dopants is, however, not the only requirement for a stable donor characteristic, the interplay between dopants and host oxide determines the redox activity. This shall be demonstrated for two similar systems, Cr-doped MgO and Mo-doped CaO, which still exhibit an entirely different behavior [81][82][83]. Chromium has a similar electronic structure as Mo, i.e., the same number of d-electrons, but is a 3d and not a 4d metal.…”

Section: Metal Growth On Doped Oxide Materialsmentioning

confidence: 90%

Model Catalysts Based on Au Clusters and Nanoparticles

Nilius

Risse

Shaikhutdinov

et al. 2013

Structure and Bonding

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Small Au particles have been shown to exhibit interesting catalytic properties. In an attempt to parallel catalytic studies on powder supports we have undertaken a series of model studies using oxide films as support. We address the formation of Au aggregates as a function of size starting from Au atoms to clusters and islands of larger size and as a function of the support. In addition we have studied different support materials such as alumina and iron oxide and we compare ultrathin and thicker oxide films of the same material (MgO). From a comparison of charge transfer through ultrathin films with the situation encountered in thicker films, we propose the use of dopants in bulk materials to control particle shape.We include the study of carbon monoxide adsorption on Au clusters of varying size. It is demonstrated how chemical modification (hydroxylation) of oxide supports influence particle growth and properties. Finally, we report on effects to study the processes involved in particle growth by wet impregnation in order to bridge the gap to catalyst preparation under realistic conditions. On that basis one may now compare properties of supported particles prepared in ultrahigh vacuum using physical vapor deposition with those prepared by wet impregnation

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“…Cr ions embedded in an MgO matrix, for instance, are inappropriate electron donors, and the Au growth morphology is hardly affected in this case [52]. Cr ions embedded in an MgO matrix, for instance, are inappropriate electron donors, and the Au growth morphology is hardly affected in this case [52].…”

Section: First Case Study: Controlling Nanoparticle Shapes On Nondopementioning

confidence: 96%

4.4 Model Systems in Catalysis for Energy Economy

Nilius¹,

Sterrer²,

Shaikhutdinov³

et al. 2012

Chemical Energy Storage

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Harvesting, saving, and storing energy are key issues in today's general energy discussions [1]. Harvesting energy through photochemistry and storing energy in compounds using thermal energy-efficient processes are attractive solutions to some problems within the grand picture [2].Heterogeneous thermal and photocatalysis are bound to play a key role in those solutions. However, while thermal heterogeneous catalysis is widespread in chemical industries, and photocatalysis not yet, there is still a strong demand in both areas for research in order to understand the process and its elementary steps as well as to rationally design the catalytic material.Investigation of model catalysts can play a decisive role in a rational approach to understand heterogeneous catalysis, and this is the topic of this chapter [3][4][5][6].In the introduction, the model systems will be defined to familiarize the reader with the approach in order to appreciate the connection to real-world catalysis. Following the introduction, we will demonstrate via four case studies various fundamental aspects in thermal and photocatalysis whereby studies on model systems might become important to unravel the foundations of reaction mechanisms.The model systems have been created under the premises that it is possible to investigate them at the atomic scale using the toolbox that has been developed in surface science during the second half of the last century up to now [7].The model systems are based on the idea to grow well-ordered oxide layers or thin films, representing the bulk material, and as such the catalyst support, on singlecrystal metal surfaces using the concepts of epitaxial growth [8]. This, in turn, allows one to investigate bulk insulators without having to worry about charging when charged information carriers such as electrons or ions are used to investigate those systems. One thus avoids one of the key difficulties hampering the detailed study of real catalysts. Also the application of scanning probe techniques including electron tunneling is possible for thin-film systems. The fact that the oxides are grown on a metal support also ensures the easy applicability of infrared reflection absorption spectroscopy at such systems. Moreover, controlling the growth parameters of the oxide film also allows one to vary the density of defects at the surface of the oxide films, a factor of importance when nanoparticles are grown on the oxide support.

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Cathodoluminescence of near-surface centres in Cr-doped MgO(001) thin films probed by scanning tunnelling microscopy

Cited by 41 publications

References 58 publications

Phonon-Mediated Electron Transport through CaO Thin Films

Phonon-Mediated Electron Transport through CaO Thin Films

Model Catalysts Based on Au Clusters and Nanoparticles

4.4 Model Systems in Catalysis for Energy Economy

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