Skip to content
6CCVD Research

Recovery of hexagonal Si-IV nanowires from extreme GPa pressure

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2016-05-12
JournalJournal of Applied Physics
AuthorsBennett E. Smith, Xuezhe Zhou, Paden B. Roder, E. Abramson, Peter J. Pauzauskie
InstitutionsUniversity of Washington, Pacific Northwest National Laboratory
Citations8
AnalysisFull AI Review Included

Technical Documentation & Analysis: High-Pressure Diamond Materials

Section titled “Technical Documentation & Analysis: High-Pressure Diamond Materials”

Reference Paper: Recovery of hexagonal Si-IV nanowires from extreme GPa pressure (arXiv:1510.04963v4)

Executive Summary

Section titled “Executive Summary”

This research successfully demonstrates the pressure-induced phase conversion and subsequent recovery of the exotic, direct-bandgap Si-IV (diamond hexagonal) phase in silicon nanowires (SiNWs). This work is highly relevant to the development of next-generation high-efficiency photovoltaic (PV) and photonic crystal (PC) materials.

  • Core Achievement: SiNWs were compressed up to 17 GPa in a Diamond Anvil Cell (DAC), inducing phase transitions from Si-I (cubic) to Si-II (tetragonal) near 9 GPa, and Si-II to Si-V (primitive hexagonal) between 14 and 17 GPa.
  • Material Recovery: The desirable Si-IV phase, a semiconductor with a reported direct band gap of 1.5 eV, was successfully recovered at atmospheric pressure (1 bar) and confirmed via Raman spectroscopy and TEM/SAED.
  • Experimental Methodology: The study relied on in situ Raman scattering using a 532 nm laser focused through high-purity diamond anvils, validating the critical role of optical-grade diamond in high-pressure physics.
  • Pressure Mechanism: Computational modeling confirmed that laser heating effects were negligible (temperature rise < 13°C), establishing near-hydrostatic pressure as the primary driving force for the phase formation.
  • 6CCVD Value Proposition: Replication and extension of this high-pressure research requires ultra-high purity, custom-dimensioned, and precision-polished Single Crystal Diamond (SCD) plates, a core offering of 6CCVD.

Technical Specifications

Section titled “Technical Specifications”

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

ParameterValueUnitContext
Maximum Pressure Achieved17GPaDAC compression limit
Si-I to Si-II Transition Onset~9GPaObserved via Raman scattering
Si-I to Si-II Transition Completion12.3GPaSi-I signal vanishes
Si-II to Si-V Transition Range14 to 17GPaLoss of Raman signal
Raman Laser Wavelength532nmExcitation source
Raman Laser Power (High P)5 or lessmWUsed near phase transitions (> 8 GPa)
Raman Spot Size~3”mFocused beam diameter
Si-IV Direct Band Gap (Reported)1.5eVPotential PV efficiency benefit
Si-IV Unit Cell Parametersa = 3.8, c = 6.27ÅConfirmed via SAED
DAC Diamond Culet Diameter0.3mmUsed for high-pressure containment
Rhenium Gasket Thickness50”mSpacer material
Theoretical Temperature Rise (Max)< 13°CCalculated for SiNW in Methanol/Ethanol

Key Methodologies

Section titled “Key Methodologies”

The experiment combined advanced material synthesis (SiNWs) with high-precision high-pressure optical measurement techniques.

  1. SiNW Synthesis: Silicon nanowires were prepared via Metal-Assisted Chemical Etching (MACE) of a <111> oriented, boron-doped silicon wafer (11 Ω cm resistivity).
  2. Etching Recipe: Immersion in a 1:1 volume ratio of 10 M HF:0.04 M AgNO3 for 3 hours, followed by cleaning in a 30% NH4OH:28% H2O2 solution to remove residual silver particles.
  3. DAC Setup: A Boehler-Almax plate DAC was utilized, employing diamonds with 0.3 mm culets. Pressure was monitored using micrometer-scale ruby grains.
  4. Gasket Preparation: A Rhenium gasket was dimpled to 50 ”m thickness, and a 150 ”m diameter hole was drilled via electrostatic-discharge machining.
  5. Pressure Medium: Near-hydrostatic conditions were achieved using either a 4:1 methanol:ethanol mixture or cryogenically loaded argon.
  6. In Situ Measurement: Raman scattering was performed by focusing a 532 nm laser through the DAC diamonds via a 50x objective. Back-scattered signal was collected and dispersed onto a liquid nitrogen-cooled CCD (resolution 0.3 cm-1).
  7. Structural Characterization: Recovered SiNWs were analyzed using Bright-Field TEM, High-Resolution TEM, and Select Area Electron Diffraction (SAED) to confirm the crystalline Si-IV domains.

6CCVD Solutions & Capabilities

Section titled “6CCVD Solutions & Capabilities”

This research highlights the critical need for high-quality, robust diamond materials capable of withstanding extreme pressures while maintaining exceptional optical transparency. 6CCVD is uniquely positioned to supply the necessary Single Crystal Diamond (SCD) components for replicating and advancing this high-pressure research.

Applicable Materials for DAC Research

Section titled “Applicable Materials for DAC Research”

To replicate the optical and mechanical demands of the Diamond Anvil Cell (DAC) used in this study, researchers require Optical Grade Single Crystal Diamond (SCD).

6CCVD MaterialKey Properties & RelevanceCustomization Options
Optical Grade SCDUltra-low birefringence and high transparency across the visible spectrum (critical for 532 nm Raman probe). High mechanical strength required for GPa pressures.Custom orientation (<100>, <111>), custom thickness (0.1 ”m to 500 ”m), and custom dimensions (up to 125 mm plates).
High Purity SCD SubstratesIdeal for use as the primary anvil material, ensuring minimal background signal interference during sensitive Raman measurements (0.3 cm-1 resolution).Custom culet sizes (e.g., 0.3 mm used here, or larger/smaller for specific pressure ranges) and custom shaping/beveling.

Customization Potential for Advanced High-Pressure Experiments

Section titled “Customization Potential for Advanced High-Pressure Experiments”

6CCVD’s in-house fabrication and processing capabilities directly address the needs of high-pressure material science:

  • Precision Polishing: DAC anvils require exceptional surface quality for alignment and optical clarity. 6CCVD guarantees Ra < 1 nm surface roughness on SCD, ensuring minimal light scattering and maximum optical throughput.
  • Custom Dimensions and Shaping: We provide custom SCD plates and wafers up to 125 mm. We can precision-cut and polish specific geometries required for specialized DAC designs (e.g., toroidal or beveled culets) or for integrating diamond windows into complex optical systems.
  • Integrated Metalization: While the reported experiment focused purely on optical measurement, advanced DAC experiments often require electrical transport measurements under pressure. 6CCVD offers internal metalization services (Au, Pt, Pd, Ti, W, Cu) for creating integrated electrodes or resistive heating elements directly onto the diamond surface.
  • Boron-Doped Diamond (BDD): For experiments requiring electrical conductivity or electrochemical sensing within the high-pressure cell, 6CCVD offers highly conductive BDD material in both SCD and PCD formats.

Engineering Support

Section titled “Engineering Support”

6CCVD’s in-house PhD team specializes in the material science of CVD diamond and can assist researchers in selecting the optimal diamond specifications (purity, orientation, and surface finish) for high-pressure Raman Spectroscopy and Photonic Crystal (PC) applications. We ensure the diamond material meets the stringent mechanical and optical requirements necessary to achieve pressures up to 17 GPa and beyond.

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

View Original Abstract

We use Raman spectroscopy in tandem with transmission electron microscopy and density functional theory simulations to show that extreme (GPa) pressure converts the phase of silicon nanowires from cubic (Si-I) to hexagonal (Si-IV) while preserving the nanowire’s cylindrical morphology. In situ Raman scattering of the longitudinal transverse optical (LTO) mode demonstrates the high-pressure Si-I to Si-II phase transition near 9 GPa. Raman signal of the LTO phonon shows a decrease in intensity in the range of 9-14 GPa. Then, at 17 GPa, it is no longer detectable, indicating a second phase change (Si-II to Si-V) in the 14-17 GPa range. Recovery of exotic phases in individual silicon nanowires from diamond anvil cell experiments reaching 17 GPa is also shown. Raman measurements indicate Si-IV as the dominant phase in pressurized nanowires after decompression. Transmission electron microscopy and electron diffraction confirm crystalline Si-IV domains in individual nanowires. Computational electromagnetic simulations suggest that heating from the Raman laser probe is negligible and that near-hydrostatic pressure is the primary driving force for the formation of hexagonal silicon nanowires.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2012 - Essentials of Geology

Reads Similar to This

Robust quantification of the diamond nitrogen-vacancy center charge state via photoluminescence spectroscopy Single Crystal Diamond Deposited by Dual Radio-Frequency Plasma Jet CVD with High Growth Rate Stimulated Raman scattering-active isotopically pure 12ĐĄ and 13ĐĄ diamond crystals - A milestone in the development of diamond photonics