Altering Mid-Gap Acceptor Levels by Morphology Tuning of Boron Doped Diamonds

• Hydrogen terminated diamond is a very promising material for high energy photocatalytic reactions1 owing to its large band gap(5.5 eV) and a unique capability of generating solvated electrons due to its negative electron affinity.2 However, a major limitation to the photoexcitation process to create solvated electrons is the need for deep UV illumination. Introducing unoccupied electronic states within the band gap of diamonds by doping with boron could provide a potential pathway for photoexcitation using visible light.Previous reports on HRTEM and EELS study of B doped polycrystalline and nanocrystalline diamonds provide insights into the local B environment.4,5,6,7 However, since these are primarily electron in-electron out techniques, they do not provide sufficient information about the existence of acceptor levels in the band gap of diamonds that are associated with boron doping. X-ray spectroscopy techniques have been shown to be sensitive to the acceptor levels arising due to boron doping.3 However, their physical origin still remains unclear.Here we use soft X-ray absorption spectroscopy (XAS) to probe the unoccupied electronic states at the carbon K edge in different boron-doped diamond materials, ranging from single crystal and polycrystalline film to diamond foam and nanodiamonds with different sizes. XAS of carbon K edges for the different B doped diamonds were characterized using partial fluorescence yield at the BESSY II synchrotron facility. Combining these results with density functional theory calculations, here we elucidate the contribution of the environment of boron to these mid gap acceptor states that vary with the morphology of diamonds. These results could have important implications on the selection of a suitable diamond based visible-light photocatalysts.

Ämnesord

NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

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