PED
What Is PED (Precession Electron Diffraction)?
PED (Precession Electron Diffraction) is a TEM-based diffraction technique that improves electron diffraction data quality by rocking (precessing) the electron beam around the optical axis while collecting diffraction patterns. This “averages” dynamical diffraction effects and produces patterns that are often more kinematical-like, making them easier to index and more reliable for phase identification and crystallographic orientation mapping at the nano-to-micron scale (tool/sample dependent).
PED is commonly used with scanning modes in the TEM (often as 4D-STEM / orientation mapping workflows) to generate spatial maps of grain orientation, phase distribution, and strain/defect-related crystallographic changes (project-dependent).
What PED Is Used For
PED is widely applied to crystallographic problems that need spatial resolution in the TEM, including:
Phase identification in multiphase materials (including minor phases, project-dependent)
Orientation mapping / “TEM-EBSD-like” maps for nanocrystalline structures
Grain size and grain boundary network mapping at very fine scales
Texture and local orientation gradients (deformation, recrystallization studies)
Precipitate, second-phase, or intermetallic identification in alloys (project-dependent)
Crystallinity changes after processing or aging (anneal, irradiation, corrosion, etc., project-dependent)
Failure analysis support: crack paths vs local microtexture, phase transformations near defects
Why PED (vs. Standard TEM Diffraction or EBSD)?
Compared with conventional TEM diffraction (SAED/NBED):
PED often yields patterns that are easier to index and more robust for automated mapping (project-dependent)
Reduced sensitivity to orientation-dependent dynamical effects in many materials
Compared with SEM-EBSD:
PED can reach much finer spatial resolution, helpful for nanograins, thin layers, and tiny precipitates
Useful when EBSD indexing is limited by grain size, surface prep constraints, or complex phase mixtures (project-dependent)
Sample Types We Support
PED is best suited for electron-transparent samples (project-dependent), such as:
Metals & alloys: nanocrystalline materials, deformed regions, precipitate-rich alloys
Thin films & coatings: multilayers, diffusion barriers, functional films (project-dependent)
Ceramics & crystalline oxides: polycrystalline ceramics, nanophases, grain boundary studies
Semiconductor materials: local phase/orientation in device-relevant layers (project-dependent)
Battery materials: phase/orientation mapping in active particles and reaction layers (project-dependent)
Failure investigation samples: regions near cracks, voids, delamination, inclusions (project-dependent)
Not ideal for: highly beam-sensitive or highly amorphous materials without special strategies (project-dependent).
Typical Workflows
Phase & Orientation Mapping (Most Common)
Best for: multiphase materials, nano-grain mapping
Select region of interest (ROI)
Acquire PED diffraction dataset (scan-based mapping)
Index patterns to generate phase maps + orientation maps (tool/software dependent)
Correlate with TEM/STEM images and, if needed, EDS/EELS
Precipitate / Minor Phase Identification
Best for: “What is this tiny particle/phase?”
Target the feature in TEM
Collect PED-enhanced diffraction patterns
Provide phase candidates + confidence notes; confirm with chemistry if needed
Process Comparison (“What Changed?”)
Best for: heat treatment drift, supplier differences, aging effects
Map reference vs suspect sample areas using the same plan
Compare phase fractions, grain size, orientation distributions (project-dependent)
Summarize the key crystallographic differences and likely implications
What You Receive
Depending on scope and sample behavior, deliverables can include:
Phase distribution maps (where applicable)
Orientation maps (IPF-style visualizations, project-dependent)
Representative diffraction patterns and indexing summary
TEM/STEM images used for correlation (if captured)
A clear interpretation: what phases/orientations are present, what changed vs reference, and why it matters
Sample Submission Guidelines
Please provide
Material system and the question (phase ID? nano-grain orientation? precipitates? comparison?)
Process history (heat treatment, forming, service exposure, aging)
If failure-related: photos/marking of the ROI and “good vs bad” samples if available
Any known phase candidates or prior data (XRD/EBSD/EDS) to speed up planning
Sample preparation (critical)
PED typically requires TEM-ready specimens:
Thin foils / lamellae (often FIB lift-out for site-specific regions)
Clean, electron-transparent thickness in the ROI
Minimization of preparation-induced damage where possible (project-dependent)
If you don’t have TEM lamellae, we can recommend a prep plan or include preparation as part of the project (project-dependent).
FAQs
Is PED destructive?
The analyzed area is exposed to the electron beam, and TEM sample prep (especially FIB lamella prep) is inherently invasive to the ROI. We minimize beam dose where beam sensitivity is a concern (project-dependent).
Can PED replace EBSD?
Not usually. EBSD is excellent for larger-area mapping and faster screening. PED is best when you need nanoscale mapping, very small features, or TEM-level correlation.
Can PED identify phases confidently?
Often yes, especially when combined with chemistry (EDS/EELS) and complementary diffraction context. Confidence depends on pattern quality, thickness, phase similarity, and reference data availability (project-dependent).
What’s the difference between PED and 4D-STEM?
PED can be used within scanning diffraction workflows and is often a component of “4D-STEM-style” datasets (scan position + diffraction pattern). The exact implementation depends on the instrument and project goals.
Do I need a reference sample?
Strongly recommended for “what changed?” studies—comparisons become faster and conclusions are more defensible.
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