In addition to being initially developed as an energy driver for an inertial confinement fusion, an intense, pulsed, light-ion beam (LIB) has been found to be applied to materials science. If a LIB is used to irradiate targets, a high-density ‘‘ablation’’ plasma is produced near the surface since the range of the LIB in materials is very short. Since the first demonstration of quick preparation of thin films of ZnS by an intense, pulsed, ion-beam evaporation (IBE) using the LIB-produced ablation plasma, various thin films have been successfully prepared, such as of ZnS:Mn, YBaCuO, BaTiO3, cubic BN, SiC, ZrO2, ITO, B, C, and apatite. Some of these data will be presented in this paper, with its analytic solution derived from a one-dimensional, hydrodynamic, adiabatic expansion model for the IBE. The temperature will be deduced using ion-flux signals measured by a biased ion collector. Reasonable agreement is obtained between the experiment and the simulation. High-energy LIB implantation to make chemical compounds and the associated surface modification are also discussed.
Efficient preparation of thin films has been achieved with a high-density ablation plasma produced by the interaction of an intense, pulsed ion beam with solid targets, a process called ion beam evaporation, having an instantaneous deposition rate of cm/s. In addition to standard front-side deposition, backside deposition, in which the substrate is placed on the reverse side of the holder, has been proposed to produce good quality thin films, though the deposition rate is one order of magnitude less than that in front-side deposition. By cooling of the ablation plasma, ultrafine nanosize ceramic powders, with a typical particle diameter of 10 nm, have been produced. The basic characteristics of the ablation plasma have been clarified by use of 1-D hydrodynamic equations with a simplified model involving primary ion-beam-driven expansion followed by adiabatic expansion into a vacuum. Analytical solutions will be given to define the plasma parameters.
Structures of periodic porous silicon multilayer, which were formed by the current density modulation method, were investigated by cross-sectional scanning electron microscopy (SEM) observation. When the layers were formed with a current density of 20 mA/cm2 or less the thickness of the layers was constant regardless of the stack position of the layer. When the layers were formed with a current density of 50 mA/cm2 or more, the thickness of the layers decreased and the porosity of the layers increased as the stack position of the layer became deep. The layer peeled off when the porosity of the layer increased up to aproximately 100%. The thickness variation of the layers and the peeling were prevented by raising the temperature of the electrolyte.
Barium titanate (BaTiO3) thin films were successfully prepared in situ on Al/SiO2/Si(100) substrates by backside deposition from intense, pulsed, ion-beam evaporation using a 1.3 MeV, 50 ns, 25 J/cm2 ion beam. Good morphology of the films prepared was observed, where no droplets appear compared to normal frontal-side deposition. The deposition rates were typically 100 nm/shot. The films were perovskite polycrystals. The capacitance of the thin films (at 1 kHz) increased from 3 to 10 nF/mm2 with increasing substrate temperature from 25 to 250 °C, respectively.
Ferroelectric (PbTiO3 or Pb(Zr, Ti)O3) thin films have been successfully prepared on Si(100) or pyrex glasses by backside deposition of intense pulsed ion beam evaporation. The ion beam parameters were typically as follows: beam energy=1.3 MeV, ion-current density on target=0.7 kA/cm2 and pulse duration=50 ns. The composition of the thin films was in good agreement with that of the original target. The relative dielectric constant at 1 kHz was obtained to be 20, while that obtained by normal front side deposition was 150.
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