Retarding potential

D) LOW-ENERGY ELECTRON BEAM (RETARDING-POTENTIAL) METHODS... 

Figure Bl.26.23. Current-voltage curves observed in the retarding potential difference method of work-fimction Miboxfmeasurement] (Hudson J B 1992 Surface Science (Stoneham, MA Butterworth-Heinemaim)).

A low-energy electron beam can also be obtained using a field emission tip and used in the field emission retarding-potential method. This combination provides an absolute measure of the sample work fiinction and the resolution is excellent [52]. 

This potential is referred to in electromagnetism texts as the retarded potential. It gives a clue as to why a complete relativistic treatment of the many-body problem has never been given. A theory due to Darwin and Breit suggests that the Hamiltonian can indeed be written as a sum of nuclear-nuclear repulsions, electron-nuclear attractions and electron-electron repulsions. But these terms are only the leading terms in an infinite expansion. 

The problems of distinguishing H+ produced from H2 by electron impact from the product of dissociative charge transfer reactions between He + and H2 can be studied by determining the kinetic energy distribution in the product H+ (6). The reaction He+ + H2 is exothermic by 6.5 e.v. if the products are atoms or atomic ions. If the reaction is studied with HD substituted for H2, then the maximum kinetic energy that can be deposited in the D + is approximately 2.16 e.v. On the other hand, D + can be produced by electron impact with 5.5 e.v. kinetic energy. If a retarding potential is applied at the repeller in the ion-source of a mass spectrometer, then it is possible to obtain curves related to the kinetic... 

The technique of measuring the 0+ kinetic energy distribution produced by reaction of He + and 02 showed promise for establishing the existence of HeO+. Experiments with He3 and He4 isotopes and 02 were carried out in the ion source of a mass spectrometer. Retarding potential curves for O + in the two systems were determined, and the com-... 

Fig. 6. Potential distribution and electron kinetic energy functions in a simple ion source using the R.P.D. method (see text) the effect of a variable retarding potential is shown schematically.

E.I. = electron impact P.I. = photoionization cross-section P.S. = photoelectron spectroscopy R.P.D. = retarding potential difference S. = spectroscopic... 

The first correction to this expression arises hecause the transmission of the electric field from one particle to anotiier is not instantaneous, but must occiw attiie speed of light. In electrodynamics diis phenomenon is called a retarded potential. Casimir and Polder[16] have investigated die consequences of this for quantum mechanics. The effect within distances aroimd 10 cm is completely negligible. 

We observed the silver doublet again, this time with a 27-Hz square-wave modulation applied to the retarding potential of the energy analyzer. The spectrometer thus was made to alternate rapidly between two different scan... 

Fig. 12. The variation in the photoelectric yield with (a) retarding potential and (b) wavelength.

Fig. 2.3 Magnetic sector mass spectrometer combined with a retarding potential ion energy filter used by Ernst et al 6 for measuring ion energy distributions in field ionization and field evaporation.

The potential energy diagram for an ion formed right at the critical distance of field ionization, xc (i.e. the most energetic ion), in a retarding potential analyzer is shown in Fig. 2.4. From this diagram, one obtains... 

Thus the onset voltage, or the retarding potential, of the ion energy... 

A contact potential correction requires that in a retarding potential measurement the work function is replaced with that of the collector, and that in a time-of-flight measurement it is replaced with the average work function of the flight tube.30 In low temperature field evaporation, Qn is only about 0.1 to 0.2 eV, or less than the uncertainty of most experimental measurements, and can be omitted for practical purposes. 

These are taken as retarded potentials (outgoing waves for zero initial conditions) with explicit forms... 

Note that the retarded potentials can be expressed as a single vector potential via... 

Note that this is also a retarded potential propagating outward at speed c. 

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