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

Abstract

Prolonged exposure to X-rays of HAuCl 4 , PtCl 4 and their mixtures, deposited from an aqueous solution onto a silicon substrate, causes chemical reduction of the metal ions to their metallic states. The corresponding oxidation reaction is the conversion of chloride ions to chlorine. The resultant metal atoms aggregate to form metallic/bimetallic nanoclusters as evidenced from their XPS chemical shifts. Hence, X-rays are usable for in-situ nanoparticle production or for direct-writing applications on silicon substrates.

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

“…3, similar changes corresponding to reduction of the Pt 4þ ions and nucleation and growth are observable in the Pt4f peaks. However, contrary to the case of Au, and in accord with our previous findings [27], complete reduction can not be achieved neither for the case of Ptonly nor Au-Pt mixtures, as also emphasized and shown in the last spectrum of Fig. 3, which corresponds to more than 24 h of X-ray exposure.…”

“…As the exposure period is prolonged the intensity of the spin-orbit doublet corresponding to the ionic gold diminishes, and at the same time the binding energy of the neutral gold decreases towards the bulk value of the metal at 84.0 eV. The latter shift is related with the nucleation and particle growth as was reported by us and numerous other workers in the field [26,27,[33][34][35]. As can also be gathered from Fig.…”

“…As we had demonstrated in our previous papers, prolonged exposure to X-rays also leads to reduction of certain metal ions like Au 3þ and Pt 4þ to their neutral states, and if the conditions are favorable, these neutral particles aggregate and form nanoparticles as a result of their large cohesive energies, both within the polymer matrix and also on silicon substrates [26,27]. XPS is a suitable technique, since the reduction can be induced by the prolonged X-ray exposure, and the binding energy differences can be simultaneously monitored.…”

“…XPS is a suitable technique, since the reduction can be induced by the prolonged X-ray exposure, and the binding energy differences can be simultaneously monitored. For example, the binding energies of the corresponding Au4f 7/2 peaks are 87.5 eV and 85.5 eV for the Au 3þ ion and neutral, isolated Au 0 atoms, respectively, at the beginning of the exposure, for the case of the polymer sample containing Au salt only (not shown) [26,27], as well as that containing Au and Pt salts together, as depicted in Fig. 3.…”

“…However, in all of these synthesis methods elevated temperature(s) and/or certain photo-sensitizers were needed. On the other hand, we have recently presented a simple room temperature method for the preparation of monometallic Au nanoparticles using deep-UV and X-ray irradiation within poly(methyl methacrylate), PMMA, matrix [26,27]. Utilization of X-rays or energetic particles for the preparation of nanoparticles is particularly important for direct-writing and patterning applications using strong Synchrotron sources [28][29][30][31].…”