a)Schematic of the STXM technique. b) Photograph of the major components of the PolLux STXM. The position and shape of the plate on which samples are mounted is indicated in green, while the interferometer beams are indicated in red.
3D rendered model of the in-vacuum components of the PolLux STXM endstation.
PolLux has a scanning transmission X-ray microscope (STXM) endstation, which is capable of producing high resolution images (better than 50 nm) and soft X-ray absorption spectra of very small sample areas. By combining imaging and spectroscopy, PolLux can map out properties such as elemental and chemical composition, molecular orientation, oxidation states, magnetic domains as well as thickness variations with high resolution. Central to the operation of a STXM is a Fresnel zone plate that focuses a monochromatic X-ray beam through an aperture (which blocks the unfocused 0th order light and the higher focus orders) and onto a sample that is thin enough to be semi-transparent at the appropriate X-ray wavelength. A detector positioned behind the sample measures the transmitted photon flux. Scanning of the sample, combined with repeated transmission measurements, build up an image of the sample, while varying the energy of the X-ray beam allows measurement of spectra and alters the image contrast with respect to the spectroscopic properties of the sample components. An interferometer measures the relative position of the sample with respect to the zone plate (and thus its focus position) and ensures accuracy of the measured image pixel positions. The PolLux STXM is controlled by Pixelator.

Zone Plates

A number of zone plates are available for use at PolLux, providing various trade-offs between efficiency, focal length and resolution. As a rule of thumb, the resolution of the instrument is similar to the outermost zone width of the zone plate. Zone plates are dispersive optics and so the focal length will vary with photon energy. Note that the difference in zone plate resolution is only useful in high resolution images and that experiments not pushing the limits of the instrument are usually better off choosing a higher efficiency zone plate. Non-standard zone plates are only available at the discretion of the beamline staff.
Outermost Zone Width Focal Length (μm/eV) Manufacturer Notes
35 nm 6.8 CXRO Longest focal length, best for environmental cells
30 nm 5.8 LMN Good efficiency
25 nm 4.8 CXRO Higher resolution
25 nm 4.8 LMN Higher resolution, made from Ni for improved performance at the C K-edge
15 nm 1.8 LMN Higher resolution. Restricted to photon energies above ~600 eV and with very short focal length.
12.5 nm 1.0 LMN Non-standard! Restricted to photon energies above ~1000 eV and with very short focal length.
A set of zone plates are maintained free of carbon for use in imaging at the carbon K-edge.


A number of different detector types are available for enabling different experiments. Non-standard detectors are only available at the discretion of the beamline staff.
Detector Notes
Photomultiplier Tube (PMT) Standard detector with high efficiency over a wide range of energies. Download drawings of the detector tip.
Silicon Avalanche Photodiode (APD) Narrower pulses enable time resolved imaging.
Fast Camera (CCD) A phosphor screen close to the sample, with transfer optics allow "differential phase contrast" type imaging with an out-of-vacuum fast CCD
Channeltron Non-standard! Total electron yield (TEY) detection of sample surface can be performed simultaneously with transmission measurements with the PMT. Note that this detector requires very good vacuum and so is difficult to use.

Sample Mounts

Name Notes
Open Mount Sample mount plate that allows a lot of open space around it. Drawings of plate.
Open Tilted Mount Sample mount plates, and thus samples, can be mounted at 30° (fixed) in either yaw or pitch. Useful for circular magnetic dichroism measurements.
Tilted Mount Sample mount plates, and thus samples, can be mounted at 30° (fixed) in either yaw or pitch. Useful for circular magnetic dichroism measurements.
Heavy Mount Stronger clamping and thicker sample mount plates for greater stability of samples involving greater weight and/or stiff connections (cables, tubes, etc). Download drawings of the standard sample mount plate and the high-stability mount plate. If you want to make something heavy, like an environmental cell, we recommend you to design it to fit the high-stability clamping mount or the "PCB mount" below.
PCB Mount Screw mounting and for samples on PCB boards (or heavy environmental cells), allowing for robust electrical (or fluid) connections. Download PDF drawings
Azimuthal Rotation Stage Computer controlled sample mount for adjusting the azimuthal position of the sample. Useful for linear dichroism experiments.

Miscelaneous Apparatus

Name Notes
Magnetic field Variable magnetic fields up to 200 mT can be applied via a permanent magnet. The magnet can be rotated by a computer-controlled motor to different angles in order to vary the coupling into the pole pieces and hence vary the field at the sample. The field at the sample can be 0-200 mT in the out-of-plane configuration, or 0-100 mT for the in-plane configuration (in which the sample is tilted at 30° to the X-ray beam propagation for in-plane XMCD sensitivity). Note that the APD detector is not affected by magnetic fields (the PMT is affected by magnetic fields).
Heating & Cooling Non-standard! Small heaters can be attached to the sample mount plates and cooling can be performed via a copper braid. A temperature range between about 100°C and -20°C is possible.
Optical Microscope An optical microscope is available that can record images of samples (including observed positions) and enable easy location of areas of interest to image in the STXM.
Spin-coater Adapter Many users wish to spin-coat films onto membranes, but the membranes are not very compatible with the vacuum-chucks commonly found on spin-coaters. Therefore we designed this adapter to make it easy - you can download the design to make your own.
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