Absorptance enhancement in fs‐laser‐treated CVD diamond
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2015-08-18 |
| Journal | physica status solidi (a) |
| Authors | P. Calvani, A. Bellucci, M. Girolami, S. Orlando, Veronica Valentini |
| Institutions | Institute of Structure of Matter, Sapienza University of Rome |
| Citations | 16 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation for 6CCVD
Section titled “Technical Analysis and Documentation for 6CCVD”Executive Summary
Section titled “Executive Summary”The analyzed research successfully demonstrated a robust method for significantly increasing the solar absorptance of Chemical Vapor Deposition (CVD) diamond via femtosecond (fs) laser surface texturing. This breakthrough is critical for the development of high-efficiency concentrated solar energy conversion devices, particularly those utilizing the Photon-Enhanced Thermionic Emission (PETE) effect.
- Core Achievement: Solar absorptance ($\alpha$) of Polycrystalline CVD (PCD) diamond was enhanced from an untreated baseline of 45.4% up to 91.7% in the 200-2000 nm wavelength range.
- Optimal Processing Window: A specific treatment dose of 5.0 kJ cm-2 resulted in ordered, periodic surface structures (LIPSS) with 170 nm ripple periodicity, maximizing light trapping while retaining excellent bulk crystallinity.
- Material Integrity: Raman spectroscopy confirmed that the high-quality crystal structure was maintained, showing negligible change in the bulk properties after texturing, especially at the optimal dose.
- Methodology: Surface modification utilized a high-power, high-vacuum fs-laser system (800 nm, < 120 fs pulses) to ablate and restructure the PCD surface morphology.
- Application Focus: This enhanced photon absorption capability paves the way for exploiting synthetic diamond as a suitable, stable, and high-performance substrate for PETE solar energy conversion.
- 6CCVD Value Proposition: 6CCVD is uniquely positioned to supply the requisite high-quality, large-area Polycrystalline Diamond (PCD) substrates and offer specialized surface finishing and metalization services necessary to transition this research into scalable commercial devices.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the analysis of the fs-laser texturing on CVD diamond.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material Used | TM180 Polycrystalline Diamond | N/A | Thermal Management Grade |
| Initial Dimensions | 10 x 10 x 0.25 | mm | Freestanding plate dimensions |
| Initial Thermal Conductivity | > 1800 | W m-1 K-1 | Producer specified thermal property |
| Initial Surface Roughness (Ra) | < 50 | nm | Producer specified surface quality |
| Fs-Laser Wavelength ($\lambda$) | 800 | nm | Laser source for texturing |
| Fs-Pulse Duration | < 120 | fs | Amplifier output specification |
| Max Power Density (on sample) | 2 x 1014 | W cm-2 | Two orders of magnitude > damage threshold |
| Optimal Treatment Dose (D) | 5.0 | kJ cm-2 | Achieved best combination of absorptance/crystallinity |
| Max Treatment Dose (D) | 12.5 | kJ cm-2 | Achieved highest solar absorptance |
| Ripple Periodicity ($\lambda_L$) | 170 | nm | High-Spatial-Frequency Laser-Induced Periodic Surface Structure (LIPSS) |
| Solar Absorptance (Untreated, $\alpha$) | 45.4 | % | Baseline performance (TM180-1) |
| Solar Absorptance (Max, $\alpha$) | 91.7 | % | Maximum achieved performance (TM180-4) |
| Diamond Raman Peak (Untreated) | 1332.2 ± 0.04 | cm-1 | Standard diamond peak location |
| Diamond Raman FWHM (Optimal) | 4.42 ± 0.13 | cm-1 | TM180-3 (Indicates high retained crystallinity) |
Key Methodologies
Section titled “Key Methodologies”The following is an ordered summary of the preparation and processing steps used to achieve enhanced diamond absorptance.
- Material Selection: Freestanding Polycrystalline CVD (PCD) diamond plates (TM180 grade) were chosen due to their high intrinsic thermal conductivity and suitability for thermal management applications.
- Laser System Configuration: The texturing system utilized a seed oscillator (Spectra Physics Tsunami-S) amplified by a high-power system (Spectra-Physics Spitfire Pro 100 F 1K XP 4W), ensuring a highly controlled 800 nm, sub-120 fs pulse duration.
- Process Environment: Laser texturing was performed in a high-vacuum chamber (< 10-7 mbar) to minimize atmospheric interaction during ablation.
- Fixed Laser Parameters: The pulse energy was held constant at 3.6 mJ pulse-1, delivered at a repetition rate of 1000 Hz, focused to a 150 µm spot size.
- Dose Variation: The radiation dose (D) was precisely controlled by translating the diamond target via an automated X-Y stage. Dose levels ranged from 2.5 kJ cm-2 (7 x 105 pulses) up to 12.5 kJ cm-2 (3.5 x 106 pulses).
- Post-Treatment Cleaning: All samples were cleaned using a strongly oxidizing solution (H2SO4:HClO4:HNO3 in a 1:1:1 ratio) to effectively remove residual sp2 graphitic debris resulting from the ablating action.
- Optical Characterization: Absorptance (A) was derived from total Transmission (T) and Reflection (R) measurements (A = 1 - T - R) across the 200-2000 nm range, providing quantitative data on solar absorptance ($\alpha$) using the global-tilt (GT) 1.5 air mass (AM) solar irradiance spectrum.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD provides the specialized MPCVD diamond material, processing flexibility, and engineering expertise required to replicate and scale this critical surface texturing research for high-efficiency PETE applications.
Applicable Materials
Section titled “Applicable Materials”The study confirms that high-quality Polycrystalline Diamond (PCD) is the optimal starting material. 6CCVD offers superior options for scaling this research:
- High-Purity Polycrystalline Diamond (PCD): 6CCVD provides MPCVD-grown PCD wafers specifically tailored for optical and high-power electronic applications, offering high thermal stability and low defect density comparable to the TM180 thermal grade used, but scalable to larger dimensions.
- Specific Substrate Requirements: To further optimize PETE performance (which relies on charge carrier generation via defect states), future work may require controlled incorporation of nitrogen or boron. 6CCVD offers:
- Nitrogen-Doped PCD: Used to control specific defect centers for customized optical response.
- Boron-Doped Diamond (BDD): Available in controlled doping levels for applications requiring tunable semiconducting properties or electrochemistry.
Customization Potential
Section titled “Customization Potential”The success of fs-laser texturing relies on highly consistent material quality and precise post-processing. 6CCVD capabilities directly address the needs of scaling this technology:
| Capability | 6CCVD Offering | Relevance to Absorptance Enhancement |
|---|---|---|
| Substrate Dimensions | Wafers/plates up to 125mm (PCD) | Enables scaling from laboratory coupons (10mm) to commercial wafer size for integrated devices. |
| Material Thickness | PCD thickness up to 500 µm | Allows researchers to select the optimal thickness based on thermal and electrical requirements of the PETE collector. |
| Precision Polishing | Ultra-smooth PCD surfaces, Ra < 5 nm (Inch-size) | Provides an ideal, uniform starting point for precise fs-laser texturing (LIPSS). |
| Laser Micromachining | High-precision laser cutting/shaping | Essential for creating specific device geometries or defining precise texturing areas beyond standard square cuts. |
| Advanced Metalization | In-house deposition of Au, Pt, Pd, Ti, W, Cu | Critical for integrating the textured diamond absorber surface with electrical contacts required for thermionic emission collection in a functional PETE device. |
Engineering Support
Section titled “Engineering Support”The paper identifies that the next critical research step is performing photoconductivity measurements to investigate the presence of defect states within the diamond bandgap caused by the fs-laser texturing.
6CCVD’s in-house PhD material science team offers dedicated engineering consultation services to support researchers in projects focusing on the optoelectronic effectiveness of textured diamond for PETE and concentrated solar applications. We specialize in correlating MPCVD growth parameters (doping, defect density) with final physical properties (Raman FWHM, optical transparency) to ensure the starting material is optimized for subsequent laser processing.
Target Applications Supported:
- High-Efficiency Concentrated Solar Power (CSP)
- Photon-Enhanced Thermionic Emission (PETE) Collectors
- High-Power Broadband Absorbers
- Custom Optical Windows requiring controlled light-trapping structures
Call to Action: For custom specifications or material consultation concerning textured diamond for high-efficiency solar conversion, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Surface texturing by fs‐laser pulses has been performed in order to enhance optical absorptance of chemical vapour deposited diamond. The induced surface structures have been studied as a function of treatment dose D . Periodic structure with ripples of 170 nm has been observed for a D = 5.0 kJ cm −2 , although not well defined texturing and damaged structures have been obtained for both lower and higher doses. Raman investigations point out negligible changes in crystal bulk for all investigated samples, thus suggesting that physical properties of the crystal were not changed by the treatment. Optical absorptance is strongly enhanced by fs‐laser texturing and it is an increasing function of the treatment dose. The absorptance of solar spectrum saturates up to values larger than 90%. The obtained outstanding enhancement of photon absorption represents a preliminary and promising step for the exploitation of synthetic diamond in future high‐efficient conversion devices for solar concentration based on photon‐enhanced thermionic emission effect.