Metal‐assisted SIMS for three‐dimensional analysis using shave‐off section processing

Abstract

Three-dimensional microanalysis of the microstructure of organic materials is important in the development and progress of analytical methods on the micro-to-nanometer scales. We have developed a novel three-dimensional microanalysis method using focused ion beams for section processing (shave-off scanning) and time-of-flight secondary ion mass spectrometry for mapping. Shave-off scanning can effectively create an arbitrary section on a sample set against composites materials with a wide variety of shapes; three-dimensional sample images are then obtained by alternately operating two focused ion beams. In this study, we adapted metal-assisted secondary ion mass spectrometry for three-dimensional microanalysis. We have devised a unique method whereby gold is deposited on a section to be analyzed after every shave-off sectioning by setting a gold plate at the back of the sample. Consequently, gold was observed to be deposited on the created cross-section concurrently with shave-off sectioning, resulting in a substantially enhanced secondary ion intensity.

Improvement of Lipid Detection in Mouse Brain and Human Uterine Tissue Sections Using In Situ Matrix Enhanced Secondary Ion Mass Spectrometry

“…Cluster ions (e.g., Bi n + or C 60 + ) indeed provided much higher sputtering and secondary ion yields than monoatomic projectiles for organic samples, and moving from large argon to water clusters proved very efficient to increase ionization of biologically relevant molecules, probably via proton transfer from the cluster. , (2) Postionization right before the entrance of the analyzer, using, for example, lasers, also showed impressive results . (3) As the right sample preparation makes a large difference in the obtained mass spectra, − several research groups investigated the idea of increasing the acquired signal by cleverly modifying the surface via spraying a thin metallic layer on top of the samples (MetA-SIMS), − exposing the sample to trifluoroacetic acid or ammoniac vapor , or depositing an organic acidic MALDI matrix layer (ME-SIMS). − Recently, an in situ MALDI matrix transfer procedure compatible with 2D and even 3D molecular imaging by SIMS was proposed and tested by the research team of Gilmore and by our team. , The idea is to take advantage of the low sputtering damage of the 10 keV Ar 3000–5000 + ion beam to transfer MALDI matrices, which have shown signal enhancement potential in SIMS, from a reservoir to the sample located next to it (Figure ). Signal enhancements were observed on different reference biomolecules after the transfer of α-cyano-4-hydroxycinnamic acid, 2,5-dihydroxybenzoic acid, formic acid, as well as 3-nitrobenzonitrile compared to the native sample analysis.…”

ToF-SIMS Depth Profiling of Metal, Metal Oxide, and Alloy Multilayers in Atmospheres of H2, C2H2, CO, and O2

“… 64 , 65 However, depth profiling combined with metal-assisted SIMS can only be performed while using a nonconventional experimental setup. 66 The ionization yield can also be increased by depositing ionic liquids 67 or graphene oxide 68 on the sample surface. Furthermore, the samples can be mixed with specific matrices, 69 − 71 but with this approach we lose the surface sensitivity.…”

“…In the case of resonant laser-SNMS, we must know exactly what is being analyzed, and in the case of the nonresonant approach, we must make sure that the laser intensity is high enough to ionize all the particles . The sputtered neutrals can also be postionized with an electron beam, similar to a laser. − We can also intentionally exploit the matrix effect by depositing a thin metal layer, usually Au or Ag. , However, depth profiling combined with metal-assisted SIMS can only be performed while using a nonconventional experimental setup . The ionization yield can also be increased by depositing ionic liquids or graphene oxide on the sample surface.…”

Method for Molecular Layer Deposition Using Gas Cluster Ion Beam Sputtering with Example Application In Situ Matrix-Enhanced Secondary Ion Mass Spectrometry

“…In situ sputter deposition has previously been employed in SIMS to apply matrix material for the purpose of ion yield enhancement, depositing elemental species (e.g., metals in metal assisted SIMS, MetA-SIMS ,− ) sputtered by atomic ion beams. If organic compounds are used for matrix enhancement, it is critical to retain the molecular structure of the matrix compound.…”