Electrical transport measurements for superconducting sulfur hydrides using boron-doped diamond electrodes on beveled diamond anvil
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-10-02 |
| Journal | Superconductor Science and Technology |
| Authors | Ryo Matsumoto, Mari Einaga, Shintaro Adachi, Sayaka Yamamoto, Tetsuo Irifune |
| Institutions | Ehime University, Osaka University |
| Citations | 12 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details the successful fabrication and application of a novel Diamond Anvil Cell (DAC) designed for stable, in-situ electrical transport measurements of high-pressure materials, specifically superconducting sulfur hydrides.
- Core Innovation: Boron-Doped Diamond (BDD) micro-electrodes and an Undoped Diamond (UDD) insulating layer were epitaxially grown directly onto the culet surface of a beveled diamond anvil.
- Performance: The developed DAC achieved stable electrical transport measurements up to 192 GPa, significantly extending the pressure range and stability compared to conventional electrode insertion methods.
- Synthesis Pathway: Sulfur hydride (H2S) was synthesized into superconducting phases using a low-temperature (200 K), rapid high-pressure (120 GPa) compression pathway.
- Superconductivity Observed: A clear two-step superconducting transition with zero resistance was observed under high pressure.
- Phase Identification: The higher transition temperature (Tc1, ~30 K class) is suggested to correspond to C2/c HS2, while the lower Tc phase (Tc2, ~15 K class) corresponds to elemental sulfur.
- Critical Field: The Tc1 phase exhibited a high upper critical field Hc2(0) of 53.0 T at 154 GPa, demonstrating robust superconducting properties.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum Pressure Achieved | 192 | GPa | Limit of measurement before anvil failure |
| Initial Compression Pressure | 120 | GPa | Pressure achieved after rapid squeeze |
| High Tc Phase (Tc1) Onset | ~35 | K | Estimated onset at 154 GPa |
| Low Tc Phase (Tc2) Onset | 15 | K | Observed at 120 GPa |
| Upper Critical Field Hc2(0) (Tc1) | 53.0 | T | Extrapolated value at 154 GPa |
| Upper Critical Field Hc2(0) (Tc2) | 28.2 | T | Extrapolated value at 154 GPa |
| Coherence Length Ο(0) (Tc1) | 2.5 | nm | Calculated using Ginzburg-Landau formula |
| Coherence Length Ο(0) (Tc2) | 3.4 | nm | Calculated using Ginzburg-Landau formula |
| Sample Space Dimensions | 15 x 20 | ”m | Area surrounded by UDD insulation |
| BDD Boron/Carbon Ratio | 2500 | ppm | Tuned using C3H9B gas during MPCVD |
| BDD Growth Pressure (MPCVD) | 70 | Torr | Total gas pressure during BDD deposition |
| BDD Microwave Power | 500 | W | Power used during BDD deposition |
| UDD Growth Pressure (MPCVD) | 35 | Torr | Total gas pressure during UDD deposition |
| UDD Microwave Power | 350 | W | Power used during UDD deposition |
| Metal Mask Annealing | 450 | °C | 1h duration in Ar gas-flow |
Key Methodologies
Section titled âKey MethodologiesâThe experiment involved two main stages: BDD/UDD fabrication on the anvil, and high-pressure synthesis/measurement.
A. BDD Electrode and UDD Insulation Fabrication
Section titled âA. BDD Electrode and UDD Insulation Fabricationâ- Lithography: Electron Beam Lithography (EBL) was used on the beveled diamond anvil to define the shape of the micro-electrodes.
- Mask Deposition: A Ti/Au thin film metal mask was deposited via a lift-off process.
- Adhesion Enhancement: The mask was annealed at 450 °C for 1 hour under Ar gas-flow to form a TiC intermediate layer, ensuring strong adhesion between the diamond and the metal.
- BDD Growth: Epitaxial BDD was selectively grown onto the uncovered diamond surface using Hydrogen-Induced Microwave-Assisted Plasma Chemical Vapor Deposition (MPCVD).
- Source Gases: CH4 (carbon source) and C3H9B (boron dopant, 2500 ppm B/C ratio).
- Conditions: 70 Torr total pressure, 300 sccm total gas flow, 500 W microwave power.
- Cleaning: The metal mask and graphite impurities were removed using a wet etching mixture of HNO3 and H2SO4 at 400 °C for 30 minutes.
- UDD Insulation: An Undoped Diamond (UDD) insulating layer was deposited around the BDD electrodes using similar MPCVD processes.
- Conditions: 35 Torr total pressure, 400 sccm total gas flow (H2 and CH4), 350 W microwave power.
B. High-Pressure Synthesis and Measurement
Section titled âB. High-Pressure Synthesis and Measurementâ- Gasket Preparation: A composite gasket was used, featuring a cubic boron nitride (cBN) center part and a rhenium (Re) outer plate. A 30 ”m sample chamber hole was fabricated in the cBN using Focused Ion Beam (FIB).
- Low-Temperature Filling: The DAC was cooled by dipping in liquid nitrogen, and the temperature was monitored (~200 K). H2S gas was introduced, solidified, and then changed to a liquid state around 200 K.
- Rapid Compression: The DAC screw was rapidly squeezed while the temperature was held around 200 K, quickly increasing the pressure up to 120 GPa (low-temperature, high-pressure pathway).
- Annealing and Measurement: The sample underwent room temperature annealing (resistance dropped from 77 kΩ to 38 Ω over 26 hours). Electrical resistance was measured using a standard four-probe method (PPMS/Quantum Design).
- Post-Compression Treatment: To further promote chemical reactions, the sample was annealed in an oven (up to 100 °C) and subsequently heated using an IR laser (1080 nm, 10-20 W).
- Characterization: Crystal structure was evaluated in-situ using Synchrotron X-ray Diffraction (XRD).
Commercial Applications
Section titled âCommercial ApplicationsâThe development of stable, integrated BDD micro-electrodes on beveled diamond anvils is a significant advancement for extreme environment research and sensing technology.
| Industry/Field | Relevance of Technology |
|---|---|
| High-Pressure Physics | Enables stable, repeatable in-situ electrical measurements (resistivity, Tc, Hc2) up to multi-megabar pressures, crucial for discovering novel materials (e.g., room-temperature superconductors). |
| Diamond Electronics | Demonstrates advanced fabrication techniques (EBL, MPCVD) for creating complex, integrated BDD/UDD micro-structures on non-planar (beveled) diamond surfaces. |
| Extreme Environment Sensing | BDD electrodes are chemically inert and mechanically robust, making them ideal for sensors (pressure, temperature, electrochemical) operating under extreme conditions (high pressure, high temperature, corrosive media). |
| Hydrogen Economy | Directly supports the design and characterization of functional materials like hydrogen-storage alloys and hydrogen-rich superconductors. |
| Quantum Materials Discovery | Provides a reliable platform for synthesizing and characterizing new high-Tc superconductors and other exotic quantum phases under pressure. |
| 6ccvd.com Relevance | Expertise in high-quality CVD diamond growth (BDD and UDD) is essential for fabricating these integrated anvil components, particularly the precise control over doping (2500 ppm B/C) and epitaxial growth required for micro-electrodes. |
View Original Abstract
Abstract A diamond anvil cell (DAC) has become an effective tool for investigating physical phenomena that occur at extremely high pressure, such as high-transition temperature superconductivity. Electrical transport measurements, which are used to characterize one of the most important properties of superconducting materials, are difficult to perform using conventional DACs. The available sample space in conventional DACs is very small and there is an added risk of electrode deformation under extreme operating conditions. To overcome these limitations, we herein report the fabrication of a boron-doped diamond microelectrode and undoped diamond insulation on a beveled culet surface of a diamond anvil. Using the newly developed DAC, we have performed in-situ electrical transport measurements on sulfur hydride H 2 S, which is a well-known precursor of the pressure-induced, high-transition temperature superconducting sulfur hydride, H 3 S. These measurements conducted under high pressures up to 192 GPa, indicated the presence of a multi-step superconducting transition, which we have attributed to elemental sulfur and possibly HS 2 .