Physicochemical and Mechanical Performance of Freestanding Boron-Doped Diamond Nanosheets Coated with C -H -N -O Plasma Polymer

At a Glance

Metadata	Details
Publication Date	2020-04-15
Journal	Materials
Authors	Michał Rycewicz, Łukasz Macewicz, Jiří Kratochvíl, Alicja Stanisławska, Mateusz Ficek
Institutions	Institute of Fluid Flow-Machinery, Gdańsk University of Technology
Citations	2
Analysis	Full AI Review Included

Technical Documentation and Analysis: Freestanding BDD Nanosheets for Flexible Electronics

Executive Summary

This research demonstrates a robust method for creating flexible, mechanically stable, composite boron-doped diamond (BDD) structures suitable for advanced chemical sensors and flexible electronics. The core achievements and value proposition include:

Mechanically Stable Composite: Freestanding, heavy BDD nanosheets (4.2 µm thick) were successfully coated with a C:H:N:O plasma polymer (nylon-like) using magnetron sputtering, creating a flexible, damage-tolerant stack.
Enhanced Adhesion and Flexibility: The polymer coating provides flexibility, preventing the inherent fragility of pristine diamond nanosheets, while the high surface energy of the C:H:N:O layer ensures strong adhesion to the polycrystalline BDD surface.
Electronic Performance Preservation: Despite coating and mechanical integration, the underlying BDD maintained excellent conductive properties (0.11 Ω cm resistivity, 6.2 x 10¹⁹ cm^-3 carrier density), confirming its suitability for electrochemical devices.
Indentation Size Effect (ISE) Analysis: Detailed nanoindentation mapping provided quantified hardness and Young’s modulus profiles for the diamond, the polymer coating, and the crucial nylon/diamond transition zone (approx. 1000 nm thick).
Application Potential: This integration technique enables the design of flexible chemical multielectrode sensors stable in aqueous environments, leveraging diamond’s wide potential window and the composite’s enhanced mechanical resilience.
MPCVD Validation: The high-quality BDD nanosheets were successfully fabricated via Microwave Plasma-Enhanced Chemical Vapor Deposition (MPECVD), validating high-throughput, customized synthesis.

Technical Specifications

The following hard data points were extracted from the synthesis and material characterization of the BDD nanosheet composite:

Parameter	Value	Unit	Context
Diamond Growth Method	MPECVD (SEKI Technotron AX5400S)	N/A	Synthesis of BDD Nanosheets
Diamond Substrate	Tantalum (Ta) foil (Polished)	1 cm x 1 cm x 0.025 mm	Substrate for Freestanding Release
Substrate Temperature (CVD)	500	°C	Diamond growth temperature
Microwave Plasma Power	1100	W	Optimized for diamond growth
Dopant Precursor	Diborane (B₂H₆)	N/A	Boron doping source
Boron/Carbon Ratio ([B]/[C])	10,000	ppm	Heavy doping level achieved
Diamond Thickness (PCD)	4.2	µm	Result of 720 min growth time
Charge Carrier Density	6.2 x 10¹⁹	cm^-3	Measured by Hall effect at Room Temperature
Hall Mobility	9	cm² V^-1 s^-1	Measured by Hall effect at Room Temperature
Resistivity (Freestanding BDD)	0.11	Ω cm	Measured by Van der Pauw method
Polymer Coating Thickness (Test 1)	500	nm	Nanoindentation test thickness
Polymer Coating Thickness (Test 2)	2000	nm	Nanoindentation test thickness
C:H:N:O Film Roughness (on Si)	6.75	nm	Estimated by spectroscopic ellipsometry
Refractive Index (n_p)	1.62	N/A	Measured at 589 nm for plasma nylon
Polymer Sputtering Power	50	W (RF, 13.56 MHz)	Deposition of C:H:N:O film
Polymer Sputtering Pressure	3	Pa	Argon working pressure
Polymer Deposition Speed	8.4 ± 0.8	nm min^-1	Measured by spectroscopic ellipsometry
Max Hardness (Diamond Nanosheet)	400+	GPa	At low indenter displacement (< 200 nm)
Max Reduced Young’s Modulus (Diamond)	450+	GPa	At low indenter displacement (< 200 nm)
Transition Zone Thickness	1000	nm	Layer mixing nylon and diamond particles

Key Methodologies

The fabrication of the flexible, boron-doped diamond composite involved two primary sequential steps: MPECVD diamond growth followed by magnetron sputtering of the polymer.

1. Boron-Doped Diamond Nanosheet Growth (MPECVD)

Substrate Preparation: Polished Tantalum (Ta) foil (1 cm x 1 cm x 0.025 mm) was seeded with a colloid of nanoscale diamond particles for 30 minutes.
CVD Setup: Samples were loaded into an MPECVD system (SEKI Technotron AX5400S, 2.45 GHz frequency).
Recipe Parameters:
- Substrate Temperature: Maintained strictly at 500 °C.
- Power: Microwave power set to 1100 W.
- Precursors: Methane concentration kept below 2%. Diborane (B₂H₆) introduced to maintain a high [B]/[C] ratio of 10,000 ppm.
- Flow/Pressure: Total gas flow rate was 300 sccm. Chamber pressure regulated to 50 Torr.
Growth Duration: Growth lasted 720 minutes (12 hours), yielding a polycrystalline film of 4.2 µm thickness.

2. Polymeric C:H:N:O Film Deposition (Magnetron Sputtering)

Target and Setup: A 3-inch balanced magnetron equipped with a Nylon 6.6 target (3 mm thickness) was used.
Vacuum and Gas Flow: The chamber was pumped to < 5 x 10^-4 Pa. Argon gas introduced at 20 SCCM.
Plasma Parameters:
- Working Pressure: Set to 3 Pa via a desk regulation valve.
- RF Power: 50 W (13.56 MHz frequency).
- Substrate Handling: Substrates were placed 6 cm from the magnetron. Substrate temperature kept below 50 °C.
Relaxation: After deposition, samples underwent a 15-minute vacuum relaxation period to improve film stability.
Transfer and Curing: The fabricated BDD nanosheets were mechanically delaminated from the Ta foil using tweezers (low adhesion) and transferred onto a p-type silicon substrate using silver paste, followed by curing in a vacuum oven at 80 °C for 3 hours.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational and advanced BDD materials necessary to replicate, optimize, and scale this research into flexible sensing technology. Our core MPCVD capabilities directly address the material requirements detailed in this paper.

Applicable Materials

To replicate or extend the development of flexible multielectrode sensors requiring heavy boron-doped conductive films, 6CCVD recommends:

Electronic Grade Polycrystalline Diamond (PCD/BDD): This material is crucial for the application. We offer custom boron doping levels, including the heavy concentration (10,000 ppm) used in this study, ensuring the requisite low resistivity (0.11 Ω cm) and high carrier density (6.2 x 10¹⁹ cm^-3).
Custom Thickness SCD/PCD: The paper used a 4.2 µm thick nanosheet. 6CCVD routinely produces SCD and PCD films in the range of 0.1 µm up to 500 µm. We can engineer the thickness to balance flexibility and robustness perfectly for any specific device geometry.
Substrate Compatibility: Although Ta was used in the study for mechanical release, 6CCVD can grow PCD/BDD on various non-diamond substrates, providing the initial film structure necessary before the polymer coating and transfer process.

Customization Potential

6CCVD’s advanced engineering services allow researchers and engineers to move beyond lab-scale prototypes:

Service Category	Paper Requirement Met	6CCVD Capability & Advantage
Dimensions & Sizing	Freestanding piece: 1.5 mm x 1 mm	We provide custom laser cutting and micromachining for precise geometries on the BDD films, ensuring accurate scaling and integration into flexible arrays.
Large Area Integration	Used 1 cm x 1 cm initial substrate	We offer large-area PCD/BDD wafers up to 125 mm diameter, enabling the high-throughput production required for industrializing flexible sensors.
Surface Engineering	Required oxygen-terminated surface for adhesion	We offer custom surface termination (e.g., -OH, =O) services post-CVD to maximize the surface energy (46 mJ/m²) and adhesion strength with subsequent polymer or metal layers, optimizing the viscoelastic interface.
Metalization Integration	Potential application as multielectrode sensors	We offer in-house custom metalization processes (including Au, Pt, Ti, Pd, W, Cu) to deposit contacts directly onto the BDD for ready-to-use flexible electrodes, bypassing the need for separate silver paste attachment.
Polishing Requirements	Surface heterogeneities pin the contact edge	We achieve ultra-smooth polishing (Ra < 5 nm for inch-size PCD), which can reduce surface heterogeneity and optimize the mechanical performance and crack formation seen in this research.

Engineering Support

The successful integration of diamond nanosheets with soft polymers depends critically on controlling interfacial properties, doping uniformity, and mechanical tolerance.

6CCVD’s in-house PhD engineering team specializes in the synthesis and characterization of BDD materials for electrochemical and flexible electronic applications, like the flexible chemical multielectrode sensors discussed in this paper.
We provide consultation on selecting the optimal boron doping profile and film thickness (0.1 µm to 500 µm) to achieve the best balance between electrical conductivity, mechanical flexibility, and viscoelastic dissipation performance required for composite structures.
We offer DDU default global shipping, with DDP options available, ensuring reliable and secure delivery of custom materials worldwide.

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

View Original Abstract

The physicochemical and mechanical properties of thin and freestanding heavy boron-doped diamond (BDD) nanosheets coated with a thin C:H:N:O plasma polymer were studied. First, diamond nanosheets were grown and doped with boron on a Ta substrate using the microwave plasma-enhanced chemical vapor deposition technique (MPECVD). Next, the BDD/Ta samples were covered with nylon 6.6 to improve their stability in harsh environments and flexibility during elastic deformations. Plasma polymer films with a thickness of the 500-1000 nm were obtained by magnetron sputtering of a bulk target of nylon 6.6. Hydrophilic nitrogen-rich C:H:N:O was prepared by the sputtering of nylon 6.6. C:H:N:O as a film with high surface energy improves adhesion in ambient conditions. The nylon-diamond interface was perfectly formed, and hence, the adhesion behavior could be attributed to the dissipation of viscoelastic energy originating from irreversible energy loss in soft polymer structure. Diamond surface heterogeneities have been shown to pin the contact edge, indicating that the retraction process causes instantaneous fluctuations on the surface in specified microscale regions. The observed Raman bands at 390, 275, and 220 cm−1 were weak; therefore, the obtained films exhibited a low level of nylon 6 polymerization and short-distance arrangement, indicating crystal symmetry and interchain interactions. The mechanical properties of the nylon-on-diamond were determined by a nanoindentation test in multiload mode. Increasing the maximum load during the nanoindentation test resulted in a decreased hardness of the fabricated structure. The integration of freestanding diamond nanosheets will make it possible to design flexible chemical multielectrode sensors.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma13081861

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