Abstract
Diamond is one of the fascinating films appropriate for optoelectronic applications due to its wide bandgap (5.45 eV), high thermal conductivity (3320 W m−1·K−1), and strong chemical stability. In this report, we synthesized a type of diamond film called nanocrystalline diamond (NCD) by employing a physical vapor deposition method. The synthesis process was performed in different ratios of nitrogen and hydrogen mixed gas atmospheres to form nitrogen-doped (n-type) NCD films. A high-resolution scanning electron microscope confirmed the nature of the deposited films to contain diamond nanograins embedded into the amorphous carbon matrix. Sensitive spectroscopic investigations, including X-ray photoemission (XPS) and near-edge X-ray absorption fine structure (NEXAFS), were performed using a synchrotron beam. XPS spectra indicated that the nitrogen content in the film increased with the inflow ratio of nitrogen and hydrogen gas (IN/H). NEXAFS spectra revealed that the σ*C–C peak weakened, accompanied by a π*C=N peak strengthened with nitrogen doping. This structural modification after nitrogen doping was found to generate unpaired electrons with the formation of C–N and C=N bonding in grain boundaries (GBs). The measured electrical conductivity increased with nitrogen content, which confirms the suggestion of structural investigations that nitrogen-doping generated free electrons at the GBs of the NCD films.
Highlights
Publisher’s Note: MDPI stays neutralDiamond material has superior properties, including a wide bandgap, the highest hardness, high thermal conductivity, biocompatibility, and chemical stability, as well as several distinctive physical and chemical properties [1,2]
nanocrystalline diamond (NCD) films are composed of diamond nanograins which are embedded in an amorphous carbon (a-C):H matrix
This unique structural configuration possesses properties between diamond and diamond-like carbon (DLC) films, and it enables the realization of low activation energy n-type doping with nitrogen
Summary
Diamond material has superior properties, including a wide bandgap, the highest hardness, high thermal conductivity, biocompatibility, and chemical stability, as well as several distinctive physical and chemical properties [1,2]. NCD films are composed of diamond nanograins which are embedded in an a-C:H matrix This unique structural configuration possesses properties between diamond and DLC films, and it enables the realization of low activation energy n-type doping with nitrogen. The objective of the present research work is to elucidate the influence of changing the nitrogen concentration on the electrical conductivities of NCD films and correlating them with the chemical structure configurations. In this regard, the NCD films were synthesized by a physical vapor method, called coaxial arc plasma gun. The synthesized films were intensively examined by sensitive spectroscopic measurement tools including X-ray photoemission and near-edge X-ray absorption fine-structure spectroscopies measured with synchrotron radiation available at Kyushu University Synchrotron Center in Saga, Japan
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