Spectrum simulation of rough and nanostructured targets from their 2D and 3D image by Monte Carlo methods

Abstract

Corteo is a program that implements Monte Carlo (MC) method to simulate ion beam analysis (IBA) spectra of several techniques by following the ions trajectory until a sufficiently large fraction of them reach the detector to generate a spectrum. Hence, it fully accounts for effects such as multiple scattering (MS). Here, a version of Corteo is presented where the target can be a 2D or 3D image. This image can be derived from micrographs where the different compounds are identified, therefore bringing extra information into the solution of an IBA spectrum, and potentially significantly constraining the solution. The image intrinsically includes many details such as the actual surface or interfacial roughness, or actual nanostructures shape and distribution. This can for example lead to the unambiguous identification of structures stoichiometry in a layer, or at least to better constraints on their composition. Because MC computes in details the trajectory of the ions, it simulates accurately many of its aspects such as ions coming back into the target after leaving it (re-entry), as well as going through a variety of nanostructures shapes and orientations. We show how, for example, as the ions angle of incidence becomes shallower than the inclination distribution of a rough surface, this process tends to make the effective roughness smaller in a comparable 1D simulation (i.e. narrower thickness distribution in a comparable slab simulation). Also, in ordered nanostructures, target reentry can lead to replications of a peak in a spectrum. In addition, bitmap description of the target can be used to simulate depth profiles such as those resulting from ion implantation, diffusion, intermixing, etc. Other improvements to Corteo include the possibility to interpolate the crosssection in angle-energy tables, and the generation of energy-depth maps.

Influence of tungsten fuzz on energy spectra of helium recoiled by 10 MeV oxygen ions

“…It is well known that ion beam analysis (IBA) methods like ERDA and NRA are quantitative methods for depth profiling of elements -at least for smooth samples. However, surface roughness can be especially a problem for ERDA, where it is well known that already moderate surface roughnesses can modify the shape of spectra significantly [19,20,21]. Simulation methods allowing to quantify IBA measurements on samples with moderate roughness have been developed [22].…”

Computer simulation of backscattering spectra from paint

“…Multiple small-angle scattering was taken into account as energy spread, dual large-angle scattering [16] was neglected. An intercomparison between the codes STRUCTNRA [11], RBS-MAST [17], CORTEO [18] and F95-Rough [19] showed very good agreement between all codes as well as with experimental data of 4 He ions backscattered from a grid structure [20].…”

Intercomparison of ion beam analysis software for the simulation of backscattering spectra from two-dimensional structures

“…See Ref. [28] for details. A mode called Full-RBS is also available where the main scattering approximation is avoided, but is computationally intensive.…”

“…F95-Rough [26] is a code for the simulation of common RBS spectra including surface roughness as 2D cuts of the measured sample. The Monte-Carlo code CORTEO [27] has been recently extended to use two-or three-dimensional sample structures as input [28].…”