Ethoxy and silsesquioxane derivatives of antimony as dopant precursors: unravelling the structure and thermal stability of surface species on SiO2.

We report here the controlled preparation of SiO2 supported Sb-(mono)layers and their thorough characterization by in situ IR, solid-state NMR and elemental analyses. This study allows for the molecular understanding of the surface Sb species derived from the grafting of ethoxy and polyhedral oligomeric silsesquioxane antimony derivatives as mono- or bi-podal Sb(iii) surface species depending on the number of surface SiOH groups. This result is different from what was observed with the phosphorus analogue (POSS-P) that yielded P(v) species. A monolayer coverage of Sb species onto silica was also obtained using both POSS-Sb and the [Sb(OEt)3]2 derivative with surface densities ranging from ∼0.3 Sb nm-2 to 1.8 Sb nm-2, respectively. It is noteworthy that under optimized conditions, a layer of antimony species or suboxides on silica was produced using POSS-Sb without significant Sb loss, highlighting the protective properties of the POSS cage. These results open new perspectives for the controlled and non-destructive Sb-doping (Molecular Layer Doping) of semiconductors dedicated to nano-device applications.

Relation between surface roughness of free films and process parameters in spray coating.

A novel spraying apparatus was developed to obtain reproducible free sprayed films. Aqueous solutions of PolyVinyl Alcohol PVA 4-98, HydroxyPropyl MethylCellulose HPMC 603 and HPMC 615 were used as reference coating materials. The apparatus is composed by a spraying system, a closed chamber containing a rotating Teflon cylinder, a pressured air supply system, a spray solution supply system, and a computerized control system. The spraying air pressure, the cylinder rotation speed, and the cylinder-spray nozzle distance were tailored in such a manner that the roughness of the obtained free films was similar to that from reference coated particles. Optimum spraying process conditions were found for all three coating materials using design of experiments. The morphology of the sprayed films obtained using the optimum conditions is evaluated by means of scanning electron microscopy (SEM), and atomic force microscopy (AFM), and then compared with those from corresponding cast films and coating layers on particles. A match was found between the morphology of sprayed films and that from the corresponding coating layer on the particle surface. The spray apparatus produced reproducible sprayed films with tuneable roughness and/or smoothness depending on the set of processing parameters.