How Scientists Map Chemicals at the Nanoscale
In the tiny world of nanomaterials, seeing is more than believing—it's the key to revolutionary innovation.
Imagine trying to understand a mosaic by looking at it from a mile away. The overall shape might be visible, but the individual colored tiles and their precise arrangement remain a mystery. This is the challenge scientists have faced for decades in trying to understand materials at the nanoscale.
Mapping chemicals with nanoscale resolution—identifying the precise chemical composition of materials at dimensions of billionths of a meter—has emerged as one of the most powerful capabilities in modern science. It allows researchers to see not just the physical landscape of tiny structures, but their very chemical essence, revealing a hidden world where composition dictates behavior.
At the nanoscale, materials display unique properties that don't exist at larger dimensions. A material's color, strength, electrical conductivity, and chemical reactivity can change dramatically based on its size and structure.
Many not-yet-understood phenomena at this scale could have a remarkable impact on both our fundamental understanding of matter and potential applications in fields ranging from medicine to computing 1 .
The behavior of nano-composite materials depends largely on nanoscale chemical inhomogeneities—tiny variations in chemical composition that occur across minute distances 1 .
Traditional light-based microscopy techniques hit a fundamental barrier called the diffraction limit, preventing them from resolving features smaller than about half the wavelength of light used—typically around 200-500 nanometers . Since many chemical features and nanomaterials are much smaller than this limit, scientists needed new approaches to visualize the chemical landscape at these tiny dimensions.
Several innovative techniques have overcome the diffraction limit by combining different physical principles
This method, demonstrated by NIST researchers, uses a tunable infrared laser combined with an atomic force microscope (AFM). The sample absorbs IR light at wavelengths determined by its chemical composition, causing thermal expansion that is detected by the AFM tip.
This approach improves spatial resolution by a factor of about a thousand compared to conventional IR microscopy while maintaining chemical specificity .
Similar to PTIR, this technique maps chemical functional groups on materials like graphene with 32 nm spatial resolution, even on monolayers just 1.7 nm thick.
It can distinguish between different molecular moieties and detect subtle spectral changes arising from chemical effects 3 .
This method combines the topographic imaging capability of scanning tunneling microscopy with the chemical specificity of Raman spectroscopy.
It can map electrochemical reactivity with ~10 nm spatial resolution, allowing scientists to observe chemical reactions occurring at specific defect sites on surfaces 5 .
This cutting-edge approach combines elastic and inelastic scattering signals to create detailed 3D chemical maps at the nanometer scale.
By merging structural and chemical information, it enables sub-nanometer resolution of chemical distribution in three dimensions 2 .
Using synchrotron x-rays, this technique provides direct elemental information and is particularly valuable for accessing chemical gradients at the nanoscale with minimal intrusiveness 1 .
| Technique | Key Principle | Spatial Resolution | Key Applications |
|---|---|---|---|
| AFM-IR/PTIR | IR absorption detected via AFM tip | ~20-30 nm 7 | Polymer blends, battery materials |
| EC-TERS | Enhanced Raman scattering at AFM tip | ~10 nm 5 | Electrochemical reactions, catalysis |
| Fused Electron Tomography | Combined elastic/inelastic scattering | <1 nm 3D resolution 2 | Nanoparticle assemblies, core-shell structures |
| XPEEM | X-ray photoelectron emission | Tens of nanometers 1 | Binary alloys, semiconductor nanostructures |
| Scanning Transmission X-ray Microscopy (STXM) | X-ray absorption at element-specific edges | Nanoscale 4 | Oxidation state mapping in geological materials |
A landmark study published in Nature Communications in 2024 demonstrated an innovative approach that overcomes long-standing limitations in nanoscale chemical imaging 2 .
The researchers configured an electron microscope to simultaneously collect two types of signals—elastic scattering (for structural information) and inelastic scattering (for chemical composition).
They recorded images of the specimen at multiple tilt angles, gathering both structural and chemical data from each orientation.
Using advanced computational algorithms developed by the team, they combined the complementary datasets to reconstruct a complete 3D map showing both structure and chemical composition.
The team compared results from their fused approach with standard methods and known structures to verify accuracy and resolution.
The power of this new method was demonstrated through several key applications:
| Material System Studied | Key Finding | Significance |
|---|---|---|
| Gold and iron oxide nanoparticle superlattice | Clear 3D visualization of self-organization | Enables design of optimized metamaterials |
| Manganese oxide shell/Cobalt oxide core nanocrystal | Precise measurement of shell thickness and coverage | Improves catalyst and battery material design |
| Multiple elemental systems (Au, O, Cu, Co) | Superior accuracy compared to standard tomography | Establishes new benchmark for chemical quantification |
The advanced techniques for nanoscale chemical mapping rely on specialized materials and instrumentation
Detects minute forces or thermal expansion
Example Use Case: Topography imaging and IR signal detection in AFM-IR 6
Provides wavelength-specific excitation
Example Use Case: IR absorption spectroscopy at specific molecular vibrations
Generates intense, tunable x-ray beams
Example Use Case: Element-specific core level excitation in XPEEM 1
Chemically interact with specific sites
Example Use Case: Mapping basic sites on catalyst particles via AFM-IR 7
Well-defined model systems
Example Use Case: Method development and validation (e.g., Ge/Si islands) 1
Structures with defined interfaces
Example Use Case: Testing 3D chemical mapping capabilities 2
The ability to map chemicals at the nanoscale is already driving innovations across multiple fields
AFM-IR nanospectroscopy has enabled researchers to map the distribution and geometry of basic sites on supported Mg-Al mixed oxide particles with ~20 nm resolution. This reveals how structural heterogeneities affect catalytic reactivity, guiding the design of more efficient catalysts for biomass conversion 7 .
AFM-IR has been used to study chemical changes in lithium iron phosphate nanocrystals during delithiation. The technique showed that delithiation starts from the external edges of nanocrystals, providing crucial insights for developing better energy storage materials 6 .
Researchers have used these techniques to study core-shell nanoparticle structures crucial for drug delivery. For example, AFM-IR can clearly distinguish between hydrophobic polystyrene cores and hydrophilic polymethacrylate shells in star block copolymer nanoparticles, enabling optimization of drug carrier designs 6 .
The semiconductor industry benefits from techniques like XPEEM that can measure stoichiometry within individual self-organized nanostructures, revealing features like silicon-rich edges versus germanium-rich centers in semiconductor islands—critical information for understanding interdiffusion dynamics 1 .
As techniques for nanoscale chemical mapping continue to evolve, scientists are working to extend these capabilities further. Future directions include:
In nano-heterostructures to understand material properties 1
Further enhancing spatial resolution and detection limits 2
The ability to see chemical composition with nanoscale resolution is transforming our understanding of the material world. As these techniques become more accessible and powerful, they will undoubtedly unlock new discoveries and innovations across science and technology. From developing more efficient energy systems to designing targeted therapeutics, the impact of seeing chemistry at the nanoscale will be felt far beyond the laboratory, shaping the technologies of tomorrow through the invisible building blocks of matter.