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A simple relationship between the ratio of atomic transport induced by ion mixing and the activation energies for the impurity diffusion of constituents in a bilayer is presented to describe quantitatively the symmetric and asymmetric atomic transport in the thermal spike induced ion mixing. The model predicts fairly satisfactorily the trend of experimental observations in the bilayer-systems which have near zero heats of mixing and relatively high spike activation energies. For instance, the Pd/Co bilayer system shows nearly symmetric atomic transport, since its constituents have similar activation energies for the impurity diffusion.4292

ABSRACTPolyimide thin films are deposited by the ionized cluster beau deposition( ICBD technique. Polymerization and crystallization of polyimide were investigated using TEM, IR, and the electronic structure of the polyimlde film was investigated using XPS. Films deposited at optimum ion acceleration voltage showed strong preferential crystal orientation. Crystalline polyimide film was obtained at ion acceleration voltage of 700 V. INTRIODUCTIONThe aromatic polyinide group is composed of thermally-stable polymers that exhibit excellent chemical resistance, good mechanical properties and high electrical insulation ( I101 ohm-cm at 20r ). They are thus used not only for microelectronic devices but also for aircraft and space applications, mainly owing to their ability to withstand temperatures up to 500r[1]. Polyimide films have conventionally been prepared by the chemical method [2]. The most widespread method for preparation of aromatic polyiaide involves a reaction of an aromatic tetracarboxylic acid dianhydride monomer [e.g.,pyromellitic dianhydride (PMDA)] with an aromatic diamine monomer [e.g.,oxydianiline(ODA)].The two monomers are mixed in a highly polar solvent [e.g.,dimethylformamide(DNF)] to form a polyamic acid solution. When being heated at the desired temperature the polyanic acid film, which can be obtained by spin coating the polyamic acid solution on a substrate, transforms to the polyiaide film through dehydration and crosslinking reactions. The problems of this chemical method are the difficulties in controlling the film thickness, the degradation of the film by the remaining solvent and pollution due to the volatile solvent.In this paper, we present a new physical method for preparation of crystalline polyimide film using the ionized cluster bean deposition (ICBD)technique[3].EXPEINErTAL PROCEDURES Fig.1 shows the ICBD system used for crystalline polyiaide deposition.Two ionized cluster beam sources were used to produce the polyimide film. Each sample was contained in a stainless-steel crucible (nozzle diameter I ma), and they were heated separately by Mo wire heaters, The molecules ejected from the heated crucible through the narrow nozzle form a cluster due to the adiabatic expansion process. After the clusters were ionized by the electron beam ejected by a tungsten filament, they were accelerated by the high voltage applied between the crucibles and the substrate holder. NaCl (100) substrates were used to facilitate IR and electron diffraction measurements.