On the Soft X‐Ray Appearance Potential Spectrum of Graphite and Less Well‐ordered Carbons

The technique of soft X‐ray appearance potential spectroscopy (APS) has been applied to pyrolytic graphite and other carbons. The prominent, sharp satellites in the spectrum are assigned, in agreement with Houston and Park, to a coupling of the CK core hole excitation to strong plasmon emission (first and higher orders of the 7 eV plasmon and first order of the 27 eV plasmon). However, the peak separations of the higher order 7 eV plasmons are found to be not constant. The broad loss peaks are assigned to coupling with interband transitions. Increasing the degree of disorder of the carbon markedly affects the spectrum. The results are discussed in the light of more direct experimental investigations of electronic excitations in graphite, and of recent theoretical considerations of plasmon coupling in APS.