FIGARO (Fluid Interfaces Grazing Angles ReflectOmeter) is a new high flux, flexible resolution time-of-flight reflectometer with a vertical scattering plane, which was commissioned at ILL in April 2009. It is used for studies of thin films at air/liquid, liquid/liquid and solid/liquid interfaces mainly in the realms of soft matter and biology. Applications involve the study of surface behaviour of surfactants, polymers and other amphiphiles in adsorption troughs and the interactions of proteins with lipid monolayers on a Langmuir trough. No polarized neutron option is currently available.

Special features of the instrument include the possibility to strike the interface from above or below in a wide q-range. With an incoming beam of wavelengths comprised between 2 and 30 Å, it is possible to attain a q-range from 0.0045 to ~ 0.42 Å^-1 by using two incoming angles of 0.62 and 3.8˚. Measurement times are similar to those used on the more established D17 reflectometer.  One useful feature of FIGARO is the ability to relax the resolution at a low incident angle hence the instrument is well suited to the study of kinetic processes with time slices possible on the order of 1 s.

The first component of the instrument is a choice of two frame-overlap mirrors to remove neutrons with wavelengths above 20 or 30 Å.  Four choppers follow, with carbon fiber discs of 800 mm diameter and 45˚ aperture, independently rotating at a speed of up to 2000 rpm. The distance between the discs is such that 6 different wavelength resolutions can be obtained, ranging from 1.2 to 9.8%, by keeping the projected chopper openings equal to zero. Choppers are followed by two guide sections covered with supermirrors of M=4 deflecting downwards or upwards to allow incoming angles of the neutron beam between 0.62 and 3.8˚. Five incident angles on the sample have currently been commissioned. The deflecting guides are followed by a 2-m collimation section, in order to eliminate off-specular scattering arising from the two supermirrors, comprising two slits and an absorbing guide on the top and bottom faces and M=4 supermirror sides to carry on the horizontal focussing down to 40 mm. A gas-filled monitor is used to measure the intensity of the incoming beam for data normalization at high angles (i.e. wide slit opening). A two dimensional multitube detector is positioned at a distance of 3 m from the sample. It can move up and down to detect the reflected and direct beams at all angles. It consists of an Aluminium plate with 64 squared holes of 7 mm internal side and 2 mm resolution along the 250 mm length. This detector allows measurements of specular and off-specular reflectivity; GISANS is currently under development. The sample stage is equipped with active and passive anti-vibration systems, x-y-z translation axis, goniometer for solid samples.

An optical sensor (Keyence, Japan) is used for the easy alignment of free liquid samples, and a phase modulated ellipsometer (Beaglehole, New Zealand) and a Brewster angle microscope (Nanofilm, Germany) is available offline for users to make preparatory and complementary optical measurements.

A thorough technical reference paper on the instrument may be found HERE.