Techniques
Time-of-flight secondary ion mass spectrometry (TOF-SIMS)
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is known to be a very versatile, extremely sensitive mass spectrometric technique that provides detailed information on the elemental as well as on the molecular composition of all kinds of solid surfaces with extremely high sensitivity.
The bombardment of a surface with energetic primary ions leads to the emission of atoms, clusters, intact molecules and fragments from the uppermost monolayer of a surface, and the ionised fraction of the emitted particles can be mass analysed.
TOF mass spectrometry is a pulsed primary ion beam tech- nique and based on the fact that secondary ions with the same energy but different masses travel with different velocities. Measuring the flight time for each ion over a fixed distance allows the determination of its mass.
The time-of-flight technique offers parallel detection of all secondary ion species with ultra-high transmission and high mass resolution. This technique can be used for virtually all kinds of conductive and non-conductive materials. In the ion microprobe mode, a highly focused ion beam is scanned over an area of interest and complete spectra are recorded for every pixel. In this way, images can be acquired for all atoms including hydrogen and molecules in parallel with high sensitivity. For a well-controlled removal of surface layers a second ion beam with low energy sputter ions like oxygen, cesium (200 eV - 2000 eV) or cluster ions is simultaneously used in order to measure depth profiles of all species with high depth resolution in the nanometer range (dual beam mode).
By the combination of imaging and sputtering, the distribution of all species in a 3-dimensional object can be analysed. For each voxel (volume pixel, 3-dimensional pixel in a 3D dataset) a complete mass spectrum with elemental and molecular in- formation is stored. This concept enables very powerful retrospective analysis capabilities. Spectra and profiles can be re- constructed from any user-defined region of interest, images and 3D distributions for every mass of interest.
This makes the technique very powerful for the 3D analysis of complex structures with “unknown” or partially “unknown” composition.
Bombardment of a surface with energetic primary ions
Scanning Force Microscopy (SFM)
Atomic Force Microscopy, or more generally Scanning Force Microscopy, has become the most versatile Scanning Probe Microscopy technique since its first application in 1986. Unlike the Scanning Tunneling Microscope, it is not limited to conductive surfaces: Applications nowadays cover varied fields such as polymers, semi-conducting quantum dots, hard discs, Nano-Electro Mechanical Systems (NEMS) or biological samples. Imaging can be performed in air, in vacuum, or in liquid. In a Scanning Force Microscope (SFM), a microscopic tip is scanned over the surface of interest and probes the local properties at each pixel of the scan region. Most commonly, a laser-beam deflection system transduces the tip-sample interaction into a macroscopic signal by measuring either the static or the dynamic deflection of a micro-mechanical lever, called a cantilever, which incorporates the force sensing tip and is usually manufactured by silicon micro-fabrication.
Various tip-sample interaction forces can be mapped and thus different properties of the surface can be imaged. An SFM cannot only map topography up to atomic resolution, it can also map other sample properties with nanometer scale resolution such as local mechanical properties, materials contrast, or electric and magnetic stray fields emanating from the surface.
Supported by FP 7 of the European Commission