Abstract
The insufficient data on a structure of the boron-doped diamond (BDD) has frustrated efforts to fully understand the fascinating electronic properties of this material and how they evolve with doping. We have employed X-ray diffraction and Raman scattering for detailed study of the large-sized BDD single crystals. We demonstrate a formation of boron-carbon (B-C) nanosheets and bilayers in BDD with increasing boron concentration. An incorporation of two boron atoms in the diamond unit cell plays a key role for the B-C nanosheets and bilayer formation. Evidence for these B-C bilayers which are parallel to {111} planes is provided by the observation of high-order, super-lattice reflections in X-ray diffraction and Laue patterns. B-C nanosheets and bilayers minimize the strain energy and affect the electronic structure of BDD. A new shallow acceptor level associated with B-C nanosheets at ~37 meV and the spin-orbit splitting of the valence band of ~6 meV are observed in electronic Raman scattering. We identified that the superconducting transitions occur in the (111) BDD surfaces only. We believe that the origin of Mott and superconducting transitions is associated with the two-dimensional (2D) misfit layer structure of BDD. A model for the BDD crystal structure, based on X-ray and Raman data, is proposed and confirmed by density functional theoretical calculation.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-1215-6) contains supplementary material, which is available to authorized users.
Highlights
A boron-doped diamond is of great interest because it exhibits a variety of intriguing physical properties, such as semiconductor metal (Mott) [1,2,3] and superconducting transitions [4]
In summary, we have demonstrated the formation of BC nanosheets and bilayers in boron-doped diamond (BDD) with increasing boron concentration that result in the elastic strain relaxation of the diamond matrix
The new shallow boron acceptor level at ~37 meV and the spin-orbit splitting of the valence band of ~6 meV were defined from the analysis of the electronic Raman spectra of BDD
Summary
A boron-doped diamond is of great interest because it exhibits a variety of intriguing physical properties, such as semiconductor metal (Mott) [1,2,3] and superconducting transitions [4]. Obtaining detailed structural information has been hindered by the fact that all superconducting BDD samples were thin chemical-vapor-deposited films, granular [11], and polycrystals [4]. To eliminate these problems, we have grown. The lattice constant is practically permanent in the range of boron concentrations from 1017 to 1020 cm−3 according to the X-ray data [12], while that should increase with the increase of the boron concentration due to Vegard law. Raman bands at 480 and 1230 cm−1 were observed by many
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