• Journal of the Korean Ceramic Society
• /
• v.48 no.4
• /
• pp.312-315
• /
• 2011

The effect of slurry composition and wafer flatness on a material removal rate (MRR) and resulting surface roughness which are evaluation parameters to determine the CMP characteristics of the on-axis 6H-SiC substrate were systematically investigated. 2-inch SiC wafers were fabricated from the ingot grown by a conventional physical vapor transport (PVT) method were used for this study. The SiC substrate after the CMP process using slurry added oxidizers into slurry consisted of KOH-based colloidal silica and nano-size diamond particle exhibited the significant MRR value and a fine surface without any surface damages. SiC wafers with high bow value after the CMP process exhibited large variation in surface roughness value compared to wafer with low bow value. The CMPprocessed SiC wafer having a low bow value of 1im was observed to result in the Root-mean-square height (RMS) value of 2.747 A and the mean height (Ra) value of 2.147 A.

• Korean Journal of Materials Research
• /
• v.2 no.2
• /
• pp.119-125
• /
• 1992

Oxygen segregation in horizontal-magnetic-field-applied Czochralski (HMCZ) silicon crystals has been studied as a function of magnetic field strength (B) and crucible rotation rate (C). Along the axis of 57mm din. <100> crystals grown under B=2, 3, 4 kG and C=4-15rpm, the oxygen distribution was usually saw-tooth shaped and fluctuated unevenly. Compared to the conventional CZ method, this result seems to indicate that the horizontal magnetic field, at levels used in the present experiment, had a destabilizing influence on oxygen transport to the growth interface. On the other hand, as C increased, the oxygen fluctuation lessened, and [0] increased overall. At B=2 kG, an oxygen profile in a level of 27-36 ppma was achieved by a programmed ramp of C. Oxygen precipitation behavior of the HMCZ silicon during a simulated device manufacturing process was compared and found to be inferior to that of typical CZ silicon. The uneven oxygen profile in the as-grown state was identified as the major source of poor precipitation uniformity in the HMCZ silicon.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.8
• /
• pp.2671-2676
• /
• 2011

Nanocrystalline $TiO_2$ spherical particle (NP) with a dimension of 5 ${\times}$ 5.5 nm and several nanorods (NR) with different aspect ratios (diameter ${\times}$ length: 5 ${\times}$ 8.5, 4 ${\times}$ 15, 4 ${\times}$ 18 and 3.5 ${\times}$ 22 nm) were selectively synthesized by a solvothermal process combined with non-hydrolytic sol-gel reaction. With varying the molar ratio of TTIP to oleic acid from 1:1 to 1:16, the NRs in the pure anatase phase were elongated to the c-axis direction. The prepared NP and NRs were applied for the formation of nanoporous $TiO_2$ layers in dye-sensitized solar cell (DSSC). Among them, NR2 ($TiO_2$ nanorod with 4 ${\times}$ 15 nm) exhibited the highest cell performance: Its photovoltaic conversion efficiency (${\eta}$) of 6.07%, with $J_{sc}$ of 13.473 mA/$cm^2$, $V_{oc}$ of 0.640 V, and FF of 70.32%, was 1.44 times that of NP with a size of 5 ${\times}$ 5.5 nm. It was observed from the transient photoelectron spectroscopy and the incident photon to current conversion efficiency (IPCE) spectra that the $TiO_2$ films derived from NR2 demonstrate the longest electron diffusion length ($L_e$) and the highest external quantum efficiency (EQE).

• Progress in Superconductivity
• /
• v.6 no.2
• /
• pp.95-98
• /
• 2005

We present results of Raman spectroscopic studies of superconducting $YBa_2Cu_3O_7$ (YBCO) coated conductors. Raman scattering is used to characterize optical phonon modes, oxygen content, c-axis misalignment, and second phases of the YBCO coated conductors at a micro scale. A two-dimensional mapping of Raman spectra with transport properties has been performed to elucidate the effect of local propertied on current path and superconducting phase. The information taken from the local measurement will be useful for optimizing the process condition.

• Progress in Medical Physics
• /
• v.11 no.2
• /
• pp.117-122
• /
• 2000

The IP(imaging plate) has been widely used to measure the two-dimensional distribution of incident radiation since it has a high sensitivity, reusability, a wide dynamic range, a high position resolution. Particularly, the easiness of acquiring digitized image using IP poses a strong merit because recent trend of data handling prefers image digitization. In order to test its usefulness in photon beam dosimetry, we measured the off-axis ratio(OAR) on portal planes and percent depth dose(PDD) within a phantom using IP, and compared the results with the data based on EGS4 Monte Carlo particle transport code, ion-chambers, conventional films. For the measurement, we used 6 MV X-rays, various field sizes. As a result, IP showed significant deviation from ion-chamber measurement: a significant overresponse, 100% greater than that of ion-chamber measurement at deep part of the phantom. Filtration of low-energy scattered photons at deep part of the phantom using 0.5 mm thick lead sheets did improve the result, only to the unacceptable extent. However, portal dose measurement showed possibilities of If as a dosimeter by showing errors less than 5%, as compared with film measurement.

• Ocean and Polar Research
• /
• v.26 no.3
• /
• pp.385-400
• /
• 2004

The Lago Sofia Conglomerate encased in the 2km thick hemipelagic mudstones and thinbedded turbidites of the Cretaceous Cerro Toro Formation, southern Chile, is a deposit of a gigantic submarine channel developed along a foredeep trough. It is hundreds of meters thick kilometers wide, and extends for more than 120km from north to south, representing one of the largest ancient submarine channels in the world. The channel deposits consist of four major facies, including stratified conglomerates (Facies A), massive or graded conglomerates (Facies B), normally graded conglomerates with intraformational megaclasts (Facies C), and thick-bedded massive sandstones (Facies D). Conglomerates of Facies A and B show laterally inclined stratification, foreset stratification, and hollow-fill structures, reminiscent of terrestrial fluvial deposits and are suggestive of highly competent gravelly turbidity currents. Facies C conglomerates are interpreted as deposits of composite or multiphase debris flows associated with preceding hyperconcentrated flows. Facies D sandstones indicate rapidly dissipating, sand-rich turbidity currents. The Lago Sofia Conglomerate occurs as isolated channel-fill bodies in the northern part of the study area, generally less than 100m thick, composed mainly of Facies C conglomerates and intercalated between much thicker fine-grained deposits. Paleocurrent data indicate sediment transport to the east and southeast. They are interpreted to represent tributaries of a larger submarine channel system, which joined to form a trunk channel to the south. The conglomerate in the southern part is more than 300 m thick, composed of subequal proportions of Facies A, B, and C conglomerates, and overlain by hundreds of m-thick turbidite sandstones (Facies D) with scarce intervening fine-grained deposits. It is interpreted as vertically stacked and interconnected channel bodies formed by a trunk channel confined along the axis of the foredeep trough. The channel bodies in the southern part are classified into 5 architectural elements on the basis of large-scale bed geometry and sedimentary facies: (1) stacked sheets, indicative of bedload deposition by turbidity currents and typical of broad gravel bars in terrestrial gravelly braided rivers, (2) laterally-inclined strata, suggestive of lateral accretion with respect to paleocurrent direction and related to spiral flows in curved channel segments around bars, (3) foreset strata, interpreted as the deposits of targe gravel dunes that have migrated downstream under quasi-steady turbidity currents, (4) hollow fills, which are filling thalwegs, minor channels, and local scours, and (5) mass-flow deposits of Facies C. The stacked sheets, laterally inclined strata, and hollow fills are laterally transitional to one another, reflecting juxtaposed geomorphic units of deep-sea channel systems. It is noticeable that the channel bodies in the southern part are of feet stacked toward the east, indicating eastward migration of the channel thalwegs. The laterally inclined strata also dip dominantly to the east. These features suggest that the trunk channel of the Lago Sofia submarine channel system gradually migrated eastward. The eastward channel migration is Interpreted to be due to tectonic forcing imposed by the subduction of an oceanic plate beneath the Andean Cordillera just to the west of the Lago Sofia submarine channel.