A new explanation on valence electron structure of C, Si, and Ge crystals with diamond structure based on photoelectron spectra

Abstract

According to the classical covalent-bond (CVB) model, the two s and two p valence electrons in C, Si, and Ge crystals with diamond structure adopt an equivalent sp3 structure and form four covalent bonds between an atom and its four adjacent atoms. Therefore, the four valence electrons (sp3) per atom should have the same energy state. However, many experimental results indicate that the valence electrons of these element crystals have different binding energies. Therefore, in this paper, we propose a local valence electron (LVE) model for these materials, on the basis of valence electron spectra for the C, Si, and Ge crystals: The states of the four valence electrons per atom in these crystals are similar to those in the free atoms (s2p2), except that the shape of their outer electron cloud shells deviates from the ball shell distribution in the crystals, forming positive ions and equivalent-negative- electrical-charge centers. One of the important reasons why all the valence electrons of diamond are local electrons is that free C atom has high first ionization energy, 11.26 eV, being much higher than those of all the metal atoms. This LVE model is accordance with that diamond has wide energy gap (5.4 eV) in the energy band theory, which forbids electron transition from the filled valence band to the vacant conduction band.