Inelastic scattering of low-energy electrons from Sn overlayers on cleaved InSb(110) surfaces

Room-temperature deposition of Sn onto a clean, cleaved InSb(110) surface results in homogeneous layers of amorphous or polycrystalline {α}-Sn with tetrahedral sp³-bonding order and semiconducting properties. Layers with a thickness exceeding about 500 A{} grow in the metallic {β}-Sn modification. High-resolution electron-energy-loss spectroscopy (HREELS) is used to study the electronic properties of the Sn overlayers. Coupled interface plasmons of the Sn/vacuum and the Sn/InSb(110) interfaces are found near loss energies of 70 and 50 meV, respectively. In addition, a significant monotonic loss background due to the free electrons in the Sn layer develops, reaches its maximum at a film thickness of about 30 A{}, and decreases again. A consistent theoretical description in terms of dipole scattering (dielectric theory) on a layered electron plasma (Sn layers) on top of an infrared-active semiconductor (InSb) is possible. The analysis allows the determination of transport parameters for the Sn overlayers.