G-SIMS : Mass spectrometry for surface and interface analysis : Research : Surface & Nanoanalysis : Science + Technology : National Physical Laboratory

G-SIMS Research at NPL

A flowchart of the four practical steps in G-SIMS,
along with the purpose and expected outputs of each step

G-SIMS [1] (Gentle Secondary Ion Mass Spectrometry) was developed at NPL for the identification of organics and complex molecules at surfaces. Using G-SIMS fragmentation pathway mapping (G-SIMS-FPM) [2,3], molecular structure may be reassembled from fragment ions, using the evolution of G-SIMS intensities as the surface plasma (with effective temperature T_p) is varied. Recently, we have developed a novel approach [4,5] based on SMILES (Simplified Molecular Input Line Entry Specification), to assist the reassembly process in an automated way. A computer program takes a parent structure, and goes through every possible fragmentation to provide a tree structure of fragmentation products and simulated fragmentation pathways. For any fragment, it is then possible to identify the molecular structure, its mass and a pathway to the parent. We find a good correlation between peak evolution in G-SIMS-FPM data and simulated pathways, which significantly enhances the application of G-SIMS-FPM to unknown materials. Once fragmentation pathways have been calculated, they are added to a database. We are currently developing a prototype web-based system, G-DB1, that allows analysts to generate and explore fragmentation pathways for any molecule. Recent further developments include G-tip technology [6] and the use of cluster ions for G-SIMS [7]. A summary flow chart for the use of G-SIMS, G-SIMS-FPM and G-DB1 is given above.

Selected Publications

[1] Static SIMS: towards unfragmented mass spectra - The G-SIMS Procedure, I S Gilmore and M P Seah, Appl Surf Sci, 161, 465 (2000).

[2] G-SIMS of crystallisable organics, I S Gilmore and M P Seah, Appl Surf Sci 203-204, 551 (2003).

[3] Organic molecule characterisation – G-SIMS, I S Gilmore and M P Seah, Appl Surf Sci, 231-232, 224 (2004).

[4] Identification of complex molecules at surfaces: G-SIMS and SMILES fragmentation pathways, F M Green, E A Dell, I S Gilmore, M P Seah, Int J Mass Spectrom, 272, 38 (2008).

[5] G-SIMS and SMILES: simulated fragmentation pathways for identification of complex molecules, amino acids and peptides, F M Green, I S Gilmore and M P Seah, Appl Surf Sci, 255, 852 (2008).

[6] Imaging G-SIMS: A novel bismuth-manganese source emitter, F M Green, I S Gilmore, M P Seah, F Kollmer and E Niehus, Rapid Comm Mass Spectrom, 22, 2602 (2008).

[7] Cluster primary ion sputtering: secondary ion intensities in static SIMS of organic materials, M P Seah, F M Green and I S Gilmore, J Phys Chem C, 114 (12), 5351 (2010)