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NG7 Horizontal Neutron Reflectometer

Side view of the NG7 Horizontal Reflectometer
Neutron reflectometry is a relatively new technique for investigating the near-surface structure of many materials. Specifically, it probes the neutron scattering density at depths of up to several thousand Å, with an effective depth resolution of a few Å. What is measured is the profile of reflectivity as a function of angle beyond the critical angle for total external reflection. The sample must thus present a smooth, flat surface, preferably several cm2 in area. The method is extensively used for studies of polymer surfaces, Langmuir-Blodgett films, and thin films and multilayers of metals and semiconductors, both magnetic and non-magnetic. 

The cold neutron reflectometer permits routine measurement of reflectivities as low as 10-6 in typical run times of a few hours. As shown in the schematic drawing below, a pyrolytic graphite monochromator array deflects neutrons onto a horizontal sample surface at a shallow angle ofincidence. Reflected neutrons are measured by a detector after passing through an exit slit system.

Independent movement of both sample and detector allows measurement of off-specular scattering. A position-sensitive detector permits simultaneous measurement of specular and off-specular scattering. 

Specifications/Capabilities

  • Pyrolytic graphite monochromator
  • Wavelength range: 0.235, 0.407, 0.47, and 0.55 nm
  • Wavelength resolution: 2.5% delta lambda/lambda
  • Beam size (continuously variable): .05 x 50 mm to 4 x 50 mm
  • Q range: 0.03 to 2.4 nm-1
  • Incident neutron wavelength λ = 4.75 A
  • Q resolution: Variable with slits from .02 to .15 delta Q/Q
  • Monochromator-to-sample distance: 2m
  • Sample-to-detector distance for reflectivity detector: 2m
  • Sub Å thickness resolution
  • In situ capabilities including:
Created October 4, 2018, Updated November 15, 2019