SURFACE PROPERTIES OF a-Si : H AND a-Si : F INVESTIGATED BY PHOTOELECTRON SPECTROSCOPY L. Ley, H. Richter, R. Kärcher, R.L. Johnson et J. Reichardt J. Phys. Colloques, 42 C4 (1981) C4-753-C4-759 DOI: 10.1051/jphyscol:19814165