Formation of a Boron‐Oxide Termination for the (100) Diamond Surface

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

Technical Documentation & Analysis: Boron-Oxide Termination on Diamond (100)

Executive Summary

This documentation analyzes the research demonstrating a novel, highly ordered boron-oxide termination on single-crystal diamond (SCD) surfaces, providing a critical pathway for advanced quantum and electronic device fabrication.

Novel Termination: Successful formation of a chemically homogeneous, highly oriented boron-oxide termination on H-terminated SCD (100) surfaces.
Methodology: Utilizes molecular deposition of Boric Anhydride (B₂O₃) under Ultrahigh Vacuum (UHV) conditions, followed by a high-temperature anneal (950 °C).
Material Requirement: The experiment required a conductive diamond surface (achieved via a thin boron-doped overlayer) on a Type-IIa SCD (100) substrate to prevent charging during XPS/NEXAFS analysis.
Key Achievement: Demonstrated bonding of the boron-oxide moiety to the diamond surface via carbon-boron single bonds, achieving a 0.4 Monolayer (ML) coverage.
Application Potential: This UHV-based functionalization method is a crucial first step toward fabricating highly controlled, narrow boron-doped delta (δ) layers in diamond, essential for quantum enhanced electrical transport and superconducting states.
6CCVD Value Proposition: 6CCVD provides the necessary high-purity, low-defect SCD (100) substrates and custom Boron-Doped Diamond (BDD) layers required to replicate and scale this advanced surface engineering technique.

Technical Specifications

The following hard data points were extracted from the experimental results and methodology:

Parameter	Value	Unit	Context
Substrate Material	Type-IIa Single Crystal (100)	N/A	CVD-grown diamond
Substrate Dimensions	4 x 4	mm	Used for XPS/NEXAFS analysis
Initial B-Doping Concentration	1 x 10¹⁸ - 1 x 10¹⁹	atoms/cm³	Overlayer to ensure surface conductivity
H-Termination Temperature	~850	°C	Microwave H₂ plasma process
H-Termination Pressure	~80	Torr	Process pressure
B₂O₃ Source Temperature	900	°C	Thermal evaporation (Knudsen cell)
Initial B₂O₃ Coverage	2.5	ML	Estimated via photoelectron attenuation
Final Annealing Temperature	950	°C	Required for H desorption and B₂O₃ reaction
Final Boron Coverage	0.4	ML	Achieved after 950 °C anneal
C1s Shift (C₂ component)	-0.90 ± 0.05	eV	Attributed to Carbon-Boron (C-B) bonds
B1s Core Level (Major Peak B₁)	191.43 ± 0.05	eV	Boron-oxide moiety
O1s Core Level (Major Peak O₁)	532.03 ± 0.05	eV	Boron-oxide moiety

Key Methodologies

The formation of the boron-oxide termination involved precise, multi-stage UHV processing steps:

Substrate Preparation: CVD-grown Type-IIa SCD (100) substrates (4 mm x 4 mm) were used, featuring a thin, lightly boron-doped overlayer to ensure surface conductivity and prevent charging.
Hydrogen Termination: Samples were H-terminated using a microwave hydrogen plasma (80 Torr, ~850 °C, 5 min) with small additions of methane (CH₄) and trimethylborane (TMB) to maintain the conductive doped overlayer.
UHV Cleaning Anneal: The H-terminated substrate was introduced into the UHV end-station and annealed at 450 °C for 1 hour to remove atmospheric adsorbates.
B₂O₃ Deposition: Boric anhydride (B₂O₃) was deposited via thermal evaporation using a Knudsen cell maintained at a source temperature of 900 °C, achieving an initial estimated coverage of 2.5 ML.
Reaction Anneal: The sample was annealed at 950 °C for 30 minutes. This temperature is critical, as it facilitates the desorption of hydrogen (creating reactive sites) and promotes the bonding reaction between the B₂O₃ adlayer and the bare diamond surface.
Characterization: Surface chemistry and orientation were analyzed using surface-sensitive X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) at the Australian Synchrotron.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification diamond materials and customization services necessary to advance this research into scalable device fabrication.

Applicable Materials

Replicating and optimizing this UHV surface functionalization requires high-purity, low-defect substrates with controlled conductivity.

Single Crystal Diamond (SCD) Substrates:
- Requirement: High-quality, low-defect SCD (100) is essential for achieving the highly oriented termination observed.
- 6CCVD Solution: We offer Optical Grade SCD (100) with extremely low defect density, ensuring optimal surface uniformity for UHV processing.
Boron-Doped Diamond (BDD) Layers:
- Requirement: The paper utilized a thin B-doped overlayer (10¹⁸ - 10¹⁹ atoms/cm³) to ensure conductivity during characterization.
- 6CCVD Solution: We provide Custom Boron-Doped SCD or PCD with precise doping control (from lightly doped semiconducting to heavily doped metallic/superconducting regimes) to meet specific conductivity requirements for advanced device characterization.

Customization Potential

6CCVD’s advanced MPCVD and post-processing capabilities directly address the needs of complex surface science experiments and future scaling efforts:

Research Requirement	6CCVD Capability	Benefit to Researcher
Substrate Size	Custom plates/wafers up to 125 mm (PCD) and large SCD.	Enables scaling from 4 mm x 4 mm research coupons to industrial wafer sizes.
Surface Quality	SCD polishing to Ra < 1 nm. Inch-size PCD polishing to Ra < 5 nm.	Ensures the ultra-smooth, low-defect surfaces critical for UHV molecular deposition and highly ordered termination.
Thickness Control	SCD/PCD layers from 0.1 µm up to 500 µm. Substrates up to 10 mm.	Allows precise control over the active layer thickness for future delta layer overgrowth experiments.
Metalization	In-house deposition of Au, Pt, Pd, Ti, W, Cu.	Essential for creating reliable electrical contacts and device structures following surface functionalization.
Custom Doping	Precise control over BDD concentration and layer thickness.	Supports the development of optimized conductive layers for charge mitigation and quantum transport studies.

Engineering Support

The formation of boron-doped delta layers (δ-layers) is a highly complex challenge. 6CCVD’s in-house PhD team specializes in the growth and characterization of advanced diamond materials. We can assist researchers with:

Material Selection: Advising on the optimal SCD orientation, doping profile, and surface preparation (e.g., H-termination recipes) required for similar Boron-Doped Delta Layer projects.
Interface Engineering: Consulting on the integration of custom metalization schemes (e.g., Ti/Pt/Au) onto functionalized diamond surfaces for device prototyping.
Global Logistics: Providing global shipping (DDU default, DDP available) to ensure rapid delivery of specialized substrates to UHV facilities worldwide.

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

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.

Tech Support

Original Source

DOI: https://doi.org/10.1002/admi.202400208