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Bent Monochromators

IP.com Disclosure Number: IPCOM000108182D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 1 page(s) / 35K

Publishing Venue

IBM

Related People

Angilello, J: AUTHOR [+2]

Abstract

Disclosed is a technique for controlling the curvature of a monochromator crystal which will be mechanically bent in its supporting fixture. These mechanically bent crystals are often used to focus beams, especially in systems such as x-ray diffractometers. The mechanical bending results in a complex 3-D curvature where a simple 2-D cylindrical curvature is often desired. This results in an off-axis divergence that is often ignored. By "prebending" the crystal, we have been able to change this curvature and sometimes cause it to result in a converging beam rather than a diverging one.

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Bent Monochromators

      Disclosed is a technique for controlling the curvature of a
monochromator crystal which will be mechanically bent in its
supporting fixture.   These mechanically bent crystals are often used
to focus beams, especially in systems such as x-ray diffractometers.
The mechanical bending results in a complex 3-D curvature where a
simple 2-D cylindrical curvature is often desired.  This results in
an off-axis divergence that is often ignored.  By "prebending" the
crystal, we have been able to change this curvature and sometimes
cause it to result in a converging beam rather than a diverging one.

      The technique is to deposit a film with a thermal expansion
coefficient substantially different from the crystal on one of the
crystals surfaces (usually the one not used to monochromate the beam)
at a temperature that has been selected to give an appropriate stress
upon return to the operational temperature of the monochromator.
This stress will cause the crystal to bend with the resulting
curvature determined by its geometry and elastic properties. We have
been able to bend a Ge wafer nearly spherical by depositing Ni on the
back side at 100~C.  A slight deviation from spherical curvature came
from the "flat" cut on one side of the wafer.  Analysis of the
crystal indicated the front side of the wafer was still a perfect Ge
structure while the back side had many defects due to plastic flow as
the induced stress exceeded the yield stress.  Th...