Liangchao Chen

New assembly design suitable for tower-shaped large size single-crystal diamond growth under high pressure and high temperature

During the synthesis of tower-shaped large size single crystal diamonds, a concave growth defect always occurs on the top surface of the diamonds when using the temperature gradient growth (TGG) method under high pressure and high temperature (HPHT) conditions. To explain the formation of these defects, we have analyzed experimental results, and performed theoretical calculations. Then, we designed a new assembly that is suitable for tower-shaped diamond growth. Compared to the traditional assembly, it can effectively eliminate the growth defects and provide a more suitable convection field for tower diamond growth. Simulation and experimental results confirm the effectiveness of the proposed design. The new assembly can be widely used in the industrial and commercial production of synthetic diamonds.

Method to eliminate the surface growth defects of large single crystal diamonds: an effective solution to improve the utilization rate for commercial production

In this work, a growth defect with bowl shaped pits has been found to form during the growth of a diamond, synthesized over a long period of time using the temperature gradient growth (TGG) method under high pressure and high temperature (HPHT) conditions. The experimental results show that the defect arises during the later growth stage of the diamond synthetic process. In order to explain the formation of the defect, the temperature and convection fields in the later growth state of the catalyst have been analyzed using the finite element method (FEM). The formation mechanism of the growth defect on the diamond crystal has been explained accurately by the simulated results and a good agreement has been obtained between the calculated results and the observed experimental data. Exhilaratingly, we propose a simple and efficient method to eliminate growth defects by adjusting the catalyst thickness. This method not only can improve the quality of large single crystal diamonds, but also may be helpful in reducing the cost of diamond cutting in the commercial market.

Significant improvement of multi-seed method of diamond synthesis by adjusting the lateral cooling water temperature

In this work, we use a multi-seed arrangement assembly with an annular carbon source to synthesize large single-crystals of diamond and investigate the influence of the external environment on the synthesis of diamonds by adjusting the lateral cooling water temperature under high pressure and high temperature conditions. The finite element method (FEM) is used to simulate the temperature and convection fields of the synthetic cavity. The simulation results show that the radial temperature distribution of the catalyst is uniform. In addition, the distribution of the convection field of the employed catalyst is also asymmetric. The asymmetric distribution of the temperature field and convection field could lead to the asymmetric consumption of carbon sources, and then lead to the asymmetric growth of the diamond crystals. Diamond synthesis experimental results proved the correctness of our simulation results.

Synthesis and characterization of NaAlSi 2 O 6 jadeite under 3.5 GPa

The high pressure and high temperature (HPHT) method is successfully used to synthesize jadeite in a temperature range of 1000 °C–1400 °C under a pressure of 3.5 GPa. The initial raw materials are Na2SiO3 9H2O and Al2(SiO3)3. Through the HPHT method, the amorphous glass material is entirely converted into crystalline jadeite. We can obtain the good-quality jadeite by optimizing the reaction pressure and temperature. The measurements of x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) and Raman scattering indicate that the properties of synthesized jadeite at 1260 °C under 3.5 GPa are extremely similar to those of the natural jadeite. What is more, the results will be valuable for understanding the formation process of natural jadeite. This work also reveals the mechanism for metamorphism of magma in the earth.

Synthesis and characterization of diamonds with different nitrogen concentrations under high pressure and high temperature conditions

In this study, {111}-oriented diamond crystals with different nitrogen concentrations were successfully synthesized in a series of experiments at 5.8 GPa pressure and 1380–1400 °C temperature. The nitrogen-vacancy (NV) centers were investigated in diamonds with different nitrogen concentrations. The Raman measurements indicated that the nitrogen atoms caused the Raman peaks to shift to a lower frequency. The photoluminescence (PL) results showed that the intensity of the negatively-charged nitrogen-vacancy (NV−) centers increased with the increase in the nitrogen content when the diamonds had low nitrogen content ( 372 ppm), the intensity of the NV− centers gradually decreased until it became undetectable. Additionally, we found that the neutral nitrogen-vacancy (NV0) centers were more common in diamonds with low nitrogen content. We believe that the results of this study provide a better understanding of the relationship between the nitrogen content and the NV centers in high pressure and high temperature (HPHT) synthetic diamonds.

Studies on the HPHT synthesis and N defects of N-rich B-doped diamonds

In this paper, high-quality N-rich single crystal diamonds with different boron additive contents were synthesized in NiMnCo alloy with high Ni content by the temperature gradient growth method under HPHT (high pressure and high temperature) conditions. The C, A and N+ centers were present in synthetic crystals simultaneously, and the evolution of different N defects versus the boron additive contents was discussed. Infra-red absorption spectroscopy results showed that with increasing content of boron additive in the growth system, the intensity of 1332 cm−1 peak related to N+ center (substitutional nitrogen atom with a positive charge) increased, and the concentrations of C center, A center and total N impurity decreased gradually. Moreover, the Raman results indicated higher crystallinity of N-rich B-doped diamond with increasing boron additive due to the formation of B–N bond in the lattice. Diamonds presented characterizations of p-type semiconductors with further increase in B additive content. However, the Hall mobility was extremely low due to scattering caused by abundance of N defects.

Synthesis and characterization of diamonds using C3H5N3O as an organic additive under high pressure and high temperature

In the NiMnCo–C system, diamond single crystals have been successfully synthesized by adding C3H5N3O as an organic additive under 5.5–6.2 GPa and 1280–1320 °C. The synthesized diamonds are initially characterized using OM, SEM, FTIR, Raman, XPS and powder XRD. With the increase of the C3H5N3O content, the color of diamonds changes from light yellow to green. The FTIR spectra of the diamond synthesized indicate that its nitrogen concentration increases with the increase of the C3H5N3O additive. The typical oxygen and hydrogen related peaks appear and the absorption intensity increases with addition of C3H5N3O. The Raman spectrum and XRD spectrum show synthesized diamonds with a good quality phase of crystallization. The XPS results again confirmed that oxygen, hydrogen and nitrogen related impurities exist in the diamond. It is meaningful to provide reference data to further recognize the composition of the natural diamond growth environment.