Dave Mitchell's DigitalMicrograph™ Scripting Website

Function

Creates a scanning hollow cone by tilting the beam azimuthally. As this is a software implementation, it is much slower than hardware systems. However, since dark field exposure times of many seconds are typical, the beam may complete several circuits (with judicious choice of parameters) during an acquisition. The scan runs as a background thread and so it can be set running and then images captured using normal camera acquisition methods.

Version

Authors

D. R. G. Mitchell, J. Olivier and J. O'Connell.

Acknowledgements

This script is closely based on Vincent Hou's 'Drift Tube Scan' script.

Comments

The shortest dwell time per tilt is 0.01s. Shorter tilts are not helpful, since the latency in the system is due to setting the tilts. Short dwells may also cause thread timing issues. If you end up with more than one scan running at the same time - use longer exposure times. The tilt purity must be set correctly for hollow cone scanning, otherwise the image will move when the beam is tilted. Minor refocusing when scanning may be necessary.

System Requirements

Tested on a JEOL 2100 running under GMS 1.9.x. The script should be compatible with GMS 2.x, but has not been tested. The script uses the generic EMControl commands, and so should be compatible with all modern instruments which support them, regardless of manufacturer. Run the script - if it runs then it is compatible.

Known Issues

The script is very slow, but using the shortest dwell time (0.01s) and a large (eg 45 degs) step size results in reasonably rapid scans. Ensure your camera acquisition time is an approximate multiple of your scan period, to ensure uniform azimuthal sampling of reciprocal space. If camera exposure times are similar to the dwell times in the hollow cone scan, moire effects will result. Use camera exposures which are much longer than the dwell times.

Supported

Yes

Included Files

Main script file.

Source Code