Deposition and stability of metal ions on oxidised silicon surfaces: electrochemical correlation

Abstract

XPS is used to determine the chemical state of Au, Hg, Tl, Pb and Bi deposited from their corresponding aqueous solutions on oxidized silicon or gold surfaces. It is determined that Au and Hg, having positive electrochemical reduction potentials, deposit in their 0-valent state, but Tl, Pb and Bi, having small positive or negative electrochemical reduction potentials, deposit in their corresponding ionic states, confirming our previous hypothesis about the electrochemical correlation. Electrochemical deposition of Au from aqueous solutions on to silicon electrodes yields 0-valent Au on both (1) and (2) polarised electrodes, with the only difference that more gold is deposited on the negatively biased one.

X-ray induced reduction of Au and Pt ions on silicon substrates

“…1, we display a set of spectra, recorded consecutively while the sample is exposed to X-rays. At the beginning the Au4f peak has a complex shape but can be decomposed into 2 different spin-orbit doublets corresponding to 2 different chemical gold species which can be assigned to Au 3+ and Au 0 on the basis of their 4f binding energies [35,36]. As time progresses the intensity of the Au 0 doublet increases at the expense of the other doublet, indicating clearly that reduction by X-rays is taking place.…”

“…The extent of reduction varies drastically from one metal ion to another and extensive efforts had been devoted to correlate this with certain chemical/ physical properties of them [24][25][26][27][28][29][30][31][32][33][34]. In one of our earlier work, we had claimed that the extent of X-ray induced reduction could be related with the electrochemical reduction potential of the metal ion [35,36]. Accordingly, gold, having a very high reduction potential of [ϵ 0 red (Au 3+ ) = 1.5 V] is one of the most amenable.…”

X-ray-Induced Production of Gold Nanoparticles on a SiO2/Si System and in a Poly(methyl methacrylate) Matrix

“…Reduction of metal ions while recording XPS (X-ray photoelectron spectroscopy) data was reported in the early days of the development of the technique and is considered as a nuisance. − However, a recent study reports on the utilization of X-rays and electron beams for inducing in situ oligomerization reactions. , In addition to X-rays, electron, ion, and other energetic particle exposures, which are frequently encountered for cleaning and/or depth profiling, also cause reduction of certain metal ions to their lower oxidation states and/or preferential removal of oxygen. − The extent of reduction varies drastically from one metal ion to another, and extensive efforts have been devoted to correlate this with certain chemical/physical properties of the metal ions. − In our earlier work, we had claimed that the extent of X-ray-induced reduction could be related to the electrochemical reduction potential of the metal ion. , Accordingly, gold, having a very high reduction potential of [ (Au 3+ ) = 1.5 V] is one of the most amenable to such changes. Although the process has long been reported, detailed information related to the mechanism such as the nature of the oxidation products and/or the fate of the reduced products (especially whether cluster formation or nucleation also takes place) is not available.…”

“…[23][24][25][26][27][28][29][30][31][32][33][34][35] In our earlier work, we had claimed that the extent of X-ray-induced reduction could be related to the electrochemical reduction potential of the metal ion. 36,37 Accordingly, gold, having a very high reduction potential of [ red 0 (Au 3+ ) ) 1.5 V] is one of the most amenable to such changes. Although the process has long been reported, detailed information related to the mechanism such as the nature of the oxidation products and/or the fate of the reduced products (especially whether cluster formation or nucleation also takes place) is not available.…”

Preparation of Au and Au–Pt nanoparticles within PMMA matrix using UV and X-ray irradiation

“…must be adequately sorted out. However, as we have tried to bring out in this work, there seems to be certain characteristics of these ions (and subsequently the nanoparticles formed), like catalytical effect of Pt ions, electrochemical reduction potentials, etc., which are apparently independent of the medium used [11,12,42].…”