Electron Emission Spectroscopies EES

Photoemission or (photo) electron emission spectroscopy (EES) is, in a strict sense, based on the photoelectric effect, where a sample irradiated by electromagnetic waves emits electrons. The number of emitted photo electrons is proportional to the intensity of the incident light, and the kinetic energy on the wavelength of the light (assuming that the minimum photon intensity is used). 

AES is based on the emission of element characteristic Auger electrons, first observed by Auger in 1925 [78], interpreted as the result of a relaxation process of core-ionized atoms after irradiation with X-rays ( Auger decay ). 

The different methods are explained in the following subsections— some experimental details are stated in the appendix. 

For AES the sample is excited by a beam of primary electrons (alternatively, with x-rays) with a kinetic energy between 1-10 keV. These electrons remove an electron from the (inner) core shells of a sample atom and the leaving electron creates a core hole. The ionized atom may return to its electron ground state via one of the two following de-excitation processes (Fig. 3.7) [68], 

An electron from a higher shell fills the hole and the energy thereby released is emitted as a quantum of characteristic radiation (X-ray fluorescence), Fig. 3.7a. 

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This chapter is dedicated to the utilized methods and their underlying theoretical background. The chapter is divided into three parts in Sect. 3.1 the synthesis of size-selected metal clusters under vacuum conditions (for both UHV and ambient experiments) is described, Sect. 3.2 deals with the experimental techniques in the UHV regime, whereas Sect. 3.3 describes the methods used for the ambient experiments. Since some of the characterizations for the ambient experiments are performed in the UHV a strict separation of the methods is difficult i.e. the electron emission spectroscopy (EES) techniques are treated in the UHV part including the XPS despite being used for ambient experiments. 

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