Using Surface Analysis to Understand your Materials
Wednesday, 10 April 2024
Surface analysis is the process of determining the structure, characteristics and elemental composition of a surface down to atomic-level resolution. It plays an integral role in materials engineering.
A surface layer is the point that a material interacts with the environment, reacts with other materials or comes into contact with people. At Warwick, we have a suite of techniques for analysing surfaces to different depths, ranging from the top nanometre of the material to analysis of properties over a few hundred micrometres.
Surface analysis is often key to solving problems with the performance of materials. Surface characteristics can affect a broad range of factors, from adhesion, corrosion, friction and porosity to the electrical, thermal, mechanical and optical properties of materials. Surface analysis methods can also be used to track reaction processes or reveal the catalytic properties of a material via analysis of surface structures and oxidation states.
By revealing information on the effectiveness of materials and identifying any defects, surface analysis gives manufacturers knowledge they can use to develop and improve their products and technologies. It has a huge range of industrial applications. Just some examples include:
- Developing composite materials and speciality glass.
- Improving the performance of battery materials, photovoltaics, energy technologies and semiconductors.
- Understanding the effectiveness of polymer materials such as coatings and food packaging.
- Studying the release of drugs from delivery platforms.
- Analysing failures in medical devices, coatings and automotive components.
What techniques are available for surface analysis?
Spectroscopic methods of surface analysis give quantitative and qualitative information about the chemical composition of surfaces. They work by exposing the surface of a material to various types of electromagnetic radiation (e.g. visible light, x-rays, infra-red rays) or charged particles (electrons, ions) and analysing the response of the material or the particles emitted from the surface as a result. Some examples include:
X-ray Photoelectron Spectroscopy (XPS)
XPS is based on the photoelectric effect, where the surface of a sample is illuminated with a single wavelength of x-rays and an energy spectrum is created by recording the number of electrons that are ejected as a function of kinetic energy. The energy corresponding to each peak of the spectrum is characteristic of an element and reveals the elemental composition of the sample.
Higher resolution information can be acquired to reveal information on the chemical environment of the atoms, such as their bonding environments and oxidation states. Imaging XPS allows the chemical composition of the sample to be mapped with a resolution of a few micrometres.
Ultraviolet Photoelectron Spectroscopy (UPS)
Based on the same principles as XPS, but using ultra-violet light to illuminate the sample, UPS measures the kinetic energy of the most loosely bound electrons at the surface of the material. The energy profile of the emitted electrons reveals information about the electronic structure of conductive or semiconductive surfaces, key for applications such as photovoltaics and power electronics.
Secondary Ion Mass Spectrometry (SIMS)
SIMS is used to analyse the composition of solid surfaces and thin films by sputtering the surface of a sample with a focused primary ion beam and analysing ejected secondary ions. By measuring the emitted secondary ions as a function of time, a depth profile of the material’s composition can be recorded.
Raman spectroscopy measures light that is scattered from a sample when it is illuminated with a laser, revealing information about the structural properties of a material and its chemical components. Combining Raman spectroscopy with a microscope allows a precise point on the surface of a sample to be selected for analysis.
Microscopy techniques for surface analysis
Microscopy techniques can be used to gain information on the physical properties of surfaces, such as surface roughness, adhesion, pore diameters and topography.
Scanning Electron Microscopy (SEM)
SEM uses electrons instead of light to image the surface of samples with resolutions at nanometre scale. They provide a large depth of field and can be used for understanding surface structure, analysing particle size and studying fractures.
AFM uses a sharp tip on a cantilever to scan a material’s surface, sensing tiny variations to generate nanometre-scale images. It reveals fine detail in the roughness of a surface by taking both vertical and horizontal topography measurements.
Surface analysis at Warwick
The University of Warwick offers a range of surface analysis techniques that can be used across a wide variety of sample types, including hard materials and thin films as well as biomolecules. We have dedicated platforms for Photoemission Spectroscopy and Electron Microscopy and a breadth of other facilities that are available to external users.
We work with industry clients ranging from SMEs to consultancy firms and global product manufacturers. By linking industry with our expert analysts and state-of-the-art infrastructure we can provide solutions to real-world problems to boost innovation and drive advantage.
Find out more about the surface analysis techniques available at Warwick or contact Claire Gerard, Warwick Scientific Services Manager (c.gerard@warwick) to discuss how we can help find a solution to your challenge.