PORTLAND, Ore. — Imaging nanoscale objects usually requires expensive electron-beam microscopes since the wavelength of visible light is too long--between 400 and 700 nanometers.

Now, features as small as 3 nanometers can be imaged with inexpensive optical microscopes using an algorithm that subtracts the differences between multiple exposures, thereby determining the shape of the object so that the image can be reconstructed.

The National Institute of Standards and Technology (NIST) developed the technique, called Through-focus Scanning Optical Microscope (TSOM) imaging. It works by taking multiple out-of-focus images at different focal lengths, then stacking them on top of each other.

An algorithm developed by NIST researcher Ravikiran Attota removes blurry images, leaving behind a clear image of tiny features.

Attota also demonstrated that the technique can accurately image nanoscale lines on silicon wafers, including their height, width and sidewall angles. Attota has also developed a technique for using his algorithm to image nanoparticles ten times smaller than the wavelength of light used to make the image.