X-ray free-electron laser based dark-field X-ray microscopy - a simulation-based study
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-01-19 |
| Journal | Journal of Applied Crystallography |
| Authors | Theodor S. Holstad, Trygve Magnus RĂŠder, Mads Carlsen, Erik Knudsen, Leora E. DresselhausâMarais |
| Institutions | Technical University of Denmark, SLAC National Accelerator Laboratory |
| Citations | 12 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Ultrafast DFXM in Diamond
Section titled âTechnical Documentation & Analysis: Ultrafast DFXM in DiamondâThis document analyzes the research paper âX-ray free-electron laser based dark-field X-ray microscopy: a simulation-based studyâ and outlines how 6CCVDâs advanced MPCVD diamond materials and customization services are essential for replicating and extending this cutting-edge research in ultrafast dynamics.
Executive Summary
Section titled âExecutive SummaryâThis simulation study validates the feasibility of using Dark-Field X-ray Microscopy (DFXM) combined with X-ray Free-Electron Lasers (XFEL) and a pump-probe scheme to visualize phonon dynamics (strain waves) in single crystal diamond (SCD).
- Core Achievement: Numerical demonstration that single-pulse DFXM imaging of longitudinal strain waves in SCD is feasible using LCLS/XCS specifications.
- Time Resolution Breakthrough: The proposed methodology enables a potential nine orders of magnitude improvement in time resolution, moving DFXM from milliseconds to the femtosecond regime (35 fs pulse duration).
- Material Requirement: The experiment relies critically on high-quality, precisely oriented SCD substrates coated with a specific Ti/Au metalization stack to generate the strain wave via laser heating.
- Strain Sensitivity: Simulations show visibility of strain pulses with a maximum amplitude of approximately 4 x 10-4.
- Future Applications: Opens the door to studying ultrafast phenomena such as strain wave interaction with defects (dislocations, twin walls), rapid material failure, and diffusionless phase transformations.
- 6CCVD Value Proposition: 6CCVD is uniquely positioned to supply the required high-purity, low-mosaic Optical Grade SCD substrates with precise custom metalization (Ti/Au) and crystallographic orientation.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the simulation parameters for the proposed XFEL-based DFXM experiment:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sample Material | Diamond Single Crystal | N/A | SCD Substrate |
| Sample Dimensions | 0.6 x 1 x 2 | mm | Required size for simulation |
| Metalization (Adhesion) | 15 | nm | Ti (Titanium) adhesion layer |
| Metalization (Heating) | 600 | nm | Au (Gold) heating layer |
| XFEL Photon Energy | 10 | keV | LCLS/XCS Instrument specification |
| XFEL Pulse Duration | 35 | fs | Ultrafast probe pulse duration |
| Pump Laser Pulse Duration | 100 | fs | Optical laser heating pulse |
| Pump Laser Wavelength | 800 | nm | Used for thermal excitation |
| Pump Laser Fluence | 0.8 | J cm-2 | Energy density on Au film |
| Maximum Strain Magnitude | 4 x 10-4 | N/A | Amplitude of simulated strain pulse |
| Diamond Sound Speed (cs) | 18 | km s-1 | Longitudinal sound wave velocity |
| Objective Magnification (M) | 27.9 | N/A | X-ray objective (CRL) |
| Detector Pixel Size (Effective) | 466 x 664 | nm | In the observation plane |
Key Methodologies
Section titled âKey MethodologiesâThe simulation demonstrates a successful pump-probe DFXM experiment based on the following critical steps and material parameters:
- Substrate Selection: Use of a high-quality Single Crystal Diamond (SCD) with (110), (110), and (001) facets, specifically oriented for Bragg scattering from the {111} planes (2Ξ0 = 35.04°).
- Surface Preparation: The (110) facet is coated with a bilayer metal stack: a 15 nm Titanium (Ti) adhesion layer followed by a 600 nm Gold (Au) layer.
- Strain Wave Generation (Pump): A 100 fs optical laser pulse (800 nm, 0.8 J cm-2) heats the Au film, causing impulsive thermal expansion which launches a longitudinal strain wave into the diamond crystal.
- Strain Wave Modeling: A one-dimensional thermomechanical model (
udkm1Dsim) is used to compute the resulting temperature profile and subsequent crystal lattice dynamics. - DFXM Imaging (Probe): A 35 fs XFEL pulse (10 keV) probes the crystal at picosecond time delays, generating a Bragg-scattered beam.
- Image Acquisition: The diffracted beam is magnified by a Compound Refractive Lens (CRL) objective (M = 27.9) and projected onto a 2D CMOS detector.
- Contrast Optimization: Simulations explored both geometrical optics and wave-optics formalisms, confirming that rocking-type weak-beam contrast provides the clearest visualization of the strain wave profile.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is an expert supplier of MPCVD diamond materials and custom fabrication services, perfectly aligned to meet the stringent requirements of XFEL-based DFXM experiments. We provide the foundational materials necessary to transition these simulations into successful experimental reality.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research, the following 6CCVD materials are required:
| Research Requirement | 6CCVD Material Recommendation | Technical Rationale |
|---|---|---|
| High-Purity Substrate | Optical Grade Single Crystal Diamond (SCD) | Essential for minimizing intrinsic defects (e.g., nitrogen vacancies) and achieving the low mosaic spread (simulated at 200 ”rad) necessary for precise Bragg condition alignment. |
| Ultrafast Strain Generation | Custom Metalized SCD | The Ti/Au stack is critical. 6CCVD provides high-adhesion, uniform metalization layers (15 nm Ti / 600 nm Au) directly onto the specified SCD facet. |
| Future High-Energy Applications | Heavy Boron-Doped Diamond (BDD) | For experiments requiring conductive substrates or alternative pump-probe mechanisms, BDD offers robust electrical and thermal properties. |
Customization Potential
Section titled âCustomization PotentialâThe success of this DFXM technique hinges on precise material engineering and alignment, areas where 6CCVD excels:
- Custom Dimensions & Orientation: The paper specifies a 0.6 x 1 x 2 mm sample with specific facets ((110), (110), (001)). 6CCVD offers custom laser cutting and shaping of SCD plates up to 125mm, ensuring the exact dimensions and crystallographic orientation required for goniometer mounting and Bragg geometry.
- Advanced Metalization Services: We offer in-house deposition of the exact Ti/Au bilayer stack used for the thermal pump mechanism. Our capabilities include Au, Pt, Pd, Ti, W, and Cu metalization, allowing researchers to explore different adhesion layers or heating materials.
- Ultra-Smooth Surface Finish: DFXM requires minimal surface interference. 6CCVD guarantees Ra < 1 nm polishing on SCD, ensuring optimal optical laser absorption and minimizing scattering noise in the X-ray probe beam.
- Thickness Control: We provide SCD substrates with precise thickness control from 0.1 ”m up to 500 ”m, allowing researchers to optimize the X-ray penetration depth and Field of View (FoV) for specific XFEL energies.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science of diamond for extreme environments and advanced optics. We can assist researchers in:
- Material Selection: Optimizing SCD grade (e.g., low nitrogen, low birefringence) for specific XFEL beamline parameters (e.g., 10 keV X-rays).
- Metalization Recipe Development: Fine-tuning adhesion and heating layer thicknesses for optimal strain wave amplitude and longevity.
- Crystallographic Alignment: Ensuring precise facet cutting and orientation necessary for complex Bragg scattering geometries (e.g., {111} reflection).
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Dark-field X-ray microscopy (DFXM) is a nondestructive full-field imaging technique providing three-dimensional mapping of microstructure and local strain fields in deeply embedded crystalline elements. This is achieved by placing an objective lens in the diffracted beam, giving a magnified projection image. So far, the method has been applied with a time resolution of milliseconds to hours. In this work, the feasibility of DFXM at the picosecond time scale using an X-ray free-electron laser source and a pump-probe scheme is considered. Thermomechanical strain-wave simulations are combined with geometrical optics and wavefront propagation optics to simulate DFXM images of phonon dynamics in a diamond single crystal. Using the specifications of the XCS instrument at the Linac Coherent Light Source as an example results in simulated DFXM images clearly showing the propagation of a strain wave.