Sung-Chae Yang

Preparation of Fullerene by Pulsed Wire Discharge

Carbon fibers were discharged in N2 and Ar gas at pressures between 200 and 750 Torr by pulsed wire discharge to prepare fullerene. In experiments using N2 gas, carbon fibers were almost completely evaporated to form soot, while the fibers were not effectively heated in Ar gas due to the occurrence of surface creepage. In the soot prepared in N2 gas, we observed C60 and C70 molecules by mass spectroscopy and ultraviolet/visible absorption spectroscopy. Since this method is very simple and inexpensive, mass production of fullerene with high energy-conversion efficiency will be possible by pulsed wire discharge.

Pulsed Power Technology and Its Applications at Extreme Energy-Density Research Institute (EDI), Nagaoka

Recent activities conserning pulsed power technology and its applications are reviewed. Using high-density ablation plasma produced due to the short range of an ion beam in targets, we have successfully prepared crystallized B4C thin films by ion-beam evaporation, which are characterized by hardness, wear resistance, and stability at high temperatures. Fullerenes have been prepared as well. Ultrafine nanosize powders were synthesized by pulsed wire discharge. Flue gas treatment of NOx was achieved by intense pulsed relativistic electron beam. Foil acceleration was observed to be ~8 km/s at the ablation pressure of 13 GPa. Pulsed laser deposition was used to prepare (Cr1-x, Alx)N films. The AlN solubility limit was found to be 77 at.% AlN. The hardness of the films increases with x up to 0.75, and decreases rapidly due to their being amorphous in structure. A highly repetitive, new pulsed power generator is operational, with the specifications of 400 kV, 13 kA, 120 ns, and 1 pps.

Preparation of polycrystalline silicon thin films by pulsed ion-beam evaporation

By intense pulsed ion beam evaporation, we have succeeded in the preparation of polycrystalline silicon thin films on silicon substrate. High crystallinity and deposition rate have been achieved without heating the substrate. The crystallinity of poly-Si film has been improved with increasing the density of the ablation plasma, where the grain size of the film has been found to be much smaller. To enhance the crystallinity and density of poly-Si thin film, bias voltage was applied to the substrate, where the quality of poly-Si film has been improved by the ion bombardment.

Characteristics of polycrystalline silicon thin films prepared by pulsed ion-beam evaporation

Using the intense pulsed ion-beam evaporation method, we have succeeded in preparing polycrystalline silicon thin films without impurities on substrates of silicon and quartz. High crystallinity and deposition rate were achieved without heating the substrate. Since the lifetime of the ablation plasma, which was obtained by a pulsed ion beam with 50-ns pulse width, is of the order of 20 μs, the instantaneous deposition rate is in the region of cm/s. The crystallinity of poly-Si film has been improved by increasing the density of the ablation plasma, whereby the grain size of the film was found to be smaller.

Blue Light Emission from Ultrafine Nanosized Powder of Silicon Produced by Intense Pulsed Ion-Beam Evaporation

Blue light emission has been observed from ultrafine nanosized powder of silicon, which was synthesized by rapid cooling of high-density ablation plasma produced by intense pulsed light-ion beam interaction with a silicon target, called pulsed ion-beam evaporation. The emission appears from the powder without heat treatment after being synthesized. Furthermore, the emission is found to be very stable; neither red- nor blue-shift is observed. In fact, the spectrum from the powder four months after the synthesis is the same as those from as-synthesized powder. The rapid heat cooling inherent to ion-beam evaporation seems to be essential for emission.

Pulsed ion beam evaporation at low temperature for the preparation of thin films

Using high-density ablation plasma produced by pulsed ion beam interaction with solid targets, it has been demonstrated by the present authors to prepare thin films at low temperature, which was called ion beam evaporation. In addition to the first preparation of ZnS in 1988, the preparation of many films has been succeeded such as YBCO, (SrBa)TiO/sub 3/, SrAl/sub 2/O/sub 4/:Eu, poly-Si, ITO, and apatite. Since some of them have been already reported elsewhere, some other new results of the preparation of thin films by IBE are presented such as Si-Ge or HfO/sub 2/.

Novel applications of intense pulsed ion beams in materials science

Using pulsed ion beam evaporation technique, experimental studies were carried out to embed metals into via holes in LSI. It will be shown that tungsten is successfully embedded in via holes with the aspect ratio of 4.3. Furthermore, light emission of blue has been observed from a poly silicon nanosize powders, which is also produced by pulsed ion beam evaporation technique.

Preparation of crystalline Si 1−x Ge x thin films by pulsed ion-beam evaporation

Thin films of single phase, polycrystalline silicon germanium (Si<inf>1−x</inf>Ge<inf>x</inf>) were prepared by ion-beam evaporation (IBE) using Si-Ge multi-phase targets. After the irradiation of the targets by an pulsed light ion beam with peak energy of 1 MV, 450 and 480 nm thick films were deposited on Si single crystal and quartz glass substrates, respectively. From XRD analysis, the thin films consisted of a single phase Si<inf>1−x</inf>Ge<inf>x</inf>, whose composition is close to those of the targets.