Energy of emitted electrons

Fig. 1.11 Photoelectron spectroscopy, (a) Schematic illustration of apparatus, comprising radiation source, sample, electron energy analyser and detector, all in a vacuum chamber, (b) Spectrum obtained from solid CdO, using X-rays of photon energy 1284 eV. (c) Interpretation of peaks in spectrum. The zero of energy in this scale corresponds to electrons with just sufficient energy to leave the solid positive values are the kinetic energies of emitted electrons, negative values correspond to the binding energies of electrons in the solid.

An important technique is UV photoemission spectroscopy (UPS) which is based on the outer photoelectric effect (in contrast to XPS, where we use the inner photoelectric effect). Photons with energies of 10-100 eV are used to ionize atoms and molecules at the surface. The energy of emitted electrons is detected. To study adsorption of molecules to surfaces, often difference spectra are analyzed which are measured before and after the adsorption. These difference spectra are compared to the spectrum of the molecules in the gaseous phase. 

It Is important to emphasise the fundamental difference between electron spectroscopy (both XPS and AES) and the other types of spectroscopy we have thus far encountered. In electron spectroscopy, thd kjnetic energy of emitted electrons is recorded. The spectrum thus consists of a plot of the number of emitted electrons, or the power of the electron beam, as a function of the energy (or the frequency or wavelength) of the emitted electrons (see Figure 21-2). 

The frequency dependence of the kinetic energy of emitted electrons in the photoelectric effect. 

Fig. 5.3. Kinetic energies of emitted electrons (in eV) for a few elements excited by MgKa (1253.6 eV) photons, and their corresponding 2s-binding energies (in eV)...

Above the threshold frequency, the number of emitted electrons increases with the light s intensity, but the kinetic energy per electron does not depend on the light s intensity. 

Bohr s hypothesis solved the impossible atom problem. The energy of an electron in orbit was fixed. It could go from one energy level to another, but it could not emit a continuous stream of radiation and spiral into the nucleus. The quantum model forbids that. 

The photoelectric method is based on the photoelectric effect. The kinetic energy of the electrons emitted during illumination of a metal with light having a frequency v obeys the Einstein equation... 

CUORE belongs to the type (b) detectors (source is part of the detector). The detection of the DBD is done by means of direct measurement of the energy of the electrons emitted in the process. 

Photoemission spectroscopy is based on the photoelectric effect. A sample that is irradiated with light of sufficiently small wavelength emits electrons. The number of photoelectrons depends on the light intensity, and the energy of the electrons on the wavelength of the light. 

The kinetic energy of the electron from the electron gun is absorbed by the phosphor, and re-emitted as the visible light seen by the viewer. 

Fig. 7.15. Photophysics associated with x-ray photoelectron spectroscopy and x-ray fluorescence. As illustrated, in the XPS experiment one monitors the energy of the electron ejected from the M shell upon photoionization (process 1). In the XRF experiment, one monitors the fluorescence emitted from either the M shell after photoionization (process 2a), or from the L shell after photo ionization and radiationless decay (process 2b).

X-ray tube—A metal anode is bombarded with high-energy electrons causing inner-shell electrons to be ejected and replaced by higher shell electrons. The loss in energy of these electrons as they drop to the lower levels is on the order of the energy of x-rays, and x-rays are emitted. 

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