Search

Oxygen evolution reaction (OER) is critical in water splitting for green hydrogen gas production due to its sluggish kinetics; however, commercial OER catalysts commonly suffer from high cost, low catalytic activity and poor stability. Herein, we developed a C+ ion implantation method to modify single crystal diamond, and the resultant surface amorphous layer not only raised the active site number but also increased the content of the C=O group, thus significantly improving the OER activity. The C+ ion implanted high-temperature and high-pressure (C+-HTHP) and chemical vapor deposition (C+-CVD) diamonds both exhibit low OER overpotential with η 10 of 317 mV and 325 mV respectively, superior to those of HTHP diamond (360 mV), CVD diamond (395 mV) and RuO 2 (364 mV). The potentiostatic testing shows that the C+ implanted diamonds almost didn't undergo the rise of OER overpotential upon catalysis for more than 12 h at a current density of 10 mA cm−2, suggesting a high catalytic stability, owing to the strong bonding between single crystal diamond and amorphous carbon layer. For the first time, we utilized carbon ion implantation to prepare diamond-based high-performance OER catalyst, which broadens the understanding of carbon-based materials in OER catalysis. [ABSTRACT FROM AUTHOR]

• Large scale all diamond microchannel has been fabricated by DC arc jet CVD and laser cutting. • Three methods have been carried out to modify the diamond microchannel surface to fulfill different terminations, including oxygen termination, hydrogen termination and fluorine termination. • The change of the surface properties of the diamond surface referring to the real situation flow was analyzed and explained in detail. The diamond microchannel heat sink (D-MCHS) has extremely ultra-high stability and heat transfer capacity, and the surface modification can further improve the heat dissipation capacity of D -MCHS. In this study, diamond microchannels were modified by three surface termination operations, including oxygen-terminated (OT), hydrogen (HT), and fluorine-terminated surfaces (FT). Referring to the real situation, after the treatment of heat flow, the hydrophobic properties of HT-diamond microchannels decreased and resulted in the increase of surface heat transfer coefficient by 11%. The hydrophilic properties of OT-diamond tend to be stable after being significantly reduced, and the heat transfer coefficient decreased by 7%. FT-diamond was the most stable; its hydrophobicity remained constant after a slight decrease in the initial stage, and the corresponding surface heat transfer coefficient increased by 14%. X-ray photoelectron spectroscopy (XPS) was used to evaluate the surface bonding state of different terminal treatments. The results show that although the F terminal has more stable hydrophobicity, its surface temperature is 5 °C higher than that of the hydrophilic terminal, and the heat transfer coefficient is reduced from 9500 to 6000 W/(m2K), decreasing by nearly 58%. [ABSTRACT FROM AUTHOR]

A plasma arc generator was used to heat treat the free-standing CVD diamond films at 1450–1900 °C. An Arrhenius curve was fit according to trends in the measured Raman peak intensity ratio of diamond to graphite as a function of heat treatment temperature, and the curve was extrapolated linearly. It was found that the extrapolation lines intersected at the Debye temperature, Θ D = 2021 K. By comparing the activation energies of diamond graphitization in literature and from different measurement modes in our study, it was found that the graphitization mechanisms were different on both sides of Debye temperature due to differences in the excited lattice vibration modes. When the heat treatment temperature was just below the Debye temperature, the graphitization process was promoted by generating vacancies or the breaking of single C C bonds, and the apparent activation energy was 366 ± 60 kJ·mol−1. When the heat treatment temperature was above the Debye temperature, the graphitization process was promoted by the simultaneous breaking of multiple C C bonds, and the apparent activation energy was 887 ± 141 kJ·mol−1. In combination with the morphology changes on the surface of the CVD diamond film after high temperature heat treatment, the mechanism of the micro-cyclic phase transition on the surface of the diamond film at temperatures lower than Debye temperature was summarized as follows. First, C C bonds on the diamond surface were activated and broken at high temperatures, and some diamond carbon atoms dissociated from solid phase sites to the gas phase by forming hydrocarbon free radicals. Then, the carbon atoms from these hydrocarbons entered the graphite lattice step by step to complete the spontaneous deposition of sp2 clusters. [Display omitted] • The morphological changes of diamond surface dependent on temperature and hydrogen plasma environment were observed. • Taking the Debye temperature as a critical point, the graphitization activation energy exhibits a significant difference. • The graphitization mechanism of CVD diamond surface was proposed based on the kinetics analysis. [ABSTRACT FROM AUTHOR]

The surface conductivity on the H-terminated diamond is still an interesting topic in the field of diamond electronics. Until now, the carrier mobility in the conductive channel has been limited to below 200cm2/Vs due to the various surface scattering mechanisms. In this paper, a high mobility conductive channel on the H-terminated diamond surface was reported. Firstly, the high quality diamond films were deposited on the commercial CVD diamond substrates. After polishing, the H-termination was obtained by hydrogen plasma treatment. The surface morphology of the H-terminated diamond was observed by atomic force microscope (AFM) and scanning electron microscope (SEM). The crystal quality on the diamond surface was characterized by Raman spectroscopy. The impurities in the crystals were tested by photoluminescence spectroscopy. The surface conductivity of H-terminated diamond was monitored comprehensively by Hall test. It can be found that the sheet resistance decreases much and the carrier mobility increases dramatically after the hydrogen plasma treatment and mechanical cleaning. The maximum mobility value is up to 365cm2/Vs with carrier density of 2.9 × 1012 cm−2, which is the highest value reported. Raman spectra of diamond surface show that a peak appears at 1121.4 cm−2 after the hydrogen plasma treatment, which corresponds to the nanocrystal diamond or carbon clusters of sp3 bonded material. The corresponding mobility enhancement mechanism on the H-terminated diamond surface was proposed. Unlabelled Image • The carrier mobility enhancement on the H-terminated diamond surface was found. • A thin carbon film on the diamond surface was observed with Raman peak at 1121 cm−1. • The H-terminated diamond surface showed high carrier mobility of 365cm2/Vs. • The corresponding mobility enhancement mechanism was proposed. [ABSTRACT FROM AUTHOR]