Nexsa - Unparalleled Sensitivity for Large and Small Area Analysis

Interview conducted by Stuart MilneJul 27 2018

Tim Nunney, Marketing Manager at Thermo Fisher Scientific, Surface Analysis & Microanalysis, talks to AZoM about the new Thermo Scientific Nexsa™ XPS system. A high performance XPS instrument with unparalleled sensitivity for large and small area analysis.

Please could you start by introducing the Nexsa?

The Thermo Scientific Nexsa Surface Analysis System is the newest XPS product from Thermo Fisher Scientific. At its heart, Nexsa is a high performance XPS instrument. It has a brand-new X-ray monochromator which has unparalleled sensitivity for large area analysis, but can operate at smaller X-ray spot size to enable small feature analysis as well. This gives the user a much better imaging than was previously available, without compromising the XPS performance for more routine, large area analysis.

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What's the benefit of being able to analyze a smaller area?

Increasingly we are seeing that materials analysts want to look at small features at the sample surface. These can be things like bond pads, or defects in the coatings that have been applied to surfaces. Having this capability with the new X-ray source really allows the Nexsa to meet those challenges.

What analytical capabilities does the Nexsa have?

As well as the XPS capabilities, with Nexsa we're able to integrate other key surface analysis techniques onto the system. These include ion scattering spectroscopy (ISS, also sometimes known as LEIS - low energy ion scattering), UV photoelectron spectroscopy (UPS), refelected electron energy loss spectrocopy (REELS), and also the possibility of adding our Thermo Scientific™ MAGCIS™ dual mode cluster and monatomic ion source. With these capabilities we're able to investigate other surface properties that XPS alone cannot look at.

Uniquely, with Nexsa we're also able to integrate a Raman Spectrometer onto the instrument adding molecular spectroscopy to the portfolio of techniques available. Rather than having to move samples from instrument to microscope to do the XPS and Raman analysis, now being able to do it on the same platform at the same time means that you can be sure that you're analyzing the same point on the sample, and getting the data from exactly the same position.  

Please can you tell us about the Thermo Scientific™ Avantage™ software package?

Like all our surface analysis instruments, Nexsa runs on Avantage, the software package that controls all vacuum operations, data acquisition, data processing, and output of data into reports.

Avantage has many features to enables you to get your sample data and processed results quickly. It has the capability to automatically interpret the scan that starts most analysis, the survey scan, to identify which elements are present and lead onto what you need to do next to understand the chemical states in the sample. We have new features that enable you to process images quickly and understand the distribution of chemical states across the surface, and also to process the other types of data we're generating from ISS, or REELS, or UPS. This includes being able to process REELS and UPS data to look at band gaps or work functions, for example.

By being able to collect data with Nexsa using a multiple array of techniques, we need to be able to process the results from ISS, XPS, Raman, UPS- in concert to be able to understand exactly what's happening at the sample surface. Avantage allows you to process the results from these different techniques together, for example ISS and XPS, or Raman and XPS, enabling you to understand exactly what's happening at the sample surface by getting a complete picture quickly.

How do SnapMaps help Nexsa users?

SnapMap not only enables the users to take rapid XPS images, but also positional information can be taken from these images, and used for subsequent analysis.

SnapMap can be used for a number of different experimental purposes. Large-area SnapMaps can be used to determine the distribution of chemistry across the sample surface. Small-area SnapMaps can be used to isolate features down to 10 microns in size. Even features invisible to the naked eye can be identified and isolated for further analysis, as SnapMaps contain full spectra, which can be used to isolate areas with differing chemistry which may not differ optically.

The speed that a SnapMap is acquired means that they can be included into a typical work flow very easily, non-intrusively, and will give spatial information that is complimentary to conventional XPS analysis. Complex analysis that may have taken hours in the past can now take minutes, thanks to the automation and ease of use of the Nexus system, with Avantage and SnapMap.

Lithium-ion battery material analysis is a key area of focus in research and industry right now. What are some of the key challenges and how does the Nexsa system help overcome these?

There are a couple of key challenges in analyzing lithium-ion battery materials.Firstly, the materials can be sensitive to air. This means that even before they've entered the system, any exposure to air can change their chemistry.

Secondly, lithium can be very difficult to detect, so a very highly sensitive instrument is required.

With Nexsa, we have an optional vacuum transfer module. This can be loaded with samples inside a glovebox, and then transported directly into the system without exposure to air. It is also possible to integrate a glove box onto the system, if the primary focus is air-sensitive materials.

XPS can be used to analyze cathodes, anodes, and separator materials. For example, looking at the surface chemistry of pristine electrodes and comparing it to the surface chemistry of used electrodes. One of the ways that the performance of a battery degrades is in the formation of an SEI layer. The composition of this can be analyzed with an XPS depth profile.

The multi-technique analysis capability of the Nexsa is particularly valuable for analyzing lithium-ion batteries. The unique capability of performing coincident XPS and Raman spectroscopy without removing the sample from the system, can be useful for fully characterising carbon-based anode materials for example.

With its high performance and multi-technique capabilities, the Nexsa is ideally suited for analysis of lithium-ion and future battery challenges.

Thin films are becoming increasingly popular for increasing the energy output and power density of batteries. How can XPS be used to analyze these materials?

Batteries with thin film solid state electrolytes are already in production, but over the next few years there'll be an increasing demand to grow the energy output and power density of these batteries. Lithium phosphorus oxynitride, or LiPON, is one material that may enable this.

To fabricate these LiPON films atomic layer deposition (ALD) is typically used. To achieve the required electrical properties of the film, the elemental concentrations or the chemical bonding of those elements is modified to produce the required perfromance. XPS is the ideal technique for analyzing the elemental concentrations and chemistry of LiPON films. It's chemically selective, surface sensitive, and you can quantify without using standards.

LiPON films can be fabricated with thicknesses anywhere from 10 nanometers up to one micron. For the thinner films we could just use XPS to analyze the chemistry, but for the thicker films, beyond 10 nanometers, we must combine XPS with ion sputtering. Traditional forms of sputtering, with monatomic Ar+, are very good at quickly profiling through films, but they destroy the very chemistry we are trying to investigate. With Nexsa, and the MAGCIS ion source, we can generate beams of ion clusters with anywhere from 75 up to 2,000 atoms of argon. With the smaller clusters between 75 and 300 atoms, we can efficiently sputter through LiPON films without modifying the chemistry.

About Tim Nunney

Dr Tim Nunney is the Marketing Manager for the Thermo Scientific Surface Analysis (X-ray photoelectron spectroscopy) & Microanalysis (EDS, WDS & EBSD) product lines. His role involves all aspects of product marketing, including collateral development, customer evaluations, product development and commercial support. He has been with Thermo Fisher Scientific since 2004, previously holding positions as an applications scientist, and in the operations group. Prior to joining Thermo Fisher Scientific, Tim worked as a post-doctoral research fellow at the University of Southampton, investigating the dynamics of molecular dissociation on metal surfaces. He completed a PhD in Surface Science at the University of Liverpool, studying the surface catalysed decomposition of methylamines on transition metal surfaces using reflection absorption infra-red spectroscopy (RAIRS) and XPS.