Photoelectric effect solids

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. 

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 ... 

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... 

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... 

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. 

One of the most direct methods is photoelectron spectroscopy (PES), an adaptation of the photoelectric effect (Section 1.2). A photoelectron spectrometer (see illustration below) contains a source of high-frequency, short-wavelength radiation. Ultraviolet radiation is used most often for molecules, but x-rays are used to explore orbitals buried deeply inside solids. Photons in both frequency ranges have so much energy that they can eject electrons from the molecular orbitals they occupy. 

When radiation of sufficiently short wavelength interacts with matter, ( electrons are emitted. This is the photoelectric effect. It can be observed in gases and solids, and with X-rays and y rays, as well as with ultraviolet j radiation. It was die phenomena observed with short-wavelength visible and < ultraviolet radiation on solids, however, which were known in 1905. Figure J 1.10 shows the apparatus used. Light or UV radiation falls on one electrode 4 in an evacuated tube. If electrons are emitted, some will reach the second <... 

Using eqn 1.12, and the principle of energy conservation, the photoelectric effect can be explained without difficulty. Let be the minimum energy required to liberate an electron from a particular solid, a quantity known as the work function. Then if each photon transmits its energy to just one electron, the maximum emitted energy must be... 

The photoelectric effect, first outlined by Einstein in the early 1900s, refers to the ejection of electrons from a surface due to photon impingement. However, it was not until the 1960s that this phenomenon was exploited for surface analysis - a technique referred to as X-ray photoelectron spectroscopy (XPS), or electron spectroscopy for chemical analysis (ESCA). This technique consists of the irradiation of a sample with monochromatic X-rays e.g., A1 Ka (1.487 keV), Mg Ka (1.254 keV), Ti Ka (2.040 keV)), which releases photoelectrons from the sample surface (Figure 131) Due to the short free mean path (EMP) of the photoelectrons in the solid, this technique provides compositional information from only the top 1-5 nm of a sample. 

Quantum mechanics represents one of the cornerstones of modem physics. Though there were a variety of different clues (such as the ultraviolet catastrophe associated with blackbody radiation, the low-temperature specific heats of solids, the photoelectric effect and the existence of discrete spectral lines) which each pointed towards quantum mechanics in its own way, we will focus on one of these threads, the so-called wave-particle duality, since this duality can at least point us in the direction of the Schrodinger equation. 

Phase diagram. A diagram showing the conditions at which a substance exists as a solid, liquid, or vapor. (11.9) Photochemical smog. Formation of smog by the reactions of automobile exhaust in the presence of sunlight. (17.6) Photoelectric effect. A phenomenon in which electrons are ejected from the surface of certain metals exposed to light of at least a certain minimum frequency. (7.2)... 

The development of the quantum theory was at first slow. It was not until 1905 that Einstein2 suggested that the quantity of radiant energy hv was sent out in the process of emission of light not in all directions but instead unidirectionally, like a particle. The name light quantum or photon is applied to such a portion of radiant energy. Einstein also discussed the photoelectric effect, the fundamental processes of photochemistry, and the heat capacities of solid bodies in terms of the quantum theory. When light falls on a metal plate, electrons arc emitted from it. The maximum speed of these photoelectrons, however,... 

Photoelectric effect - The complete absorption of a photon by a solid with the emission of an electron. 

In the Compton effect, the photon interacts with an election of an ion in the solid and transfers part of its eneigy to this electron. The result is a Compton scattered photon with energy hr> (v < v) and a so-called Compton electron with energy Ej. The scattered photon may leave the scintillator or may interact with the scintillator (but at a site different from the first interaction). In the latter case the incident photon gives two light centers at different sites which makes the Compton effect undesirable for po.sition-sensitive detection. If the scattered photon leaves the scintillator crystal, less luminescent radiation is produced than in the case of the photoelectric effect. 

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