Giant Metal Compression at Liquid-Solid (Pb-Si, In-Si) Schottky Junctions

Using a high-energy x-ray transmission-reflection scheme we have studied the density profile of solid-liquid Schottky contacts close to the interface. We found a massive disturbance of the electronic system on the liquid metal side at different interfaces with pronounced density anomalies on a new length scale. The liquid metal at the interface forms a strongly compressed layer followed by a density depleted layer. The experimental evidence points to a charge transfer phenomenon in the metallic system. Control experiments performed at a metal-insulator interface confirm this picture.

Figure 1

Band structure of a Schottky junction across the interface with ${ϵ}_F$ as the Fermi energy of the metal. Band bending occurs on the semiconductor side ($n$ doped) of the interface. The center part shows a sketch of the x-ray reflectivity experiments for the determination of the density profile across the interface (blue circle). Selected detector scans of the reflected x-ray beam at various perpendicular momentum transfer values $q_z$ are shown on the right side for a Pb-Si(100) interface. The measured width is $160\mu \mathrm{rad}$.

Figure 2

(a) Reflectivity from the Pb-Si(100) (black), In-Si(100) (red), Pb-Si(111) (blue), and $\mathrm{In}\mathrm{\text{−}}{\mathrm{Al}}_2{\mathrm{O}}_3$ (green) interface (the curves are offset for clarity). Solid lines denote best fits to the data using the generic two-layer model, while dashed lines indicate the corresponding Fresnel reflectivities of an ideally sharp interface. (b) Electron density profiles for each interface deduced from the final fit of the reflectivity profile.

Figure 3

(a) Sketch of the density profile of the interface using the interpolated values of the ionic radii. (b) Ionic radius of Pb in different oxidation states. The straight line is a fit to the data taken from Ref. 13.

Figure 4

Measured and calculated (black line) in-plane structure factor $S(q_{\parallel })$ constructed from compressed (red line) and stretched (blue line) pair distribution functions $g(r_{\parallel })$ in the two layers.