Long wave-length x-ray diffraction crystal

DETAILED DESCRIPTION It is a principal object of the invention to provide a new, multilayer Langmuir-Blodgett crystal capable of diffracting x-rays of at least twice the wavelength of state of the art crystals.
It is another object of the invention to provide a method of making multilayer Langmuir-Blodgett crystals capable of diffracting x-rays of at least twice the wavelength compared to the state of the art crystals.
These and further objects of the invention will appear as the specification progresses.
In accordance with the invention the crystal consists of alternate monolayers of a first, heavy divalent metal soap, and monolayers of either a fatty acid alone or a second, lighter divalent metal soap.
Selecting cations with a significant difference in atomic number and dispersing power, such as Pb and Be, Mg, Ca, etc.
, increases the effective 2d spacing of the crystal since the Pb planes cause the predominant x-ray diffraction.
Thus, the terms "heavy" and "lighter", as used above in modifying "divalent metal", mean that the "heavy metal" is chosen to have a higher atomic number than the "lighter metal".
The sequence of the fatty acid or lighter metal soap monolayers between the heavy element layers gives the 2d spacing.
Thus, for stearic acid or metal-stearate monolayers, 2d=100 A+N(100 A); N=1, 2, 3, .
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where N represents the number of layers placed between the heavy metal soap layer pairs.
Preferably, the heavy metal soap is a lead salt of a fatty acid such as lead stearate, and the other monolayers, separating the heavy metal soap monolayers, are beryllium stearate, magnesium stearate, calcium stearate or stearic acid.
These crystals are built up in accordance with the invention, for example, by depositing in the desired pattern on a solid substrate, monomolecular layers of Pb-stearate and layers of a lower atomic number metal stearate or a fatty acid.
Thus, a fatty acid, for example stearic acid, in, for example, an n-hexane solution is placed on the surface of two separate water solutions containing, respectively, either (a) the heavy metal cation or (b) the lighter metal cation or no metal cation at all