Kramer electron emission

Fig. 9. Simulation of 8 electron emission by low energetic protons (left) and carbon ions (right) when penetrating tissue tissue is assumed to be water equivalent. The dashed line at x= 0 represents the trajectory of the primary ions, the full lines represent the paths of individual secondary electrons. The size of a DNA heUx is shown for comparison in the left panel. (Courtesy M. Kramer for details see [60])...

Mechanical processing (e.g., abrasion) of metallic surfaces causes the emission of electrons this is known as the Kramer effect (Kramer 1950). The effect has been shown by the measurement of selfgenerated voltages between two metallic surfaces under boundary lubrication (Anderson et al. 1969, Adams and Foley 1975). The exoelectrons have a kinetic energy from 1 to 4 eV (Kobzev 1962) and they may initiate some chemical reactions. For instance, if the metal (whose surface has been worked) is placed in an aqueous solution of acrylonitrile, the latter forms an abundant amount of an insoluble... 

Field emission is a tunneling phenomenon in solids and is quantitatively explained by quantum mechanics. Also, field emission is often used as an auxiliary technique in STM experiments (see Part II). Furthermore, field-emission spectroscopy, as a vacuum-tunneling spectroscopy method (Plummer et al., 1975a), provides information about the electronic states of the tunneling tip. Details will be discussed in Chapter 4. For an understanding of the field-emission phenomenon, the article of Good and Muller (1956) in Handhuch der Physik is still useful. The following is a simplified analysis of the field-emission phenomenon based on a semiclassical method, or the Wentzel-Kramers-Brillouin (WKB) approximation (see Landau and Lifshitz, 1977). 

Besides the diseontinuous states there are also wstates forming a continuous range (with positive energy) they correspond to the hyperbolic orbits of Bohr s theory. The jumps from one hyperbola to another or to a stationary state give rise to the emission of the continuous X-ray spectrum emitted when electrons are scattered or caught by nuclei. The intensity of this spectrum has been calculated by Kramers (1923) from the standpoint of Bohr s theory by a very ingenious application of the correspondence principle. His... 

As discussed in [22], the spherical symmetry of is destroyed when these ions are situated in solids, so that a multiplet term level can be split up to 2/ + 1 crystal field levels for a non-Kramers ion. Due to the parity selection mle for pure electronic transitions in solids, the 41 (i) 4 (f) transition between states i and f is ED forbidden to first order. Parity describes the inversion behavior of the wavefunction of an electronic orbital, so that s,d... orbitals have even parity whereas p,f... orbitals are odd. The spectral feature representing the pure electronic transition is termed the electronic origin or the zero phonon line. An ED transition requires a change in orbital parity because the transition dipole operator (pe) is odd, and the overall parity for the nonzero integral involving the Einstein coefficient of spontaneous emission, A(ED) ... 

With help of the Wentzel-Kramers-Brillouin approximation the field dependent transmission coefficient was calculated for the vacuum potential barrier. Integrating over all energies for a free electron gas at room temperature results in an exponentially increasing I-V curve that reaches 1 nA at 0.7 kV. With a band gap well above 2 eV proteins are good insulators, their electric breakdown is believed to be a conduction mechanism, which occurs at a voltage of about 200 V. The necessary potential for tip-emission can be further decreased to about 100 V using nano-fibers. To create transparent... 

The polarized absorption spectra show both quartet bands due to A2g-> T2g, Tij, transitions split by about 1000 cm". Intensity relations for different polarization directions are consistent with selection rules for C, symmetry. The strong jR lines, representing the zero-phonon transitions into the two Kramers sublevels of Eg, exhibit polarizations as expected for the mirror-site ions. The respective origins due to T g have been identified by comparing the low-temperature emission spectrum with absorption spectra at different temperatures. The most intense sharp lines centered near 470 nm were associated with transitions into the split-levels of T2g that is the highest state with (tig) electron configuration. However, a more profound analysis due to the pronounced vibronic sideband structure has not been given so far. 

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