PolLux: Illuminating the Nanoscale with Polarized X-Ray Vision

Seeing the Invisible

Imagine needing to study a single nanoparticle 1,000 times smaller than a human hair, or mapping the intricate magnetic whirlpools in next-generation computer memory materials. For decades, scientists struggled to probe such minuscule domains without destroying their subjects.

Enter PolLux, Switzerland's cutting-edge soft X-ray microspectroscopy facility at the Swiss Light Source (SLS), where polarized X-rays illuminate the nanoscale universe with unprecedented clarity. Recently upgraded during the landmark SLS 2.0 transformation, PolLux combines the precision of a nanometer-scale probe with the chemical sensitivity of X-ray spectroscopy. This powerhouse enables breakthroughs from clean energy to quantum computing—all by seeing what was once invisible ¹ ⁶ .

The PolLux Advantage: Polarized Light Meets Nanoscale Precision

Core Technology Simplified

PolLux operates as a scanning transmission X-ray microscope (STXM). Unlike conventional microscopes, it uses focused X-rays rather than visible light or electrons. This approach offers unique advantages:

Gentle imaging

X-rays penetrate thicker samples than electrons, allowing studies of biological tissues or functional devices in near-natural conditions ⁴ .

Chemical fingerprinting

By tuning X-ray energies to specific atomic transitions, researchers identify elements and their chemical states within materials ⁶ .

Magnetic sensitivity

Circularly polarized X-rays selectively interact with magnetic structures, revealing whirlpool-like "skyrmions" for ultra-dense data storage ¹ .

Key Specifications ¹ ⁸

Parameter	Capability
Energy Range	250–1600 eV (covers carbon, oxygen, iron)
Spatial Resolution	<40 nm (future optics: <20 nm)
Polarization Modes	Linear horizontal; Circular (left/right)
Sample Environment	Vacuum (10⁻⁶ mbar) to 1 atm inert gas

Table 1: PolLux's core specifications enable versatile experiments across physics, biology, and materials science.

Revolutionizing Research: 3 Key Discoveries

3D Magnetic Skyrmions Unraveled

Tiny magnetic whirlpools called skyrmions could revolutionize computing, but their 3D structure remained elusive. PolLux researchers combined circularly polarized X-rays with laminography (a slice-by-slice imaging technique) to reconstruct the first 3D map of a skyrmion's topology. This revealed how magnetic fields twist through the material—critical for designing skyrmion-based memory devices ¹ .

Solar Cells Get a Nanoparticle Boost

Organic solar cells struggle with inefficient charge extraction. A breakthrough came when PolLux's TEY-STXM mode (measuring electron emissions from X-ray absorption) confirmed that doped nanoparticles form perfectly uniform hole-transport layers. Unlike liquid-based methods, these nanoparticles prevent solubility issues, boosting solar cell efficiency by 15% ¹ .

Antiferromagnetic Nanomembranes

Ultra-thin antiferromagnetic materials promise energy-efficient computing. Using PolLux's high-resolution spectromicroscopy, Oxford researchers imaged reconfigurable magnetic states in freestanding nanomembranes, revealing how topological patterns respond to electrical stimuli—a gateway to adaptive spintronics ¹ .

Inside a Landmark Experiment: Mapping Dopants in Solar Nanoparticles

Methodology: Step-by-Step ¹ ⁴

Nanoparticles of the hole-transport material (e.g., Spiro-OMeTAD) are doped with lithium ions and spun into a thin film.

A zone plate (concentric rings etched into silicon) focuses incident X-rays to a 40-nm spot.

The sample is raster-scanned through the X-ray probe while maintaining helium atmosphere to prevent oxidation.

Two detectors operate simultaneously:
- Transmission detector: Measures X-rays passing through, revealing sample thickness.
- Total Electron Yield (TEY) detector: Captures electrons emitted from the surface, mapping lithium dopant distribution.

X-ray energy is scanned across the lithium absorption edge (≈55 eV) to confirm chemical bonding.

Results and Impact

The TEY-STXM data proved dopant homogeneity within ±5% across nanoparticles—a first for solvent-free deposition. This eliminated performance-robbing "dead zones" in solar cells. After optimization, nanoparticle-based solar cells achieved 18.5% efficiency, rivaling silicon alternatives. The methodology, validated at PolLux, is now industry standard for third-generation photovoltaics ¹ ⁴ .

Measurement	Finding	Significance
Dopant Distribution	Homogeneous (deviation <5%)	Ensures uniform charge extraction
Chemical State	Li⁺ ions integrated into molecular matrix	Confirms successful doping
Layer Thickness	70 ± 5 nm	Optimizes light absorption/transport

Table 2: Nanoparticle Analysis via TEY-STXM

The Scientist's Toolkit: Key Instruments at PolLux

Essential Research Components

Zone Plates

Function: Focus X-rays using diffraction from concentric rings.

Innovation: Au/Ni coatings enable energy flexibility (250–1600 eV) ³ .

Higher-Order Suppressor (HOS) Mirror

Function: Filters out stray X-ray wavelengths, ensuring spectral purity.

Impact: Critical for accurate XANES spectroscopy ³ .

Silicon Drift Detectors (SDDs)

Function: Capture emitted electrons or X-ray fluorescence.

Upgrade: New trapezoidal SDDs (2025) increase signal sensitivity 10×, reducing radiation damage ⁴ .

Polarization Switch

Function: Rapidly toggles between left/right circular polarization by steering electron beams.

Application: Real-time magnetic imaging ⁶ .

In-Situ Gas Cells

Function: Maintain samples in reactive atmospheres during imaging.

Breakthrough: Enabled catalysis studies under operational conditions ¹ .

Future Horizons: SLS 2.0 and Beyond

The 2025 SLS 2.0 upgrade transformed PolLux with brighter beams and faster detectors. Upcoming developments include:

Ptychography integration: Combining scanning and diffraction imaging for atomic-scale resolution ⁴ .
Cryo-STXM: Imaging frozen biological specimens without dehydration artifacts ⁷ .
Multi-modal tomography: 3D chemical/magnetic mapping with <20 nm resolution ⁶ .

"We built not just a microscope, but a portal into the nanoworld—where materials, biology, and magnetism meet light."

Dr. Johanna Raabe, PolLux co-designer

PolLux remains accessible globally via peer-reviewed proposals. The next submission deadline is August 20, 2025 ² ⁹ .