Dissociative recombination as primary dissociation channel in plasma chemistry

Molecule formation, surface modification and deposition in plasmas can in first order be described as dissociation in the plasma and association of fragments at the surface. In active plasmas ionization and dissociation by electrons is accompanied by excitation. But besides these direct electron processes also a second dissociation channel is active: that by charge transfer followed by dissociative recombination. This latter route is the dominant one in the colder recombining phase of the plasma. Atomic and molecular radicals diffuse or flow to the surface, where new molecules are formed. As a result the original molecules are, after being dissociated in the plasma, converted at the surface to new simple molecules, as H\u3csub\u3e2\u3c/sub\u3e, CO, N\u3csub\u3e2\u3c/sub\u3e, H \u3csub\u3e2\u3c/sub\u3eO, O\u3csub\u3e2\u3c/sub\u3e, NO, NH\u3csub\u3e3\u3c/sub\u3e, HCN, C\u3csub\u3e2\u3c/sub\u3eH \u3csub\u3e2\u3c/sub\u3e, CH\u3csub\u3e4\u3c/sub\u3e, to name a few in C/H/O/N containing plasmas. There is evidence that the molecular fragments resulting from dissociative recombination are ro-vibrationally (and possible electronically) excited. Also the molecules resulting from association at the surface may be ro-vibrationally or electronically excited. This may facilitate follow up processes as negative ion formation by dissociative attachment. These negative ions will be lost by mutual recombination with positive ions, giving again excited fragments. Rotational or other excitation may change considerably plasma chemistry. © 2009 IOP Publishing Ltd. U7 - Export Date: 24 March 2010 U7 - Source: Scopus U7 - Art. No.: 01201

Molecule synthesis in an Ar-CH4-O2-N2 microwave plasma

The formation of new mols. in a microwave plasma, created from a mixt. of Ar, CH4, N2 and O2, is investigated by means of an in-depth study of the mol. abundance in the plasma. The mols. are detected by means of tunable diode laser absorption spectroscopy and by abs. mass spectrometry. Three groups of mols. can be discerned in terms of mol. abundance: CO is predominantly formed, together with H2O, N2 and H2. The mols. CH4 and O2 are significantly depleted, but still abundant in a finite quantity. The third group is formed by several other species like NH3, NO, HCN etc. This tendency is expected to occur in every low temp. plasma contg. C, O, H and N atoms. Furthermore, the combination of both techniques also allows us to make a clear distinction between the etching mode and deposition mode of the microwave reactor. Etching mainly occurs when the ratio of admixed gas flows F(O2)/F(CH4) > 0.5. [on SciFinder (R)