field emission properties
- The surface appearance developed in the Institute of Nuclear Physics of Moscow State University named after MV University SAG material. Photo from: www.i-mash.ru
In SINP MSU University developed a nanostructured material with unique field emission properties which make it promising for the realization of vacuum electronics applications, including X-ray sources, lights, vacuum microwave devices, neutralizing the charge of ion fluxes.
In recent years, carbon nanomaterials are the object of intense study by researchers. It is caused by the fact that the nanostructures have some unique properties related to size effects underlie a number of electronics applications. In this case, the entire set of forms of carbon nanostructures can select two of the most promising from the point of view of practical application — it nanotubes and graphene, characterized by high electronic conductivity and a relatively low effective work function.
However, most of the devices based on the use of single carbon nano structures, despite the unique results not beyond the laboratory. This is due to the fact that at present there is no effective technology to enable, on the one hand, to lead the mass production of such devices, and on the other — to reduce the cost of the product to an economically viable level. Therefore, the most promising areas of application of carbon nanostructures are still those that are based on the use of thin films consisting of arrays of nanoscale structures.
To improve the efficiency of electronic devices, such as miniature microfocus X-ray tubes, compact microwave amplifiers and other carbon films should have a uniform on the surface of the field emission properties, good adhesion to the substrate, as well as the ability to pass high currents. In addition, increasing the life of the device is connected directly with a decrease in the degree of degradation of the cathodes by the flow of currents. All of these methods satisfy the criteria that are based on the film deposition of carbonaceous plasma. Thus the final properties of carbon films is largely determined by the processes occurring in the plasma during their synthesis.
Nanocrystalline graphite developed in SINP is formed in the form of thin films that can be deposited on electrically conductive as well as on the dielectric substrate by chemical vapor deposition without use of catalysts. SAG films have a distinctive texture mikrorebernoy (Figure 1) formed predominantly vertically oriented graphite plates of different thickness and also contain a number of nanowhiskers (whiskers).
For the synthesis of nano-crystalline graphite films (SAG), the method of plasma deposition in a dc discharge. In addition, the proposed new method for the creation of centers of nucleation of nanocrystalline graphite films, based on the use of plasma-chemical surface treatment on the combined RF / microwave discharge.
By SAG field emitters significantly surpass the best world analogues on the basis of diamond films and carbon nanotubes on key parameters: stability, high emission current density, low noise, resource record in a wide range of vacuum conditions.
Application SAG material opens in principle possible and mnogokatodnyh extended X-ray sources, which opens the possibility of implementing spatial scanning technology with the control electronics. The problem of spatial scanning x-ray tube around the object under study is the key number of applications, such as creating 3D-ray images stationary or moving objects. As an example, the two are now highly sought-after, the application: the creation of inspection systems (security issue) and kardiotomografov (medicine) that can operate in real time.
The use of nano-crystalline graphite creates energy-efficient environmentally friendly and inexpensive household light sources based on cathodoluminescence lamps with SAG cathodes. The preliminary study showed that the energy efficiency of cathodoluminescence lamp cathodes will be more than 2 times higher than the efficiency of incandescent lamps, and durability will not assign household fluorescent lamps. Over the last decade, actively developed the concept of transition in a number of applications in space research from single large spacecraft to a set of highly specialized small satellites (<100 kg). At present, domestic and foreign space vehicles (SV) used Hall and ion electric rocket engines (ERE) to ensure the correction and maintenance of the orbit for a long period of operation.
Considering the different embodiments of electro-motor it is important to note that in all of them the principle of ionic linkage, i.e. particles that make up the jet carry a positive charge, which allows us to give them an extra boost by the application of an external electric field.
The best option to provide compensation of the electrostatic charge of the ion flux ERE, a neutralizer based on field emission electron source that its operation does not require the flow of the working gas and thereby almost ideal for use in small space due to limitations on the total weight and tolerance for changing alignment by making the working substance.
Finally, a significant advantage of using a field emission cathode is its inclusion zero time — it allows to realize the catalytic converter is not only continuous but also in a pulse-periodic mode in which the constant total energy in a wide range of possible parameter values to vary the instantaneous current converter.
Despite considerable interest in the use in the construction of electric propulsion low power (<500 W) field emission cathode technology, up to the present time in the world for not completing the development of both the motors and converters based on carbon nanomaterials. Compared with the field emitter based on carbon nanotubes, whose properties have been well studied, developed in SINP field-emission electron source based on nanocrystalline graphite have significantly higher emission characteristics that make them suitable for use in future models of electric propulsion.