Browsing by Subject "SiO2/Si"

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    Investigation of electrical properties of surface structures by X-Ray photoelectron spectroscopic technique under external voltage stimuli
    (2005) Demirok, U. Korcan
    Electrical properties of surface structures are analyzed using XPS (X-Ray Photoelectron Spectroscopy) by means of external stimuli together with a novel technique allowing the user to record 200 conventional spectra in a period of one second with a time resolution of 5ms. Charging processes of surface structures such as SiO2 and C12-thiol-capped gold nanoclusters are monitored by time resolved XPS technique which gives an approximate charging constant of the system (RC), and electrical parameters like resistance and capacitance are estimated using external biasing and other relevant time resolved XPS data. Moreover, development and optimization of the technique are carried out by certain parameters and observing the changes in the time constants and binding energy shifts. It is also shown that application of positive and negative external bias can be used to identify two different forms of gold that exist together in the same sample, as nanoparticles and bulk metal, by means of stimulating the charging-induced-separation of the Au 4f peaks which would otherwise appear as overlapped photoemission signals in the grounded spectrum.
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    ItemOpen Access
    X-ray photoelectron spectroscopic investigation of gold particles deposited on (formula) system
    (2003) Karadaş, Ferdi
    Gold particles on SiO2/Si system were investigated by X-ray Photoelectron Spectroscopy (XPS) technique. A suitable reference point was first established in order to investigate the physical/chemical factors affecting chemical shift of gold particles. Gold particles were: i) deposited directly from aqueous solution, ii) capped with citrate agent and then deposited, iii) reduced chemically by NaBH4 and deposited on SiO2/Si system. In addition, gold particles were deposited onto different substrates (quartz, glass). Similar chemical shift of Si4+ 2p and Au 0 4f peak upon the application of external bias gave a strong evidence to the assumption that SiO2 could be chosen as reference. In addition, the derived Auger Parameters have shown that chemical shifts observed during the application of external bias are solely due to charging. It was shown that reduction and nucleation processes occur at the same time during X-ray exposure when gold particles are deposited from aqueous solution. Differential charging of gold particles was investigated by measuring the changes in: i) binding energy, ii) FWHM and iii) intensity values of Au 0 and Si4+ peaks. Our findings obtained from Angle Resolved XPS method supported the assumption that gold particles deposited from aqueous solution prefer to grow three-dimensionally. Assuming the Si 2p binding energy of Si4+ peak as a reference, the binding energy of gold particles is: i) 84.30 ± 0.05 eV when gold is deposited from aqueous solution, ii) pdfMachine trial version V 84.00 ± 0.05 when citrate capped gold particles are used, iii) 84.10 ± 0.05 when gold is chemically reduced by NaBH4. Vis-absorption and electrophoresis methods have shown that capped gold particles have negative charges and they aggregate reversibly (i.e. without coagulation) when they are deposited on SiO2/Si system from their aqueous solution (and transferred back).