Among transition metal nitrides, molybdenum nitrides have been much less studied even though their mechanical properties as well as their electrical and catalytic properties make them very attractive for many applications. The δ-MoN phase of hexagonal structure is a potential candidate for an ultra-incompressible and hard material and can be compared with c-BN and diamond. The predicted superconducting temperature of the metastable MoN phase of NaCl-B1-type cubic structure is the highest of all refractory carbides and nitrides. The composition of molybdenum nitride films as well as the structures and properties depend on the parameters of the process used to deposit the films. They are also strongly correlated to the electronic structure and chemical bonding. An unusual mixture of metallic, covalent and ionic bonding is found in the stoichiometric compounds.

NH3 and NHx<3 radicals are produced downstream a microwave discharge containing Ar-N2-H2 gas mixture. The chemical mechanism under investigation consists of heterogenous reactions between adsorbed species NH or NH2 (denoted NHs and NH2s) and H or H2 flowing downstream the discharge. NHs is adsorbed on the stainless steel reactor wall and reacts with H or H2 producing NH2s or . Then, part of NH2s produced reacts with H atoms producing ; another part is desorbed from the tube wall: . We assume that NH3 is spontaneously and totally desorbed. From the balance equations, we determine analytical relations for NH2s, NH2 and NH3 concentrations. We then measure values of reaction rate constants and compare the numerical results to measurements performed in the afterglow by means of mass spectrometer versus the %H2 injected in the discharge. We measure values in two different initial gas mixtures, 98.7% Ar-1.3% N2 and 66.6% Ar-33.3% N2. In the first gas mixture, k1, k2(NHs), k3(NHs) and ksg range between 1×10-17 and 2×10-17 m3 s-1, 0.035 and 0.045 m s-1, 9 and 11 m s-1, and 0.30 and 0.35 m-1 s-1, respectively. In the second gas mixture, as expected, similar values are found for k1 and ksg but the other two values increase by a factor of 5. Such an increase for k2(NHs) and k3(NHs) is probably due to the increase of the (NHs) concentration on the reactor wall. The recombination coefficient γ is deduced from the previous rate constant values. We find γ1 = 4.12×10-4, γ2 = 4.91×10-6 and γ3 = 7.93×10-4, using the mean values of reaction rate constants determined for k1, k2 and k3, respectively, in the first gas mixture. To our knowledge, these results have never been published before. They are in good agreement with values given in the literature for other similar mechanisms. Finally, we conclude that the loss of H atoms on the reactor wall mainly results in producing NH2s and NH3.

Different hexamethyldisiloxane (HMDSO) dissociation processes are investigated by means of absorption spectroscopy and mass spectrometry. All of these processes are expected to occur in plasma containing Ar-HMDSO gas mixture. We successively study interactions of the HMDSO molecule with electrons (energy ranges from 15 to 70 eV), with Ar((3)P(2)) metastable species (internal energy 11.55 eV) and with VUV photon (7.3 to 10.79 eV). The studies of HMDSO interactions with Ar((3)P(2)) and VUV photon provide new results concerning the dissociation pathways and the collision cross-sections. In the case of Ar((3)P(2)), the dissociation mechanisms result mainly in Si-C or Si-O bond breaking, producing SiMe(2,1) radicals. Less efficient mechanisms involve also Si-C and Si-O bond breaking producing Me, Si(2)Me(5)O, or SiMe(3), on one hand, and, on the other hand, Si-C and C-H bond breaking producing Si(2)Me(4)OH. In the case of photon interaction, the dissociation process is more selective and mainly produces Si(2)OMe(5) pentadisiloxane and methyl radicals due to Si-C bond breaking. Si-O bond breaking produces also SiMe(3) in a lower concentration. Dissociation cross-section values of HMDSO ranging from σ = 45 × 10(-20) m(2) to 180 × 10(-20) m(2) and from σ = 0.7 × 10(-22) m(2) to 18.3 × 10(-22) m(2), correspond to a global dissociation mechanism by Ar((3)P(2)) collision and to a selective dissociation mechanism (producing Si(2)OMe(5) and Me) by VUV photon interaction, respectively. All results are compared and discussed.

This work is devoted to the study of the electron density measured by means of a Langmuir probe at the ion saturation current. Investigations are performed in a microwave expanding plasma in an Ar-N 2 gas mixture. We show that in such a plasma the electron energy distribution function (EEDF) is not a Maxwell-Boltzmann distribution function and we study the ion velocity at the sheath edge and the sheath thickness around the probe in that case. On the basis of previous works given in the literature and by considering a general expression for the EEDF (no assumption concerning the distribution function), we develop a model describing the ion motion in the sheath around the probe by considering both the sheath expansion and the effect of ion-neutral collision processes. This model is tested in Ar-N 2 gas mixtures using different experimental conditions. Results show a good agreement between the electron density values measured in ion saturation current conditions using this model and values measured using other classical methods. These investigations mainly show the efficiency of the method.

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