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Self-formed nanopatterns on Si (001) substrates fabricated by ion beam sputter etching were investigated by atomic force microscopy (AFM). The ion beam sputtering was performed with an Ar` ion beam produced from a Kaufman type ion gun. In order to fabricate the periodic nanoscale patterns on Si surface, the effects of sputter parameters such as ion energy, flux, incident angle and etching time on surface morphology was investigated. As a result, nanometer scale ripples and 3-dimensioal nanodots were formed uniformly after ion beam sputtering. The surface morphology of Si was significantly dependent on incident angle and ion beam flux, however, it was independent of ion beam energy and etching time. (Received August 3, 2004)

keyword : Ion beam sputter-etching, Topography of Si (001), Self-formed nanopatterns, AFM

The n-Type thermoelectric compounds of Bi₂Te_(2.75)Se_(0.15) doped with 0.1 wt% SbI₃ were fabricated by gas atomization process and extruded under ratio of 16:1 and 28:1 at 450℃. The effect of extrusion ratio on the microstructures and thermoelectric properties were investigated by a combination of microscopy, XRD and thermoelectric properties. Grains of extruded bars are smaller than those of heated powder at extrusion temperature (450℃) due to the dynamic recrystallization but with increasing the amount of plastic deformation, grains of specimen extruded with 28:1 were slightly coarse. The compressive strength of hot extruded bar under 28:1 is 160 MPa and with decreasing the extrusion ratio to 16:1, the value is 250 MPa. The Seebeck coefficient a and electrical resistivity p were decreased with increasing ratio, while thermal conductivity x was increased. this results from decrease of carrier scattering and increase of carrier mobility. Extruded bar under ratio of 16:1 shows the higher value of figure of merit (Z=2.50x10^(-3)/K) than that of 28:1 (Z=2.07x10^(-3)/K). (Received June 24, 2004)

keyword : Thermoelectric properties, Extrusion ratio, Compressive strength, Bi2Te2.75Se0.15

Ever since its first appearance in the Korean peninsula, bronze must have been playing an important role in Korean history. Due to the lack of metallurgical work, however, the archaeological study, based primarily on artifact typology, has produced little information on the technical aspects of bronze production in Korea. With this problem in mind and to understand the evolution of Korean bronze, the present study has examined microstructure of bronze artifacts excavated from the Boonhwang temple site in Kyongju. Three artifacts from other sites were also examined for comparison. Important evidence of technical transition was noticed in alloy composition and also in various thermo-mechanical treatments. The Sn content approaching the peritectic point in the Cu-Sn phase diagram and the removal of Pb from alloys were clearly evident with time. This change was coupled with the introduction, subsequent to casting, of special treatments such as quenching and forging. This study is to establish a general framework, though rough, that may be referenced and refined in future studies to the better assessment of Korean bronze technology with respect to its progressive development and its role in history. (Received June 8, 2004)

keyword : Metallurgical microstructure, Bronze artifacts, Boonhwang temple, Technology, Transition