Phonon spectra of clean and Ni-terminated diamond (111) surfaces: An ab-initio study
Graphical abstract
Introduction
Growth of diamond has attracted a great deal of interest due to its technological importance in a wide range of applications, such as machine tools, optical coatings, high-temperature electronics, and next-generation power devices [[1], [2], [3], [4], [5], [6]]. The C(111) surface in diamond is a growth surface and natural cleavage plane with lower surface formation energy than other surfaces. Its surface structure is known to play an important role in determining the morphology and quality of the growing diamond, as well as many other physical properties [[7], [8], [9]]. Although the detailed atomic geometry of the reconstructed clean C(111) surface is still controversial, most experimental and theoretical studies [10,11] support the Pandey π-bonded 2 × 1 chain model of C(111) [Fig. 1(c)]. The sp2 surface bonding character in the π-bonded chain model of 2 × 1 reconstructed C(111) would prevent C adatoms from making sp3 bonds for the growth of diamond, instead promoting the growth of undesired graphite.
To overcome this obstacle to diamond growth, diamond synthesis has typically been conducted using catalytic metals such as Fe, Ni, and Co [12,13]. Until recently, Ni has been the main catalytic metal element used [[14], [15], [16], [17], [18]]. In previous work, we theoretically studied the microscopic role of catalytic metal Ni in the growth of diamond through ab-initio total-energy and electronic-structure calculations [19]. The results showed that surface Ni atoms can enhance the formation of a thermodynamically stable Ni–C interface with a diamond bulk-like 1 × 1 structure, which is essential for the formation of sp3-bonded carbon in diamond. Further investigations showed that this feature originates from (i) strengthening of the C2–C3 bond, (ii) the covalent-like interaction of Ni with the dangling bond of the interfacial C1 atom in 1 × 1 Ni/C(111), and (iii) weakening of the π-bond in the Pandey chain structure of 2 × 1 Ni/C(111) (Fig. 1). These findings provide a good explanation for the efficacy of Ni as a catalyst for diamond growth.
Despite these studies, experimental information on the structures, bonding, and dynamics of Ni/C(111) surfaces remains limited. In particular, surface vibrational measurements are very useful for studying diamond surfaces. There have been no experimental or theoretical works on the vibrational properties of the growth surfaces of diamond in the presence of catalytic metal Ni. In this study, the phonon densities of states (ph-DOSs) of clean and Ni-terminated C(111) surfaces with 1 × 1 and 2 × 1 surface structures were studied by conducting ab-initio calculations based on density functional perturbation theory (DFPT) [20,21]. The calculation revealed discernible features in the vibrational spectra of the C(111) and Ni/C(111) surfaces depending on the surface and interface structures. This could play a significant role in experimentally verifying the atomic structures at Ni/C(111), as well as understanding the microscopic mechanism of the catalytic metal (Ni) in diamond growth.
Section snippets
Computational method
All calculations were performed using the plane-wave pseudopotential method within the framework of spin-unpolarized density functional theory (DFT), as implemented in the Vienna Ab-initio Simulation Package (VASP) code [22,23]. For the exchange-correlation interactions of electrons, the Perdew-Burke-Ernzerhof (PBE) formulation within the generalized gradient approximation (GGA) was used [24]. The pseudopotentials for electron-ion interactions were described using the projector augmented-wave
Phonon DOSs
We calculated the phonon spectra from the geometry-optimized atomic structures of C(111) and Ni/C (111). Fig. 2 shows the simulated ph-DOS for the 1 × 1 and 2 × 1 models of C(111) and Ni/C(111), where the phonon eigenvalues were broadened using a Gaussian function of width 30 cm−1. The phonon spectra of the clean C(111) surfaces are the projected ph-DOS of the three upper C layer atoms of the model slab, whereas the projected ph-DOS of the Ni/C(111) surfaces also include the surface Ni layer
Summary
Using DFPT calculations, we investigated the ph-DOS of clean and Ni-terminated C(111) surfaces with 1 × 1 and 2 × 1 surface structures. For the 1 × 1 clean C(111) surface, the ph-DOS showed three bands in the regions of 200–400, 400–1000, and 1000–1400 cm−1. The ph-DOS peaks were positioned at 360, 690, and 1240 cm−1, respectively. The ph-DOS of 1 × 1 Ni/C(111) showed an intense band and a broad band with respective peaks at 150 and 1200 cm−1. The ph-DOS of 2 × 1 C(111) showed two bands, whose
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was partially supported by Global Frontier Program through the Global Frontier Hybrid Interface Materials (GFHIM) of the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIT) (No. NRF-2013M3A6B1078874), the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2020R1A5A6017701), and BK21PLUS SNU Materials Division for Educating Creative Global Leaders (21A20131912052).
References (29)
- et al.
Wear resistance and thermal stability enhancement of PDC sintered with Ti-coated diamond and cBN
Int. J. Refract. Metals Hard Mater.
(2020) - et al.
Thermal stability of polycrystalline diamond compact sintered with boron-coated diamond particles
Diam. Relat. Mater.
(2020) - et al.
Effect of surface termination on the reactivity of nano-sized diamond particle surfaces for bio applications
Carbon
(2018) - et al.
Adhesive transfer at copper/diamond interface and adhesion reduction mechanism with fluorine passivation: a first-principles study
Carbon
(2018) - et al.
Effects of Fe-Ni solvent with different Fe contents on the boron concentration in colorless diamonds
J. Cryst. Growth
(2018) - et al.
Efficient phosphorescence from synthetic diamonds
Carbon
(2018) - et al.
Beyond-carbon-solvency effects of catalytic metal Ni on diamond growth
Diam. Relat. Mater.
(2020) - et al.
Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set
Comput. Mater. Sci.
(1996) - et al.
First principles phonon calculations in materials science
Scripta Mater.
(2015) - et al.
Surface vibrational studies of CVD diamond
Diam. Relat. Mater.
(1995)