Representative wide scan SXPS spectra obtained from substrate D at selected stages of Fe growth: (a) prior to deposition (clean substrate), (b) , (c) , and (d) .
Curve-fitted SXPS spectra of the As (left) and Ga (right) EDCs after thermal desorption of the capping layer.
The evolution of the As core level with increasing Fe coverage for the (001) system. After of Fe growth, the surface components observed for the “bare” substrate are still visible. For greater coverages , the onset of substrate disruption leads to the arrival of metallic “reacted” components As(I) and As(II). Once a coverage of is reached, only the component originating from surface-segregated As [As(I)] is observed.
The evolution of the Ga core level with increasing Fe coverage for the (001) system. By analogy with Fig. 3, no signs of significant chemical reactivity after of Fe have been deposited. For coverages between 3.5 and , these components have been replaced by three lines related to metallic “reacted” Ga though their number is reduced to 2 when the coverage is increased to . Once a coverage of is reached, only a single, outdiffused component [Ga(I)] remains; though this line, too, vanishes when the coverage is further increased.
Plot of integrated intensity vs Fe thickness for the deconvoluted As components. For clarity, eye-guiding curves have been added to the plot such that the general trends are highlighted. Whereas the bulk substrate component is reduced with the expected exponential decay, component As(II) undergoes a peak in intensity after only of Fe have been deposited, before vanishing in tandem with the bulk substrate line. Having peaked between 7.5 and of Fe coverage, the As(I) line is still detectable at the highest coverage studied .
Plot of integrated intensity vs Fe thickness for the deconvoluted Ga components. For clarity, eye-guiding curves have been added to the plot such that the general trends are highlighted. Note also the change of scale on the ordinate axes as compared with that of Fig. 5. In the likeness of the As case, the bulk substrate components decay with the expected exponential behavior. Whereas component Ga(I) shows clear signs of outdiffusion, components Ga(II) and Ga(III) are confined to the interfacial region.
The variation of the total integrated intensities with Fe thickness for the As and Ga core levels. Also included in the plot is the predicted intensity “drop-off” if the absence of outdiffusion, layer-by-layer Fe growth, and an attenuation length of are assumed. While the Ga signal closely follows the theoretical decay up to coverages in excess of , the As signal rapidly veers away from this “unreactive interface” picture after only a few angstroms of Fe deposition.
The effect of increasing levels of exposure on the As EDC obtained from a sample of the form Fe (001). The initial dose of results in the arrival of an oxidized As component. After a dose of , the relative intensities of the two peaks are inverted and, by (the greatest exposure used), the oxide-derived peak dominates the EDC.
Schematic of the chemical structure of the (001) system after of Fe growth, the structure of which is based in the intensity variations of the deconvoluted Ga and As components. An outdiffused FeGa-like phase sits between an intermixed interfacial region and “bulklike” Fe, above which rides a thin layer of segregated As in an FeAs-like environment.
Binding energy shift (BE shift), full width at half maximum (FWHM), and As to Ga ratio (As:Ga ratio) parameters concerning the four substrates used for the core level evolution study.
Full width at half maximum (FWHM) and relative BE shift parameters for the reacted As and Ga components (present for coverages of and above). The superscripted letters in parentheses (left most column of the table) indicate which substrate was used (A, B, C, or D) for each Fe coverage (see Table I for details of the parameters associated with each substrate).
Article metrics loading...
Full text loading...