Articles

AbstractThe mainstream polishing methods were reviewed in light of polycrystalline CVD diamond wafer with large area. The principles, equipment, and processes of the mainstream polishing methods were reviewed, and the processing characteristics of these methods were compared. The material removal rate (MRR), polishing rate (PR), and minimum surface roughness (Ra) obtained by each polishing method were summed up. The non-contact method has a relatively higher MRR than the contact method, while the contact method has a relatively smaller final roughness than the non-contact method. Two factors, K (K = ΔRa/Δm, ΔRa is the reduction of the surface roughness, Δm is the mass loss) and CI (CI = K/t, t is the total polishing time), were proposed to evaluate the influence of the polishing parameters on the polishing course in the contact polishing methods and to describe the feature of each polishing method, respectively. The variation of the K value indicated that the polishing load and the polishing plate speed did not always influence the polishing effect monotonically in every contact polishing method, and it should be optimized to obtain fine surface roughness with the tiny mass loss. The CI value showed that the non-contact polishing method possessed the feature of high roughness improvement with low mass loss in the unit polishing time. These results reveal how to move forward on the path to polishing large area polycrystalline CVD diamond wafer.

AbstractNanodiamond (ND) has strong chemical stability, the initial oxidation temperature of ND is above 500 °C. A variety of oxygen-containing functional groups are adsorbed on the surface of ND, which makes ND has certain conductivity. Then ND can be used as highly stable catalyst or ideal support material. This paper reviews the properties, functionalization and electrochemical applications of ND. In this review, the catalytic activity and stability of diamond-based catalysts can be further improved by appropriately functionalizing ND, and the research progress in the field of electrochemistry can be increased.

The high frequency H-diamond metal-oxide-semiconductor field effect transistors (MOSFETs) were fabricated on single diamond substrate using 300°C ALD grown Al₂O₃ as gate dielectric and passivation layer. The devices gate length, gate/drain spacing and dielectric thickness are 100 nm, 2 μm, and 10 nm, respectively. The direct-current and frequency characteristics were investigated. The device shows a maximum saturation drain current of −492.6 mA/mm and g_m of 135.2 mS/mm. The device shows good high temperature working performance, and the maximum saturation drain current only has a little decreasing of 7.6%. at 200°C. In addition, the device exhibits a maximum cut-off frequency of 36.2 GHz and maximum oscillation frequency of 70.5 GHz. The transient drain current response measurement indicates that the drain current can follow the changing of gate voltage at the frequency of 1 MHz. These results indicate that the Al₂O₃ dielectric is suitable for using in high frequency or the high-speed switching devices.

A resonator with a high Q factor is generally pursued in the single-crystal diamond (SCD) microelectromechanical system (MEMS) for high-performance sensors. In this report, we investigate the oxygen etching effect of SCD on the Q factors of the SCD resonators by using the Raman spectroscopy spatial mapping. We aim to establish the etch pit effect on the Q factors of the SCD MEMS resonators. The 2D Raman imaging technique discloses the dislocations and the local stress in the SCD MEMS resonators in microscale. It is observed that the full width half maximum (FWHM) of the Raman spectra of the SCD resonators has marked relationship with the Q factors of the SCD resonators. The etch pits resulted from the dislocations have weak influence on the Q factors of the SCD resonators.

Incorporating two-dimensional (2D) diamond nanosheets with fluorescent color centers exhibits great potential in the application of quantum sensing. However, color centers always show poor optical emission in chemical-vapor-deposited (CVD) diamond nanomaterials. To address this issue, Si doped diamond/graphite hybrid films were successfully fabricated in microwave-plasma CVD device. The films consist of diamond-core/graphite-shell nanosheets with high amount of diamond nanocrystalline particles. Two post treatments of acid oxidation and annealing in air were used to tailor photoluminescence (PL) of silicon-vacancy (SiV) centers. The SiV centers in the oxidized samples exhibit small PL increase compared with the as-deposited samples with SiV PL quenching. It is found that the graphite phase is selectively etched away with the presence of nanocrystalline diamond particles during the treatment of acid oxidation while the nanocrystalline diamond particles are efficiently removed with the presence of graphite using the air annealing method. Based on this result, a two-step approach of acid oxidation followed by air annealing was conducted to etch the non-diamond phase, forming diamond nanosheets. The SiV centers exhibit significant PL enhancement with a maximum value of 28 folds, compared with the single-step oxidized samples. The Raman and XPS results reveal that such PL increase originates from direct bonding of oxygen on the carbon. Therefore, our work provides a feasible approach to prepare 2D diamond nanosheets with high-brightness color centers.

In the future, electronic parts will penetrate everything, generating a new and fast-growing pollution problem. Future devices therefore need to be environmentally friendly with strong recycling options. A paradigm change in semiconductor technology is predicted based on applications of better suited materials which can fulfil these criteria. Carbon based materials and here especially diamond are promising candidates. Bulk and surface properties of diamond are introduced in combination with applications in power electronics, quantum technology, bio-and electrochemistry and MEMS. Large amounts of diamond seeds and wafers will be required to approach commercial markets. Their availability in combination with quality and size as well as required energies for production are introduced. The production of CVD diamond is currently about 100–250 times more intense with respect to energy than Silicon. A problem which is addressed by use of new solid-sates microwave sources. The definition of “green diamond” is given taking into account requirements with respect to energy and methane/hydrogen production. A brief discussion and comparison of diamond global markets and related potentials in comparison to SiC and GaN is given.

Peculiarities of the processes of self-assembly of carbon under pressure up to 8 GPa and temperatures up to 1600°C in pure carbon, hydrocarbon, fluorocarbon, organometallic systems and binary mixtures of all-carbon, hydrocarbon, and fluorocarbon compounds have been revealed in the course of studies of pressure and temperature-induced transformations of different carbon-containing systems. It was shown that the character of the processes of self-assembly of carbon in different systems is controlled in the first place by the mobility of carbon atoms. The low diffusion mobility of carbon atoms in a condensed state at temperatures below 2000° C leads to the fact that in pure carbon systems studied on the examples of fullerite C60 and closed polyhedral carbon nanoparticles, carbon self-organization can occur only due to processes associated with small movements of carbon atoms that ensure the formation of intermolecular bonds in cases of polymerization of C60 or the restructuring of the internal structure of a polyhedral particle, strictly limited to the confines of a single nanoparticle. In the hydrocarbon and fluorocarbon systems, the character of transformation changes drastically due to formation of volatile low-molecular hydrocarbon and fluorocarbon fractions, which ensure a high gas-phase or fluid mobility to carbon atoms. Studies of pressure and temperature-induced transformations of different hydrocarbon, fluorocarbon compounds and their homogeneous binary mixtures revealed a clear synergistic effect of fluorine and hydrogen on processes of carbonization, graphitization, and formation of diamond in these systems in relation to industrially significant reduction of p,T parameters for formation of graphite, diamond and increase in the content of nanosize diamond fractions in the products of transformations of binary mixtures in comparison with pure hydrocarbon and fluorocarbon compounds. Discovery of this synergistic effect opens new opportunities for synthesis of high-purity and doped ultranano-, nano-, submicro-, and micronsized diamonds with the specific properties for different applications in quantum physics and biomedicine. Studies of particularities of self-assembly of carbon in processes of thermal transformations of ferrocene at high pressures demonstrated the possibility of preparation of iron carbide nanoparticles encapsulated into carbon shells, Fe7C3@C and Fe3C@C, considered as perspective magneto-controlled platforms for different biomedical nanocomplexes.

Combining diamond with GaN can significantly improve the heat dissipation performance of GaN-based devices. However, how to avoid the destructive damage to the GaN epi-layer caused by high-temperature hydrogen plasma during the diamond growth is still a problem. This study employed a Si transition layer and double-substrate structure microwave plasma chemical vapor deposition (MPCVD) to prepare diamond film on GaN epi-layer. The effects of double-substrate structure on the diamond growth were studied. The microwave plasma parameters of both single-substrate structure and double-substrate structure MPCVD diagnosed by emission spectra were comparatively investigated. It has been found that the microwave plasma energy of double-substrate structure MPCVD is relatively more concentrated and has higher radicals activity, which is beneficial to the diamond growth. The impacts of the Si transition layer on the diamond growth were also investigated. It demonstrates that the Si transition layer can effectively protect the GaN epi-layer from being etched by hydrogen plasma and improve the diamond growth. The relationship between the thickness of the Si transition layer and the diamond growth and the relationship between diamond film thickness and adhesion has been studied in detail.

Diamond and graphene are considered to be one of the most promising thermal interface materials (TIMs) for electronic devices benefited from their highest thermal conductivity in the natural world. However, orientated fabrication of high thermal conductivity diamond and graphene hybrid arrays with three dimensions (3 D) thermal conductive networks are still problematic. Here, we used a unique one-step microwave plasma chemical vapor deposition, n-butylamine, as the liquid source to prepare a novel high thermal conductivity 3 D vertical diamond/graphene (VDG) hybrid arrays films. The orientated 3 D thermal conduction path of the VDG is regulated by the growth temperature, and the through-plane thermal conductivity value of the VDG700 films up to 97 W m−1 K−1. In the actual TIM performance measurement, the system cooling efficiency with our VDG as TIM is higher than the state-of-the-art commercial TIM, demonstrating the superior ability to solve the inter-facial heat transfer issues in electronic systems.

Carbon, the fourth most abundant element in the Universe, possesses numerous allotropes with diverse bonding character (sp1-, sp2- and sp3-hybridized bonds) and structural motif of the constituting atoms. In particular, the carbon materials with a fully or nearly 100% sp3-hybridized strong C-C bonds often lead to excellent mechanical properties, chemical stability, thermal and optical properties, such as crystalline diamond and diamond-like amorphous carbon (DLC). In this review, we systematically summarize the synthesis, microstructure, mechanical properties, thermal and optical properties of ultrahard carbon materials with current experimental results on nano-polycrystalline diamond (NPD), nanotwinned diamond (NTD), micro-grained polycrystalline diamond (MPD), and amorphous diamond/carbon. In addition, we discuss the difference of spectra of XRD, Raman and EELS between various nanocrystalline diamond powder and ultrahard carbon materials. Finally, we provide our insights into the future development and applications in the research of ultrahard carbon bulk materials by high-pressure and high-temperature techniques according to the current advantages, limitations and challenges in the experiment.