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¥3,000,000 (Direct Cost : ¥3,000,000)
Fiscal Year 2003 : ¥1,000,000 (Direct Cost : ¥1,000,000)
Fiscal Year 2002 : ¥1,000,000 (Direct Cost : ¥1,000,000)
Fiscal Year 2001 : ¥1,000,000 (Direct Cost : ¥1,000,000)
The Si(111)-√<3>×√<3> -Ag surface can be formed by depositing one monolayer of Ag atoms on a Si(111)-7×7 surface, and the surface-state band at this surface provides an ideal two-dimensional conduction-electron system (2DES). This electron system is confined in each √<3> ×√<3>-Ag domain surrounded by atomic steps or out-of-phase boundaries. Electronic excitations in this 2DES involves some interesting characteristics, such as low dimensionality, quantum-size effects, and presence of both edge and area excitations.
First, we have investigated two-dimensional plasmons (PL's) in the metallic monolayer of infinite area. This investigation has shown that, owing to low dimensionality, the exchange-correlation effects begin to appear remarkably with an increase in PL wave number q, though the 2DES has a high effective density. Our calculation has given a virtually quantitative description of the experimental results of high-resolution electron energy-loss spectroscopy (HREELS).
Next, by means o
f the local-density approximation, we have examined low-dimensional PL's in a 2DES restricted to a strip region with constant width D and infinite length. We have found a series of PL dispersion branches where the node number increases one by one with ascending energy. Here, the node number is specified from the distribution of the induced electron density δn across the strip. The 0-node and 1-node modes are edge PL's with different parity in the δn distribution. With a decrease in D, the 0-node modes evolve into one-dimensional PL's. Each higher-order mode with more than one node has a standing-wave pattern in its δn distribution in a smaller q region, which evolves into area PL's with an increase in q. In a mode with more nodes, the standing-wave pattern persists up to a larger q range. As the width D becomes larger, the energy separation between neighboring PL dispersion branches becomes smaller, and the evolution into the area PL's occurs at smaller q values. Our analysis in relation to HREELS has shown that loss peaks due to a series of PL dispersion branches should appear clearly in the energy-loss spectrum, and that the loss peaks should have observable intensity, if a probe electron follows a trajectory in the vicinity of the strip region. Less