The Role of Ethanol in Inherently Selective Atomic Layer Deposition and in Making Bioactive Coating

The role of ethanol in inherently selective atomic layer deposition (ISALD) and in making bioactive coating is discussed in this dissertation. ISALD of zirconia on Si and not on Cu (electroplated and electroplated followed by chemical mechanical polishing) was achieved using ZyALDTM and ethanol, which was further enhanced by multi-fold by using ZMB and ethanol. A simulation based on group contribution method (GCM) was developed for the ISALD process in which the optimum chemisorption of the precursor molecules at the thermodynamic equilibrium was determined using the efficient ant colony optimization (EACO) algorithm. Multi-objective optimization was used to determine the selectivity window over the selected range of temperature by maximizing zirconia deposition on silicon while minimizing the same on copper. The chemical nature of the deposited zirconia film was amorphous by using both ZyALDTM and ZMB at 200 °C. However, it was interesting to note that the amorphous film deposited via ZMB turned crystalline within minutes of exposure to high energy electron beam during characterization using transmission electron microscopy (TEM). Under similar conditions such as that of ISALD, zirconia was found to nucleate faster on silver than on silicon which was almost the exact opposite of what was observed between silicon and copper. Even though silver and copper are present under the same group on the periodic table, silver possesses higher catalytic activity and is more resilient to air oxidation than copper, which may have caused the early nucleation of the ALD film. Use of ethanol as the precursor co-reactant further enabled the room-temperature ALD of magnesium oxide on temperature-sensitive substrate collagen. The literature review conducted on Mg alloy-based biomedical implants indicated that rapid corrosion of magnesium may cause inflammation in the host body along with other health complications such as bacterial invasion at the wound site. Non-uniform microstructure, presence of secondary phases and higher grain size in the Mg alloys were identified to be the key factors that caused accelerated corrosion. ALD is a pristine coating technique that can deposit uniform, conformal, pin-hole free metal and metal oxide films even on organic substrates that usually have higher surface roughness. The magnesium oxide coating on collagen was also shown to be amorphous throughout the deposited layer and free from any secondary phases. Early results from the in vitro and in vivo studies performed in Brazil indicate the MgO-coated collagen membranes possess superior antibacterial properties and promote bone growth in rats along with osteoconductive properties.