The surface core-level shifts (SCLSs) of the Ga 3d state for SIS3 purchase the S1′, S2′, and S3′ components relative to the bulk at 19.58 eV are −0.302, +0.251, and +0.613 eV, respectively. The Gaussian widths of the bulk and surface are 0.33 and 0.45 eV, respectively. For the As 3d state, the S1, S2, and S3 components relative to the bulk located at 40.43 eV (the 3d 5/2 state) were found to be +0.159, −0.249, and −0.599 eV, respectively. A ‘+’ or ‘−‘

sign indicates a shift towards a higher or lower binding energy, respectively. The Gaussian width is about 0.31 eV. The lifetime is 0.22 eV. In Figure 2b,d, the change in intensity of the components at 60° emission angle is displayed, clearly identifying the surface components. The smallest As component, S3, is most likely associated with the As in the tilted As-Ga dimers in the defaulted terrace. The shifted magnitude of component S3 is the greatest among those reported in the literature, suggesting that the tilted

angle of the dimer is great so as to cause a large charge transfer. Figure 2 Analysis of the core-level spectra for the clean Ga-rich GaAs(001)-4 × 6 surface. (a) As 3d state, θ e = 0°, (b) As 3d state, θ e = 60°, (c) Ga 3d state, θ e = 0°, and (d) Ga 3d state, θ e = 60°. check details Figure 3 displays a fit to the TMA-exposed surface prior to exposure to H2O. As shown in Figure 3a, two Al 2p states are well resolved with an energy separation of 0.650 eV. The one with lower binding energy is associated

with a charge transfer from As to Al. This is possible when a methyl ligand is replaced by a direct bond to an As atom. Considering that the GaAs(001)-4 × 6 surface is ‘As-terminated’ and component S3 shows a negative SCLS, we assumed that dimethylaluminum (DMA) bonds with the dangling bond of the As in the As-Ga dimer. Figure 3 Analysis of the core-level spectra influenced by 1 cycle of TMA-only exposure. (a) Al 2p, (b) As 3d, and (c) Ga 3d states. Because the high-binding-energy Al 2p state remains in the same position and with similar line width after the subsequent water purge, the TMA precursor must have maintained the Al in the molecular charge state while residing on the surface. That indicates that this TMA does not form a bond tuclazepam with a surface atom. That is in agreement with the absence of a new surface As level and leads to the conclusion that the TMA is physisorbed on the S1 As atoms. For the As 3d core-level spectrum, the TMA-exposed surface reveals only minor changes from the clean surface. First, the widths of both top-surface S1 and S3 components are 15% to 20% broader than the subsurface S2 component. Second, the SCLS of the S1 component becomes 0.056 eV without changing the strength. Third, the intensity of the S3 component slightly decreases concurrently with a slight increase of the S2 intensity. Because the Al in DMA bonds with S3 As atom, this As underneath the Al behaves as a subsurface atom.