The role of hydrogen in the electronic structure of amorphous carbon: an electron spectroscopy study

Abstract

Two processes are examined by electron spectroscopy techniques, namely hydrogen incorporation into amorphous carbon (a-C) and hydrogen evolution from hydrogenated amorphous carbon (a-C:H). The energy E p of the π + σ plasmon loss (related to the material mass density) turns out to be the most sensitive indicator of the degree of H incorporation. Other spectral features, on the other hand, consistently confirm that H acts as a stabilizer of the sp 3 phase in amorphous carbon systems. H evolution is thermally activated from a-C:H once the material stability threshold (≈ 100∘C for the film of the present study) is exceeded. It first leads to massive sp 3 to sp 2 conversion, followed by graphitic order development. No univocal relationship exists between the sp 2 fraction and the π band photoemission intensity