Browsing by Subject "Vacuum"

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    Time-resolved XPS analysis of the SiO2/Si system in the millisecond range
    (2004) Demirok, U. K.; Ertas, G.; Süzer, Şefik
    By applying voltage pulses to the sample rod while recording the spectrum, we show, for the first time, that it is possible to obtain a time-resolved XPS spectrum in the millisecond range. The Si 2p spectrum of a silicon sample containing a ca. 400-nm oxide layer displays a time-dependent charging shift of ca. 1.7 eV with respect to the Au 4f peaks of a gold metal strip in contact with the sample. When gold is deposited as C12-thiol-capped nanoclusters onto the same sample, this time the Au 4f peaks also display time-dependent charging behavior that is slightly different from that of the Si 2p peak. This charging/discharging is related to emptying/filling of the hole traps in the oxide layer by the stray electrons within the vacuum system guided by the external voltage pulses applied to the sample rod, which can be used to extract important parameter(s) related to the dielectric properties of surface structures.
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    XPS characterization of Au (core)/SiO2 (shell) nanoparticles
    (American Chemical Society, 2005) Tunc, I.; Süzer, Şefik; Correa-Duarte, M. A.; Liz-Marzán, L. M.
    Core-shell nanoparticles with ca. 15-nm gold core and 6-nm silica shell were prepared and characterized by XPS. The Au/Si atomic ratio determined by XPS is independent of the electron takeoff angle because of the concentric spherical shape of the nanoparticles. The formula given by Wertheim and DiCenzo (Phys. Rev. B 1988, 37, 844) for spherical nanoparticles and the modified one by Yang et al. (J. Appl. Phys. 2005, 97, 024303) for core-shell nanoparticles are used to correlate the XPS-derived composition with the geometry of the nanoparticles only after significantly modifying either the bulk density of the silica shell or the attenuation length of the photoelectrons. © 2005 American Chemical Society.