Information for LR Users

Liquids Reflectometer

LIQREF | BL-4B | SNS

Measurement Types

Standard measurements are carried out in at 30Hz (frame skipping mode) to provide an extended wavelength band and the sample is tilted to reach varying incident angles (θ-2θ geometry). The position-sensitive detector is used to maximize use of guide divergence whilst recovering qz resolution. These can be carried out in either a reflection up or a reflection down geometry.

For free-liquids and other systems that cannot be tilted, the sample angle is kept horizontal and the incident angle is varied via the guide divergence (θ - θ geometry). These measurements are carried out at 60Hz.

Data are collected in event mode which enables retrospective slicing of the data in time to provide variable temporal resolution for kinetic measurements or time-dependent systems.

Measurement times will depend on the samples, conditions and hypothesis being tested so should be discussed with a member of the beamline team.

Preparation for Beam-time

How to design an experiment?
It is always best to discuss your experiment ideas with a member of the beamline team who can help in preparing your proposal and optimizing experiment scope, sample setup and measurement plans.

Reflectivity simulation tools are very useful for testing technique sensitivity and choosing contrasts. See below for example links and resources.

Important aspects to consider: what is the hypothesis to be tested and what similar structures need to be differentiated? What sample conditions (sample environment) are required? What scattering contrast is best to use? How long will the experiment require? Are changes needed to the sample to make it suitable for the neutron reflectometry measurement?

What makes a “good” sample?
Neutron reflectometry experiments typically require a surface with very low roughness, waviness and uniformity across the surface. For a solid-liquid interfacial measurement, it also requires high neutron transmission through the solid phase (e.g. silicon, quartz, alumina).

Complementary measurements
It is good practice to carry out pre-testing of the system and samples with complementary techniques to optimize use of the beam-time and strengthen proposal submissions. Depending on the system, these can include x-ray reflectivity, ellipsometry, QCM-d, Langmuir trough, XPS, or FTIR. If you do not have access to these techniques at your home institution, there are some user facilities at the Center for Nanophase Materials Science (CNMS) (https://www.ornl.gov/facility/cnms) and in the SNS User labs (https://neutrons.ornl.gov/lab).

On award of neutron beam-time, users are expected to attend the experiment in person with appropriate staffing to cover the full length of the experiment, which runs 24-hours per day. Typically this is a minimum of 2-3 people.

There is detailed information on the User area of the website (https://neutrons.ornl.gov/users) covering all aspects of beam-time experiments. Of particular note: