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6CCVD Research

Dimer ribbon structures on diamond (001) surfaces revealed with atomic force microscopy

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-04-10
JournalPhysical Review Research
AuthorsRunnan Zhang, Y. Yasui, Masahiro Fukuda, Masahiko Ogura, Toshiharu Makino
InstitutionsNational Institute of Advanced Industrial Science and Technology, The University of Tokyo
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research utilizes high-resolution Atomic Force Microscopy (AFM) and Density Functional Theory (DFT) to achieve an atomic-level understanding of diamond film growth, addressing limitations in current Chemical Vapor Deposition (CVD) techniques.

  • Key Discovery: Distinct carbon adatom configurations, termed “dimer ribbons,” were observed on clean diamond (001) surfaces.
  • Structural Stability: These ribbons were found to predominantly consist of an odd number of dimers (e.g., 3, 5, 11), terminated at the energetically preferred Site A.
  • Theoretical Validation: DFT calculations confirmed that these odd-numbered, Site A terminated structures represent the most stable configurations formed in the non-equilibrium plasma environment.
  • Methodological Advance: Near-contact Frequency-Modulation AFM (FM-AFM) with reactive Si tips was successfully employed to achieve atomic resolution on insulating diamond, overcoming previous technical challenges.
  • Growth Insight: The findings provide crucial guidelines for optimizing CVD parameters, suggesting that the observed structures are fundamental elemental entities carrying growth information.
  • Ribbon Interaction: Adjacent dimer ribbons are stabilized by clustering, showing only a small energy difference (0.2 eV per eight dimers) compared to separate ribbons.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Substrate Misorientationless than 0.1°Ib diamond substrate for CVD growth
Total Gas Flow Rate400sccmChemical Vapor Deposition (CVD)
CVD Pressure25TorrCVD growth environment
C/H2 Ratio0.3%Gas mixture composition
B/C Ratio0.005%Boron doping concentration (trimethylborane)
Substrate Temperature800°CMaintained during microwave radiation
Microwave Power / Frequency750 / 2.45W / GHzCVD plasma generation
Film Thickness / Growth Time400 / 4nm / hoursResulting homoepitaxial diamond film
UHV Annealing Temperature1020°CPre-AFM surface dehydrogenation
Cantilever Resonance Frequency~167kHzSilicon cantilever specifications
Cantilever Elasticity34.9N/mForce constant used for AFM
AFM Frequency Shift Set Point (Δfs)-15HzImaging parameter (Fig. 1)
Isolated Dimer Formation Energy (Site A)9.05eVDFT calculation (most stable site)
Isolated Dimer Formation Energy (Site B)4.51eVDFT calculation (less stable site)
Force on Inner Dimer (Experimental)-2.4nNMaximum attractive force during active imaging
DFT Force Threshold0.0003Hartree/bohrGeometry optimization convergence criterion

Key Methodologies

Section titled “Key Methodologies”

The study combined advanced diamond synthesis with state-of-the-art atomic imaging and computational modeling.

  1. Diamond Film Synthesis (CVD):
    • Boron-doped homoepitaxial diamond films were grown on Ib diamond substrates using H2, CH4, and trimethylborane.
    • Growth occurred at 800 °C under 750 W microwave radiation (2.45 GHz) for 4 hours, yielding 400 nm thick films.
  2. Surface Preparation:
    • A 5-minute hydrogen etching process was performed post-growth to achieve a well-defined hydrogen-terminated surface.
    • Films were subsequently annealed at 1020 °C for two hours in an Ultrahigh Vacuum (UHV) chamber (5x10-9 Pa base pressure) to dehydrogenate the surface.
  3. AFM Tip Engineering:
    • Reactive Si tips were prepared using Ar ion sputtering.
    • These tips were positioned near maximum attractive forces to form strong silicon-carbon bonds, enhancing spatial resolution for atomic imaging on the insulating diamond surface.
  4. High-Resolution Imaging:
    • AFM measurements were performed at room temperature in Frequency-Modulation (FM) mode.
    • The active imaging method was used, maintaining z feedback around the maximum short-range force region to obtain atomic contrast.
  5. Computational Modeling (DFT):
    • DFT calculations (using OpenMX code and GGA approximation) were performed to determine the geometry and energetics of ad-dimer structures.
    • Formation energies were calculated to identify the most stable configurations, confirming the preference for odd-numbered dimer ribbons terminated at Site A.

Commercial Applications

Section titled “Commercial Applications”

The atomic-level understanding of diamond surface growth is critical for advancing diamond-based semiconductor and quantum technologies.

  • High-Frequency and High-Power Electronics:
    • Application: Field-Effect Transistors (FETs) and high-power switches.
    • Relevance: Optimizing the surface flatness and minimizing defects (like steps and ad-dimers) is essential for maximizing carrier mobility and device reliability, leveraging diamond’s wide bandgap and high thermal conductivity.
  • Quantum Sensing and Computing:
    • Application: Nitrogen-Vacancy (NV) centers and other solid-state quantum devices.
    • Relevance: Controlled, high-quality crystal growth and precise doping (like boron) rely on understanding surface kinetics to minimize structural imperfections that degrade quantum coherence times.
  • Advanced Semiconductor Manufacturing:
    • Application: Epitaxial growth processes and interface engineering.
    • Relevance: The data provides a structural prediction guideline for CVD, allowing engineers to tune plasma parameters to suppress unstable ad-dimer configurations and promote the formation of desired, flat, Site A terminated surfaces.
  • Surface Functionalization:
    • Application: Creating stable, patterned carbon surfaces for chemical or biological interfaces.
    • Relevance: The identification of highly stable, ribbon-like structures offers a template for controlled surface modification and functionalization.
View Original Abstract

The potential of diamond films for future semiconductor applications is partly limited by current growth techniques. This limitation can be addressed by achieving an atomic-level understanding of the growth processes. Using atomic force microscopy with atomic resolution, we examined diamond surfaces and observed specific structures, where odd numbers of dimers form ribbonlike configurations. Formed in the nonequilibrium environment of plasma, these structures were evaluated as the most stable configurations through density-functional-theory calculations. Our findings provide a crucial foundation for optimizing the film growth process.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2001 - Properties, Growth and Applications of Diamond

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