Kinetic photoelectric effect

Photoelectron spectroscopy provides a direct measure of the filled density of states of a solid. The kinetic energy distribution of the electrons that are emitted via the photoelectric effect when a sample is exposed to a monocluomatic ultraviolet (UV) or x-ray beam yields a photoelectron spectrum. Photoelectron spectroscopy not only provides the atomic composition, but also infonnation conceming the chemical enviromnent of the atoms in the near-surface region. Thus, it is probably the most popular and usefiil surface analysis teclmique. There are a number of fonus of photoelectron spectroscopy in conuuon use. 

X-ray photoelectron spectroscopy (XPS) is among the most frequently used surface chemical characterization teclmiques. Several excellent books on XPS are available [1, 2, 3, 4, 5, 6 and 7], XPS is based on the photoelectric effect an atom absorbs a photon of energy hv from an x-ray source next, a core or valence electron with bindmg energy is ejected with kinetic energy (figure Bl.25.1) ... 

The minimum energy needed to remove an electron from a potassium metal surface is 3.7 X 10 J. Will photons of frequencies 4.3 X 10 s (red light) and of 7.5 X 10 s (blue light) trigger the photoelectric effect If so, what is the maximum kinetic energy of the ejected electrons ... 

C07-0105. In a photoelectric effect experiment, photons whose energy is 6.00 X 10 J are absorbed by a metal, and the maximum kinetic energy of the resulting electrons is = 2.70 X 10 J. 

XPS is based on the photoelectric effect An atom absorbs a photon of energy hv so that a core or valence electron with binding energy i, is ejected with kinetic energy (Figure 4.6) ... 

X-ray photoelectron spectroscopy (XPS) is based on the photoelectric effect. When a sample is irradiated with monochromatic X-rays, such as the K lines of Mg (1253.6eV) or Al (1486.6 eV), core-level electrons from the inner shells of atoms in the sample will be ejected from the sample to the surrounding vacuum. The kinetic energy, Er, of the emitted photoelectron is given by... 

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... 

The photoelectric effect, in which the photon is absorbed and an electron is produced with kinetic energy equal to the difference between the photon energy and the binding energy of the electron (Einstein equation). 

Figure 12.5 The photoelectric effect. Light with photons of energy hc/k approaches from the left, strikes the atoms in the metal, and ejects a photoelectron with a kinetic energy equal to the photon energy minus the work function of the metal. This demonstrates the particulate nature of light.

PHOTOION IZATT ON. This process, which is also called the atomic photoelectric effect, is the ejection of a bound electron from an atom by an incident photon whose entire energy is absorbed by the ejected electron. This statement means that photoionization cannot occur unless tlie energy of the photon is at least equal at the ionization energy of the particular electron in the particular atom any excess of energy in the photon above this value appears as kinetic energy of the ejected electron. 

The XPS mechanism, which can be used for quantitative and qualitative chemical analysis of surfaces, is based on the photoelectric effect. A monochromatic soft Mg or Al anode X-ray source is used to irradiate the surface. The absorbed X-rays ionize die core shell, and in response, the atom creates a photoelectron that is transported to the surface and escapes. The ionization potential of a photoelectron that must be overcome to escape into vacuum is the binding energy (BE) plus the work function of the material. The emitted photoelectrons have a remaining kinetic energy (KE), which is measured by using an electron analyzer. Individual elements can be identified on the basis of their BE. The resulting XP spectrum is a characteristic set of peaks for a specific element, with BE as the abscissa and counts per unit time as... 

Two papers by Albert Einstein ultimately led to acceptance of the idea of quantization of energy for radiation, and were central to the development of the quantum theory (ironically, in later years Einstein became the most implacable critic of this same theory). The first of these papers, in 1905, concerned the photoelectric effect. Light ejected electrons from a metallic surface if the light had a greater frequency than some threshold frequency v0 which depended on the particular metal. The kinetic energy K of the emitted electrons was proportional to the excess frequency, v — v0 (Figure 5.4). Only the number of emitted electrons, not the kinetic energy, increased as the intensity increased. 

Einstein s explanation of the photoelectric effect was not his only contribution to chemistry. His Ph.D. dissertation, submitted in 1905, was entitled A New Determination of Molecular Dimensions. His investigation of Brownian motion (the random movement of microscopic particles suspended in liquids or gases) was intended to establish the existence of atoms as being indispensable to an explanation of the molecular-kinetic theory of heat. And the concept of relativity has shed light on the motions of electrons in the core orbitals of heavy elements, see also Quantum Chemistry. 

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