Phase Transitions in Amorphous Germanium under Non-Hydrostatic Compression

At a Glance

Metadata	Details
Publication Date	2022-06-24
Journal	Crystals
Authors	Jianing Xu, Lingkong Zhang, Hailun Wang, Gao Yan, Tingcha Wei
Institutions	Chinese Academy of Sciences, Center for High Pressure Science and Technology Advanced Research
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Phase Transitions in Amorphous Germanium

This document analyzes the research paper “Phase Transitions in Amorphous Germanium under Non-Hydrostatic Compression” to highlight the critical role of high-quality diamond materials in extreme pressure research and to position 6CCVD’s capabilities as the ideal solution provider for replicating and extending this work.

Executive Summary

This research successfully demonstrated that the phase transition pathway of amorphous Germanium (a-Ge) is fundamentally controlled by the presence of shear stress, achieved through non-hydrostatic compression in a Diamond Anvil Cell (DAC).

Shear-Induced Reversibility: Under non-hydrostatic compression (no PTM), a reversible Low-Density Amorphous (LDA) to High-Density Amorphous (HDA) transition was observed, with a critical transition pressure around 14.1 GPa.
Contrast to Hydrostatic Conditions: This contrasts sharply with hydrostatic compression (using Ethanol PTM), which resulted in irreversible crystalline phases (β-Sn, followed by the pressure-quenchable ST12 phase).
Extreme Conditions: Experiments utilized high-pressure DACs to achieve pressures up to ~33 GPa, requiring robust, high-purity diamond components.
Methodology: The study relied on in situ synchrotron X-ray Diffraction (XRD) and high-pressure Raman spectroscopy to track structural changes under controlled compression/decompression cycles.
Scientific Impact: The findings emphasize the significant, often overlooked, role of shear stress in controlling material structure and properties, opening new avenues for developing advanced semiconductor and memory materials.
6CCVD Value Proposition: The success of this high-pressure research is directly dependent on the quality and mechanical integrity of the diamond anvils, a core specialization of 6CCVD’s Single Crystal Diamond (SCD) manufacturing.

Technical Specifications

The following hard data points were extracted from the experimental results and methodology sections of the paper:

Parameter	Value	Unit	Context
Max Non-Hydrostatic Pressure	~33	GPa	Achieved using DAC without PTM (shear stress environment)
Max Hydrostatic Pressure	~18	GPa	Achieved using DAC with Ethanol PTM
LDA-HDA Transition Pressure	~14.1	GPa	Non-hydrostatic compression critical point
a-Ge to β-Sn Transition Pressure	~11.3	GPa	Hydrostatic compression critical point
DAC Anvil Culet Size	300	µm	Standard size used for high-pressure generation
Sample Gasket Hole Diameter	~100	µm	Used for sample containment
ALS Synchrotron Wavelength	0.4959	Å	Used for non-hydrostatic XRD measurements
APS Synchrotron Wavelength	0.3100	Å	Used for hydrostatic XRD measurements
ALS X-ray Beam Size	~30 x 30	µm²	Used for non-hydrostatic XRD measurements
Raman Laser Wavelength	532	nm	Used for high-pressure spectroscopy
Raman Spectral Resolution	< 1	cm^-1	Achieved using 2400 lines·mm^-1 grating

Key Methodologies

The experiment relied on precise control of the pressure environment within a Diamond Anvil Cell (DAC) setup, coupled with advanced synchrotron and spectroscopic characterization.

Sample Synthesis: Amorphous Germanium (a-Ge) samples were fabricated using a magnetron sputtering system.
Pressure Generation: Diamond Anvil Cells (DACs) were employed for uniaxial compression at room temperature.
Non-Hydrostatic Environment: Experiments designed to detect the shear effect utilized no Pressure-Transmitting-Medium (PTM), resulting in a large pressure gradient and shear stress (up to ~10 GPa difference from center to edge).
Hydrostatic Environment: Ethanol was used as the PTM to maintain isotropic pressure conditions for comparison.
Pressure Measurement: Pressure was calibrated in situ using a micro-sized ruby ball standard, tracking its fluorescence R1-R2 line shift.
Structural Characterization (XRD): In situ high-pressure angle-dispersive XRD was performed at the Advanced Light Source (ALS) and Advanced Photon Source (APS) using highly focused monochromatic X-ray beams.
Vibrational Characterization (Raman): High-pressure Raman spectroscopy (532 nm laser) was used without PTM to track the Transverse Optic (TO) phonon mode shift and Full Width at Half Maximum (FWHM) changes, confirming the LDA-HDA transition.

6CCVD Solutions & Capabilities

The successful execution of high-pressure experiments up to 33 GPa, particularly those designed to isolate and measure the effects of shear stress, demands the highest quality diamond components. 6CCVD specializes in providing the MPCVD diamond materials necessary for next-generation DAC research.

Applicable Materials

To replicate or extend this high-pressure Germanium research, the following 6CCVD materials are required:

Optical Grade Single Crystal Diamond (SCD): Essential for the diamond anvils themselves. SCD offers unparalleled hardness, chemical inertness, and high optical transparency (crucial for both Raman and synchrotron XRD measurements). Our SCD material ensures minimal birefringence and defect density, maximizing signal integrity at extreme pressures.
Boron-Doped Diamond (BDD): For future extensions of this work (e.g., measuring the superconducting transition temperature (T_c) of the HDA phase, as mentioned in the literature), BDD substrates provide the necessary electrical conductivity for in situ electrical transport measurements under pressure.

Customization Potential

The precision required for DAC experiments, especially those focusing on shear stress, necessitates highly customized diamond components.

Research Requirement	6CCVD Customization Service	Technical Benefit
Anvil Geometry & Pressure Profile	Custom Dimensions & Laser Cutting	We provide SCD plates up to 500 µm thick and offer precision laser cutting to achieve specific culet sizes (e.g., 300 µm) and complex geometries (e.g., beveled or toroidal anvils) required to optimize pressure generation and shear distribution.
Integrated Sensing/Heating	Custom Metalization (Au, Pt, Ti, W)	6CCVD offers internal metalization capabilities to deposit thin films directly onto the diamond surface. This is critical for creating integrated micro-heaters or electrodes for in situ thermal or electrical measurements on the compressed sample.
Surface Quality for Shear Control	Precision Polishing (Ra < 1 nm)	Our advanced polishing techniques ensure the SCD anvil surfaces achieve roughness (Ra) < 1 nm. This ultra-smooth finish is vital for minimizing friction, ensuring uniform stress application, and achieving predictable shear environments.
Large-Scale Experiments	PCD Plates up to 125 mm Diameter	While SCD is preferred for anvils, our Polycrystalline Diamond (PCD) plates (up to 125 mm) are available for large-area high-pressure windows or backing plates where extreme optical clarity is not the primary constraint.

Engineering Support

6CCVD’s in-house team of PhD material scientists specializes in the application of MPCVD diamond in extreme environments. We can assist researchers in optimizing material selection and design parameters for similar high-pressure rheology and phase transition projects, ensuring the diamond components meet the stringent mechanical and optical demands of synchrotron facilities.

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

View Original Abstract

As the pioneer semiconductor in transistor, germanium (Ge) has been widely applied in information technology for over half a century. Although many phase transitions in Ge have been reported, the complicated phenomena of the phase structures in amorphous Ge under extreme conditions are still not fully investigated. Here, we report the different routes of phase transition in amorphous Ge under different compression conditions utilizing diamond anvil cell (DAC) combined with synchrotron-based X-ray diffraction (XRD) and Raman spectroscopy techniques. Upon non-hydrostatic compression of amorphous Ge, we observed that shear stress facilitates a reversible pressure-induced phase transformation, in contrast to the pressure-quenchable structure under a hydrostatic compression. These findings afford better understanding of the structural behaviors of Ge under extreme conditions, which contributes to more potential applications in the semiconductor field.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst12070898

References

2009 - Pressure-induced phase transitions in amorphous and metastable crystalline germanium by Raman scattering, x-ray spectroscopy, and ab initio calculations [Crossref]
1963 - A New Dense Form of Solid Germanium [Crossref]
1964 - The crystal structures of new forms of silicon and germanium [Crossref]
1996 - Immaphase of germanium at ~80 GPa [Crossref]
1986 - Phase-Transition Studies of Germanium to 1.25 Mbar [Crossref]
2000 - High-pressure Cmca and hcp phases of germanium [Crossref]
2011 - β−tin→Imma→sh Phase Transitions of Germanium [Crossref]
2004 - Phase transformations induced in relaxed amorphous silicon by indentation at room temperature [Crossref]
1973 - Electronic Properties of Complex Crystalline and Amorphous Phases of Ge and Si. II. Band Structure and Optical Properties [Crossref]
2017 - Properties of the exotic metastable ST12 germanium allotrope [Crossref]