Numerical investigation of depth profiling capabilities of helium and neon ions in ion microscopy

Abstract

The analysis of polymers by secondary ion mass spectrometry (SIMS) has been a topic of interest for many years. In recent years, the primary ion species evolved from heavy monatomic ions to cluster and massive cluster primary ions in order to preserve a maximum of organic information. The progress in less-damaging sputtering goes along with a loss in lateral resolution for 2D and 3D imaging. By contrast the development of a mass spectrometer as an add-on tool for the helium ion microscope (HIM), which uses finely focussed He+ or Ne+ beams, allows for the analysis of secondary ions and small secondary cluster ions with unprecedented lateral resolution. Irradiation induced damage and depth profiling capabilities obtained with these light rare gas species have been far less investigated than ion species used classically in SIMS. In this paper we simulated the sputtering of multi-layered polymer samples using the BCA (binary collision approximation) code SD_TRIM_SP to study preferential sputtering and atomic mixing in such samples up to a fluence of 1018 ions/cm2. Results show that helium primary ions are completely inappropriate for depth profiling applications with this kind of sample materials while results for neon are similar to argon. The latter is commonly used as primary ion species in SIMS. For the two heavier species, layers separated by 10 nm can be distinguished for impact energies of a few keV. These results are encouraging for 3D imaging applications where lateral and depth information are of importance.

Comparison between Focused Electron/Ion Beam-Induced Deposition at Room Temperature and under Cryogenic Conditions

“…However, this process could be relevant for the diffusion of carbon and oxygen atoms under Ga irradiation in Cryo-FIBID, meaning that the surface concentrations of oxygen and carbon in the simulations might be overestimated and that of tungsten underestimated. In a previous study on the rare gas ion irradiation of polymer samples, including diffusion processes was essential for a correct modelling of the processes under ion irradiation [60,61].…”

Defect formation in multiwalled carbon nanotubes under low-energy He and Ne ion irradiation

“…This is required for the simulation of helium and neon ion bombardment of organic samples. The diffusion coefficients for the different noble gas species have been taken from previous work [ 43 ]. For He, a diffusion coefficient of 4.8 × 10 −6 cm 2 s −1 was used, and for Ne a value of 1.1 × 10 −6 cm 2 s −1 .…”

“…For instance, the HIM has already been used for the imaging of graphene flakes [ 36 ] and their etching [ 37 ], as well as the imaging of SWCNTs [ 38 ]. After the development of a compact mass spectrometer for this instrument [ 39 – 40 ], the detection and imaging of sputtered ions can also be used for process control [ 41 ], including carbon-containing materials [ 42 – 43 ].…”

Structural and chemical evolution of Au-silica core–shell nanoparticles during 20 keV helium ion irradiation: a comparison between experiment and simulation

“…In the present work, this option was applied to helium. The parameter for diffusion is kept identical to previous work [34][35][36] . Although the diffusion coefficient in the core-shell particles is certainly lower than in polymer samples, TEM imaging gives no evidence for helium accumulation in the nanoparticles.…”