Photoelectric effect The ejection

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 ... 

An apparently quite separate (but in science no two phenomena are really ever unrelated) phenomenon that led to Eq. 4.3, which is to say to quantum theory, is the photoelectric effect the ejection of electrons from a metal surface exposed to light. 

Photoelectrical effect The ejection of an electron from a soHd or a Hquid by a photon. 

An apparently quite separate (but in science no two phenomena are really ever unrelated) phenomenon that led to Eq. (4.3), which is to say to quantum theory, is the photoelectric effect the ejection of electrons from a metal surface exposed to light. The first inkling of this phenomenon was due to Hertz, who in 1888 noticed that the potential needed to elicit a spark across two electrodes decreased when ultraviolet light shone on the negative electrode. Beginning in 1902, the photoelectric effect was first studied systematically by Lenard," who showed that the phenomenon observed by Hertz was due to electron emission. 

Phospholipid bilayer a part of a biological membrane consisting of two layers of phosphoUpid molecules, (p. 514) Photoelectric effect the ejection of electrons from the surface of a metal or other material when light shines on it. (7.2)... 

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. 

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. 

Photoelectric effect they eject electrons particularly from atoms of higher atomic weights, the photons being annihilated. 

In the photoelectric effect, the number of electrons emitted depends on the intensity of the radiation and not on its frequency. The kinetic energy of the electrons that are ejected depends on the frequency of the radiation. This was explained, by Einstein, by the idea that electromagnetic radiation consists of streams of photons. The photon energy is hv, where h is the Planck constant and v the frequency of the radiation. To remove an electron from the solid a certain minimum energy must be supplied, known as the work funaion, ( ). Thus, there is a certain minimum threshold frequency Vq for radiation to eject electrons hvQ = 6. If the frequency is higher than this threshold the electrons are ejected. The maximum kinetic energy (W) of the electrons is given by Einstein s equation-. 

As in the photoelectric effect, the radiation must have a certain minimum threshold frequency. The energy of the photoelectrons ejected is given hyW=hv-I, where I is the ionization potential of the atom or molecule. Analysis of the energies of the emitted electrons gives information on the ionization potentials of the substance - a technique known as photoelectron spectroscopy. 

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) ... 

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. 

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. 

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 ... 

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

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