REFSANS

The TOF reflectometry and GISANS techniques can be used to characterise thin films in general. Reflectometry provides information about the structure along the sample’s normal, while GISANS gathers information about the in-plane correlations. Typical reflectometry experiments include:

• Characterisation of polymer thin film structure and their swelling behaviour in presence of various vapors
• Biological systems such as solid or liquid supported membranes (e.g determination of the morphology and localisation of proteins at interfaces)
• Metallic multilayers (e.g magnetically active films)
• Coatings

GISANS complements these measurements and has been successfully applied to polymer thin films (lateral correlations e.g in dewetted systems, detection and identification of polymer lamellae in immiscible blends or semicristalline systems), composites, nanopatterned metallic surfaces for which Bragg truncation rods have been reconstructed.

The optimal sample size is 70 × 70 mm². Various environments are available:

• Simple sample changer for three substrates
• Vibration controlled Langmuir trough for liquid-air interfaces studies
• Magnetic fields up to 7 Tesla
• Cryostats

A heavy load Huber goniometer (max. load 200 kg) is normally used to carry the experimental set-up, but it can easily be removed and replaced by custom equipments.

Primary beam

• Neutron guide NL2b
• Astrium choppers with wavelength resolution to be chosen in the range 0.2 – 10% for wavelengths in the range 2 – 20 Å. Rotation speed up to 6000 rpm
• Collimation: 2 vertical adjustable slits (0 – 12 mm) separated by 8.68 m
• For reflectometry, the horizontal divergence is maximized by use of supermirrors (m = 2 – 3)

Flux at sample

• Typical values (ΔQ / Q = 3%):
  • 1 · 10⁴ n s^-1 (incident angle 0.2°)
  • 3 · 10⁶ n s^-1 (at 2.5°) in the wavelength range 2 to 6 Å for a 60 × 60 mm² sample.

Accessible Q-range

• Reflectometry:
  • Q_z up to 0.3 Å^-1 for reflectivities down to the 10^-7 range.
• GISANS:
  • Q_y = 9.5 · 10^-5 Å^-1 to 0.18 Å^-1 (corresponding to distances from 6 µm down to 3.5 nm)

Detector
High performance 2D 500 × 500 mm² multiwire ³He detector (pixel size 2.7mm, efficiency 80% at 7 Å, gamma sensitivity < 10^-6) positioned between 1.5 m and 12 m from the sample. The detector is installed in a liftable vacuum tube in order to reach exit angles up to 6 degrees at the maximum distance.

TOF analysis
The data are acquired in list mode, each neutron arrival time and impact position being stored for later analysis. This makes it possible to perform various rebinnings in order to tune the resolution/ intensity trade-off.