Si/TiN Nanocomposites Exhibit Stable Capacities as Anode Material for Li-Ion Batteries
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of 1–3 composite made of epoxy and PZT was cut into a strip (1.5 mm long × 20 mm wide × 1.4 mm thick) and glued onto the glass ball. Using a pulse generator connected to the transducer to provide an electrical pulse, a Rayleigh wave with frequency ~1.1 MHz was excited. The transducer was subsequently used to monitor the resulting wave propagation. Waveform measurements show that the width of the Rayleigh wave was ~20 mm (the width of source transducer) and support the model of diffraction-free propagation of the Rayleigh wave around a solid sphere. The single transducer generated both surface and bulk acoustic waves. Other measurements were performed in which a second transducer was placed collinear with the first and excited with opposite polarity. In these experiments, the ratio of surface-to-bulk acoustic waves was strongly enhanced. Work is under way to calculate the beam propagation of Rayleigh waves for further comparison with experiment. According to Tsukahara, this phenomenon is probably not limited to Rayleigh waves. “We anticipate that the same mechanism of diffraction-free propagation will be applicable to other waves, such as light and quantum mechanical wave functions, given that the waves are confined to the surface of a sphere with an appropriate diameter-to-wavelength ratio.” STEFFEN K. KALDOR
Abnormal Oxidation of TiSi2 in Gate Stacks Found at 750–850°C A team of researchers at the Hyundai Electronics Industries Company Ltd. has recently reported abnormal oxidation behavior of TiSi2 sidewalls in patterned TiSi2/polysilicon gate stacks at temperatures above 800°C. The enhanced oxidation of the TiSi2 film was attributed to structural aspects, as it was not observed in unpatterned gate stacks. This suggests that the gate reoxidation of TiSi2/polysilicon stacks has to be performed at temperatures below 750°C. “Low-resistivity gate electrodes are often required for device performance, as silicon devices are scaled down. A common approach is to adopt a structure that is composed of a low-resistivity silicide and doped polysilicon (polycide structure),” said Dae-Gyu Park in the November issue of Electrochemical and Solid-State Letters. Gate reoxidation after the patterning process is necessary to increase the reliability of devices. While recent experiments on WSi2/polysilicon gate stacks showed oxidation of the metal instead of the silicon at low temperatures, In-Seok Yeo and his co-workers found that 10
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Figure 1. Transmission electron microscopy images of samples oxidized at (a) 750°C and (b) 850°C.
TiSi2/polysilicon gate stacks displayed abnormal oxidation behavior at high temperatures. A 900-Å-thick film of in situ phosphorus-doped polysilicon was deposited on a 50-Å-thick gate oxide, followed by deposition of an 800-Å-thick film of TiSi2. A 20-s anneal at 850°C was performed in order to obtain the desired low-resistivity C54-TiSi2 phase as confirmed by x-ray diffraction. The stack was patterned after deposition of a hard oxide mask layer by etching with Cl2 and O2 and reoxidized in a dry atm
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