The NanoESCA III Photoemission Electron Microscope: What is it and why should you use it?

By Benjamin Chambers and Tanglaw Roman – Flinders University, Flinders Microscopy and Microanalysis

The ScientaOmicron NanoESCA III Photoemission Electron Microscope (PEEM) at Flinders Microscopy and Microanalysis is now available to everyone through Microscopy Australia’s open access policy.

Photoemission electron microscopy is suitable for measuring the chemical and physical properties of conductive samples in an ultra-high vacuum (UHV) environment. Photoemission electrons generated by monochromatic UV light (21.2 / 40.8 eV) can be focused and detected to construct an image of the surface. PEEM images have contrast created by variations in the surface morphology, probability of photoemission, and work function across the surface. The PEEM energy-filtered images have a lateral resolution of <50 nm and fields of view ranging from 10-160 µm.

In addition to imaging the surface in real space, the electrons can be focused onto the detector in a way to map the momentum of the photoemission electrons; known as momentum microscopy (MM). These momentum images map the variation in electron ejection angles, providing a form of angle-resolved photoelectron spectroscopy (ARPES). In contrast to traditional ARPES, the sample angle is fixed and all angles are measured simultaneously. Small areas (~10 µm) can be selected for µARPES studies. The µARPES is a powerful technique for investigating the electronic band structure of materials.

Full wavevector ARPES images: Ag (111) FoV 5Å-1

Using a monochromatic X-ray source (Al K_α 1486 eV) the NanoESCA III is also capable of chemical analysis by imaging photoemission electrons (XPEEM) and small spot (~500 nm – 200 µm) X-ray photoelectron spectroscopy (XPS).

The NanoESCA III preparation chamber is equipped with a suite of tools:

• Heating stage and argon ion source for cleaning or annealing surfaces in UHV
• UHV cleaver to prepare mineral surfaces in UHV.
• Electron beam evaporator (EFM-3) for thin-film growth in UHV (4-20 mm).
• Low-energy electron diffraction (LEED) for determination of structure for single-crystalline materials.
• ScientaOmicron variable temperature atomic force microscopy (VT-AFM) is capable of UHV AFM (contact and non-contact) and scanning tunnelling microscopy (STM) facilitating atomically resolved imaging of surfaces to be collected prior to spectroscopic studies.

The NanoESCA III enables the direct correlation between electron band-structure of advanced materials with device function. This is essential for understanding electron transport in materials including topological insulators and transistors for quantum computing, nanomaterials for energy-storage devices and catalysis, and minerals for geoscience.

Real space PEEM image: 20µm FoV, E-Ef: 4.5eV, gold on silicon

Real space PEEM image: 76µm FoV, E-Ef: 4.825eV, CVD grown MoS2 on silicon