Effect of crystallographic orientation on the potential barrier and conductivity of Bessel written graphitic electrodes in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-12-26 |
| Journal | Diamond and Related Materials |
| Authors | Akhil Kuriakose, Andrea Chiappini, Pietro AprĂ , Ottavia Jedrkiewicz |
| Institutions | University of Turin, Istituto di Fotonica e Nanotecnologie |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the critical role of crystallographic orientation in fabricating highly conductive, barrier-free graphitic microelectrodes within monocrystalline CVD diamond using pulsed Bessel beams.
- Orientation Impact: The (110) crystallographic orientation completely eliminates the potential barrier observed in current-voltage (I-V) measurements, a barrier typically present in (100) oriented samples fabricated in the femtosecond (fs) regime.
- Conductivity Achievement: Electrodes fabricated in (110) diamond achieved resistivities as low as 0.013 Ω cm (200 fs, 6 ”J), which is reported as one of the lowest values for in-bulk graphitic micro-electrodes written perpendicular to the surface using laser micromachining.
- Morphological Advantage: (110) oriented wires are significantly thinner (approximately 1 ”m) and exhibit a smoother, more uniform core compared to the 2.5 ”m wires in (100) diamond.
- Mechanism of Barrier Elimination: The absence of the potential barrier in (110) is attributed to an additional heating mechanism resulting from the directionality of cracking (along the beam path), which enhances diamond-to-sp2 carbon transformation and reduces microscopic gaps between graphitic globules.
- Pulse Duration Effect: Fabrication in the picosecond (ps) regime (10 ps) eliminates the potential barrier in both (100) and (110) orientations, confirming that longer pulse durations generally lead to better sp2 conversion.
- Thermal Annealing Effect: Annealing at 950 °C reduces the resistivity of the electrodes but has no effect on the height of the potential barrier when it is present.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Type | Monocrystalline CVD, Type IIa | N/A | Sample material |
| Sample Thickness | 500 | ”m | Diamond substrate |
| Crystal Orientations Tested | (100) and (110) | N/A | Top surface planes |
| Laser System | Ti:Sapphire Amplified | N/A | 20-Hz repetition rate |
| Wavelength | 790 | nm | Laser writing |
| Pulse Durations Tested | 200 fs and 10 ps | N/A | Femtosecond and Picosecond regimes |
| Pulse Energy Range | 1 to 10 | ”J | Energy used for fabrication |
| Bessel Beam Core Size | 2.7 | ”m | Transverse size of the central core |
| Bessel Zone Length | 700 | ”m | Non-diffracting length |
| Graphitic Wire Diameter ((110) cut) | â 1 | ”m | Transverse size of conductive electrode |
| Graphitic Wire Diameter ((100) cut) | â 2.5 | ”m | Transverse size of conductive electrode |
| Lowest Resistivity Achieved | 0.013 | Ω cm | (110) cut, 200 fs, 6 ”J, after annealing |
| Annealing Temperature | 950 | °C | Ultra-high vacuum thermal treatment |
| Annealing Time | 1 | hour | Duration of thermal treatment |
| I-V Voltage Range | -450 to 450 | V | Electrical characterization range |
| I-V Compliance Current | 25 | mA | Maximum current limit |
| Potential Barrier Height ((100) cut, low energy) | Up to 295 | V | Measured before ohmic behavior begins |
| Raman Diamond Peak | 1332.2 | cm-1 | Characteristic diamond signal |
| Raman Graphite G Peak | â 1590 | cm-1 | Characteristic organized sp2 carbon signal |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication and characterization process involved three main stages: laser micromachining, electrical/structural characterization, and post-processing thermal annealing.
-
Bessel Beam Generation:
- A 5 mm Gaussian beam (790 nm, linear polarization) was converted into a Bessel beam (BB) using a fused silica axicon (178° apex angle).
- A telescopic system (250 mm lens and 0.45 N.A. 20Ă objective) focused the BB orthogonally onto the diamond surface.
- The BB parameters resulted in a 12° cone angle, 2.7 ”m core, and 700 ”m Bessel zone, matching the 500 ”m sample thickness.
-
Graphitic Wire Fabrication:
- Microstructures were written in a transverse configuration without sample translation, utilizing the elongated focal zone of the BB.
- Pulse durations of 200 fs and 10 ps were used, with pulse energies varied between 1 ”J and 10 ”J.
- A multiple-shot regime was employed (9000 pulses per electrode) to ensure complete through-wires (500 ”m length).
-
Electrical and Structural Characterization:
- I-V Measurements: Conducted using a 2-probe configuration on a custom probe station after metal deposition (400 nm silver) on the electrode ends.
- Morphology: Optical microscopy was used to analyze wire continuity, transverse size, and cracking phenomena.
- Structural Analysis (Micro-Raman): Performed using a 532 nm DPSS laser to confirm the transformation of diamond (sp3) into amorphous/graphitic carbon (sp2).
-
Thermal Annealing (Post-Processing):
- Samples were annealed in a home-made chamber under ultra-high vacuum (up to 5 x 10-8 mbar).
- The annealing temperature was fixed at 950 °C for 1 hour.
- I-V measurements were repeated after annealing to assess changes in resistivity and potential barrier height.
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to rapidly fabricate high-quality, low-resistivity, three-dimensional conductive structures within insulating diamond bulk opens pathways for advanced devices in several high-tech sectors.
- Radiation Detection:
- 3D Diamond Detectors: Fabrication of 3D electrode geometries for highly energetic radiation detection, crucial for nuclear physics experiments and medical dosimetry.
- Quantum and Photonic Devices:
- Photonic Chips: Creation of integrated conductive channels for electric field generation within diamond photonic circuits, often used in conjunction with NV centers for quantum communication and sensing.
- Microfluidic Sensing Systems: Integration of electrodes for biosensing and microfluidic control within diamond platforms due to diamondâs biocompatibility and chemical resistivity.
- High-Performance Electronics:
- High-Conductivity Interconnects: Utilizing the achieved low resistivity (0.013 Ω cm) for robust, high-speed electrical interconnects embedded within the diamond matrix, leveraging diamondâs superior thermal properties.
- Laser Processing Technology:
- Fast Fabrication: The use of pulsed Bessel beams allows for fast fabrication without sample translation, improving throughput for complex 3D microstructuring in transparent materials.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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