Surface Modification of Silver Thin Films Using Low Power Chlorine Plasmas

Abstract

Modification of silver thin films to create Ag/AgCl thin film electrodes, using a plasma process, was investigated and the efficiency of the plasma technique was assessed. X-ray photoelectron spectroscopy measurements revealed the presence of AgCl within the thin film after plasma treatment. The observed binding energy peak shifts corroborated with values found in literature. Auger spectroscopy depth analysis showed that, under low input power conditions, the plasma process is controlled by the chlorine flow and the chamber pressure. The quantity of Cl integrated into the silver matrix increased with increasing chamber pressure.Silver chloride is an important material as an electrochemical electrode sensor, typically fabricated by screen printing of silver loaded inks followed by chemical chloriding 1 or electrochemical chloriding. 2 In order to develop microsensor arrays based on Ag/ AgCl, a thin film approach is required, but electrochemical chloriding of such films can lead to their destruction. There have been very limited attempts to create Ag/AgCl electrodes via thin film compatible techniques and no satisfactory outcome has been established so far. Indeed, chemical chloriding of thin films, which offers very restricted process control, was shown to be surface limited, while deposition under vacuum of AgCl barely achieved satisfactory electrode characteristics. 3 Chlorine-based plasmas 4 have found widespread use in thin film and semiconductor materials etching. 5 More recently there have been attempts to understand and control the plasma chemistry making sensitive modification of surfaces a possibility. 6,7 In this paper, we investigate the use of chlorine plasma processing as an alternative to chemical/electrochemical techniques for partial surface conversion of Ag to AgCl. Plasma exposed Ag was examined by X-ray photoelectron spectroscopy ͑XPS͒ and Auger analysis to evaluate species formation at and below the surface. ExperimentalSilver thin films underwent plasma immersion in a PlasmaTech reactive ion etch ͑RIE͒ 80 capacitively coupled radio frequency ͑rf͒ plasma system, with a 17 cm diam driven electrode. Plasma conditions were 10 to 60 W nominal input power, for 5 to 240 s, at chlorine gas flow 3 to 30 cm 3 /s. The samples were placed on the driven electrode and the dc bias was 10 V. XPS investigations were carried out on a Kratos XSAM 800 apparatus. The X-ray source was run with Mg K␣ X-rays at 240 W ͑13.8 kV, 18 mA͒. Auger analysis was performed with a Nanosonde Auger Cameca ͑Nano-scan 100͒ which includes an argon ion canon for etching and depth analysis purposes.The samples were etched for various times, and the depth in each case was calculated using an estimated etch rate of 0.7 nm/s, determined from a complete etch on a sacrificial sample of known thickness.Step heights of Ag and modified Ag thin films were measured using a mechanical step profiler ͑Talystep͒. The typical sample thickness was around 100 nm, before being processed. Results and DiscussionSamples were first exposed to a chlorine ga...

Micro‐chemical surface investigation of brittle carthaginian and roman silver artefacts

“…The XPS spectrum revealed also the presence of C as organic contaminant coming from the soil as for chloride ions [4,8,13] . The overall results allow to establish that the chloride compound has a chemical structure similar to AgCl [12][13][14] . The second case study is a brittle Carthaginian bracelet whose micro-chemical composition and whose micro-structure was investigated by means of the combined use of the above-mentioned analytical techniques.…”

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Plasma Chloriding of Thin-Film Silver

“…3. 11 Matsunaga et al 17 have shown that several types of nonstoichiometric structure, Ag x Cl y , can exist due to the possible presence of interstitial Ag as well as cation vacancies, 18 leading to structural flexibility and higher conductivity. This decrease in the impedance locus may also be a consequence of a larger active surface area, as it affects the pseudocapacitance component.…”