Crystal field effects on the reactivity of aluminum-copper cluster anions

Roach, Patrick J.; Woodward, W. Hunter; Reber, Arthur C.; Khanna, Shiv N.; Castleman, A. W.

doi:10.1103/physrevb.81.195404

Cited by 61 publications

(56 citation statements)

References 39 publications

(57 reference statements)

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“…1. As we recently showed, the degeneracy in the P, D… electronic states can be broken by the potential of the ionic cores forming the cluster and can lead to highly stable species at subshell filling (27).…”

Section: Resultsmentioning

confidence: 96%

Hund’s rule in superatoms with transition metal impurities

Medel

Reveles

Khanna

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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112

105

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The quantum states in metal clusters bunch into supershells with associated orbitals having shapes resembling those in atoms, giving rise to the concept that selected clusters could mimic the characteristics of atoms and be classified as superatoms. Unlike atoms, the superatom orbitals span over multiple atoms and the filling of orbitals does not usually exhibit Hund's rule seen in atoms. Here, we demonstrate the possibility of enhancing exchange splitting in superatom shells via a composite cluster of a central transition metal and surrounding nearly free electron metal atoms. The transition metal d states hybridize with superatom D states and result in enhanced splitting between the majority and minority sets where the moment and the splitting can be controlled by the nature of the central atom. We demonstrate these findings through studies on TMMg n clusters where TM is a 3d atom. The clusters exhibit Hund's filling, opening the pathway to superatoms with magnetic shells.magnetic superatoms | jellium model | superatomic shells T he quantum confinement of electrons in small compact symmetric metal clusters results in electronic shell sequence 1S, 1P, 1D, …, much in the same way as in atoms. This analogy, originally introduced through the electronic states in a "jellium sphere" where the electron gas is confined to a uniform positive background of the size of the cluster, extends beyond this oversimplified model (1-9). Numerous first principles electronic structure studies on metal clusters have demonstrated the close grouping of electronic states into shells and have further shown that the shapes of the cluster electronic orbitals resemble those in atoms. Experiments on the reactivity of clusters have provided evidence that clusters and atoms of similar valence shells exhibit analogous chemical patterns. For example, although bulk aluminum is readily oxidized by oxygen, an Al 13 − cluster with filled 1S 2 , 1P 6 , 1D 10 , 2S 2 , 1F 14 , and 2P 6 shells exhibits strong resistance to etching by oxygen typical of inert atoms (5, 10). Further Al 13 has a large electron affinity of 3.4 eV close to that of a Cl atom (9). These analogies have prompted the concept that selected stable clusters could mimic the electronic behavior of elemental atoms and be classified as superatoms forming a third dimension of the periodic table (10-21). Because the properties of clusters change with size and composition, the superatoms offer the prospect of serving as the building blocks of nanomaterials with tunable characteristics (16,18).The electronic orbitals in superatoms, although resembling those in real atoms in shape, do spread over multiple atoms. This affects the way in which the electrons fill the shells because of two competing effects. Hund's rule favors high spin states in open shell systems stabilized by exchange coupling, and indeed higher spin multiplicities have been seen in some clusters (22) and even quantum dots spanning several nanometers (23). However, unlike the case of atoms, small clusters can undergo structu...

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Section: Resultsmentioning

confidence: 96%

Hund’s rule in superatoms with transition metal impurities

Medel

Reveles

Khanna

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

112

105

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“…Cu 15 Al + shows the largest cross section of 23.8 Å 2 , which corresponds approximately to half of the Langevin cross section 26 (σ LGS = 49.2 Å 2 ) estimated using the polarizability, α(NO) = 1.70 Å 3 . 27 When a hard-sphere model used by Roseń and co-workers is applied, 20 where the geometric sizes of a cluster and a molecule are included, the measured reaction cross section for Cu 15 Al + is estimated to be ∼20% of the hardsphere cross section (σ HS = 109.8 Å 2 ). Here, the radius of Cu 15 Al + is assumed to be equal to that of Cu 16 .…”

Section: Methodsmentioning

confidence: 99%

Stability of Aluminum-Doped Copper Cluster Cations and Their Reactivity toward NO and O₂

Hirabayashi

Ichihashi

2015

J. Phys. Chem. A

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Aluminum-doped copper cluster cations, CunAl(+), were produced via an ion sputtering method and analyzed by mass spectrometry. The measured size distributions show that Cu6Al(+) and Cu18Al(+) are highly stable species, which can be understood in terms of the electronic subshell 1P and 2S closings, respectively. Furthermore, the reactions of size-selected CunAl(+) (n = 4-6 and 8-16) with NO and O2 were studied at near thermal energies by using a tandem-type mass spectrometer. The doping of an Al atom improves the reactivity of the clusters toward NO in particular for n = 9, 11, 13, and 15, whereas it does not change the reactivity toward O2 significantly. Consequently, it was found that CunAl(+) (n = 9, 11, 13 and 15) are more reactive toward NO than toward O2. The high reactivity of Cu9Al(+) toward NO compared to that of Cu10(+) is explained in terms of the increase of the adsorption energy and the lowering of the barrier to dissociative adsorption, with the aid of calculations based on density functional theory. Moreover, the multiple-collision reactions of CunAl(+) (n = 9, 11, and 13) with NO result in the production of cluster dioxides, Cun-3AlO2(+), (i.e., release of N2), which clearly indicates that NO decomposition proceeds on these clusters.

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“…The trivalent aluminum (Al=[Ne] 3s 2 3p 1 ) is a suitable material to apply the shell model for metal clusters [1] in order to account for cluster size dependent electronic effects since its valence electrons exhibit free-electron-like character [2]. In particular, the search for 'magic' structures with enhanced stability against dissociation that could be used as building blocks in cluster-assembled materials drew considerable attention to the 13-atomic anionic aluminum cluster.…”

Section: Introductionmentioning

confidence: 99%

Cage Structure Formation of Singly Doped Aluminum Cluster Cations Al_nTM⁺(TM= Ti, V, Cr)

Lang

Claes

Neukermans

et al. 2011

J. Am. Soc. Mass Spectrom.

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Structural information on free transition metal doped aluminum clusters, Al n TM + (TM=Ti, V, Cr), was obtained by studying their ability for argon physisorption. Systematic size (n=5 -35) and temperature (T=145 -300 K) dependent investigations reveal that bare Al n + clusters are inert toward argon, while Al n TM + clusters attach one argon atom up to a critical cluster size. This size is interpreted as the geometrical transition from surface-located dopant atoms to endohedrally doped aluminum clusters with the transition metal atom residing in an aluminum cage. The critical size, n crit , is found to be surprisingly large, namely n crit =16 and n crit =19 -21 for TM=V, Cr, and TM=Ti, respectively. Experimental cluster-argon bond dissociation energies have been derived as function of cluster size from equilibrium mass spectra and are in the 0.1-0.3 eV range.

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Crystal field effects on the reactivity of aluminum-copper cluster anions

Cited by 61 publications

References 39 publications

Hund’s rule in superatoms with transition metal impurities

Hund’s rule in superatoms with transition metal impurities

Stability of Aluminum-Doped Copper Cluster Cations and Their Reactivity toward NO and O₂

Cage Structure Formation of Singly Doped Aluminum Cluster Cations Al_nTM⁺(TM= Ti, V, Cr)

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Crystal field effects on the reactivity of aluminum-copper cluster anions

Cited by 61 publications

References 39 publications

Hund’s rule in superatoms with transition metal impurities

Hund’s rule in superatoms with transition metal impurities

Stability of Aluminum-Doped Copper Cluster Cations and Their Reactivity toward NO and O2

Cage Structure Formation of Singly Doped Aluminum Cluster Cations AlnTM+(TM= Ti, V, Cr)

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Stability of Aluminum-Doped Copper Cluster Cations and Their Reactivity toward NO and O₂

Cage Structure Formation of Singly Doped Aluminum Cluster Cations Al_nTM⁺(TM= Ti, V, Cr)