Nanodiamonds (NDs) are mainly obtained by bursting or high pressure high temperature (HPHT) methods. They are usually encapsulated by a non-diamond shell, which leads to emission bursts and color-center instability. In addition, functional groups on the surface of oxygen- and nitrogen-containing particles lead to hard agglomerations.NDs can be obtained after high temperature, high pressure diamond pulverization, and they have sharp edges that scratch surfaces and contain metallic impurities in the working environment. Both techniques are time consuming. Other methods of preparing NDs include high-energy ball milling and laser shock waves.

Typically, CVD-prepared NDs nucleate directly on the substrate or crystal seed substrate, and the nucleation and growth processes occur continuously in the growth environment, leading to the easy formation of interconnections between particles. Considering independent particles, growth must be stopped before they come into contact, which leads to low yields. In addition, the particles are difficult to collect due to their strong adhesion to the substrate. Due to the limitations of these methods, new preparation methods must be developed. In a microwave plasma-assisted chemical vapor deposition (MPCVD) growth environment, diamond may be able to nucleate in the gas phase. However, the nucleation environment and growth mechanism have not been further investigated.

Recently, the Infrared Thin Films and Crystals Team of Harbin Institute of Technology (HIT) has used microwave plasma-assisted chemical vapor deposition (MPCVD) technology for gas-phase nucleation by regulating the plasma state, and prepared NDs with the advantages of high dispersion, high purity, controllable shape, and low defect density, which has greatly contributed to the competitiveness of the application of NDs in high-precision application fields.

The related research results have been published in Powder Technology under the title of “Vapor phase nucleation and sedimentation of dispersed nanodiamonds by MPCVD”, and have been awarded a patent of invention by China. Invention Patent.

/ graphic guide / 

Fig. 1. (a) Schematic of the OES and filter observation method for measuring plasma; (b) Schematic of the molybdenum tray; (c) Relative positions of the molybdenum tray and the molybdenum column.

Fig. 2. (a) Spatial distribution of Hα without MoC (b) Spatial distribution of Hα with MoC

Figure 3. (a) SEM of NDs prepared without MoC; (b-d) SEM & TEM of NDs prepared with MoC

Fig. 4. (a) Raman patterns of nanodiamond before and after the use of MoC; (b) XRD patterns of nanodiamond before and after the use of MoC; (c) nanodiamond dispersions

 

/ Application Prospects /

Currently, nanodiamond is used in precision polishing, electrochemistry (drug detection, sewage treatment, environmental monitoring, etc.), biomedicine (pharmaceutical skin care, biofluorescence imaging, drug transport, gene therapy, cancer diagnosis and treatment, etc.), quantum optics (single-photon light source) and other cutting-edge applications, by virtue of its high specific surface area, stable properties, wide electrochemical window, etc., modifiability of surface groups, stable color center, etc. Fields.

Figure 5. Ultra-sensitive in vitro HIV diagnostic test strips developed using the ultra-sensitive fluorescent labeling function of NV color cores within nanodiamonds.

Application environments require nanodiamonds with different morphologies. Nanodiamond with regular crystalline shape has a wide scope for development in quantum devices, biofluorescent labeling imaging, and quantum medical diagnostics because it can provide a high-quality environment for color centers.

Fig. 6. Surface modification of fluorescent nanodiamonds with specific binding to target substrates and signal-to-noise ratio of nanodiamonds combined with lock-in algorithm versus conventional gold nanoparticles

Spherical nanodiamonds not only have high specific surface area, stability and biocompatibility, but also do not scratch the surface of application objects, such as biological skin, blood vessels and precision devices, etc. They can be loaded and carried with drugs through chemical modification, which is of high value for applications in cosmetic skin care, drug transportation, targeted therapy and electrochemical monitoring and sensing.

/ summarize /

By designing the structure of the molybdenum tray, the researchers regulated the distribution of groups in the plasma to create gas-phase nucleation space for nanodiamond. The nanodiamond particles prepared by this method are purer compared with the explosion bombardment method and HPHT method, breaking through the limitations of nanodiamond yield and film morphology prepared by the traditional CVD method, and the particles not only have high yield, but also remain dispersed and have a high degree of crystallinity, which makes them highly competitive for applications in the fields of drug transportation, bio-imaging, and quantum light source, among others.

Original message：Liang Y, Liu K, Liu B, Li, Y, Fan, S, Dai, B, Zhang, Y, Zhu, J. Vapor phase nucleation and sedimentation of dispersed nanodiamonds by MPCVD[J]. Powder Technology 2024, 436.

https://doi.org/10.1016/j.powtec.2024.119507.

/ Related Patents /

Patent number：202210360654X

Invention name: A method for preparing nanodiamond particles with regular crystalline shape on Mo substrate

Abstracts:

A method for preparing nanodiamond particles with regular crystalline shape on Mo substrate, the present invention is designed to solve the existing problem of small quantity and irregular shape of nanodiamond obtained by preparing nanodiamond by CVD method with metal substrate. Method for preparing nanodiamond particles with regular crystal shape:

I. Cleaning the Mo sheet and Mo rest; 

ii. placing the Mo sheet in the chamber of the deposition system of the MPCVD device, placing the Mo rest on the Mo sheet, evacuating and then passing H2 and CH4, adjusting the microwave power, and carrying out vapor phase deposition to obtain the Mo sheet with nanodiamonds;

Third, the deposition system is closed, and after cooling, the Mo sheet with nanodiamond is put into deionized water for ultrasonication to obtain the nanodiamond dispersion. In the present invention, the plasma position was raised by the Mo torus to keep the plasma edge away from the Mo sheet and reduce the H plasma etching, and nanodiamond particles with regular crystalline shape were prepared and obtained on the Mo substrate.