The contact angle and surface energy values of diamond are systemically investigated in terms of surface treatments (hydrogen- and oxygen-terminations), structure feature (single crystal diamonds and polycrystalline diamond films), crystal orientation ((100), (111) and mixed (100)/(111) orientations), different fluids (probes of polar deionized water and nonpolar di-iodomethane). It is found that the hydrophobic/hydrophilic characteristic and surface energy values of diamond are mainly determined by the surface hydrogen/oxygen termination, and less related to the structural features and crystal orientation. Based on the contact angle values with polar water and nonpolar di-iodomethane, the surface energies of diamond are estimated to be about 43 mJ/m² for hydrogen-termination and about 60 mJ/m² for oxygen-termination. Furthermore, the varying surface roughness of diamond and fluids with different polarities examined determine the variation of contact angles as well as the surface energy values. These results would be helpful for a more detailed understanding of the surface properties of diamond films for further applications in a broad number of fields, such as optical and microwave windows, biosensors, and optoelectronic devices, etc.

Graphitic carbon nitride (g−CN), a promising visible-light-responsive semiconductor material, is regarded as a fascinating photocatalyst and heterogeneous catalyst for various reactions due to its non-toxicity, high thermal durability and chemical durability, and “earth-abundant” nature. However, practical applications of g−CN in photoelectrochemical (PEC) and photoelectronic devices are still in the early stages of development due to the difficulties in fabricating high-quality g−CN layers on substrates, wide band gaps, high charge-recombination rates, and low electronic conductivity. Various fabrication and modification strategies of g−CN-based films have been reported. This review summarizes the latest progress related to the growth and modification of high-quality g−CN-based films. Furthermore, (1) the classification of synthetic pathways for the preparation of g−CN films, (2) functionalization of g−CN films at an atomic level (elemental doping) and molecular level (copolymerization), (3) modification of g−CN films with a co-catalyst, and (4) composite films fabricating, will be discussed in detail. Last but not least, this review will conclude with a summary and some invigorating viewpoints on the key challenges and future developments.

The trench diamond junction barrier Schottky (JBS) diode with a sidewall enhanced structure is designed by Silvaco simulation. Comparing with the conventional trench JBS diode, Schottky contact areas are introduced on the sidewall of the trench beside the top cathode. The sidewall Schottky contact weakens the junction field-effect transistor effect between the trenches to realize a low on-resistance and a high Baliga’s figure of merit (FOM) value. In addition, the existence of the n-type diamond helps to suppress the electric field crowding effect and enhance the reverse breakdown voltage. With the optimal parameters of device structure, a high Baliga’s FOM value of 2.28 GW/cm² is designed. Therefore, the proposed sidewall-enhanced trench JBS diode is a promising component for the applications in diamond power electronics.

In this paper, diamond-based vertical p-n junction diodes with step edge termination are investigated using a Silvaco simulation (Version 5.0.10.R). Compared with the conventional p-n junction diode without termination, the step edge termination shows weak influences on the forward characteristics and helps to suppress the electric field crowding. However, the breakdown voltage of the diode with simple step edge termination is still lower than that of the ideal parallel-plane one. To further enhance the breakdown voltage, we combine a p-n junction-based junction termination extension on the step edge termination. After optimizing the structure parameters of the device, the depletion regions formed by the junction termination extension overlap with that of the p-n junction on the top mesa, resulting in a more uniform electric field distribution and higher device performance.

High-quality polycrystalline diamond films with dominated (100)-oriented grains are realized by combining the thermally oxidation and the homogeneous second growth processes. Moreover, we investigate the wettability property of the polycrystalline diamonds in various stages. Different surface structures (with various grain sizes, voids, and orientations, etc.) and terminations (hydrogen or oxygen) have significant effects on the wettability of polycrystalline diamond films. The wettability is further closely related to the polarity of solutions. By measuring the contact angle and calculating the dispersion and polarity components, we estimate the surface energy of polycrystalline diamond films, and explore the factors affecting the surface energy. The modulations in growth quality and wettability property of polycrystalline diamond films provide valuable data for development of diamond-based multiple devices in practical applications.