The LTA’s high-performance chemical analysis and imaging platform has two new state-of-the-art machines:
- a PHI nanoTOF II TOF-SIMS mass spectrometer
- a PHI VersaProbe III scanning XPS microprobe
X-ray photoemission spectroscopy is a tried and tested technique for determining elemental composition and chemical states in solids. In particular, the intrinsic surface sensitivity of this technique makes it an important tool for characterising surface chemistry.
Quantitative (0.1 atomic %)
Sensitive to all elements except H and He
10 µm spatial resolution
Core level chemical shifts identify oxidation states, bonding environments and electronic structure
How does it work ?
X-ray Photoemission spectroscopy (XPS) is based on the physical principle of the photoelectric effect. XPS measures the kinetic energy of photoelectrons that are emitted from a material when it is irradiated with X-rays. These photoelectrons are emitted from atomic orbitals, which have well-defined energy levels, and which are characteristic for each element of the periodic table. Since the kinetic energy of the photoelectrons is defined by these characteristic energy levels, it can be used to identify which elements are present in the material. The strength of the XPS signal for each element is proportional it’s concentration, which allows the relative abundance of different elements to be quantitatively determined. Only electrons from the surface of the material contribute to the signal.
XPS probes approximately the top 10 nm of the sample surface making it ideal for studying surface chemistry. In order to probe deeper in the sample, we can employ Argon ion sputtering to remove material from the sample surface. Progressive cycles of sputtering and XPS measurements allow chemical depth profiles to be generated, which can be used to study the chemistry or electronic properties of thin film heterostructures and functional interfaces. The surface sensitivity of XPS can also be controlled by performing angle dependent XPS (ADXPS) measurements. In ADXPS, by varying the take-off angle, the surface and bulk contributions to the signal can be distinguished. This approach has the advantage that it is non-destructive. Our machine has a focused scanning X-ray source. This enables chemical mapping of the sample which can be used to identify chemical inhomogeneities or defects. With a minimum spot size of 10 microns we can also study defect chemistry or small patterned features. Our dual charge neutralization system, that simultaneously compensates for static charge and the change generated by the photoemission process, allows insulating samples to be measured. XPS measurements are performed under ultra-high vacuum conditions. Our system is also equipped with a transfer vessel that allows us to introduce samples directly from a glove box. This means that we can measure sensitive or reactive samples that must be kept in a protective atmosphere. We also have the ability to add electrical contacts to samples and perform in situ transport experiments, for example to perform operandi XPS studies of solid-state battery interfaces.
Time of Flight Secondary Ion Mass Spectrometry is a technique for determining the elemental and molecular composition of solid samples. Its surface sensitivity, high sensitivity and high spatial resolution makes it an important tool for trace chemical analysis of surface composition.
High sensitivity (0.1-1 ppm for elements)
Elemental and molecular identification
100 nm spatial resolution
Improved identification with parallel MSMS
How does it work ?
Time of Flight Secondary Ion Mass Spectrometry is a mass spectrometry technique where elemental and molecular ions are generated from the upper few nm of a sample surface by hitting it with a highly focused high energy ion beam. The flight time of the generated ions is measured and their mass can be calculated from this data. The mass of the detected ions tell us their identity and as a result the chemical composition of the sample surface.
Due to its high elemental and molecular sensitivity and surface sensitivity, TOF-SIMS can be employed to analyze defects and to detect and identify contaminants on surfaces. Another common use for the technique is to study the composition of surface coatings while the different sputter beams enable the determination of bulk composition, depth profiling and 3D imaging of both organic and inorganic samples. For example, depth profiling can be utilized to study the diffusion of compounds in multilayer systems such as solar cells. The soft sputtering using argon cluster ions preserves the integrity of organic samples and is well suited for the depth profiling and 3D imaging of polymer systems such as drug delivery devices or even biological samples such as single cells. The cold intro and cold stage of the system makes it possible to image tissue sections or single cells under cryo conditions to better preserve their chemical composition. Combined with the high spatial resolution and parallel MSMS capability of the instrument it makes the TOF-SIMS mass spectrometer of the platform a valuable tool for both biomedical and pharmaceutical research.