Surface processes: Ruthenium film growth, silicon nanocrystal synthesis, and methylene partial oxidation.

摘要

This dissertation focuses on advancements of several surface processes. First, a generalizable method to screen organometallic molecules suitable for chemical vapor deposition (CVD) is described. Of four candidates, one precursor, [Ru(C₅H₅)(CO)₂]₂, was proven suitable for CVD. Using O₂ as a reaction gas, pure, conformal, conductive ruthenium films were produced on patterned Si₃N ₄ and flat (Ba,Sr)TiO₃ substrates. Without O₂, significant amounts of carbon were incorporated into the film. X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and four point probe techniques were used to analyze the effect of O ₂ and substrate temperature on the deposition of ruthenium films.; Next, the nucleation and growth of Si nanocrystals on SiO₂ and Si₃N₄ is discussed. The effect of substrate temperature, reactive gas composition, and surface chemistry is discussed. The thrust is to understand the impact of the surface and gas phase chemistries on the nucleation and growth characteristics of Si nanocrystals.; Then, the oxidation of Si nanocrystals is reported. Even though the oxidation of planar Si is well understood, the confined geometry of nanocrystals affects the oxidation process significantly. In this report, Si nanocrystals are oxidized in NO and O₂ ambients at temperatures ranging from 650 to 1050°C. The extent of nanocrystal oxidation is analyzed using X-ray photoelectron spectroscopy, transmission electron microscopy and energy filtering transmission electron microscopy techniques. NO oxidation leads to highly self-limited growth; O₂ oxidation at 1050°C leads to complete nanocrystal oxidation. At 850°C, in O₂ atmospheres there is positive evidence for self-limiting oxidation. Sequentially oxidizing nanocrystals, first in NO and then in O₂, has been shown to lead to very controlled oxide shell thickness.; Finally, the reactions of CH₂I₂ on clean and O(a) precovered Ag(111) have been examined using temperature programmed desorption and reflection adsorption infrared spectroscopy. On clean Ag(111), CH ₂I₂ dissociates to CH₂(a) and I(a). CH₂(a) groups recombine in a reaction limited process to form C₂H ₄(g). On oxygen precovered Ag(111), the extent of C₂H ₄ formation decreases and CH₂O evolves in a reaction limited process. The formation of gas phase CO₂ suggests that the formation of formate is a secondary reaction product.