tailieunhanh - The Materials Science of Thin Films Episode 7

Tham khảo tài liệu 'the materials science of thin films episode 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 278 Characterization of Thin Films Figure 6-14. Schematic of electron energy transitions a initial state b incident photon or electron ejects K shell electron c X-ray emission when 2s electron fills vacancy d Auger electron emission. KLL transition shown. For example he _ _ . . T - - L 6-15 akU where h c and X have their usual meaning. 2. The emitted X-rays are characteristic of the particular atom undergoing emission. Thus each atom in the Periodic Table exhibits a unique set of K L M etc. X-ray spectral lines that serve to unambiguously identify it. These characteristic X-rays are also known as fluorescent X-rays when excited by incident photons . X-rays and gamma rays . There is however an alternative process by which the electron hole in Fig. 6-14b can be filled. This involves a complex transition in which three rather than two electron levels as in EDX participate. The Auger process which is the basis of AES first involves an electron transition from an outer level . L to the K hole. The resulting excess energy is not channeled into the . Chemical Characterization 279 creation of a photon but is expended in ejecting an electron from yet a third level . L2 . As shown in Fig. 6-14d the atom finally contains two electron holes after starting with a single hole. The electron that leaves the atom is known as an Auger electron and it possesses an energy given by KLL L2 L 6-16 The last equality indicates KL L2 and KL2L transitions are indistinguishable. Similarly other common ưansitions observed are denoted by LMM and MNN. Since the K L and M energy levels in a given atom are unique the Auger spectral lines are characteristic of the element in question. By measuring the energies of the Auger electrons emitted by a material we can identify its chemical makeup. To quantitatively illustrate these ideas let US consider the X-ray and Auger excitation processes in titanium. The binding energies of each of the core electrons are indicated in Fig. 6-15 where .