Calibration of High-Resolution X-Ray Tomography With Atomic Force Microscopy.

Area of Science:

• Materials Science
• Nanotechnology
• X-ray Imaging

Background:

• Scanning transmission x-ray microscopy (STXM) achieves nanoscale resolution (40 nm) for 2D imaging of thin films.
• Calibration of 3D tomographic images from STXM data at this scale presents unique challenges not seen in larger-scale X-ray tomography.
• Existing calibration methods like optical imaging are insufficient due to the small feature sizes, and higher-resolution methods like atomic force microscopy (AFM) are destructive and provide surface-only information.

Purpose of the Study:

• To develop and describe a novel procedure for calibrating 3D tomographic images obtained using STXM.
• To overcome the limitations of existing calibration methods, particularly the inability to use optical imaging and the destructive nature of AFM.
• To achieve accurate calibration by correlating STXM tomography data with high-resolution surface imaging techniques.

Main Methods:

• A germanium star-shaped pattern was imaged using STXM at a synchrotron.
• Nineteen high-resolution 2D projection images were acquired and reconstructed into a 3D tomographic image.
• The STXM tomography data was calibrated against images obtained from atomic force microscopy (AFM) and scanning electron microscopy (SEM) of the same sample.

Main Results:

• Features as small as 40 nm were resolved in 2D STXM images and 80 nm in the 3D reconstructed tomographic image.
• Transverse length scales derived from AFM, SEM, X-ray transmission, and tomographic reconstruction agreed within 10 nm.
• The sample thickness calculated from projection images (51 ± 15 nm) showed good agreement with the tomographic reconstruction (80 ± 52 nm), within two standard deviations.

Conclusions:

• The developed procedure successfully calibrates STXM tomography images at the nanoscale.
• This method overcomes limitations of previous techniques, enabling more accurate 3D nanoscale imaging.
• The results demonstrate the feasibility of high-resolution 3D reconstruction and calibration for STXM, advancing nanoscale imaging capabilities.