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X-ray photoelectron spectroscopic study of the formation of catalytic gold nanoparticles on ultraviolet-ozone oxidized substrates
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Image of FIG. 1.
FIG. 1.

XPS spectra of different peaks of gallium obtained from the GaAs standard sample shows the peak of Ga (from GaAs) located at 1117.02 eV. Peaks at 107.90 and 104.37 eV correspond to and , respectively. Peaks at 19.37 and 18.92 eV represent and , respectively.

Image of FIG. 2.
FIG. 2.

XPS spectra from the GaAs standard show the peak of As (from GaAs) located at 1322.63 eV. Peaks at 41.60 and 40.89 eV correspond to the and peaks of As (from GaAs), respectively.

Image of FIG. 3.
FIG. 3.

and peaks obtained from the elemental As standard. The binding energy associated with is 1323.29 eV. The doublet is positioned at 42.25 and 41.55 eV.

Image of FIG. 4.
FIG. 4.

XPS spectra from the standard. The peak of Ga (from ) is located at 1117.75 eV. The doublets of Ga (from ) are at 105.61 and 109.01 eV. The peaks are at 20.07 and 20.52 eV. Small amounts of an unidentified impurity (possibly metallic gallium) give rise in the fitting process to a doublet marked “*”.

Image of FIG. 5.
FIG. 5.

Formation of an intermediate species during the UV-ozone oxidation process in which Ga bonds with O by breaking one of its four bonds with As in GaAs, while retaining the remaining bonds. This process continues until eventually complete oxides are formed.

Image of FIG. 6.
FIG. 6.

XPS spectra (Ga peaks) of UV-ozone oxidized GaAs, showing the presence of , , and in the oxide layer. The contributions from different species as a percentage of total gallium are shown.

Image of FIG. 7.
FIG. 7.

Arsenic high-resolution XPS spectra from UV-ozone oxidized GaAs showing the contribution from different As components in the oxide layer. Relative contribution from different species as a percentage of total As is also shown.

Image of FIG. 8.
FIG. 8.

Effect of annealing on UV-ozone oxidized GaAs. Annealing at for 300 s results in complete desorption of and , eventually making the oxide layer rich in .

Image of FIG. 9.
FIG. 9.

Cross-sectional view in TEM of UV-ozone oxidized GaAs after deposition of a nominally 4 nm thick gold film (a) before annealing and (b) after annealing. Dewetting of the gold on the oxide film during annealing leads to the formation of Au nanoparticles. The scale bar corresponds to 20 nm.

Image of FIG. 10.
FIG. 10.

Au peaks obtained from samples (a) before and (b) after the formation of Au nanoparticles on UV-ozone oxides having a thickness of 3.5 nm. Samples with oxide thicknesses of (c) 2.5 nm and (d) 4.5 nm are also examined after annealing. As indicated by the dotted line, there is no significant chemical shift in the Au peak, indicating Au does not make an alloy with Ga.


Generic image for table
Table I.

Binding energies of different peaks of elemental gallium, GaAs, , and elemental arsenic as obtained experimentally in this study. Data from the NIST database (http://srdata.nist.gov/xps) is shown for comparison. In keeping with convention, only one of the peaks in the Ga , Ga , and As duplets is reported.

Generic image for table
Table II.

Literature values for the binding energy of Au for different compositions of AuGa (from the NIST database http://srdata.nist.gov/xps).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: X-ray photoelectron spectroscopic study of the formation of catalytic gold nanoparticles on ultraviolet-ozone oxidized GaAs(100) substrates