Selective Deposition of Mo2C-Containing Coatings on {100} Facets of Synthetic Diamond Crystals

At a Glance

Metadata	Details
Publication Date	2022-07-31
Journal	International Journal of Molecular Sciences
Authors	Arina V. Ukhina, Boris B. Bokhonov, Dina V. Dudina
Institutions	Institute of Solid State Chemistry and Mechanochemistry, Lavrentyev Institute of Hydrodynamics
Citations	6
Analysis	Full AI Review Included

Technical Documentation & Analysis: Selective Mo₂C Coating on Diamond

Executive Summary

This research validates a highly efficient, gas-phase transport method for selectively depositing Molybdenum Carbide (Mo₂C) coatings on synthetic diamond microcrystals, a critical step for enhancing thermal management composites.

Core Achievement: Selective deposition of Mo₂C-containing island structures was achieved predominantly on the {100} facets of synthetic diamond crystals via Hot Pressing (HP) in an Argon atmosphere.
Mechanism: The coating forms through gas-phase transport of volatile Molybdenum Dioxide (MoO₂), which sublimes from the Mo powder, selectively adsorbs onto the {100} facets, and is subsequently reduced by diamond carbon to form metallic Mo, followed by carbidization to Mo₂C.
Application Relevance: This surface modification improves the wettability of diamond by metal matrices (e.g., Copper), directly enhancing the mechanical strength, wear resistance, and crucial thermal conductivity of metal-diamond composites used in high-power devices.
Process Influence: Increasing treatment time (up to 30 min) and temperature (up to 1000 °C) increased the concentration of the desired Mo₂C phase in the coating.
Atmosphere Impact: Spark Plasma Sintering (SPS) in forevacuum resulted in a homogeneous, non-selective coating, contrasting sharply with the selective deposition achieved via HP in Argon, highlighting the importance of process atmosphere control.
6CCVD Value Proposition: 6CCVD provides the high-purity MPCVD diamond substrates (SCD/PCD) and custom metalization capabilities (including Ti, W, and Mo precursors) necessary to scale and optimize this selective coating technology for industrial heat spreader applications.

Technical Specifications

The following hard data points were extracted from the experimental methodology and results:

Parameter	Value	Unit	Context
Diamond Substrate Type	Synthetic Diamond D (MBD12)	N/A	Average particle size 100 µm
Molybdenum Purity	99.1	%	Starting metal powder (MPCh)
Mo Concentration (Tested)	10, 50	vol.%	Concentration in diamond powder mixture
Hot Pressing (HP) Temperature	900, 1000	°C	Used for selective deposition
Spark Plasma Sintering (SPS) Temp.	1000	°C	Used for homogeneous deposition study
HP Holding Time (Tested)	5, 15, 30	min	Influenced Mo₂C concentration
HP Atmosphere Pressure	20	kPa	Argon gas environment
SPS Residual Pressure	10	Pa	Forevacuum environment
Uniaxial Pressure Applied	10	MPa	Constant pressure for HP and SPS
Heating Rate	50	°C min^-1	Constant rate in all experiments
Key Coating Phase	Mo₂C	N/A	Molybdenum Carbide (desired phase)
Gas Phase Transport Precursor	MoO₂	N/A	Volatile oxide enabling selective deposition

Key Methodologies

The Mo₂C coatings were deposited using high-temperature treatment of diamond/molybdenum powder mixtures in controlled atmospheres.

Powder Mixing: Synthetic diamond microcrystals (100 µm) were thoroughly mixed with metallic Molybdenum powder (99.1%) at concentrations of 10 vol.% or 50 vol.%.
Sample Preparation: Mixtures were loaded into a graphite die (10 mm inner diameter), protected by graphite foil, and subjected to uniaxial pressure.
Hot Pressing (HP) Treatment:
- Atmosphere: Argon (20 kPa pressure).
- Conditions: Heated to 900 °C or 1000 °C.
- Duration: Held for 5, 15, or 30 minutes under 10 MPa uniaxial pressure.
Spark Plasma Sintering (SPS) Treatment:
- Atmosphere: Forevacuum (10 Pa residual pressure).
- Conditions: Heated to 1000 °C.
- Duration: Held for 15 minutes under 10 MPa uniaxial pressure.
Pre-Oxidation Study: Molybdenum powder was pre-annealed in air at 400 °C for 30 minutes to increase the MoO₂/MoO₃ content, then mixed with diamond and treated via HP (900 °C, 30 min).
Characterization: Samples were analyzed post-treatment using X-ray Diffraction (XRD) for phase composition (Mo, Mo₂C, MoO₂, MoO₃) and Scanning Electron Microscopy (SEM) with Energy-Dispersive Spectroscopy (EDS) for morphology and elemental mapping.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-quality MPCVD diamond substrates and custom processing required to replicate, scale, and advance this selective Mo₂C coating technology for high-performance thermal applications.

Requirement from Research Paper	6CCVD Solution & Value Proposition
Diamond Substrate Material (Synthetic microcrystals, 100 µm)	Optical Grade SCD & High-Purity PCD: We provide low-defect, high-thermal conductivity MPCVD diamond plates and wafers, offering superior consistency and purity compared to the synthetic microcrystals used. Available in thicknesses from 0.1 µm up to 500 µm.
Carbide-Forming Coating (Mo$_{2}$C)	Custom Metalization Services: 6CCVD offers internal, high-precision metalization capabilities for critical carbide-forming metals, including Titanium (Ti), Tungsten (W), and Copper (Cu), as well as Platinum (Pt), Palladium (Pd), and Gold (Au). We can assist researchers in developing Mo-based coatings or alternative carbide layers.
Scaling and Geometry (Microcrystals)	Large Area PCD Wafers: We offer custom dimensions up to 125 mm in diameter (PCD), enabling the scaling of this selective coating technology from microcrystals to industrial-sized heat spreader substrates and thermal management components.
Surface Quality & Selectivity (Selective deposition on {100})	Ultra-Low Roughness Polishing: Our Single Crystal Diamond (SCD) substrates feature surface roughness Ra < 1 nm, providing an atomically smooth, well-defined surface ideal for precise, selective deposition studies and minimizing scattering losses in optical applications. Inch-size PCD is polished to Ra < 5 nm.
Process Optimization & Atmosphere Control (HP vs. SPS, Argon vs. Forevacuum)	Expert Engineering Support: Our in-house PhD material science team specializes in diamond surface preparation, high-temperature processing, and optimizing CVD recipes. We offer consultation to tailor material selection and surface finish for specific selective deposition requirements in thermal management projects.
Global Logistics	Worldwide Shipping: We ensure reliable, global delivery of sensitive diamond materials and coated substrates (DDU default, DDP available).

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

View Original Abstract

An efficient way to improve the properties of metal-diamond composites (mechanical strength, wear resistance, thermal conductivity) is the preliminary modification of the diamond surface to improve its wettability by the metal matrix. In the present work, Mo2C-containing coatings were deposited on the diamond crystals under different conditions: hot pressing (atmosphere of argon), spark plasma sintering (forevacuum), and annealing in air. The influence of the sintering parameters on the morphology and phase composition of the coatings deposited on diamond was studied. Mo2C-containing coatings were selectively deposited on the facets of synthetic diamond microcrystals by annealing of the latter with a molybdenum powder. Experiments were carried out to deposit coatings under different conditions: during hot pressing (argon atmosphere), spark plasma sintering (forevacuum), and annealing in air. The process parameters were the temperature, holding time, and concentration of molybdenum in the initial mixture. Experiments with a pre-oxidized molybdenum powder were also conducted. The coated diamond crystals were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The deposition was enabled by the gas phase transport of molybdenum dioxide, MoO2, contained in the starting powder. The following sequence of the coating formation stages was proposed. First, MoO2 sublimes and is adsorbed mainly on the {100} facets of diamond. Then, it is reduced to metallic molybdenum by carbon of the diamond, which further reacts with carbon to form the Mo2C carbide phase. These processes occurred during treatment of the mixtures in the hot press and the spark plasma sintering facility. When the mixture was annealed in air, no selective deposition was observed. During annealing, MoO3 particles adhered to the diamond surface.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ijms23158511

References

2020 - Research progress of diamond/copper composites with high thermal conductivity [Crossref]
2021 - Influence of sputtering and electroless plating of Cr/Cu dual-layer structure on thermal conductivity of diamond/copper composites [Crossref]
2020 - Enhanced thermal conductivity in diamond/copper composites with tungsten coatings on diamond particles prepared by magnetron sputtering method [Crossref]
2021 - Optimization of process parameters, microstructure, and thermal conductivity properties of Ti-coated diamond/copper composites prepared by spark plasma sintering [Crossref]
2020 - Study on surface modification of diamond particles and thermal conductivity properties of their reinforced metal-based (Cu or Mg) composites [Crossref]
2018 - Effect of the Surface Modification of Synthetic Diamond with Nickel or Tungsten on the Properties of Copper-Diamond Composites [Crossref]
2010 - Thermal conductivity of SPS consolidated Cu/diamond composites with Cr-coated diamond particles [Crossref]
2017 - Design of of interfacial Cr3C2 carbide layer via optimization of sintering parameters used to fabricate copper/diamond composites for thermal management applications [Crossref]
2015 - Tungsten carbide coating on diamond particles in molten mixture of Na2CO3 and NaCl [Crossref]
2013 - Preparation of high thermal conductivity copper-diamond composites using molibdenum carbidecoated diamond particles [Crossref]