Structure and properties of a chiral polymorph of diamond with a crystal lattice of the SA3 type

At a Glance

Metadata	Details
Publication Date	2021-12-01
Journal	Letters on Materials
Authors	V. A. Greshnyakov, E. A. Belenkov
Institutions	Chelyabinsk State University
Citations	3
Analysis	Full AI Review Included

Technical Analysis and Documentation for 6CCVD: Chiral SA3 Diamond Polymorph

Executive Summary

This study, analyzed using Density Functional Theory (DFT), confirms the structural stability and wide-gap semiconductor properties of a hypothesized chiral diamond polymorph, SA3. This phase, potentially synthesized via the polymerization of carbon nanotubes, represents a high-potential material for next-generation nanoelectronics and ultra-hard coatings.

Novel Material Potential: SA3 is confirmed as a stable, wide-gap semiconductor with a direct minimum band gap of 4.56 eV, positioning it favorably for extreme environment electronics (HT/HF).
Structural Characteristics: The SA3 phase exhibits a stable hexagonal crystal structure (P6₁22/P6₅22) with a cohesive energy only 9.1% less than standard cubic diamond (3C).
Thermal Stability Verified: Molecular Dynamics modeling at 300 K confirms the structural stability of the SA3 phase under normal operating conditions.
Experimental Identification Roadmap: The research provides specific, calculated signatures for unambiguous experimental verification using Powder X-Ray Diffraction (PXRD), Raman Spectroscopy (5 distinct peaks), and X-ray Absorption Spectroscopy (XAS).
6CCVD Critical Role: Replication or extension of this research requires extremely high-purity MPCVD substrates (SCD or PCD) for precursor deposition (e.g., carbon nanotubes or graphene layers) or as transparent anvils for high-pressure synthesis experiments.
Supply Chain Advantage: 6CCVD offers the custom thickness, large area, and metallization services necessary to support advanced synthesis techniques (e.g., thin film SA3 identification via XAS).

Technical Specifications

Data extracted from Greshnyakov and Belenkov (2021) regarding the theoretical SA3 diamond polymorph.

Parameter	Value	Unit	Context
Crystal Structure	Hexagonal	N/A	Space Groups P6₁22 or P6₅22
Lattice Parameter (a)	0.40696	nm	Hexagonal unit cell
Lattice Parameter (c)	0.24779	nm	Hexagonal unit cell
Atoms per Unit Cell	6	Carbon atoms	Primitive hexagonal cell
Cohesive Energy	0.525	Rydberg/atom	9.1% less than cubic diamond
Thermal Stability	Stable	N/A	MD simulation at 300 K for 7 ps
Minimum Direct Band Gap	4.56	eV	Wide-gap semiconductor properties
Polymorph Comparison	1.05	eV	Direct gap is 1.05 eV lower than cubic diamond
Raman Shift Range (Peaks)	660 to 1210	cm^-1	Five distinct peaks for unambiguous identification
XAS Photon Energy Range	290 to 315	eV	Range where spectrum differs significantly from 3C diamond and graphite
PXRD Interplanar Distances (d)	0.35244	nm	Most intense maximum (100)
PXRD Interplanar Distances (d)	0.20309	nm	Intense maximum (101)

Key Methodologies

The theoretical structure and properties of the SA3 polymorph were determined using ab initio calculations based on Density Functional Theory (DFT).

Computational Framework: DFT calculations utilized the Quantum ESPRESSO package.
Approximation: Calculations employed the Generalized Gradient Approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional.
Pseudopotential: Norm-conserving Troullier-Martins pseudopotentials were used to model core-valence interactions.
Brillouin Zone Integration: A $12 \times 12 \times 14$ k-point mesh was used for the primitive hexagonal cell structure calculations.
Cut-off Energy: Kinetic energy cut-off was set at 60 Rydberg.
Structural Relaxation Criteria: Relaxation continued until the force on any single atom was less than 15 meV/nm and internal stress was less than 50 MPa.
Stability Testing (MD): Thermal stability was tested using Molecular Dynamics (MD) modeling of a 24-atom supercell at 300 K over 7 ps.
Spectroscopic Calculation: PXRD was calculated using the standard method (Cu-K$_{a1}$ wavelength: 0.15405 nm), Raman spectra using methodology detailed in Reference [13], and XAS using a $2 \times 2 \times 3$ supercell methodology detailed in Reference [14].

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational and specialized diamond materials required to experimentally synthesize, test, and apply novel diamond polymorphs like SA3.

Applicable Materials

The synthesis of highly controlled carbon polymorphs, often requiring high-pressure processing or deposition on ultra-pure surfaces, demands the best available diamond materials.

Research Requirement	6CCVD Material Solution	Specification Match
High-Pressure Synthesis Window	High Purity SCD (Single Crystal Diamond) Plates	Excellent optical transparency (necessary for laser heating/Raman/XAS monitoring in DACs) and maximum mechanical robustness.
Precursor Substrates	Optical Grade SCD or Electronic Grade PCD	Highly polished surfaces (Ra < 1 nm for SCD, Ra < 5 nm for PCD) are critical for uniform deposition and polymerization of precursors (nanotubes, graphene layers).
Thin Film Fabrication (XAS/RAMAN Testing)	PCD or SCD Wafers (0.1 µm minimum thickness)	The ability to synthesize and analyze thin SA3 films requires high-quality, ultra-thin diamond substrates for transmission spectroscopy.
Large-Area Scalability	Polycrystalline Diamond (PCD) Wafers	Available in diameters up to 125 mm, ideal for scaling up experimental synthesis if the SA3 phase proves viable for industrial coating or electronic applications.

Customization Potential

Experimental validation of new polymorphs often requires unique component geometries and measurement setups. 6CCVD’s specialized engineering services directly support advanced synthesis and characterization projects.

Custom Dimensions: 6CCVD manufactures wafers and plates up to 125 mm in diameter (PCD), enabling large-scale synthesis attempts or the creation of large sample sizes for bulk material studies.
Precision Thickness Control: We offer precise control over layer thickness, from 0.1 µm films (SCD/PCD) required for characterization techniques like XAS/Raman on thin films, up to 10 mm substrates for high-pressure apparatus.
Surface Preparation: Achieving the optimal starting surface for precursor materials (e.g., carbon nanotube bundles or graphene sheets) is crucial. We guarantee superior surface polishing: Ra < 1 nm (SCD) and Ra < 5 nm (Inch-size PCD).
Metalization Services: While SA3 research is foundational, potential future device applications would require electrode integration. 6CCVD provides in-house custom metalization stacks, including Au, Pt, Pd, Ti, W, and Cu, suitable for prototyping electronic devices based on wide-gap SA3 films.
Global Logistics: We provide reliable global shipping solutions (DDU default, DDP available) to ensure rapid delivery of mission-critical materials worldwide.

Engineering Support

6CCVD maintains an in-house team of PhD-level material scientists and engineers specializing in MPCVD diamond growth and application development. Our team is available to assist researchers in selecting the optimal diamond substrate purity, dimension, and surface quality needed to successfully replicate or extend synthesis attempts of highly complex polymorphs like SA3.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

An ab initio study of a chiral polymorphic type of diamond (SA3), in which all atoms are in crystallographically equivalent states, was carried out. The calculations of the structure and properties were performed using the density functional theory method in the generalized gradient approximation. The crystal structure of the SA3 diamond polymorph can be formed during the polymerization of close-packed chiral carbon nanotubes (5, 4). The SA3 phase has a hexagonal unit cell with parameters a = 0.40696 nm and c = 0.24779 nm, which contains six carbon atoms. The crystal lattice of the SA3 diamond polymorph belongs to the space symmetry group P6122 (P6522). The cohesive energy of the SA3 phase is 0.525 Rydberg / atom, which is only 9 % less than the cohesive energy of cubic diamond. Molecular dynamics modeling showed that the structure of the SA3 phase should be stable under normal conditions. The chiral diamond polymorph can exhibit the properties of a wide-gap semiconductor, since its minimum direct band gap is 19 % less than the corresponding value for diamond. The SA3 diamond polymorph can be unambiguously identified experimentally using diffraction and spectral analysis methods. It is found that the calculated powder X-ray diffraction pattern of this phase is characterized by the five most intense maxima, which correspond to the following interplanar distances: 0.35244, 0.20309, 0.17622, 0.14361, and 0.11740 nm. The X-ray absorption spectrum of the SA3 phase differs significantly from similar spectra of diamond and graphite in the photon energy range from 290 to 315 eV. The calculated Raman spectrum of the chiral phase contains five peaks in the range of wavenumbers from 660 to 1210 cm−1; therefore, the identification of the SA3 phase should not cause difficulties.

Tech Support

Original Source

DOI: https://doi.org/10.22226/2410-3535-2021-4-479-484