Observation of dust particle growth and fallout in RF-excitedsilane discharges

Particles formed during plasma enhanced chemical vapor deposition of amorphous silicon thin films which fall to the film surface, either during or after the process, may have a severely deleterious effect on film properties. In order to understand the mechanisms of particle formation and fallout we have investigated the growth and dynamics of particles in RF discharges in pure silane. The diameter of particles formed within the first 20 s of the discharge was investigated by electron microscopy of substrates with fallen out particles. Furthermore we used a He-Ne laser in combination with a diode array camera to measure temporally and spatially resolved light scattering from particles and deduced their sinking speed after switching off the discharge. The results are compared to a theoretical model on the particle dynamics     

Foreword to this special issue

Plasma Chemistry and Plasma Processing -     

Superhard nitride-based nanocomposites: role of interfaces and effect of impurities

Recently, a hardness similar to that of diamond has been reported for a quasiternary, nitride-based nanocomposite. The related, quasibinary nanocomposite "nc-TiN/a-Si3N4," which may be regarded as the prototype of the family of superhard nc-metal-N/a-Si3N4 systems, also exhibits a significant hardness enhancement. Extensive density-functional theory calculations indicate that the superhardness is related to the preferential formation of TiN(111) polar interfaces with a thin beta-Si3N4-derived layer. The strength of TiN in the 111 direction is similar to that of the weakest bonding direction in diamond. Oxygen impurities cause a significant reduction of the interface strength.     

Revealing the Pressure-Induced Softening/Weakening Mechanism in Representative Covalent Materials

Diamond, cubic boron nitride(c-BN), silicon(Si), and germanium(Ge), as examples of typical strong covalent materials, have been extensively investigated in recent decades, owing to their fundamental importance in material science and industry. However, an in-depth analysis of the character of these materials' mechanical behaviors under harsh service environments, such as high pressure, has yet to be conducted. Based on several mechanical criteria, the effect of pressure on the mechanical properties of these materials is comprehensively investigated.It is demonstrated that, with respect to their intrinsic brittleness/ductile nature, all these materials exhibit ubiquitous pressure-enhanced ductility. By analyzing the strength variation under uniform deformation, together with the corresponding electronic structures, we reveal for the first time that the pressure-induced mechanical softening/weakening exhibits distinct characteristics between diamond and c-BN, owing to the differences in their abnormal charge-depletion evolution under applied strain, whereas a monotonous weakening phenomenon is observed in Si and Ge. Further investigation into dislocation-mediated plastic resistance indicates that the pressure-induced shuffle-set plane softening in diamond(c-BN), and weakening in Si(Ge), can be attributed to the reduction of antibonding states below the Fermi level, and an enhanced metallization, corresponding to the weakening of the bonds around the slipped plane with increasing pressure, respectively. These findings not only reveal the physical mechanism of pressure-induced softening/weakening in covalent materials, but also highlights the necessity of exploring strain-tunable electronic structures to emphasize the mechanical response in such covalent materials.     

X-ray photoelectron study of amorphous phosphorus preparedbyplasmachemical transport. Comparison with crystalline polymorphs

Amorphous phosphorus prepared by chemical transport in a low pressure hydrogen plasma shows a remarkable stability upon exposure to air. Samples stored in air at room temperature or at 150°C for several hours, as well as in dry air for several weeks did not show any oxide formation observable by XPS. Only the crystalline orthorhombic black phosphorus modification showed similar behaviour. The measured energies of bulk plasmons, 18.3 ± 0.5 eV and 20.3 ± 0.5eV for the amorphous and black phosphorus, respectively, agree reasonably with the theoretical values. The valence band density of states shows two maxima at 3 eV and 11 eV which are attributed to 3p and 3s Orbitals.     

Thermodynamic and Kinetic Aspects of Heterogeneous Reactions in a Nonisothermal Low Pressure Plasma

Because of its high energy content and a relatively low translational temperature, the plasma of an intense low pressure discharge in a molecular gas is suitable for deposition of thin films and growth of crystals. A simple theoretical approach for estimation of chemical equilibrium composition in such systems has been developed. This approach is useful for planning of experiments, and it opens a way for further, more rigorous theoretical investigations.     

Operator ordering, ellipticity and spurious solutions in k · p calculations of III-nitride nanostructures

We analyze the ellipticity of the standard k · p wurtzite model for the symmetrized and the Burt–Foreman operator ordering. We find that for certain situations the symmetrized Hamiltonian is unstable, leads to unplausible results and can cause spurious solutions. We show that the operator ordering in wurtzite must be completely asymmetric to be stable. The asymmetric operator ordering is elliptic and consequently no spurious solutions are obtained. Therefore we recommend the use of a complete asymmetric operator ordering for nitride device simulation.