In this study, we prepared a silicon nanocone structure using a relatively high-pressure H2 plasma in the range of 3.3–27 kPa. The silicon sample with the prepared nanocone structure exhibited a black surface. We investigated the dependence of the silicon nanocone formation behavior on various experimental parameters such as H2 pressure, processing time, substrate temperature, input power, and substrate bias. A small amount of air feed and a thin native oxide layer are desirable for the nanocone formation. Furthermore, the silicon temperature during plasma exposure plays an important role in increasing the silicon nanocone height. In addition, the polarity of the substrate bias drastically changes the surface structure from the nanocone in the case of a negative bias to a low-aspect-ratio pyramidal structure in that of a positive bias. This result implies that the anisotropic ion incidence is important for nanocone formation, despite the relatively high process pressure.
In situ B-doped Si epitaxial growth by atmospheric-pressure plasma chemical vapor deposition (AP-PCVD) using porous carbon electrode was investigated. Heavy B doping for a carrier concentration of 8×10 19 cm −3 was achieved using B 2 H 6 as a doping gas, with a high average growth rate of 0.20 µm min −1 at 570 • C. The relation between the hole mobility and carrier concentration in heavily B-doped Si films can be well fitted with that reported for bulk Si single crystals up to the carrier concentration of 5 × 10 19 cm −3 . This result demonstrates that the electrical quality of heavily doped Si epitaxial films grown by AP-PCVD is sufficiently high for semiconductor device applications. The activation ratio of B atoms as acceptors in the heavily doped films is nearly 100% for a carrier concentration range reaching approximately 2 × 10 19 cm −3 . Cross-sectional transmission electron microscopy examination of heavily B-doped epitaxial Si with a carrier concentration of 2 × 10 19 cm −3 revealed both a defect-free film and film/substrate interface. In the present experiment, the required B 2 H 6 /SiH 4 ratio is much higher than the resultant B composition in the Si films, due to thermal decomposition of B 2 H 6 molecules in the porous carbon electrode. To increase the efficiency of B 2 H 6 gas usage, cooling of the porous carbon electrode during the AP-PCVD process may be effective. Copyright
For assess ment of body movement during sleep, a sys tem for monitoring press ure in bed has been developed. The sys tem consists of an optical fiber press ure sensor and a notebook personal computer with an NO converter. Changes in optical in tensity due to changes in pressure were detected, then converted to voltage output and transferred to the computer. The time of body movement was determined when two of three signals changed. Upon comparison with a video recording, this estima tion showed good agreement. Pressure measurement in bed provides a high-resolution estimate of posture change during sleep.
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