Comment on “Local Methylthiolate Adsorption Geometry on Au(111) from Photoemission Core-Level Shifts”

A Comment on the Letter by A. Chaudhuri et al., Phys. Rev. Lett. 102, 126101 (2009). The authors of the Letter offer a Reply.

Figure 1

Left: XPS spectra (markers) of Au $4f_{7/2}$ taken at $h\nu =135\mathrm{eV}$ and emission angle of 60° from the clean Au(111) surface (top) and the $(\sqrt{3}\times \sqrt{3})R30°\mathrm{\text{−}}\mathrm{MT}/\mathrm{Au}(111)$ SAM (bottom). Right: Same measurements at normal emission angle. The spectral components (full lines) are labeled according to Ref. 1. The bulk $B$ component has a binding energy of 84.02 eV ($\mathrm{FWHM}=0.40\mathrm{eV}$). The clean surface $S_C$ component is shifted by $-0.32\mathrm{eV}$ ($\mathrm{FWHM}=0.45\mathrm{eV}$). The thiolate $T$ component is shifted by $+0.38\mathrm{eV}$ ($\mathrm{FWHM}=0.47\mathrm{eV}$), while $S_T$ is shifted by $-0.24\mathrm{eV}$ ($\mathrm{FWHM}=0.43\mathrm{eV}$). The overall uncertainty is $\pm 15\mathrm{meV}$. The relevant intensity ratios are also shown. Constraining the $T$ and $S_T$ peaks to have the same width of $S_C$ yielded scant fits (yet, with a $S_T:T\sim 2.3$ ratio for both geometries).