Silicon Monochromator

Features

• Silicon perfect crystal double focusing monochromator

• Fixed real-space vertical focusing by segmentation.

• Optimized momentum-space horizontal focusing (in diffraction) by the selection of silicon cut angle, thickness and bending radius.

• Monochromator design optimized for the take-off angle, Source-Monochromator and Monochromator-Sample distances of your application.

• 5 different reflecting planes and wavelengths available at a fixed 90^o take-off angle^.

  
  

  Adjusting screw  at top:  (115) 1.478 A (113) 2.316 A (335) 1.171 A

  Adjusting screw at bottom:  (331) 1.762 A (551) 1.075 A

  
  
•  Fankuchen compression of the monochromatic beam: typical 4x intensity gain.

• No in-pile (primary) collimation required – the monochromator acts as its own collimator.

• Excellent characteristics for small specimen size (3 mm dia) powder diffraction applications.

Description

The monochromator is fabricated from 9 single crystal silicon slabs typically* 145 x 5 x 190 mm³ that have been cut from the same silicon wafer. These blades are bent horizontally by a 4-point bending apparatus to a radius of 10-12 m*. In the vertical direction, the blades are arranged in a polygonal approximation to the surface of a sphere of radius 1.76 m*. The normal to the concave surface of the silicon slabs is at 29.8º to the (115) axis* while the  (1-10) axis is oriented vertically

The monochromator is shown with the bending screw at the top, appropriate for use of the (115), (113) and (335) reflections.

In principle, all of the reflections in the [110] zone are accessible and several of these can provide useful beams. The first three reflections (Adjusting screw at top) are accessed with the same monochromator orientation. The latter two reflections (Adjusting screw at bottom) require that the monochromator be turned over.

With the (115) reflection at a 90⁰ take-off angle and 3mm sample, the resolution for powder diffraction is comparable to that achieved with a 10’ primary collimator and 10’ mosaic monochromator in a conventional (multi-detector) diffractometer with the same take-off angle.

The monochromator is shipped to the customer with the blades in an unstressed condition to minimize the chance of damage in transit. It is prepared for installation by turning the adjustment screw clockwise 3/4 turn before the device is inserted into the monochromator cavity.




* Actual radii, angles and dimensions are dependent on the particular installation distances and take-off angle