Static Time-of-Flight Secondary Ion Mass Spectrometry
NREL uses static time-of-flight (TOF) secondary ion mass spectrometry (SIMS) on a variety materials for analyzing surface sensitivity, elemental or molecular composition, images, and depth profiling.
How It Works
We used the high mass resolution and mass accuracy of TOF SIMS to study surface cleanliness of in-oxide-coated glass after different types of isolation scribes and cleaning processes. Not all processes were equal. As-received in tin oxide was heavily contaminated with silicone oils (not shown). An acidic wash resulted in contamination by Fe and other metals. Without high mass accuracy, the CaO signal might be mistaken for Si2 or Fe mistaken for CaO.
Static SIMS uses a pulsed primary ion beam to sputter-remove material from the top monolayer of a sample. Secondary ions are collected and focused into a reflectron TOF mass spectrometer. The combination of low primary-ion density (low surface damage) and high transmission of the TOF analyzer (high sensitivity) makes the technique extremely useful for studying the top monolayer of a surface. The large mass range of the TOF analyzer makes the instrument well suited for detecting trace levels of organic contaminants on surfaces.
Depth profiling is also possible in combination with high-current, low-energy cesium and argon sputter sources. Information on chemical structure is especially useful when combined with X-ray photoelectron spectroscopy analysis.
Applications
Surface Sensitive
Uses low doses of primary ions to ensure that below the static limit, energy secondary ion comes from an undisturbed region of the surface. High vacuum promotes a clean specimen surface. Multiple ion sources (liquid-metal gallium and argon) promote analytical flexibility.
Elemental and Molecular Analysis
Performs mass analysis to determine the elemental or molecular composition (or both) of the top monolayer of a material's surface. Can distinguish elements and molecules with masses ranging from 1 to >10,000 amu. High mass resolution (M/ΔM > 7000) allows precise differentiation of secondary-ion species.
Wide Range of Materials
Used for a wide range of organic and inorganic materials, including thin films, solid-state materials, ceramics, polymers, biological samples, and catalyst particles.
Imaging
Generates images using a raster scanned probe to determine the lateral distribution of surface elemental and molecular species, with spot sizes down to 0.5 µm for the gallium liquid-metal ion source. Collecting a complete spectrum at every pixel allows for retrospective analysis of the image data.
Depth Profiling
Provides high-resolution depth-profiling capabilities using low-energy cesium, and argon or oxygen sputter guns. Collecting an entire spectrum for each point allows for retrospective analysis of depth-profile data.
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