The Effect of Surface Treatment on Structural Properties of CVD Diamond Layers with Different Grain Sizes Studied by Raman Spectroscopy

At a Glance

Metadata	Details
Publication Date	2021-03-08
Journal	Materials
Authors	Anna Dychalska, W. Koczorowski, Marek Trzciński, Lidia Mosińska, Mirosław Szybowicz
Institutions	Bydgoszcz University of Science and Technology, Institute of Mathematics
Citations	15
Analysis	Full AI Review Included

Technical Documentation: Surface Engineering of CVD Diamond via Hydrogen Termination

Reference Paper Analysis: The Effect of Surface Treatment on Structural Properties of CVD Diamond Layers with Different Grain Sizes Studied by Raman Spectroscopy (Materials 2021, 14, 1301).

Executive Summary

This documentation analyzes a study demonstrating the critical role of post-growth hydrogen plasma treatment (H-termination) in modifying the structural and chemical properties of CVD diamond layers, a key process for advanced electronic and electrochemical applications.

Core Achievement: Successful modification and characterization of microcrystalline (MCD) and nanocrystalline (NCD) CVD diamond surfaces using hot filament (HF) hydrogen plasma treatment.
Structural Improvement: Hydrogenation effectively etched away non-diamond (sp²) carbon phases, leading to a significant increase in the diamond Quality Factor Q(A) (up to 100% increase for NCD samples).
Surface Chemistry Control: XPS and Contact Angle (CA) measurements confirmed successful H-termination, resulting in highly hydrophobic surfaces (CA up to 110°).
Material Dependence: Layers with smaller grain sizes and higher initial sp² content (NCD) showed greater susceptibility to structural modification and etching during the H-treatment process.
Analytical Methodology: The study emphasized the necessity of localized, high-resolution analysis (using T-shaped markers and micro-Raman mapping) to accurately track subtle structural changes induced by surface treatment.
6CCVD Value Proposition: 6CCVD provides the high-purity, customizable SCD and PCD starting materials required for replicating and advancing this critical surface engineering research.

Technical Specifications

Parameter	Value	Unit	Context
Deposition Method	HF CVD	N/A	Used for all diamond layer growth.
Substrate Material	Silicon (100)	N/A	Starting material for deposition.
Substrate Temperature	900	K	During CVD growth process.
Filament Temperature (Growth)	2000	K	During CVD growth process.
Filament Temperature (H-Treatment)	2300	K	Post-growth hydrogen plasma activation.
Diamond Layer Temperature (H-Treatment)	1100	K	During post-growth hydrogen plasma treatment.
Working Gas Pressure (Growth)	27	mbar	During CVD growth process.
Working Gas Pressure (H-Treatment)	30	mbar	During post-growth treatment (15 min duration).
CH₄ Concentration Range	1.0 to 3.8	%	Used to control grain size (MCD to NCD).
Layer Thickness	2 to 3 ± 0.5	µm	Estimated thickness of deposited diamond films.
Average Grain Size (MCD)	2.0 to 2.5 ± 0.8	µm	Microcrystalline Diamond (MCD) samples.
Average Grain Size (NCD)	0.06 to 0.2 ± 0.1	µm	Nanocrystalline Diamond (NCD) samples.
Maximum Contact Angle (CA)	110	°	Achieved for MCD2.5 after H-termination (hydrophobic).
Q(A) Improvement (NCD0.02)	100	%	Increase in Quality Factor (sp³ content) inside the marker.
m/I_G Improvement (NCD0.02)	359	%	Increase in photoluminescence parameter outside the marker, indicating higher H concentration.

Key Methodologies

The study involved two primary phases: CVD diamond deposition and post-growth hydrogen plasma treatment, followed by localized characterization.

CVD Diamond Deposition (HF CVD):
- Silicon (100) substrates (5 x 5 mm²) were mechanically scratched using 0.2 µm diamond powder for effective nucleation.
- Working gas mixture consisted of H₂ (>96%) and CH₄.
- Deposition parameters were fixed: Pressure at 27 mbar, Filament T at 2000 K, and Substrate T at 900 K.
- Four distinct diamond layers (MCD2, MCD2.5, NCD0.2, NCD0.02) were produced by varying CH₄ concentration (1.0% to 3.8%) and deposition time (1.0h to 6.0h) to control grain size.
Localized Marker Fabrication:
- A characteristic T-shape marker was fabricated on the surface of each layer using Focused Ion Beam (FIB) patterning (Ga⁺ ion, 30 keV, 9-21 nA current). This ensured subsequent Raman, SEM, and XPS measurements were performed on the exact same micro-area before and after treatment.
Post-Growth Hydrogen Treatment (H-Termination):
- The diamond layers were exposed to pure hydrogen plasma in a CVD chamber.
- Filament temperature was maintained at 2300 K to activate H₂ into radical atoms.
- Diamond layer temperature reached 1100 K.
- Treatment duration was 15 minutes at a pressure of 30 mbar.
Characterization:
- Structural analysis was performed using micro-Raman spectroscopy (488 nm excitation, 1 µm spatial resolution) to track changes in sp³/sp² hybridization and photoluminescence background ($m/I_{G}$).
- Surface morphology was analyzed via Scanning Electron Microscopy (SEM).
- Chemical composition and termination were analyzed via X-ray Photoelectron Spectroscopy (XPS) (Monochromatic Al Kα source).
- Surface wettability was quantified using Contact Angle (CA) measurements.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality, structurally consistent CVD diamond layers for advanced surface engineering applications, such as creating highly conductive H-terminated surfaces for FETs or hydrophobic coatings. 6CCVD is uniquely positioned to supply the foundational materials and customization services required to replicate and extend this work.

Applicable Materials

To replicate or extend the research on surface termination effects, 6CCVD recommends the following materials, which correspond directly to the MCD and NCD layers studied:

Research Requirement	6CCVD Material Solution	Key Capability Match
Microcrystalline Diamond (MCD)	Standard Polycrystalline Diamond (PCD)	High-quality, large grain size CVD diamond for bulk property studies and high-power applications.
Nanocrystalline Diamond (NCD)	Fine-Grain Polycrystalline Diamond (PCD)	Highly uniform, small grain size material ideal for surface-dominated applications (e.g., electrochemistry, sensing) where high grain boundary volume is desired.
Surface Chemistry Analysis	Optical Grade SCD or PCD	Low defect density and high purity are essential for accurate photoluminescence (PL) and Raman analysis, minimizing background noise.
Future Electronic Applications	Boron-Doped Diamond (BDD)	For extending H-termination studies into p-type conductivity enhancement for Field Effect Transistors (FETs) or electrochemical electrodes.

Customization Potential

The study relied on precise control over material dimensions, thickness, and localized patterning. 6CCVD offers comprehensive customization capabilities that streamline the research process:

Custom Dimensions and Thickness: 6CCVD supplies PCD plates/wafers up to 125mm in diameter. The required layer thicknesses (2-3 µm) are well within our standard range for PCD (0.1 µm - 500 µm). We also provide custom substrates up to 10mm thick.
Advanced Patterning and Marking: While the researchers used FIB for T-shaped markers, 6CCVD offers high-precision laser cutting and patterning services. This allows for the creation of precise fiducial markers or complex electrode geometries with minimal subsurface damage, providing a cleaner starting point for sensitive surface treatments.
Surface Preparation: The structural changes observed are highly dependent on the initial surface quality. 6CCVD provides ultra-smooth polishing (Ra < 5nm for inch-size PCD) to ensure a highly controlled, uniform surface morphology prior to plasma treatment.
Integrated Metalization: H-terminated diamond is frequently used in electronic devices. 6CCVD offers in-house metalization services (Au, Pt, Pd, Ti, W, Cu) for researchers requiring subsequent electrode fabrication or contact layers on their terminated diamond films.

Engineering Support

6CCVD’s in-house PhD team specializes in CVD diamond growth parameters and post-processing effects. We can assist researchers in optimizing material selection (grain size, sp² content, defect density) for similar Hydrogen Termination and Surface Modification projects, ensuring the starting material meets the exact specifications required for targeted structural and chemical outcomes.

Call to Action: For custom specifications or material consultation regarding high-quality PCD or SCD for surface engineering, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Extensive Raman spectroscopy studies combined with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) measurements were performed to investigate structural and chemical changes in diamond layers deposited by chemical vapour deposition (CVD) upon post-growth treatment with hydrogen. The aim of this study is to characterize the changes in micro-structural properties of diamond layers with different grain sizes and different contents of sp2 carbon phase. Hydrogenation or oxidization of diamond layer surface is often performed to modify its properties; however, it can also strongly affect the surface structure. In this study, the impact of hydrogenation on the structure of diamond layer surface and its chemical composition is investigated. Owing to their polycrystalline nature, the structural properties of CVD diamond layers can strongly differ within the same layer. Therefore, in this project, in order to compare the results before and after hydrogen treatment, the diamond layers are subjected to Raman spectroscopy studies in the vicinity of a T-shape marker fabricated on the surface of each diamond layer studied.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma14051301

References

2015 - Structure and wettability property of the growth and nucleation surfaces of thermally treated freestanding CVD diamond films [Crossref]
2003 - Control wettability of the hydrogen-terminated diamond surface and the oxidized diamond surface using an atomic force microscope [Crossref]
1989 - Resistivity of chemical vapor deposited diamond films [Crossref]
2012 - Electronic properties of H-terminated diamond during NO2 and O3 adsorption and desorption [Crossref]
2010 - Electronic and surface properties of H-terminated diamond surface affected by NO2 gas [Crossref]
1997 - Diamond surface-channel FET structure with 200 V breakdown voltage [Crossref]
2004 - Influence of epitaxy on the surface conduction of diamond film [Crossref]
2006 - Application of diamond film to cold cathode fluorescent lamps for LCD backlighting [Crossref]
2001 - Diamond surface conductivity experiments and photoelectron spectroscopy [Crossref]
2009 - Ultrananocrystalline diamond thin films functionalized with therapeutically active collagen networks [Crossref]