Beamline Phone Number:
+44 (0) 1235 778201
Principal Beamline Scientist:
Francesco Carlà
Tel: +44 (0) 1235 778023
E-mail: francesco.carla@diamond.ac.uk
Email: cephise.cacho@diamond.ac.uk
Tel: +44 (0)1235 778290
The Double crystal deflector (DCD) allows reflectivity from liquid surfaces without the need to move the sample. It can be combined with GISAXS or GIXD for most energies. If required, it is possible to approach the interface from above or below.
Details of the different modes of operation and their capabilities are given in the table below.
Energy |
Standard working energy: 12.5 keV
Energy range available: 11 – 24 keV (but please consult beamline staff if required, e.g. for liquid-liquid experiments) |
Using Excalibur |
Qz: 0–1 Å-1 (may also go up to 2.5 Å-1 but consult beamline staff if required) Qxy: Energy and sample environment limited. Typical max for GID at 12.5 keV ~ 3 Å-1 Approximate time for data collection: 15–20 min for air-water XRR, <5 min for GID or GISAXS |
Using P2M | Qz: 0–1 Å-1 (Energy and detector distance limited)
Qxy: Energy and detector distance limited. Typical for GISAXS at 12.5 keV min ~ 0.01–0.02 Å-1, max ~ 0.7 Å-1 Approximate time for data collection: 20 min for air-water XRR, <5min for GISAXS |
Using both detectors | Can switch between detectors as the stages are motorised, although this takes a few minutes. Simultaneous measurements not usually possible. |
Anomalous measurements | Switching energy takes time, so experiment should be planned to minimise the number of energy changes. Please consult beamline staff if required. |
The standard DCD setup includes an anti-vibration table, which is essential for liquid surface measurements. Most experiments are carried out in our Nima Langmuir trough (400x200 mm, ~ 500 ml volume, pictured at the top of the page) which features remote barrier control, pressure measurement and temperature control via a circulating water bath. The trough is housed under a lid, which can be filled with helium to reduce air scatter. This setup is shown on the left below.
As an alternative, we have a set of small, low volume troughs that can be used in conjunction with our sample changer (shown on the right below with a selection of interesting, coloured solutions).
It is also possible for users to bring their own sample environments. Please contact the beamline team to discuss this.
The geometry of the system is similar to a standard double-crystal-monochromator, but uses two different crystals, InSb(111) and InSb(220), to achieve an overall beam deflection. Rotation of this pair of crystals around the incident beam then allows the angle of incidence at the sample position to be varied.
You can view an animation of the motions involved in making a reflectivity measurement using the DCD together with the diffractometer.
The DCD can also be used with the P2M detector for GISAXS measurements in combination with reflectivity. However because of the associated horizontal deflection, the position of the P2M detector is limited:
Full details of the design have been published:
Journal of Synchrotron Radiation, 2012, 19, 3, 408-416.
This article is available here.
The geometry of the beamline optics has a considerable influence on the intensity of the incident beam at the sample position. In particular, the flux transmitted through the DCD depends on the rotation angle φ (shown below), relative to the double-crystal monochromator (DCM) which always scatters in the vertical plane.
This arises from two factors: The first is the dependence of the Bragg reflectivity on the polarisation of the incident beam, while the second is because the DCM-DCD system selects different ranges of X-ray wavelengths and directions as φ is varied. The reasons for this behaviour are discussed in detail in the published paper. In particular, this publication discusses the variation of intensity and polarisation of the transmitted beam with incident angle. This behaviour results from the particular geometry of the optical components of the beamline. The variation is energy dependent and results in a greater loss of flux at higher energies. The flux was improved by replacing the original Si crystals with InSb (see below)
(a) Flux transmission as a function of φ (the rotation angle of the DCD about its axis) for four different energies covering the full operational range. The experimental data (crosses) has been arbitrarily scaled to match the theoretical prediction. (b) The proportion of the transmitted flux that is vertically polarised as a function of φ and energy
(a) The calculated flux transmission through the DCD as a function of energy at Qz = 0. For silicon the transmission is only 5-10% whereas this has been significantly improved by replacing the DCD crystals with InSb. (b) Maximum flux before the DCD, at a ring current of 300mA. Collimation and windows etc. can reduce this by up to half, which for example, gives a flux at the sample position of ~2x1012 photons/s/0.1% b/w (at 12.5keV and Qz = 0).
The figure below shows a fit (red) of reflectivity data from pure water measured at 12.5 keV (blue) and 20 keV (green). In both cases the background has been subtracted. Fit parameters: Background = 10-10 Roughness = 2.9 Å, calculated using Motofit (Nelson, 2006).
The following is an example of reflectivity (and corresponding fit) from a lipid layer (DPPC) on water containing 0.1 mM Ca2+ at a surface pressure of 30 mN m-1 (measured by Roser et al.) Also shown is an example Pilatus image used for GIXD of DPPC at 35 mN m-1 using the pin-hole geometry (Meron et al., 2009) and the variation of this integrated peak as a function of surface pressure.
References:
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