A fast ACOM/EBSD system

Our system consists of the dedicated hardware detector NORDIF 500UF and two separated programs which control the digital beam scan of the SEM as well as pattern store and off-line indexing and interpretation of the backscatter Kikuchi patterns (BKP). The patterns, after binning to 100x100 pixels on the sensor chip, are stored on the hard disk as a sequence of bitmap images rather than a reduced data set such as Hough peaks in order to enable the access to the original raw data at any time.

The detector contains a high sensitive CCD camera with GigE vision interface to the computer. Thus a high speed is obtained. GigE vision is the most economic camera interface because no frame-grabber is required. A standard fast Ethernet board and a CAT-5 patch cable are sufficient. The detector can be placed up to 100 m remote from the SEM.

Some advantages of off-line over conventional on-line evaluation of the diffraction patterns are:
+  Dwell time per pattern is constant whereas time for indexing depends on the current grain orientation and phase.
+  No artifacts which, however, occur with on-line indexing when synchronization between the acquisition and interpretation of patterns is missing.
+  The extremely high speed of acquisition is only limited by the sensitivity of the camera and speed of storing the patterns on the hard disk.
+  A high acquisition speed is favorable for fast in-situ dynamic experiments.
+  A high acquisition speed is economic since the turn-round of the SEM is short.
+  Cold field emitters with typically low stability are accommodated as well.
+  No compromise is made between speed and reliability of indexing.
+  Pattern indexing and interpretation can be repeated at any time by using the original data.
+  The parameters of the indexing program can be optimized after the acquisition session.
+  Enables thorough check for reliability of indexing and a priori unknown phases.

At present the acquisition speed exceeds 500 - 750 patterns per second.

Download presentation at EBSD Meeting in Zuerich, 14 - 15 June 2007 (in German, 0.5 MB pdf file for Acrobat Reader 5 or higher ).