Polaron-Driven Surface Reconstructions

Abstract

Geometric and electronic surface reconstructions determine the physical and chemical properties of surfaces and, consequently, their functionality in applications. The reconstruction of a surface minimizes its surface free energy in otherwise thermodynamically unstable situations, typically caused by dangling bonds, lattice stress, or a divergent surface potential, and it is achieved by a cooperative modification of the atomic and electronic structure. Here, we combined first-principles calculations and surface techniques (scanning tunneling microscopy, non-contact atomic force microscopy, scanning tunneling spectroscopy) to report that the repulsion between negatively charged polaronic quasiparticles, formed by the interaction between excess electrons and the lattice phonon field, plays a key role in surface reconstructions. As a paradigmatic example, we explain the (1 × 1) to (1 × 2) transition in rutile TiO 2 ð110Þ.

Interplay between Adsorbates and Polarons: CO on Rutile TiO2(110)

“…Formation of polarons is particularly favorable in transition-metal oxides and is further promoted in the vicinity of the surface, where the crystal lattice is more flexible [27][28][29][30]. Here, we address the interactions between electron polarons and adsorbates.…”

Handbook of Materials Modeling

“…Close to the critical concentration the free energy of the reconstructed surface is lower than the corresponding unreconstructed one, thereby marking the structural phase transition. Remarkably, by neglecting polaron effects [panel (a), delocalized setup], DFT+U calculations find the (1×2) phase unstable, in disagreement with observations [98].…”

“…The ability to control the amount of defects and the concentration of polarons is extremely important, as this can be used to tune the chemical and physical properties of the surface. For instance, under extreme reducing conditions, TiO 2 (110) undergoes a structural reconstruction, from the (1×1) to a (1×2) phase, doubling the periodicity along [110] [98,[107][108][109]. Different models have been proposed to describe the atomic structure of this reconstruction.…”

“…Different models have been proposed to describe the atomic structure of this reconstruction. The debate is still open, but the Ti 2 O 3 model proposed by Onishi appears to be the most probable one [98,110].…”

“…The (1×1) surface undergoes a (1×2) reconstruction, specifically the Ti 2 O 3 model [98,107], which is able to conveniently handle a larger reduction of the system (50%), as discussed in Ref. [98]. This surface reconstruction problem can be described by DFT+U by construction of an appropriate phase stability diagram [see Fig.…”