Fluid Interfaces Grazing Angles ReflectOmeter
Grazing incidence small angle scattering (GISANS) and near surface small angle scattering (NSSANS) can be used to obtain in-plane correlations and structural information within thin films. For GISANS, incident neutrons strike the sample below the critical angle for reflection and generate an evanescent wave with a penetration depth of ~100 Å. In this case, scattering from the sample is restricted to the interface. For NSSANS, neutrons impinging above the critical angle penetrate deeper into the sample (10-100 µm) and scatter from the bulk material.
As a time-of-flight instrument, FIGARO records the scattering pattern as a function of lambda (resulting in different critical angles for reflection) and can simultaneously acquire GISANS and NSSANS data. For the standard sample to detector separation, the detector receives an angular acceptance of ± 5° parallel to the sample plane and +5° perpendicular to the sample plane. This yields a maximum QY = ± 0.1 Å-1 and QZ = 0.1 Å-1 for 5 Å and a maximum QY = ± 0.035 Å-1 and QZ = 0.035 Å-1 for 15 Å neutrons.
An estimate of the range of lengthscales of lateral correlations that can be probed on FIGARO is 8-200 nm. In special cases, the detector can be moved closer to the detector to increase the angular acceptance to ± 25° parallel to the sample plane and 25° perpendicular to the sample plane. GISANS (left) and NSSANS (right) images of pluronic polymer micelles at the solid/liquid interface are shown below.
The GISANS and NSSANS features of FIGARO were commissioned in the second half of 2011. Promising results have already been generated with further improvements in performance expected. Proposals involving such measurements are now welcomed. For further information about the instrument capabilities or to discuss appropriate counting times when writing a GISANS/NSSANS proposal then please contact the instrument responsibles.
Adsorption troughs are used as a platform to study interfacial layers of molecules self-assembled from solution. The troughs assembly involves six sample positions each of which contains a PTFE trough of dimensions 220 mm x 50 mm. The volume required are 45 ml for liquids of high surface tension (such as water) and 25 ml for liquids of low surface tension (such as a concentrated surfactant solution). There are 20 trough inserts available so that some can be cleaned while others are in use. The alignment of samples is done through the instrument control software using a high-precision height sensor. The neutron windows (sapphire) and height sensor window (quartz) are all heated gently to avoid condensation. The option exists to heat the liquid in each trough with a dedicated strip heater, and there is also an option for three troughs to be connected to a thermostated water bath which is useful for cold measurements. The former heating option has not been fully commissioned yet, so for measurements away from ambient temperature please make this requirement clear to the instrument team well in advance of your experiment.
A Langmuir trough is available for measurements concerning insoluble monolayers at the air/water interface. Typically the monolayer is made from a spreading solution of the material in a carrier solvent, and then barriers are used to compress the film. Measurement of the surface pressure is carried out in situ. The standard trough is 500 x 250 mm in area and takes about 600 ml of liquid. There is an insert available which reduced the area and volume by about three quarters.
There are also borated (poorly reflecting to neutrons) glass plates which can sit in the large trough to reduce the volume by about one third without any detrimental effect to the maximum compression ratio that can be obtained. There are two boxes for the trough to sit in. The first is a essentially a dust cover where the pressure sensor sits on an aluminium bridge above the free liquid surface. There are sapphire windows for the neutrons and optical sensor which are heated to prevent condensation. The second box is an air-tight reaction chamber provided by Dr Christian Pfrang (Reading University, UK) suitable for gas phase reactions.
It has a heated lid making it suitable for measurements at elevated temperature. In each case the trough has a conduction plate underneath it so that temperature can be controlled using a thermostated circulating water bath. Measurements at 37 ºC have been carried out routinely on the beamline in the absence of particular problems concerning the uniformity of heating or condensation effects. In such a case the sealed reaction chamber would be used as the box of choice both to limit evaporation and also to prevent rain falling on the sample! The Langmuir trough is fully linked to the instrument control software NOMAD so that commands to reach a given surface area or surface pressure can be automated among neutron data acquisitions.
Solid/liquid interface cells are used to investigate the structure and composition of thin molecular films immersed in bulk liquids. Neutrons are transmitted through the solid substrate (i.e. a single crystal of silicon, quartz, or sapphire) and reflect from the bulk liquid at the solid/liquid interface. There are a range of cells that have been developed on FIGARO which are available for all users: 100 x 50 mm, 80 x 50 mm (most common; see picture left) or 50 x 50 mm. Fabricated from polyether ether ketone (PEEK), the base plate consists of a 0.5-mm deep solution reservoir, an o-ring for sealing to the substrate face, and inlet and outlet ports for solution exchange.
These components are sandwiched between aluminium plates containing with circulating water channels for temperature control. Up to 7 solid-liquid cells can be mounted simultaneously on the sample table and translated into the neutron beam. For maximum flexibility, it is possible to mount the crystals with the solid above the liquid (reflection up at the sample) or the liquid above the solid (reflection down at the sample). Solution changes can be automated through the instrument control software NOMAD using an HPLC pump and valve system (Knauer, Smartline; see picture centre) employing four independent input and six output lines.
This system provides greater automation of measurements and precision control of solution mixing for contrast matching. First time users are welcome to contact the instrument responsibles for arranging to use FIGARO's substrates: there are some 100 x 50 mm, 80 x 50 mm and 50 x 50 mm silicon as well as 100 x 50 mm and 80 x 50 mm sapphire crystals available. A recent development is the production of two sets of reflection up/down cells compatible with 80 x 50 mm (see picture right) or 50 x 50 mm crystals. Each cell has two solid/liquid interfaces: one with the solid oriented above the liquid (facing down) and the other with the solid oriented below the liquid (facing up). The cells have been used to good effect to determine the effects of bulk phase separation and gravity on the interfacial properties of several synthetic and biophysical polyelectrolyte/surfactant systems.
An overflowing cylinder has been developed on the FIGARO beamline for measurements at a dynamic air/liquid interface. There is a flow of liquid up a vertical cylinder which then at the top flows radially out from the centre and down the sides for recirculation. The neutron beam reflects off the continually expanding steady state liquid surface. Information can be gained about the adsorption kinetics of amphiphilic materials at short timescales (typically < 1 s). Also, as the surface is constantly regenerated the device can be used to gain information about adsorption mechanisms by separating the effects of surface and bulk interactions in strongly associating mixed systems.
Regretably we do not yet have cells for studies of thin molecular layers at the liquid/liquid interface. Hopefully there will progress in the provision of appropriate sample cells in the future. But for the time being, it is necessary for users to provide sample cells for measurements at the oil/water interface . This could perhaps be based on the approach of Prof. Ali Zarbakhsh and co-workers, which is to spin coat a contrast matched oil film on a silicon substrate then in the frozen state mount it in a custom-built round solid/liquid interface cell. The neutron beam then transmits through the solid and the oil film to reflect at the oil/water interface. Careful determination of the attenuation of the neutron beam through the oil is required. You are also welcome also to get in touch with the instrument responsibles at any time to check if there is any recent progress in this area.
FIGARO has also experienced measurements involving a range of other sample environments.
Some examples are listed here:
- There is a rheometer which has been mounted on the beamline for measurements at the solid/liquid interface while the bulk liquid is under shear. This option exploits the reflection down configuration of the instrument.
- A user-supplied dedicated sample box has been used to investigate solvent drying effects at the solid/liquid interface.
- A user-supplied pressure cell has been used to probe the structure of films at the solid/liquid interface at high pressures.
- Two sets of solid/liquid cells now exist for reflection up/down comparison experiments.
These cells are used for distinguishing surface induced self assembly versus bulk self assembly and transport of aggregates under gravity to explain the formation of thick mesostructured films in strongly interacting mixed systems.
For further information about any of these possibilities or to discuss the compatibility (e.g. geometric constraints) of any equipment you wish to mount on the FIGARO sample table please contact the instrument responsibles.
In the following link you can find the latest copy of the FIGARO manual for users and local contacts. It contains information about how to use the instrument, how to set up an experiment including a solid/liquid interface experiment involving a horizontal sample offset, instructions for setting up adsorption troughs or Langmuir trough experiments, how to reduce and transfer your data, and what to do in case of instrument problems. Please send any suggestions for additional information to the instrument responsibles.
The calibration parameters can be found here (pdf - 210 Ki).
FIGARO/D17 Data Reduction Software
A new version of Cosmos (v3.0) with an enhanced graphical interface was launched at the start of the June 2012 cycle. The functionality is much improved with the display now tabbed rather than having lots of separate windows, copy/paste in the data table, seemless interchange from 2 to 3 angles, an automatic normalization feature, an option to select only the data output formats you want, and an interactive plot feature with animation. This development was possible due to the great work of Eric Pellegrini and Miguel Gonzales both of whom we thank warmly.
To run the new Cosmos please do a 'live update' of your current version of Lamp. Then re-start the software and launch Cosmos. If you have a very old version of Lamp, however, you may get v2.39 along with a message to re-install Lamp. This is because the new Cosmos runs on the programming code IDL8. In this case you do not need to uninstall your old version of Lamp, but you do need to install the new version, which can be downloaded here.
Note that the new Cosmos must be used for all FIGARO data recorded from June 2012 onwards due to an update of the sample-to-detector distance calculations and the chopper parameters in the data files which affects Q. Further changes can be found in the 'news' section of the new Cosmos. If you encounter any problems or if you have suggestions for future improvements the instrument running team would be very grateful for your feedback.
Reduced Data Formats
Fourth and fifth data output formats have been launched over the last few years.
One is called .mft and has normalized, binned data with a fourth column for the Q resolution. In addition there is some useful information in the header about the experiment, the settings and the files used to reduce the data. A feature of the .mft format is the possibility to have up to nine configurable parameters listed in the header from the raw data files or calculation options. This allows the header of the reduced data from a given experiment to include tailored information from the experiment itself (e.g. a lipid monolayer experiment on a Langmuir trough experiment could have 'Langmuir area' whereas a solid/liquid bilayer phase transition experiment may prefer 'sample temperature'). Input into this concept from Ángel Piñeiro and Adrian Rennie is gratefully acknowledged.
The other new format is called .lam which is equivalent to .mft but has a fifth column as lambda and skips the optional extra header information. This file is used for the application of wavelength-dependent transmission corrections to the reflectivity while retaining all the other information. An example of these experiment is liquid/liquid interface measurements. Transmission corrections should be carried out by the user and then the file may need to be converted back to four columns (i.e. deletion of the lambda column) depending on the analysis software used. Input into this concept from Ali Zarbakhsh is gratefully acknowledged.
Here is a short summary of the five formats available. AFT = binned, normalised data in three columns (Q, R, dR); 4 lines of header; all points included over the q-ranges selected.
DAT = binned, normalised data in three columns (Q, R, dR); 0 lines of header; negative points removed. MFT = binned, normalised data in four columns (Q, R, dR, dQ); 23 lines of header; all points included over the q-ranges selected. OUT = unbinned, unnormalised data in four columns (Q, R, dR, dQ); 42 lines of header; all points included over the q-ranges selected. LAM = binned, normalised data in five columns (Q, R, dR, dQ, lambda); 13 lines of header; all points included over the q-ranges selected.
The updates to Cosmos from 2009 until 2011 can be found in the following file. Subsequent updates, implemented in the new Cosmos from June 2012 onwards, are listed in the software itself in the 'news' section. Such updates will not be duplicated in the following file, so this file is now fixed and will not be updated again.
A manual for COSMOS can be found here.
Normalization of 2d detector images
A siimple list of LAMP commands can be used to reduce 2D detector images into normalized wavelength vs. scattering angle space:
;Instrument parameters (You can find them when loading the raw measurement into LAMP and clicking on the "Data Params" buton):
x40 = 358.32 ;Poff (degrees)
x41 = 1418. ;Chop Actual Speed (rpm)
x42 = -123.76 ;(Trailing) Chop Actual Phase (deg) (relative to leading chopper)
x44 = 169.28 ;Open Offset (deg)
x45 = 40 ;TOF Channel Width (microsec)
x46 = 20000 ;TOF E-delay (microsec)
x47 = 5497. ;(Mid-) Chopper-Sample Distance (mm) (D1)
x48 = 2829. ;Sample-Detector Distance (mm)
y57 = 128.219 ;xcenter of reflected beam
y56 = 2.726 ;Wanted Theta (deg)
y58 = -1. ;-1 for reflection down, +1 for reflection up
;load OSS pattern into w2
x56=1800.0*5 ;OSS counting time (sec)
;load direct beam into w1
x55=1800./9. ;DB counting time (sec)/Attenuation
;rotate image to make it look like D17
;convert y-axis to wavelength:
;2d_norm You can choose the wavelength range you want according to the FO used
;convert x-axis to 2theta
;restrict to the useful pixel range of the detector
This list of commands can be found in an .xbu file (xbu - 1.98 Ki) as well. Note that this procedure does not include a gravity correction, which becomes significant for neutron wavelengths longer than 2 nm.
To further transform into q-space and load the maps into common programs please go here and follow the instructions in the D17 LAMP Book.
FIGARO Data Format List
Here are all the versions of the FIGARO data format. Subsequent numbered versions will be uploaded here. A document containing a brief list of changes to each version is then listed. Also, a document explaining the changes to the data block format in v12 is listed. The old versions of the data format are retained. Examples of the raw data file from the old and new data block formats are then given. Note that in the document stating the changes, the definition of the parameter blocks is that the first entry starts at 0 (not 1). If you require any explanations of the parameter labels then please get in touch with the instrument responsibles.
FIGARO Data Format Version 12 (05/06/15 to present).
150605-figaro-data-format-list-changes.pdf (pdf - 31 Ki)
List of changes to the data format (last on 05/06/15).
130405-figaro-data-format-v11.pdf (pdf - 49 Ki)
FIGARO Data Format Version 11 (05/04/13 to 05/06/15).
130219-figaro-data-block-format.pdf (pdf - 21 Ki)
FIGARO Data Block Format (19/02/13 to present).
130219-figaro-data-format-v10.pdf (pdf - 21 Ki)
FIGARO Data Format Version 10 (19/02/13 to 05/04/13).
120419-figaro-data-format-v9.pdf (pdf - 21 Ki)
FIGARO Data Format Version 9 (19/04/12 to 19/02/13).
101129-figaro-data-format-v8.pdf (pdf - 21 Ki)
FIGARO Data Format Version 8 (29/11/10 to 19/04/12).
101028-figaro-data-format-v7.pdf (pdf - 21 Ki)
FIGARO Data Format Version 7 (28/10/10 to 29/11/10).
100623-figaro-data-format-v6.pdf (pdf - 21 Ki)
FIGARO Data Format Version 6 (23/06/10 to 28/10/10).
090819-figaro-data-format-v5.pdf (pdf - 21 Ki)
FIGARO Data Format Version 5 (19/08/09 to 23/06/10).
090625-figaro-data-format-v4.pdf (pdf - 21 Ki)
FIGARO Data Format Version 4 (25/06/09 to 19/08/09).
090617-figaro-data-format-v3.pdf (pdf - 21 Ki)
FIGARO Data Format Version 3 (17/06/09 to 25/06/09).
090603-figaro-data-format-v2-changes.pdf (pdf - 15.96 Ki)
FIGARO Data Format Version 2 (03/06/09 to 17/06/09).
090415-figaro-data-format-v1.pdf (pdf - 20 Ki)
FIGARO Data Format Version 1 (15/04/09 to 03/06/09).
356092 ( - 2.08 Mi)
Example of a tof raw data file with the old data block format: #356092.
365860 ( - 2.00 Mi)
Example of a tof raw data file with the new data block format: #365860.
FIGARO Horizontal Geometry
The document below gives a description of the horizontal geometry of components of the FIGARO instrument. The only change from v1 to v2 is a refinement by a couple of centimetres of the sample-to-detector distance.