Skip to content
6CCVD Research

Controlled seeding density of nanodiamonds on silicon and its influence on diamond film adhesion

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-03-03
JournalFunctional Diamond
AuthorsZhixue Xing, Stephan Handschuh‐Wang, Tao Wang, Peigang Han, Bin He
InstitutionsShenzhen Institutes of Advanced Technology, Advanced Energy (United States)
Citations3
AnalysisFull AI Review Included

Controlled Seeding Density of Nanodiamonds and Diamond Film Adhesion

Section titled “Controlled Seeding Density of Nanodiamonds and Diamond Film Adhesion”

Executive Summary

Section titled “Executive Summary”

This study investigates the critical relationship between nanodiamond (ND) seeding density and the adhesion reliability of microcrystalline diamond (MCD) films on silicon substrates, providing a controlled methodology for CVD processes.

  • Controlled Seeding Strategy: An electrostatic self-assembly method was employed, utilizing highly stable ND colloids (ca. 30 nm diameter, +32 mV Zeta potential) to achieve precise control over seeding density by simple dilution.
  • Density Range Achieved: Seeding density was successfully varied over two orders of magnitude, from 4 x 108 cm-2 (sparse) up to 2.0 x 1011 cm-2 (near full coverage).
  • Optimal Adhesion Identified: Best adhesion (shortest crack length of 107 ± 8 ”m and minimal sample-to-sample variation) was achieved at an optimal seeding density of 1.81 x 1011 cm-2 (using 0.005 wt% ND solution).
  • Failure Mechanism at High Density: Counterintuitively, further increasing the ND concentration (≄ 0.01 wt%) resulted in poorer adhesion. This decline was attributed to the formation of ND aggregates during seeding, which either desorb or create areas of weak diamond-silicon bonding.
  • Film Consistency: The resulting MCD films maintained a consistent thickness (3.1 ± 0.1 ”m) and residual compressive stress (ca. -0.96 GPa surface, ca. -1.59 GPa subsurface) across most seeding densities, isolating seeding density as the primary variable affecting adhesion.
  • Engineering Impact: The findings are crucial for commercial applications, particularly diamond-coated cutting tools, where high seeding densities are often used but aggregation leads to spurious adhesion and premature coating failure.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Substrate MaterialSingle crystal siliconN/A<100>/<110> orientation, UV-Ozone oxidized
ND Particle Size (Hydrodynamic Diameter)ca. 30nmMeasured via DLS; constant across dilutions
ND Zeta Potentialca. +32mVMeasured via ELS; constant across dilutions
Surfactant Concentration (TMAEMC)5 x 10-6mol/LUsed for colloidal stability
Optimal Seeding Density1.81 x 1011cm-2Achieved using 0.005 wt% ND solution
Seeding Density Range Tested4 x 108 to 2.0 x 1011cm-2Controlled via ND colloid dilution
Diamond Film Thickness (MCD)3.1 ± 0.1”mConstant for adhesion comparison
Diamond Crystallite Size1.0 ± 0.3”mMicrocrystalline diamond (MCD)
Residual Stress (Surface)ca. -0.96GPaCompressive stress (Raman analysis)
Residual Stress (Subsurface)ca. -1.59GPaCompressive stress (closer to Si interface)
Adhesion Test Load50NVickers Indentation (single crystal diamond tip)
Best Adhesion Crack Length107 ± 8”mAt optimal seeding density (1.81 x 1011 cm-2)
CVD Pressure1000PaHFCVD growth environment
H2 Flow Rate500sccmGrowth gas flow
CH4 Flow Rate25sccmGrowth gas flow (20:1 H2:CH4 ratio)
CVD Power10.5kWHFCVD system power

Key Methodologies

Section titled “Key Methodologies”

The experiment utilized a highly controlled electrostatic self-assembly seeding process followed by Hot Filament Chemical Vapor Deposition (HFCVD).

  1. Substrate Pretreatment:

    • Polished single crystal silicon wafers were cleaned (DI water/propanol).
    • Substrates were oxidized using UV ozone for 15 min to create a negatively charged, hydrophilic surface, conducive to electrostatic adsorption of positive ND particles.

  2. Nanodiamond Colloid Preparation:

    • ND particles (5 nm, positive Zeta potential) were stabilized using the surfactant TMAEMC (5 x 10-6 mol/L).
    • The ND concentration was diluted from 0.1 wt% down to 0.00033 wt% to control seeding density.
    • The pH was meticulously adjusted to pH 3 for all solutions to ensure maximum colloidal stability (constant +32 mV Zeta potential and ca. 30 nm diameter).

  3. Seeding Process (Electrostatic Self-Assembly):

    • Oxidized Si substrates were immersed in the prepared ND colloids and sonicated for 15 min.
    • The resulting seeding density was quantified using Atomic Force Microscopy (AFM) particle counting.

  4. Diamond Film Growth (HFCVD):

    • All samples were coated in a single batch using a commercial HFCVD chamber to eliminate batch-to-batch variations.
    • Growth parameters were fixed: 1000 Pa pressure, 500 sccm H2, 25 sccm CH4, and 10.5 kW power.
    • Growth time was set to achieve a consistent MCD film thickness of 3.1 ± 0.1 ”m.

  5. Film Characterization:

    • Morphology/Thickness: Scanning Electron Microscopy (SEM) cross-sections confirmed columnar MCD growth and film thickness uniformity.
    • Stress Analysis: Raman spectroscopy was used to measure the shift of the diamond peak (1332.0 cm-1) to calculate residual compressive stress (ranging from -0.96 to -1.59 GPa).
    • Adhesion Testing: Adhesion was qualitatively assessed using Vickers indentation (50 N load), measuring the average length and variance of radial cracks orthogonal to the crater.

Commercial Applications

Section titled “Commercial Applications”

The findings directly impact industries requiring high-reliability diamond coatings, particularly where adhesion to non-diamond substrates is challenging.

  • Machining and Cutting Tools:
    • Application: Diamond-coated cemented carbide (WC-Co) tools and microdrills.
    • Relevance: The study provides a method to avoid ND aggregation, which is a major cause of poor adhesion and premature failure in high-density seeding processes commonly used for industrial tools.
  • Wear-Resistant Coatings:
    • Application: Coatings for mechanical components, bearings, and artificial joints.
    • Relevance: Maximizing adhesion reliability ensures long service life and performance under high mechanical stress.
  • Advanced Electronics and Optics:
    • Application: Ultrathin diamond films (less than 100 nm) for optical coatings, photo-electrochemistry, and sensors on silicon substrates.
    • Relevance: Achieving high seeding density (> 1011 cm-2) without aggregation is essential for growing uniform, ultra-smooth films.
  • Electrochemical Applications:
    • Application: Boron-doped diamond (BDD) electrodes for water splitting, sensing, and supercapacitors.
    • Relevance: Adherent, high-surface-area films are necessary for stable electrochemical performance.
View Original Abstract

Several parameters are known to influence the adhesion of diamond coatings to non-diamond substrates. In the current work, we investigate the effect of seeding density on the adhesion of microcrystalline diamond coatings on silicon substrates. To this end, controlled seeding densities on silicon substrates were established by an electrostatic self-assembly seeding strategy. The seeding density was altered by changing the wt% of the ND colloidal seed solution while maintaining the pH and surfactant concentration. This resulted in colloidally stable ND particles with virtually constant hydrodynamic diameter (ca. 30 nm) and Zeta potential (ca. +32 mV) while the wt% of the ND in the colloid was altered between 0.00033 and 0.1 wt%. With these diluted solutions the seeding density was controlled between 4 × 108 cm−2 and 1.95 × 1011 cm−2. Subsequently, microcrystalline diamond coatings with a thickness of 3.1 ± 0.1 ”m were grown. The adhesion of the diamond coating to the silicon substrate was evaluated by indentation. Best adhesion was found for a seeding density of 1.81 × 1011 cm−2, featuring no delamination and low sample to sample variation. Counterintuitively, further increase in seeding density resulted in an increase of crack length and sample to sample variation. This decline in adhesion was attributed to ND aggregates formed during the seeding step, which either desorb or form areas with poor diamond-silicon bonding upon diamond growth. Therefore, this result is of import for diamond film adhesion studies and commercial diamond coated cutting tools using high seeding densities being prone to aggregation.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2024 - Anomalously strong size effect on thermal conductivity of diamond microparticles [Crossref]
  2. 2024 - Applications of diamond films: a review [Crossref]
  3. 2020 - Robust biomimetic hierarchical diamond architecture with a self-cleaning, antibacterial, and antibiofouling surface [Crossref]
  4. 2019 - Biocompatibility and functionalization of diamond for neural applications [Crossref]
  5. 2019 - Quantum nanophotonics with group IV defects in diamond [Crossref]
  6. 2016 - Diamond electrochemistry at the nanoscale: a review [Crossref]
  7. 2018 - Boron doped diamond: a designer electrode material for the twenty-first century [Crossref]
  8. 2021 - Ultrathin diamond nanofilms—development, challenges, and applications [Crossref]
  9. 2000 - Diamond thin films: a 21st-century material [Crossref]
  10. 2023 - Bottom-up strategy of multi-level structured boron-doped diamond for the durable electrode in water purification [Crossref]

Reads Similar to This

Structural and optical properties of cubic GaN films on high-thermal conductivity substrates How Fast Can NV and SiV Centers in Diamond Be Electrically Triggered? Nuclear-spin relaxation in solid-state-defect quantum bits via electron-phonon coupling in the optically excited state