Take‐off angle and film thickness dependences of the attenuation length of X‐ray photoelectrons by a trajectory reversal method

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Abstract
The meaning of attenuation length (AL) of x‐ray photoelectrons (and Auger electrons) in solids is reviewed in the light of new evidence pointing to strong dependences of AL on take‐off angle and film thickness, which can be traced back to elastic scattering. Since signal attenuation in XPS (and AES) can deviate significantly from an exponential form, it is concluded that the AL can no longer be regarded as a material constant. Instead, the AL becomes an approximating parameter whose numerical value must be determined for each experimental condition. The take‐off angle dependence of the AL was investigated by an efficient Monte Carlo computer code, which is based on the concept of trajectory reversal; this concept is explained. Strong dependences of the AL on take‐off angle and film thickness were found for the more oblique (> 60° off‐normal) emission.

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