Cluster assembled materials: a novel class of nanostructured solids with original structures and properties

Abstract

The low-energy cluster beam deposition technique (LECBD) is applied to produce cluster assembled films with hitherto unknown nanostructured morphologies and properties. Neutral clusters having the very low energy gained in the supersonic expansion at the exit of the inert gas condensation-type source are deposited without fragmentation upon impact on the substrate. Depending on the deposition conditions (nature, size and flux of incident clusters, nature and temperature of the substrate, vacuum conditions), granular nanostructures resulting from the diffusion and coalescence of supported clusters are obtained with materials of any type (covalent or metallic). A critical size for coalescence limits the supported grain size and, finally, highly porous thick films growing by random stacking of nanoparticles are obtained. A recent model developed by combining several dynamical processes simultaneously occurring on the substrate (deposition - diffusion - aggregation, DDA) is used to simulate the cluster assembled film morphology in good agreement with the experimental observations. Examples of novel materials obtained by LECBD are presented to illustrate the interesting potentialities of the technique. In the case of covalent materials such as carbon and silicon, 'amorphon'-type disordered structures, different from the conventional amorphous structures (a-C and a-Si), are obtained with some unique properties. With transition metal (Fe, Co and Ni) cluster assembled films, a specific magnetic behaviour, resulting from the competition between the intrinsic properties of the grains (magnetocrystalline anisotropy) and the interactions between grains, is observed. Also, films of clusters embedded in various co-deposited matrices are produced in order to control the interactions between grains via the matrix materials (insulating, conducting ...). Interesting optical properties (from metallic clusters in ) or giant magnetoresistance effects (from Co clusters in silver) are reported for such systems, emphasizing the future role of LECBD in various fields of applications such as optical and optoelectronic nanostructures, magnetic and magneto-optic nanostructures and quantum devices.

Correlation between the extraordinary Hall effect and resistivity

“…technique [19,20]. silica clusters increases, fractal structure is developed and, finally, the percolation threshold is reached.…”

“…The analysis was successful also in high resistivity systems, where the side jump mechanism is automatically taken as the only dominating source of the EHE. -Co-Pt arrays; -Fe-Cr multilayers [5]; -Fe-Ag granular alloys [19]; , , -three Pt/Au/Co/Pt sandwiches [16]; , -Fe films (19 and 75 nm thick) [13]; -Ni films [15]; -Co-Cu superlattice [18]; -polycrystalline Fe films [14]; -Fe-Cr multilayers [17]. …”

Photoelectron spectroscopic and computational studies of the Pt@Pb101- and Pt@Pb121-/2- anions

“…Since that time, scientists have pursued new materials utilizing various Zintl ion precursors to both ionically and covalently link the cluster anions into oligomers (14)(15)(16)(17)(18), polymers (19,20), network solids (21)(22)(23), and nanomaterials (24)(25)(26). Simultaneously, gas-phase chemists have prepared bare (e.g., ligand-free) clusters in molecular beams, studied their size-dependent properties, and explored possible condensed-phased manifestations (27)(28)(29)(30). Especially notable was the discovery of C 60 (31) 20 ), but they can also be prepared in macroscopic quantities, fully characterized, and used in subsequent reactions.…”

Structure and magnetism in Cr-embedded Co nanoparticles

“…Atomic structure change has been reported in Fe and Co nanoparticles embedded in various matrices [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. A convenient way of embedding nanoparticles in a matrix, directly from the gas phase, is provided by the low energy cluster beam deposition (LECBD) method [22]. This is a highly controllable technique in which nanoparticles (from a gas aggregation type source) are co-deposited with the matrix material (from a molecular beam epitaxy -MBEsource) onto a solid substrate.…”