Below is an incomplete list of commonly asked questions which we hope may be useful, please feel free to add to it (with answers).
How do I get beamtime?
All facilities have different access mechanisms, but most operate on a schedule of proposal submissions, where you can submit a short (~ few pages) science proposal. The proposals are ranked by a panel of experts and the time available is awarded to the top applications. Many facilities offer a variety of access mechanisms and it is better to check the websites of the individual facilities to find out more:
or see information for specific instruments available at the
Most facilities offer remote access for user data as long as you are associated with the experiment. Check the website of the facility, or for the following facilities go to these pages:
If you have been assigned a local contact at the beamline then they will be your first point of contact, otherwise contact the instrument responsible. Contact details are usually available on the instrument web pages: neutrons & synchrotrons.
I have done this __ type of experiment, what fitting software should I use?
As detailed on this site, there are a myriad of fitting packages available to use, and most will work for every type of data. We do not recommend some over others, but if you are unfamiliar with the packages, then there are links to training resources associated with some of the packages. Note that not all packages are currently supported, and it is best to check the webpage of the software for up to date information.
What does reflectivity tell you?
We are glad you asked! Please check out our introduction and tutorial about the technique for an in-depth tutorial on what can be extracted, and how. Briefly, the information which can be extracted from specular reflectivity is the scattering length density (average atomic scattering length multiplied by the material density) as a function of distance perpendicular to the film surface. Note that the same principles apply for both x-rays and neutrons.
What should my sample look like?
For most reflectivity experiements to be sucessful, several factors should be considered, including the surface area, surface roughness and overall flatness. The requirements for each of these will vary by technique, for example x-ray reflectometers can in general measure smaller surface areas than neutron reflectometers since they have a higher flux. A comprehensive list for neutrons is detailed here, but in general, reflectoemetry is limited to film thicknesses below ~400 nm (ideally much below), above 0.5 nm, and with surface roughnesses less than 5 nm. These are rough guidelines and are neither necessary nor sufficient.
Should I use x-rays, neutrons or both?
A very important question. There are many ways to answer this, we will take quite a high level view here. One of the biggest questions to consider when planning a reflectivity experiment is contrast. In the most basic approach x-rays itneract with electrons and neutrons with the nucleus. There are Scattering Length Density calculators available here and elsewhere on the web. This can be used as simulations to determine where the best contrast can be found. Some experiments, particualrly solid/liquid are more suited to neutron reflectometry due to the penetrating ‘power’ of neutrons.
How can I join ORSO/help?
Please contact the chair of the working group which most interests you, or dive straight into the Github issues and take ownership of one (e.g. for reproducibility)