Auxiliary electron sources

The plasma can be formed using a number of configurations, as described in Ch. 5. The most common configuration is where an electrically conductive substrate is the cathode. When the substrate or the depositing film is an electrical insulator, the plasma can be formed by making the substrate an rf electrode in an rf plasma system or a pulsed (dc or bipolar) voltage can be used. In some cases, the plasma can be enhanced by an auxiliary electron source or by the electrons used to evaporate the source material. 

Auxiliary electron source (triode) - low pressures (0.01-0.2 Torr)... 

In principle the introduction of symmetry constraints, i.e. invariances permits to cast the separability problem into a manner differing from the standard approach. This can be achieved by defining an auxiliary electronic problem. The dynamical variables R are replaced by parameters a locating general external sources of Coulomb potential a=(a i,...,ccm), equivalent to that set up by the charged nuclei. 

Further, the corrodible metal will act as the electron-source electrode for the electronation reaction, which would otherwise have produced its corrosion. Hence, what is done is to set up a new corrosion cell in which an auxiliary metal is made to corrode in place of the metal to be protected and in which the entire surface of the latter metal is converted into an electron-source area. For example, if a steel structure has to be protected, one can use zinc or magnesium as a sacrificial electron sink and save the structure from corrosion. 

The electrons pumped into the corrodible metal have come, in the above method, from the dissolution of a scarificial auxiliary metal. Instead, they can come from an external current source (i.e., an electrical power supply). The electrical circuit, however, has to be completed, and toward this end, an auxiliary inert electrode can be immersed in the corrosive electrolyte to provide a return path for the electron current (Fig. 12.38). The external source can then be adjusted so that the potential difference between the corrodible metal and its environment becomes negative with respect to its equilibrium potential. Under these circumstances, the whole of the metal to be protected against corrosion will function as an electron source for the electronation reaction, and the second electrode will serve as an electron sink for some deelectronation reaction (Hoar). 

Cone-carrying metal foil at its truncated apex. Foil has one or several leaks through which the gas and ions enter the pumping and electrode chamber. 9. Heater and thermocouple wells for temperature control of ion source. 10. Auxiliary electron gun for gas purity determinations. 11-19. Electrodes focusing ion beam into magnetic mass analyzer. Note in later versions of the apparatus the distance from the alpha source to the ion exit slit was shortened, which increases the effective intensity. 

Cementation, the deposition of small amounts of an auxiliary metal on a support metal, has been used for a long time as an activation method. A common example is surface alloying with mercury, i.e., amalgamation. The properties of the couple largely depend on the redox potentials of both constituents. In general, the base metal is considered to behave as an electron source, while the "true chemistry" is effected by the superficial auxiliary metal. Several examples illustrate this principle. 

Operation in the UHV regime is even more important in SSIMS than in XPS. When studying insulating samples such as polymers it is necessary to overcome charging problems by use of an auxiliary source of electrons. Thus an electron source is an essential component of a SSIMS instrument. 

Figure 10.7 illustrates the use of an external power supply to provide the cathodic polarisation of the structure. The circuit comprises the power source, an auxiliary or impressed current electrode, the corrosive solution, and the structure to be protected. The power source drives positive current from the impressed current electrode through the corrosive solution and onto the structure. The structure is thereby cathodically polarised (its potential is lowered) and the positive current returns through the circuit to the power supply. Thus to achieve cathodic protection the impressed current electrode and the structure must be in both electrolytic and electronic contact. 

There is now a great interest in developing different kinds of fuel cells with several applications (in addition to the first and most developed application in space programs) depending on their nominal power stationary electric power plants (lOOkW-lOMW), power train sources (20-200kW) for the electrical vehicle (bus, truck and individual car), electricity and heat co-generation for buildings and houses (5-20 kW), auxiliary power units (1-100 kW) for different uses (automobiles, aircraft, space launchers, space stations, uninterruptible power supply, remote power, etc.) and portable electronic devices (1-100 W), for example, cell phones, computers, camcorders [2, 3]. 

The sample pressure, electron beam current, auxiliary magnetic field, and ion residence time in the ion source are not stated and cannot be inferred from the data given. As will be seen below, the details of the ion source are quite important in the production of doubly-charged negative ions. 

Fig. 2-36. Scheme of laboratory installation for recording polarisation curves of electronic conductors 1- electronic conductor (mineral or metal) 2- solution of electrolyte A- current electrode B- auxiliary current electrode M- measuring electrode N- non-polarisable measuring (reference) electrode cp- potentiometer CS- electric current source I- ammeter (reproduced with permission from Putikov, 1993). 

New lithium-based and the more conventional Ni-Zn batteries may eventually replace lead-acid batteries as new technology and advanced manufacturing techniques reduce their costs. Metal-air batteries, both rechargeable (zinc) and nonrechargeable fuel-cell types (aluminum), may ultimately be successful as an economical primary source for short-trip transportation. The demand for increasing electronic equipment will require increased auxiliary power, which may be fulfilled by improved lithium-based and Ni-Zn systems. 

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