Hard X-ray Photoelectron Spectroscopy (HAXPES)

Hard X-ray Photoelectron spectroscopy extends normal sampling depths of XPS (5-10 nm) into the bulk of the material (30-50 nm), and analysis of the background can obtain information from depths up to several hundred nm. This enables elemental compositions and the chemical state of the atoms in a material to be quantified and profiled from the surface into the bulk.

The instrument from Scienta Omicron GmbH, the first of its kind in the world, was acquired by Henry Royce Institute in 2019. It utilises a 9.25 keV X-ray source (Excillum), over 6 times the energy of traditional XPS lab sources, a bespoke monochromator, and EW4000 energy analyser. The analyser has a wide acceptance angle allowing angle-resolved HAXPES from the surface towards the bulk in one snapshot. The X-rays have an increased flux of > 1000 times greater than traditional lab XPS sources, required to overcome the drop in photoionization cross sections using higher photon energies. The X-ray beam is micro-focussed to 50 μm.

The system is connected to a flexible preparation chamber and a high throughput standard XPS system that also includes UPS (ultraviolet photoelectron spectroscopy) and argon cluster etching (Ionoptika GCIB 10S). The HAXPES chamber also has a standard Al X-ray source for fast comparison between the surface and bulk-like regions. A vacuum suitcase is available, as well as inert transfer via an Ar glove box and vacuum vessel.

Applications are across a broad range of advanced materials research. The technique is particularly suited to probing through oxide passivation layers and measuring buried or layered structures. As such applications include metallurgy, batteries and energy materials systems such as photovoltaics, 2D material structures, coatings, actinides and nuclear materials, biomaterials, and more.