Cathode dark space

Figure 1 Schematic of DC glow-discharge atomization and ionization processes. The sample is the cathode for a DC discharge in 1 Torr Ar. Ions accelerated across the cathode dark space onto the sample sputter surface atoms into the plasma (a). Atoms are ionized in collisions with metastable plasma atoms and with energetic plasma electrons. Atoms sputtered from the sample (cathode) diffuse through the plasma (b). Atoms ionized in the region of the cell exit aperture and passing through are taken into the mass spectrometer for analysis. The largest fraction condenses on the discharge cell (anode) wall.

Figure 2. Schematic diagram of the model of the cathode dark space. Concentration of the ions is denoted by N0...

Figure 4. Calculated energy distribution of the argon ions at the cathode of a glow discharge in a mixture of 99% argon and 1 % nitrogen for two different optically measured cathode dark space lengths...

Gas phase free radicals will be formed throughout the discharge. However, due to the significantly higher field strength in the region of the cathode dark space, the rate of radical production will be maximized there. This is advantageous since it shortens the distance for radical diffusion from the gas phase to the cathode surface. 

Aston Dark Space -1 Cathode Layer Cathode Dark Space Negative Glow... 

Figure 17.16 The influence of input power on the cathodic dark space thickness //stmax= 1550G, a= 1.5 cm, Z = 8.0cm, Ar mass flow rate = 1 seem.

Figure 17.18 depicts the influence of gap distance on the cathodic dark space thickness. CDST el become slightly smaller while the CDST e2 expands with a decrease of the gap distance in the AMT glow discharge. Since a constant Ar is fed... 

Figure 17.20 The influence of electrode distance on the cathodic dark space thickness input power = low, a = 0.0cm, Ar mass flow rate= 1 seem.

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