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3. Chemically induced graphene to diamond transition: a DFT study

Author

Ke, Changcheng, Fan, Dong, Chen, Chengke, Guo, Difeng, Li, Xiao, Jiang, Meiyan, and Hu, Xiaojun

Subjects
Condensed Matter - Materials Science, Physics - Computational Physics
Abstract

The conversion of graphene into diamond is a new way for preparing ultrathin diamond film without pressure. Herein, we investigated the transformation mechanism of surface-hydrogenated bilayer graphene (SHBG) into surface-hydrogenated single-layer diamond (SHSLD) crystal, inserting fifteen kinds of single metal atoms without any pressure, by using the systematical first-principles calculations. Compared with the configuration without metal atom, SHBG can be transformed into SHSLD spontaneously in thermodynamics under the action of single metal atom, and its formation energy can even decrease from 0.82 eV to -5.79 eV under the action of Hf atom. According to our results, the outer electron orbits and atomic radius of metal atom are two important factors that affect the conversion. For the phase transition to occur, the metal atom needs to have enough empty d orbitals, and the radius of the metal atom is in the range of 0.136-0.159 nm. Through further analysis, we find that the p orbitals of carbon atoms and d orbital of metal atom in SHBG will be strongly hybridized, thereby promoting the conversion. The results supply important significance to experimentally prepare diamond without pressure through hydrogenated graphene., Comment: Corresponding author withdraws

Published
2021

7. Oxygen-assisted monodisperse transition-metal-atom-induced graphite phase transformation to diamond: a first-principles calculation study.

Author

Lu, Shaohua, Zhang, Xiongtao, Chen, Chengke, Jiang, Meiyan, Li, Xiao, and Hu, Xiaojun

Abstract

The low-pressure phase transformation of graphite to diamond has been confirmed with the help of a tantalum, hydrogen, and oxygen composited atmosphere in chemical vapor deposition. Subsequent theoretical calculations revealed the phase-transformation mechanism induced by a monodisperse transition-metal (TM) with an appropriate atomic radius (1.36–1.60 Å) and unfilled d-orbitals (d2s2–d7s2) on an H-terminated diamond substrate. However, the specific role of oxygen in TM-induced phase transformation remains unclear. Herein, we employed first-principles calculations to elucidate how oxygen assists the monodisperse TM in inducing ordinary-pressure phase transformation of graphite to diamond. Results show that the adsorption energy of the TM on the O-terminated diamond substrate was lower and the diffusion barrier was higher than that for its hydrogen counterpart, thereby effectively promoting their existence in a monodisperse state. These monodisperse TM atoms reduce the energy barrier of the phase transformation. This is attributed to the hybridization of unpaired electrons in the d-orbitals of the TM with the pz-orbitals of carbon, resulting in charge transfer within graphene from a horizontal to a vertical direction, leading to a transition from sp2-C to sp3-C. Specifically, TMs with the electronic configuration of d9s1, such as Au, have a weak role in phase transition on H-terminated diamond, while on O-terminated diamond, oxygen takes away the electrons of Au to generate more unpaired electrons that can bond to carbon, significantly promoting the phase transformation. For TMs with electronic configurations of d7s2 to d3s2, the bonding of their unpaired electrons to carbon is largely unaffected by oxygen; thus, oxidation has little influence on the phase transition. In the case of d2s2, oxygen takes away all the unpaired d-orbital electrons, thus preventing the TMs from bonding to carbon and providing no contribution to the phase transformation. Our findings offer guidance for the preparation of diamond based on graphite at ordinary pressure. [ABSTRACT FROM AUTHOR]

Published
2024
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16. CH4/(Ar–H2) plasma post-treatments produce nano-diamond aggregation and improvement in field emission properties of ultrananocrystalline diamond films.

Author

Chen, ChengKe, Zhang, Yizhong, Yeh, Chien-Ray, Jiang, Meiyan, Li, Xiao, Lu, Shaohua, Lin, I.-Nan, and Hu, Xiaojun

Subjects
*DIAMOND films, *FIELD emission, *ELECTRON field emission, *NANODIAMONDS, *CHEMICAL vapor deposition, *TANTALUM, *ELECTRON transport
Abstract

We performed the CH4/(Ar–H2) plasma post-treatments on ultrananocrystalline diamond films prepared by hot filament chemical vapor deposition. The results show that during the CH4/(Ar–H2) plasma treatment, 3–5 nm diamond grains agglomerate and regrow, and the graphite between the grains transformed into diamond due to the combined action of hydrogen and tantalum atoms in the samples. This produces bigger diamond grains in size of 200 nm with a large number of stacking faults formed during the grain aggregation, and the graphite phase is greatly reduced. Moreover, the electron field emission (EFE) performance of the films is significantly improved after the CH4/(Ar–H2) plasma treatment. This suggests that the improved EFE performance is not caused by the graphite phase, but by the diamond grains with lots of stacking faults that provide transport channels for electrons. This provides a method for enhancing the EFE properties of diamond films. [ABSTRACT FROM AUTHOR]

Published
2024
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17. Application of Nano-Crystalline Diamond in Tribology

Author

Xia, Yue, primary, Lu, Yunxiang, additional, Yang, Guoyong, additional, Chen, Chengke, additional, Hu, Xiaojun, additional, Song, Hui, additional, Deng, Lifen, additional, Wang, Yuezhong, additional, Yi, Jian, additional, and Wang, Bo, additional

Published
2023
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36. Design and optimization of diamond mid-infrared phase shifter

Author

Chen, Chengke, He, Zhi, Xu, Ancha, Li, Xiao, Jiang, Meiyan, Xu, Tao, Yan, Bo, and Hu, Xiaojun

Abstract

AbstractHerein, the mid-infrared (7.7–13.7 μm) diamond-based phase shifter was designed and optimized by finite-element analysis. The ridge-shaped diamond waveguide is designed and doped to form the internal p–n structure, and the internal carrier distribution is changed by applying forward and reverse voltages to change the effective refractive index to achieve the effect of π-phase shift. The results show that when p-doping concentration is 4 × 1017 cm−3and n doping concentration is 1 × 1018 cm−3, upon the reverse voltage (8 V) is applied, the change of the real part of effective refractive index (ΔR) is 1.6 × 10−5, and the length of the phase shifter (L) required to realize the π-phase shift is 241 mm; upon the forward voltage (–8 V) is applied, ΔR increases to 3.2 × 10−4, and the length of the phase shifter required is shortened to 12.03 mm. Such a short length is relatively easy in industrial production. In order to make the refractive index distribution more uniform, the carrier concentration has been optimized as 1 × 1017 cm−3for p-type and 4 × 1017 cm−3for n-type, respectively.

Published
2022
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