Effect of the Microstructure of Copper Films on the Damping of Oscillating Quartz Resonators*

An electrochemical procedure is described which allows the preparation of copper films of various crystallinity. Impedance spectra recorded for copper loaded quartz resonators were analysed in terms oft he lumped-element circuit of the Butterworth-Van Dyke type to obtain their electrical and mechanical properties. Plots of the damping resistance versus film thickness indicate that the film's dissipation factor is significantly smaller in the case of disordered films with a finer crystallinity (10—100nm) than in the case of more ordered structures having a grain size between 600—1500nm. This observations states, that the finely structured copper phase behaves more rigid than the coarse material. The suggested explanation relates this effect to energy losses which occur during oscillation at the phase boundary of the grains by wearless internal friction. No contributions to the damping from surface roughness were observed for films thicker 0.5pm. Thus, the damping of the quartz oscillator caused by different degrees of surface roughness of the generated copper films was of secondary importance, compared with the effect of the crystallinity

XPS observation of OH groups incorporated in an Ag(111) electrode

An Ag(111) single crystal electrode emersed from NaF+NaOH electrolyte (pH 11) under anodic polarisation has been studied ex situ by means of X-ray photoelectron spectroscopy (XPS). “Underpotential” oxidation has been found at +0.2 and 0.0 V vs. Hg/HgO, that is by 0.2–0.4 V more negative than the reversible potential of the Ag2O phase formation. The generation of a number of surface and bulk oxygen-containing species, including surface Ag2O-like species, surface and bulk OH groups (OHads and OHbulk, respectively), surface and bulk atomic oxygen, has been observed on the emersed electrode. The present work provides the first direct evidence of the hydroxide incorporation in the bulk of an Ag(111) electrode in the course of underpotential oxidation. OHbulk is characterised by a O 1s peak at approximately 532.8 eV, while surface OHads manifests itself as the peak at ca. 531.6 eV. The origin of the positive binding energy shift is discussed. Surface and bulk OH groups demonstrate substantially different thermal stability. Surface species desorb below 470 K, while dissolved OH groups exhibit high stability towards prolonged annealing in vacuum at temperatures up to 750 K; they remain in the near-surface region even after sputtering by Ar+ and He+ ions. The oxide-like species is characterised by the O 1s peak at 529.5 eV and decomposes after heating in vacuum at a temperature of about 470 K. The He(I) and He(II) UP spectra of the emersed electrode along with the XPS data provide evidence that the coverage with surface oxide is less than 1 ML. A tentative scheme of Ag(111) underpotential oxidation is discussed

Ex situ scanning tunneling microscopy study of under-potential oxidation of a Ag(111) electrode in an alkaline electrolyte

A Ag(111) single crystal electrode emersed from NaF+NaOH electrolyte (pH 11) under potential control in the interval between -0.8 V and +0.2 V vs. Hg | HgO was studied by scanning tunneling microscopy (STM) in an inert atmosphere. The STM images show that the oxidation of the Ag(111) surface starts above the point of zero charge and exhibits a nucleation-growth mechanism. It starts at the steps and extends to the terraces as the electrode potential is scanned positive. Potential reversal restores the initial surface morphology. The reaction-induced features imaged in STM as dark spots are assigned as islands of chemisorbed oxygen-containing species. The irregular shape of the islands points to the diffusion of ad-species as the limiting step of the process

On the mechanism of Ag(111) sub-monolayer oxidation: a combined electrochemical, in situ SERS and ex situ XPS study

In the present work in situ surface enhanced Raman spectroscopy (SERS), ex situ X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) are used to study the interface between a Ag(111) electrode and an alkaline electrolyte. Formation of a number of potential-dependent adsorbates is observed above the point of zero charge (Epzc) of the Ag electrode. These are: OH groups (OHadsγ−) and oxide-like species (Oadsδ−). Electrochemisorbed hydroxide species show by the appearance of Raman bands at 540–560 cm−1 and at 803–819 cm−1, attributed to Ag–OH stretching and AgO–H bending vibrations respectively. Strong isotope shift of the Raman bands towards lower frequencies is observed in D2O solutions, proving their assignment. The Oadsδ− and OHadsγ− species are characterised by the O 1s peaks at ca. 529.5 and 531.6, respectively. Formation of the above-mentioned species is verified also by the UP spectra of the emersed electrodes, showing the bands at 3.0 eV typical for the oxide-like adsorbates and 9.0 and 11.1 eV for hydroxo-groups. The OHadsγ− and Oadsδ− species are negatively charged, as evidenced by the adsorption of Na+ on the Ag electrode positive to the Epzc. A mechanism of the Ag(111) sub-monolayer oxidation is suggested on the basis of combined evidence from cyclic voltammetry, in situ SERS, ex situ XPS and UPS