XPS studies of low-temperature plasma-produced graded oxide-silicate-silica layers on titanium

Abstract

A method has been developed to produce a silica coating bonded to an oxidized titanium substrate, graded in composition and structure through the surface layer, providing the base for deposition of bioactive glasses and hydroxyapatite. A low‐temperature air/water/tetraethoxysilane plasma coating method is reported. Characterization of the graded surface layer using XPS and SEM is compared with previously reported studies of similar layers on nickel substrates. Depth profiling and the modified Auger parameter were used to elucidate the structure of the interphase region between the titanium and silica. A functionally‐graded layer, from the titanium metal through the oxide, orthosilicates, pyrosilicates, chain silicates and layer silicates to bulk silica, was demonstrated. The thickness of the layer was in the range 30–50 nm, depending on the duration of oxidation and tetraethoxysilane deposition. © 1998 John Wiley & Sons, Ltd.

Plasma enhanced chemical vapour deposition of silica onto titanium: Analysis of surface chemistry, morphology and hydroxylation

“…The elemental composition of these surfaces comprised approximately of 60 at.% oxygen, 10 at.% carbon and 30 at.% silicon (Fig. 7B), which is similar to previous reports obtained using this technique [8–10]. The oxygen/silicon ratio of 2.1±0.2 is close to 2.0 expected for silicon dioxide.…”

“…Silica is grown on Ti from Si-O species, formed in the air/TEOS plasma, becoming embedded as silicate species in the plasma grown Ti oxide layer [8]. Interestingly, the water present in the air supply acts as a catalyst in the hydrolysis of TEOS through a possible hydrolysis reaction shown below: $$\text{Si}{false({\text{OC}}_2{\text{H}}_{5}false)}_4+4{\text{H}}_2\text{O}\to \text{Si}{false(\text{OH}false)}_4+4{\text{CH}}_3{\text{CH}}_2\text{OH}$$…”

“…Also, other species such as SiO − ions and SiO radicals formed in the air/TEOS plasma can react and become embedded in the Ti oxide [8–9]. …”

“…The process produces a compositionally and structurally graded metal/oxide/silicate/silica surface layer that strongly adheres to the material substrate. PECVD-Si films have already been used by our research team as a corrosion resistance coating, a scaffold for growing hydroxyapatite (HA) or HA-like layers and as a surface coating for Ti biomedical implants [8–11]. Since it’s development, we have been fine-tuning the parameters of the PECVD process to enable the production of high quality and reproducible PECVD-Si coatings.…”

The effect of silicon doping on the transformation of amorphous calcium phosphate to silicon-substituted α-tricalcium phosphate by heat treatment

“…5 shows the Si 2p XPS spectra of 1.5Si-HA, 4.0Si-HA and 5.0Si-HA before and after sintering, representing low, middle and high Si dopant content, respectively. The peaks at 100.8 and 101.2 eV were assigned to SiO 4 4− in the lattice of Si-HA or Si-α-TCP [34,35]. The peak at 102.1 eV was assigned to surface calcium silicate (sharing two oxygen atoms only) [36], which would remain undetected in the XRD analysis because of its small quantity.…”