Table 1 Surface characterization techniques for nHEAs

Technique

Information

Features

TEM (HRTEM, STEM)¹¹⁸

Bulk crystal structure, lattice defects (dislocations, stacking faults)

composition (qualitative and quantitive)

atomic-scale imaging

Bulk-sensitive (penetrates entire sample thickness).

Lateral: ~0.05–0.2 nm; depth resolution depends on sample thickness (bulk averaging).

Crystal defect analysis, nanoparticle morphology, interfacial atomic structure, in situ reactions.

EELS (Electron Energy-Loss Spectroscopy)¹¹⁹

Light element (B C N O)

Element composition (qualitative and quantitive)

Chemical state

Electronic configuration

The spatial resolution is higher (subnanometer), but it is greatly affected by the sample thickness.

LEIS (Low-Energy Ion Scattering)¹²⁰

Surface element composition

Detection depth 0.1-0.3 nm.

All elements (including H), but the signal is weaker for heavy elements.

Single atomic layer surface composition, adsorption molecular coverage, catalyst surface reconstruction.

AET (Atomic Electron Tomography)¹²¹

3D atomic distribution

Destructive (layer by layer evaporation of atoms), combined with mass spectrometry and location detection.

Lateral resolution ~0.3 nm, depth resolution ~0.1 nm.

Slow acquisition speed.

APT (Atom Probe Tomography)¹²²

Lateral resolution up to 0.1 nm (atomic level), low depth resolution ( ~ 1 nm).

Multi-angle fast imaging.

XPS (X-ray Photoelectron Spectroscopy)¹²³

Surface chemical state

Surface element composition (qualitative)

Quantitative elemental concentration

No direct structural data (only chemical states).

Surface adsorption, oxide layer analysis, interfacial chemistry.

XAS (synchrotron X-ray absorption spectroscopy)⁶⁸

Local atomic coordination (bond lengths, coordination numbers, disorder) electronic states

Limited to specific absorption edges (requires tuning X-ray energy).

sensitivity to coordination environments; suitable for probing local atomic arrangements (e.g., amorphous materials, defects, catalytic sites).

AES (Auger Electron Spectroscopy)¹²⁴

Chemical state (oxidation state, bonding environment)

Detection depth 1-3 nm.

Light elements (above Li) to heavy elements, but H, He can not be detected.

XRD (X-ray Diffraction)⁶⁹

Crystal structure (space group, cell parameters, preferred orientation)

phase composition analysis

Long range order ( > 10 nm).

Surface/interface structure cannot be characterized.

Not sensitive to amorphous/nano.

PDF (Pair Distribution Function)¹²⁵

Atomic spacing, coordination number, local bond length distortion

Short-range order (0.1-5 nm) reveals atomic spacing and local coordination environment.

Dependent model fitting (e.g. RMC, MD).

ND (Neutron Diffraction)¹²⁶

lattice distortion, defect sites, and lattice strain, neutron diffraction affords atomic-level information

lattice distortion, defect sites, and lattice strain, neutron diffraction affords atomic-level information.