DEVELOPMENT AND APPLICATION OF NOVEL DIAGNOSTICS TO PROBE DYNAMICALLY COMPRESSED MATERIALS

At a Glance

Metadata	Details
Publication Date	2015-01-01
Journal	Munich Personal RePEc Archive (Ludwig Maximilian University of Munich)
Authors	S. J. Ali
Analysis	Full AI Review Included

Diamond Materials for Extreme Dynamics Research

This technical documentation analyzes the findings from “Development and Application of Novel Diagnostics to Probe Dynamically Compressed Materials” (Ali, 2015), focusing on the critical role of high-quality Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) in cutting-edge shock physics and high-energy-density (HED) experiments.

6CCVD provides the specialized CVD diamond required to replicate and advance this pioneering work on semiconductor-to-metal transitions and anisotropic fracture dynamics.

Executive Summary

Advanced Diagnostics Validation: The research successfully employed the Shock Wave Optical Reflectivity Diagnostic (SWORD) and 2D Velocity Interferometry System for Any Reflector (2D VISAR/JHRV) to probe material response under nanosecond shock compression.
Fundamental Phase Transition: The study confirmed the dynamic semiconductor-to-metal transition in germanium (Ge) under shock (18-29 GPa), observing a significant (up to two-fold) increase in NIR reflectivity using the novel broadband SWORD technique (0.5 ns time resolution).
Diamond Anisotropy Quantification: Single-crystal diamond (SCD) in <100>, <110>, and <111> orientations demonstrated clear acoustic and plastic deformation anisotropy under spherical shock waves, behavior which is predictable using known elastic constants.
Dynamic Fracture Toughness Defined: The research precisely determined the dynamic fracture toughness ($K_c$) for CVD polycrystalline diamond: 103±14 MPa m^1/2 for microdiamond and 44±8 MPa m^1/2 for nanodiamond.
Microstructural Impact: A crucial difference in deformation response and velocity roughness was observed between microcrystalline and nanocrystalline PCD, validating the dependence of inelastic behavior on grain size, highly relevant for ICF ablator design.
Material Requirement: Replicating these advanced velocimetry and reflectivity measurements demands ultra-high quality, precisely oriented SCD, and well-characterized PCD materials manufactured via MPCVD.

Technical Specifications

Parameter	Value	Unit	Context
SWORD Time Resolution	0.5	ns	Broadband reflectivity measurements
SWORD Wavelength Range	450 to 1150	nm	Visible and near-infrared spectral range
Ge Phase Transition Pressure (Dynamic)	18 to 29	GPa	Semiconductor-to-metal transition observed
Ge Reflectivity Increase (NIR)	80-90	%	Observed upon phase transition
Ge Absorption Peak Shift	1.5 eV (18 GPa) to 1.7 eV (29 GPa)	eV	Strong absorption peak shift confirmed via Drude-Lorentz fit
SCD/PCD Peak Pressure Range	~52 to ~84	GPa	Inelastic deformation and fracture studies
Single Crystal Diamond Thickness	0.8 to 1.1	mm	Used for wave propagation studies
PCD Sample Thickness	500	µm	Micro- and nanocrystalline fracture samples
Microdiamond Fracture Toughness ($K_c$)	103±14	MPa m^1/2	Free surface, microcrystalline samples
Nanodiamond Fracture Toughness ($K_c$)	44±8	MPa m^1/2	Free surface, nanocrystalline samples
2D-VISAR Spatial Resolution	~4	µm	Used for imaging fracture networks
Metalization Layer (LiF window)	104	nm	Aluminum sputter coating for reflectivity enhancement

Key Methodologies

The dynamic compression experiments utilized laser-driven shock generation combined with highly sensitive optical diagnostics requiring precise material specification and processing:

Laser Compression Source: Experiments were conducted at the Jupiter Laser Facility (Janus Target Area) using frequency-doubled (527 nm) Nd:glass lasers delivering 4-6 ns square pulses with energies up to ~300 J.
Shock Drive Geometry: Planar shock waves utilized phase plates for uniform energy deposition (1 mm² or 0.28 mm² focal spot). Spherical shocks utilized a tightly focused beam (150-200 µm diameter).
Broadband Light Generation (SWORD): High-intensity white light was generated via supercontinuum generation (self-focusing and self-phase modulation) using an ultrafast Ti:sapphire laser pulse (800 nm, 50-100 fs) focused into a 1-cm water cell.
Time Resolution: Nanosecond time resolution for SWORD was achieved using an optical pulse stacker (four beamsplitters/delay paths) generating up to 16 time-displaced spectra with 0.5 ns intervals.
Target Stacking: Samples (Ge or Diamond) were arranged in layered stacks (ablator / pusher / sample / window). SCD and PCD samples were fixed between an aluminum pusher and a Lithium Fluoride (LiF) optical window.
Interface Control: For VISAR/JHRV diagnostics, LiF windows were sputter-coated with a 104 nm Aluminum layer to enhance reflectivity at the sample/window interface. Target assembly avoided glue layers (especially LiF/Ge interface) by using a four-point fixture.
Diamond Materials: SCD samples were sourced in <100>, <110>, and <111> orientations. PCD samples featured microcrystalline (~50 µm grain size) and nanocrystalline (~20-100 nm grain size).

6CCVD Solutions & Capabilities

6CCVD’s specialized MPCVD diamond capabilities directly address the rigorous material demands of high-pressure shock experiments, facilitating the replication and extension of the research presented in this dissertation.

Applicable Materials

The precision physics detailed requires diamond characterized by specific crystal orientation and controlled microstructure, exactly matching 6CCVD’s core production offerings:

Research Requirement	6CCVD Material Solution	Application Benefit
Anisotropic Wave Studies	Optical Grade Single Crystal Diamond (SCD): Custom-cut <100>, <110>, and <111> orientations. Ra < 1 nm polished finish ensures maximum optical fidelity for VISAR/JHRV.	Guarantees the necessary crystal purity and orientation control to accurately study acoustic anisotropy and plastic slip systems at extreme pressures.
Heterogeneous Fracture Studies	Polycrystalline Diamond (PCD) Plates: Available in both Nanocrystalline (for low fracture toughness studies, $K_c$ ~44 MPa m^1/2) and Microcrystalline (for higher fracture toughness, $K_c$ ~103 MPa m^1/2) grain sizes.	Enables reproducible studies correlating grain size effects, as observed in the paper, to dynamic yield strength and brittle fracture mechanisms relevant to HED and armor materials.
Conductivity/Metallization	Boron-Doped Diamond (BDD) Wafers: Can be custom-produced for applications requiring an intrinsic conductor or semi-metal interface, extending shock studies beyond Ge, particularly in the study of conductivity changes under compression.	Allows researchers to investigate electrical properties and reflectivity dynamics in shock-compressed conductive diamond materials, relevant to planetary cores and ICF implosions.

Customization Potential

The success of the SWORD and 2D-VISAR diagnostics is highly dependent on precise target engineering and interface preparation. 6CCVD supports these needs directly:

Custom Dimensions and Thickness: The paper utilized SCD/PCD samples ranging from 500 µm to 1.1 mm thick, and lateral dimensions of 3 mm squares or 2 mm discs. 6CCVD manufactures SCD/PCD plates up to 500 µm standard thickness and substrates up to 10 mm thick, with PCD lateral sizes up to 125 mm, ensuring scalability beyond small laser facilities.
Precision Polishing: Achieving a high-quality reflective interface for VISAR is critical. 6CCVD offers unmatched polishing services, guaranteeing Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, maximizing probe reflectivity and reducing spurious scatter.
Interface Metallization: The paper required a 104 nm Aluminum coating. 6CCVD provides in-house sputter metalization services, including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to choose the optimal reflective layer or electrical contact material for customized dynamic experiments.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers specializes in diamond synthesis for extreme environments. We offer consultation on:

Material Selection: Assistance in choosing the correct SCD crystal orientation or PCD grain size to optimize signal response and mechanical performance in high-pressure shock experiments.
Target Design Optimization: Support for material integration and interface optimization to maximize diagnostic throughput for similar dynamic reflectivity and velocimetry projects (SWORD/VISAR/JHRV).
Global Logistics: Efficient global shipping solutions (DDU default, DDP available) ensure time-sensitive HED experiments are supported worldwide.

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

View Original Abstract

Two particular experimental approaches have been experiencing increased interest, that of dynamic spectroscopy and that of 2D measurements. The first allows us to obtain a better understanding of the electronic and chemical processes taking place under shock loading while the second provides a detailed view into the microscopic and macroscopic heterogeneities which directly influence material behavior and have been difficult to identify in the bulk material. In order to better understand these behaviors and their origins, two approaches have been utilized. A novel dynamic broadband optical reflectivity diagnostic was developed to probe changes in material properties on the scale of electronic structure and an existing, but only recently developed high resolution velocimetry system was used to observe the aforementioned changes on larger, microstructural scales.In order to expand understanding of the chemical and mechanical responses of condensed matter to dynamic shock compression two projects were undertaken. The first was the development of a broadband optical reflectivity diagnostic with both time and wavelength resolution. The Shock Wave Optical Reflectivity Diagnostic (SWORD) has enabled us to study the dynamic optical reflectivity in shocked samples over the visible and near-infrared, across a time span of nanoseconds and with a resolution of 0.5 ns and 10 nm. Laser velocimetry was used in tandem with the SWORD to determine kinematic properties of the shocked samples, such as pressure and density. This novel diagnostic has been applied to the semiconductor-to-metal transition in single-crystal germanium and used to observe both a general reflectivity increase on metallization and a wavelength dependent response as a function of pressure.The second project involved the application of the recently developed two dimensional Velocity Interferometry System for Any Reflector (2D VISAR, alternatively Janus High Resolution Velocimeter, JHRV) to study anisotropic shock wave propagation and dynamic heterogeneous deformation and fracture in diamond. In combination with the aforementioned laser velocimetry (also VISAR), we have obtained velocity histories and two-dimensional velocity maps and images of the shocked target at various time points after breakout. Significant anisotropy in both the elastic and inelastic waves was observed in single-crystal diamond samples. Characteristic length scales for the fracture of polycrystalline diamond samples of varying grain size were also determined.

Tech Support

Original Source

DOI: None