Effect photoelectric

Photoelectric absorption can only occur if the energy of the photon E is equal or higher than the binding energy 4 of the electron. For example, an X-ray photon with an energy of 15 keV can eject a K-electron (0 = 7.112 keV) or an L3-electron [4 u = 0.706 keV) out of a Fe atom. However, a 5 keV electron can only eject L-shell electrons from such an atom. 

Since photoelectric absorption can occur at each of the (excitable) energy levels of the atom, the total photoelectric cross section T is the sum of (sub)sheU-specific contributions  

Accordingly, the total cross section for scattering o can be written as the sum of two components  

Compton scattering occurs when X-ray photons interact with weakly bound electrons. After inelastic scattering over an angle / , a photon (see Fig. 11.5), with initial energy E, will have a lower energy E given by the Compton equation  

The photoelectric effect was originally described by Albert Einstein and helped to establish the quantized nature of light. The photoelectric effect has many extremely 

We should note that the photoelectric effect often leaves an inner shell vacancy in the atom that previously contained the ejected electron. This vacancy will be filled by an atomic transition, called fluorescence, and generally produces an X-ray photon. In an interesting twist of fate, the X-ray photon will have an energy that is just below the sharp rise in the attenuation coefficient due to conservation of momentum and can often escape from the absorber. Recall that the direction of the fluorescence photon will be uncorrelated with the direction of the incident photon and a fraction will be emitted backwards from the absorber. The absorber will thus emit its own characteristic X-rays when it is irradiated with high-energy photons. 

In 7-ray spectroscopy lead shields are commonly used. This can result in the production of Pb X-rays that can interfere with the measurement of low-energy photons. Lining the Pb shields with layers of A1 and Cu that absorb the Pb X-rays and other subsequent radiation ameliorates these problems. 

FIGURE 10.7 Schematic of the measurement of the photoelectric effect. Note the opposite polarity of the stopping potential part of the circuit. 

One might ask what is the constant C Einstein then used Planck s proportionality constant and equated the total energy of the incoming light photon to the kinetic energy and the energy to knock the electron out of the metal, the work function Wf. 

FIGURE 10.9 The stopping potential for photoelectrons from sodium versus frequency of the exciting light (photons). The modem value of the work function of sodium is 2.36 eV. (From Tide, D.R. Ed., CRC Handbook of Chemistry and Physics, 90th Edn., CRC Press, Boca Raton, EL, 2009-2010, pp. 12-121.) 

FIGURE 10.10 Work function versus stopping frequency for selected Group I and II metals. 

The unique importance of Planck s law was not clear until 4 years later (1905) when Albert Einstein noted it and used it in connection with his derivation of the photoelectric effect. Einstein needed quanta of energy in the incoming radiation to be able to explain photoelectron radiation. 

Usnally, it is possible to decrease the span of frequencies in a ray to a single frequency V (for all practical purposes) and this radiation is called monochromatic 

FIGURE 1,1 Black-body radiation at different temperatures. 

FIGURE 1.2 Photoelectric effect. The vertical full-drawn line corresponds to the v-axis in the XPS experiment. The fine structure depends on how the atom is bound in the molecule. 

The maximum kinetic energy of a photoelectron is given by the following 

In this equation, m is the mass of an electron, vmax is the maximum velocity of the electrons, h is the Planck s constant,/is the frequency of the incident light, (p (pronounced phi) is the work function of the metal. The entity //represents the energy of the incident photon. 

The minimum energy required to eject a photoelectron is the work function of the metal and the ejected photoelectrons come from the top of the Fermi surface. By increasing the photon energy, electrons that lie deeper in the Fermi well can be ejected and the numbers and energies of the photoelectrons coming off can be measured. This technique is called photoelectron spectroscopy. If an ultraviolet lamp is used as the photon source, the technique is called ultraviolet photoelectron spectroscopy or UPS. Similarly, if x-rays are used as the photons, the technique is called x-ray photoelectron spectroscopy or XPS. 

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We use the X or gamma rays power penetrating to detect possible heterogeneities in inspected pieces. These rays are absorbed by the matter crossed, essentially by the photoelectrical effect, (fig. 02). 

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 final technique addressed in this chapter is the measurement of the surface work function, the energy required to remove an electron from a solid. This is one of the oldest surface characterization methods, and certainly the oldest carried out in vacuo since it was first measured by Millikan using the photoelectric effect [4]. The observation of this effect led to the proposal of the Einstein equation ... 

Another phenomenon that was inexplicable in classical terms was the photoelectric effect discovered by Hertz in f 887. When ultraviolet light falls on an alkali metal surface, electrons are ejected from the surface only when the frequency of the radiation reaches the threshold... 

The explanation of the hydrogen atom spectmm and the photoelectric effect, together with other anomalous observations such as the behaviour of the molar heat capacity Q of a solid at temperatures close to 0 K and the frequency distribution of black body radiation, originated with Planck. In 1900 he proposed that the microscopic oscillators, of which a black body is made up, have an oscillation frequency v related to the energy E of the emitted radiation by... 

Einstein, in 1906, applied this theory to the photoelectric effect and showed that... 

Photoelectron spectroscopy involves the ejection of electrons from atoms or molecules following bombardment by monochromatic photons. The ejected electrons are called photoelectrons and were mentioned, in the context of the photoelectric effect, in Section 1.2. The effect was observed originally on surfaces of easily ionizable metals, such as the alkali metals. Bombardment of the surface with photons of tunable frequency does not produce any photoelectrons until the threshold frequency is reached (see Figure 1.2). At this frequency, v, the photon energy is just sufficient to overcome the work function

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Phofoelectron spectroscopy is a simple extension of the photoelectric effect involving the use of higher-energy incident photons and applied to the study not only of solid surfaces but also of samples in the gas phase. Equations (8.1) and (8.2) still apply buf, for gas-phase measuremenfs in particular, fhe work function is usually replaced by fhe ionization energy l so fhaf Equation (8.2) becomes... 

Even though Einstein developed the theory of the photoelectric effect in 1906 photoelectron spectroscopy, as we now know it, was not developed until the early 1960s, particularly by Siegbahn, Turner and Price. 

Xps is based on the photoelectric effect when an incident x-ray causes ejection of an electron from a surface atom. Figure 7 shows a schematic of the process for a hypothetical surface atom. In this process, an incident x-ray photon of energy hv impinges on the surface atom causing ejection of an electron, usually from a core electron energy level. This primary photoelectron is detected in xps. 

S. M. Ryvkin, Photoelectric Effects in Semiconductors, Consultants Bureau, New York, 1964. 

Practical X-ray energies do not exceed 100 keV. The primary beam is mainly attenuated by the photoelectric effect. Scattering, both elastic (Rayleigh) and inelastic (Compton), represents a minor contribution to attenuation at energies below 100 keV. 

When Max Planck wrote his remarkable paper of 1901, and introduced what Stehle (1994) calls his time bomb of an equation, e = / v , it took a number of years before anyone seriously paid attention to the revolutionary concept of the quantisation of energy the response was as sluggish as that, a few years later, whieh greeted X-ray diffraction from crystals. It was not until Einstein, in 1905, used Planck s concepts to interpret the photoelectric effect (the work for which Einstein was actually awarded his Nobel Prize) that physicists began to sit up and take notice. Niels Bohr s thesis of 1911 which introduced the concept of the quantisation of electronic energy levels in the free atom, though in a purely empirical manner, did not consider the behaviour of atoms assembled in solids. 

Photoelements and photodiodes Both photoelements and photodiodes are photoelectric components depending on internal photoelectric effects. 

A. Einstein (Berlin) services to theoretical physics, especially discovery of the law of the photoelectric effect. 

None of Einstein s first four papers published between 1901 and 1904 foreshadowed his explosive creativity of 1905, his annus mirabilis, in which he produced in March, his proposal of the existence of light quanta and the photoelectric effect, work for which in 1922 he received the Nobel Prize in April, a paper on the determination of molecular dimensions, which earned him his Ph.D. m Zurich m May, his theory of special relativity in September, a sequel to the preceding paper containing the relation E = mc. Any one of these papers would have made him greatly renowned their totality made him immortal. 

In the course of his research on electromagnetic waves Hertz discovered the photoelectric effect. He showed that for the metals he used as targets, incident radiation in the ultraviolet was required to release negative charges from the metal. Research by Philipp Lenard, Wilhelm Hallwachs, J. J. Thomson, and other physicists finally led Albert Einstein to his famous 1905 equation for the photoelectric effect, which includes the idea that electromagnetic energy is quantized in units of hv, where h is Planck s con-... 

The photoelectric effect (the creation of an electrical current when light shines on a photosensitive material connected m an electrical circuit) was first obseiwed in 1839 by the French scientist Edward Becqiierel. More than one hundred years went by before researchers in the United States Bell Laboratories developed the first modern PV cell in 1954. Four years later, PV was used to power a satellite in space and has provided reliable electric power for space exploration ever since. 

Many elements were found to experience the photoelectric effect. Germanium, copper, selenium, and cuprous oxide comprised many of the early experimental cells. In 1953 Bell Laboratories scientists Calvin Fuller and Gerald Pearson were conducting... 

German physicists Julius Elster and Hans F. Geitel invent the first photoelectric cell as a result of studying the photoelectric effect. The first hydroelectric generator at Niagara Falls, New York, produces alternating current from a Nikola Tesla design. 

Photoelectric Effect (Pe). Only one service company was offering a commercial Pe log. The readings of the LWD tool were very sensitive to washouts. For a qualitative lithology identification of the strata, the LWD Pe curve is satisfactory. 

A hundred years ago it was generally supposed that all the properties of light could be explained in terms of its wave nature. A series of investigations carried out between 1900 and 1910 by Max Planck (1858-1947) (blackbody radiation) and Albert Einstein (1879-1955) (photoelectric effect) discredited that notion. Today we consider light to be generated as a stream of particles called photons, whose energy E is given by the equation... 

The short-wavelength limit of the continuous spectrum is clearly a quantum phenomenon. X-ray generation by electron bombardment in principle resembles cathodoluminescence, and both processes are inverse photoelectric effects. The short-wavelength limit, Xq, discovered by Duane and Hunt6 obeys the relationship... 

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