Micro-area composition analysis is a specialized materials characterization service that determines the elemental and chemical composition of localized regions—such as inclusions, coatings, weld zones, defects, and foreign particles—at spatial resolutions ranging from the millimeter down to the nanometer scale. By combining scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), electron probe microanalysis (EPMA-WDS), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and ToF-SIMS, accredited third-party laboratories deliver accurate qualitative and quantitative results for failure analysis, quality control, and product development. This article explains the core principles, applicable standards, sample requirements, analytical capabilities, and typical industrial applications of micro-region compositional analysis.
Technical Overview
Materials are rarely chemically uniform. Inclusions, second phases, segregation, coatings, surface oxide layers, diffusion zones, weld interfaces, and contaminants often exist within regions only a few micrometers—or even nanometers—across. Bulk analytical techniques such as X-ray fluorescence (XRF) or ICP-OES provide only an average composition of the entire specimen and cannot resolve these local features. Micro-area composition analysis (also called micro-region or micro-volume analysis) solves this problem by focusing an excitation probe—an electron beam, ion beam, X-ray source, or laser—onto a precisely defined small region and collecting the characteristic signals emitted from that volume.
The fundamental principle relies on probe–matter interactions. When a finely focused electron beam strikes a specimen, it generates characteristic X-rays whose energies are unique to each element; when ions sputter the surface, emitted secondary ions carry elemental and molecular information; when X-rays irradiate a surface, photoelectrons and Auger electrons reveal both elemental identity and chemical bonding states. By detecting and spectrally resolving these signals, the elemental composition of a targeted micro-region can be determined qualitatively, semi-quantitatively, or with high quantitative accuracy against certified reference standards.
Key performance parameters that distinguish the available techniques include lateral resolution (from ~1 µm for SEM-EDS down to ~10 nm for AES and sub-nanometer for TEM-based methods), information depth (from several micrometers for X-ray-based methods down to 1–10 nm for surface-sensitive techniques), detection limits (from ~0.1 wt% for EDS down to ppm–ppb levels for WDS, SIMS, and LA-ICP-MS), and the ability to characterize light elements and chemical states. Standardized procedures are defined in documents such as ISO 22309, ASTM E1508, ISO 17470, ISO 14594, ISO 15472, ISO 17560, GB/T 17359, and GB/T 17365, which accredited third-party laboratories follow to ensure repeatable, defensible results.
Testing Samples
Metals and Alloys
Steels, stainless steels, aluminum alloys, copper alloys, titanium alloys, superalloys, and castings are analyzed for non-metallic inclusions, intermetallic phases, segregation bands, nitriding and carburizing layers, and weld or braze joints. Specimens are typically sectioned, mounted, and polished to a mirror finish to reveal microstructural constituents clearly.
Coatings, Platings, and Thin Films
Galvanized and zinc-aluminum coatings, electroplated nickel, chromium and gold layers, anodized films, PVD/CVD hard coatings, thermal spray coatings, and multilayer stacks can be examined in cross section to measure layer composition, thickness, interdiffusion, and interface defects.
Ceramics, Glasses, and Inorganic Materials
Technical ceramics, refractories, glass products, cementitious materials, and minerals are analyzed for phase composition, impurity phases, glaze layers, and reaction products. Because these materials are usually non-conductive, a thin conductive coating of gold, platinum, or carbon is applied before electron-beam analysis.
Polymers, Rubbers, and Composites
Fillers, fibers, delamination surfaces, inhomogeneous additives, brittle and ductile fracture surfaces, and contaminant inclusions in polymeric materials can be characterized. Complementary molecular techniques such as micro-FTIR and micro-Raman spectroscopy are often combined with elemental analysis for organic identification.
Semiconductors and Electronic Components
IC devices, package interconnects, solder joints, bond pads, thin-film metallizations, and cross-sectioned PCBs are analyzed for layer integrity, intermetallic formation, diffusion barriers, and defect chemistry at very high spatial resolution.
Particles, Contaminants, and Residues
Foreign particles filtered from liquids, residues on surfaces, corrosion products, stains, and unknown deposits—sometimes only a few micrometers in size—can be individually located and identified to support root-cause contamination investigations.
General sample requirements include: overall dimensions compatible with the instrument chamber (typically disks or blocks up to ~100 mm across and ~20–50 mm high, with larger parts subsampled), vacuum compatibility (no volatile or liquid components unless frozen-transfer is available), and appropriate preparation such as cleaning, sectioning, mounting, polishing, or conductive coating. Surface-sensitive analyses (XPS, AES, SIMS) additionally require careful handling to avoid adventitious contamination before measurement.
Testing Items
Micro-area composition analysis is delivered through a set of well-defined analytical tasks tailored to the investigative question:
- Point (spot) analysis: full-spectrum qualitative identification of the elements present at a selected point, particle, or microstructural feature.
- Quantitative analysis: determination of elemental concentrations at a point using standardless algorithms (ZAF/PPRZ) or certified reference materials, with typical relative accuracy of 1–5% for major and minor elements.
- Line scan analysis: elemental concentration profiles along a line across an interface, coating, diffusion zone, or compositional gradient.
- Elemental mapping (X-ray dot mapping): two-dimensional distribution images showing the spatial arrangement of each element, revealing phases, segregation, and inclusions at a glance.
- Coating and multilayer characterization: composition and thickness measurement of individual layers in cross section, including interfacial reaction layers and interdiffusion zones.
- Depth profiling: composition as a function of depth from the topmost surface using ion sputtering, essential for oxide films, passivation layers, and implanted layers.
- Inclusion and second-phase identification: automated or manual classification of non-metallic inclusions or precipitates by size, morphology, and chemistry.
- Light element analysis: quantification of boron, carbon, nitrogen, and oxygen in carbides, nitrides, oxides, and borides, preferably by WDS.
- Trace and ultra-trace microanalysis: detection of minor and trace elements at ppm to ppb levels in small regions by WDS, ToF-SIMS, or LA-ICP-MS.
- Chemical state analysis: determination of oxidation states and chemical bonding of surface species by XPS, for example distinguishing metallic iron from its oxides.
Testing Methods
SEM-EDS (Energy-Dispersive X-ray Spectroscopy)
The workhorse of micro-area analysis. A scanning electron microscope generates characteristic X-rays that an energy-dispersive silicon-drift detector resolves by energy. It covers elements from boron (or carbon with a windowless detector) to uranium, with detection limits of roughly 0.1–0.5 wt%, a typical interaction volume of about 0.5–5 µm, rapid element mapping, and point, line, and map modes. Quantification follows ISO 22309, ASTM E1508, and GB/T 17359.
EPMA-WDS (Electron Probe Microanalysis with Wavelength-Dispersive Spectrometers)
Wavelength-dispersive spectrometers use diffracting crystals to achieve much higher spectral resolution than EDS, enabling accurate quantification of overlapping peaks and light elements, with detection limits down to the 10–100 ppm range and relative accuracy of 1–2% for major elements. It is the reference method for high-accuracy quantitative microanalysis per ISO 14594, ISO 17470, and GB/T 17365.
XPS (X-Ray Photoelectron Spectroscopy)
A surface-sensitive technique probing only the top 1–10 nm of a specimen. XPS identifies elements from lithium to uranium at concentrations above roughly 0.1–1 at% and, uniquely, provides chemical state information (oxidation state, bonding). It is ideal for ultrathin films, surface treatments, and contamination films. Relevant standards include ISO 15470 and ISO 15472.
AES (Auger Electron Spectroscopy)
Combining ~10 nm lateral resolution with 1–5 nm information depth, AES excels at analyzing nano-scale particles, grain boundaries exposed by fracture, and thin surface films, with depth profiling via argon ion sputtering. Guidance is provided in ISO 17973 and ASTM E1078.
ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry)
Secondary ions sputtered from the surface are mass-analyzed, providing elemental detection down to ppm–ppb levels together with molecular and isotopic information. ToF-SIMS offers retrospective analysis of the entire surface and excellent depth profiling, governed in part by ISO 17560 for depth profiling methodology.
TEM-EDS / EELS (Transmission Electron Microscopy)
For nanometer and sub-nanometer resolution, thin foils or extracted particles are analyzed in the TEM using EDS for elemental composition and electron energy-loss spectroscopy (EELS) for light elements and chemical bonding. This is the method of choice for nanoparticles, nanostructures, and ultrafine precipitates.
Micro-Raman and Micro-FTIR Spectroscopy
Complementary molecular techniques with ~1–10 µm spot sizes that identify compounds, polymorphs, and organic species (e.g., distinguishing anatase from rutile TiO2, or identifying polyamide contamination) even when elemental analysis alone is insufficient.
LA-ICP-MS (Laser Ablation ICP-MS)
A focused laser ablates a 5–200 µm spot, and the aerosol is analyzed by ICP-MS, achieving trace and ultra-trace elemental quantification (ppb level) and isotopic analysis in localized regions of solid samples.
Applications
Micro-area composition analysis underpins a wide spectrum of industrial and research activities:
- Failure analysis: identifying brittle inclusions at fracture origins, intergranular embrittlement from segregation, decarburization, hydrogen-related features, and corrosive attack at crack sites.
- Contamination and foreign particle identification: determining the chemistry of stains, residues, fibers, and particles isolated from products, processes, or filtered fluids to trace their source.
- Weld, braze, and solder joint evaluation: characterizing intermetallic layers, incomplete mixing, porosity, filler composition, and heat-affected-zone changes.
- Coating verification and development: confirming plating composition and thickness, detecting coating defects and interdiffusion, and qualifying surface treatments for corrosion protection.
- Corrosion diagnosis: identifying corrosion products and their distribution to distinguish mechanisms such as pitting, galvanic attack, or high-temperature oxidation.
- Thermal treatment and diffusion studies: measuring case depth, nitrided layers, carburized regions, and diffusion profiles in processed components.
- Electronics and semiconductor quality: analyzing bond-pad contamination, solder intermetallics, layer stacks, and defect structures at high resolution.
- Material R&D and reverse engineering: phase identification in new alloys and ceramics, competitor-product teardowns, and verification of supplied materials against specification.
- Dispute resolution and quality arbitration: producing standards-based, traceable analytical evidence acceptable for supplier claims and incoming-inspection conflicts.
FAQ
What is the smallest region that can be analyzed?
For SEM-EDS, the practical analytical volume is about 0.5–5 µm due to electron beam spreading inside the specimen. AES reaches roughly 10 nm laterally on the top few nanometers, and TEM-EDS/EELS achieves nanometer to sub-nanometer resolution on electron-transparent specimens. WDS on an electron probe microanalyzer typically works with a ~1 µm analytical volume but far better spectral resolution.
Which elements can be detected, and what are the detection limits?
EDS covers approximately boron to uranium with detection limits around 0.1–0.5 wt%. WDS extends reliable quantification to light elements and reaches 10–100 ppm detection limits. XPS covers lithium to uranium in the top few nanometers, while ToF-SIMS and LA-ICP-MS reach ppm to ppb trace levels. Hydrogen and helium cannot be measured by X-ray-based techniques.
Is the analysis destructive?
SEM-EDS and EPMA-WDS analysis itself is non-destructive, although specimen preparation (sectioning, polishing, coating) may consume or alter the sample. Sputter depth profiling in XPS, AES, and SIMS progressively removes material and is therefore destructive. Micro-Raman and micro-FTIR are generally non-destructive.
Can light elements such as carbon, nitrogen, oxygen, and boron be quantified?
Yes. WDS is preferred for accurate light-element quantification because of its superior spectral resolution and sensitivity. EDS with modern detectors provides semi-quantitative light-element results, while EELS and XPS are excellent for light elements in thin specimens and surfaces, respectively.
How accurate is quantitative microanalysis?
With certified reference materials and standards-based calibration, WDS and EDS typically achieve relative errors of 1–2% and 2–5%, respectively, for major and minor elements under favorable conditions (flat, polished, homogeneous specimens). Standardless EDS quantification is suitable for screening but less defensible for arbitration.
What standards govern the testing?
Commonly applied documents include ISO 22309 (quantitative EDS in SEM), ASTM E1508 (EDS microanalysis), ISO 17470 (qualitative EPMA point analysis), ISO 14594 (quantitative EPMA), GB/T 17359 and GB/T 17365 (Chinese national standards for EDS and EPMA microanalysis), ISO 15470 and ISO 15472 (XPS), ISO 17973 and ASTM E1078 (AES and specimen handling), and ISO 17560 (SIMS depth profiling).
What information should be provided with a sample?
Clients should describe the material and its history, the purpose of the analysis, the exact region or feature of interest (ideally marked or photographed), known processing conditions, and any suspected elements. This allows the laboratory to select the optimal technique, preparation route, and reporting format.
How long does a typical analysis take?
Straightforward SEM-EDS point or mapping analyses are usually completed within a few working days, while multi-technique investigations involving XPS/AES depth profiling, TEM specimen preparation, or automated inclusion analysis may require additional time. Accredited third-party laboratories can usually provide expedited scheduling for urgent failure investigations.