Question: Electrons are used for what?
About the article "Electrochemistry", section "Neutral medium".

Candidate passages:
The key terms involved in redox are often confusing to students.
For example, an element that is oxidized loses electrons; however, that element is referred to as the reducing agent.
Likewise, an element that is reduced gains electrons and is referred to as the oxidizing agent.
Acronyms or mnemonics are commonly used to help remember what is happening:  "OIL RIG"—Oxidation Is Loss of electrons, Reduction Is Gain of electrons.
"LEO the lion says GER" — Loss of Electrons is Oxidation, Gain of Electrons is Reduction.
"LEORA says GEROA" — Loss of Electrons is Oxidation (Reducing Agent) and Gain of Electrons is Reduced (Oxidizing Agent).
"RED CAT" and "AN OX" — Reduction occurs at the Cathode and the Anode is for Oxidation.  
The backscattered electrons are conventionally associated with those electrons emanating from the beam-specimen interaction by having energies greater than 50 eV up to the primary beam energy for reflected electrons.
For the detection and imaging with these electrons, scintillating and solid state materials have been used in the SEM.
These materials have been adapted and used also in ESEM in addition to the use of the GDD for BSE detection and imaging. 
In physics, a charge carrier is a particle free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors.
Examples are electrons, ions and holes.
In a conducting medium, an electric field can exert force on these free particles, causing a net motion of the particles through the medium; this is what constitutes an electric current.
In different conducting media, different particles serve to carry charge:  In metals, the charge carriers are electrons.
One or two of the outer valence electrons from each atom is able to move about freely within the crystal structure of the metal.
The free electrons are referred to as conduction electrons, and the cloud of free electrons is called a Fermi gas.
In electrolytes, such as salt water, the charge carriers are ions, atoms or molecules that have gained or lost electrons so they are electrically charged.
Atoms that have gained electrons so they are negatively charged are called anions, atoms that have lost electrons so they are positively charged are called cations.
Cations and anions of the dissociated liquid also serve as charge carriers in melted ionic solids (see e.g.
the Hall–Héroult process for an example of electrolysis of a melted ionic solid.)
Proton conductors are electrolytic conductors employing positive hydrogen ions as carriers.
In a plasma, an electrically charged gas which is found in electric arcs through air, neon signs, and the sun and stars, the electrons and cations of ionized gas act as charge carriers.
It carries external electrons which are found in certain ionic lattices such as copper.
In a vacuum, free electrons can act as charge carriers.
These are sometimes called cathode rays.
In a vacuum tube, the mobile electron cloud is generated by a heated metal cathode, by a process called thermionic emission.
In semiconductors (the material used to make electronic components like transistors and integrated circuits), in addition to electrons, the travelling vacancies in the valence-band electron population (called "holes"), act as mobile positive charges and are treated as charge carriers.
Electrons and holes are the charge carriers in semiconductors.
It can be seen that in some conductors, such as ionic solutions and plasmas, there are both positive and negative charge carriers, so an electric current in them consists of the two polarities of carrier moving in opposite directions.
In other conductors, such as metals, there are only charge carriers of one polarity, so an electric current in them just consists of charge carriers moving in one direction. 
As the electrons used for HREELS are low energetic they do not only have a very short free mean path length in the sample materials but also under normal atmospheric conditions.
Therefore one has to set up the spectrometer in UHV.
The spectrometer is in general a computer simulated design that optimizes the resolution while keeping an acceptable electron flux.
The electrons are generated in an electron source, by heating a tungsten cathode, which is encapsulated by a negatively charged so called repeller that prevents stray electrons from coming into the detector unit.
The electrons can leave the source only through a lens system, like e.g.
a slot lens system consisting of several slits all on different potential.
The purpose of this system is to focus the electrons on the entrance of the monochromator unit, to get a high initial electron flux.
The monochromator is usually a concentric hemispherical analyser (CHA).
In more sensitive setups an additional pre-monochromator is used.
The task of the monochromator is to reduce the energy of the passing electrons to some eV due to the help of electron lenses.
It further lets only those electrons pass which have the chosen initial energy.
To achieve a good resolution it is already important to have incident electrons of a well defined energy one normally chooses a resolution of formula_6 for the monochromator.
This means, the electrons leaving the monochromator with e.g.
10 eV have an energy accurate to 10−1 eV.
The beam’s flux is then in the orders of 10−8 A to 10−10 A.
The radii of the CHA are in the order of several 10 mm.
And the deflector electrodes have a saw tooth profile to backscatter electrons which are reflected from the walls in order to reduce the background of electrons with the wrong Ei.
The electrons are then focused by a lens system onto the sample.
These lenses are, in contrary to those of the emitter system very flexible, as it is important is to get a good focus on the sample.
To enable measurements of angular distributions all those elements are mounted on a rotate able table with the axis cantered at the sample.
Its negative charge causes the electron beam to broaden.
What can be prevented by charging the top and bottom plates of the CHA deflectors negative.
What again causes a change in the deflection angle and has to be considered when designing the experiment.
In the scattering process at the sample the electrons can lose energies from several 10−2 eV up to a few electron volt.
The scattered electron beam which is of around 10−3 lower flux than the incident beam then enters, the analyzer, another CHA.
The analyzer CHA again allows only electrons of certain energies to pass to the analyzing unit, a channel electron multiplier (CEM).
For this analyzing CHA the same facts are valid as for the monochromator.
Except that a formula_7 higher resolution as in the monochromator is wanted.
Hence the radial dimensions of this CHA are mostly bigger by like a factor 2.
Due to aberrations of the lens systems the beam has also broadened.
To sustain a high enough electron flux to the analyzer the apertures are also about a factor 2 bigger.
To make the analysis more accurate, especially to reduce the background of in the deflector scattered electrons often two analyzers are used, or additional apertures are added behind the analyzers as scattered electrons of the wrong energy normally leave the CHAs under large angles.
In this way energy losses of 10−2 eV to 10 eV can be detected with accuracies of about 10−2 eV. 
Carbon fixation.
Cyanobacteria use the energy of sunlight to drive photosynthesis, a process where the energy of light is used to split water molecules into oxygen, protons, and electrons.
While most of the high-energy electrons derived from water are used by the cyanobacterial cells for their own needs, a fraction of these electrons are donated to the external environment via electrogenic activity.
Cyanobacterial electrogenic activity is an important microbiological conduit of solar energy into the biosphere.