| 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 |
- Core Methodology: A high-resolution Confocal Polarized Raman Spectroscopy (CPRS) technique was developed and validated for analyzing the internal structural heterogeneity of natural and synthetic diamonds.
- Resolution Achieved: The method operates at high spectral resolution (0.5-0.6 cm-1) and high spatial resolution (1 ”m), enabling detailed 2D mapping of crystal defects and stress fields.
- Key Parameters: Analysis focuses on the F2g vibrational mode parameters: line position (p), measured width (FWHM), and the relative contributions of Gaussian (structural disorder) and Lorentzian (impurity-induced) broadening.
- Structural Analysis: The technique successfully visualizes the distribution of structural stresses, deformations, twins, and impurity defects (N, B) across the crystal surface, correlating these features with growth zoning.
- Typomorphism Tool: Statistical characteristics (unimodal vs. bimodal distributions, dispersion width) of the F2g parameters, derived from large datasets (approx. 103 points), serve as robust typomorphic features to distinguish diamonds from different geological sources (e.g., Yakutia kimberlites vs. Western Cis-Urals placers).
- Orientation Mapping: An analytical procedure was implemented to determine the crystallographic orientation (Euler angles) of crystal fragments with an error of approx. 8-15°, crucial for accurate stress calculations.
| Parameter | Value | Unit | Context |
|---|
| Spectral Resolution | 0.5-0.6 | cm-1 | Confocal Raman Spectroscopy (Horiba LabRam HR800) |
| Spatial Resolution (Lateral) | 1-3 | ”m | Confocal Raman Spectroscopy |
| Spatial Resolution (Depth) | 2-6 | ”m | Dependent on objective and confocal aperture |
| Excitation Wavelength | 633 | nm | He-Ne Laser (Linearly Polarized) |
| Diffraction Grating | 1800 | lines/mm | Cherny-Turner Monochromator |
| Measurement Temperature | 300 | K | All Raman measurements |
| EBSD Acceleration Voltage | 20, 25 | keV | Electron Backscatter Diffraction (EBSD) |
| Crystallographic Orientation Error | 8-15 | ° | Error in determining Euler angles (alpha, beta, gamma) |
| FWHMcorr Range (Natural Samples) | 1.8-4.5 | cm-1 | Corrected width of F2g mode |
| Line Position (p) Range (Natural Samples) | 1331.5-1333.3 | cm-1 | Position of F2g mode |
| Minimum Residual Stress Detected | 0.7 | GPa | Estimated from line position shift (Inter-66 sample) |
| Statistical Sample Size | approx. 103 | points | Number of analytical points per sample map |
| Intrinsic Lorentzian Width (N-doped) | 1.50-1.55 | cm-1 | Reference value for HPHT diamond at 300 K |
- Crystallographic Orientation Determination: The sampleâs orientation (Euler angles: alpha, beta, gamma) relative to the spectrometer coordinate system (X, Y, Z) is determined by measuring the angular dependence of the scattered light intensity.
- Polarization Diagram Measurement: Polarized Raman spectra are collected by rotating a half-wave plate (Thorlabs RSP05/M) in 20° steps, varying the polarization direction of the scattered light (es).
- Orientation Refinement: The experimental polarization diagrams are fitted to the theoretical Loudon model (Equation 6) using a non-linear minimization algorithm (fmincon in MATLAB) to determine the optimal Euler angles, confirming the crystal orientation and identifying misoriented zones.
- 2D Surface Mapping: Confocal Raman spectra are acquired across the entire polished crystal surface on a regular grid (50-100 ”m spacing) to generate maps containing approximately 103 analytical points.
- Spectral Parameter Extraction: The F2g mode contour is fitted using the pseudo-Voigt function (or Voigt function with fixed Gaussian width) to extract the line position (p), measured FWHM, and the Gaussian contribution (g).
- FWHM Correction: The measured FWHM is corrected for instrumental broadening (spectral resolution, s = 0.6 cm-1) using an approximate formula (VĂĄczi, 2014) to obtain the intrinsic FWHMcorr, representing the true structural disorder.
- Statistical Characterization: Frequency distribution diagrams (histograms) are generated for p and FWHMcorr. These diagrams are analyzed for statistical characteristics (unimodality, bimodality, and distribution dispersion) to classify the internal structural heterogeneity of the samples.
- Advanced Diamond Quality Control: Precise, non-destructive mapping of residual stress and strain fields in synthetic CVD and HPHT diamonds, essential for manufacturing high-performance electronic substrates and optical components.
- Geological Sourcing and Exploration: Utilizing the statistical distribution of F2g parameters (p and FWHMcorr) as a robust typomorphic fingerprint to rapidly link placer diamonds back to their primary kimberlite source, aiding mineral exploration efforts.
- High-Power Laser Optics: Characterization of structural defects and internal strain (e.g., identifying regions with 0.7 GPa stress) that affect birefringence and thermal management in diamond optical windows and heat sinks.
- Semiconductor Manufacturing: Detailed analysis of growth zoning and localized impurity concentrations (N, B) in doped diamond substrates, critical for optimizing doping profiles and minimizing structural defects in quantum sensing and high-frequency electronics.
- Crystallography and Materials Research: Providing high-resolution data on crystallographic misorientation (e.g., 60° twin boundaries) and structural disorder, offering feedback for optimizing crystal growth parameters to achieve higher structural perfection.
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 ÎŒm) 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 â8-15°; (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 (â10 3 ): unimodality (uni-, bimodal distributions) and distribution dispersion (from â0.1 to â0.6 cm -1 for width and from â0.04 to â0.6 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.