Structural phase transition at a finite thickness of cerium overlayers on Si(111)

Hangil Lee, Dohyun Lee, Sehun Kim, Chanyong Hwang
2008 New Journal of Physics  
We found that Ce on the Si(111) system exhibited nonmetallic behavior at a critical coverage of 4.0 ML. We observed a large binding energy shift of 2.5 eV in x-ray photoelectron spectroscopy (XPS), and a band gap of 0.6 eV in scanning tunneling spectroscopy (STS), whereas normal metallic behavior was observed at other coverages. Moreover, a strong downward surface relaxation was observed at this critical coverage with increased surface roughness. We expect that this phase transition at a
more » ... nsition at a critical coverage is due to the breakdown of bulk modulus as a result of the release of tensile stress along the in-plane direction. The interactions between metal and Si substrate have been intensively studied to clarify the mechanism of interface formation and other properties of the Schottky barrier, including its height [1, 2] . Metal overlayers on semiconductor surfaces often exhibit critical coverage behavior such as a strong chemical reaction and intermixing, whereas only weak chemical interactions occur below this critical coverage [3, 4] . Cerium (Ce) is a light rare earth metal with extraordinary characteristics. Even at zero pressure, Ce exhibits four different crystal structures (α, β, γ and δ) depending on the temperature [5] . In a series of papers on Ce nanostructures on an Si substrate, we have shown various properties related to the low-dimensional characteristics 4
doi:10.1088/1367-2630/10/4/043008 fatcat:e5kohisz7ngl3eubcuszxwri4u