Electrons photoelectric effect

The Daly detector uses a photomultiplier rather than an electron multiplier. Ions leaving the analyzer are directed onto a conversion dynode, and the ejected electrons are accelerated onto a plate coated with a fast-acting scintillant. Each electron releases a photon from the scintillant. The photons then enter a photomultiplier tube and impact on a photocathode, producing electrons (photoelectric effect) and initiating an electron cascade (Pigure 2.40). The output from the photomultiplier is further amplified electronically, similarly to the output of dynode type electron multipliers. The level of amplification is similar to that of electron multipliers. Photomultiplier tubes last longer than electron multipliers, but the scintillant-coated plates require replacement every few years. 

Shell electrons Photoelectric effect a ocZ Rayleigh scattering acxZ Compton effect ... 

Positive Ions Negative ions - Electrons Photoelectric effect Recomblnation 3hoton emisslo Limit of the disruptive a Limit of file plasma are... 

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... 

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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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. 

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. 

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... 

To achieve this successful theory, Planck had discarded classical physics, which puts no restriction on how small an amount of energy may be transferred from one object to another. He had proposed instead that energy is transferred in discrete packets. To justify such a dramatic revolution, more evidence was needed. That evidence came from the photoelectric effect, the ejection of electrons from a metal when its surface is exposed to ultraviolet radiation (Fig. 1.15). The experimental observations were as follows ... 

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. 

Example H2(g) + Cl2(g) 2 HCl(g). photoelectric effect The emission of electrons from the surface of a metal when electromagnetic radiation strikes it. 

A detailed study of the photoelectric effect reveals how the behavior of the electrons is related to the characteristics of the light ... 

Einstein applied the law of conservation of energy to the photoelectric effect, as shown schematically in Figure 7-7. When a metal surface absorbs a photon, the energy of the photon is transferred to an electron ... 

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 ... 

In the photoelectric effect, energy absorbed from photons provides information about the binding energies of electrons to metal surfaces. When light interacts with free atoms, the interaction reveals information about electrons bound to individual atoms. 

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. 

C07-0106. In a photoelectric effect experiment, the minimum frequency needed to eject electrons from a... 

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) ... 

Based on the photoelectric effect, electrons in evacuated tubes (photoelectrons) are released from a metal surface if it is irradiated with photons of sufficient quantum energy. These are simple photocells. Photomultipliers are more sophisticated and used in modem spectrophotometers where, via high voltage, the photoelectrons are accelerated to another electrode (dynode) where one electron releases several electrons more, and by repetition up to more than ten times a signal amplification on the order of 10 can be obtained. This means that one photon finally achieves the release of 10 electrons from the anode, which easily can be measured as an electric current. The sensitivity of such a photomultiplier resembles the sensitivity of the human eye adapted to darkness. The devices described are mainly used in laboratory-bound spectrophotometers. 

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... 

Ernest Rutherfords proposed atomic structure added to the problems posed to nineteenth century physics by the ultraviolet catastrophe and the photoelectric effect. Rutherfords atom had a negatively charged electron circling a positively charged nucleus. The physics of the day predicted that the atom would emit radiation, causing the electron to lose energy and spiral down into the nucleus. Theory predicted that Rutherfords atom could not exist. Clearly, science needed new ideas to explain these three anomalies. 

Photoelectric effect The effect produced when electromagnetic radiation knocks electrons out of a metal. Einstein used this phenomenon to show that light was quantized and came in energy packets called photons. 

When a photon of light hits the surface of a piece of metal, it may, if there is sufficient energy, eject an electron from the metal. Such an electron is called a photoelectron, and the mechanism is known as the photoelectric effect. The diagram at the right shows a setup for measuring the photoelectric effect. 

Photoelectric Effect—An attenuation process observed for x and gamma radiation in which an incident photon interacts with a tightly bound inner orbital electron of an atom delivering all of its energy to knock the electron out of the atom. The incident photon disappears in the process. 

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