Multiwire Laboratories, Ltd.

MWL 110 X-Ray Detector:

• Consists of a position sensitive x-ray proportional counter connected to a custom Pentium PC computer system
• Rapidly orients and characterizes single crystals quickly in real-time.
• NorthStar software can index cubic, hexagonal, trigonal, tetragonal, orthorhombic, monoclinic, and triclinic crystals.
• Stereographic projections can be made from the current indexed pattern.
• Orientation accuracy of 1/4 degree in regular mode of operation and 0.05 degree in high-resolution mode.
• Laue patterns can be easily stored, displayed, and printed to paper to completely avoid the use of film.
• Greatly reduces the personnel time necessary to achieve any crystallographic orientation.
• Ideal for crystals of silicon, gallium arsenide, sapphire, quartz, SiC, nickel, tungsten, turbine blades,...geogological minerals such as olivine, etc.
• Ideal for industrial research applications or academic laboratories.
• Accessories include a motorized jack and translation stage, motorized three-axis rotation stage, motorized base for barrel holder, and a 6-axis motor controller with joystick control.

MWL110 detector system shown installed in x-ray enclosure.  On the upper left is the NIM instrument bin with readout electronics and below it is computer for displaying images, performing indexing.  On the right side is the proportional counter that makes the images and before it is a motorized three-axis rotation placed on top of the jack and translation stage. A gas cylinder supplying 90% Argon and 10% CO2 to the proportional chamber detector is located behind the computer.

Examples of images from the MWL110 system

These images have been collected on a PC computer equipped MWL110 Real-Time Back-Reflection Laue Camera system with the NorthStar Program, version 5.00. Bold text refers to Menu Items within the NorthStar software.

Collect Data

Laue patterns can be collected directly into the computer memory. Signal averaging over a few seconds of time enhances the image contrast. Silicon crystal example for 5 seconds of integration time with conditions of 13 kV, 16 mA.

Find HKL

After loading a suitable table of angles between planes, click on 4 to 6 spots to calculate the Miller indices (up to a maximum Miller index of 9) of spots in the image. A general table of angles between planes is provided to index cubic Laue patterns. (Angles for other hexagonal, ... triclinic systems can be generated with the Utility tools). The first two spots entered into the program must have HKL's in the table. All the others are calculated by the program and are calculated in a self-consistent fashion from the orientation matrix generated by the choice of the first two spots entered.  For the example shown here, the first two spots entered were the 112 point and the 211 points.  These points are relatively far apart and are low index values contained in the indexing table.  The program generated all the remaining points in less than 1 second of computation time including the high index 731 and 733 spots, for instance. 

Stereo - Last Points

Stereographic Projection consistent with the Laue pattern made after indexing the crystal with the Find HKL routine. The example shows spots in red that are in common with the two view whose max Miller index is 3 or less, namely the 111, 213, 313, 211, etc. planes.

A stand-alone option generates a projection about a 001 reference axis. The projections can be rotated with math routines or individual spots rotated into the center with a Move-To feature. 

Data Report

Working with the 0.05 degree high resolution mode

The HiRes feature in the NorthStar program is a utility that does not yet communicate with other parts of the software such as MOVE TO, STEREO, etc.  It is a little stand alone routine that at the moment, works by itself.

The basic idea is that you first offset the x-ray track horizontally by about 5 degrees (exact value not important) or so that an highly oriented crystal (less than several degrees off) can diffract an oriented Laue spot to an area near the collimator, but off to one side.  (The Jack and Translation stage has a curved slot in it to make this easy to do.)   If the crystal is rotated in azimuth through 360 degrees on an external precision rotary stage (not supplied by MWL), then the perfectly oriented Laue spot stays fixed in position on the detector surface and doesn't wander off.  If the crystal is off-axis a fraction of a degree, however, then when you rotate through 360 degrees, it traces out a small cone.  The worse the misorientation, the larger the cone diameter that is traced out by this Laue spot onto the detector surface.

The HiRes feature has you take two images of the same Laue spot (no indexing is involved at this point), one with the sample up (0 degree azimuth) and another with it down (azimuth = 180 degrees).  The operator clicks on just this one Laue spot each time.  The average of the two readings tells you the center or perfectly oriented position of that Laue spot.  The deviation of the observed position relative to the center position gives the misorientation down to the 0.05 degree level in both x and y (gamma and delta angles).  This is essentially the Bond Method used on diffractometers applied to our Laue camera.  This method works to remove the small non-linearities in the delay which cause the 0.25 degree limit in the first place.

In tests with silicon and quartz (really perfect crystals with good strong Laue spots), we actually could see changes down to the 0.03 degree level with a 200 mm film-to-specimen distance.  If the signal to noise of your crystal is not as good as silicon or quartz, then the resolution accuracy will suffer slightly.