Cluster-assembled Films Research Articles

Poly( N-vinyl-2-pyrrolidone) cluster-assembled nanostructured films prepared by low energy cluster beam deposition

Poly( N-vinyl-2-pyrrolidone) (PVP) cluster-assembled nanostructured films have been prepared by low energy cluster beam deposition method. TEM micrographs show that the films are assembled by spherical particles, which are distributed uniformly and randomly in the films. The pressure of helium carrier gas has a significant effect on the particle sizes and their distribution. Fourier transform infra-red and UV–Vis absorption spectra measurement have been performed so as to determine the structures and analyze the optical properties of the films. It is shown that the structural units of the nanoparticles of PVP cluster-assembled films are almost the same as that of original PVP. When compared to the original PVP casting film, PVP cluster-assembled film has 18 nm blue shift of maximum absorption and 0.67 eV blue shift of band gap.

Acoustic phonon propagation and elastic properties of cluster-assembled carbon films investigated by Brillouin light scattering

Acoustic phonon propagation and elastic properties of cluster-assembled carbon films investigated by Brillouin light scattering

Impact induced chemisorption of C 20 isomers on diamond (0 0 1)–(2×1) surface

The adsorption of low-energy C 20 isomers on diamond (0 0 1)–(2×1) surface was investigated by molecular dynamics simulation using the Brenner potential. The energy dependence of chemisorption characteristic was studied. We found that there existed an energy threshold for chemisorption of C 20 to occur. Between 10 and 20 eV, the C 20 fullerene has high probability of chemisorption and the adsorbed cage retains its original structure, which supports the experimental observations of memory effects. However, the structures of the adsorbed bowl and ring C 20 were different from their original ones. In this case, the local order in cluster-assembled films would be different from the free clusters.

Magnetic behaviour of exposed and embedded nanoclusters

Cluster-assembled films made by depositing nanoscale Fe clusters from a UHV-compatible gas aggregation source have been studied in situ using STM, X-ray dichroism and magnetometry. We follow the evolution of the properties of the films supported on substrates and exposed in UHV, as a function of cluster size and coverage. The STM images show that there is no significant diffusion of the Fe clusters deposited onto Si(111) surfaces at room temperature and that dense films of clusters do not coalesce but maintain their granular nature, X-ray magnetic circular dichroism measurments show that isolated 300-atom clusters adsorbed on graphite have an orbital moment per atom that is double the bulk value and a spin moment enhanced by 4% giving a total moment 10% greater than the bulk. Both moments tend towards the bulk value as either the cluster size or the density of clusters on the surface increases. The isolated clusters are superparamagnetic above 10K but the films have an increasing magnetic remanence at higher temperatures as the cluster density is increased. Thick cluster films have a strong in-plane anisotropy. Films of Fe clusters embedded in Cu and Ag show a giant magneto-resistance that peaks sharply with volume fraction.

Cluster-assembled carbon films with different nanostructures: a spectroscopic study

Carbon thin films with different nanostructures grown by Cluster Beam Deposition are studied by means of Raman Spectroscopy, X-ray photoemission spectroscopy (XPS), and electron energy loss spectroscopy (EELS). Raman and EELS of the as-grown specimens show a correlation between the properties of the free carbon clusters and the properties of the films obtained by deposition of different sized clusters. In contrast, the inhomogeneous character of the films is not reflected in the valence band states as seen by XPS.

Self-affine properties of cluster-assembled carbon thin films

Surface morphologies of nanostructured carbon films, produced by supersonic cluster beam deposition, have been investigated by atomic force microscopy. From topographical images, we evaluated the surface roughness corresponding to different scan lengths and thicknesses, and deduced that the images examined are self-affine. Experimental scaling exponents and the hypothesis of non-destructive primeval cluster aggregation suggest that quenched noise effects may be important in the process of growth of the nanostructured surfaces.

Properties of silicon and silicon-carbon cluster assembled films

Si-and SiC cluster-assembled films have been produced in a laser vaporization source and analyzed in terms of electronic structure and vibrational density of states. In small silicon clusters (nanometer size range), we put on evidence five-fold rings into the films. In the case of SiC clusters, we observe the lack of the chemical order.

Synthesis and Characterization of Cluster-Assembled Carbon Films

ABSTRACTNanostructured carbon films have been grown by deposition of supersonic cluster beams. A novel pulsed microplasma cluster source allows to obtain cluster beams of high intensity and stability. Cluster growth and beam formation have been charaterized. Separation effects typical of supersonic expansions cause inhomogeneities of cluster distribution in the beam, depending on their masses. This effect, observed for the first time, has been carefully characterized. The deposited films have a low density porous structure based on nanometer-size grains. The coordination is essentially three-fold with a large number of defects. Film density, morphology and surface roughness can be controlled by varying the precursor cluster mass distribution. Applications of cluster-assembled carbon films will be presented.

Electronic signature of the pentagonal rings in silicon clathrate phases: Comparison with cluster-assembled films

The valence-band spectrum of the silicon Si-34 clathrate phase has been measured by photoemission spectroscopy. In contrast with tetrahedral Si (diamond phase), the clathrate structure presents mainly five-member rings. From the comparison between the tetrahedral Si and the clathrate spectra, we show that the presence of odd-member rings induces the merging between s-like and sp-like bands and a strong reduction of the valence-band width. These results are corroborated by first-principles calculations within an accurate quasiparticle approach.

Synthesis and characterization of cluster-assembled carbon thin films

Nanostructured carbon thin films have been produced by deposition of supersonic cluster beams. The clusters are generated by a pulsed arc cluster ion source modified in order to achieve high fluxes and stability. Scanning electron microscopy, Raman, and optical spectroscopy show that the films are a low density network of nanometer-size particles. The nature of the films is essentially graphite-like with a large number of distorted bonds. The formation of structures based on sp3 bondings is not observed. The use of cluster beam deposition for the synthesis of nanocrystalline thin films is discussed.

Cobalt and nickel cluster-assembled thin films obtained by low-energy cluster beam deposition

Abstract Nanostructured films of cobalt and nickel have been prepared using the low-energy neutral cluster beam deposition technique on various substrates. The nucleation-and-growth process of the films has been studied by in-situ electrical conductivity measurements and transmission electron microscopy observations. Complementary results obtained from X-ray diffraction and absorption measurements on films 100 nm thick confirm the nanostructured morphologies of both Co and Ni films consisting of a random stacking of well crystallized fcc grains having a diameter of around 3–4 nm. In terms of magnetic properties the granular structure leads to films which roughly behave like amorphous ferromagnets but with local order of the extent of a grain. From magnetization measurements and ferromagnetic resonance experiments which showed spin-wave oscillations, the magnetic parameters characteristic of the cluster-assembled films (i.e. magnetocrystalline anisotropy and intergrain exchange coupling energies) have been...

FROM FREE CLUSTERS TO CLUSTER-ASSEMBLED MATERIALS

In this paper the specific properties of free clusters and the formation of new cluster-assembled materials using the low energy cluster beam deposition (LECBD) technique are discussed. Recent results obtained for free clusters are summarized with special attention to new observed structures. As for the specific structures and properties of cluster-assembled materials, two main aspects are specially emphasized: the memory effect of the free cluster properties leading to the formation of new phases and the effect of the specific nanostructure of the cluster-assembled materials related to the random cluster stacking mechanism characteristic of the LECBD. These effects and the corresponding potential applications are illustrated using some selected examples: new diamond-like carbon films produced by fullerene depositions (memory effect) and grain effect on the magnetic properties of cluster-assembled transition metal films.

Production of Ultra-Thin Metal Films Using Neutral Cluster Beams

ABSTRACTGold clusters (diam. = 1.0 ± .5 nm) are prepared in a gas aggregation source (MECS), expanded into a vacuum chamber to form a neutral cluster beam, and deposited at low impact velocity on room temperature substrates. When several monolayers of these clusters are deposited on clean substrates (nitrocellulose, glass, mica, NaCl), they form smooth ultra-thin films. These cluster-assembled films appear to be similar in quality to those produced by the Takagi-Yamada ion cluster beam process. They exhibit finite electrical conductivity at thicknesses much smaller than is the case with atomically evaporated films. They are extremely uniform and smooth with a surface height that typically varies less than 1 nm across the entire film.