Tomihiro Sonegawa

APPLICATIONS OF INTENSE PULSED ION BEAM TO MATERIALS SCIENCE

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 co...

Preparation of Thin Films and Nanosize Powders by Intense, Pulsed Ion Beam Evaporation

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.

Preparation of thin films of dielectric materials using high-density ablation plasma produced by intense pulsed ion beam

Abstract By use of a high-density ablation plasma produced by the interaction of an intense pulsed light-ion beam with a solid target, the preparation of thin films has been successfully demonstrated, and is called ion beam evaporation (IBE). In addition to a standard front-side deposition of thin films (FS/IBE), significant improvement of the films has been achieved with much better morphology as well as electrical properties by back-side deposition (BS/IBE), In the BS/IBE configuration, the substrate is placed on the reverse side of the target holder, being free from droplets sometimes observed by the FS/IBE. Using BaTiO3, (Ba0.5, Sr0.5)TiO3 and SrTiO3 targets, experimental results are presented in detail on the preparation of these thin films by the BS/IBE.

Preparation of BaTiO3 thin films by backside pulsed ion‐beam evaporation

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.

Low-temperature preparation of BaTiO 3 thin films by intense, pulsed, ion beam evaporation

Cubic barium titanate (BaTiO 3 ) thin films have been prepared in situ , on a low-temperature substrate, Al/SiO 2 /Si(100), by intense, pulsed ion beam evaporation. We have first proposed a new deposition configuration, backside deposition, which, in comparison with standard frontside deposition, produces very smooth thin films, R α (mean roughness) ≈ 3 ∼ 9 nm, without any droplets. There is no significant change of the dielectric constant in the frequency range of 10 ∼ 10 5 Hz. The dielectric constant for the film deposited at the substrate temperature of 200˚C is typically ∼90 at 1 kHz.

Analysis of Layer Structure Variation of Periodic Porous Silicon Multilayer

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.

Thin-film deposition of (Ba/sub x/Sr/sub 1-x/)TiO/sub 3/ by pulsed ion beam evaporation

An ablation plasma generated by intense, pulsed ion beam was used for thin-film deposition of commercially interesting material (Ba/sub x/,Sr/sub 1-x/)TiO/sub 3/ (0<x<1). The deposition has been carried out in vacuum and on the substrate at the room temperature. The deposited thin films were analyzed by using Rutherford backward scattering, X-ray photoelectron spectroscopy, atomic force microscope and scanning electron microscopy. It has been understood that the film deposition rate was /spl sim/20 nm/shot and the thin film had the same composition as the target. Maximum dielectric constant was obtained at x=0.5.

Ferroelectric Thin Films Prepared by Backside Pulsed Ion-Beam Evaporation

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.

Measurement of Porosity of Porous Silicon Using X-Ray Refraction Effect

A new method for the measurement of porosity in porous silicon , which enables us to determine the porosity of inner layers as well as that of each layer in multilayers using X-ray diffraction, is proposed. This method essentially applies the refraction of X-rays incident on the surface at a very small glancing angle for the separation of diffraction angles. To demonstrate the applicability of this method, the porosities of three samples of monolayers with different porosities and of a sample including multilayers were measured. The obtained values of porosities in monolayers are in good agreement with those obtained by the conventional gravimetric technique, and the value for each layer in the multilayers is consistent with the designed values for the multilayers. Thus, this method yields the porosities of various porous layers nondestructively; this has never been measured by conventional methods.

Applications of intense pulsed light ion beams to materials science

By an intense pulsed light ion beam (LIE) interaction with target, high density ablation plasma is produced (ion beam ablation plasma: IBAP) due to short range of LIE. Since the first preparation of thin films of ZnS by IBAP in 1988 (ion beam evaporation: IBE), we prepared various kinds of thin films. In addition to standard front side deposition by IBE (FS/IBE), where a substrate is located in front of the target, significant improvement has been achieved of the film quality by back side deposition (BS/IBE), where the substrate is placed just behind the holder. Characteristics of the films by BS/IBE are shown. By rapid cooling of IBAP, we synthesized nanosize powders. Fullerene has also been successfully prepared. Furthermore, foil acceleration has been studied by the irradiation of LIE on a target. Quick overview is given on the applications of IBAP in materials science.