High-pressure behavior of superconducting boron-doped diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-05-25 |
| Journal | Physical review. B./Physical review. B |
| Authors | Mahmoud Abdel-Hafiez, Dinesh Kumar, R. Thiyagarajan, Q. Zhang, Ross T. Howie |
| Institutions | Indian Institute of Technology Madras, Lomonosov Moscow State University |
| Citations | 20 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: High Pressure BDD Superconductors
Section titled âTechnical Documentation & Analysis: High Pressure BDD SuperconductorsâThis document analyzes the research on the high-pressure behavior of superconducting Boron-Doped Diamond (BDD) grown via CVD. It highlights the material requirements and experimental achievements, directly correlating them with 6CCVDâs specialized capabilities in MPCVD diamond manufacturing.
Executive Summary
Section titled âExecutive SummaryâThis study successfully investigates the structural and electronic properties of thick, freestanding superconducting BDD films under extreme hydrostatic pressure (up to 30 GPa).
- Material Achievement: A 60 ”m thick, freestanding polycrystalline BDD film was synthesized via HFCVD, exhibiting bulk superconductivity with an offset transition temperature ($T_c$) of 4.3 K.
- High Compressibility: The BDD film demonstrated an exceptionally high bulk modulus ($B_0$) of $510 \pm 28$ GPa, confirming the materialâs extreme incompressibility, though slightly lower than pure single-crystal diamond.
- Phase Transformation: An irreversible phase change was observed in the $sp^{2}$ carbon components located in the grain boundaries, transforming into hexagonal diamond above 14 GPa.
- Vibrational Correlation: The blue shift (hardening) of the pressure-dependent vibrational modes was found to correlate directly with the negative pressure coefficient of $T_c$ (-0.09 K/GPa), supporting phonon-mediated mechanisms.
- Doping Level: The material required a high boron concentration ($n_B \approx 2.7 \times 10^{21}$ cm-3) to achieve the insulator-to-metal transition necessary for superconductivity.
- Critical Parameters: Key superconducting parameters were determined, including an upper critical field ($H_{c2}(0)$) of 5.9 T and a coherence length ($\xi_{GL}$) of 7.4 nm.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the high-pressure BDD study:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Superconducting Transition Temperature ($T_c$) | 4.3 | K | Offset transition (measured via resistivity) |
| Boron Concentration ($n_B$) | $2.7 \times 10^{21}$ | cm-3 | Estimated via Raman spectroscopy |
| Film Thickness | 60 | ”m | Freestanding Polycrystalline BDD |
| Grain Size | < 1 | ”m | Polycrystalline structure |
| Bulk Modulus ($B_0$) | 510 ± 28 | GPa | Determined via Vinetâs Equation of State (EOS) |
| Critical Field ($H_{c2}(0)$) | 5.9 | T | Estimated using WHH model |
| Coherence Length ($\xi_{GL}$) | 7.4 | nm | Estimated using Ginzburg-Landau (GL) extrapolation |
| $T_c$ Pressure Coefficient | -0.09 | K/GPa | Rate of $T_c$ suppression under pressure |
| Phase Change Pressure | 14 | GPa | Irreversible $sp^{2}$ to hexagonal diamond transformation |
| Substrate Temperature ($T_{sub}$) | 850 | °C | HFCVD growth parameter |
| Filament Temperature ($T_{fil}$) | 2200 | °C | HFCVD growth parameter |
| Chamber Pressure (Growth) | 7 | Torr | HFCVD growth parameter |
Key Methodologies
Section titled âKey MethodologiesâThe superconducting BDD film was synthesized using Hot Filament Chemical Vapor Deposition (HFCVD), followed by high-pressure characterization using Diamond Anvil Cells (DAC).
BDD Synthesis (HFCVD)
Section titled âBDD Synthesis (HFCVD)â- Seeding: Silicon substrate was seeded using a nano-diamond solution immersed in Dimethyl sulfoxide.
- Chamber Conditions: Chamber evacuated to a base pressure of $10^{-3}$ Torr.
- Filament Heating: Filaments heated to 2200 °C by passing high current.
- Substrate Heating: Substrate temperature maintained at 850 °C.
- Process Pressure: Chamber pressure maintained at 7 Torr during deposition.
- Gas Flow Rates (sccm):
- $\text{H}_2$: 3000 sccm
- $\text{CH}_4$: 80 sccm
- $(\text{CH}_3)_3\text{B}$ (Boron source): 35 sccm
- Duration & Post-Processing: Deposition lasted 110 hours, yielding a 60 ”m film. The Si substrate was etched away using KOH to create a freestanding film.
High-Pressure Characterization
Section titled âHigh-Pressure Characterizationâ- Pressure Generation: Symmetrical Diamond Anvil Cell (DAC) employing diamond anvils with a 300 ”m culet size.
- Sample Preparation: Sample size of 50 ”m placed in a 150 ”m diameter hole on a SS T301 gasket.
- Pressure Medium: Silicon oil (hydrostatic pressure up to 30 GPa).
- Pressure Calibration: Determined by the ruby fluorescence method.
- Measurements:
- Raman Spectroscopy: 632.8 nm He-Ne laser, 1800 gr/mm gratings.
- X-ray Diffraction (XRD): Synchrotron facility (HPCAT at APS, USA) using a wavelength of 0.3100 Ă .
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research requires highly specialized, thick, heavily doped polycrystalline diamond films cut to precise dimensions for high-pressure DAC experiments. 6CCVD is uniquely positioned to supply materials that meet or exceed these demanding specifications.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research into high-pressure superconductivity, the following 6CCVD material is required:
| Material Grade | Description | Application Relevance |
|---|---|---|
| Heavy Boron-Doped Polycrystalline Diamond (BDD) | Superconducting Grade PCD/BDD with high substitutional boron concentration ($n_B > 10^{21}$ cm-3). | Essential for achieving the Insulator-to-Metal Transition (IMT) and bulk superconductivity ($T_c$ up to 10 K+). |
| Thick PCD Substrates | Polycrystalline Diamond (PCD) substrates optimized for mechanical robustness and high-pressure stability. | Required for freestanding films up to 500 ”m thick, necessary for high-pressure studies where sample integrity is critical. |
Customization Potential
Section titled âCustomization PotentialâThe experimental setup utilized custom dimensions (50 ”m samples) and required electrical contacts. 6CCVD offers comprehensive customization services to streamline high-pressure research:
| Research Requirement | 6CCVD Capability | Technical Specification |
|---|---|---|
| Custom Thickness | Supply of thick, freestanding BDD films. | SCD/PCD thickness ranging from 0.1 ”m up to 500 ”m. Substrates available up to 10 mm. |
| Precision Sizing | Custom laser cutting for DAC sample preparation. | Plates/wafers available up to 125 mm (PCD). Precision cutting to micron-level tolerances (e.g., 50 ”m squares or discs). |
| Electrical Contacts | Integrated metalization for transport measurements. | Internal capability to deposit Au, Pt, Pd, Ti, W, or Cu contact pads directly onto BDD surfaces, ensuring low-resistance ohmic contacts for low-temperature resistivity studies. |
| Surface Finish | High-quality polishing for optimal contact adhesion. | Polishing services available for PCD, achieving surface roughness (Ra) < 5 nm on inch-size wafers. |
Engineering Support
Section titled âEngineering SupportâHigh-pressure physics and superconductivity research demand precise material engineering. 6CCVDâs in-house PhD team provides authoritative support for projects involving:
- Material Selection: Guidance on optimizing boron doping profiles and concentrations to maximize $T_c$ and minimize $sp^{2}$ content for high-pressure stability.
- DAC Preparation: Consultation on optimal sample thickness and geometry for specific DAC designs (e.g., maximizing hydrostatic pressure range).
- Advanced Characterization: Assistance in correlating material properties (grain size, $sp^{2}$ content, surface roughness) with observed high-pressure phenomena and superconducting performance.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
This work investigates the high-pressure structure of freestanding superconducting (Tc=4.3 K) boron-doped diamond (BDD) and how it affects the electronic and vibrational properties using Raman spectroscopy and x-ray diffraction in the 0-30 GPa range. High-pressure Raman scattering experiments revealed an abrupt change in the linear pressure coefficients, and the grain boundary components undergo an irreversible phase change at 14 GPa. We show that the blueshift in the pressure-dependent vibrational modes correlates with the negative pressure coefficient of Tc in BDD. The analysis of x-ray diffraction data determines the equation of state of the BDD film, revealing a high bulk modulus of B0=510±28 GPa. The comparative analysis of high-pressure data clarified that the sp2 carbons in the grain boundaries transform into hexagonal diamond. ©2017 American Physical Society.