Material Removal on Hydrogen-Terminated Diamond Surface via AFM Tip-Based Local Anodic Oxidation

At a Glance

Metadata	Details
Publication Date	2025-08-26
Journal	Micromachines
Authors	Jinyan Tang, Zhongliang Cao, Zhongwei Li, Yuan-Liu Chen
Institutions	Zhejiang University
Analysis	Full AI Review Included

Technical Documentation & Analysis: AFM Tip-Based Material Removal on H-Terminated Diamond

6CCVD Reference Document: TSD-2025-LAO-H-DIAMOND Source Paper: Tang et al., Material Removal on Hydrogen-Terminated Diamond Surface via AFM Tip-Based Local Anodic Oxidation, Micromachines 2025, 16, 981.

Executive Summary

This research successfully addresses the critical challenge of nanoscale fabrication and machining of ultra-hard diamond materials using a novel AFM tip-based local anodic oxidation (LAO) technique.

Core Value Proposition: Demonstrates a method to efficiently remove material from hydrogen-terminated (H-terminated) diamond surfaces, significantly improving diamond machinability for advanced semiconductor applications.
Mechanism: Material removal is achieved by applying a high negative bias (> -5 V) to an AFM tip, inducing localized anodic oxidation and subsequent heating.
Efficiency Breakthrough: The removal area far exceeded the tip size (340 nm depressed structure created by a < 30 nm tip), offering higher efficiency than conventional LAO methods on silicon.
Material Softening: The process reduces the hardness of the material surrounding the removal zone, enabling subsequent mechanical scratching using a standard silicon tip.
Material Requirement: The technique relies fundamentally on high-quality, low-stress Single Crystal Diamond (SCD) with precise (100) orientation and stable H-termination achieved via Microwave Plasma CVD (MPCVD).
Application Potential: This method opens pathways for high-resolution, mask-less nanofabrication, surface polishing, and integration of diamond into MOFETs and quantum devices.

Technical Specifications

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

Parameter	Value	Unit	Context
Substrate Material	Single Crystal Diamond (SCD)	N/A	(100) crystallographic plane
Initial Surface Roughness (Ra)	≈ 1	nm	Required for reliable H-termination
Acid Cleaning Temperature	300	°C	H₂SO₄ and KNO₃ solution
H-Plasma Etching Temperature	800	°C	Standard MPCVD process temperature
H-Plasma Pressure	80	Torr	Standard MPCVD process pressure
H-Plasma Microwave Power (Max)	3000	W	Used for Sample I H-termination
AFM Tip Material	Silicon, Platinum (Pt) coated	N/A	Conductive tip (Nominal radius < 30 nm)
LAO Bias Voltage Range (Removal)	-5 to -10	V	Applied to tip (Sample grounded)
Removed Layer Thickness	≈ 0.5	nm	Confined to the thin conductive H-layer
Maximum Depressed Structure Diameter	340	nm	Achieved at -9 V, 1 s duration
Hardness Change	Decreased	N/A	Surrounding material became scratchable by Si tip

Key Methodologies

The experiment relied on precise material preparation using MPCVD techniques, followed by controlled AFM-based local anodic oxidation.

Substrate Preparation: High-quality SCD samples (5 × 5 × 0.5 mm³, (100) orientation) were mechanically polished to achieve an ultra-low surface roughness (Ra ≈ 1 nm).
Chemical Cleaning: Samples were rinsed in an acidic solution (H₂SO₄ and KNO₃) at 300 °C for 30 minutes to remove surface impurities.
MPCVD Chamber Conditioning: The Microwave Plasma CVD chamber was pre-cleaned using H₂ plasma (850 °C, 2500 W, 90 min) to prevent the formation of non-diamond layers.
Hydrogen Termination: Samples were treated with H₂ plasma etching in the MPCVD chamber (800 °C, 80 Torr, 2500-3000 W) to create the conductive two-dimensional hole gas (2DHG) layer on the surface.
Sample Preservation: H-terminated samples were transported under nitrogen (N₂) packaging to prevent surface oxidation and degradation of the C-H bonds.
Local Anodic Oxidation (LAO): Experiments were conducted using a commercial AFM in contact mode. A conductive Pt-coated silicon tip was used as the cathode, and the grounded diamond sample served as the anode.
Material Removal: High negative bias voltages (-5 V to -10 V) were applied to induce localized heating and oxidation, resulting in the detachment and removal of the modified surface layer by the AFM tip.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality, precisely engineered diamond substrates to enable advanced nanoscale fabrication. 6CCVD is uniquely positioned to supply the materials and customization required to replicate and extend this work.

Applicable Materials for Replication and Scaling

The success of AFM-based LAO relies entirely on the quality and stability of the H-terminated conductive layer, which requires ultra-low-stress, high-purity diamond.

Material Recommendation: Optical Grade Single Crystal Diamond (SCD)
- Justification: Our SCD material provides the necessary high purity and low lattice stress (confirmed by the sharp 1332 cm^-1 Raman peak observed in the paper) essential for reliable H-termination and 2DHG formation.
- Surface Quality: 6CCVD guarantees polishing to Ra < 1 nm, matching the stringent surface roughness requirements of the study and ensuring optimal conditions for subsequent plasma processing.

Customization Potential & Device Integration

6CCVD’s in-house capabilities directly address the dimensional and integration needs of advanced diamond research.

Research Requirement	6CCVD Customization Capability	Benefit to Client
Substrate Size	Custom dimensions up to 125mm (PCD) or large-area SCD plates (up to 10mm thick).	Enables scaling from small research samples (5x5 mm²) to production-ready wafer sizes.
Surface Termination	Expertise in MPCVD H-Termination Recipes.	We can replicate the specific 800 °C, 80 Torr H-plasma conditions or optimize recipes for enhanced 2DHG stability and conductivity.
Metalization/Grounding	In-House Metalization Services (Au, Pt, Ti, W, Cu).	Eliminates the need for conductive silver adhesive (used in the paper) by providing pre-patterned ohmic contacts or grounding pads, improving experimental reliability and device integration.
Polishing Control	SCD polishing to Ra < 1 nm; Inch-size PCD polishing to Ra < 5 nm.	Ensures the starting material is atomically flat, minimizing artifacts and maximizing the uniformity of the thin conductive layer.

Engineering Support

The successful implementation of this LAO technique requires deep expertise in both diamond material science and MPCVD processing.

Specialized Consultation: 6CCVD’s in-house PhD team specializes in optimizing MPCVD growth and post-processing, including precise control over surface termination and defect engineering.
Application Focus: We offer material selection and process consultation for similar AFM-Based Nanofabrication, Diamond Machinability, and H-Terminated MOFET projects. We can help researchers select the optimal material (SCD vs. PCD) and orientation for their specific device goals.
Global Logistics: We provide reliable Global Shipping (DDU/DDP), ensuring sensitive H-terminated materials are delivered quickly and safely, minimizing degradation before use.

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

View Original Abstract

Diamond is a promising next-generation semiconductor material, offering a wider band gap, higher electron mobility, and superior thermal conductivity compared with silicon. However, its exceptional hardness makes it challenging to fabricate. In this study, we demonstrate a novel approach to realize material removal on hydrogen-terminated diamond surfaces by atomic force microscope (AFM) tip-based local anodic oxidation. By adjusting both the applied voltage and hydrogen plasma etching parameters, the material is removed over an area larger than the AFM tip size. Notably, the hardness of the material surrounding the removal zone is significantly reduced, enabling it to be scratched with a silicon tip. These findings open a promising pathway for improving the machinability of diamonds in future device applications.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi16090981

References

2023 - Bandgap evolution of diamond [Crossref]
2018 - Thermal conductivity of high purity synthetic single crystal diamonds [Crossref]
2023 - Carrier Mobility up to 106 cm2 V−1 s−1 Measured in Single-Crystal Diamond by the Time-of-Flight Electron-Beam-Induced-Current Technique [Crossref]
2023 - All-optical nuclear quantum sensing using nitrogen-vacancy centers in diamond [Crossref]
2013 - Mechanism of hole doping into hydrogen terminated diamond by the adsorption of inorganic molecule [Crossref]
2021 - Surface transfer doping of diamond: A review [Crossref]
2018 - Characterization and Modeling of Hydrogen-Terminated MOSFETs With Single-Crystal and Polycrystalline Diamond [Crossref]
2016 - Surface properties of hydrogenated diamond in the presence of adsorbates: A hybrid functional DFT study [Crossref]