Question: In order to receive the energy required, what does an emitted electron require?
About the article "Photoelectric effect", section "Emission mechanism".

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In the charged current interaction, a neutrino converts the neutron in a deuteron to a proton.
The neutrino is absorbed in the reaction and an electron is produced.
Solar neutrinos have energies smaller than the mass of muons and tau leptons, so only electron neutrinos can participate in this reaction.
The emitted electron carries off most of the neutrino's energy, on the order of 5–15 MeV, and is detectable.
The proton which is produced does not have enough energy to be detected easily.
The electrons produced in this reaction are emitted in all directions, but there is a slight tendency for them to point back in the direction from which the neutrino came. 
Thermionic emission is the flow of electrons from a heated charged metal or metal oxide surface, caused by thermal vibrational energy overcoming the work function (electrostatic forces holding electrons to the surface).
The thermionic emission current density, J, rises rapidly with increasing temperature, releasing a significant number of electrons into the vacuum near the surface.
The quantitative relation is given in the equation  formula_20 This equation is called the Richardson-Dushman or Richardson equation.
(ф is approximately 4.54 eV and AR ~120 A/cm2 for tungsten).
Once the electrons are thermionically emitted from the TC surface they require an acceleration potential to cross a gap, or in this case, the plasma sheath.
Electrons can attain this necessary energy to escape the SCL of the plasma sheath if an accelerated grid, or electron gun, is used.
The equation formula_21 shows what potential is needed across the grid in order to emit a certain current entering the device.
Here, η is the electron gun assembly (EGA) efficiency (~0.97 in TSS-1), ρ is the perveance of the EGA (7.2 micropervs in TSS-1), ΔVtc is the voltage across the accelerating grid of the EGA, and "I""t" is the emitted current.
The perveance defines the space charge limited current that can be emitted from a device.
The figure below displays commercial examples of thermionic emitters and electron guns produced at Heatwave Labs Inc.TC electron emission will occur in one of two different regimes: temperature or space charge limited current flow.
For temperature limited flow every electron that obtains enough energy to escape from the cathode surface is emitted, assumimg the acceleration potential of the electron gun is large enough.
In this case, the emission current is regulated by the thermionic emission process, given by the Richardson Dushman equation.
In SCL electron current flow there are so many electrons emitted from the cathode that not all of them are accelerated enough by the electron gun to escape the space charge.
In this case, the electron gun acceleration potential limits the emission current.
The below chart displays the temperature limiting currents and SCL effects.
As the beam energy of the electrons is increased, the total escaping electrons can be seen to increase.
The curves that become horizontal are temperature limited cases. 
The photons of a light beam have a characteristic energy proportional to the frequency of the light.
In the photoemission process, if an electron within some material absorbs the energy of one photon and acquires more energy than the work function (the electron binding energy) of the material, it is ejected.
If the photon energy is too low, the electron is unable to escape the material.
Since an increase in the intensity of low-frequency light will only increase the number of low-energy photons sent over a given interval of time, this change in intensity will not create any single photon with enough energy to dislodge an electron.
Thus, the energy of the emitted electrons does not depend on the intensity of the incoming light, but only on the energy (equivalently frequency) of the individual photons.
It is an interaction between the incident photon and the outermost electrons.
Electrons can absorb energy from photons when irradiated, but they usually follow an "all or nothing" principle.
All of the energy from one photon must be absorbed and used to liberate one electron from atomic binding, or else the energy is re-emitted.
If the photon energy is absorbed, some of the energy liberates the electron from the atom, and the rest contributes to the electron's kinetic energy as a free particle.
To use electron affinities properly, it is essential to keep track of sign.
For any reaction that "releases" energy, the "change" Δ"E" in total energy has a negative value and the reaction is called an exothermic process.
Electron capture for almost all non-noble gas atoms involves the release of energy and thus are exothermic.
The positive values that are listed in tables of "E"ea are amounts or magnitudes.
It is the word, "released" within the definition "energy released" that supplies the negative sign.
Confusion arises in mistaking "E"ea for a change in energy, Δ"E", in which case the positive values listed in tables would be for an endo- not exo-thermic process.
The relation between the two is "E"ea = −Δ"E"(attach).<br>However, if the value assigned to "E"ea is negative, the negative sign implies a reversal of direction, and energy is "required" to attach an electron.
In this case, the electron capture is an endothermic process and the relationship, "E"ea = −Δ"E"(attach) is still valid.
Negative values typically arise for the capture of a second electron, but also for the nitrogen atom.
The usual expression for calculating "E"ea when an electron is attached isThis expression does follow the convention Δ"X" = "X"(final) − "X"(initial) since −Δ"E" = −("E"(final) − "E"(initial)) = "E"(initial) − "E"(final).
Equivalently, electron affinity can also be defined as the amount of energy "required" to detach an electron from a singly charged negative ion, i.e.
the energy change for the process :X− → X + e− If the same table is employed for the forward and reverse reactions, "without switching signs", care must be taken to apply the correct definition to the corresponding direction, attachment (release) or detachment (require).
Since almost all detachments "(require +)" an amount of energy listed on the table, those detachment reactions are endothermic, or Δ"E"(detach) > 0. 
Energy distribution measurements of field-emitted electrons were first reported in 1939.
In 1959 it was realized theoretically by Young, and confirmed experimentally by Young and Mueller that the quantity measured in spherical geometry was the distribution of the total energy of the emitted electron (its "total energy distribution").
This is because, in spherical geometry, the electrons move in such a fashion that angular momentum about a point in the emitter is very nearly conserved.
Hence any kinetic energy that, at emission, is in a direction parallel to the emitter surface gets converted into energy associated with the radial direction of motion.
So what gets measured in an energy analyzer is the total energy at emission.
With the development of sensitive electron energy analyzers in the 1960s, it became possible to measure fine details of the total energy distribution.
These reflect fine details of the surface physics, and the technique of Field Electron Spectroscopy flourished for a while, before being superseded by newer surface-science techniques.