Femtosecond-Laser Nanostructuring of Black Diamond Films under Different Gas Environments
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-12-17 |
| Journal | Materials |
| Authors | M. Girolami, A. Bellucci, Matteo Mastellone, S. Orlando, Valerio Serpente |
| Institutions | Institute of Structure of Matter, Sapienza University of Rome |
| Citations | 11 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Femtosecond-Laser Nanostructuring of Black Diamond Films
Section titled âTechnical Documentation & Analysis: Femtosecond-Laser Nanostructuring of Black Diamond FilmsâDocument Reference: Girolami et al., Femtosecond-Laser Nanostructuring of Black Diamond Films under Different Gas Environments (Materials 2020, 13, 5761)
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates a pathway for cost-effective, large-scale manufacturing of âBlack Diamondâ films for solar energy conversion by replacing complex Ultra-High Vacuum (UHV) processing with ambient conditions.
- Core Achievement: High solar absorptance ($\alpha_s$) black diamond films were fabricated using femtosecond (fs) laser-induced periodic surface structures (LIPSS) under a constant Helium (He) flow at atmospheric pressure.
- Performance Validation: The He-treated polycrystalline CVD diamond achieved a solar absorptance of 86.2%, closely matching the 88.4% performance previously reported for UHV-treated counterparts of the same crystalline quality.
- Material Requirement: The process requires high-quality, thermal management grade Polycrystalline CVD (PCD) diamond substrates capable of withstanding high accumulated laser fluence ($\Phi_A$).
- Process Optimization: The use of He flow ensures uniform LIPSS distribution and structural integrity (evidenced by compressive stress, 1335.1 cm-1 Raman shift), which is crucial for effective light trapping, unlike treatments performed under Air or N2 flow.
- Manufacturing Impact: This finding significantly simplifies the manufacturing workflow, paving the way for easier and more cost-effective production of diamond-based solar energy converters and thermionic emission devices.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental methodology and results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | Polycrystalline CVD | TM Grade | 10 x 10 x 0.3 mm3 samples (TM1, TM2, TM3) |
| Laser Wavelength ($\lambda_{fs}$) | 800 | nm | Ti:sapphire, linearly polarized |
| Pulse Duration | ~100 | fs | Ultrafast regime for precise LIPSS control |
| Repetition Rate ($f$) | 1 | kHz | Constant rate used for raster scanning |
| Laser Spot Diameter ($2w$) | 150 | ”m | 1/e2 width on focal plane |
| Single Pulse Fluence ($\Phi_p$) | 4.44 | J/cm2 | Slightly above ablation threshold (~3 J/cm2) |
| Total Accumulated Fluence ($\Phi_A$) | 5.0 | kJ/cm2 | Optimal value for 1D periodic structures |
| LIPSS Periodicity ($\Lambda$) | 170 $\pm$ 10 | nm | Matches theoretical value (166 nm) |
| LIPSS Depth | 480 $\pm$ 20 | nm | Inferred from tilted SEM images |
| Optimal Gas Environment | He (Purity > 99.5%) | Flow | Ensures uniform LIPSS distribution |
| Solar Absorptance ($\alpha_s$) - He | 86.2 | % | Calculated using AM 1.5 GT solar irradiance |
| Solar Absorptance ($\alpha_s$) - Air | 79.1 | % | Resulted in irregular surface morphology |
| Solar Absorptance ($\alpha_s$) - N2 | 78.4 | % | Resulted in irregular surface morphology |
| Diamond Raman Peak (He) | 1335.1 | cm-1 | Indicates compressive stress (optimal structural integrity) |
| Diamond Raman Peak (Reference) | 1332.0 | cm-1 | Untreated crystalline diamond reference |
Key Methodologies
Section titled âKey MethodologiesâThe black diamond films were fabricated using a controlled femtosecond laser raster scanning process under varying gas environments.
- Substrate Preparation:
- Three 10 x 10 x 0.3 mm3 polycrystalline CVD diamond samples (TM1, TM2, TM3) were used.
- Standard cleaning procedure involved dipping in a boiling oxidizing mixture (HNO3:H2SO4:HClO4 = 1:1:1) for 15 minutes, followed by ultrasound cleaning in acetone and 2-propanol.
- Laser Setup:
- A linearly polarized fs-pulsed Ti:sapphire laser ($\lambda_{fs}$ = 800 nm, 100 fs pulse duration) was used at a 1 kHz repetition rate.
- Single pulse energy ($E_p$) was fixed at 785 ”J, corresponding to $\Phi_p$ = 4.44 J/cm2.
- Raster Scanning:
- The laser beam ($2w$ = 150 ”m) scanned an 8 x 8 mm2 area in a raster pattern.
- Scanning speed ($v_x$) was set to 1 mm/s, achieving an accumulated horizontal fluence ($\Phi_x$) of 0.67 kJ/cm2.
- Vertical shift ($\Delta y$) was 20 ”m, resulting in a total accumulated laser fluence ($\Phi_A$) of 5.0 kJ/cm2.
- Environmental Control:
- Treatments were performed at room temperature and atmospheric pressure under a constant flow of gas directed at a near-90° angle to the surface normal.
- Gases tested: Compressed Air (TM1), N2 (TM2), and He (TM3).
- Post-Treatment Cleaning:
- All samples were subjected to the same boiling oxidizing mixture cleaning to remove ablation debris.
- Characterization:
- Morphology was assessed via Field Emission Scanning Electron Microscopy (FE-SEM) after ultra-thin (~2 nm) Au coating (subsequently removed via aqua regia).
- Structural modifications were analyzed using Raman spectroscopy (Ar+ laser, 514.5 nm).
- Optical properties (Absorptance $\alpha$) were measured via spectrophotometry (0.25-2.5 ”m range) using an integrating sphere to determine solar absorptance ($\alpha_s$).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful replication and scaling of this breakthrough Black Diamond fabrication technique rely on high-quality, customizable CVD diamond substrates. 6CCVD is uniquely positioned to supply the necessary materials and engineering support to transition this research from lab-scale to industrial application.
Applicable Materials for Replication and Scaling
Section titled âApplicable Materials for Replication and ScalingâThe research utilized âthermal management gradeâ polycrystalline diamond. 6CCVD offers materials optimized for both thermal and optical applications:
| 6CCVD Material | Description | Application Relevance |
|---|---|---|
| Optical Grade PCD | High-purity Polycrystalline CVD diamond plates. | Ideal for replicating the TM-grade material used in the study, offering superior uniformity necessary for large-area LIPSS fabrication. |
| High-Purity SCD | Single Crystal Diamond (SCD) substrates. | Recommended for extending the research to high-performance devices, as SCD minimizes grain boundary effects (which hampered Air/N2 treatments) and offers superior electronic properties for active solar devices. |
| BDD (Boron-Doped Diamond) | Conductive PCD or SCD films. | Essential for future development of active devices, such as thermionic emission-based solar cells, where conductive electrodes are required. |
Customization Potential for Industrialization
Section titled âCustomization Potential for IndustrializationâThe paperâs findings enable a shift toward large-area, cost-effective manufacturing. 6CCVDâs capabilities directly address the scaling challenges:
- Large-Area Substrates: While the paper used 10 x 10 mm plates, 6CCVD provides Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter, facilitating the transition to high-volume, inch-size processing required for solar concentrator systems.
- Custom Dimensions and Thickness: We offer PCD and SCD plates in custom dimensions and thicknesses ranging from 0.1 ”m to 500 ”m (films) and up to 10 mm (substrates). This supports optimization for specific device geometries.
- Precision Polishing: The quality of the LIPSS depends heavily on the initial surface finish. 6CCVD guarantees ultra-smooth polishing:
- PCD: Surface roughness (Ra) < 5 nm on inch-size wafers.
- SCD: Surface roughness (Ra) < 1 nm.
- Integrated Metalization Services: Although not used in the primary nanostructuring, future active devices (like those mentioned for thermionic emission) require electrodes. 6CCVD offers in-house deposition of standard metal stacks (Au, Pt, Pd, Ti, W, Cu) for immediate integration into device prototypes.
Engineering Support
Section titled âEngineering SupportâThe research highlights the critical role of material quality and surface integrity in achieving uniform LIPSS distribution, especially when moving away from UHV.
- Material Selection for R&D: 6CCVDâs in-house PhD team can assist researchers in selecting the optimal diamond grade (PCD vs. SCD) and surface preparation (polishing grade) required to replicate or extend this research, particularly for projects involving Concentrated Solar Energy Conversion and Thermionic Emission Devices.
- Advanced Nanostructuring Support: The paper suggests future work on optimizing $\Phi_A$ and exploring complex 2D LIPSS. We provide materials with the necessary crystalline quality and low defect density to ensure reproducible results in these advanced nanostructuring experiments.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Irradiation of diamond with femtosecond (fs) laser pulses in ultra-high vacuum (UHV) conditions results in the formation of surface periodic nanostructures able to strongly interact with visible and infrared light. As a result, native transparent diamond turns into a completely different material, namely âblackâ diamond, with outstanding absorptance properties in the solar radiation wavelength range, which can be efficiently exploited in innovative solar energy converters. Of course, even if extremely effective, the use of UHV strongly complicates the fabrication process. In this work, in order to pave the way to an easier and more cost-effective manufacturing workflow of black diamond, we demonstrate that it is possible to ensure the same optical properties as those of UHV-fabricated films by performing an fs-laser nanostructuring at ambient conditions (i.e., room temperature and atmospheric pressure) under a constant He flow, as inferred from the combined use of scanning electron microscopy, Raman spectroscopy, and spectrophotometry analysis. Conversely, if the laser treatment is performed under a compressed air flow, or a N2 flow, the optical properties of black diamond films are not comparable to those of their UHV-fabricated counterparts.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2015 - Absorptance enhancement in fs-laser-treated CVD diamond [Crossref]
- 2016 - Infrared absorption of fs-laser textured CVD diamond [Crossref]
- 2016 - Optimization of black diamond films for solar energy conversion [Crossref]
- 2017 - Graphite distributed electrodes for diamond-based photon-enhanced thermionic emission solar cells [Crossref]
- 2016 - Black diamond for solar energy conversion [Crossref]
- 2012 - Femtosecond laser-induced periodic surface structures [Crossref]
- 2017 - Laser-induced periodic surface structures on bismuth thin films with ns laser pulses below ablation threshold [Crossref]
- 2017 - Femtosecond laser induced robust periodic nanoripple structured mesh for highly efficient oil-water separation [Crossref]
- 2020 - Femtosecond laser fabrication of LIPSS-based waveplates on metallic surfaces [Crossref]