The dependence of Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy sensitivity factors on the detailed atomic and electronic environment has been studied for several materials containing C and/or Si. The matrices containing these elements include diamond, graphite, Si0.5C0.5, and Si. It was found that correcting the sensitivity factors for atomic density, electron attenuation length, and electron backscattering improved the agreement between the measured and the true composition by up to an order of magnitude except for AES transitions involving valence band electrons. The effects of changing surface composition due to oxidation and surface segregation are also discussed.