We report on a source for producing size-selected nanoclusters based on the combination of radio frequency magnetron plasma sputtering and gas condensation. The use of plasma sputtering to vaporize a target is applicable to a large range of materials; Ag, Au, Cu, and Si have been attempted to date. The source, combined with a time-of-flight mass filter, can produce clusters in the size range from 2 up to at least 70 000 atoms, depending on the target material, with a constant mass (M) resolution (M∕ΔM∼25) at an intensity that produces atomic monolayer coverage in as little as a few minutes. The source is also attached to an ultrahigh vacuum analysis chamber, which allows in situ surface chemical and structural analysis. Examples of cluster deposition experiments with the source are also presented.

The deposition of ionized beams of size-selected atomic clusters onto well-defined substrates represents a new method of preparing nanostructured surfaces, with lateral feature sizes in the range 1-10 nm. 'Pinning' of the incident clusters prevents the diffusion of the clusters on the surface, and thus preserves the gas-phase cluster size, even at room temperature and above. At the same time, advances in diblock copolymer techniques allow the preparation of ordered two-dimensional arrays of clusters. Here we discuss the creation and applications of these nanostructured surfaces, ranging from the fabrication of semiconductor nanostructures to the immobilization of protein molecules.

Understanding the growth mechanism in molecular organic thin films is fundamental to their applications in organic electronics. We present an extensive study of the growth mechanism of pentacene thin films on silicon dioxide (SiO 2 ) using atomic force microscopy. For a fixed substrate temperature T s , the deposition rate is found to be a key parameter in controlling the nucleation density in the submonolayer regime and hence transport properties in the first layer of the organic field effect transistors. At a fixed T s ϭ338 K the maximum number of pentacene islands per unit area N follows the scaling law Nϰ ␦ with ␦ϭ1.16Ϯ0.10. A mechanism of homogeneous nucleation followed by diffusive growth accounts for this behavior and allows us to estimate the critical nucleus size of the pentacene islands. The results obtained from a statistical analysis of the island size distribution are fully consistent with a phenomenological capture zone model. The validity of this model depends on the extent of reevaporation of pentacene admolecules during deposition, which is moderated by the deposition rate. We demonstrate that the rate dependence of island nucleation has important implications for the density of grain boundaries, which may play an important role in the transport mechanism.

We present a comparative study of the nucleation and growth of pentacene monolayer islands in the submonolayer regime onto inorganic substrates of SiO 2 and sapphire ͑Al 2 O 3 ͒ and organic substrates of poly͑methyl-metacrylate͒ ͑PMMA͒. We have determined the scaling laws that govern the saturated nucleation density per unit area N as a function of two essential deposition parameters: the deposition rate and the substrate temperature T s . For all substrates, we found N ϰ ␦ , with 0.8ഛ ␦ ഛ 1.2, and the T s dependence of the nucleation density follows a typical activated Arrhenius law. Whereas a critical nucleus size of i = 2 is obtained for all investigated substrates, the activation energy for nucleation depends significantly on the dielectric. The difference in activation energy of nucleation on PMMA and SiO 2 is due to different molecule-substrate interactions.