NPL Management Limited – UK
Products and Services
NPL offers a unique wide range of measurement services, contract research, consultancy and training services. Other areas of expertise include the design and characterisation of engineering materials and mathematical software, especially its application to measurement and instrumentation.
For advanced and nanoscale materials of relevance to the Oyster project, we offer in particular XPS, SIMS and AFM.
X-ray Photoelectron Spectroscopy (XPS)
XPS is used for investigating the surface chemistry of electrically conducting and non-conducting samples. A surface is irradiated with X-rays (commonly Al Kα at 1486.6 eV) in
vacuum. When an X-ray photon hits and transfers this energy to a core-level electron, it is emitted from its initial state with a kinetic energy dependent on the incident Xray and binding energy of the atomic orbital from which it originated. The energy and intensity of the emitted photoelectrons are analysed to identify and determine the concentrations of the elements present. These photoelectrons originate from a depth of <10 nm therefore the information obtained is from within this depth. UPS uses a much lower energy source, He(I) and He(II), 21.2 eV and 40.8 eV respectively.
XPS provides the following information from the top 10nm of a sample with a spatial resolution between three to a few hundred μm.
- Elemental composition with up to 0.1% sensitivity
- Chemical state information
- Thickness measurement of overlayers of up to 8 nm on a substrate
- Surface chemical imaging with a resolution of 3 μm
- Angle resolved XPS for thickness and depth-distribution of chemical species
- Depth profiling using an ion gun to sputter away the surface during analysis
- Ultraviolet photoelectron spectroscopy (UPS) available in the same instrument provides information on the density of states in the valence band and electron work function.
XPS provides the following information from the top 10nm of a sample with a spatial resolution between three to a few hundred μm.
- Elemental composition with up to 0.1% sensitivity
- Chemical state information
- Thickness measurement of overlayers of up to 8 nm on a substrate
- Surface chemical imaging with a resolution of 3 μm
- Angle resolved XPS for thickness and depth-distribution of chemical species
- Depth profiling using an ion gun to sputter away the surface during analysis
- Ultraviolet photoelectron spectroscopy (UPS) available in the same instrument provides information on the density of states in the valence band and electron work function.
Secondary ion mass spectrometry (SIMS)
Mass spectrometry is a powerful tool for elemental, molecular and isotopic analysis which we use to amass huge amounts of detail about biological, materials and agricultural samples.
In fact, the technique can be applied to all research fields. This helps us understand the make-up of cancer tumors, locate and quantify nuclear materials, and investigate advanced materials. It can be used to take a sample, separate each molecule that makes up that sample, and then provide the data that allow each of those molecules to be identified and quantified. We use mass spectrometry imaging (MSI) to uncover new spatially-resolved information about the molecular and isotopic composition of biological and inorganic materials in unprecedented detail.
SIMS is capable of providing:
- Identification of trace elements, organic molecules and polymers on surfaces and interfaces, with better than 1 ppm sensitivity for some molecules and ppb sensitivity for some elements
- Surface chemical imaging with better than 200 nm resolution
- Extremely surface-sensitive information from top 1 nm of sample
- 3D chemical imaging of inorganics and organics with better than 5 nm depth resolution
Atomic force microscopy (AFM)
Atomic force microscopy is a powerful surface analytical technique used in air, liquid or vacuum to generate very high-resolution topographic images of a surface down to molecular/atomic resolution. Depending on the sharpness of the tip it gives spatial resolutions of 1-20 nm. It can record topographic images as well as mapping other information on nanoscale such as mechanical (modulus, stiffness, viscoelastic, frictional, adhesion), chemical, electrical and magnetic properties.
In AFM, a sharp microfabricated tip attached to a cantilever is scanned across a sample. The deflection of this cantilever, caused by the forces developed between the tip and the sample, is monitored using a laser and photodiode and is used to generate an image of the surface. The AFM can image in a number of ways using either contact mode or an oscillating technique where the tip taps the surface.The AFM can also be used for force spectroscopy and mapping. Here it applies forces as a function of height from 5pN to 50 µN to one spot on a surface to analyse mechanical or in some cases chemical properties at surfaces. Either pushes into the surface to measure nanomechanical properties of a surface such as modulus, stiffness and adhesion or pulls away from the surface to investigate bond rupture and adhesion.
AFM is commonly used for:
- Polymers, coatings, inorganics, biological samples and other commercial products
- Healthcare, personal care products – e.g. measuring the change in nanoscale mechanical properties (modulus and friction) of hair, teeth and skin as a function of time or actives
- The topography and nanomechanical properties of nanoparticles, particles, graphene, 2D materials and coatings.
Other techniques available at NPL include scanning electron microscopy (SEM), Raman spectroscopy, particle and nanoparticle characterisation including sizing, charge and nanoparticle number concentration, Auger electron spectroscopy (AES), contact angle analysis, quartz crystal microbalance (QCM), specific surface area/BET (SSA/BET), spectroscopic ellipsometry.