Optical spectra of silicon oligomers

Optical absorption spectra have been measured for finite-chain analogs of linear polysilane, silicon oligomers CH3[Si(CH3)(2)]nCH3, with controlled chain length n(= 2 to 16). The intense lowest electronic absorption peak and its higher-lying side bands, which correspond to the one-dimensional exciton series in the infinite chain. shift to higher energy with decrease of the chain length because of the confinement of the excited states. The oscillator strength of the main absorption peak increases with the chain length, while the linewidth of the main peak drastically decreases, especially in the region n = 2 to 6. These finite size effects of the electronic (excitonic) absorption are argued in terms of spatial extension of the excited states, motional narrowing and electron correlation effect.