Abstract
The following invention - Graphene Enhanced Secondary Ion Mass Spectrometry - (pending European patent application no. EP 16461554.4) is related to a method of analysing a solid substrate by means of Secondary Ion Mass Spectrometry (SIMS). It comprises the steps of providing a graphene layer over the substrate surface and analysing ejected secondary anions through mass spectrometry analysis. The graphene layer acts as a kind of filament that emits a lot of secondary electrons during the experiment which significantly increases the negative ionization probability and thus the intensity of the SIMS signal can be more than two orders of magnitude higher than that of a similar sample without graphene. The method is particularly useful for the analysis of surfaces, 2D materials and ultra-thin films. The intensity of dopants and contamination signals can be enhanced up to 35 times, which approaches the detection limit of ~1015atoms/cm3, otherwise unreachable in a standard static SIMS analysis.
Highlights
Secondary Ion Mass Spectrometry (SIMS) is a very precise analytical technique for determining the elemental composition of a sample[1,2,3,4,5,6]
In this work we present Graphene Enhanced Secondary Ion Mass Spectrometry (GESIMS) - a new technique for enhancing the detection limit in the analysis of thin materials
To understand the process correctly it is necessary to remember that the intensity of SIMS signals depends on the secondary ion yield, which is defined as the number of emitted ions A−/A+ per incident ion
Summary
SIMS is a very precise analytical technique for determining the elemental composition of a sample[1,2,3,4,5,6]. For most materials it is reported to be in the range of 1015–1016 atoms/cm[311], sometimes even as good as 1012 atoms/cm[312] These optimum detection limits, are achieved during the dynamic SIMS (dSIMS) mode. 2D materials and ultra-thin films are analysed ideally in a special mode called static SIMS (sSIMS)[13,14,15], in which a low density ion beam ensures that ions are emitted only from monolayers 1 to 3. Oxygen flooding can further enhance the secondary ion yields of some negative ions[21,22,23] Using these techniques yields acceptable results, but in the cases of surfaces, 2D materials and ultra-thin films, it is often not enough to reach the desired detection limit, in the case of trace elements. All these methods employed SIMS for characterising the graphene layer, while the composition of support material underneath was not analysed
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