A real-time correction method for sample drift in STXM based on Fourier transform image registration

Scanning transmission X-ray microscopy (STXM) has high-resolution imaging capabilities of tens of nanometres by using a Fresnel zone plate (FZP) to focus the X-rays. It is an important technique for synchrotron radiation experiments. Combined with energy scanning across an X-ray absorption edge of the element of interest, STXM provides a nanoscale chemical analysis capability for samples. This scan mode is also called stack scan. During stack scan, to obtain two-dimensional high-resolution imaging, samples should be on the FZP focal plane, which varies with energy, as the FZP focal length is proportional to the photon energy. The stack mode of STXM can automatically adjust the ZP position in the beam direction with respect to the FZP focal length. Due to thermal drift of the motor and misaligning of the X-ray beam path with respect to the sample plane, the scanning area of the sample can drift continuously during a stack scanning, resulting in an increased scanning area and an extended scan time. In this paper, an online drift correction method for stack scan is proposed by combining a Fourier transform image registration algorithm with the position information of a laser interferometer. With this method, the sample drift of a 100-image stack scan is reduced from over 1 µm to less than 120 nm in STXM. Therefore, the sample drift in stack scan is effectively eliminated and redundant scan area is greatly reduced, which improves experimental efficiency.