Helium diffraction study of the nucleation and growth of palladium clusters on MgO (100)

doi:10.1016/0022-0248(93)90475-C

Journal of Crystal Growth

Volume 129, Issues 3–4, April 1993, Pages 416-420

https://doi.org/10.1016/0022-0248(93)90475-C Get rights and content

Abstract

Helium diffraction is used for the first time to study the nucleation and growth of three-dimensional metallic clusters on a crystalline substrate. It is shown that from the attenuation of the first diffraction peak from the MgO substrate it is possible to derive the growth rate and the nucleation kinetics of the Pd clusters. Transmission electron microscopy (TEM) observation of the final deposit allows one to determine the width of the diffuse scattering zone around the clusters. The first results obtained at two different substrate temperatures are analysed following the atomistic theory of nucleation and growth.

References (11)

C. Duriez et al.
Surface Sci.
(1990)
C.R. Henry et al.
Surface Sci.
(1991)
C. Chapon et al.
Surface Sci.
(1985)
A. Chemam
Thesis
(1986)
S. Stoyanov et al.
A. Sanchez et al.
Surface Sci.
(1987)

There are more references available in the full text version of this article.

Cited by (27)

Pd diffusion on MgO(1 0 0): The role of defects and small cluster mobility
2006, Surface Science
Density functional theory is used to explore the energy landscape of Pd atoms adsorbed on the terrace of MgO(1 0 0) and at oxygen vacancy sites. Saddle point finding methods reveal that small Pd clusters diffuse on the terrace in interesting ways. The monomer and dimer diffuse via single atom hops between oxygen sites with barriers of 0.34 eV and 0.43 eV respectively. The trimer and tetramer, however, form 3D clusters by overcoming a 2D–3D transition barrier of less than 60 meV. The trimer diffuses along the surface either by a walking or flipping motion, with comparable barriers of ca. 0.5 eV. The tetramer rolls along the terrace with a lower barrier of 0.42 eV. Soft rotational modes at the saddle point lead to an anomalously high prefactor of 1.3 × 10¹⁴ s⁻¹ for tetramer diffusion. This prefactor is two order of magnitude higher than for monomer diffusion, making the tetramer the fastest diffusing species on the terrace at all temperatures for which diffusion is active (above 200 K). Neutral oxygen vacancy sites are found to bind Pd monomers with a 2.63 eV stronger binding energy than the terrace. A second Pd atom, however, binds to this trapped monomer with a smaller energy of 0.56 eV, so that dimers at defects dissociate on a time scale of milliseconds at room temperature. Larger clusters bind more strongly at defects. Trimers and tetramers dissociate from monomer-bound-defects at elevated temperatures of ca. 600 K. These species are also mobile on the terrace, suggesting they are important for the ripening observed at ⩾600 K during Pd vapor deposition on MgO(1 0 0) by Haas et al. [G. Haas, A. Menck, H. Brune, J.V. Barth, J.A. Venables, K. Kern, Phys. Rev. B 61 (2000) 11105].
Reaction dynamics on supported metal clusters
2003, Chemical Physics of Solid Surfaces
Citation Excerpt :
The temperature of the sample is regulated between RT and 500°C during the experiments. The nucleation and growth of the metal clusters can be studied in real time by measuring the attenuation of a first order diffraction peak of He [48] (see Section 3.2.1). After deposition the metal clusters can be characterized in situ by AES and ELS [49, 50].
Reaction dynamics is of key importance to understand the mechanism of catalytic reactions on solid surfaces. This chapter provides review on the reaction dynamics studies, which has been performed on supported model catalysts to unravel the elementary steps of heterogeneous catalytic reactions. It focuses on the aspects that cannot be studied on extended surfaces, such as the effect of the size and shape of the metal particles and the role of the substrate in the reaction kinetics. The chapter describes the experimental methods and techniques used in these studies. It presents an overview of the preparation and the structural characterization of the metal particle. It also provides a review of the adsorption studies of nitrogen monoxide (NO), carbon monoxide (CO), and oxygen (O₂) and the two reactions that have been investigated on the supported model catalysts: the CO oxidation and the NO reduction by CO.
Effects of the support on the morphology and electronic properties of supported metal clusters: Modern concepts and progress in 1990s
1999, Applied Catalysis A: General
Modern trends in studying the influence of the support on the electronic state, morphology, and catalytic properties of supported metal particles are reviewed. The analysis of new developments in techniques for catalyst characterization is given. Metal–support interaction effects are discussed in terms of electronic modification of the supported clusters and their morphological transformations induced by the support. Special attention is paid to the recent concepts of the structure of the metal–support interface. The support effects on the catalytic properties of metal particles are revealed as (1) changes due to metal particle charging, (2) effects related to variations in metal particle shape and crystallographic structure and, (3) appearance of the specific active sites at the metal–support boundary.
Adsorption of transition metal atoms on oxygen vacancies and regular sites of the MgO(001) surface
1999, Surface Science
Adsorption of Cu, Ni, Ag, and Pd atoms on F_s and F⁺_s oxygen vacancy sites as well as on regular O²⁻ centers of the MgO(001) surface has been studied by means of gradient-corrected density functional calculations using cluster models embedded in a matrix of model potentials and point charges. Scalar relativistic effects have been taken into account for adsorbed Ag and Pd species. The electronic structure, geometric parameters, and binding energies of the adsorption complexes have been calculated and analyzed with reference to the electronic properties of the vacancy sites and the metal atoms in question. For all adsorbates considered, adsorption is found to be stronger on F_s sites by 1–2.4 eV compared with regular O²⁻ sites, with Pd and Ni forming the most stable complexes. On the F⁺_s site the single valence electron of Cu and Ag atoms couples with an unpaired electron of the vacancy forming a covalent bond. As a result the adsorption energy of these atoms on F⁺_s is by more than 1 eV stronger than on the F_s sites; on the other hand, the adsorption energies of Ni and Pd are reduced on F⁺_s by 0.5 eV and 1.3 eV respectively. The whole series of M/F⁺_s complexes is characterized by rather uniform values of adsorbate–substrate distances (1.5–1.7 Å) and adsorption energies (2.2–2.6 eV).
Oxide surfaces and metal/oxide interfaces studied by grazing incidence X-ray scattering
1998, Surface Science Reports
Experimental determinations of the atomic structure of insulating oxide surfaces and metal/oxide interfaces are scarce, because surface science techniques are often limited by the insulating character of the substrate. Grazing incidence X-ray scattering (GIXS), which is not subject to charge effects, can provide very precise information on the atomic structure of oxide surfaces: roughness, relaxation and reconstruction. It is also well adapted to analyze the atomic structure, the registry, the misfit relaxation, elastic or plastic, the growth mode and the morphology of metal/oxide interfaces during their growth, performed in situ. GIXS also allows the analysis of thin films and buried interfaces, in a non-destructive way, yielding the epitaxial relationships, and, by variation of the grazing incidence angle, the lattice parameter relaxation along the growth direction. On semi-coherent interfaces, the existence of an ordered network of interfacial misfit dislocations can be demonstrated, its Burger's vector determined, its ordering during in situ annealing cycles followed, and sometimes even its atomic structure can be addressed. Careful analysis during growth allows the modeling of the dislocation nucleation process.
This review emphasizes the new information that GIXS can bring to oxide surfaces and metal/oxide interfaces by comparison with other surface science techniques. The principles of X-ray diffraction by surfaces and interfaces are recalled, together with the advantages and properties of grazing angles. The specific experimental requirements are discussed. Recent results are presented on the determination of the atomic structure of relaxed or reconstructed oxide surfaces. A description of results obtained during the in situ growth of metal on oxide surfaces is also given, as well as investigations of thick metal films on oxide surfaces, with lattice parameter misfit relaxed by an array of dislocations. Recent work performed on oxide thin films having important physical properties such as superconductivity or magnetism is also briefly reviewed.
The strengths and limitations of the technique, such as the need for single crystals and surfaces of high crystalline quality are discussed. Finally, an outlook of future prospects in the field is given, such as the study of more complex oxide surfaces, vicinal surfaces, reactive metal/oxide interfaces, metal oxidation processes, the use of surfactants to promote wetting of a metal deposited on an oxide surface or the study of oxide/liquid interfaces in a non-UHV environment.
Power laws in the growth kinetics of metal clusters on oxide surfaces
1998, Vacuum
The possibility of expressing the growth kinetics of metal on weakly interacting substrates (oxides and insulators) by a power law is examined. By a model taking into account for direct growth and growth by capture of diffusing adatoms it is shown that the growth rate can be locally expressed by a power law. The model is restricted to the growth of three-dimensional clusters. In the case of a strong competition between clusters for the capture of adatoms a single exponent, between 0.33 and 0.35 is obtained before the coalescence stage. In the limit of isolated clusters the exponent increases continually from $13$ –1 during the growth. The model is compared with growth kinetics of Pd clusters on MgO(100) obtained in situ and continuously by diffraction of He atoms. The agreement with the calculations is very good if we take into account for the finite nucleation rate. The present calculations have been also applied satisfactorily to the published data for other systems.

View all citing articles on Scopus

^∗: Laboratoire propre du CNRS associé aux Universités d'Aix-Marseille II et III.

View full text

Helium diffraction study of the nucleation and growth of palladium clusters on MgO (100)

Abstract

Surface Sci.

Surface Sci.

Surface Sci.

Thesis

Surface Sci.