Determination of the internal structural heterogeneity of natural diamond - Methodological aspects of using confocal Raman spectroscopy with polarization analysis

At a Glance

Metadata	Details
Publication Date	2024-05-07
Journal	LITHOSPHERE (Russia)
Authors	L. I. Bogdanova, Yu. V. Shchapova, L. Ya. Sushanek, E. A. Vasiliev, S. L. Votyakov
Institutions	Saint Petersburg Mining University, Zavaritsky Institute of Geology and Geochemistry
Analysis	Full AI Review Included

Technical Documentation & Analysis: Internal Structural Heterogeneity in Diamond via Confocal Polarized Raman Spectroscopy

Reference: Bogdanova et al. (2024) Determination of the internal structural heterogeneity of natural diamond: Methodological aspects of using confocal Raman spectroscopy with polarization analysis. Lithosphere (Russia), 24(2), 347-363.

Executive Summary

This document analyzes a critical methodology for characterizing internal structural quality in diamond using Confocal Raman Spectroscopy (CRS) combined with polarization analysis. This technique is highly relevant for engineers and scientists requiring precise control over diamond material properties.

Core Achievement: Development of a robust analytical procedure to map and statistically characterize structural heterogeneity (stress, strain, defects, and growth zoning) in both natural and synthetic CVD diamond crystals.
High Resolution: The methodology achieves high spectral resolution (0.5-0.6 cm^-1) and exceptional spatial resolution (1 µm lateral, 2-6 µm depth).
Key Parameters: Analysis focuses on the F_2g vibrational mode parameters: peak position (p), measured width (FWHM), and the Gaussian contribution (g) to line broadening.
Structural Insights: Variations in these parameters are directly correlated with internal structural stresses (up to 0.7 GPa estimated), lattice constant changes, and the concentration/association of impurity defects (N and B).
Typomorphic Feature: Statistical characteristics of heterogeneity (unimodal/bimodal distributions, dispersion) are proposed as a reliable typomorphic feature for identifying the geological source or growth conditions of diamond crystals.
CVD Validation: The methodology was successfully tested and validated using synthetic CVD single crystals doped with Nitrogen and Boron, confirming its applicability to 6CCVD materials.

Technical Specifications

The following hard data points were extracted from the research paper detailing the experimental setup and measured material characteristics.

Parameter	Value	Unit	Context
Spectral Resolution	0.5-0.6	cm^-1	High resolution achieved by Horiba LabRam HR800.
Spatial Resolution (Lateral)	1-3	µm	Confocal microscope resolution.
Spatial Resolution (Depth)	2-6	µm	Confocal microscope resolution, dependent on objective/diaphragm.
Raman Mode Analyzed	F_2g	N/A	Triply degenerate optical phonon mode in diamond.
Ideal F_2g Position	~1332.2	cm^-1	Position in ideal diamond structure.
Temperature of Measurement	300	K	Room temperature analysis.
Crystallographic Orientation Error	8-15	°	Precision of Euler angle determination.
FWHM_corr Range (Synthetic N-doped)	1.67-2.0	cm^-1	Corrected width, showing broadening due to N impurities.
FWHM Range (Natural/Heterogeneous)	Up to 4.5	cm^-1	Observed in the intermediate layer of the heterogeneous Inter-66 sample.
Line Position Shift (p)	1333.0 to 1332.8	cm^-1	Shift observed in B-doped CVD crystal (C23).
Estimated Internal Stress (Inter-66)	0.7	GPa	Calculated based on line position shift (p).
Statistical Sample Size	~10³	points	Number of analytical points mapped per sample surface.

Key Methodologies

The study utilized advanced Confocal Raman Spectroscopy (CRS) with polarization analysis to map and quantify structural defects. The analytical procedure involved three main steps:

Crystallographic Orientation Determination:
- Measurement of circular diagrams showing the dependence of F_2g intensity on the polarization direction of the scattered light.
- Use of a half-wave plate (Thorlabs, RSP05/M) rotated in 20° steps.
- Calculation of Euler angles (Z-Y-Z rotation) via non-linear minimization (MATLAB program) to align the crystal axes (x=[100], y=[010], z=[001]) with the spectrometer coordinate system.
2D Surface Mapping of Spectral Parameters:
- Acquisition of 2D spectral arrays across the crystal surface using a motorized stage (50-100 µm grid spacing).
- Mapping the distribution of key F_2g parameters: position (p), measured width (FWHM), and Gaussian contribution (g).
- Visualization of structural stresses, deformations, twins, and defect associations based on parameter variations.
Spectral Line Shape Analysis and Statistical Characterization:
- Approximation of the F_2g line shape using the Voigt or pseudo-Voigt function to separate Gaussian (instrumental/structural disorder) and Lorentzian (phonon lifetime/impurity-induced) contributions.
- Correction of FWHM for instrumental broadening (FWHM_corr) using the Váczi approximation.
- Generation of frequency distribution diagrams (histograms) for FWHM_corr and p, using ~10³ statistically significant points to characterize unimodal or bimodal heterogeneity.

6CCVD Solutions & Capabilities

The research demonstrates the critical role of high-quality, precisely characterized diamond materials—especially synthetic CVD SCDs—in advanced structural analysis and materials science. 6CCVD is uniquely positioned to supply the materials and customization required to replicate and extend this research.

Applicable Materials for Structural Analysis

The paper validated its methodology using synthetic CVD SCDs doped with Nitrogen and Boron. 6CCVD offers direct equivalents and superior quality control essential for this type of high-resolution spectroscopy:

Optical Grade Single Crystal Diamond (SCD): Required for high-purity reference standards and low-defect studies (Trend I in Fig. 6). Our SCD offers Ra < 1 nm polishing, crucial for minimizing surface scattering and achieving 1 µm spatial resolution.
Boron-Doped Diamond (BDD): Essential for replicating the B-doped results (C23 sample). 6CCVD provides custom BDD materials, allowing researchers to precisely control the concentration and distribution of the dopant, which directly influences the Raman line shift (p) and FWHM.
Polycrystalline Diamond (PCD) Substrates: While the paper focused on SCD, the methodology for mapping strain and structural disorder is highly applicable to large-area PCD, which 6CCVD supplies up to 125 mm diameter.

Customization Potential for Advanced Research

Replicating the polarization analysis and structural mapping requires materials with specific dimensions, orientations, and surface finishes. 6CCVD provides comprehensive customization services:

Research Requirement	6CCVD Capability	Technical Advantage
Precise Crystallographic Orientation	Custom SCD/PCD growth on specific planes (e.g., [100], [111], or off-axis orientations).	Enables direct comparison with calculated Raman tensor models and accurate stress calibration (Grimsditch method).
High-Quality Surface Finish	SCD polishing to Ra < 1 nm; Inch-size PCD polishing to Ra < 5 nm.	Minimizes surface defects and scattering, ensuring the high spatial resolution (1 µm) necessary for confocal mapping.
Custom Dimensions	Plates/wafers up to 125 mm (PCD); SCD thickness from 0.1 µm to 500 µm.	Supports large-area mapping and the production of thick substrates (up to 10 mm) for 3D structural analysis.
Integrated Electrodes/Contacts	Internal metalization capability (Au, Pt, Pd, Ti, W, Cu).	Allows for in situ stress/strain measurements under applied electric fields, extending the scope of the polarization analysis.

Engineering Support

The complexity of interpreting polarized Raman data, including the calculation of Euler angles and the deconvolution of Voigt profiles (separating Gaussian structural disorder from Lorentzian phonon lifetime effects), necessitates expert knowledge.

6CCVD’s in-house PhD team specializes in CVD diamond growth, defect physics, and advanced characterization techniques. We offer consultation services to assist researchers in:

Selecting the optimal SCD or BDD material grade based on required FWHM and defect tolerance.
Designing custom crystal orientations for specific polarization experiments.
Interpreting structural heterogeneity maps (p-FWHM diagrams) for similar materials science or geological typomorphism projects.

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

View Original Abstract

Aim. To describe a technique for studying the internal structural heterogeneity of natural diamond crystals, based on confocal Raman spectroscopy with polarization analysis, including angular resolution, at high spectral (0.5-0.6 cm -1 ) and spatial (1 μm) resolution. Results . The parameters of the F 2g vibrational mode in diamond (position, width, intensity, shape, including the Gaussian and Lorentzian contributions to the broadening) are determined by the superposition influence of a number of factors, including the type and content of structural stresses, deformations, various types of defects, as well as orientation of crystallographic axes of the crystal relative to the directions of incident and scattered rays and the directions of their electric polarization vectors. The proposed analytical technique includes: (1) analysis of the crystallographic orientation of the sample in the spectrometer coordinate system and possible misorientations of its fragments with an error of ≈8-15°; (2) visualization of the distribution of structural stresses, deformations, twins, impurity defects and their associates based on sample surface mapping by spectral parameters of the F 2g vibration mode; (3) obtaining statistical characteristics of the internal structural heterogeneity of the samples based on diagrams of spectral parameter frequency with a statistically significant number (≈10 3 ): unimodality (uni-, bimodal distributions) and distribution dispersion (from ≈0.1 to ≈0.6 cm -1 for width and from ≈0.04 to ≈0.6 cm -1 for line position). The procedure was tested using two synthetic CVD diamond single crystals doped with nitrogen and boron. The possibility of typification of natural samples by statistical characteristics of internal heterogeneity is considered using the example of samples from kimberlite pipes of Yakutia and placers of the Western Cis-Urals. Conclusions . A method for determining the internal structural heterogeneity of natural diamond crystals based on confocal Raman spectroscopy with polarization analysis is proposed. The possibility of using statistical characteristics of heterogeneity as a typomorphic feature of the original diamond source is demonstrated. The proposed diagrams are promising for sample comparison and typification.

Tech Support

Original Source

DOI: https://doi.org/10.24930/1681-9004-2024-24-2-347-363