Nanostructured SiC as a promising material for the cold electron emitters

In this paper, the novel cold electron emitters based on nanostructured SiC layers covering the Si(001) substrate have been proposed. Their main advantage is an extremely simple and cost-effective manufacturing process based on the standard microelectronics-grade silicon wafers with no ultra-high vacuum required and no complicated chemical deposition processes or toxic chemicals involved. It integrates within a single technological step both the SiC growth and nanostructuring the surface in the form of nanosized protrusions, which is extremely beneficial for cathode applications. A simple mathematical model predicts field emission current densities and turn-on electric fields, which would allow practical device applications. According to our estimations, emission currents in the milli-Amp range can be harvested from one square centimeter of the cathode surface with electric field close to 107 V/m. So, the nanostructured SiC can be the promising material for the cold electron emitters.

Vacuum-plasma processes at extreme field emission in diamond electron sources

Background and Objectives: The use of high-current field electron sources that satisfy various circuitry requirements as a part of electronic devices for various purposes suggests the possibility of matching their operation modes with the operating characteristics of the devices, as well as high reproducibility of emission parameters, stability and the necessary resource of reliability and durability. The stability and durability of field electron sources are extremely sensitive to the changes in the geometry of emission centers and to the state of their surface, which undergoes various destructive influences during operation. These changes are especially important in the case of high-current field-emission cathodes, which, as a rule, work under conditions of technical vacuum and high electric field intensities. The aim of the work was to study the possibility of creating field sources of electrons based on thin-film planar-end nanodiamond-graphite structures that satisfy various circuit requirements, as well as to study fundamental factors that lead to a change in their I–V characteristics and limit the maximum value of their field emission currents, stability and durability of high-current field emission. Materials and Methods: Emission structures were made of carbon films deposited in a microwave plasma of a low pressure gas discharge. The surface resistance of the films was 120 kOhm/□ and 1.2 mOhm/□. In the first type of emission structure, diamond-graphite films were mechanically separated into two parts. One part of the film was the cathode, the second served as the anode. Measurement of field emission characteristics in vacuum (2–4)·10-3 Pa. Between the cathode and the anode, voltage pulses with a duration of 10 μs and an amplitude of 0 to 3000 V were applied. In the second type of emission structure, field emission was carried out from the end face of a diamond-graphite film deposited on a polycor substrate. Field emission-voltage characteristics were measured in constant electric fields. Determination of the elemental composition of the surfaces of field emission structures after electrical tests was carried out using an energy dispersive microanalysis system. Results: It is shown that the steepness of the current-voltage characteristics, as well as the stability and durability in extreme operating conditions of high-current field electron sources based on film diamond-graphite nanocomposites, is determined by their surface resistance. Electron field sources based on low-resistance diamond-graphite structures, in comparison with high-resistance, have a high slope of the I–V characteristic, a lower threshold for the field intensity at the beginning of field emission, and the maximum field emission current is achieved at a lower electric field strength. The range of operating voltages providing the same maximum field emission current is many times higher for high-impedance electron sources than for low-impedance ones. The various nature of vacuum-plasma processes is established for extreme field emission in diamond-graphite electron sources with different surface resistance. In the case of lowresistance diamond-graphite composite film structures under extreme operating conditions of high-current planar-face autoemission structures, the main reasons for the instability of the emission and destruction parameters are the appearance of electrothermal breakdowns at the cathode of the “grid” characteristic of thin dielectric coatings during a sliding surface electric discharge. In the case of high-resistance diamond-graphite film structures, there is no branched network of electrothermal electrical breakdowns. In this case, as well as for high-current end field emission structures, the main nature of destruction under extreme operating conditions is erosion of the cathode part of the film. Erosion is caused by the processes of explosive electron emission, which is carried out from the nanodiamond emission centers of the composite carbon film structure with the appearance of a cathode plasma plume and the graphite component of the cathode material is sprayed onto the anode and into the interelectrode gap. Conclusion: The results can be used to predict the durability and stability of high-current field electron sources based on diamond-graphite film structures depending on their design, electrophysical characteristics, and vacuum operating conditions.

Effects of Antimony Deposition on Field-Emission Current Density of Ge/Si

To estimate the field-emission current density of a Ge/Si heterosystem, 20-nm germanium/silicon (100) samples were grown by molecular beam epitaxy. The surface of one sample was covered with a layer of antimony, which was removed in vacuum prior to the samples being measured. A second sample of Ge/Si was exposed to room air in the absence of antimony. The current–voltage characteristics of both samples obtained by scanning tunneling microscopy (STM) were discovered to be in agreement with classical Fowler–Nordheim theory. The density of emission current from Ge nanocrystal exceeds the density of emission current from the wetting layer of Ge/Si. The density of emission current of pure Ge nanocrystal is less than the density of emission current of Ge nanocrystal with adsorption layers.