Formation of a Boron‐Oxide Termination for the (100) Diamond Surface
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2024-05-30 |
| Journal | Advanced Materials Interfaces |
| Authors | Alex K. Schenk, Rebecca Griffin, Anton Tadich, Daniel M. Roberts, Alastair Stacey |
| Institutions | Australian Nuclear Science and Technology Organisation, Princeton Plasma Physics Laboratory |
| Citations | 4 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research demonstrates a novel Ultrahigh Vacuum (UHV) method for forming a highly ordered boron-oxide termination on the (100) diamond surface using molecular deposition.
- Core Achievement: Successful formation of a chemically homogeneous and highly oriented boron-oxide termination on hydrogen-terminated (100) diamond using molecular B2O3 deposition followed by annealing.
- Chemical Structure: The termination involves boron-oxygen moieties (predominantly B=O) bonded directly to the surface carbon atoms (C-B bonds). No carbon-oxygen (C-O) bonds were detected.
- Process Parameters: The critical step is annealing the B2O3 layer at 950 °C, which facilitates hydrogen desorption and subsequent reaction with the B2O3 decomposition products.
- Surface Quality: Angle-dependent Near Edge X-ray Absorption Fine Structure (NEXAFS) confirms a high degree of orientational ordering, with approximately 80% of the boron-oxide sites being chemically identical.
- Coverage Limitation: The resulting coverage is low (0.4 Monolayers, ML), limited by the competing thermal desorption of intact B2O3 molecules at the 950 °C reaction temperature.
- Strategic Value: This UHV-based functionalization approach offers a potential alternative pathway for fabricating high-quality, narrow boron-doped delta (δ) layers in diamond, bypassing complex Chemical Vapor Deposition (CVD) or ion implantation methods.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | Diamond (100) | N/A | Type-IIa single crystal, 4 mm x 4 mm. |
| Initial Substrate Doping | 1 x 1018 to 1 x 1019 | atoms/cm3 | Boron doping used to ensure surface conductivity for XPS measurements. |
| Precursor Molecule | Boric Anhydride (B2O3) | N/A | Deposited via thermal evaporation. |
| B2O3 Source Temperature | 900 | °C | Temperature of the Knudsen cell during deposition. |
| Initial B2O3 Coverage | 2.5 | ML | Estimated coverage following deposition. |
| Reaction Annealing Temperature | 950 | °C | Temperature used to desorb hydrogen and initiate surface bonding (30 min duration). |
| Final Boron Coverage (Post-Anneal) | 0.4 | ML | Coverage achieved after annealing, indicating significant desorption. |
| C1s Component C1 Shift | -0.63 ± 0.05 | eV | Attributed to C=C surface dimers (60% of surface sites). |
| C1s Component C2 Shift | -0.90 ± 0.05 | eV | Attributed to Carbon-Boron (C-B) bonds (40% of surface sites). |
| Estimated δ-Layer Doping Density | > 2 x 1020 | cm-3 | Projected density if 0.4 ML B is incorporated via subsequent overgrowth (based on N-doping analogy). |
Key Methodologies
Section titled “Key Methodologies”The boron-oxide termination was achieved through a controlled UHV surface engineering process:
- Substrate Preparation: A CVD-grown (100) diamond substrate was hydrogen-terminated using a microwave plasma containing methane (CH4) and trimethylborane (TMB) to ensure surface conductivity and H-termination.
- Initial Cleaning: The H-terminated sample was annealed in UHV at 450 °C for 1 hour to remove atmospheric adsorbates.
- Molecular Deposition: Molecular B2O3 was deposited onto the H-terminated surface via thermal evaporation using a Knudsen cell heated to 900 °C, achieving an estimated initial coverage of 2.5 ML.
- Reaction Annealing: The sample was annealed to 950 °C for 30 minutes. This temperature is sufficient to desorb the surface hydrogen (creating reactive sites) and initiate the reaction between the diamond surface and the B2O3 decomposition products.
- Surface Analysis: Surface chemistry and bonding were characterized in situ using:
- XPS (X-ray Photoelectron Spectroscopy): High-resolution core level scans (C1s, B1s, O1s) were used to determine chemical states and coverage (0.4 ML B).
- NEXAFS (Near Edge X-ray Absorption Fine Structure): Angle-dependent measurements were performed at the Boron and Oxygen K-edges to confirm the high orientational ordering and the presence of B=O moieties.
Commercial Applications
Section titled “Commercial Applications”This research contributes to advanced diamond technology, particularly in areas requiring precise control over surface termination and nanoscale doping profiles.
- Advanced Electronic Devices:
- Boron Delta (δ) Layers: Provides a foundation for fabricating ultra-narrow, highly doped conductive layers in diamond, crucial for high-speed field-effect transistors (FETs) and quantum transport devices.
- High Power/High Frequency Electronics: Diamond’s wide bandgap and high thermal conductivity make it ideal for high-power radio frequency (RF) components; controlled surface termination is key to device stability and performance.
- Quantum Technology:
- Quantum Enhanced Transport: Fabrication of highly ordered interfaces is essential for realizing predicted quantum effects (e.g., high carrier mobility, quantized electronic states) in boron-doped diamond structures.
- Heterostructure Engineering:
- Diamond/Boron Interfaces: The UHV molecular deposition technique can be adapted to form ordered interfaces between diamond and other boron-based materials (e.g., Boron Nitride), enabling novel heterojunction devices.
- Surface Functionalization:
- Chemical Synthesis: The highly oriented boron-oxide termination can serve as a chemically active template for subsequent complex UHV-based synthesis processes, allowing for the attachment of other functional species in an ordered fashion.
View Original Abstract
Abstract A boron‐oxide termination of the diamond (100) surface has been formed by depositing molecular boron oxide B 2 O 3 onto the hydrogen‐terminated (100) diamond surface under ultrahigh vacuum conditions and annealing to 950 °C. The resulting termination is highly oriented and chemically homogeneous, although further optimization is required to increase the surface coverage beyond the 0.4 monolayer coverage achieved here. This work demonstrates the possibility of using molecular deposition under ultrahigh vacuum conditions for complex surface engineering of the diamond surface, and may be a first step in an alternative approach to fabricating boron doped delta layers in diamond.