Raman evidence for pressure-induced formation of diamondene

At a Glance

Metadata	Details
Publication Date	2017-07-14
Journal	Nature Communications
Authors	Luiz G. P. Martins, Matheus J. S. Matos, Alexandre Rocha Paschoal, Paulo Freire, N. F. Andrade
Institutions	Universidade Federal de Minas Gerais, Universidade Federal do Ceará
Citations	158
Analysis	Full AI Review Included

Technical Analysis and Documentation: Diamondene Formation

Source Paper: Raman evidence for pressure-induced formation of diamondene (Nature Communications, DOI: 10.1038/s41467-017-00149-8)

Executive Summary

The analyzed research provides compelling spectroscopic evidence for the pressure-induced formation of diamondene, an atomically thin, two-dimensional (2D) crystalline diamond material. This work is highly relevant to 6CCVD’s commitment to advancing MPCVD diamond technology and ultra-thin film applications.

Novel 2D Diamond Material: The study confirms the transition of double-layer graphene (sp² carbon) into diamondene (sp³ carbon network) under high hydrostatic pressure, confirming the existence of a stable 2D diamond phase.
Unique Electronic Properties: Diamondene is predicted to be a ferromagnetic semiconductor with spin-polarized bands, offering superior potential for next-generation spintronic and quantum computing devices, an area where high-purity Single Crystal Diamond (SCD) is highly valued.
Chemical Catalysis Requirement: The transformation requires not only high pressure (critical threshold ~4.7 GPa) but also the presence of specific chemical groups (hydroxyl or hydrogen, provided by water PTM) to catalyze the sp²-to-sp³ rehybridization.
Spectroscopic Verification: The formation was confirmed by observing a unique, irreversible splitting and blueshift of the G band in the Raman spectra, correlated with the quantum confinement effect within the remaining sp² sites.
Relevance to CVD Engineering: This process validates pathways for synthesizing ultra-thin diamond structures via catalytic, pressure-assisted rehybridization, informing the development of next-generation low-dimensional diamond materials beyond standard CVD growth.
6CCVD Market Opportunity: Replicating and scaling this synthesis requires precursor material expertise (high-quality, large-area graphene/PCD/SCD substrates) and advanced characterization tools, positioning 6CCVD as a crucial partner for ultra-thin diamond material supply.

Technical Specifications

Hard data extracted from the experimental and theoretical sections of the research paper.

Parameter	Value	Unit	Context
Maximum Experimental Pressure (DAC)	~14	GPa	Applied pressure for Raman analysis (Water PTM)
Critical Transition Pressure (MD/DFT)	4.57 - 4.7	GPa	Pressure threshold required for diamondene formation
Excitation Laser Energy (Green)	2.33	eV	Used for Raman shift analysis (E_L green)
Excitation Laser Energy (Blue)	2.54	eV	Used for Raman shift analysis (E_L blue)
Interlayer C-C Bond Length (Diamondene)	1.66	Å	Calculated length post-relaxation (sp³ covalent bond)
Initial Interlayer Distance (Graphene)	2.7 - 2.8	Å	Starting geometry in DFT/MD simulations
Theoretical Lattice Parameter (Diamondene)	2.55	Å	Lattice parameter of the resulting 2D compound
G Band Frequency Splitting ($\Delta \omega_G$)	~3.9	cm^-1	Observed difference between $E_L$ blue and $E_L$ green (P > 7.5 GPa)
Stabilization Time (MD)	2	ns	Minimum time required for structural stabilization during pressure equilibration
Relative Energy Difference (Lonsdaleite vs. Diamondene)	50	meV per primitive cell	Diamondene conformation is more energetically favorable

Key Methodologies

The experimental approach utilized high-pressure techniques combined with advanced in situ spectroscopy and corroborated by computational modeling.

Sample Preparation: Double-layer graphene (G/G) was synthesized and transferred onto a chemically inert Teflon substrate (T) to prevent chemical bonding with the bottom carbon layer. The resulting structure was G/G/T.
High-Pressure Setup: The G/G/T sample was loaded into a Diamond Anvil Cell (DAC) capable of reaching pressures up to ~15 GPa. A ruby crystal was included for pressure calibration.
Pressure Transmission Medium (PTM): Water (H₂O) was selected as the PTM. The critical role of water is to provide hydroxyl (-OH) or hydrogen (-H) radicals, which act as necessary chemical groups to promote and stabilize the sp³ rehybridization of the top graphene layer.
Spectroscopic Analysis: In situ Raman spectroscopy was performed under increasing pressure (up to ~14 GPa) and during pressure release, monitoring the G band evolution using two distinct excitation laser energies ($E_L = 2.33$ eV and $E_L = 2.54$ eV).
Computational Modeling (DFT & MD): Density Functional Theory (DFT) and Molecular Dynamics (MD) simulations were employed to determine the critical pressure threshold (4.7 GPa) and clarify the formation mechanism, specifically the role of hydroxyl/hydrogen groups in lowering the energy barrier for the sp²-to-sp³ transformation.
Cross-Check Experiments: Control experiments using single-layer graphene (G/T) with water PTM (no diamondization observed below 14 GPa) and double-layer graphene (G/G/T) with mineral oil (Nujol) PTM (lacking reactive chemical groups) confirmed that both double-layer stacking and reactive PTM are necessary conditions.

6CCVD Solutions & Capabilities

This research demonstrates a clear path toward developing atomically thin diamond films suitable for high-demand applications like spintronics and quantum sensors. 6CCVD is uniquely positioned to supply the high-quality SCD and PCD materials required to replicate, scale, and integrate this emerging 2D technology.

Applicable Materials for Diamondene Research

Replicating the sp²-to-sp³ transition process requires materials with extreme purity, controllable layer thickness, and potentially pre-existing doping for electronic applications.

Material Grade	6CCVD Specification	Relevance to Research & Application
Optical Grade SCD	Substrates up to 125mm, Thickness 0.1 µm - 500 µm, Ra < 1 nm (Polished)	Ideal high-purity, stable base for synthesizing and characterizing diamondene or related ultra-thin films post-transfer. The low Ra is crucial for interface studies.
Polycrystalline Diamond (PCD)	Plates up to 125mm, Thickness 0.1 µm - 500 µm, Ra < 5 nm	Cost-effective alternative for large-area diamondene production, particularly where grain boundaries are acceptable or manageable in the 2D film integration.
Boron-Doped Diamond (BDD)	Custom doping levels (Heavy B-doping available), SCD or PCD formats.	Diamondene is predicted to be a ferromagnetic semiconductor. BDD materials are essential for related spintronic and superconducting applications (e.g., nitrogen vacancy centers, charge injection studies).

Customization Potential

The diamondene synthesis pathway, whether using the DAC or eventual industrial scale-up, depends on precise material engineering and integration. 6CCVD provides necessary services for device prototyping.

Ultra-Thin Diamond Precursors: While the paper used graphene layers, future research into scaling this process may involve CVD-grown precursors. 6CCVD offers ultra-thin SCD/PCD films down to 0.1 µm thickness, allowing engineers to bridge the gap between 2D and 3D diamond structures.
Advanced Metalization Services: Integration of 2D diamond materials into electronic or spintronic devices necessitates robust contacts. 6CCVD offers in-house deposition of critical metal layers, including Ti, Pt, Au, Pd, and W, which are essential for ohmic contacts and electrode patterning on diamond substrates.
Custom Dimensions and Substrate Handling: The use of specific substrates (like Teflon in this study) requires flexible processing. 6CCVD supports custom laser cutting, shaping, and handling of diverse substrates up to 125mm diameter, ensuring compatibility with demanding experimental setups like DACs or specialized transfer protocols.

Engineering Support

The transition from a high-pressure experimental technique to scalable device fabrication requires specialized knowledge in diamond crystallography, surface functionalization, and electronic doping.

6CCVD’s in-house PhD-level material science and technical engineering team is available to assist researchers and engineers with:

Material Selection: Guiding the selection of optimal SCD or BDD substrates based on the required electrical properties and lattice matching for diamondene integration.
Surface Preparation: Consulting on necessary pre-treatment and polishing (Ra < 1 nm SCD) to facilitate controlled graphene transfer and interface engineering.
Spintronics Integration: Providing expertise in highly doped BDD and managing crystallographic orientation critical for high-performance ferromagnetic semiconductor projects.

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

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-017-00149-8