In AES the composition and chemistry of surfaces are revealed in the secondary electron spectrum from the surface. All elements except H and He can be detected and quantified with a spatial resolution of 30 nm. High resolution SEM locates areas of interest. The field emission electron source has excellent spatial resolution at low electron energy permitting analysis of insulating materials. Because of the shallow escape depth of Auger electrons, the analysis depth is only a few atomic layers. Line scans and maps show the composition of exposed surfaces or interfaces. Successive analysis and ion beam etching produces depth profiles for analysis of thin films and buried interfaces. A fracture stage allows study of internal surfaces such as grain boundaries or fiber/matrix interfaces in composites.
SAM Elemental Maps of NiAl Fracture Site 
Fracture initiated at HfC inclusion in a NiHf phase.
Samples irradiated with x-rays emit photo-electrons with binding energies characteristic of the elements in the sample and the chemical bonding of those elements. The depth of analysis is typically 3 nm to 10 nm with lateral resolution from 150 micrometer diameter to 2 mm by 5 mm. The chemical sensitivity and nondestructiveness of XPS make it suitable for polymer surface analysis.
Gold 4f binding energy changes with chemical bonding in Au-Ga alloys.
From the absorption of infrared and scattering of visible radiation, FTIR and Raman spectroscopies provide identification of molecular species through their vibration states. They often provide chemical bond information and molecular orientation nondestructively with little sample preparation. Incorporation of an optical microscope permits selection of the analysis area which can be as small as 10 micrometer in FTIR and 1 micrometer in Raman. Monolayer sensitivity is attainable at ambient conditions. Chemical band shift and intensity information also provides a probe of the physical environment and can be used, for example, to determine residual stress in a surface layer after deformation, or the crystalline phase of a material.
Infrared (IR) Microscopy
Analysis of Egyptian antiquities to determine composition. Samples
(often micrograms or less) were obtained from the Cleveland Museum of
Art through an agreement with the Commercial Technology Office to
assist them in determinimg how ancient artisans constructed their
masterpieces and, more importantly, to provide useful information on
their restoration. These artisans frequently employed waxy-varnish to
protect the final artwork. In these instances, one waxy-varnish is
predominately bees wax, and the other is varnish.
Raman Spectroscopy
Raman microscopy is used to nondestructively map stresses in a
thermal barrier coating. Small shifts in the Raman spectra are
correlated with compressional stress in crystalline materials. Mapping
the area of a thermal barrier blister indicates residual stress exists
at the perimeter after the failure.
Image on TV - Spectrum on computer monitor.
When a sample, in vacuum, is scanned by a focused electron beam, a variety of signals is produced by the electrons impinging on the surface. Secondary and backscattered electrons are used to form SEM images with contrast representing topography and/or atomic number. X- rays produce an EDS spectrum used to identify the elements in the imaged area.
Working much like a miniature stylus profilometer, the AFM images topography to subnanometer scales. The AFM uses a micromachined cantilever beam tip to sense sample surface height as a function of position creating a quantitative 3-dimensional map of the surface as the tip rasters over the sample. Vertical forces range from nanoN to microN, while lateral force and modulated force data allow additional probes of the tip/sample interaction. A noncontact mode can be used for delicate samples in air or in solution.
Multiatomic layer, spiral-growth steps on a silicon carbide
(0001) epitaxial film. Note vertical and horizontal scales.
Analytic Probes |
|||||||
|---|---|---|---|---|---|---|---|
| Technique | Depth Resolution |
Lateral Resolution |
Depth Profiling |
Imaging & Mapping |
Quantitative Accuracy |
Detection Limits |
Sample Considerations |
| XPS/ESCA | 5 to 30 nm | > 250 um | Ion-etching Angle-resolved |
None | 5% | 0.1 monolayer 0.1 at. % Z > 2 |
Ultra-high vacuum |
| AES/SAM | 2 to 30 nm | > 30 nm | Ion-etching Angle-resolved |
SEM elemental & chemical |
20% | 0.1 monolayer 0.1 at. % Z > 2 |
UHV e-beam damage Charging |
| FTIR | ZnSE-ATR: 2-4µ GE-ATR: 0.4-1µ |
10 µ | see ATR | No | Low%(solution) | ng µg | Yes |
| Raman | 5µ | 1 µ | Limited | Yes | No | µg | Yes |
| EDS | ~1 um | ~1 um | No | SEM elemental line-scans |
5% | 10 ppm Z > 5 |
High vacuum e-beam damage |
Topographic Probes |
|||||||
| Technique | Lateral | Vertical | Sample Considerations | Additional Capabilities |
|||
| Resolution | Range | Resolution | Range | ||||
| SEM | 3 nm | N/A | N/A | N/A | High vacuum e-beam damage |
Backscatter mode |
|
| AFM/STM | < 0.1 nm | 100 um | < 0.1 nm | 7 um | Air or Liquid < 25 mm diam. < 10 mm high | Lateral force, nano-scale indentation |
|
. . . Last updated July 3, 2001 -acz
. . . Last edited August 21, 2003 -pba