Type of presentation: Oral

MS-2-O-2037 Local boron environment in B-doped diamond films studied by advanced TEM and spatially resolved EELS

Turner S.1, Lu Y.1, Idrissi H.1, Janssens S. D.2,3, Haenen K.2,3, Sartori A. F.4, Schreck M.4, Verbeeck J.1, Van Tendeloo G.1
1EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium, 2Institute for Materials Research (IMO), Hasselt University, Wetenschapspark 1, B-3590 Diepenbeek, Belgium , 3IMOMEC, IMEC vzw, Wetenschapspark 1, B-3590 Diepenbeek, Belgium, 4Universität Augsburg, Institut für Physik, D-86135 Augsburg, Germany
stuart.turner@uantwerpen.be

Diamond is an attractive material for many technological applications, because of its extreme hardness, chemically inert surfaces, high Young’s modulus and large band gap of 5.5 eV. One of the most commonplace synthesis methods for nanocrystalline diamond (NCD) and epitaxial, single crystal thin films is microwave plasma assisted chemical vapour deposition (MPCVD). Many of the technological applications of diamond require specific semiconducting properties of the material and therefore doping is necessary. The most effective doping with p-type character is obtained by inserting boron in-situ during the growth process. Boron doping of diamond allows from mild p-type character for low [B] to a metallic regime and also superconducting properties at liquid helium temperatures for very high [B].1

However, much debate surrounds the question of the position and coordination of the B dopants in the diamond, especially in defective regions of the material. As B doping leads to an increase in defects in diamond grains and films upon growth, it is plausible that the boron dopants are preferentially embedded in defective regions.

In this work, conducting films of B-doped nanocrystalline diamond and single crystal diamond grown by MPCVD have been investigated in both plan-view and cross-section orientation by a combination of aberration-corrected (scanning) transmission electron microscopy (HR-ADF-STEM) and spatially resolved electron energy-loss spectroscopy (STEM-EELS) performed on a state-of-the-art aberration corrected instrument. Using these tools, the B concentration, distribution and the local B environment in this type of thin nanocrystalline diamond films have been determined.

Concentrations of ~1 at.% of boron are found to be embedded within the pristine diamond lattice. Boron distribution maps however clearly reveal a preferential enrichment of boron at defective areas like twin boundaries, incoherent defects and even dislocations in diamond thin films. Inspection of the EELS fine structure reveals a distinct difference in coordination of the B dopants in “pristine” diamond areas and in defective regions, identified through comparison of the experimental EELS fine structure to density functional theory (DFT) calculated fine structure signatures.2,3,4

1) Ekimov E.A. et al. (2004) Nature, 428, 542-545

2) Turner S. et al. (2012) Nanoscale, 4, 5960-5964

3) Lu Y.-G. et al. (2012) Applied Physics Letters, 101, 041907

4) Lu Y.-G. et al. (2013) Applied Physics Letters, 103, 032105

S.T. gratefully acknowledges financial support from the Fund for Scientific Research Flanders (FWO).

Fig. 1: B:NCD film. (a)&(b) Overview ADF-STEM images. (c) Image of a single defected diamond grain. (d)&(e) Survey image and quantitative B distribution map. B is clearly enriched at defects. (f) B-K edge fine structure from a diamond (black) and defect region (red). (g) C-K edge fine structure from a diamond (black) and defect region (red).

Fig. 2: Epitaxial B:diamond thin film. (a) ADF-STEM image of the thin film on a diamond substrate. A high density of dislocations is present in the film. (b)&(c) ADF image of a single dislocation and B map. B is enriched at the dislocations. (d) B-K edge from a pristine film region (black), a dislocation-rich region (red) and an etch pit (green).