Study on the growth characteristics of type Ⅰb silicon-doped diamond in FeNi catalyst under high temperature and pressure

Abstract

Silicon-related impurities are widely present in natural diamonds. Exploring the properties of silicon-doped diamonds provides vital guidelines for elucidating the composition of the mantle and the growth mechanism of natural diamonds. In this study, a high-capacity cubic high-pressure device was used to simulate the high-temperature and high-pressure environment for diamond growth. The regulation of transition-metal solvent catalyst (silicon) in the crystallization process, morphology, and impurity concentration of diamond crystals is reported. In a series of experiments, silicon powder was added to regulate its concentration in the diamond growth system. An Fe/Ni alloy was used as the catalyst, with a pressure of 5.8 GPa, a temperature range of 1600–1700 K, and a growth time of 12 h. As the silicon concentration increased, the diamond crystal displayed a slower growth rate, its color changed from yellow to light yellow, and the number of diamond inclusions gradually increased. The nitrogen concentration in the diamond crystals gradually decreased from 279 to 68 ppm, and nitrogen mainly existed in the form of single atoms (C-centers). Raman data showed that the Si-doped diamond crystal displayed a high-quality sp3 structure. The first-order Raman peak of the Si-doped diamond shifted from 1331.75 to 1331.18 cm−1, and its half-peak width increased from 4.18 to 5.41 cm−1. Silicon doping can increase the internal stress of the diamond crystal and decrease its crystalline quality. The X-ray photoelectron spectroscopy results of the diamond crystal indicated that silicon in the Fe–Ni–C–Si system entered into the diamond lattice. The photoluminescence spectroscopy results revealed that after silicon atoms entered the diamond lattice, crystal defects and more vacancies were formed. The vacancies combined with displaced nitrogen atoms to form nitrogen-vacancy centers. Moreover, this study provides guidelines for exploring the formation environment and morphology of natural diamonds.