untethered atom · TEM

CBED Thickness Tool

The microscope already told you the thickness. This just makes it say it in nanometers.

Upload a two-beam CBED pattern (JPG, PNG, TIFF 8/16/32-bit, or Velox EMD), mark the 000 and hkl disc centres, and the tool detects the Kossel–Möllenstedt fringe minima and fits the Kelly–Allen extrapolation: lamella thickness t with uncertainty, plus the extinction distance ξg. Everything runs in your browser; the image never leaves your machine. The theory behind every step lives in the companion CBED & lamella-thickness schematic.

Load a CBED pattern (JPG · PNG · TIFF 8/16/32-bit · Velox EMD) or try the demo.
display

1 Mark the two discs

Click the button, then click the disc centre on the image. Drag markers (or the ring handle ◆) to refine. Scroll = zoom, drag empty area = pan.

2 Fringe detection

Dark-fringe markers: drag to refine · alt-click the profile to add · double-click a marker to delete · drag the green s = 0 line onto the bright central fringe.

3 Physics inputs

λ = pm
or

4 Kelly–Allen fit

n₁ assignment:

5 Overlay style

Templates

The active style applies to the pattern view and the exported PNG, same as the SAED indexer. Download templates as a .json to reuse or share them; load the file in a future session to get them back.

Intensity profile along 000 → hkl (band-averaged)

Kelly–Allen extrapolation  (si/ni)² vs (1/ni)²

What an ideal pattern looks like (for the easiest measurement)

✓ ideal separated · symmetric · straight ✗ hard overlap · bent fringes · saturated
  • Clean two-beam: only 000 and one strong hkl disc; everything else faint (tilt using Kikuchi bands until the bright band sits in the hkl disc).
  • Discs clearly separated: convergence α ≈ 0.3–0.7 θB; the gap between disc edges should be comparable to a disc radius. Overlap (Kossel regime) makes the profile unreadable.
  • Bright s = 0 band near the disc centre with dark fringes symmetric on both sides: that symmetry is your check that the tilt is right.
  • ≥ 3 crisp dark fringes per side (t ≈ 2–5 ξg at that spot). Too few → move to a thicker area or a stronger (smaller-ξg) reflection; washed-out → thinner area or zero-loss filtering.
  • Straight, parallel fringes perpendicular to the 000→hkl line: probe on a flat, unbent, unstrained region.
  • Sharp disc edges (diffraction focus) and no saturation in either disc (a clipped 000 disc flattens the profile top and shifts detected minima).
  • Flat dark background: zero-loss energy filtering if available; short exposure sum beats one long saturated frame.

Physics: dark fringes at t·seff = n with seff = √(s² + 1/ξg²); si = (xi/X)·λ/d² (self-calibrating: camera length cancels); plot (si/ni)² vs (1/ni)²: intercept = 1/t², slope = −1/ξg². Companion pages: CBED & lamella thickness (the theory, interactive) · back focal plane & diffraction focus. Decoders: UTIF.js (MIT), jsfive (BSD), pako (MIT), inlined; no network needed.

Cite this page: Tripathy, Manisha. “CBED Thickness Tool.” untethered atom, 2026, https://untetheredatom.com/tem/cbed-thickness-tool.
BibTeX 
@misc{tripathy2026cbedthicknesstool,
  author = {Tripathy, Manisha},
  title  = {CBED Thickness Tool},
  year   = {2026},
  howpublished = {\url{https://untetheredatom.com/tem/cbed-thickness-tool}},
  note   = {Interactive web tool}
}
Last updated 18 August 2026.