Resolution Tests for JEOL High Tilt Retainer (HTR)

high tilt retainer

The JEOL room temperature high tilt retainer is very narrow and has a tilt range of ±70° in our JEOL JEM 3200FS. It is quite stable and produces high resolution images over the entire tilt range, though the defocus gradient at high tilt becomes an issue when evaluating the quality of very high resolution images. Resolution tests were conducted using a holey carbon film that has both graphite fragments and "islands" of (poly)crystalline gold.

The images below were recorded using a microscope magnification of 300,000x (~377,000x at the CCD) and an exposure time of 1 second:

    untilted:

untilted imagesub-image and FFT of full image

Mouse over the image above to see the Fourier transform of the full image.

Both the spacing between the graphite layers (3.4 Å) and between the gold atoms (2.35 Å) are clearly resolved in the untilted image.

    +70°

tilted +70sub-region and FFT of full imageMouse over the image above to see the Fourier transform of the full image.

The tilt axis runs at ~35° counter-clockwise from horizontal in these images, and due to the high tilt, there is a defocus gradient of about 440 nm across the 160 nm field of view of this image. However, because of the hole covering the lower right half of this image, the Fourier transform is not as impacted by this gradient as it would be otherwise. tilted image with FFT's of different areasThe Fourier transform clearly shows high resolution information along the tilt axis and there is even some diffuse diffraction at the resolution of the gold spacing (2.35 Å) in the direction perpendicular to the tilt axis.

In the image to the right, Fourier transforms calculated from small regions of the highly tilted image have been inserted at their exact positions in the original image. In these Fourier transforms, the diffraction of the graphite layers still forms a diffuse ring while the islands of crystalline gold give rise to discrete diffraction spots. it is much easier to see in these small Fourier transforms that the resolution perpendicular to the tilt axis is quite good (at least to the 2.35 Å spacing of the gold lattice) in some regions of the highly tilted image.

 

    -70°

tilted -70sub-region and FFT of full image

Mouse over the image above to see the Fourier transform of the full image.

Although the diffraction due to the crystalline gold is very weak in the Fourier transform from this image, the thick region of graphite produces very strong and reasonably isotropic diffraction despite the large defocus gradient present in the image. A second image at -70° was recorded to show the information from the gold lattice:

2nd image tilted -70image with inserted FFT's

The strong defocus gradient from the upper left corner to the lower right corner is clearly visible in this image. Diffraction from the gold lattice is not nearly as isotropic as that of the graphite in the Fourier transform above, but there are clear indications of information at the 2.35 Å spacing of the crystalline gold in many parts of this image.

All these images were recorded on 16-june-2009.