Synthesis and characterization of metastable crystalline st12 germanium
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-08-02 |
| Journal | Acta Crystallographica Section A Foundations and Advances |
| Authors | Bianca Haberl, Mary-Ellen Donnelly, Yan Wu, Emily Kroll, Matthias Frontzek |
| Institutions | Oak Ridge National Laboratory |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: High-Pressure Diamond Applications
Section titled âTechnical Documentation & Analysis: High-Pressure Diamond ApplicationsâExecutive Summary
Section titled âExecutive SummaryâThis research highlights the critical role of high-quality Single Crystal Diamond (SCD) in synthesizing and characterizing advanced metastable semiconductor materials under extreme pressure.
- Core Achievement: Successful synthesis and characterization of the metastable st12 phase of Germanium (Ge), a promising material for next-generation solar power conversion and high-temperature superconductivity.
- Methodology: The experiment relied on combining neutron scattering techniques with in situ high-pressure generation using a Paris-Edinburgh press.
- Diamondâs Role: Double-toroidal diamond anvils were essential to achieve and maintain extreme pressures (up to ~15 GPa) necessary for converting the diamond-cubic Ge to the metallic $\beta$-Sn phase.
- Pressure Milestone: This work represents the first successful use of double-toroidal anvils on the WAND2 beamline, achieving pressures > 10 GPa at the HFIR facility.
- Material Requirement: The success of such high-pressure physics is directly dependent on the mechanical integrity and purity of the SCD material used for the anvils.
- 6CCVD Value Proposition: 6CCVD provides the ultra-high purity, custom-dimensioned, and precision-polished MPCVD SCD required for demanding high-pressure research applications.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the critical parameters and material phases extracted from the research abstract.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum Synthesis Pressure | ~15 | GPa | Applied pressure using double-toroidal diamond anvils. |
| $\beta$-Sn Phase Formation Pressure | ~11 | GPa | Compression threshold from standard diamond cubic Ge (Fd-3m). |
| Minimum Synthesis Pressure | >10 | GPa | Required for recoverable sample volumes and achieved at HFIR. |
| High-Pressure Duration | Several | hours | Time required to ensure full conversion to the $\beta$-Sn phase. |
| Incident Neutron Energy (ARCS) | 30, 50, 70 | meV | Used for fine resolution phonon density of states measurement. |
| Initial Ge Phase | Fd-3m | Crystal Structure | Standard diamond cubic Germanium. |
| Intermediate Ge Phase | I41/amd | Crystal Structure | Metallic $\beta$-Sn phase (high-pressure polymorph). |
| Recovered Ge Phase | P43212 | Crystal Structure | Metastable st12 phase. |
Key Methodologies
Section titled âKey MethodologiesâThe synthesis and characterization of the metastable st12 Ge phase involved a complex, multi-step high-pressure process utilizing specialized diamond components:
- Sample Preparation: Small pieces of a Germanium (Ge) wafer were prepared for compression.
- High-Pressure Synthesis: Samples were loaded into a Paris-Edinburgh press utilizing double-toroidal diamond anvils.
- Compression: The sample was pressurized to above ~15 GPa.
- Phase Conversion: Maximum pressure was maintained for several hours to ensure complete conversion of the diamond-cubic Ge to the metallic $\beta$-Sn phase.
- In Situ Diffraction: High-pressure diffraction was performed on the WAND2 beamline to confirm the transition pathway and perform Rietveld refinement, confirming full conversion.
- Recovery: Controlled decompression yielded the metastable st12 Ge phase.
- Characterization: Recovered pellets were measured using inelastic neutron scattering (INS) on the ARCS beamline at incident energies of 30, 50, and 70 meV to determine the phonon density of states.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful execution of this high-pressure research hinges on the quality and precision of the diamond anvils. 6CCVD is an industry leader in supplying the MPCVD diamond materials necessary for extreme environment research, including high-pressure physics and neutron scattering applications.
| Research Requirement | 6CCVD Applicable Materials | Customization Potential & Advantage |
|---|---|---|
| High-Pressure Anvils (>15 GPa) | Optical Grade Single Crystal Diamond (SCD) | Our SCD offers superior purity and mechanical strength, essential for maintaining structural integrity at extreme pressures and minimizing background noise during neutron scattering. |
| Custom Anvil Geometry (Double-Toroidal) | Custom Dimensions & Precision Laser Cutting | We supply SCD plates/wafers up to 125mm and provide in-house laser cutting services to achieve the precise, complex geometries required for double-toroidal or beveled anvil designs. |
| Optical/Spectroscopic Access | Ultra-Low Roughness Polishing (Ra < 1nm) | Anvil faces must be highly polished to ensure minimal scattering and distortion. 6CCVD guarantees Ra < 1nm for SCD, optimizing in situ measurement quality. |
| Future Electrical Measurements | Boron-Doped Diamond (BDD) | For extending this research to measure the conductivity of the metallic $\beta$-Sn phase, 6CCVD supplies highly conductive BDD substrates, which can be used as conductive anvils or electrodes. |
| Contact/Gasket Metalization | Internal Metalization Services | We offer custom deposition of Au, Pt, Pd, Ti, W, and Cu, critical for creating robust electrical contacts or protective layers on the diamond surface for gasket or electrode applications. |
| Material Thickness Optimization | SCD Thickness Control (0.1Âľm - 500Âľm) | We provide precise thickness control, allowing researchers to optimize the anvil thickness for maximum pressure generation while maintaining adequate optical or neutron transmission path lengths. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science of diamond under extreme conditions. We can assist researchers in material selection, orientation, and finishing specifications for similar high-pressure metastable semiconductor synthesis projects, ensuring optimal performance and longevity of high-pressure components.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
This work uses neutron scattering to characterize a metastable crystalline phase of germanium recovered from high pressure.Such metastable phases of silicon and germanium exhibit interesting functionality.They could potentially yield a Si or Ge structure with ideal band gap characteristics for solar power conversion, improved thin-film characteristics or -in the form of a hydride -even become a useful material for very high temperature superconductivity.Several of such metastable, crystalline phases can be recovered from the metallic high-pressure polymorph of Si and Ge, the so-called β-Sn phase (I4[sub]1[/sub]/amd).This metallic polymorph forms upon room temperature compression to ~11 GPa from the standard diamond cubic Si or Ge (Fd-3m).Upon decompression, this transition is not reversible and instead these metastable phase form.The exact crystal structure that is nucleated is thereby dependent on the exact decompression parameters such as temperature, rate or hydrostaticity.However, the need for synthesis pressures above ~10 GPa has typically limited the recoverable sample volumes.Hence, the majority of studies have been conducted computationally and fewer experimental characterizations have been performed.Thus, there are many open questions on the behavior and characteristics of these metastable phases.Here, we focus on the simple tetragonal st12 structure of Ge (P4[sub]3[/sub]2[sub]1[/sub]2) by combining synthesis capabilities of the SNAP diffractometer of the Spallation Neutron Source with in situ high pressure diffraction on the WAND[sup]2[/sup] beamline of the High Flux Isotope Reactor and inelastic neutron scattering on recovered samples on the ARCS beamline of the Spallation Neutron Source.The st12 structure is synthesized using double-toroidal diamond anvils in a Paris-Edinburgh press from small pieces of a Ge wafer.The sample is pressurized to above ~15 GPa and kept at maximum pressure for several hours to ensure full conversion to the β-Sn phase.The transition pathways is confirmed by in situ diffraction on WAND[sup]2[/sup].Rietveld refinement of the Ge material under pressure confirms that all diamond-cubic material was indeed converted to the metallic β-Sn phase.It is noteworthy that this experiment represents the first use of the double-toroidal anvils on the WAND2 beamline and that pressures above 10 GPa were achieved for the first time at the HFIR facility.Several such pellets were then measured on ARCS using incident energies of 30, 50, and 70 meV, which were combined to provide a fine resolution phonon density of states.The result closely matches the DFT predictions, although subtle differences may be detected.Thus, in summary, these findings yield new insights into the potential use of the st12 phase as future semiconductor material and also open avenues for further characterization of such metastable phases of Si and Ge.