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Case studies

Calibrating innovative XPS instruments to boost sales and market adoption

The need

X-ray Photoelectron Spectroscopy (XPS) is important for determining the surface chemistry and structure of materials and coatings. Mobile phone displays and medical devices, for example, need functional and protective coatings to work. Reducing thickness can cut cost dramatically, but doing so increases the risk of problems such as holes and contaminants that cause failure. Better understanding of coating chemistry and thickness will promote better design and manufacturing decisions.

For 50 years, UK-based Kratos Analytical Ltd has led the world in XPS and development of new instruments.  95% of instruments are exported, where they are used by coatings and advanced materials companies to research new products and spot defects and contaminants that may compromise material performance. Kratos has recently developed a new XPS instrument – a High Energy Ag L alpha X-ray source – which can measure at twice the depth of normal XPS. However, the current calibration and measurement infrastructure is not designed for XPS at these energies, making it hard to be confident in what exactly is being measured.

XPS works by firing X-rays at a surface, causing electrons to be emitted, which are then measured by a detector. The electron binding energy is different for each element, so XPS can identify which elements exist within a material.  The electron kinetic energy is the difference between the X-ray energy and the binding energy, so higher energy X-rays mean faster electrons. Traditionally XPS has an X-ray energy of around 1500 electron volts, allowing electrons to escape from only 5-10nm into a material’s surface. Kratos’ new X-ray source doubles the X-ray energy and increases the electron escape depth.

The new instrument could identify the presence of elements deeper in the sample, but could not quantify them with sufficient certainty. Kratos approached NPL to explore methods to determine exactly how they could turn data from their new instrument into meaningful information.

The solution

NPL used fundamental physical parameters and theoretical models of how electrons at different energies would be emitted from materials to predict the intensities in the new instrument. These were compared to experimental intensities from material samples of known composition to understand the efficiency of the instrument. This produced a set reference data to allow accurate calibration of the instrument and sensitivity factors for every element, enabling the composition of any sample to be accurately measured. These NPL procedures are being incorporated into Kratos’ instrument software.

The impact

Kratos can now demonstrate that the instrument generates quantitative data about the amount of each element in the surface of a sample. This innovation could boost revenue by £500k. It provides customers with a new capability to measure chemical composition accurately and at greater depths. It also allows direct comparison with traditional XPS, giving users more information about the depth each element appears.

This is valuable for investigating surface chemistry of advanced materials and coatings, including pharmaceutical release systems, smart glass and touchscreens. It can also be used for analysing protective coatings for sensitive components such as wind turbines, automotive engines and energy storage devices. XPS is a key technique for quality control particularly for spotting defects, identifying contaminants and in patent protection.

Dr Chris Blomfield, Surface Analysis Business Manager at Kratos, says: “Calibration of our advanced instrumentation is a complex challenge, requiring detailed understanding of the fundamental physics and data. Thanks to world-leading measurement expertise at NPL, this project turned out extremely well for us. We can now collect truly quantitative data about chemical composition, making our instrument more valuable, and creating sales opportunities in new areas. We anticipate growth in sales revenue of the order £500K per annum as a direct result of NPL’s work on this project. This is the first formal collaboration we have had with NPL, and we looked forward to further opportunities to develop the technique in future together.”

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We anticipate growth in sales revenue of the order £500K per annum as a direct result of NPL’s work on this project.

Dr Chris Blomfield, Surface Analysis Business Manager - Kratos