In-situ organization of nanoparticles by scanning force microscopy under terrestrial and microgravity conditions

Abstract

Scanning force microscopy (SFM) is proposed as a tool to organize logical and other operative nanostructures constructed from prefabricated, 10-nm-sized particles randomly deposited onto suitable substrate materials by a “bottom-up” technology. The “nanoconductors” are prepared from metals or semiconductors by evaporating into a thermalizing background gas: the vapour is cooled down to a supersaturated state until particle nucleation sets in. The choice of gas pressure and vaporization rate serves to controlling both the size and total number of particles in a wide range. Fitting to the present purpose, by this technique, individual nanoconductors can be produced in a very small number and — using several independent heaters — also from different substances. The application of a metal-covered tip-cantilever system in an SFM instrument does not only allow to study the surface morphology of conducting and insulating particles, but also to analyse their electronic and optical properties. Upon selection, it is intended to displace specified particles to predetermined positions on the substrate surface and to build up functional schemes. By modifying the force detection system, the SFM may be used to measure forces acting on these particles. Under terrestrial and microgravity (μg) conditions, comparative studies are suggested to examine (a) the influence of gravity on nucleation behaviour and particle growth, (b) basic physical phenomena, and (c) the possibility of organizing logical and cybernetic systems: (a) There is general agreement that even tiny influences may have significant effects on non-equilibrium processes such as nucleation. For modem nanotechnology, where the respective habitus and structure of single particles are of considerable importance, comparative fabrication under μg-conditions is strongly recommended. (b) The characterization of forces acting between the SFM tip and a nanoparticle, between nanoparticles among one another, as well as between nanoparticles and substrate materials on a nanometer- or even atomic-scale is essential for the elucidation of interaction phenomena and estimation of friction coefficients. In addition, structural, electronic, and optical properties of individual particles will be inspected as a function of size and material. (c) The fashioning of systems consisting of two or more nanoparticles and the investigation of the resulting electrical properties as a function of size, material, and separation of adjacent particles. μg-conditions also open up access to the third dimension. Many degrees of freedom provided by μg-conditions, the specific physical properties of nanoparticles, and the “bottom-up” technology permit the formation of electrical devices or sensors on a nanometer-scale exhibiting well known characteristics. Moreover, the range of potential applications can be much more extended by the opportunity of constructing various ingenious particle arrangements operating as logical or cybernetic systems.