Since the advent of the chemical vapor deposition (CVD) diamond film 1980s, Chinese researchers quickly follow up in a short time from the national level layout. In the era when China’s science and technology need to catch up, the implementation of the “863 Program” has strongly promoted the progress of the CVD diamond film technology in China from 1987 to 2016. Until now, the national key research and development program is still supporting the application research of CVD diamond in various fields. The review of the development of CVD diamond film in the past 30 years has important reference significance for the design of science and technology strategy, the formulation of science and technology policy, the implementation of scientific research plan and the implementation of scientific and technological achievements in China.

Chemical vapor deposition (CVD) technology has enabled synthetic diamonds to be applied in many fields, in which the excellent comprehensiveness of diamond has been fully developed, and may lead to a leap-forward development. The color center makes the diamond quantum accelerator initially show the feasibility of great power. Various scenarios, including the application of UV laser writing technology windows, maximize the comprehensive advantages of diamond windows in terms of optics, electricity, heat and mechanics. Ultra-wide bandgap diamond semiconductor applications will soon be realized, and diamond heat dissipation applications are constantly expanding. By summarizing the preparation methods and characteristics of CVD diamond, according to the intrinsic characteristics of diamond, CVD diamond is classified into quantum grade, electronic grade, optical grade, thermal grade and mechanical grade. The current status of research and application of CVD diamond are reviewed in detail, which is of great significance for judging the future development trend of CVD diamond.

As the Ⅲ-Ⅴ binary compound with the face-centered cubic structure of sphalerite, cubic boron nitride (c-BN) exhibits the largest band gap as one of the typical third-generation semiconductors, as well as other excellent properties including high thermal conductivity, high hardness, high-temperature oxidation resistance, chemical stability, wide range of light transmission wavelength, and can be both doped into p-type or n-type. It can be not only widely used as a superhard materials in the processing fields of various industries, but also has potential applications value as extreme electronics materials in high-power semiconductor and optoelectronic devices, making it suitable for extreme environments such as high temperature, high power, high pressure, high frequency and strong radiation. This article reviews the development of c-BN crystal preparation and epitaxial growth of c-BN thin films in recent years, focusing on the progress of growth technology and the improvement of crystal quality, as well as their mechanical, optical and electrical properties. Finally, the paper summarizes the content of the paper and prospects the challenges of c-BN application.

MEMS, deep space and deep sea exploration tasks put forward higher requirements for long-term and portable power supply. Due to its high energy density and stable power output, isotopic battery can continuously provide energy for Lunar Rover and seabed detector in extreme environments such as high and low temperature and no sunlight. As the main type of isotope battery, radio-voltaic effect isotope battery has been widely studied because of its high theoretical energy conversion efficiency and easy miniaturization, and it has been successfully applied to cardiac pacemaker. The isotope battery made of energy converters using semiconductor with wide band gap can obtain higher energy conversion efficiency. The 5.5 eV band gap and radiation resistance of single crystal diamond make it the best choice for making energy converters for radio-voltaic effect isotope batteries. With the development of chemical vapor deposition technology, the epitaxial technology of diamond crystal has made rapid progress, which has laid a material foundation for the development of diamond semiconductor devices. The characteristics of common semiconductor materials for energy converters and radiation source materials for isotopic battery are compared in this paper, the basic principle of radio-voltaic effect is introduced, then the key parameters of radio-voltaic effect isotopic battery is analyzed, and the literatures on the research of diamond radio-voltaic effect isotopic battery are summarized. The development status and existing problems of diamond isotope battery are pointed out. By analyzing the current performance and application of hetero pn junction composed of diamond and other n-type semiconductor materials, the structural design of high-performance isotope battery based on diamond hetero pn junction is given, summarized and prospected.

Owing to their small volume, strong radiation resistance and fast time response, diamond detectors show the obvious advantage of application in nuclear radiation area. At early stage, diamond nuclear radiation detectors were made of natural diamond materials. With the development of chemical vapor deposition (CVD) diamond synthetic technology, the development and application of diamond radiation detector has been greatly promoted. In this paper, starting with the CVD synthetic diamond material, the impurities and defects that restrict the performance of diamond detectors, the synthetic process of CVD diamond, the characterization method of impurities and defects in detector grade diamond are analyzed systematically. Based on the performance indicators such as the product of carrier mobility and life, the charge collection efficiency of detector, etc., the effects of impurities and defects in CVD diamond on the performance of the detector are summarized. The application status of diamond nuclear radiation detectors abroad is introduced and the development prospect of domestic diamond nuclear radiation detectors is also viewed.

Diamond is a superhard and multi-functional material with excellent properties. Synthetic diamond can own unique properties by doping. Boron-doped diamond has both conductive characteristics of p-type semiconductor and excellent physical and chemical properties. It has wide application value in national defense, medical treatment, exploration, scientific research and other fields. Based on boron-doped diamond and boron co-doped diamond single crystals synthesized by high pressure and high temperature (HPHT) method in our laboratory, the synthesis and properties of boron-doped diamond, boron-hydrogen co-doped diamond and boron-nitrogen co-doped diamond are discussed. The influence of different additives on the synthesis properties of the synthetic diamonds through the optical and electrical characterization are analyzed, which provides some ideas for further synthesizing high-performance semiconductor diamonds.

Diamond as an ultra-wide band gap semiconductor material shows excellent properties in thermal conductivity, carrier mobility and breakdown field strength, and has broad application prospects in the field of power electronics. The realization of p-type and n-type conduction is essential to fabricate diamond electronic devices. Between them, the development of p-type diamond is relatively mature, and boron is the mainstream doping element. However, the hole mobility decreases rapidly at a high doping concentration. The main doping element of n-type diamond is phosphorus. At present, there are still challenges such as deep impurity level, large ionization energy, and defects in diamond crystals after doping, resulting in low carrier concentration and mobility, and the resistivity is difficult to meet the requirements of devices. Therefore, the realization of high quality p-type and n-type diamond has become the focus of researchers. This paper mainly introduces the unique physical properties of single crystal diamond, outlines the basic principles and key parameters of the chemical vapor deposition method and ion implantation method of doping, then reviews the research progress on the p-type and n-type doping of single crystal diamond films by the two methods, systematically summarizes the facing problems and the prospects of future development.

Nanodiamonds have shown excellent mechanical properties, thermal conductivity, biocompatibility and structural tunability, and have been widely demonstrated their application in the fields of composite materials, electrochemistry, catalysis, medicine and so on. In industry, the mass production of nanodiamonds by detonation method provides a foundation for their application. Due to the complex surface structure of nanodiamonds, precise control is required to achieve the target performance and the research on surface functionalization is of great practical significance. This review firstly introduces various surface modification methods of nanodiamonds, then focuses on the impact of surface functionalization research on the application of nanodiamonds in mechanical properties, catalytic properties and biomedical fields, and finally prospects the future research direction of nanodiamonds.

In this paper, doping, electric conductivity, field emission and electrochemical properties of nanocrystalline diamond films are reviewed, which contain n-type nanocrystalline diamond (NCD) films prepared by chemical vapor deposition, improvement of n-type electrical conductivity in NCD films by ion implantation, excellent field emission properties of NCD films prepared by metal ion implantation, high mobility n-type conductivity obtained by low dose ion implantation and oxygen termination on grain surface, regulation of the structure of NCD/graphene and its influence on electrical and electrochemical properties, microstructure and electrochemical regulation of boron-doped NCD film electrodes and so on. It shows through comprehensive analysis that grain doping and surface/interface coordination can improve the electrical properties, field emission properties and electrochemical properties of thin films, which has important application prospects in the fields of diamond-based nano-electronic devices and electrochemical electrodes.

Functional materials with highly desirable properties have been highly pursued for a long time due to their potential applications in many fields. High pressure can effectively reduce the interatomic distances and modulate the bonding patterns of materials without changing their chemical compositons, which has been considered as a powerful and important approach to design new functional materials with desired structures and properties. Many interesting types of functional carbon materials, such as optical transparent carbon, super strong and elastic carbon, and ultrahard bulk amorphous carbon have been obtained from different carbon precuresors under high pressure. Recent progress on the high pressure research of low dimensonal carbon composite materials are introduced. Based on the predesigned carbon-based precursors, new carbon materials with superhard properties, covalent polymerization and anomalous photoluminescence enhancement by the application of high pressure have been obtained.

Transition metal light elements compounds (TMLEs) are a kind of robust functional materials due to high hardness, high melting point, superior conductivity, magnetic properties, and superconductivity. And high hardness allows TMLEs can be used in extreme evironment. While, synthesizing TMLEs need high pressure and high temperature (HPHT) conditions to overcome the energy barrier. Although many TMLEs were synthesized by HPHT, the growth mechanism is still mysterious. Summary of TMLEs synthesized by HPHT is significant to understand the growth process and developing of new TMLEs. In this work, the TMLEs synthesized by HPHT which include our groups research experience and other relevant literatures are summarized. The TMLEs include transition metal borides (TMBs), transition metal carbides (TMCs), and transition metal nitrides (TMNs). The starting materials, experimental conditions, and morphologies etc. are analyzed. It can be found that proportion of starting materials and the suitable temperature are very important to obtain the single phase of TMBs; the boron subunit in TMBs is related to growth kinetics, which induces step growth process; choosing different starting materials of carbon and nitrogen will define the growth process of TMLEs. Synthesizing single crystal with millimeter size in the future is meaningful to understand the basic properties of TMLEs. And study the new structure of TMLEs which has high of light elements is still urgent. With developing of new materials, TMLEs will be a kind of irreplaceable robust materials in the future.

The breakthrough of high quality and high efficiency diamond doping is the premise of realizing high-performance diamond power electronic devices. In this paper, the homoepitaxial growth of high-quality boron doped single crystal diamond was prepared by MPCVD with trimethylboron as the source gas. The surface roughness is 0.35 nm, the full width at half maximum (FWHM) of XRD (004) rocking curves is 28.4 arcsec, and the FWHM of Raman spectrum is 3.05 cm-1. By changing the boron concentration in the gas component, the controlled p-type diamond doping with the concentration from 1016 cm-3 to 1020 cm-3 was realized. Then, the effects of deposition conditions such as B/C ratio, growth temperature and methane content on the electrical properties of p-type diamond were studied. The hole mobility of 207 cm2/(V·s) has been obtained with the B/C ratio of 20×10-6, the growth temperature of 1 100 ℃, the CH4/H2 ratio of 8% and the chamber pressure of 160 mbar. Furthermore, the crystal quality of boron doped diamond can be improved with the adding of oxygen in the gas component, that is to say, reducing the impurity scattering. When the O2/H2 ratio is 0.8%, the hole mobility increases significantly to 614 cm2/(V·s).

Single crystal diamond film has been developed as high efficiency thermal management substrate, which has a promising potential in the field of wide bandgap semiconductor electronic devices. However, the slow production yield and rough surface of diamond film grown by microwave plasma chemical vapor deposition (MPCVD) make it unavailable as the substrate for semiconductor devices. In this work, single crystal diamond films were grown by MPCVD step by step, of which the growth rate was compared and the surface morphology and crystal quality was estimated by photos, XRD, AFM and Raman measurements. High-speed single crystal epitaxial diamond layer which could reach 20 μm/h with smooth surface was acquired by two-step growth technique of adjusting methane concentration. It is beneficial to solve the problems of rough surface morphology and processing difficulties of diamond epitaxial films in the subsequent fabrication of related electronic devices, so as to support the development of high power electronic devices.

2022-02-25

Nanodiamond combines the properties of both nanomaterials and diamond materials, resulting in different characteristics from that of micron and bulk diamond. In this work, the structure, optical properties and thermal stability of diamond samples with different sizes were studied by scanning electron microscopy, X-ray diffraction, spectroscopy techniques and thermogravimetric analysis. The results show that the sizes of three samples are 300 μm, 30 μm and 100 nm, respectively. Diamond samples with larger size present better crystal quality, and are confirmed to be Ⅰb type diamond because single nitrogen impurities are observed. In contrast, the crystallinity of nanodiamond samples is poor, and residual graphite is detected in nanodiamond samples from both XRD and Raman results. In addition, H2O, N—H and C—H bonds are observed in nanodiamond, suggesting there may be many organic reactive groups on surface. Two emission peaks are observed in both samples of 300 μm and 30 μm, originated from two types of nitrogen vacancy defects with neutral and negative charge respectively. In contrast, no emission is observed for nanodiamond because of fluorescence quenching from nonradiative center originated from organic groups and surface defects in the nanodiamond. Diamond samples with large size have the intensive absorption in the range from 300 nm to 525 nm, while the nanodiamond sample show strong absorption in the entire UV-visible-NIR region resulting in much lower transmittance. With the decrease of particle size, both the initial oxidizing temperature and oxidizing rate gradually decline. As a result, larger size samples have better thermal stability.

In this paper, the low-temperature Raman and photoluminescence (PL) spectroscopy were employed to study the crystallization degree, stress distribution of the pure diamond film. Combined with electron irradiation and rapid annealing, the impurity defect structure of the pure diamond film was studied. Raman spectroscopy analysis shows that the stress distributions in edge and surface of the film are higher than in interior, which may be ascribed to the diamond growth mechanism, physical cutting and polishing damage to the films. The zero phonon lines in PL spectra show obvious temperature dependent, and the spectra peaks redshift, intensity reduction and low-temperature splitting with increase of temperature were explained by Jahn-Teller effect and electron-phonon coupling theory. Low temperature PL spectra observed distinct NV defects in the film after electron irradiation and 700 ℃ annealing，which indicate that the nitrogen mainly existed in the lattice with a form of substitution impurities.

To better understand the influence mechanism of transition metal elements (Ti, V, Ni, Mo) on the nucleation of chemical vapor deposition (CVD) diamond coating, the intrinsic mechanism of the CH3 adsorption on impregnated diamond cemented carbides through geometry, interaction energy, Mulliken charge distribution, visualization of the interactions, charge density difference and density of state (DOS) were investigated theoretically. All the calculations were performed by density functional theory. The calculated results indicate that diamond surface doped with Ti/V/Ni/Mo, rather than pure diamond surface, exhibits stronger interactions. The adsorption capacity is related to the valence electron structure of each atom, and the surface doped with Ti has the most stable adsorption capacity. The charge transfer between CH3 and Ni is more easier to form covalent bond, Mo is beneficial to promote the dehydrogenation reaction of CH3. Ti, V, Ni and Mo are conducive to increasing the nucleation density and improving the strength of CVD diamond coating.

Due to its excellent physical properties, diamond is regarded as a next-generation semiconductor material. However, its extremely high hardness, brittleness, and corrosion resistance cause the diamond difficult to process, especially for large-size chemical vapor deposition (CVD) single crystal diamonds (SCD). Currently, researchers have not explored an efficient and low-cost method for ultra-precision processing diamond wafers. Based on the rotary infeed surface grinding, integrated processing technology of grinding and polishing by the concentric double grinding wheel was proposed in this paper. In one clamping, the SCD surface is flattened by the inner ring ceramic grinding wheel that the abrasive is diamond, and then the surface after grinding is polished by sol-gel (SG) polishing wheel that the abrasives are diamond mixed with CuO. In the processing of grinding and polishing integration, the surface roughness of SCD can be reduced from about 46 nm to less than 0.3 nm in a short time. In the grinding, the ceramic grinding wheel with diamond abrasive scratches the SCD surface at high speed. The strong mechanical action causes the large material removal, obtains nano-level smooth surface of SCD, and causes the surface amorphization. In the SG polishing, the diamond abrasive scratches the SCD surface at high speed to form a high-temperature and high-pressure environment, which further induces the oxidation-reduction reaction between the CuO powder and the amorphous carbon for realizing reactive polishing. The integrated processing technology of grinding and polishing provides a reference for the industrial production of SCD wafers and polycrystalline diamond (PCD) wafers in the future.