Direct Laser Writing of Nucleation Sites for Patterned Diamond Growth
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-03-11 |
| Journal | Journal of Electronic Materials |
| Authors | Sumeer Khanna, J. Narayan, Roger J. Narayan |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details a novel, highly controlled method for fabricating patterned diamond structures using Direct Laser Writing (DLW) combined with thermal processing and Hot-Filament Chemical Vapor Deposition (HFCVD).
- Novel Fabrication Sequence: A polymer structure is created via two-photon polymerization (DLW), carbonized (pyrolyzed) at 540°C, and then used as a selective, barrier-less nucleation template for diamond growth via HFCVD.
- High sp3 Content Nucleation Sites: The carbonized structures exhibit a high sp3 content (45-55%), confirmed by Raman and XPS analysis, which effectively initiates diamond growth without traditional surface roughening methods.
- High-Quality Patterned Diamond: Continuous diamond crystallites (average size ~2 ”m) were successfully grown in precise 2D patterns on both Si (100) and sapphire (0001) substrates. The diamond quality is high, evidenced by a sharp Raman peak (FWHM less than or equal to 5 cm-1).
- Controlled Morphology: The crystallites display a fourfold faceting morphology, indicating growth along the fast <100> direction with {111} facets. The growth rate was determined to be rapid (~0.7 ”m/h).
- Q-Carbon Enhancement: Pulsed Laser Annealing (PLA) of the carbonized structures successfully converted the material into the Q-carbon phase, achieving an ultra-high sp3 content (70-80%) with embedded nanodiamonds (2-30 nm), promising enhanced nucleation density for future work.
- Versatility: The method allows for the arrangement of diamond crystallites in innovative 2D geometric designs, critical for advanced device fabrication.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| DLW Minimum XY Feature Size | ~160 | nm | Smallest available resolution for 3D printing. |
| DLW XY Resolution | 400 | nm | Smallest available resolution for 3D printing. |
| Polymerization Laser Wavelength | 780 | nm | Two-photon polymerization (2PP) process. |
| Polymerization Laser Pulse Duration | 80-100 | fs | 2PP process parameters. |
| Carbonization Temperature (Final) | 540 | °C | Thermal annealing temperature (15 min hold). |
| Carbonized Structure sp3 Content | 45-55 | % | Measured via Raman and XPS after 540°C annealing. |
| Q-Carbon sp3 Content | 70-80 | % | Measured via Raman after Pulsed Laser Annealing (PLA). |
| Diamond Raman Peak Shift | 1333-1335 | cm-1 | Up-shift indicating minor residual strain. |
| Diamond Raman FWHM | less than or equal to 5 | cm-1 | Full Width at Half Maximum (indicator of high crystal quality). |
| Diamond Crystallite Average Size | ~2 | ”m | Observed size after 3 hours of HFCVD growth. |
| Diamond Growth Rate | ~0.7 | ”m/h | Calculated growth rate. |
| HFCVD Substrate Temperature | ~700 | °C | Temperature during diamond deposition. |
| HFCVD CH4 Pressure | 2 | T | Methane gas pressure during deposition. |
| HFCVD H2 Pressure | 100 | T | Hydrogen gas pressure during deposition. |
| HFCVD Total Chamber Pressure | 20 | T | Total pressure during deposition. |
| PLA Energy Density | ~0.7 | J/cm2 | Pulsed Laser Annealing treatment (for Q-carbon formation). |
| Nanodiamond Size (in Q-carbon) | 2-30 | nm | Embedded crystallites after PLA. |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication sequence involves four primary steps: CAD design, 3D printing via DLW, thermal carbonization, and HFCVD diamond growth.
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Computer-Aided Design (CAD):
- 3D models of triangular rod structures (150 ”m x 150 ”m footprint, 100 ”m height) were designed in SolidWorks.
- The geometry was chosen to ensure symmetric shrinkage during carbonization, resulting in sharp, thin carbonized features.
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3D Printing (Direct Laser Writing - DLW):
- The process utilized two-photon polymerization (2PP) on a Nanoscribe PPGT2 instrument.
- Resin/Substrate: IP-S negative-tone photo-polymeric resin applied to Si (100) and sapphire (0001) substrates.
- Laser Parameters: 780 nm wavelength, 80 MHz repetition rate, 50 mW average power.
- Structures were printed in a 25x25 array format (1 cm x 1 cm area).
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Thermal Annealing (Carbonization):
- The process was conducted in ambient air, relying on internal oxygen depletion for carbonization.
- Stabilization: Temperature ramped (40°C/min) to 420°C and held for 15 minutes.
- Carbonization: Temperature ramped (40°C/min) to 540°C and held for 15 minutes.
- This process resulted in a volume reduction (shrinkage) and the formation of glassy carbon structures with 45-55% sp3 content.
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Optional Q-Carbon Formation (Pulsed Laser Annealing - PLA):
- Carbonized structures were exposed to ultrafast PLA (e.g., ~0.7 J/cm2) to induce a highly nonequilibrium thermal melt and fast quench.
- This converts the carbonized layer into the Q-carbon phase, embedding nanodiamond crystallites (2-30 nm) and increasing the sp3 content to 70-80%.
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Diamond Growth (Hot-Filament Chemical Vapor Deposition - HFCVD):
- Tungsten filaments were used to atomize H2 and CH4 gases.
- Deposition Conditions: Substrate temperature ~700°C, CH4 pressure (2 T), H2 pressure (100 T), Total pressure (20 T).
- Growth: Deposition was performed for approximately 3 hours, resulting in continuous diamond crystallites nucleating selectively along the carbonized patterns.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology provides a highly precise, mask-less method for integrating high-quality diamond structures into microdevices, offering significant advantages over traditional etching and seeding techniques.
- Quantum Computing and Sensing:
- Fabrication of nitrogen vacancy (NV) diamond center-based quantum devices and sensors (by doping nitrogen during growth).
- Precise placement and alignment of diamond crystallites are essential for scalable quantum architectures.
- High-Power Electronics:
- Utilizing diamondâs exceptional thermal conductivity and electrical properties in patterned structures for high-frequency and high-power devices.
- Superconducting Materials:
- The ability to form the Q-carbon phase (which exhibits distinct superconducting transition temperatures) provides a pathway for fabricating novel superconducting devices.
- Biomedical and Electrochemical Sensors:
- Creation of patterned diamond electrodes and selective coatings for applications like neurotransmitter detection and lab-on-CMOS electrochemical systems.
- Metamaterials and Photonics:
- Fabricating complex 3D carbon/diamond structures with sub-micrometer features for controlling electromagnetic waves and light.
- Selective Coatings:
- Enabling the growth of diamond coatings only in desired 2D geometric patterns, reducing material waste and simplifying device integration.
View Original Abstract
Abstract Direct laser writing (3D printing) is rapidly emerging as a versatile method for fabricating novel 3D structures that are needed for quantum computing, superconducting devices, selective coatings, and biomedical sensors. Here, we have created 2D patterns with potential for 3D diamond structures by direct laser writing lithography, which are carbonized in an inert Ar atmosphere at 540°C and then used as nucleation sites for diamond growth via hot-filament chemical vapor deposition (HFCVD). An array of 3D structures was fabricated via a two-photon polymerization process using a photo-polymeric resin on Si (100) and sapphire (0001) substrates. These 3D structures carbonized by thermal annealing show approximately 45-55% sp 3 content, as confirmed by Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) analytical techniques. As per the end application of the device, the computer-aided design (CAD) of the structure can be modified to innovative shapes that can be carbonized to provide selective nucleation sites for placing diamond crystallites at the desired locations, which is an important component for device fabrication. The diamond crystallites show a distinctive Raman peak upshift in the range of 1333-1335 cm â1 with a full width at half maximum of †5 cm â1 , indicating some strain across the diamond and Si (100) substrate. A fourfold growth morphology with {111} planes of diamond crystallites is shown by high-resolution scanning electron microscopy (HR-SEM), which correlates with the <100> growth of diamond. Additionally, we show the possibility of creating 3D structures in Q-carbon phase with embedded nanodiamond crystallites via pulsed laser annealing (PLA) of carbonized structures. Graphical Abstract