Stress Evolution during Ge Nanoparticles Growth in a SiO2 Matrix.

Superstructures are explored that were obtained by multilayer magnetron deposition at room temperature of 20 SiO2 and SiO2:Ge bilayers, each 2 × 4 nm thick, and subsequently annealed in inert N2 atmosphere at different temperatures in the range of 500-750 °C. The structural and optical changes induced by annealing and the formation and growth of Ge nanoparticles (nps) from early clusters to their full growth and final dissolution were studied by the simultaneous grazing-incidence small- and wide-angle X-ray scattering, transmission electron microscopy, and (time-resolved) photoluminescence (PL). It is shown that in as-deposited multilayers aggregation of small clusters already occurred, and the clusters were reasonably well intercorrelated in the lateral plane. During annealing at Ta = 550 °C or higher temperatures, Ge nps start to form and remain partly amorphous at lower Ta but crystallize completely at about 600 °C. At even higher temperatures, the Ge nps dissolve and Ge diffuses out almost completely, leaving voids in the SiO2 matrix. Visible PL from the samples was detected and attributed to defects in the nps/matrix interface layers rather than to the nps itself because PL persisted even after Ge nps dissolution.

Reactions in silicon-nitrogen plasma.

Reaction mechanisms that lead to creation of silicon-nitrogen bonds are studied in detail. These reactions are of fundamental importance for silicon nitride synthesis by plasma enhanced chemical vapour deposition from the gas mixture of silane (SiH4) and ammonia (NH3). All reactions in SiH4-NH3 plasma can be categorised as some of the basic types of reactions: bond dissociation, neutral nucleophilic substitution, radical neutralisation, neutral-radical addition, silylene addition, silylene rearrangement, radical nucleophilic addition or hydrogen abstraction reaction. Energetics of these reactions is analysed in detail for a great number of reactions belonging to these categories, by using theoretical modelling. Geometry optimisations are carried out with the MP2/aug-cc-pVTZ level of theory and energetics is further determined with high level ab initio calculations at the CASPT2/aug-cc-pVTZ level, which enabled confirmation of relevance of several mechanisms as reactions that lead to silicon nitride growth from plasma enhanced chemical vapour deposition, as well as introduction of new, energetically favourable mechanisms. Besides amine radical assisted eliminative addition and proton transfer reactions, silylene addition reactions are thermodynamically and kinetically favourable since they lack energy barriers. A new reaction pathway for synthesis of silicon nitride from plasma is proposed. This pathway is enabled by the ability of silylene to create two weak dative bonds, which enables silylene-amine complexes to stick to the silicon nitride surface. Upon dissociation of amine from the surface-bound complex, silylene remains on the surface, available for reaction with other reactive species from plasma.

GISAXS Analysis of the In-Depth Morphology of Thick PS-b-PMMA Films.

The morphological evolution of cylinder-forming poly(styrene)-b-poly(methyl methacrylate) block copolymer (BCP) thick films treated at high temperatures in the rapid thermal processing (RTP) machine was monitored by means of in-depth grazing-incidence small-angle X-ray scattering (GISAXS). The use of this nondisruptive technique allowed one to reveal the formation of buried layers composed of both parallel- and perpendicular-oriented cylinders as a function of the film thickness (24 ≤ h ≤ 840 nm) and annealing time (0 ≤ t ≤ 900 s). Three distinct behaviors were observed depending on the film thickness. Up to h ≤ 160 nm, a homogeneous film consisting of perpendicular-oriented cylinders is observed. When h is between 160 and 700 nm, a decoupling process between both the air-BCP and substrate-BCP interfaces takes place, leading to the formation of mixed orientations (parallel and perpendicular) of the cylinders. Finally, for h > 700 nm, the two interfaces are completely decoupled, and the formation of a superficial layer of about 50 nm composed of perpendicular cylinders is observed. Furthermore, the through-film morphology affects the nanodomain long-range order, which substantially decreases in correspondence with the beginning of the decoupling process. When the thick samples are exposed to longer thermal treatments, an increase in the long-range order of the nanodomains occurs, without any sensible variation of the thickness of the superficial layer.