Background #
This section explores the underlying theoretical concept of FIBs. The ion solid interactions are absolutely essential knowledge for successful FIB experiments. Knowledge of these interactions informs interpretation of results. Without solid understanding of these underlying principles, misinterpretation, poor quality results, artifacts as well sample damage can easily occur.
This section introduces the basic ion solid interactions. And explores how the different applications, like nano/microstructuring, imaging, defect engineering, nanoscale analysis and lithography come out of the ion-solid interactions. Lastly, this section will highlight the differences between the different FIB ion species; what makes the GaFIB, PFIB and the HIM special.
Overview Ion Solid Interactions #
Let’s take a look at the possible ion-solid interactions which occur when an energetic ion hits a sample. The sample consists of atoms with which the ion beam interacts. The ions (no matter the ion species) lose their energy in collisions with the sample atoms. The ion comes to rest in the sample at a certain depth leading to implantation.
Until the ion comes to rest, the collisions can lead to a multitude of interactions (see figure below) such as: (1) ion implantation, (2) sputtering of sample surface atoms, (3) sample atom displacements including vacancies, (4) a collision cascade and replacement collisions and dislocations, (5) phonons, (6) backscattered ions. (7) Secondary electron, (8) secondary ion emission, and/or (9) polymerization.
Here is a link to the definition page for ion solid interactions which goes into detail explaining the different interaction types. It provides the opportunity to explore the underlying nuclear and electronic interactions in more detail.
Energy Losses #
Charged particles, electrons or ions, interact with the atoms in the sample in two predominant ways:
1. They interact with the sample atom’s electron cloud (inelastic collisions). 2. They interact with the sample atom’s nucleus (elastic interactions). With every interaction, energy is transferred (and/or lost). The entire energy loss 𝑑𝐸/𝑑𝑥 consists of both contributions, the nuclear (elastic) energy losses [𝑑𝐸/𝑑𝑥]𝑛𝑢𝑐𝑙 and the electronic (inelastic) energy losses [𝑑𝐸/𝑑𝑥]𝑒𝑙𝑒𝑐 :
𝑑𝐸/𝑑𝑥= [𝑑𝐸/𝑑𝑥]𝑛𝑢𝑐𝑙+ [𝑑𝐸/𝑑𝑥]𝑒𝑙𝑒𝑐
These 2 types of interaction give rise to all the different interactions described in the overview section. Which of these interactions occurs depends on the energy transfer, the ion species as well as on the sample itself. In general, all of the different interactions occur. A lot of ions hit the sample throughout FIB work and the statistics behind the ion solid interactions are important: some interactions occur more frequently than others for different ion species / FIB parameters.
Special Interest Note: Inelastic collisions with the nucleus as well as elastic collisions with the electrons can theoretically occur. This, however, is extremely unlikely for the energies used in ion microscopes and these interactions are therefore not consider
Energy Losses VS Interaction Type #
Nuclear energy losses (interactions with the sample atom nucleus): Elastic collisions, sputtering, SI, dislocations, amorphization, vacancies, phonons, energy is conserved, large discrete energy losses in interact
Electronic energy losses (interactions with the sample atom electrons):Inelastic collisions, SE, phonons, plasmons (in metals), energy is not conserved, small energy loss per collision, ion deflection is negligible, induced Lattice disorder (sample) can be neglected, induce heat
Further / Detailed Information and Definitions #
Further, in depth information and definitions about the different interactions can be found in the following subpage: HERE LINK ‘Definitions Ion Solid Interactions’
