Visualization
Iatia's QPI improves visualization of objects in the nanoscale by providing a highly effective contrast mechanism.
QPI calculates the phase distribution of a sample from a minimum of 2 differentially focused conventional intensity based brightfield images and rendering this phase data as a grayscale image. These QPI phase images are phase distribution maps independent of intensity/amplitude information showing the relative optical thickness across the sample, resulting in improved visual differentiation irrespective of the effects of intensity/amplitude.
Case study - silicon nitride
The following silicon nitride (Si3N4) images are courtesy of HREM Research, Inc (Japan) who have developed QPt for DigitalMicrograph™ incorporating QPI technology.
These images were taken at NCEM, Berkeley using a Philips CM300 equipped with a field emission gun and the phase images were generated by QPt for DigitalMicrograph™.
The following brightfield image is an out of focus image (in order to achieve some phase contrast) of a substrate monolayer.
By utilizing pairs of images separated by approximately 11.6nm, the QPI algorithm was able to construct phase images that clearly resolve the atomic structure of the sample. Back propagating this phase image to the sample exit surface yields the view seen in the upper half of this image. The phase corresponding to the minimum amplitude variation is shown in the lower half, where some of the Silicon (red) and Nitrogen (green) atoms have been indicated.
The following is a 3D rendering of a section of the minimum amplitude phase image produced with Research Systems IDL software.
For more information about this sample please see the HREM Research Inc. EMC 2004 poster available here.
References
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Phase Measurement of atomic resolution using Transport of Intensity Equation
Kazuo Ishizuka, and Brendan Allman, Journal of Electron Microscopy, 54, 191-197 (2005). -
Phase Measurement in Electron Microscopy Using the Transport of Intensity Equation
Kazuo Ishizuka, and Brendan Allman, Microscopy Today, 13, 22-24 (2005).