Ultra-Low Thermal Conductivity of Moiré Diamanes

At a Glance

Metadata	Details
Publication Date	2022-09-25
Journal	Membranes
Authors	Suman Chowdhury, V. A. Demin, Л. А. Чернозатонский, Alexander G. Kvashnin
Institutions	Institute of Biochemical Physics NM Emanuel, Shiv Nadar University
Citations	7
Analysis	Full AI Review Included

Technical Documentation & Analysis: Ultra-Low Thermal Conductivity of Moiré Diamanes

This document analyzes the findings of the research paper “Ultra-Low Thermal Conductivity of Moiré Diamanes” (Membranes 2022, 12, 925) and aligns the material requirements with the advanced capabilities of 6CCVD’s MPCVD diamond portfolio.

Executive Summary

The research demonstrates the extreme tunability of thermal conductivity (K_L) in quasi-2D diamond membranes (Diamanes) by controlling the Moiré twist angle ($\theta$) and surface passivation (Hydrogen/Fluorine).

Extreme Thermal Tunability: K_L is shown to be tunable across two orders of magnitude, ranging from ultra-high (1360 W/mK) in untwisted hydrogenated diamanes to ultra-low (32 W/mK) in highly twisted hydrogenated structures ($\theta=27.8^\circ$).
Material Basis: Diamanes, derived from fully passivated bi-layer graphene, exhibit diamond-like sp³ hybridization, making them ideal for high-performance thermal management and electronic applications.
Mechanism for Low K_L: The sharp decrease in thermal conductivity is attributed to structural disorder caused by the twist angle, leading to high anharmonicity and enhanced phonon scattering (Umklapp scattering).
Electronic Potential: Moiré diamanes possess ultra-wide electronic band gaps of up to 4.5 eV, confirming their potential as high-quality protective and insulating materials for nanodevices.
Passivation Effect: Fluorination (heavy atoms) stabilizes the diamane structure, resulting in generally lower K_L values than hydrogenated counterparts at $\theta=0^\circ$, but higher K_L values at high twist angles due to reduced anharmonicity influence.
Application Focus: The ability to achieve both extremely high and extremely low K_L values positions diamanes as prospective candidates for advanced thermoelectric devices and thermal management systems (heat sinks and insulators).

Technical Specifications

The following hard data points were extracted from the study, focusing on the thermal and electronic properties achieved through structural tuning.

Parameter	Value	Unit	Context
Max Lattice Thermal Conductivity (K_L)	1360	W/mK	Hydrogenated Diamane ($\theta=0^\circ$) at 300 K
Min Lattice Thermal Conductivity (K_L)	32	W/mK	Hydrogenated Moiré Diamane ($\theta=27.8^\circ$) at 300 K
Fluorinated K_L (Untwisted)	361	W/mK	Fluorinated Diamane ($\theta=0^\circ$) at 300 K
Fluorinated K_L (Twisted)	90	W/mK	Fluorinated Moiré Diamane ($\theta=27.8^\circ$) at 300 K
Electronic Band Gap (Max)	Up to 4.5	eV	Moiré Diamanes (Strong dependence on twist angle)
Twist Angles Studied ($\theta$)	0, 13.2, 21.8, 27.8	°	Used for Moiré pattern formation
C-C Bond Length Range (Twisted)	1.5 to 1.8	Å	Observed in disordered Dn13 structure
Simulation Temperature Range	300 to 900	K	Used for K_L temperature dependence fitting

Key Methodologies

The study relied on a sophisticated combination of ab initio methods and machine learning potentials to overcome the computational complexity of large Moiré supercells.

Geometry Optimization: Performed using DFT (VASP package) within the generalized gradient approximation (Perdew-Burke-Ernzerhof functional) and the projector augmented wave method.
Energy Cutoff & Spacing: Plane-wave energy cutoff set to 500 eV. Smallest allowed spacing between k-points was 0.25 Å^-1. Vacuum distance set to no less than 15 Å.
Machine Learning (ML) Potentials: Moment Tensor Potentials (MTP) were chosen for their high accuracy in reproducing phononic properties, replacing resource-consuming DFT calculations for anharmonic force constants.
AIMD Training: MTPs were trained over short ab initio molecular dynamic (AIMD) trajectories, using two configuration sets: 50 K constant temperature and temperature reduction from 1000 K to 200 K (2000 time steps each). Time step was 1 fs.
Lattice Thermal Conductivity (K_L) Calculation: Determined by solving the phonon Boltzmann Transport Equation (BTE) within the relaxation time approximation, implemented using the ShengBTE package. Fifth-nearest neighbor interactions were included.

6CCVD Solutions & Capabilities

The research highlights the critical role of high-quality, diamond-like materials in achieving extreme thermal properties for next-generation thermal management and electronic devices. 6CCVD is uniquely positioned to supply the foundational MPCVD diamond materials necessary to replicate, test, and scale this research.

Applicable Materials for Thermal Management

The paper identifies two critical thermal regimes: ultra-high conductivity (for heat sinks) and ultra-low conductivity (for insulators/thermoelectrics). 6CCVD provides the necessary baseline materials for both.

Application Requirement	6CCVD Material Solution	Key Capability Alignment
High K_L Baseline (Heat Sinking)	Optical Grade Single Crystal Diamond (SCD)	SCD offers the highest intrinsic thermal conductivity (> 2000 W/mK), far exceeding the 1360 W/mK baseline achieved in the untwisted diamanes. Ideal for high-power electronics and thermal spreaders.
Tunable/Low K_L Research	Polycrystalline Diamond (PCD) Wafers	PCD allows for large-area processing (up to 125mm diameter) and is suitable for subsequent surface functionalization (H/F) and thin-film deposition required to create the Moiré diamane structures.
Thermoelectric Devices	Heavy Boron-Doped Diamond (BDD)	BDD provides tunable electrical conductivity while maintaining high thermal stability, essential for optimizing the Seebeck effect in advanced thermoelectric applications mentioned in the paper.

Customization Potential for Moiré Diamane Integration

The fabrication of 2D Moiré structures requires precise handling, thin films, and integration with device architectures. 6CCVD offers specialized services to meet these demands:

Custom Dimensions and Thickness: The research involves ultra-thin films. 6CCVD supplies SCD and PCD plates/wafers with thicknesses ranging from 0.1 µm to 500 µm, allowing researchers to select the optimal starting substrate thickness for subsequent transfer or growth processes.
Large-Area Substrates: We provide inch-size PCD wafers (up to 125mm), crucial for scaling up experimental results from computational models to practical, large-area device prototypes.
Advanced Surface Preparation: Our internal polishing capabilities achieve ultra-low roughness (Ra < 1 nm for SCD, Ra < 5 nm for PCD), ensuring an atomically flat surface necessary for controlled bi-layer graphene deposition and subsequent diamane formation.
Custom Metalization Services: For integrating diamanes into functional devices (e.g., thermoelectric junctions), 6CCVD offers in-house deposition of standard and custom metal stacks, including Au, Pt, Pd, Ti, W, and Cu.

Engineering Support

6CCVD’s in-house PhD team specializes in the fundamental properties and growth of MPCVD diamond. We can assist researchers in material selection and optimization for similar 2D Diamond Membrane and Thermal Management projects. Our expertise ensures that the starting diamond substrate meets the stringent requirements for advanced functionalization and device integration.

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

View Original Abstract

Ultra-thin diamond membranes, diamanes, are one of the most intriguing quasi-2D films, combining unique mechanical, electronic and optical properties. At present, diamanes have been obtained from bi- or few-layer graphene in AA- and AB-stacking by full hydrogenation or fluorination. Here, we study the thermal conductivity of diamanes obtained from bi-layer graphene with twist angle θ between layers forming a Moiré pattern. The combination of DFT calculations and machine learning interatomic potentials makes it possible to perform calculations of the lattice thermal conductivity of such diamanes with twist angles θ of 13.2∘, 21.8∘ and 27.8∘ using the solution of the phonon Boltzmann transport equation. Obtained results show that Moiré diamanes exhibit a wide variety of thermal properties depending on the twist angle, namely a sharp decrease in thermal conductivity from high for “untwisted” diamanes to ultra-low values when the twist angle tends to 30∘, especially for hydrogenated Moiré diamanes. This effect is associated with high anharmonicity and scattering of phonons related to a strong symmetry breaking of the atomic structure of Moiré diamanes compared with untwisted ones.

Tech Support

Original Source

DOI: https://doi.org/10.3390/membranes12100925

References

2022 - Updates in phase change materials for thermoelectric devices: Status and challenges [Crossref]
2009 - Diamond-like C 2 H nanolayer, diamane: Simulation of the structure and properties [Crossref]
2014 - Lonsdaleite Films with Nanometer Thickness [Crossref]
2010 - Influence of Size Effect on the Electronic and Elastic Properties of Diamond Films with Nanometer Thickness [Crossref]
2021 - Two-Dimensional Diamond—Diamane: Current State and Further Prospects [Crossref]
2021 - Properties of diamane anchored with different groups [Crossref]
2019 - Giant thermal conductivity in diamane and the influence of horizontal reflection symmetry on phonon scattering [Crossref]
2019 - Suppressed thermal conductivity in fluorinated diamane: Optical phonon dominant thermal transport [Crossref]