Papers by Author: Keisuke Yamaoka

Abstract: Low-temperature plasma-enhanced chemical vapor deposition of amorphous carbon (a-C:H) films was investigated for surface passivation of carbon-doped silicon oxide (SiOCH) films. The a-C:H films were deposited using CH4 and Ar gases at 40–65°C. FT-IR results showed that the deposited films are a-C:H which incorporates hydrocarbon groups. In current−voltage measurements, the a-C:H showed a low leakage current of ~10–10 A/cm2 in air, indicating that the a-C:H films have a potential as a surface passivation layer to prevent moisture absorption in air. The insulating properties of room-temperature deposited SiOCH covered by the a-C:H strongly depended on radio frequency (RF) power in the SiOCH deposition. In the SiOCH film deposited at high RF power of 200 W, the resistivity in air was improved by the a-C:H passivation.

Abstract: D03-ordered Fe3Al single crystals containing 23, 25 and 28at.%Al were cyclically deformed at [ 49 1 ] loading axis in tension-compression mode. Giant pseudoelasticity took place in Fe-23 and 25at.%Al single crystals at an early stage of cyclic deformation, while a slight strain recovery was observed in Fe-28at.%Al. In Fe-23 and 25at.%Al single crystals, superpartial dislocations with Burgers vector of 1/4[111] moved individually dragging the nearest neighbour anti-phase boundary (NNAPB). The NNAPB pulled back the superpartials during unloading, resulting in giant pseudoelasticity and low residual dislocation density. In contrast, a couplet of the superpartials was observed to bow out leaving two superpartials in Fe-28at.%Al. This means that the dislocation couplet dragged the next-nearest neighbour anti-phase boundary (NNNAPB). The surface tension of NNNAPB is lower than that of NNAPB resulting in a slight strain recovery in Fe-28at%Al. As cyclic deformation proceeded, residual dislocation density increased with an increase in the number of cycles even in Fe-23 and 25at.%Al. In particular, persistent slip bands (PSB) were formed in Fe-23at.%Al single crystals, though PSB is seldom observed in fatigued intermetallic compounds. To-and-fro motion of superpartials during loading and unloading was suppressed by dislocation bundles, resulting in a reduced shape recovery. However, large strain recovery occurred in Fe-25at.%Al single crystals at a strain amplitude of 1.0% even at 20cycles. It was also noted that Fe-23 and 25at.%Al demonstrated tension-compression asymmetry even at [ 49 1 ] orientation; the yield stress in compression was higher than that in tension. This implies that the core structure of <111> screw dislocation played an important role in the deformation behaviour of Fe3Al single crystals.