Surface Profile Analysis Reflectometer | SPEAR

The Surface Profile Analysis Reflectometer (SPEAR), located on Flight Path 9 in the Lujan Neutron Scattering Center, is ideally suited to study thin (from 5 to 3000 Å) organic and inorganic layers in a variety of different environments.

The instrument uses an unpolarized neutron beam to study a broad range of materials including polymers, nano engineered films, and biological systems. SPEAR is a time-of-flight (TOF) reflectometer using two choppers to define a typical wavelength range of 1.5 Å to 16 Å. With this polychromatic beam, a range of momentum transfer vectors (Qz) can be measured without altering the angle of the incident beam.

An important feature of SPEAR's design is that the beam is inclined to the horizon at 0.9°. This inclination allows for reflectivity measurements from liquid/air interfaces. Using a position sensitive detector, the TOF and reflected position of individual neutrons can be measured and converted to a wavelength and reflection angle. With this arrangement, statistics can be obtained down to a minimum reflectivity of about 5x10e-7 in 3 to 4 hours.