The high-resolution x-ray-photoemission-spectroscopy (XPS) valence-band spectrum from a cleaved natural-diamond single crystal is reported. The absence of extrinsic structure allows a reliable comparison with band theory. The XPS molecular-orbital spectra of methane, silane, and germane are also given. The modulation of photoelectric cross sections in the valence bands of diamond, Si, and Ge are discussed and compared with atomic XPS cross sections derived from the spectra of C${\mathrm{H}}_4$, Si${\mathrm{H}}_4$, and Ge${\mathrm{H}}_4$.

• Received 27 November 1972

DOI:https://doi.org/10.1103/PhysRevB.7.5313