Antibacterial and Film Characteristics of Copper-Doped Diamond-like Carbon Films via Sputtering Using a Mixed Target of Copper and Graphite

At a Glance

Metadata	Details
Publication Date	2025-05-07
Journal	Coatings
Authors	Kazuya Kanasugi, Takayoshi NAKAJIMA, Kenji Hirakuri
Institutions	Tokyo Denki University
Analysis	Full AI Review Included

Technical Documentation & Analysis: Copper-Doped Diamond-like Carbon Films

Executive Summary

This research successfully demonstrates a simplified Ar-sputtering method utilizing mixed C/Cu targets to produce Copper-Doped Diamond-Like Carbon (Cu-DLC) films with high antibacterial efficacy. This work provides a critical foundation for developing advanced hygienic coatings.

Core Achievement: Fabrication of stable, uniform Cu-DLC films on SUS304 substrates using a single C/Cu mixed target, simplifying the deposition process compared to dual-source methods.
Hygienic Performance: All prepared Cu-DLC films exhibited strong antibacterial activity (R > 2.0, up to 4.2 ± 0.00) against Staphylococcus aureus (ISO 22196 standard).
Material Control: The Cu concentration in the film (ranging from 40.0 to 54.1 at%) was successfully controlled by adjusting the C/Cu ratio of the mixed target.
Tribological Excellence: The Cu-DLC films maintained excellent sliding properties, achieving dynamic friction coefficients (0.14-0.17) comparable to standard DLC films.
6CCVD Advantage: While this study used amorphous DLC, 6CCVD specializes in high-purity, high-hardness MPCVD Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD), offering superior platforms for next-generation hygienic coatings requiring extreme wear resistance and chemical stability in medical and industrial environments.

Technical Specifications

The following hard data points were extracted from the experimental results, focusing on the characteristics of the best-performing Cu-DLC samples (B and C).

Parameter	Value	Unit	Context
Target Film Thickness (Nominal)	1000	nm	Target thickness for all Cu-DLC samples
Substrate Material	SUS304	N/A	Standard test piece
Sputtering Gas Purity	99.9995	%	Argon (Ar) gas used
Sputtering Pressure	3.5 - 3.7 x 10^-1	Pa	Operating gas pressure
Maximum Deposition Rate	26.5	nm/min	Cu-DLC (C) (50:50 C:Cu target)
Maximum Film Cu Concentration (EPMA)	54.1	at%	Cu-DLC (C)
Surface Roughness (Rq, Max)	5.97 ± 0.11	nm	Cu-DLC (C) (AFM measurement)
Dynamic Friction Coefficient (Min)	0.16 ± 0.02	N/A	Cu-DLC (A, B, C) vs. SUS304 ball
Antibacterial Activity (R Value)	4.2 ± 0.00	N/A	Cu-DLC (B) and (C) against S. aureus
Cu Release Amount (Max, ICP-OES)	0.56	ppm	Cu-DLC (C) after 24h immersion in water
Carbon Structure Ratio (ID/IG, Max)	2.04	N/A	Cu-DLC (B) (Indicates high sp² content)

Key Methodologies

The Cu-DLC films were prepared using magnetron sputtering with a unique C/Cu mixed target approach.

Substrate Preparation: SUS304 base materials were ultrasonically cleaned in acetone and ethanol for 10 minutes each to remove contaminants.
Chamber Evacuation: The sputtering chamber was evacuated to a base pressure of 3.0 x 10^-3 Pa.
Gas Introduction: Argon gas (20 sccm flow rate) was introduced to achieve an operating pressure of approximately 3.5 x 10^-1 Pa.
Target Composition: Three mixed targets were manufactured by sintering C and Cu powders in C/Cu ratios of 70:30, 60:40, and 50:50.
Deposition Parameters: Magnetron sputtering was initiated with a discharge voltage (Bias Voltage) controlled at approximately 530 V (except for pure Cu film).
Thickness Control: Deposition time was adjusted (ranging from 40 to 80 minutes for Cu-DLC) to achieve a target film thickness of 1000 nm.
Characterization: Films were analyzed using EPMA (elemental composition), XPS (surface composition, bonding states), AFM (roughness), Raman spectroscopy (sp²/sp³ ratio), ball-on-disk testing (friction), and ICP-OES (Cu release).

6CCVD Solutions & Capabilities

This research highlights the growing demand for durable, hygienic surface coatings, particularly those leveraging the stability and hardness of carbon films. 6CCVD, as an expert in MPCVD diamond, is uniquely positioned to supply the next generation of materials required to advance this technology beyond standard sputtered DLC.

Applicable Materials for Advanced Hygienic Coatings

The amorphous DLC used in this study provides a baseline for antibacterial coatings. For applications requiring superior mechanical durability, chemical inertness, and high thermal conductivity (critical for medical devices and high-wear industrial components), 6CCVD recommends transitioning to high-purity MPCVD diamond materials:

Optical Grade Polycrystalline Diamond (PCD): Ideal for replicating and scaling this research. 6CCVD offers PCD plates up to 125mm in diameter, significantly exceeding the small test pieces used in the study (10 mm x 10 mm). PCD provides extreme hardness and wear resistance far surpassing standard DLC, ensuring long-term stability of the hygienic surface.
High-Purity Single Crystal Diamond (SCD): Recommended for high-precision, high-purity medical or sensor applications where ultimate material quality (Ra < 1nm polishing) and controlled doping are paramount.
Boron-Doped Diamond (BDD): While the paper focused on Cu doping, BDD offers a highly stable, conductive matrix. BDD can be used to create advanced electrochemical platforms for controlled ion release or integrated sensing capabilities in wet environments, extending the functionality of the hygienic coating.

Customization Potential for Replication and Extension

6CCVD’s in-house manufacturing capabilities directly address the customization needs inherent in advanced coating research:

Research Requirement	6CCVD Capability	Specification Range
Custom Dimensions	Plates and wafers available in large formats.	PCD up to 125mm diameter.
Film Thickness	Precision control over SCD and PCD layer thickness.	SCD/PCD from 0.1µm to 500µm.
Substrate Flexibility	Deposition on various customer-supplied substrates.	Substrates up to 10mm thick (e.g., Si, Sapphire, Ceramics, Metals).
Surface Finish	Ultra-low roughness polishing for critical interfaces.	Ra < 1nm (SCD), Ra < 5nm (Inch-size PCD).
Interface Engineering	Internal metalization services for controlled interfaces.	Au, Pt, Pd, Ti, W, Cu (Crucial for controlling Cu release kinetics).

Engineering Support

The successful control of Cu concentration and release kinetics demonstrated in this paper requires deep material science expertise. 6CCVD’s in-house PhD team specializes in CVD growth parameters, doping mechanisms, and surface functionalization. We offer comprehensive engineering consultation to assist researchers and engineers in:

Optimizing material selection (SCD vs. PCD vs. BDD) for specific hygienic coating or medical device projects.
Designing custom metalization stacks (e.g., Ti/Pt/Au) to enhance adhesion and control the electrochemical environment for sustained ion release.
Scaling up successful lab-scale processes to industrial dimensions (up to 125mm wafers).

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

View Original Abstract

Copper-doped diamond-like carbon films (Cu-DLC) are effective antibacterial materials and are fabricated using different techniques. By controlling the ratio of the graphite and diamond structures as well as the hydrogen bonds, the biocompatibility, chemical stability, wear resistance, and high hardness of Cu-DLC can be regulated. In this study, three types of Cu-DLC films were deposited on SUS304 substrates using Ar-sputtering with mixed targets comprising different C/Cu ratios. The films’ structures, surface, and antibacterial properties were investigated using electron probe microanalysis, Raman and X-ray photoelectron spectroscopy, atomic force microscopy, and ball-on-disk tests. The Cu concentration in the Cu-DLC films increased with an increase in its content in the target; however, no significant differences were observed in the Raman spectra. The surface composition, roughness, and dynamic friction coefficients were similar across all Cu-DLC films, which displayed smoothness and friction properties similar to those of standard DLC films without Cu. The antibacterial activity (R value) was evaluated as per ISO 22196. Although DLC films exhibited no antibacterial activity (R < 2), all the prepared Cu-DLC films displayed good antibacterial activity (R ≥ 2). The proposed deposition process facilitated Cu-DLC coating, thus promoting its use in the healthcare fields.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings15050559

References

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