This applications note demonstrates the use of both conventional (Al Kα) and higher photon energy (Ag Lα) excited X-ray Photoelectron Spectroscopy (XPS) to characterise the solid electrolyte interphase layer formed on a graphite anode during charge/discharge cycles. Samples were prepared in a glove box at the manufacturing site and transported to the XPS analysis laboratory using an air sensitive sample transport accessory.
Na-ion batteries are considered to be environmentally favourable alternatives to Li-ion batteries, particularly in the extremely large-scale application of grid storage, given the abundance of Na. Among them, sodium layered oxides are very important cathode materials with good sodium mobility and high specific capacity. Layered transition metal oxides NaXMeO2 consist of layers of MeO6 octahedra to preserve 2D transport channels for direct Na ion diffusion. For metal selections, Me can be Fe, Mn, Co, Cr, Ni, Ti, V and their combinations. Interestingly, single transition metal oxides show worse battery performance than binary or ternary transition metal systems, making composition studies imperative. Metal combinations can achieve tuneable properties with structure, electrochemical performance, and cycling stability.
In this application note, air/moisture stability is effectively and systematically investigated with XPS, paving the way for material stability to be modified through rational design.
The high temperature gas reaction cell allows sample modification under high temperature and high pressure conditions. The reaction cell is a small volume, quartz chamber with facility for gas introduction, purging and evacuation. Maximum operating temperature is 1000 ͦ C. Maximum operating pressure is 30 bar. The accessory has integrated sample and gas handling allowing transfer under UHV conditions directly to the sample analysis chamber or via the surface science station, depending on which chamber the reaction cell has been mounted.
Nitrogen-doped GaAs (GaAs1-xNx) is finding application in high efficiency solar cells and vertical cavity surface emitting lasers (VCSELs). Nitrogen doping has been shown to cause perturbation of the host band structure. Determination of chemical state and nitrogen concentration is pivotal in defining the material’s electronic structure. X-ray photoelectron spectroscopy (XPS) is a commonly used technique for surface characterisation of this dilute N doped material.
In this application note we contrast the use of Al Kα and Ag Lα as excitation sources for XPS analysis of GaAs1-xNx. The advantage of using the higher photon energy excitation source to ‘remove’ overlapping Auger transitions with the N 1s core-level photoemission peak is demonstrated. Also introduced are advantages relating to the increased sampling depth provided by using the Ag Lα excitation for characterisation of a thin-film material.
The last few decades have seen rapid development in computational and theoretical tools for fabricating, simulating, and characterizing material systems. In this applications note the potential of surface characterization by X-ray photoelectron spectroscopy to provide rapid elemental and chemical state information is presented. The development of the group analysis array functionality is of significant importance in the application of XPS analysis to combinatorial materials discovery to allow the processing and display of large data sets. As will be demonstrated, group array analysis provides a more detailed understanding of the chemical distribution across the sample.
Small area X-ray Photoelectron Spectroscopy in the 10’s of micron range has become an important tool for the surface analyst. Two approaches to producing small area XPS information are currently used in commercial XPS instrumentation. One approach employs a micro-focused X-ray probe to limit the sample area illuminated by X-rays during measurement. The second approach, utilised in the AXIS range of spectrometers, is to use a system of electrostatic lenses and apertures to limit the acceptance area of the analyser. In both cases the analysed area on the sample surface is determined by measuring the distance required to receive a 20 to 80% signal increase when scanning the spot across a sharp edge. This is standard practice as described in the literature.
Published work  has highlighted the fact that signal can be obtained over an area many times greater than the quoted spot size when recording XPS data using X-ray microprobe technology. This investigation utilises an approach similar to the aforementioned work to determine quantitatively the total area measured during small area XPS measurements using the virtual probe approach.
 U. Scheithauer, Surf. Int. Anal., 40, 706-709 (2008).
Graphene flakes prepared and deposited on SiO2 were analysed using X-ray Photoelectron Imaging. Small-spot spectroscopy allowed for thickness measurements to be determined for individual flakes. This method allowed for the metrological determination of layer number.
2D materials are becoming increasingly relevant in state of the art device development. Using a combination of the surface sensitive techniques Inverse Photoelectron Spectroscopy (IPES) and Ultraviolet Photoelectron Spectroscopy (UPS), we demonstrate how the analyst can obtain information on the nature of the electronic properties for single and multi-layer stacks. In this example the properties of a thin layer of MoS2 are investigated. Bulk MoS2 is a diamagnetic, indirect bandgap semiconductor similar to silicon, with a bandgap of ~1.2 eV. However, with reduced thickness the bandgap increases with a confinement-induced shift of the indirect gap from the bulk value. Thickness/growth control is therefore critical to the performance of this material in next-generation devices.
A corroded tinplate sample was analysed by XPS and AES techniques using the Kratos AXIS Supra+ to gain an insight into the extent and mechanism of corrosion. XPS was firstly used to analyse the composition of the surface and from this, characterize the Sn 3d and Fe 2p oxidation states. The corroded area was then examined using SEM to pinpoint significant positions for further analysis with AES. The resulting data indicates the position at which corrosion is initiated and examines the extent of this corrosion across an area of the surface.
GaN is one of many materials which are difficult to analyze with the conventional Al Kα X-ray source due to a strong overlap between the N 1s core line and the Ga LMM Auger series. This brings difficulties with accurate quantification and also chemical state assignment. In this applications note, GaN was analyzed using different X-ray excitation sources with the aim of shifting the binding energy position of the Ga LMM Auger series to prevent its interference with the N 1s region. Automation of changing between the Al Kα and Ag Lα excitation sources when using the Kratos AXIS Supra+ is an added benefit.
DOI : 10.5281/zenodo.431123