Surface Properties of Diamond (111): 1 × 1, 2 × 1, and 2 × 2 Reconstructions

Localized Graphitization on Diamond Surface as a Manifestation of Dopants

Doped diamond electrodes have attracted significant attention for decades owing to their excellent physical and electrochemical properties. However, direct experimental observation of dopant effects on the diamond surface has not been available until now. Here, low-temperature scanning tunneling microscopy is utilized to investigate the atomic-scale morphology and electronic structures of (100)- and (111)-oriented boron-doped diamond (BDD) electrodes. Graphitized domains of a few nanometers are shown to manifest the effects of boron dopants on the BDD surface. Confirmed by first-principles calculations, local density of states measurements reveal that the electronic structure of these features is characterized by in-gap states induced by boron-related lattice deformation. The dopant-related graphitization is uniquely observed in BDD (111), which explains its electrochemical superiority over the (100) facet. These experimental observations provide atomic-scale information about the role of dopants in modulating the conductivity of diamond, as well as, possibly, other functional doped materials.

Boron position-dependent surface reconstruction and electronic states of boron-doped diamond(111) surfaces: an ab initio study

Boron-doped diamond (BDD) has attracted much attention in semi-/superconductor physics and electrochemistry, where the surface structures and electronic states play crucial roles. Herein, we systematically examine the structural and electronic properties of the unterminated and H-terminated diamond(111) surfaces by using density functional theory calculations, and the effect of the boron position on them. The surface energy increases compared to that of the undoped case when the boron is located at a deeper position in the diamond bulk, which indicates that boron near the surface can facilitate the surface stability of the BDD in addition to the H-termination. Moreover, the surface energy and projected density of state analyses suggest that the boron can enhance the graphitization of the pristine (ideal) unterminated (111) surface thanks to the alternative sp2-sp3 arrangement on that surface. Finally, we found that surface electronic states depend on the boron's position, i.e., the Fermi energy (EF) is located around the mid-gap position when the boron lies near the surface, instead of showing a p-type semiconductor behavior where the EF lies closer to the valence band maximum.