Ordered Arrays of Size-Selected Oxide Nanoparticles

Abstract

A bottom-up approach to produce a long-range ordered superlattice of monodisperse and isomorphic metal-oxide nanoparticles (NP) supported onto an oxide substrate is demonstrated. The synthetic strategy consists of self-assembling metallic NP on an ultrathin nanopatterned aluminum oxide template followed by a morphology-conserving oxidation process, and is exemplified in the case of Ni, but is generally applicable to a wide range of metallic systems. Both fully oxidized and core-shell metal-metal-oxide particles are synthesized, up to 3-4 nm in diameter, and characterized via spectroscopic and theoretical tools. This opens up a new avenue for probing unit and ensemble effects on the properties of oxide materials in the nanoscale regime. DOI: 10.1103/PhysRevLett.108.195507 PACS numbers: 81.16.Pr, 61.46.Df, 75.75.Cd, 81.16.Rf Metal-oxide nanoparticles (NP) find widespread interest in fundamental science and bear promise for high-level applications in many emerging fields of the advanced nanotechnologies, from nanospintronics and high-density magnetic storage devices [1][2][3] to chemical sensing [4,5] and nanocatalysis [6,7]. The size, shape, and mutual interactions among the particles play a key role in determining the novel properties of these nanosized oxide materials [8,9]. For example, oxide NP may display anomalous magnetic behavior such as ferromagnetism vs antiferromagnetism in the bulk [2,3] or size-dependent magnetic structures and unusual spin couplings [8,10]. Model systems of NP with atomic-level control of size, shape, chemical composition, and interparticle distance are therefore crucial to clarify the emergent phenomena in oxide materials at the nanometer scale, and to disentangle the effects of the various intra-, inter-and support-particle interactions. However, such systems are difficult to prepare especially for particles below 50-100 nm, which are not accessible to lithographic techniques [5], while the traditional wet chemical methods only allow moderate design variations [11]. Here we describe the fabrication of one such system: an ordered superlattice of monodisperse and isomorphic nickel oxide NP, and its characterization via spectroscopic and theoretical tools. Both fully oxidized and core-shell metal-metal-oxide particles (the latter of interest, e.g., for exchange bias effects [1]) are synthesized via a bottom-up template-directed self-assembly strategy, opening up a new avenue for probing unit and ensemble effects on the physical and chemical properties of oxide materials, from molecule-type cluster sizes to the solid state limit. Our strategy consists of self-assembling metallic NP on an ultrathin nanopatterned aluminum oxide template followed by a morphology-conserving oxidation process, thus producing a superlattice of oxide NP decoupled from a conducting metal substrate by an ultrathin oxide layer, with a very narrow size distribution and identical shapes. We illustrate the procedure for the case of NiO NP, but the method is general (it has been tested for CoO particles with e...

Interlayer exchange coupling in ordered Fe nanocluster arrays grown onAl2O3/Ni3Al(111)

“…Amongst the transition metal elements investigated so far, Pd is the only one diffusing into the corner holes [14,16]. Therefore it has been used as seed to nucleate other transition metal elements leading to well ordered arrays of quasibimetallic nanoparticles of AuPd [17], FePd and CoPd [14,18], and NiPd [19].…”

“…Despite many recent efforts to reveal the structure of the surface layers of Al 2 O 3 / Ni 3 Al(111) [14,19,26], an accurate characterization of the composition of those layers interfacing the oxide from below, and of the resulting magnetic properties, is still lacking. Here we report a detailed investigation of the magnetic properties of the pristine substrate before and after the growth of alumina and finally after the growth of Fe nanoparticles on top.…”

Self-organized nano-structuring of CoO islands on Fe(001)

“…Such a strategy has already been successful in many cases where, in particular, either metallic or semiconducting ordered nano-structure assemblies have been obtained by growing the relative materials on interfaces containing dislocation networks [3][4][5][6]. In other cases, the growth of nanostructures has been realized on oxide substrates similarly characterized by a peculiar distribution of defects [7][8][9]. Much scarcer appears to be the record of cases in which the nanostructured systems consist of the oxide materials themselves [10,11].…”

Atomistic and Electronic Structure Methods for Nanostructured Oxide Interfaces

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