The team of Professor Xiaojun Hu of Zhejiang University of Technology innovatively "recreated" the growth process of chemical vapor deposition diamond, and turning "stone" into "diamond" under low pressure, providing a new strategy and theory for the synthesis of large-area diamonds in accordance with.

The results were reported online in the latest issue of the Proceedings of the National Academy of Sciences(PNAS) on April 13, 2022. Zhejiang University of Technology is the sole correspondent of the article, Prof. Xiaojun Hu is the sole corresponding author, and team members Dr. Meiyan Jiang and Dr. Chengke Chen are co-first authors.

Significance

Artificial diamond plays a vital role in the manufacturing industry, jewelry, and future photoelectronic devices, but it is a key challenge to prepare the required large-area diamonds. A distinctive way to solve this problem possibly hides in the undiscovered formation mechanism of thermodynamically metastable diamond compared to graphite in low-pressure chemical vapor deposition. We design a series of short-term growth on the margins of cauliflower-like nanocrystalline diamond particles and find that diamond is formed by the transformation from graphite, not by the piling up of sp3 carbon. Atomically dispersed Ta atoms let the transition spontaneously occur. This subverts the general knowledge and supplies a way to prepare large-area diamonds based on large-sized graphite under normal pressure.

Abstract

It is a key challenge to prepare large-area diamonds by using the methods of high-pressure high-temperature and normal chemical vapor deposition (CVD). The formation mechanism of thermodynamically metastable diamond compared to graphite in low-pressure CVD possibly implies a distinctive way to synthesize large-area diamonds, while it is an intriguing problem due to the limitation of in situ characterization in this complex growth environment. Here, we design a series of short-term growth on the margins of cauliflower-like nanocrystalline diamond particles, allowing us to clearly observe the diamond formation process. The results show that vertical graphene sheets and nanocrystalline diamonds alternatively appear, in which vertical graphene sheets evolve into long ribbons and graphite needles, and they finally transform into diamonds. A transition process from graphite (200) to diamond (110) verifies the transformation, and Ta atoms from hot filaments are found to atomically disperse in the films. First principle calculations confirm that Ta-added H- or O-terminated bilayer graphene spontaneously transforms into diamond. This reveals that in the H, O, and Ta complex atmosphere of the CVD environment, diamond is formed by phase transformation from graphite. This subverts the general knowledge that graphite is etched by hydrogen and sp3 carbon species pile up to form diamond and supplies a way to prepare large-area diamonds based on large-sized graphite under normal pressure. This also provides an angle to understand the growth mechanism of materials with sp2 and sp3 electronic configurations.

Click to view original article:https://doi.org/10.1073/pnas.2201451119