Wavevector-resolved electron-energy-loss spectroscopy on the dangling-bond states of Si(111)(2 × 1)

Low-energy-loss spectra of the clean cleaved Si(111)(2 × 1) surface with wavevector resolution are discussed. Parallel to the γ-J line in the surface Brillouin zone large disperson in the dangling-bond bands is found near the energy gap at the J-K′ line. This is in contradiction to the formerly accepted buckling model and favours the recently suggested π-bonded chain model for the (2 × 1) reconstruction.