Browsing by Subject "X rays"

Now showing 1 - 3 of 3

Open Access
Preparation of Au and Au-Pt nanoparticles within PMMA matrix using UV and X-ray irradiation
(2009) Ozkaraoglu, E.; Tunc, I.; Süzer, Şefik
Au and Au-Pt alloy nanoparticles are prepared and patterned at room temperature within the PMMA polymer matrix by the action of 254 nm UV light or X-rays. The polymer matrix enables us to entangle the kinetics of the photochemical reduction from the nucleation and growth processes, when monitored by UV-vis spectroscopy. Accordingly, increase of the temperature to 50 °C of the reaction medium increases the nucleation and growth rates of the nanoparticle formation by more than one order of magnitude, due to enhanced diffusion and nucleation at the higher temperature, but has no effect on the photochemical reduction process. Presence of Pt ions also increases the same rate, but by a factor two only. Similar photochemical reduction and particle growth take also place within the PMMA matrix, when these metal ions are subjected to prolonged exposure to X-rays, as evidenced by XPS analysis. Both angle-resolved and charge-contrast measurements using XPS reveal that the resultant Au and Pt species are in close proximity to each other, indicating the Au-Pt alloy formation to be the most likely case.
Open Access
X-ray induced reduction of Au and Pt ions on silicon substrates
(2007) Ozkaraoglu, E.; Tunc, I.; Süzer, Şefik
Prolonged exposure to X-rays of HAuCl4, PtCl4 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. © 2007 Elsevier B.V. All rights reserved.
Open Access
X-ray photoemission for probing charging/discharging dynamics
(American Chemical Society, 2006) Süzer, Şefik; Dâna, A.
A novel technique is introduced for probing charging/discharging dynamics of dielectric materials in which X-ray photoemission data is recorded while the sample rod is subjected to ± 10.0 V square-wave pulses with varying frequencies in the range of 10-3 to 103 Hz. For a clean silicon sample, the Si2p(Si0) peak appears at correspondingly -10.0 eV and +10.0 eV binding energy positions (20.0 eV difference) with no frequency dependence. However, the corresponding peak of the oxide (Si4+) appears with less than 20.0 eV difference and exhibits a strong frequency dependence due to charging of the oxide layer, which is faithfully reproduced by a theoretical model. In the simplest application of this technique, we show that the two O1s components can be assigned to SiOx and TiO y moeties by correlating their dynamical shifts to those of the Si2p and Ti2p peaks in a composite sample. Our pulsing technique turns the powerful X-ray photoemission into an even more powerful impedance spectrometer with an added advantage of chemical resolution and specificity. © 2006 American Chemical Society.