How FIB-SIMS is Revolutionizing Science
In the hidden nanoworld, a powerful tool slices materials atom by atom, revealing a spectacular three-dimensional reality invisible to the naked eye.
Imagine being able to slice a human hair lengthwise thousands of times, map the exact chemical composition of each infinitesimally thin slice, and then reconstruct a perfect three-dimensional model—all without physically touching it.
This is the power of nanoscale tomographic imaging using Focused Ion Beam sputtering, Secondary Electron Imaging, and Secondary Ion Mass Spectrometry (FIB-SIMS). This groundbreaking technology allows scientists to deconstruct and analyze materials with breathtaking precision, revealing a hidden world that holds the key to advancements in everything from smartphone electronics to life-saving medicines.
FIB-SIMS enables analysis at scales smaller than 50 nanometers, revealing details invisible to conventional microscopy.
At its core, nanoscale tomography is similar to creating a 3D medical CT scan, but for microscopic objects and with far greater resolution. The process involves repeatedly slicing away layers of a material and analyzing each newly exposed surface. The result is a three-dimensional "map" that shows not just the structure, but also the exact chemical elements and isotopes present at every single point in the volume.
The magic happens through the seamless integration of three powerful techniques inside a single instrument, often called a FIBSEM (Focused Ion Beam-Scanning Electron Microscope).
This is the nanoscale scalpel. A beam of gallium (Ga) ions is focused to a fine point—often less than 10 nanometers wide—and scanned across the sample surface. When these high-energy ions strike the surface, they knock off, or "sputter," atoms and molecules, meticulously etching the material away layer by layer. Modern plasma FIBs can use heavier xenon (Xe) ions for faster milling, removing material at rates on the order of cubic micrometers per nanoampere per second 3 5 .
As the ion or a separate electron beam hits the surface, it knocks loose "secondary electrons." By collecting these electrons, a highly detailed, topographical image of the freshly exposed surface can be created. This acts as the structural photograph for each slice, showing the physical landscape with a resolution that can approach a single nanometer 5 .
This is the chemical detective. Some of the particles sputtered by the ion beam are electrically charged, becoming "secondary ions." These ions are instantly vacuumed into a mass spectrometer—a device that sorts them by their mass and charge. By identifying these ions, SIMS can determine the precise elemental and isotopic composition of the surface with exceptional sensitivity, sometimes detecting impurities in the parts-per-billion range 5 6 .
In a FIBSIMS instrument, these processes are run in a cycle: the FIB mills away a thin slice, the SEM images the new surface, and the SIMS analyzes its chemistry. A computer then stacks this data, slice by slice, to reconstruct a complete 3D model 5 .
To understand the power of this technique, consider its application in the semiconductor industry, where understanding the 3D distribution of dopants (trace elements that control electrical properties) is crucial for making faster, more efficient chips.
In a pivotal demonstration, researchers used a FIB-SIMS system equipped with a Time-of-Flight (TOF) mass spectrometer to analyze a cross-section of a complex integrated circuit 5 . The goal was to pinpoint the location and concentration of specific dopants like boron and phosphorus within the silicon matrix, features that are utterly invisible to even the most powerful electron microscopes.
The experimental procedure was a marvel of precision 5 :
A small piece of the semiconductor was carefully mounted inside the vacuum chamber of the FIBSEM instrument.
The SEM was first used to image the region of interest, identifying a specific transistor or structure for analysis.
This critical phase involved three simultaneous processes: slicing with the FIB, imaging with the SEM, and chemical analysis with SIMS.
The stack of secondary electron images was aligned to create a 3D structural volume. The mass spectrometry data for each "voxel" (a 3D pixel) was then overlaid, creating a corresponding 3D chemical map.
The experiment produced spectacular results. The 3D reconstruction allowed engineers to see, for the first time, the precise three-dimensional shape of doped regions and how they interacted with other components. The data was often visualized as 3D renderings where colors represented different elements—for example, red for boron and green for oxygen 5 .
| Parameter | Capability | Implication |
|---|---|---|
| Lateral Resolution | < 50 nanometers 5 | Allows mapping of features in modern computer chips. |
| Depth Resolution | < 10 nanometers 5 | Enables precise layer-by-layer analysis of thin films. |
| Useful Yield | 10⁻⁴ to 10⁻² ions/detected particle 5 | Determines the efficiency and speed of chemical detection. |
| Mass Resolution | Can distinguish between masses differing by ~0.01 amu 6 | Allows separation of atomic ions from molecular interferences. |
| Element/Isotope | Detected Mass (amu) | Relative Concentration | Significance |
|---|---|---|---|
| Boron (¹¹B⁺) | 11 | High in doped regions | Confirms accurate dopant placement for transistor function. |
| Silicon (²⁸Si⁺) | 28 | Matrix (Very High) | Forms the primary structure of the semiconductor chip. |
| Oxygen (¹⁶O⁺) | 16 | Medium | Can indicate unwanted oxidation, which degrades performance. |
| Phosphorus (³¹P⁺) | 31 | High in doped regions | Another key dopant used to modulate electrical properties. |
The analysis revealed whether the dopant profiles were sharp and confined as designed, or if they had diffused unintentionally during manufacturing. This information is critical as transistors shrink to atomic scales, where a few misplaced atoms can cause a chip to fail. The ability to conduct such analysis with tens of nanometers resolution directly accelerated the development of more powerful and reliable electronic devices 5 .
Pulling back the curtain on this complex technique reveals a suite of sophisticated tools and reagents.
The core platform housing both the ion "scalpel" and electron "microscope."
The most common FIB source, providing a finely focused beam of Ga+ ions for precise milling 5 .
Maintains a pristine environment, preventing air molecules from interfering with the ion beams or contaminating the sample.
Precisely position and orient the sample, often with sub-micrometer stability, for days-long analyses.
Processes the massive datasets and reconstructs the 3D models with elemental mapping.
FIB-SIMS tomography is no longer confined to semiconductors. It is now a cornerstone of modern materials science. Researchers use it to study the distribution of drugs in polymer nanoparticles for targeted therapies, to analyze the solid-electrolyte interface in battery electrodes for longer-lasting energy storage, and to map isotopic ratios in geological samples to unravel the history of our solar system 5 7 .
The future of this field lies in pushing the limits of resolution and speed. Emerging techniques like tomographic ptychography, a coherent X-ray imaging method, can provide complementary high-resolution data on organic and inorganic interfaces 8 . Furthermore, new machine learning algorithms are being developed to tackle the "missing wedge" problem in tomography, dramatically improving 3D reconstructions even when data is incomplete 9 . As these tools continue to evolve, our vision into the nanoscale world will only become sharper, unlocking new possibilities across science and technology.
FIB-SIMS enables precise mapping of drug distribution within nanoparticles, optimizing targeted drug delivery systems for more effective treatments with fewer side effects.
By analyzing the solid-electrolyte interphase in batteries, FIB-SIMS helps develop longer-lasting, faster-charging energy storage solutions critical for electric vehicles and renewable energy.
Isotopic mapping of geological samples provides insights into Earth's history and the formation of our solar system, with applications in resource exploration and planetary science.
From analyzing corrosion in alloys to studying failure mechanisms in composites, FIB-SIMS provides crucial insights for developing stronger, more durable materials.