Surface Nanotexturing of Boron-Doped Diamond Films by Ultrashort Laser Pulses

At a Glance

Metadata	Details
Publication Date	2023-02-04
Journal	Micromachines
Authors	Matteo Mastellone, Eleonora Bolli, Veronica Valentini, S. Orlando, Antonio Lettino
Institutions	Institute of Structure of Matter, National Research Council - Institute of Methodologies for Environmental Analysis
Citations	8
Analysis	Full AI Review Included

Technical Documentation & Analysis: Surface Nanotexturing of Boron-Doped Diamond Films

Executive Summary

This research validates the use of ultrashort femtosecond laser pulses for highly controlled surface functionalization of Boron-Doped Diamond (BDD) films, opening pathways for advanced photo-electrochemical and electronic applications.

Material Validation: Polycrystalline BDD films (4 µm thick, ~5 x 10^-3 Ω cm resistivity) are confirmed as suitable substrates for Laser-Induced Periodic Surface Structures (LIPSS) fabrication.
Tunable Nanostructuring: Successful creation of Low Spatial Frequency LIPSS (LSFL) with a highly desirable periodicity of 630 nm, corresponding closely to the visible light spectrum.
Morphological Control: The morphology is tunable by accumulated fluence (Φ_A), transitioning from irregular ripples (<14.4 J cm^-2) to highly regular, deep LSFL (up to 230.4 J cm^-2).
Depth Achievement: Achieved peak-to-valley LIPSS depths of 150 ± 20 nm, critical for enhancing optical absorption and creating anisotropic THz components.
Structural Alteration: Laser treatment induces a functional sp² graphitic layer on the BDD surface, which is beneficial for improving electrochemical performance.
High-Value Applications: The resulting nanostructured BDD is optimized for use as efficient solar photo-electrodes and advanced THz components, requiring high-quality, heavily doped diamond substrates.

Technical Specifications

The following hard data points were extracted from the experimental results and material characterization:

Parameter	Value	Unit	Context
Material Type	Polycrystalline BDD	N/A	Deposited on Si wafer
Film Thickness	4	µm	CVD growth
Boron Doping Level	~2.8	at.%	Heavily doped
Resistivity	~5 x 10^-3	Ω cm	High conductivity
Single Pulse Duration	100	fs	Ultrashort laser source
Laser Wavelength (λ)	800	nm	Near-infrared
Single Pulse Fluence (Φ_p)	1.44	J cm^-2	Fixed parameter for all tests
Accumulated Fluence Range (Φ_A)	1.44 to 230.4	J cm^-2	P1 to P160 samples
Regular LIPSS Threshold	14.4	J cm^-2	Minimum fluence (P10) for LSFL formation
LIPSS Periodicity (Λ)	630 ± 30	nm	Low Spatial Frequency LIPSS (LSFL)
LIPSS Depth (Peak-to-Valley)	150 ± 20	nm	Measured for P100 and P160 samples
Roughness Average (R_a) (Treated)	77.3 ± 5.0	nm	30% decrease compared to untreated sample
Root Mean Square Roughness (R_ms) (Treated)	61.4 ± 4.5	nm	Indicates regular patterning

Key Methodologies

The experiment involved three primary stages: material synthesis, laser texturing, and structural characterization.

1. Diamond Growth (HF-CVD)

Seeding: Detonation diamond nanoparticles were used for seeding the silicon wafer substrate.
Temperature: Substrate temperature was maintained at approximately 850 °C.
Gas Flow: A gas mixture of 2.4% CH₄/H₂ (72 sccm/3000 sccm) was utilized.
Doping: Boron doping was achieved using 40 sccm of trimethylborane (TMB).

2. Laser Texturing (Femtosecond Ablation)

Laser Source: Ti:Sapphire femtosecond laser (100 fs pulse duration, 800 nm wavelength).
Irradiation Environment: Performed in a high vacuum chamber (<5 x 10^-7 mbar) to prevent sample oxidation or nitridation.
Fluence Control: Single pulse fluence was fixed at 1.44 J cm^-2.
Accumulation: Accumulated fluence (Φ_A) was controlled by varying the number of pulses (N) per spot from 1 (P1) to 160 (P160).

3. Characterization Techniques

Morphology: Field-Emission Gun Scanning Electron Microscopy (FEG-SEM) and Atomic Force Microscopy (AFM) were used to analyze surface patterning and depth.
Periodicity Analysis: 2D Fast Fourier Transformation (2D-FFT) analysis of SEM images was used to calculate LIPSS periodicity (Λ).
Structural Analysis: Micro-Raman spectroscopy (532 nm laser) was employed to assess the formation of sp² graphitic content and disorder (D and G bands).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-performance Boron-Doped Diamond (BDD) required to replicate and scale this advanced nanostructuring research for commercial applications like photo-electrodes and THz components.

Applicable Materials

The research relies on heavily doped, conductive diamond films. 6CCVD offers materials optimized for this requirement:

Heavy Boron Doped PCD (BDD): We provide Polycrystalline Diamond (PCD) films with high boron concentrations, achieving the low resistivity (~10^-3 Ω cm range) necessary for the material to absorb 800 nm radiation and exhibit semiconductor/metallic-like behavior during femtosecond laser irradiation.
Thickness Control: The paper used 4 µm films. 6CCVD offers precise thickness control for PCD films ranging from 0.1 µm up to 500 µm, allowing researchers to optimize material usage and thermal management for high-power laser processing.

Customization Potential

Scaling this research from single spots to functional devices requires large-area, high-precision substrates and post-processing capabilities, which 6CCVD provides:

Requirement from Research	6CCVD Capability	Benefit to Customer
Large Area Processing	Plates/wafers available up to 125 mm (PCD).	Enables scaling of LIPSS fabrication from laboratory spots to industrial-sized photo-electrode or THz device wafers.
Surface Quality	Polishing capability to Ra < 5 nm (Inch-size PCD).	While the paper used a rougher starting material, 6CCVD can provide smoother BDD, potentially reducing the “noisy” 2D-FFT spectrum observed and improving LIPSS homogeneity and regularity.
Device Integration	In-house custom metalization services (Au, Pt, Pd, Ti, W, Cu).	Essential for creating ohmic contacts and integrating the nanostructured BDD into functional photo-electrochemical cells or THz components.
Custom Dimensions	Precision laser cutting and dicing services.	We can supply BDD pieces in the exact 1.5 x 1.5 cm² dimensions used in the study, or any custom geometry required for device prototyping.

Engineering Support

The successful implementation of BDD LIPSS for advanced applications requires specialized material knowledge.

Application Expertise: 6CCVD’s in-house PhD team specializes in the synthesis and characterization of functional diamond materials. We can assist clients with material selection for similar solar photo-electrode and anisotropic THz component projects.
Doping Optimization: We offer consultation on optimizing boron doping profiles and concentrations to fine-tune the optical absorption properties of the BDD, ensuring maximum efficiency for the 800 nm femtosecond laser process.
Global Logistics: We ensure reliable, global delivery of sensitive diamond materials, with DDU as the default shipping method and DDP available upon request.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Polycrystalline boron-doped diamond (BDD) films were surface nanotextured by femtosecond pulsed laser irradiation (100 fs duration, 800 nm wavelength, 1.44 J cm−2 single pulse fluence) to analyse the evolution of induced alterations on the surface morphology and structural properties. The aim was to identify the occurrence of laser-induced periodic surface structures (LIPSS) as a function of the number of pulses released on the unit area. Micro-Raman spectroscopy pointed out an increase in the graphite surface content of the films following the laser irradiation due to the formation of ordered carbon sites with respect to the pristine sample. SEM and AFM surface morphology studies allowed the determination of two different types of surface patterning: narrow but highly irregular ripples without a definite spatial periodicity or long-range order for irradiations with relatively low accumulated fluences (<14.4 J cm−2) and coarse but highly regular LIPSS with a spatial periodicity of approximately 630 nm ± 30 nm for higher fluences up to 230.4 J cm−2.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi14020389

References

2014 - Boron Doped Diamond Biotechnology: From Sensors to Neurointerfaces [Crossref]
2016 - Diamond-Based Supercapacitors: Realization and Properties [Crossref]
2015 - Porous Diamond with High Electrochemical Performance [Crossref]
2013 - Photo-Illuminated Diamond as a Solid-State Source of Solvated Electrons in Water for Nitrogen Reduction [Crossref]
2016 - Diamond Electrochemistry at the Nanoscale: A Review [Crossref]
2020 - Nanostructured Boron Doped Diamond Electrodes with Increased Reactivity for Solar-Driven CO2 Reduction in Room Temperature Ionic Liquids [Crossref]
2018 - Laser-Induced Periodic Surface Structures (LIPSS) on Heavily Boron-Doped Diamond for Electrode Applications [Crossref]
2016 - Black Diamond for Solar Energy Conversion [Crossref]
2021 - Strain-Tuning of the Electronic, Optical, and Vibrational Properties of Two-Dimensional Crystals [Crossref]
2022 - Diamond Semiconductor and Elastic Strain Engineering [Crossref]