Articles

Diamond and carbon nanostructures possess outstanding advantages, such as chemical inertness, stable fluorescence, tunable surface characteristics and excellent biocompatibility. In particular, diamond has extremely strong mechanical properties, and therefore the nanostructures have been developed for unique applications. Herein, we systematically review the very recent applications of these structures in drug delivery, bioimaging and biosensing, followed by discussion of their advantages, limitations and challenges in translation to potential clinical applications and presentation of our insights of their future development.

With the increasing power density and reduced size of the GaN-based electronic power converters, the heat dissipation in the devices becomes the key issue toward the real applications. Diamond, with the highest thermal conductivity among all the natural materials, is of the interest for integration with GaN to dissipate the generated heat from the channel of the AlGaN/GaN high electron mobility transistors (HEMTs). Current techniques involve three strategies to fabricate the GaN-on-diamond wafers: bonding of GaN with diamond, epitaxial growth of diamond on GaN, and epitaxial growth of GaN on diamond. As a result of the large lattice mismatch and thermal mismatch, the integration of GaN-on-diamond wafer is suffered from stress, bow, crack, rough interfaces, and large thermal boundary resistance. The interfaces with transition or buffer layers impede the heat flow from the device channel and greatly influence the device performance. In this review, we summarize the three different techniques to achieve the GaN-on-diamond wafers for the fabrication of AlGaN/GaN HEMTs. The problems and challenges of each method are discussed. In addition, the effective thermal boundary resistance between GaN and diamond, which characterizes the heat concentration, is analyzed with regard to different integration and measurement methods.

Diamond with an ultra-wide bandgap shows intrinsic performance that is extraordinarily superior to those of the currently available wide-bandgap semiconductors for deep-ultraviolet (DUV) photoelectronics and microelectromechanical systems (MEMS). The wide-bandgap energy of diamond offers the intrinsic advantage for solar-blind detection of DUV light. The recent progress in high-quality single-crystal diamond growth, doping, and devices design have led to the development of solar-blind DUV detectors satisfying the requirement of high Sensitivity, high Signal-to-Noise ratio, high spectral Selectivity, high Speed, and high Stability. On the other hand, the outstanding mechanical hardness, chemical inertness, and intrinsic low mechanical loss of diamond enable the development of MEMS sensors with boosted sensitivity and robustness. The micromachining technologies for diamond developed in these years have opened the avenue for the fabrication of high-quality single-crystal diamond mechanical resonators. In this review, we report on the recent progress in diamond DUV detectors and MEMS sensors, which includes the device principles, design, fabrication, micromachining of diamond, and devices physics. The potential applications of these sensors and a perspective are also described.

Antibiotic resistance in bacteria is a current threat causing an increasing number of infections of difficult clinical management. While the overuse and misuse of antibiotics are investigated to reduce them, the need for alternatives to approaches is rising. Carbon-based materials shown recent moderate to high antibacterial properties and diamond, thanks to its superior mechanical, tribological, electrical, chemical and biological quality is a choice material to investigate for safe antibacterial films, coatings and particles. Here, the antibacterial properties of diamond films, nanodiamonds, DLC films and a comprehensive list of the composites developed from them are discussed along with a summary of the bacterial strains used and the most efficient composition and/or concentration discovered. In a later stage, the mechanisms of action and the parameters that are believed to influence them are discussed and finally, an overview of the biomedical and food industry applications is given.

Because of its ultrahigh hardness, synthetic diamond has been widely used in advanced manufacturing and mechanical engineering. As an ultra-wide bandgap semiconductor, on the other hand, diamond recently shows a great potential in electronics industry due to its outstanding physical properties. However, like silicon-based electronics, the electrical properties of diamond should be well modulated before it can be practically used in electronic devices. In this work, we briefly review the recent progresses in producing high-quality, electronic grade synthetic diamonds, as well as several typical strategies, from the conventional element doping to the emerging “elastic strain engineering,” (ESE) for tuning the electrical and functional properties of microfabricated diamonds. We also briefly show some device application demonstrations of diamond and outline some remaining challenges that are impeding diamond’s further practical applications as functional devices and offer some perspective for future functional diamond development.

Waste heat recovery is significant for improving energy utilization, reducing carbon emissions, and neutrality. The gravity heat pipe (GHP) has excellent thermal performance due to the cyclic phase transformation of the working fluid. As an important thermal management device for waste heat recovery, the heat transport capacity of GHP improves, the efficiency and performance of the waste heat recovery increase, and more wasted heat can be stored more quickly. Nano-diamond has the highest thermal conductivity and can be dispersed in water to form a diamond nanofluid, enhancing the thermal performance of GHP. In contrast, the study on the heat transfer behavior of the diamond nanofluid in GHP is insufficient. Besides, the influences of filling ratio (FR), mass fraction (MF), and heat flux on thermal performance are in demand for further study. In this article, the heat transfer behavior is investigated by studying the flow patterns of diamond nanofluids. The influences of filling ratio and mass fraction on flow patterns are analyzed. An orthogonal experiment is conducted; the heat flux has the most significant effect on the thermal performance, followed by the filling ratio and mass fraction. The thermal performance is the best when the optimal parameters (FR = 20%, MF = 1 w.t.%) are selected under a heat flux of 20 × 104 W/m2. The equivalent heat transfer coefficient reaches 3485 W/(m2·°C). This article can achieve a deeper understanding of the diamond nanofluid heat transfer mechanism in GHP and enhance the thermal performance of GHP for better waste heat recovery.

As one of the representatives of carbon-based semiconductors, diamond is called the “Mount Everest” of electronic materials. To maximize its properties and realize its industrial applications, the fabrication of wafer-scale high-quality diamonds is critical. To date, heteroepitaxy is considered as a promising method for the growth of diamond wafers with considerable development. In this review, fundamentals of diamond heteroepitaxy is firstly introduced from several perspectives including nucleation thermodynamics and kinetic, nucleation process at the atomic level, as well as the interplay between the epitaxial film and substrate. Second, the bias enhanced nucleation (BEN) method is reviewed, including BEN setup, BEN process window, nucleation phenomenology (mainly on Iridium), nucleation mechanism by ion bombardment, and large-scale nucleation realization. Third, the following textured growth process is presented, as well as grain boundary annihilation, and dislocation and stress reduction technologies. Fourth, the applications of diamonds in electronic devices are studied, showing its excellent performances in the future power and electronic devices. Finally, prospects in this field are proposed from several aspects.

Microorganisms promoted corrosion has caused significant loss to marine engineering and the antibacterial coatings have served as a solution that has gained attention. In this study, the chemical vapour deposition technique has been employed to grow three different types of diamond coatings, namely, ultrananocrystalline diamond (UNCD), nanocrystalline diamond (NCD), and microcrystalline diamond (MCD) coatings. The evolution of associated surface morphology and the surface functional groups of the grown coatings have demonstrated antibacterial activity in seawater environments. It is found that different ratio of sp3/sp2 carbon bonds on the diamond coatings influences their surface property (hydrophobic/hydrophilic), which changes the anti-adhesion behaviour of diamond coatings against bacteria. This plays a critical role in determining the antibacterial property of the developed coatings. The results show that the diamond coatings arising from the deposition process kill the bacteria via a combination of the mechanical effects and the functional groups on the surface of UNCD, NCD, and MCD coatings, respectively. These antibacterial coatings are effective to both Gram-negative bacteria (E. coli) and Gram-positive bacteria (B. subtilis) for 1–6 h of incubation time. When the contact duration is prolonged to 6 h or over, the MCD coatings begin to reduce the bacteria colonies drastically and enhance the bacteriostatic rate for both E. coli and B. subtilis.

The irradiation effect of X-ray on the electrical properties of Schottky-barrier diode (SBD) and metal-semiconductor field-effect transistors (MESFET) based on the surface conductivity of hydrogen-terminated single-crystal diamond (SCD) epilayers was investigated. The Ohmic contact was formed by a Pd/Ti/Au multilayer and the Schottky metal was Al thin film for the fabrication of the diamond SBDs and MESFETs. The X-ray irradiation was performed with a dose of 100 kGy. It was observed that both the forward current of the SBDs and the drain current of the MESFETs experienced a reduction after the X-ray irradiation. The type of the single-crystal diamond substrate had an obvious effect on the radiation properties. For the MESFETs on the type-Ib SCD substrate, the variation of the drain currents as the irradiation was inhomogeneous across the devices. For the MESFETs on the type-IIa SCD substrate, the reduction of the drain currents is more uniform and the threshold voltage changed little upon X-ray irradiation. The partial oxidation in the air of the exposure area in the device and the edge of the Al gate may be responsible for the degradation of the device performance under X-ray irradiation. The passivation technique with radiation-robustness is needed for diamond devices based on the surface conductivity of diamond.

This review focuses on describing the fundamental/applied materials science and technological applications of a transformational multifunctional diamond-based material named ultranano­crytalline diamond (UNCDTM) in film form. The UNCDTM films are synthesized using microwave plasma chemical vapor deposition (MPCVD) and hot filament chemical vapor deposition (HFCVD), via patented Ar/CH4 gas flown into air evacuated chambers, using microwave power, or hot filaments’ surface, to crack CH4 molecules to generate C atoms and CHx (x = 1, 2, 3) species, which produce chemical reactions on substrates’ surfaces, producing diamond film with grain sizes in the range 3–5 nm (smallest grain size known today for any polycrystalline diamond film), providing the bases for the name UNCD. UNCD coatings exhibit a unique combination of properties, namely: (1) super high hardness and Young modulus, similar to the crystal gem of diamond; (2) lowest coefficient of friction compared to other diamond or diamond-like coatings; (3) no mechanical surface wear; (4) highest resistance to chemical attach by any corrosive fluid; (5) only diamond film exhibiting electrical conductivity via Nitrogen inserted in grain boundaries, binding to C atoms and providing electrons for electrical conduction, or B atoms substituting C atoms in the diamond lattice, providing electrons to the conduction band; and (6) best biocompatibility, since UNCD coatings are formed by C atoms (element of life in human DNA, cells/molecules). The UNCD films’ properties provide unique multifunctionalities, enabling new generations of industrial, electronic, high-tech, and implantable medical devices/prostheses, enabling substantial improvement in the way and quality of life of people worldwide.