129 I and 119 Sn Mössbauer spectroscopy , reversibility window and nanoscale phase separation in binary Ge x Se 1 x glasses
The molecular structure of the prototypical chalcogenide glass system—GexSe1 x in the 0oxo3 range, has received much scrutiny over the years. These glasses have been probed by modulated DSC, Raman scattering, Sn absorption and I emission Mössbauer spectroscopy, and neutron scattering. The I measurements utilize Te parent as a dopant in glasses, and reveal a bimodal (A, B) distribution of sites, with the site intensity ratio, IB/IA (x), tracking changes in glass structure as a function of x. At low x (o0.15) Senchains are stochastically cross-linked by Ge additive, and IB/IA (x) sharply declines with x. But at x40:15, rigid regions nucleate at the expense of floppy ones, and the ratio IB/IA (x) reverses slope to display a global maximum in the 0:20oxo0:25 range. The latter coincides with the reversibility window usually taken as signature of self-organization of these networks. At x40:26, these glasses enter a stressed-rigid elastic phase and in the 0:31oxo1 3 range nanoscale phase separate into Se-rich and Ge-rich regions. The signature of the latter is saturation of IB/IA (x) at a high value of 1.5 at x 1⁄4 13. Sn Mossbauer spectroscopy measurements independently support the picture of broken chemical order of the stoichiometric glass inferred from the I Mössbauer experiments. These observations using local probes are well correlated to Raman scattering, modulated differential scanning calorimetric and diffraction measurements. r 2006 Elsevier B.V. All rights reserved. PACS: 61.40.Fs; 63.50.+x; 78.30.Ly; 76.80.+y
Mössbauer Spectroscopy—A Rewarding Probe of Morphological Structure of Semiconducting Glasses
It has been fashionable to discuss the structure of stoichiometric melt-quenched network glasses in terms of chemically-ordered continuous random networks (CRN) since Zachariasen’s pioneering work on the subject nearly 50 years ago [1]. Glasses of the type AB2, such as SiO2and GeSe2in analogy to a-Ge, for example, have been described as random networks of geometrically well-defined A(B1/2)4 tetrahedral units.
Electrochemical detection of copper(II) at a gold electrode modified with a self-assembled monolayer of penicillamine
A penicillamine (PCA) self-assembled monolayer (SAM) was prepared on a gold electrode. It has been found that the modified electrode exhibited a selective response to copper ions. As demonstrated by cyclic voltammetric experiments, the SAM-based electrode showed an attractive ability to preconcentrate efficiently traces of copper(II) from solutions. Under optimum conditions, the anodic peak current was proportional to the concentration of Cu(II) in the range from 8.0 × 10−7 to 1.0 × 10−4 M with a detection limit of 4.0 × 10−7 M. Moreover, this modified gold electrode is also characterized by excellent repeatability, showing a relative standard deviation of 3.2% for nine successive measurements of 1.0 × 10−5 M Cu(II). The PCA/Au SAM gold electrode was used for the determination of Cu(II) in a tap water sample and the results showed a good agreement with the data obtained by atomic emission spectrometry.