Structural Investigation of Palladium Clusters on γ-AlO<sub>3</sub>(111)/NiAl(110) with Transmission Electron Microscopy

Nepijko, S. A.; Klimenkov, M.; Adelt, Maik; Kuhlenbeck, Helmut; Schlögl, Robert; Freund, Hans‐Joachim

doi:10.1021/la981012p

Cited by 65 publications

(44 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Further, we have shown that the origin of the initial state effect is a lattice contraction that is part of the cluster growth morphology [14,15]. In particular, the BE shift is related to the d hybridization being larger for shorter bond distances.…”

Section: P H Y S I C a L R E V I E W L E T T E R Smentioning

confidence: 98%

“…In order to study only the effect of cluster size on the BE's, we have used the bulk a 0 3:59 A. However, there is evidence from transmission electron microscopy of Pd and Pt on Al 2 O 3 that the effective a 0 for small clusters is reduced by 5%-7% [14,15]; these contractions are much larger than those found for matrix isolated Cu clusters [28]. The much larger lattice strain for supported clusters may be due to their weak interaction with the support.…”

Section: P H Y S I C a L R E V I E W L E T T E R Smentioning

confidence: 99%

“…In the present work, we show that the initial and final state contributions to the BE are of comparable magnitude. Further, we relate the initial state BE to a lattice strain that exists because the average bond distances in small clusters are shorter than in the bulk [14,15]. The chemical bonding is different at the shorter bond distances and this, in turn, leads to changes in the core-level BE's.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Cluster Core-Level Binding-Energy Shifts: The Role of Lattice Strain

et al. 2004

Self Cite

View full text Add to dashboard Cite

Our combined experimental and theoretical analysis of the shifts, with particle size, of core-level binding energies (BE's) of metal nanoparticles on insulating supports, shows that these shifts have an important initial state contribution arising, in large part, because of lattice strain. This contribution of BE shifts has not been recognized previously. Lattice strain changes the chemical bonding between the metal atoms and this change induces BE shifts. DOI: 10.1103/PhysRevLett.93.026805 PACS numbers: 73.22.-f, 79.60.-i Photoelectron spectroscopy (PES) is often used to deduce information on the electronic structure of molecules, solids, and at surfaces [1]. There is increasing interest in nanostructured materials, especially in clusters grown on inert surfaces since they may have high catalytic activity [2]. Thus, the question of how the PES of deposited nanoparticles reflects their electronic and geometric structures is quite important. It is known that the corelevel BE's of metal clusters on insulating supports [3][4][5][6][7][8][9][10][11][12] shift to lower BE with increasing size by BE 1 eV from small clusters to bulk metal. However, there is substantial disagreement over the assignment of these shifts to initial or final state effects; see Ref.[13] for a rigorous definition of these two contributions. Mason [7] argued that changes in the electron configuration of the atoms in smaller clusters, not relaxation energies, were primarily responsible for the shift. On the other hand, Wertheim and collaborators [4,5] assigned the shift as due to final state screening effects and related the magnitude of BE to an effective cluster radius. For Cu clusters grown on thin Al 2 O 3 films, Wu et al. [11] concluded from an Auger parameter analysis that initial state contributions are small and may be significant only for very small clusters. This separation is quite important since the initial state BE reflect changes in the electronic structure before ionization of a core level and, hence, are of direct interest for materials properties. In the present work, we show that the initial and final state contributions to the BE are of comparable magnitude. Further, we relate the initial state BE to a lattice strain that exists because the average bond distances in small clusters are shorter than in the bulk [14,15]. The chemical bonding is different at the shorter bond distances and this, in turn, leads to changes in the core-level BE's. The chemical changes important for the BE involve an increased d to sp promotion, or hybridization, for shorter bond distances.Our work is based on a combination of experimental and theoretical methods that allow us to decompose the BE into initial and final state contributions. Our theoretical approach involves the calculation of electronic wave functions (WF's) for clusters and the determination of the BE's where relaxation in response to ionization is excluded, a pure initial state BE, and where this relaxation is allowed [13]. Our experimental approach involves use of an Auger para...

show abstract

Section: P H Y S I C a L R E V I E W L E T T E R Smentioning

confidence: 98%

Section: P H Y S I C a L R E V I E W L E T T E R Smentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Cluster Core-Level Binding-Energy Shifts: The Role of Lattice Strain

et al. 2004

Self Cite

View full text Add to dashboard Cite

show abstract

“…The sizes for which properties are altered depend upon the material and the specific property. This information was extracted from many sources including lattice constants, [24] surface energy, [25] Hall-Petch breakdown, [26] superparametric temperatures, [27] hematite-maghemite phase transition, [28] TiO 2 phases, [29] CuO, [30] and oxide film thickness on Fe. [31] .…”

Section: What Makes It Nano?mentioning

confidence: 99%

Characterization challenges for nanomaterials

Baer

Amonette

Engelhard

et al. 2008

Surface & Interface Analysis

123

View full text Add to dashboard Cite

Nanostructured materials are increasingly subject to nearly every type of chemical and physical analysis possible. Due to their small sizes, there is a significant focus on tools with high spatial resolution. It is also natural to characterize nanomaterials using tools designed to analyze surfaces, because of their high surface area. Regardless of the approach, nanostructured materials present a variety of obstacles to adequate, useful, and needed analysis. Case studies of measurements on ceria and iron metal-core/oxide-shell nanoparticles are used to introduce some of the issues that frequently need to be addressed during analysis of nanostructured materials. We use a combination of tools for routine analysis including X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and x-ray diffraction (XRD) and apply several other methods as needed to obtain essential information. The examples provide an introduction to other issues and complications associated with the analysis of nanostructured materials including particle stability, probe effects, environmental effects, specimen handling, surface coating, contamination, and time.

show abstract

“…First, the decrease in the chemisorption energy can result from the contraction of the lattice parameter of a small metal nanoparticle. Previously, it has been demonstrated experimentally 19,20 that the interatomic bond length in small metal particles decreases with decreasing particle size. It is now well established also by computational studies of various metals including Pd ͑Refs.…”

mentioning

confidence: 98%

Particle-size dependent heats of adsorption of CO on supported Pd nanoparticles as measured with a single-crystal microcalorimeter

et al. 2010

View full text Add to dashboard Cite

We present calorimetric measurements of the effect of cluster size on the adsorption enthalpy of carbon monoxide on Pd nanoclusters sized from 120 to 4900 Pd atoms per particle, which were grown in situ on a well-ordered Fe 3 O 4 / Pt͑111͒ film. A substantial decrease in the initial heat of adsorption amounting to about 20-40 kJ mol −1 was observed on the smallest Pd nanoparticles as compared to the larger Pd clusters and the extended Pd͑111͒ single-crystal surface. We discuss this effect in terms of the size-dependent properties of the Pd nanoparticles. DOI: 10.1103/PhysRevB.81.241416 PACS number͑s͒: 68.43.Ϫh, 82.65.ϩr This Rapid Communication addresses the question: how does the heat of chemisorption of a molecule change when comparing a metal single-crystal surface with a supported metal nanoparticle, and how does it depend on particle size? This is an exceptionally important question that lies at the very heart of understanding particle size effects in catalysis. 1 The energetics of interaction of gaseous molecules, particularly carbon monoxide, with well-defined metal nanoparticles were previously addressed indirectly in nonisothermal temperature-programed desorption ͑TPD͒ experiments 2 and in isothermal modulated molecular-beam studies, 3 where the adsorption energies were obtained by modeling the desorption process and analyzing the lifetimes of the adsorbate on the surface. However, these indirect methods did not provide a clear trend in the changes in the adsorption energy with the particles size: whereas the TPD studies found a decrease in the adsorption energy by about 10 kJ mol −1 on the 2.5 nm sized Pd particles as compared to the extended single-crystal surfaces, the kinetic model used for analysis of the molecular-beam experiments predicted a pronounced increase in the adsorption energy by about 35 kJ mol −1 on the particles smaller than 1.5 nm.A strategy to overcome the shortcomings of such indirect methods based on the model assumptions is direct calorimetric measurement of adsorption enthalpies. Recently, two types of calorimeters were developed that allow direct adsorption energy measurements on single-crystal surfaces. 4,5 However, many phenomena inherent to dispersed supported catalysts and technically relevant nanoparticle-based materials cannot be addressed on such simplified model systems since they do not reproduce some properties of realistic surfaces such as different particles sizes or interactions between nanoparticles and their support material. Only a limited amount of calorimetric data is available today on dispersed supported metal powder catalysts, 6,7 suffering, however, from a high degree of inhomogeneity in metal particle size distribution and low support homogeneity. A strategy to surmount this shortcoming was the development of welldefined, single-crystal-based model surfaces, consisting of metal nanoparticles deposited on flat thin oxide films. 8 The structural properties of these model systems such as particle size and shape can be controlled and characterized in grea...

show abstract

Structural Investigation of Palladium Clusters on γ-AlO₃(111)/NiAl(110) with Transmission Electron Microscopy

Cited by 65 publications

References 31 publications

Cluster Core-Level Binding-Energy Shifts: The Role of Lattice Strain

Cluster Core-Level Binding-Energy Shifts: The Role of Lattice Strain

Characterization challenges for nanomaterials

Particle-size dependent heats of adsorption of CO on supported Pd nanoparticles as measured with a single-crystal microcalorimeter

Contact Info

Product

Resources

About

Structural Investigation of Palladium Clusters on γ-AlO3(111)/NiAl(110) with Transmission Electron Microscopy

Cited by 65 publications

References 31 publications

Cluster Core-Level Binding-Energy Shifts: The Role of Lattice Strain

Cluster Core-Level Binding-Energy Shifts: The Role of Lattice Strain

Characterization challenges for nanomaterials

Particle-size dependent heats of adsorption of CO on supported Pd nanoparticles as measured with a single-crystal microcalorimeter

Contact Info

Product

Resources

About

Structural Investigation of Palladium Clusters on γ-AlO₃(111)/NiAl(110) with Transmission Electron Microscopy