Articles

A GaN-on-diamond structure is the most promising candidate for improving the heat dissipation efficiency of GaN-based power devices. Room-temperature bonding of GaN and diamond is an efficient technique for fabricating this structure. However, it is extremely difficult to polish diamond to an average roughness (Ra) below 0.4 nm, especially for polycrystalline diamond. In this work, Room-temperature bonding of GaN and rough-surfaced diamond with a SiC layer was successfully achieved by a surface-activated bonding (SAB) method. The diamond surface’s initial Ra value was 0.768 nm, but after deposition of the SiC layer, the Ra decreased to 0.365 nm. The SiC layer formed at the as-bonded GaN/diamond interface was amorphous, with a thickness of about 7 nm. After annealing at 1000-°C, the amorphous SiC layer became polycrystalline, and its thickness increased to approximately 12 nm. These results indicate that the deposition of a SiC layer on diamond can efficiently lower the diamond surface’s roughness and thus facilitate room-temperature bonding.

It has been half of a century since the publication of the early reports about CVD diamond films in the world in the early 1970’s. The reports for meaningful laboratory growth of diamond films with much higher growth rate and higher quality could be found in the early 1980’s, under the so-called “Diamond Fever” initiated all over the world. In less than 10 years later, CVD diamond research had started in China as “863 Plan” (High Technology Research and Development Plan in China), a newly launched program in 1987. 35 years later, it is very interesting to explore what really happened to the CVD diamond in China. As a multi-functional material with a vast combination of extraordinary electrical, mechanical, thermal, optical, acoustic, and electro-chemistry properties, the CVD diamond has wide applications potentially in the field of multidiscipline high technologies. Therefore, this article aims to provide a general review on the CVD diamond by presenting a clearer picture about the history, the research status and its development, particularly the commercialization in China. Finally, the general trend in the near future is discussed.

The dislocation identification method using X-ray topography by reflection mode geometry was applied to characterize IIa, Ib and highly B doped high pressure high temperature (HPHT) grown crystals. In both IIa and Ib crystals, dislocations are found to propagate in the <111> grown direction, with dominant vectors of [110] and [1-10], neither of which has no c-axis segment. For Ib crystal, many dislocations are also generated in the <112> and <121> directions, which are slightly tilted to <111>. It was confirmed that the dislocations in the same direction have the same Burgers vectors, but the dislocations are spread in broad area. A total of up to 20 HPHT crystals were measured and found to exhibit different dislocation distributions. This indicates an immature growth technique in terms of dislocation. Measurements of four chemical vapor deposition (CVD) substrates showed numerous dislocation bundles, making individual dislocation directions analysis impossible. CVD substrates suffer from an increase in dislocations due to CVD growth, resulting in poor diamond quality in terms of dislocation. XRT analysis on dislocations of epitaxial growth will be very important prior to CVD substrates analysis.

In recent years, there have been more and more researches on the surface modification of diamonds, however, the exact types and quantities of oxygen-related species on diamond surfaces and the method to control the condition parameters to obtain as many oxygen-containing groups as possible have been rarely studied so far. Therefore, in this work, we focused on these questions. And we find out that ozone oxidation would not affect the overall crystal structure and morphology of diamonds. Besides, changing oxidation time and ozone concentration would significantly influence the density of hydroxyl groups, which is manifested as a change of oxygen content. In order to make the hydroxyl density on diamond surface reach a high level (3.12 × 1014 units/cm2), so that diamonds can be better combined with the resin matrix, the ozone oxidation time should be 15 min, and the ozone concentration should be 115 g•m−3. And under these conditions, the thermal conductivity of diamond and polysiloxane composites can reach 8.02 W/mK.

Fluorescent nanodiamonds (FNDs) with nitrogen-vacancy (NV) centers have been extensively studied in numerous fields because of their distinct magneto-optical properties. The NV center is a perfect candidate for a nanosensor because of its stable photoluminescence and manipulable spin state by microwave/magnetic field. Considering the controllable sizes (5–100 nm), abundant surface groups, and good biocompatibility, FNDs are valuable in biosensing to study the physiological activity at the cellular scale. This review summarizes the recent applications of FNDs in detecting physiological parameters (such as temperature, pH) as well as proteins, free radicals, viruses, etc. Highlights include the development of FND-based biosensors and the NV center transduction system that responds to signal changes or concentrations fluctuations of target species.

Diamond is an ultrawide bandgap semiconductor with excellent electronic and photonic properties, which has great potential applications in microelectronic and optoelectronic devices. As an allotrope of diamond, graphene also has many fantastic properties like diamond, which caught much attention in combing them together. In this work, a direct sp3-to-sp2 conversion method was proposed to fabricate graphene layers on single crystal diamond by thermal treatment with Ni film catalyst. By optimizing the conversing conditions, a thin graphene layer with low sheet resistance was obtained on diamond. Based on this, an all-carbon sandwich structural graphene-diamond-graphene (GDG) detector was fabricated, which shows low dark current of 0.45 nA at 0.5 V μm−1 applied electric field. The maximum sensitivity of this detector is obtained when the incident X-ray is 12 keV, with the value of 2.88 × 10−8 C Gy−1. Moreover, the rise time and delay time of the GDG detector is about 1.2 and 22.8 ns, respectively, which are very close to that of diamond detector with Ti/Au electrode. The realization of the direct in-situ sp3-to-sp2 conversion on diamond shows a promising approach for fabricating diamond-based all-carbon electronic devices.

Sub-monolayers of titanium were deposited onto oxidised (100) single-crystal diamond surfaces and annealed in vacuo at temperatures up to 1000 °C to find a temperature-stable termination procedure that produces a surface with Negative Electron Affinity (NEA). The samples were analysed by X-ray Photoelectron Spectroscopy, Ultraviolet Photoelectron Spectroscopy and Energy-Filtered Photoemission Electron Microscopy to determine their electron affinity and work function values. NEA values were observed on samples following annealing above 400 °C, with the largest NEA value being –0.9 eV for a sample coated with a half-monolayer of Ti annealed at 400 °C. Work function values were ∼4.5 eV for all samples annealed at temperatures between 400 and 600 °C, then rose at higher temperatures due to the loss of substantial amounts of O from the surface. Work-function maps indicated that the surface was uniform over areas 5700 μm2, suggesting that the deposition and annealing steps used are reliable methods to produce films with homogeneous surface properties.

This article describes key material science/technology issues to implement polycrystalline diamond scaffolds to enable processes for biological cells growth relevant for using cells grown in the laboratory for the treatment of human biological conditions. Issues investigated include

Diamond/aluminum composite material has the advantages of high thermal conductivity, low expansion, and lightweight, which has a wide range of application prospects in the field of electronic packaging thermal management. However, the serious interface problems between diamond and aluminum limit the full play of the thermal conductivity of composite materials. A reasonable interface design can maximize the thermal conductivity of composite materials. This article focuses on the interface modification of diamond/aluminum composites, briefly describing the theoretical basis of interface design, the research status of interface modification, interface reaction and composite stability, and prospects for diamond/aluminum composites material development.

Aiming at developing inch-sized processing of diamond, B-doped layer was grown on mosaic single-crystallin diamond wafers by using hot-filament chemical vapor deposition (CVD), which is expected to have an advantage in terms of the deposition area compared with microwave plasma (MWP) CVD. Uniformity in horizontal and vertical directions is studied. It is found that the junctions of the monocrystalline diamond domains in the mosaic wafer and the direction of the crystal off-angles against to these junctions are less effective to the uniformity of the impurity concentrations. On the other hand, it is suggested that excess incorporation of W from the filament suppresses the growth and incorporation of B. It is shown that millimeter scale or more precise control of the arrangement of the wafer and the filament enables to obtain more uniform and efficient doping.