Lucia D’Urzo

An electrochemical impedance investigation of the behaviour of anodically oxidised titanium in human plasma and cognate fluids, relevant to dental applications

In dental applications, the contact between the metal implant and the receiving living tissue is made through the oxide layer on the implant surface, which allows the osseointegration process. In dentistry, the passive film formed on titanium seems to be more stable and protective than that formed on the Ti alloys, customarily used in other medical applications. Corrosion of titanium alloys in the mouth can result from the presence of a number of corrosive species, such as the hydrogen ion (H+), sulfide compounds (S2−), dissolved oxygen (O2) and Cl− and can result in the release of Ti4+ ions that, in turn, brings about the reduction of alkaline phosphatase activity of osteoblastic cells. The present study reports a time-dependent electrochemical corrosion study of titanium in contact with the following biologically relevant solutions: (i) SBF (simulating the inorganic part of human plasma), (ii) SBF with added ovalbumin (a protein simulating the post-implant environment) and (iii) human plasma. To the best of the authors’ knowledge, this is the first report on the corrosion of Ti in human plasma. The electrochemical measurements are based on electrochemical impedance spectrometry. Impedance spectra were interpreted on the basis of the equivalent-circuit approach and estimates of the time-variation of oxide film thickness and resistance were computed. Surface Raman spectroscopy was used to characterise the structure of as-anodised and corroded TiO2 films: the effects of phosphate and organic incorporation were highlighted. EIS and surface Raman measurements have demonstrated that the corrosion resistance of the oxide films formed on Ti is strongly affected by the presence of biomolecules in the chloride- and phosphate-based aqueous solution. In particular, ovalbumin increases corrosion performance and human plasma is found to be remarkably more aggressive in comparison to SBF. These results suggest some caution in extrapolating corrosion results obtained in simulated biological fluids to the actual behaviour in vivo.

Electrodeposition of Cu from Acidic Sulfate Solutions in the Presence of Bis-(3-sulfopropyl)-disulfide (SPS) and Chloride Ions

This paper reports an in situ Raman study of Cu electrodeposition from an acidic sulfate solution in the presence of bis-3- sulfopropyl-disulfide Na salt SPS. In the absence of chloride, in situ surface-enhanced Raman spectra scarcely show few labile features in a narrow range of cathodic potential. When Cl The widely investigated processes of Cu electrodeposition for ultralarge scale integration ULSI fabrication rely heavily on the use of complex blends of organics. Notwithstanding the consider- able number of papers published on the subject and the relatively widespread use of such bath chemistries in the industry, the role of the single additives and the reasons underlying the well-document synergistic actions developing among them have not yet been un- ravelled. The organic additives in acid Cu plating baths are commonly categorised as: i carriers, ii brighteners or accelerators, and iii levellers. Carriers and levellers are sometimes denominated suppres- sors, implying the fact that they hinder the deposition rate and con- sequently enhance the electrodeposition overvoltage. Usually, i carriers are polyethylene glycols, ii brighteners are molecules with thiol RSH and disulfide RSSR bonds and sulfonic acid groups, and iii levellers are molecules with amine functionality or aromatic rings. A host of different chemistries has been proposed in the lit- erature, a review of which is beyond the scope of this paper. In a typical bath chemistry, bis-3-sulfopropyl-disulfide Na salt SPS: NAO3SCH23SSCH23SO3Na acts as the accelerator. 1-28 Accelerators are believed to adsorb on the growing Cu surface and to participate in charge transfer; accelerators coad- sorbed with suppressors would thus offer growth sites on the cath- ode surface, otherwise occupied by other additives exhibiting inhib- iting action. 29 Estimates of the total surface coverage with cathode-blocking species have been evaluated on the basis of electrochemical mea- surements in Ref. 9 for baths containing polyethylene glycol PEG, SPS, and Janus Green B JGB; SPS was shown to lower the total cathode coverage. This scavenging action was reported to be positively correlated with the SPS concentration and to be a function of the potential. If SPS is the sole additive, preferential deposition at the peaks of a saw-tooth profile was found, but use of both SPS and JGB brings about higher deposition rates at the valleys. 3 Enhance- ment of the depolarization effect of SPS in recesses has been dem- onstrated in Ref. 18 by systematic use of through-mask cathodes with different aspect ratios. The accelerating effect has been shown to depend on the pres- ence of Cland to be positively correlated with SPS concentration. 18 The use of SPS in the electrodeposition of Cu for ULSI applications

SPE-HPLC Detection of Organic Additives in Acidic Copper Plating Baths I. Sulfopropyl Disulfide-Based Brighteners

A technique has been developed for the study of reaction mechanism and the monitoring of copper electroplating baths utilizing a combination of solid phase extraction (SPE) and high-performance liquid chromatography (HPLC). This method appears suitable for live plating bath control as well as for organic identification, concentration measurement, and reaction mechanism studies. While in the past the total amount of carbon (TOC) present in the deposition bath was used to quantify the decomposition of organics and to determine the plating bath quality, a strong correlation between the TOC measurement and effective plating bath composition was not possible. Moreover, a direct way to thoroughly analyze the organic components of the bath is not commonly available using current electrochemical techniques. However, the results from experiments conducted with the technique described in this paper show how the monitoring of a few diagnostic peaks recovered from a live bath sample can be used directly for this purpose. The identification and quantification of by-products is also proven. Two copper sulfuric plating baths at different acidity were used for this study, and the stability of bis(sodiumsulfopropyl) disulfide and polyethylene glycol additive components, as well as their degradation mechanism and by-products, are studied in this work.

Electrodeposition of Cu from Cyanoalkaline Solutions in the Presence of CPC and PEG An Electrochemical and In Situ SERS Investigation

The behavior of a cyanoalkaline copper plating system was studied with a special focus on the role of two organic additives, cetylpyridinium chloride (CPC) and poly(ethylene glycol) Mw 1500 (PEG). The influence of these additives on the adsorption behavior of the CN - ligands released during the Cu(I) complex reduction process has been investigated. Spectroelectrochemical results obtained by in situ Raman spectroscopy were complemented with cyclic voltammetric measurements. The potential-dependent surface-enhanced Raman spectroscopy spectra showed two prominent features at ca. 2090 and 2040 cm - 1 , within the Raman shift range typical of C≡N stretching v(CN - ). Using a double-Gaussian model, a numerical elaboration of the two v(CN - ) bands was done, estimating the potential-dependent values of the (i) peak position, (ii) peak intensity, and (iii) full-width at half-maximum. Our results show (i) a chemical interaction of CPC with adsorbed CN - , weakening the Cu-CN - adsorption bond, (ii) an interaction of PEG with the Cu surface giving rise to cathode-blocking and alteration of the Cu growth mode.

Solid Phase Extraction–High-Performance Liquid Chromatography Detection of Organic Additives in Acidic Copper Baths II. Polyethylene-Glycol Based Suppressors

A technique has been developed for the study of the reaction mechanism and the monitoring of copper electroplating baths utilizing a combination of solid phase extraction and high-performance liquid chromatography. This method appears suitable for live electroplating bath control as well as for organic identification, concentration measurement, and reaction mechanism studies. The results from the experiments carried out with the technique described in this paper show how the monitoring of a few diagnostic peaks recovered from a live bath sample can be directly used for this purpose. Two copper sulfuric plating baths at different acidity were used for this study. The stability, degradation mechanism, and by-products of bis(sodiumsulfopropyl) disulfide were addressed in Part I, while polyethylene glycol (PEG) behaviors are studied in Part II. The identification of PEG breakdown by-products was achieved in this work.

Study of Surface Compositional Waves in Electrodeposited Au–Cu Alloys by Synchrotron-Based High Lateral-Resolution X-Ray Photoemission Spectroscopy

In this research we observed surface compositional waves developing during galvanostatic electrodeposition of Au-Cu alloys from cyanocomplex solutions. Our study was carried out by synchrotron-based scanning photoemission spectro-microscopy. Scanning electron microscopy and X-ray diffraction analyses complemented the sample characterization. We found that the compositional wavefront developing between two homogeneous regions with different Cu enrichment consists of a progressive localization of Cu, initially at the crystallite boundaries and eventually in the formation of Cu-enriched crystallites.