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Distribution, segregation and chemical state identification of Lithium salts on Cu electrodes

Rechargeable metal-based batteries (Li, Na and Al) are among the most versatile platforms for high-energy storage. Unfortunately however there are several pitfalls for these energy storage systems, one of which is deposition and dendrite formation during repeated cycles of charge and discharge. Many studies have been performed in search of a dendrite-free, deposition-free system for lithium batteries using novel materials such as 3D structures and carbon nanofibers.[1,2]  Here we will explore the distribution of Lithium in different chemical environments on electrode surfaces. We employ conventional surface analysis techniques (XPS) to yield large area, quantitative, information regarding the distribution of surface species. To explore the lateral and depth distribution of Li we also utilise XP imaging and Argon cluster depth profiling.

Surface analysis of strip coated materials pre- and post- 'cleaning'

Strip coating materials are commonly used in optic applications for the removal of grease and small particulates form the surfaces of delicate materials. Typically these include mask gratings, laser optics, telescope lenses and refractors. A clear red solution consisting of a blend of polymers is applied using a small brush and is then left to set. Once set, the polymer coating is peeled away leaving a pristine surface free of particulates.

Quantification of layer composition in compound semiconductors

Compound semiconductors are the key underpinning technology in optoelectronics, and also used in electronic applications with specialist requirements (e.g. power). The ability to engineer the electronic and optical properties of compound semiconductor alloys, for example in terms of their alloy composition, which may be binary, ternary, quaternary or quinary, and grow multiple layers of different semiconductor alloys on top of each other (heterostructures), is a key part of their success.

Excellent and extreme examples of this are devices that contain distributed Bragg reflectors: alternating layers of high- and low refractive-index material (typically GaAs/AlxGa1-xAs) to create a stop-band where a very particular set of wavelengths are almost fully reflected (ideally over 99.9%). For example, vertical cavity surface emitting lasers (VCSELs) are tiny (low-cost) semiconductor lasers that use a pair of DBRs to form the mirrors of the lasing cavity. In VCSELs, the quality and consistency of the DBRs is important, as a VCSEL has a gain length on average 105 times smaller than an edge-emitting laser, and therefore needs ultra-high reflectivity mirrors to achieve a reasonable threshold current. Examples of other, emerging, devices that use DBRs are single photon LEDs (SPLEDs); these are needed for quantum key distribution in quantum cryptography networks. This study focuses on these DBRs, and methods to accurately characterise their structure, including determining whether the semiconductor layer growth has proceeded as desired. X-ray photoelectron spectroscopy (XPS) depth profiles are taken to measure the chemical composition of the DBR layers to further characterise the growth. Even a small change in Al composition affects the refractive index, thus changing the optical path length of the layer, with consequences for everything from mirror characteristics to laser output wavelength. XPS yields quantitative information regarding Al content for the DBR structure, which directly relates to device performance.



Analysis of drug coated polymer stents studied by XPS

Cardiovascular interventional therapy with stents has emerged as the most effective method for coronary heart disease. However, thrombosis and hyperplasia are the usual pathological responses to the implantation of foreign devices. To suppress this immune response and that of overgrowth and subsequent restenosis anti-inflammatory drugs are now loaded onto the surface of stent implants. Here we investigate the surface of drug loaded polymer stents. The stents are made of polylactic acid (PLA) dosed with an anti-inflammatory drug with a molecular structure of C51HxNO13. XPS yields quantitative information regarding drug distribution and using Argon cluster sputtering we can see the distribution of the drug into the stent structure. Analysis is also performed on stents submerged in buffer solution (PBS) to see the effects on ageing and the propensity for the drug to migrate into the solution with time.

XPS analysis of frozen 1,4-dibromobenzene

The molecule 1,4-dibromobenzene is of interest as a precursor for the synthesis of conjugated polymers with applications in nanoelectronic and electronic devices. 1,4-dibromobenzene has a vapour pressure of 0.0575 mmHg at 25˚C such that it will volatilise in vacuum at room temperature. To achieve XPS characterisation this organic material requires cooling to < -100˚C before pumping and introduction to the analysis chamber.

Combined Argon cluster UPS-XPS depth profile of OLED thin-film

Low-energy argon cluster ions were used to depth profile through an organoelectronic (TCTA) thin-film deposited on ITO. XPS and UPS spectra were acquired after each etching cycle. Compositional changes were seen through the film and at the interface with the substrate. Changes in UPS spectra were directly compared to changes in compositional change.

Investigating the surface and interface of Li ion thin-film battery materials

Here we use conventional surface analysis techniques of XPS and sputter depth
profiling to understand the surface and bulk chemistry of LiPON films formed
via atomic-layer deposition (ALD).  Comparisons are made between the results obtained from conventional monatomic depth profiling and cluster depth profiling.

Spherical mirror analyser (SMA)

This technical note outlines the properties and uses of the spherical mirror analyser (SMA) for XPS imaging and it's integration into a modern photoelectron spectrometer.  It details the electron optical properties of the analyser for high energy and spatial resolution imaging.