HomeInstrumentsCrispSample design and preperation

Sample design and preparation

Recommended and optimal sample dimensions.

For condensed matter experiments it is important that samples be as big as possible, while taking account of the sample environment that is to be used.

This is because that in comparison to an x-ray source the flux of a neutron source is much lower. This coupled with the difficulty in focusing neutron beams requires that samples be large to maximize the use of all available flux.

The average size of sample that is used is roughly 25 mm x 25 mm square this provides a decent count time and reasonable max Q range.

Crisp can measure film thicknesses up to about 3000 Å and still resolve fringes on a single layer that thick. The lower limit on thin samples than can still obtain a measurable signal is about 10 Å. Though this can be circumvented by the use of multilayers to boast the signal. The average sample thickness is that is used is usually between 0 -1500 A for condensed matter systems.

It is always worth contacting the local contact before submitting a proposal, or coming to ISIS, about the best sample dimensions for the experiment in question.

Surface quality is paramount. Crisp can deal with roughness's on the atomic scale of up  to and around 500 Å RMS. If however the sample is rough to the naked eye then it is very unlikely a specular reflection can be achieved. There are exceptions to this for instance deliberately patterned media can give rise to in-plane Bragg peaks.

In off-specular scattering Crisp can resolve features on the order of 0.5 micrometers to approximately 40-50 micrometers. The best result being obtained for features on the order of about 4 microns in size. It is also important that the surface coverage be high otherwise the count times become very large especially when if polarized neutrons are being used (on the order of several days).

  • Crisp magnet only:

100mm (long) x 40 mm (wide) Optimal

10mm (long) x 6 mm (wide) be warned the count time and max Q reachable will increase and decrease dramatically Minimum

  • Crisp cryostat (magnet is always included)

40 mm  x 40 mm square Optimal

10mm (long) x 6 mm (wide) be warned the count time and max Q reachable will increase and decrease dramatically Minimum

  • Soft Matter Experiments

Liquid and biological experiments have standard sample sizes of 200mm (long) x 80 mm (wide) due to the sample troughs provided.

  • Polymer Samples

Polymer films require large areas as well but must be flat to the eye in-order to get good reflectivity. 

Successful experiments have used polymer systems spin coated onto thick Si blocks about 25 to 30 mm in diameter. Again the bigger the surface area the better.

If two or more polymers are to be used it is important that at least one polymer is deuterated. This is due to the fact that most polymer compounds have almost identical contrasts making it very hard to distinguish between them with neutrons, unless deuterated material is used for at least one of them. Deuterated Polystyrene being a classic example.

Characterization Measurements 

it is highly recommended that some basic characterization measurements are made, if possible, before coming to the beam line. it is fully understood that this may not be possible in the case of certains samples and systems. 

Condensed Matter Experiments: (minimum)

It is suggested at a minimum that a Cu Kα x-ray or equivalent structural x-ray be taken before hand. (Both specular and off-specular curves).

If the experiment is polarized it is also recommended that the equivalent magnetometry also be performed. (MOKE/VSM/SQUID). 

With both of these it is much easier to plan a successful CM experiment as you will have a rough idea of where to look and what fields to use. Which seen as count times can be on the order of days is invaluable in avoiding mistakes.

This data is also invaluable in fitting the neutron data as it allows you to tie down variables like the total moment of a sample and layer thickness and roughness.This makes the data analysis easier and more rigorous.

Other very helpful Characterization measurements:

Other Characterization techniques that are of great help in neutron experiment planning and data fitting are:

MFM/AFM - Can provide top surface roughness as well as Magnetic domain size for estimating in-plane magnetic features. FFT of AFM/MFM images is also useful for validating off-specular data.

TEM - TEM images are brilliant for fitting data. If done well you can literally see the Nb variation in the images allowing you to set up a fitting model correctly. They are also brilliant justification to referees for why a model has been set up. 

Transport data: Resistivity/TMR/GMR/etc - Either as a function of field or temperature. This allows us to set fields and temperatures correctly if we are looking for transitions e.g. superconducting phase change. Again very useful for planning a successful experiment.

These techniques are but a few of the many available. It is worth contacting the local contact as some of these can be provided at the lab.

If you have these measurements done before hand they are brilliant for papers/thesis write ups/experimental reports/follow up proposals. 

Soft Matter Experiments:

For soft matter experiments, there is again a vast range of characterization techniques available some of which are listed below. It’s understood that different groups have their own way of working and techniques. We strongly suggest characterizing the property under study and optimizing your experimental conditions prior to beam-time. Below are a list of surface characterization techniques often employed in soft matter experiments to provide complimentary information to interfacial structure described by neutron reflectometry data. Some of these techniques are available at the lab.

Atomic Force Microscopy : Widely used microscopy technique for examining structures at the solid/air or solid/liquid interfaces.

Brewster Angle Microscopy/ Imaging Ellipsometry (BAM): Microscopy techniques which have high Z axis resolution and are generally employed to gain in-plane information on the structure of interfacial films. .

Surface Infra-Red Spectroscopy: Infrared techniques such as Attenuated Total Reflectance (ATR) and External reflection (sometimes known as IRRAS) allow for the chemical composition of interfacial films to be examined and can be very effective in examining interactions at interfaces.

Surface Pressure Measurements: Users working at the Air/Liquid interface are likely to measure surface pressure prior to or during NR measurements. It is highly desirable that users also conduct these measurements prior to beam-time.  

Surface Plasmon Resonance: A widely used technique to monitor interactions at the Solid/liquid interface. Most universities will have access to this apparatus.

TEM: Electron microscopy: Excellent Imaging technique, although sample preparation for interfacial films can be challenging.

Quartz Calorimetry: Surface calorimetry technique, provides similar information to SPR, although QC instruments are often orders of magnitude cheaper to obtain.

Please note that if you require help with sample preparation that you are advised to contact Cameron Neylon or Luke Clifton from the ISIS Biolab. This is a facility is available to assist users with sample preparation / optimization measurements prior to ISIS beam time.

If you have these measurements done before hand they are brilliant for papers/thesis write ups/experimental reports/follow up proposals etc. 

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