Laser-Induced Graphitization of Diamond Under 30 fs Laser Pulse Irradiation
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2022-03-18 |
| Journal | The Journal of Physical Chemistry Letters |
| Authors | Bakhtiar Ali, Han Xu, D. Chetty, R. T. Sang, I. V. Litvinyuk |
| Institutions | Quantum (Australia), Griffith University |
| Citations | 21 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Ultra-Short Pulse Laser Processing of CVD Diamond
Section titled āTechnical Documentation & Analysis: Ultra-Short Pulse Laser Processing of CVD DiamondāExecutive Summary
Section titled āExecutive SummaryāThis research demonstrates the potential of ultra-short 30 fs laser pulses for highly localized, non-thermal structural transformation (graphitization) of Single Crystal Diamond (SCD), opening new avenues for advanced opto-electronic device fabrication.
- Non-Thermal Precision: 30 fs laser irradiation minimizes the Heat Affected Zone (HAZ) and thermal cracking, achieving highly localized spĀ³-to-spĀ² conversion driven primarily by photo-ionization, crucial for high-density device integration.
- High-Quality Conversion: Below the critical fluence of 3.9 J/cmĀ², the process yields a highly crystalline spĀ²-aromatic graphitic fraction, ideal for forming robust āgraphene-on-diamondā heterostructures.
- Reduced Ablation Threshold: The use of sub-50 fs pulses significantly reduces the CVD diamond ablation threshold (by 20-30%) compared to longer fs pulses, enhancing processing efficiency.
- Non-Linear Depth Control: A fractional (~20%) increase in fluence near the ablation threshold (3.3 J/cmĀ² to 3.9 J/cmĀ²) resulted in a substantial three-fold increase in the depth of the graphitized layer, demonstrating precise volumetric control.
- Material Requirement: The study utilized n-type <100> Ib CVD diamond, confirming the suitability of high-quality, low-defect SCD substrates for advanced femtosecond laser processing applications.
- Applications: Findings directly support the development of miniaturized thermionic solar cells, broad-beam light detectors, IR polarization filters, and ultra-wide bandgap āall carbonā opto-electronic devices.
Technical Specifications
Section titled āTechnical Specificationsā| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Material | n-type <100> Ib CVD SCD | N/A | Sample dimensions: 3x3x1 mm |
| Nitrogen Content | ~200 | ppm | High N content (Ib type) |
| Laser Pulse Duration | 30 | fs | Ultra-short pulse regime |
| Laser Wavelength | 800 | nm | Ti3+:sapphire system |
| Repetition Rate | 1 | kHz | Pulse frequency |
| Fluence Range Tested | 2.2 to 6.8 | J/cm2 | Range used for graphitization |
| Critical Fluence Threshold | 3.9 | J/cm2 | Transition point: Crystalline spĀ² (below) to Amorphous Carbon (above) |
| Nominal Ablation Threshold | 3.0 - 4.0 | J/cm2 | Ablation threshold for longer fs pulses (60-100 fs) is higher |
| Graphitized Layer Depth (d) | 0.025 (low fluence) to 0.2 (high fluence) | Āµm | Calculated depth of spĀ² layer |
| Crystallite Size (La) | 19 to 10 | nm | Decreased with increasing fluence (2.2 J/cm2 to 6.8 J/cm2) |
| Raman Diamond Peak | ~1332 | cm-1 | spĀ³ tetrahedral diamond mode |
| Raman Graphite G Peak | ca. 1582 | cm-1 | spĀ² aromatic E2g mode |
Key Methodologies
Section titled āKey MethodologiesāThe experiment focused on ultra-short pulse photo-ablation and structural reorganization of CVD diamond, characterized primarily by Raman spectroscopy and microscopy.
- Material Preparation: n-type <100> Ib CVD diamond samples (3x3x1 mm, ~200 ppm N) were used as the substrate for irradiation.
- Laser System: A commercial 800 nm Ti3+:sapphire laser system was employed, delivering a linearly polarized Gaussian beam with a fixed 30 fs pulse duration and 1 kHz repetition rate.
- Fluence Control: The source pulse energy (0.8 mJ) was attenuated using pellicle beam splitters to achieve four distinct peak fluences ranging from 2.2 J/cm2 to 6.8 J/cm2.
- Irradiation Process: Samples were positioned normal to the beam and irradiated at a scanning speed of 15 mm/s, delivering 667 pulses per irradiation site. The focal spot size was precisely controlled at 10 Āµm (at 1/e maximum intensity).
- Structural Characterization (Raman): Micro-Raman spectra were obtained using an unpolarized 514 nm Ar+ ion laser at 293 K. Data analysis involved linear photoluminescence (PL) background subtraction and fitting using fully symmetric Gaussians to determine I(D)/I(G) ratios and crystallite size (La).
- Topography and Depth Analysis: Optical and Scanning Electron Microscopy (SEM) were used to study track width (w). Graphitized layer depth (d) was calculated using the Beer-Lambert law based on the attenuation of the 1332 cm-1 diamond core mode intensity.
6CCVD Solutions & Capabilities
Section titled ā6CCVD Solutions & CapabilitiesāThe findings of this research highlight the critical need for high-quality, precisely engineered CVD diamond substrates to achieve reproducible, non-thermal laser processing for advanced opto-electronic applications. 6CCVD is uniquely positioned to supply the materials and customization required to replicate and scale this work.
Applicable Materials for Replication and Extension
Section titled āApplicable Materials for Replication and Extensionā| Research Requirement | 6CCVD Material Solution | Technical Advantage |
|---|---|---|
| High-Quality SCD Substrate | Optical Grade Single Crystal Diamond (SCD) | Our SCD offers superior crystalline quality (<100> orientation standard) and extremely low defect density, essential for minimizing non-linear absorption variations during fs-laser processing. |
| Low Nitrogen Content | Electronic Grade SCD (Low N) | While the paper used Ib diamond (~200 ppm N), achieving optimal optical and electronic properties for devices (e.g., detectors, solar cells) requires lower nitrogen content. 6CCVD provides SCD with N < 1 ppm. |
| Graphene-on-Diamond Heterostructures | Polycrystalline Diamond (PCD) Wafers | For scaling up applications like broad-beam detectors, 6CCVD offers large-area PCD wafers up to 125 mm in diameter, allowing for large-scale graphitization tracks. |
| Doping for Conductivity | Boron-Doped Diamond (BDD) | For applications requiring conductive graphitic electrodes (like thermionic solar cells), BDD substrates can be used. Laser graphitization of BDD offers unique opportunities for creating complex, highly conductive interfaces. |
Customization Potential for Device Integration
Section titled āCustomization Potential for Device IntegrationāThe precise control over graphitization depth (0.025 Āµm to 0.2 Āµm) demonstrated in the paper requires highly uniform starting material and subsequent device integration capabilities.
- Custom Dimensions: 6CCVD provides SCD plates and PCD wafers in custom dimensions far exceeding the 3x3x1 mm samples used in the study. We offer plates up to 125 mm (PCD) and custom thicknesses (SCD/PCD 0.1 Āµm - 500 Āµm).
- Thickness Control: The ability to control the graphitized layer depth down to tens of nanometers (0.025 Āµm) necessitates precise substrate thickness. 6CCVD offers SCD substrates with thickness control down to 0.1 Āµm.
- Surface Finish: The quality of the starting surface is paramount for consistent fs-laser coupling. 6CCVD guarantees ultra-smooth polishing with Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring minimal scattering and reproducible ablation thresholds.
- Integrated Metalization: Graphitized tracks often serve as electrodes. 6CCVD offers in-house metalization services (Au, Pt, Pd, Ti, W, Cu) applied directly to the diamond surface, enabling seamless integration of the laser-processed graphitic structures into functional devices (e.g., X-ray detectors or solar cells).
Engineering Support
Section titled āEngineering Supportā6CCVDās in-house PhD team specializes in MPCVD growth and post-processing techniques. We can assist researchers and engineers in selecting the optimal diamond grade (e.g., low-N SCD vs. high-purity PCD) and surface preparation required to replicate or extend this non-thermal, ultra-short pulse processing technique for similar opto-photonic and ultra-wide bandgap device projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The degree of laser-induced graphitization from a sp<sup>3</sup>-bonded to a sp<sup>2</sup>-bonded carbon fraction in a single crystal chemical vapor deposited (CVD) diamond under varying fluence of an ultrashort pulsed laser (30 fs, 800 nm, 1 kHz) irradiation has been studied. The tetrahedral CVD sp<sup>3</sup> phase is found to transition to primarily an sp<sup>2</sup> aromatic crystalline graphitic fraction below the critical fluence of 3.9 J/cm<sup>2</sup>, above which predominantly an amorphous carbon is formed. A fractional increase of fluence from 3.3 to 3.9 J/cm<sup>2</sup> (ā¼20%) results in a substantially (ā¼3-fold) increased depth of the sp<sup>2</sup> graphitized areas owing to the nonlinear interactions associated with a fs laser irradiation. Additionally, formation of a CāO carbonyl group is observed below the critical threshold fluence; the CāO cleavage occurrs gradually with the increase of irradiation fluence of 30 fs laser light. The implications for these findings on enhancement of fs driven processing of diamonds are discussed.