Detailed analysis reveals differences between single-crystal and polycrystalline nickel features
Detailed analysis reveals differences between single-crystal and polycrystalline nickel features lead image
Nickel is widely used as a catalyst in plasma-enhanced chemical vapor deposition for making carbon nanotubes and for transforming methane in plasma-enhanced chemistry. However, secondary electrons emitted from plasma-facing surfaces have been found to reduce plasma electron temperatures and enhance surface chemistry.
Secondary electron emission (SEE) can therefore affect devices with plasma-facing walls, including the previously described applications which utilize nickel surfaces. But polycrystalline and single-crystal nickel can exhibit significantly different SEE yields.
Research from Patino et al. looks to understand the emission properties of one type of single-crystal nickel. They present their findings on the SEE behavior of Ni(110) under temperature-controlled conditions. Examining electrons with 50 to 1500 eV of energy impacting single crystal nickel from 0 degrees to 35 degrees, 50 degrees, and 78 degrees, the authors discovered a noncosine dependence on electron incidence angle.
The group found that the maximum SEE yield for primary electrons at 0 degrees is up to 36 percent larger for Ni(110) compared to its polycrystalline form, suggesting the angular dependence is due to increased secondary electron generation when primary electrons are directed along a closed packed direction. Similarly, minima in SEE yield occurred at +/−12 degrees, which is along nonclosed packed directions.
Furthermore, carbon monoxide was found to react strongly with Ni(110) and decrease SEE yield by up to 25 percent, while subsurface hydrogen had little effect on SEE yield.
These results cast further evidence of the unique SEE properties of single-crystal materials when compared to their polycrystalline counterparts, and highlight the need to further understand the effect of the crystal lattice and gas adsorption sites on electron transport.
Source: “Angular, temperature, and impurity effects on secondary electron emission from Ni(110),” by M. I. Patino, R. E. Wirz, Y. Raitses, and B. E. Koel, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5025344 .
