Scanning Transmission X-Ray Microspectroscopy

The PolLux soft X-ray STXM beamline allows the quantitative nanoscale mapping of chemical and physical properties such as elemental distribution, magnetisation, oxidation states, organic species (molecular structure) and molecular order and orientation. Such analyses serve materials science in a wide range of applications and scientific disciplines. Prominent research at PolLux includes:

  • the time-resolved study of magneto-dynamical processes in nanostructures, which could ultimately lead to new magnetic storage systems,
  • nanoscale quantification of composition and molecular conformation in conjugated polymers for improved optoelectronic devices such as organic solar cells and light emitting diodes, and
  • in situ studies of chemical and physical effects in organic micro- and nanoparticles for improved understanding of environmental processes.
Beamline Resolving Power
3000 [deltaE/E]
Beamline Energy Range
270 - 1600 [eV]
Max Flux On Sample
1 * 107 [ph/s] @ 1000 [eV]
Spot Size On Sample Hor
20 - 30 [nm]
Spot Size On Sample Vert
20 - 30 [nm]
Photon Sources

X07DA

Type
Bending Magnet
Available Polarization
Linear horizontal, Elliptical
Variable Polarization
Yes
Monochromators

SGM

Energy Range
250 - 1600 [eV]
Type
Spherical Grating Monochromator
Resolving Power
8 * 103 [E/deltaE] @ 550 [eV]
Number Of Gratings
2
Grating Type
Spherical, Ni coated, 300 l/mm
Spherical, Au coated, 600 l/mm
Other Optics

Higher Order Suppressor

Description
Set of three MgF2 coated mirrors inserted during operation at photon energies below 600 eV to remove higher order grating reflections (especially 3rd order).
Description of design and performance published in DOI: http://dx.doi.org/10.1063/1.3463232
Endstations or Setup

STXM

Description
Scanning Transmission soft X-ray Microscope
Base Pressure
1 * 10-6 [mbar]
Endstation Operative
Yes

Sample

Sample Type
Crystal, Amorphous, Fiber, Powder, Gel, Liquid, Other: Thin Section
Mounting Type
TEM grids and silicon nitride membranes

Techniques usage

Absorption / NEXAFS
Absorption spectra measured via the transmitted beam by comparison to the incident beam, which is measured by the beam intensity transmitted by an empty sample region. Spectra can be measured at a single point on the sample, along a line across the sample, or by a "stack" of images of the same sample region repeated at each photon energy value.
Absorption / Time-resolved studies
Pump-probe stroboscopic measurements with 100 ps time resolution.
Absorption / XMCD
Measure spectra (or images at dichroic NEXAFS resonance) with circular right and left helicity.
Imaging / X-ray microscopy
Images are measured by raster-scanning the sample across the focused X-ray beam while the transmitted beam intensity is recorded as a function of sample position.

Sample Environment

Description
Computer controlled gas environment for in-situ measurements. Temperature, Humidity and ozone concentration can all be varied to simulate conditions in the upper atmosphere. Further details published in DOI: https://doi.org/10.1063/1.3494604
Pressure (min)
1 * 10-3 [mbar]
Pressure (Max)
5 * 102 [mbar]
Temperature
260 - 300 [K]
Humidity
0 - 98 [%]

Magnetic Fields

DC Fields
Variable, computer controlled.
Max DC Field
1 * 10-1 [T]
DC Fields
Variable, computer controlled
Max DC Field
2 * 10-1 [T]
Detectors

Channeltron Electron Multiplier

Description
The channeltron detector collects electron emitted from the downstream surface of the sample. Requires very good vacuum for reliable operation.
Pixel Size
X = 5000 [um], Y = 5000 [um]
Passive or Active (Electronics)
Active

Detection

Detected Particle
Electron

Fast CCD

Type
Andor DV860 electron multiplying charge-coupled device.
Description
Used for differential phase contrast measurements, and luminescence detection mode where the sample substrate (e.g. MgO) is utlised as a phosphor screen for the conversion of X-rays to visible photons. Luminescence detection mode is useful for measurements of samples grown on single-crystal substrates that cannot the thinned for conventional transmission measurements. Frame rate up to 3500 Hz.
Array Size
X = 128 [pixel], Y = 128 [pixel]
Passive or Active (Electronics)
Active

Detection

Detected Particle
Photon

Photomultiplier Tube

Type
Pulse counting
Description
A phosphor screen converts X-rays into visible light, which is funneled into a photomultiplier tube to create voltage pulses that are discriminated and then counted by computer.
Pixel Size
X = 3000 [um], Y = 3000 [um]
Passive or Active (Electronics)
Active
Dynamic Range
1 * 107 [counts/s]

Detection

Detected Particle
Photon

Silicon Avalanche Photodiode

Type
Pulse counting, or current integrating
Description
A photodiode that is operated close to the breakdown limit so that an absorbed photon creates an electronic avalanche much larger than the energy carried by the photon. This effect provides very high amplification and good detection efficiency.
Time Resolved
Yes
Pixel Size
X = 500 [um], Y = 500 [um]
Passive or Active (Electronics)
Active
Dynamic Range
1 * 1010 [counts/s]

Detection

Detected Particle
Photon
Support Laboratories

Sample Preparation Room

Description

The room provides:

* 2 laminar flow hoods

* Soldering iron

* Spin-coater

* heating plate (up to 300°C)

* Plasma cleaner (O2 or H2)

* Common solvents (DI water, Acetone, Ethanol)


Visible Light Microscope

Description

A visible light microscope is available with position-encoders on the sample table so that imaged regions of mounted samples can be quickly located in the STXM.


contacts
Joerg Raabe
Benjamin Watts
Techniques
Absorption
  • NEXAFS
  • Time-resolved studies
  • XMCD
Imaging
  • X-ray microscopy
Disciplines
Chemistry
  • Other - Chemistry
Energy
  • Other - Energy
Life Sciences & Biotech
  • Medicine
  • Molecular and cellular biology
Material Sciences
  • Knowledge based multifunctional materials
  • Other - Material Sciences
Physics
  • Other - Physics
control/Data analysis
Control Software Type
  • Graphical user interface with python scripting functionality
Data Output Type
  • hyperspectral images and spectra
Data Output Format
  • NeXus based HDF5 (NXstxm): https://aip.scitation.org/doi/abs/10.1063/1.4937536
Softwares For Data Analysis
  • aXis2000: http://unicorn.mcmaster.ca/aXis2000.html<br />MANTiS: http://spectromicroscopy.com/
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