Measuring the d-spacing of lattice fringes is the key to identifying the crystal structure and phase of your material. Once your High-Resolution TEM (HRTEM) image is cleaned up, there are two standard ways to measure this in ImageJ: in real space (measuring the stripes directly) or in reciprocal space (using the FFT).
Before doing either, you must ensure your image is calibrated.
Step 0: Calibrate your image
If your image doesn't already have physical units (nm or Å) embedded in its metadata, you need to set the scale using the scale bar on the TEM image.
Select the Straight Line tool.
Draw a line exactly over the scale bar in your image.
Go to Analyze > Set Scale...
Enter the known distance of the scale bar in the Known distance box, and set the Unit of length (e.g., nm).
Check Global if you want this scale applied to other images you open. Click OK.
Method 1: The Profile Plot (Real Space)
This method is highly visual and great for a quick measurement. The golden rule here is never measure just one fringe, as it introduces massive human error. Always measure across multiple fringes and average them.
Select the Straight Line tool.
Draw a line perpendicular to the lattice fringes, crossing as many clear fringes as possible (e.g., 10 fringes).
Go to Analyze > Plot Profile (or press Ctrl+K / Cmd+K).
A graph will pop up showing the peaks and valleys of the pixel intensity. Each peak is a lattice plane.
Measure the total distance L from the first peak to the last peak.
Count the number of gaps (fringe spacings) between those peaks, let's call this n.
Calculate the d-spacing using the formula:
d = L/n
Method 2: The FFT Method (Reciprocal Space)
This is the most accurate and professionally accepted method for HRTEM analysis. It averages the spacing over the entire selected area, eliminating local distortions or measurement errors.
Use the Rectangle Tool to select a clean, square region of your lattice fringes.
Go to Process > FFT > FFT. A new window will open showing a central bright spot with symmetrical spots around it.
Select the Straight Line tool.
Draw a line from the exact center of the central bright spot to the exact center of one of the outer diffraction spots.
Tip: To be even more accurate, draw a line connecting two opposite outer spots (passing through the center) and divide the final length by 2.
Go to Analyze > Measure (or press Ctrl+M / Cmd+M).
Look at the Length value in the Results window. Because the FFT is in reciprocal space, the distance you measured is the reciprocal vector R.
If ImageJ automatically converted the FFT axes to real-space units (which it often does if calibrated), the length might already be your d-spacing. If the axes are in reciprocal units (1/nm), ,you calculate the d-spacing as:
d=1/R
Shortcut trick: If your image is properly calibrated, simply hover your mouse cursor over the center of an outer diffraction spot in the FFT window. Look at the ImageJ status bar (the text right below the toolbar). It will often display the
d-spacing directly as d=... nm!