Characterization of nanomaterials relies on complementary spectroscopic, microscopic, scattering and diffraction, and particle analysis methods to determine size, shape, crystal structure, surface chemistry, and interfaces with high precision at the 1–100 nm scale.

Why characterization matters

Nanomaterials exhibit size-dependent optical, electronic, catalytic, and mechanical properties, so measuring size distribution, morphology, crystallinity, and surface chemistry is essential for design, quality control, safety, and application performance across energy, health, and electronics.

Spectroscopic methods

Spectroscopy probes how electromagnetic radiation interacts with matter to reveal composition, bonding, and surface states, often in a nondestructive, high-sensitivity manner for nanomaterials.

Raman spectroscopy: Inelastic scattering of monochromatic light produces a fingerprint spectrum whose peak positions, widths, and intensities report on molecular vibrations, crystal order or disorder, stress or strain, and phase in systems such as graphene, CNTs, and quantum dots.

FTIR spectroscopy: Absorption bands identify functional groups and surface modifications, enabling tracking of coatings, ligand exchange, and polymer–nanoparticle interactions in diverse sample forms (powders, films, dispersions).

XPS (X-ray photoelectron spectroscopy): Surface-sensitive (1–10 nm) technique quantifying elemental composition and chemical states, widely used to determine oxidation states, adventitious carbon, and depth profiles of oxides, metals, and hybrids.

UV–Vis spectroscopy: Monitors plasmonic peaks of noble-metal nanoparticles and excitonic features of semiconducting nanocrystals, aiding size estimation, aggregation assessment, and reaction monitoring in colloids.

NMR and SERS (selected cases): NMR informs ligand binding and dynamics on nanoparticle surfaces, while SERS boosts vibrational signals near plasmonic nanostructures for trace-level detection of adsorbates.

Microscopic methods

Microscopy directly visualizes morphology, size, and interfaces; combining techniques improves confidence and mitigates artifacts from any one method.

TEM (transmission electron microscopy): Atomic-to-nanometer resolution imaging of internal structure, grain boundaries, and defects. With EDX or EDS it provides local composition. In situ TEM enables real-time observation of reactions and phase changes, although sample preparation is demanding and beam damage may occur.

SEM (scanning electron microscopy): High-depth-of-field surface imaging for shape and agglomeration. Signals such as secondary or backscattered electrons provide topography and Z-contrast. Small or uncoated particles can show low contrast and may need conductive coatings.

AFM (atomic force microscopy): Three-dimensional topography with sub-nanometer z-resolution in air or liquids, capturing height distributions, nanomechanics, and electrical or magnetic maps. It offers material-independent contrast but can be sensitive to cleanliness and tip convolution laterally.

Scattering and diffraction

Reciprocal-space methods give ensemble-averaged size, structure, and stability information, critical for powders and dispersions.

XRD (X-ray diffraction): Determines crystal structure, phase purity, and crystallite size via peak positions and broadening. It is indispensable for nanocrystal identification and monitoring synthesis outcomes.

SAXS or DLS: Small-angle scattering and dynamic light scattering estimate particle size and distribution in suspensions. DLS returns a hydrodynamic diameter influenced by solvation and aggregation state.

Surface area, porosity, and charge

Surface-driven properties require metrics beyond size and phase for accurate performance prediction and toxicology.

BET gas adsorption: Quantifies specific surface area and pore size distributions, pivotal for catalysts, adsorbents, and high-surface nanostructures.

Zeta potential: Assesses surface charge and colloidal stability, informing dispersion protocols and functionalization efficacy in aqueous and nonaqueous media.

Compositional and chemical mapping

Coupled or correlative measurements localize chemistry at the nanoscale for core–shells, heterostructures, and doped systems.

TEM-EDS or EDX: Elemental mapping of internal features, interfaces, and shell thicknesses with nanometric resolution in cross-sections and particles.

XPS depth profiling: Angle-resolved or ion-etching approaches reveal surface gradients, oxide layers, and interdiffusion across 1–10 nm depths.

Practical selection guide

Technique choice depends on what needs measuring, sample form, and acceptable preparation or beam exposure. Multiple orthogonal methods are typically combined for robust results.

Size and shape: TEM for highest resolution, SEM for surface morphology at scale, AFM for three-dimensional height and nanomechanics in air or liquid, DLS or SAXS for dispersions.

Crystal structure: XRD for phase and crystallite size, Raman for order or strain, TEM for lattice-resolved imaging and defects.

Surface chemistry: XPS for elemental states and contaminants, FTIR or Raman for functional groups, UV–Vis for optical signatures of size and aggregation [7][6].

Stability and porosity: Zeta potential for colloidal stability, BET for surface area and pores, UV–Vis or DLS time series for aggregation kinetics.

Typical workflow for nanoparticles

A practical, high-confidence workflow often proceeds from ensemble to local probes and back for validation and scale-up.

Screen colloidal size and stability with DLS and UV–Vis to verify dispersion quality and detect aggregation.

Determine morphology and size distribution by TEM and cross-check with AFM for height statistics in air or liquid when relevant.

Identify phase and crystallinity using XRD and assess disorder and strain by Raman where applicable.

Quantify surface functionalization via FTIR and XPS and profile near-surface chemistry if coatings or oxidation layers are engineered.

Notes on limitations and artifacts

Awareness of technique-specific pitfalls improves data quality and interpretation consistency across labs and instruments.

Beam and preparation effects: TEM or SEM may alter sensitive samples, coatings improve SEM contrast but introduce dimensional error, and low-dose protocols or cryo-preparation controls mitigate damage.

Convolution and ensembles: AFM tip shape broadens lateral size, DLS overweights larger aggregates, and reporting methods, models, and uncertainty is key for comparability.