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2 Lasers
Published in Peter K. Cheo, Handbook of Molecular Lasers, 2018
In a plasma cathode, electrons are extracted from a low-density plasma specially created for each emission event. Often, such cathodes use no auxiliary heater power supply to create the plasma (hence the name “cold” cathode); the plasma creation process is initiated by the application of the electron gun voltage pulse itself. Cold cathodes are used in several geometries: The foil-edge cathode, where the emission is confined to a very narrow region such as the edge of one or more thin foils or a thin strip of upright fibers. In the absence of an external guide magnetic field, electron optics can be used to expand the beam so that its area at the laser gas interface is much larger. The Los Alamos Helios laser electron gun used this design.The extended cathode, which usually uses a graphite velvet or brush surface whose area is comparable to the required beam area at the laser-gas interface. The electron beam flow is rectilinear. This design is particularly suitable for intense beams requiring a guide magnetic field to avoid pinching. Graphite is a favorite material because a plasma forms at the tips of the carbon filaments with particular ease when the external electric field pulse is applied (but the consequences of the deposition of carbon debris on the electron gun chamber surface need to be considered). This cathode geometry is usually used in excimer lasers such as the Los Alamos Large Aperture Module, where the cathode area is 1 m × 2 m (see Fig. 5.8).The “spark” cathode, a sparse version of the extended cathode. The physical cathode area is comparable to the final beam area, but the plasma is produced by arc formation made to occur at a large number of point locations within the physical cathode boundaries. Often, one employs an array of small metal “dots” insulated from the main body of the cathode but coupled capacitively to it (and to ground). Upon application of the electron gun pulse, the dots assume a potential determined by the capacitative voltage division; the potential difference is large enough to cause an arc to occur between the dot and the cathode substrate. The process is illustrated in Fig. 5.9.
The effect of nitrogen concentration on N-doped diamond-like carbon films prepared by plasma-electrolytic method
Published in Inorganic and Nano-Metal Chemistry, 2021
S. Sarihi, S. Padervand, S. M. Mousavi khoei, N. Shakiba
Over the past decades, a growing interest has been reported in the field of N-doped diamond-like carbon coatings, given their considerable field emission properties. Hence, they could be used as cold cathode in vacuum microelectronic systems and in flat panel display technologies.[23] Some authors[23,24] reported low threshold emission for N-doped DLC films. More investigations showed an increase from 160 µA to 1.52 mA with the addition of a 200 Å thick N doped hydrogen-free DLC coating on the Mo tips.[25] While in another study, authors perused the application of N-doped porous carbon for Zn-air batteries, which showed good activity as a metal-free electrocatalyst.[26] In a comparative research, N-doped diamond-like carbon films were obtained by the pulsed laser deposition process. Raman spectroscopy showed interesting results for disordered graphite[27] and graphite[26] peaks of DLC = 1396 cm−1, 1554 cm−1 and DLC:N = 1372 cm−1 and 1551 cm1. Also, the ID/IG for diamond-like carbon and N-doped films were obtained 1.09 and 1.3, respectively.[28] The other areas of applying N-doped carbon quantum dots in optical imaging and sensors were investigated by researchers in which the presence of amorphous carbon was proved based on XRD results, a weak peak at 45.3°.[29] In Shengyin et al.’s research, XRD spectra of N-doped diamond-like carbon films presented obvious peaks at 2θ = 40.04° correspond to the formation of a CNx phase on Si substrate synthesized by pulsed laser deposition (PLD) process.[30] Also, the presence of diamond-like carbon on 43.9° within Wu et al. research was an approval for previous research.[31] More studies performed by different authors rendered carbon allotropes among the other compounds at 2θ ∼43.2°, 74.06°, and 89.9° which could be classified with reflections form (1 1 1), (2 2 0) and (3 1 1) plane of the diamond.[32].