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Excitation profiles of resonant second-harmonic and hyper-Raman scattering in a CdS quantum-dot system are reported. Two maxima have been found in the related two-photon excitation spectra near the fundamental absorption region. Relative to the one-photon absorption spectrum, the maxima are more pronounced and shifted in energy. The result has revealed quantum-confined electron-hole pair states with a total angular momentum of odd number. Effective masses in the quantum dots have been estimated.

We measured the lattice spacing of the cellulose in sugi (Cryptomeria japonica D. Don) and hinoki (Chamaecyparis obtusa Endl.) cell walls under wet and dry conditions. We gave all specimens repeated wet-and-dry treatments and tried to induce substantial changes in the microstructure of the wood cell wall. Macroscopic dimensions, measured using a micrometer, showed well-known behaviors, that is, shrinkage by drying and swelling by wetting, which were unaffected after the repeated wet-and-dry treatments in both longitudinal and tangential directions. On the other hand, lattice spacing, measured using an X-ray diffractometer, showed different results. In particular, d 200 lattice spacing expanded considerably with drying in the early stages of repeated wet-and-dry treatments. The d 200 lattice spacing in the dried specimen then became gradually smaller in the later stages, whereas no such dynamic change was observed in d 004 lattice spacing throughout the repeated wet-anddry treatments. Once the d 200 lattice spacing in the dried specimen had become smaller after giving wetand-dry treatments, it did not recover, even after soaking in distilled water for 1 month. These results suggest that repeated drying and re-swelling caused structural changes in the wood cell wall, specifically an interfacial separation between cellulose microfibrils and matrix substances.

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