Do I need the camera length to index a SAED pattern with this tool?

No. The tool uses ratios of reciprocal-space distances and the angle between spots, so the camera constant cancels out and no calibration is required.

Which crystal structures are supported?

FCC, BCC, simple cubic, diamond cubic, and HCP are built in, and you can define a custom lattice with your own a, c and structure-factor rules.

Is my diffraction image uploaded to a server?

No. Everything runs locally in your browser; the image never leaves your computer.

SAED Zone-Axis Indexer — Index Electron Diffraction Patterns Online (Free)

Load an image (or the demo), then click the transmitted beam 000.

1 · Crystal

Preset

Lattice / extinctions

a (Å)

b (Å)

c (Å)

α (°)

β (°)

γ (°)

Max index

Ratio tol (%)

Angle tol (°)

2 · Calibration (optional)

Camera constant λL (Å·px) — enables measured d-spacings

3 · Points

Click the brightest matrix net only: 000, then the two shortest non-collinear spots (they define the basis g₁, g₂). Extra spots are used as consistency checks. Don’t click superlattice / precipitate spots.

4 · Analyze

5 · Label style

Font

Size (%) 100

Font color

Outline color

Marker shape

Marker color

bold text outline zone-axis stamp

Templates

Saved templates

New template name

The active style applies to every image you annotate in this session (screen + PNG export). Download your templates as a .json to reuse or share them; load the file in a future session to get them back.

About SAED indexing — and how this tool works

Indexing a selected-area electron diffraction (SAED) pattern means assigning Miller indices (hkl) to the diffraction spots and identifying the zone axis [uvw] — the crystallographic direction along which the electron beam travels through the crystal. It is one of the most common tasks in transmission electron microscopy (TEM), and one of the most error-prone to do by hand with a ruler and a table of d-spacings.

This tool automates the classic ratio method. You upload a diffraction pattern, click the transmitted (central) beam and the two shortest independent spots, and it measures the two reciprocal distances R₁ and R₂ and the angle between them. Because the analysis uses the ratio R₂/R₁ together with the inter-spot angle, the camera constant cancels out — no camera-length calibration is needed. The measured ratio and angle are compared against every allowed reflection pair for the chosen structure, and matching zone axes are ranked. A predicted diffraction net is then overlaid on your image so you can verify the assignment against the actual spots rather than trusting a table.

Supported crystal structures

Built-in structure-factor rules cover FCC (e.g. Al, Cu, Ni, austenitic steels), BCC (e.g. ferrite, W, Mo), simple cubic, diamond cubic (Si, Ge), and HCP (e.g. Ti, Zn, Mg) — plus a custom-lattice mode where you supply your own lattice parameters.

Tips for reliable indexing

Use an on-axis single-crystal pattern (a clean symmetric net, not rings or overlapping grains); click spot centers as precisely as possible, since the angle measurement drives discrimination between similar nets; and always check the overlay — a correct index reproduces all spots of the net, not just the two you clicked. Patterns from polycrystalline regions or heavily strained material may need a smaller selected-area aperture.

Privacy

The tool runs entirely in your browser — your image is never uploaded to any server.