Electron Micro Probe
Cameca SX 100
In use is an advanced device with five WD spectrometers and an ED detector (Cameca SX100). The system allows for full spatially resolved chemical analysis of solids (2 ~ 3 microns resolution). Elements with AM> 4 are quantitatively detected. The accuracy allows for measurments in tenths of one percent. Suitable for analysis are separated mineral grains, mineral grains in rock mass, engineered materials, building materials, metals, corrosion products, dust and medical material. In addition, element distribution patterns can be mapped, concentration profiles can be measured and gemological, forensic and dental problems can be worked on.
In detail:
Cameca SX100
Electron Micro Probe (EMP) highly accurate, automated elemental analysis in the micro range
As of springtime 1995 a digital CAMECA SX100 Electron Microprobe (introduced Sept'94) was being installed in Freiburg. An electron microprobe is a highly sophisticated instrument for measuring element contents of (anorganic) materials on the micrometer scale.
Basics of EMPA measurements:
• physical principle: registration of characteristic X-ray emission spectra produced by electron bombardment
• minimum spacial resolution: micrometer scale, depending on acceleration voltage and resulting penetration depth of the electron beam
• detection limits: element and matrix dependent, some tens to some hundreds ppm
• accuracy: element and matrix dependent, 1 - 3 relative percent (for Z < 11 much worse)
• reproducability: concentration and measuring time dependent: ~ 1 relative percent
• analysis time: concentration and necessary accuracy dependent: some ten to some hundred seconds per element (WDS)
Sample requirements:
• For quantitative work all samples must be flat and mounted perpendicular to the electron beam.
• Materials must be stable under electron bombardment and vacuum conditions.
• Standard geological applications require uncovered thin sections with 0.5 mm diamond powder polishing.
• Samples have to be electronically conductive or coated with some conductive material (typically carbon).
• In general samples have to be regarded as being homogeneous on the micrometer scale. Special correction procedures are needed for thin films and single particles.
Features of our SX100:
• 50 kV electron gun, W-filament
• Spectrometers:
Five vertical wavelength-dispersive spectrometers (PC0 - PC3 = synthetic multilayers):
| No. | Crystals | Special features |
| 1 | TAP, PCO | -- |
| 2 | LIF, PET | "high pressure" proportional counte |
| 3 | LIF, PET | "high pressure" proportional counte |
| 4 | TAP, PET, PC1, PC3 | -- |
| 5 | TAP, PET, LIF, PC2 | extended 2theta range, allowing O Ka to be measured on the TAP xtal |
Element range covered (theoretically, element specific inconveniences occur):
| Crystal | Formula | 2d [Å] | K shell | L shell |
| PC3 | Mo/B4C Multilayer | 200 | Be-B | |
| PC2 | Ni/C Multilayer | 95 | B-O | |
| PC1 | W/Si Multilayer | 60 | C-F | |
| PC0 | W/Si Multilayer | 45 | O-F | |
| TAP | C8H5O4Tl | 27.745 | F-P | Mn-Nb |
| PET | C5H12O4 | 8.742 | Si-Mn | Sr-Tb |
| LIF | LiF | 4.027 | Sc-Rb | Te-U |
The system is integrated with a Link (Oxford) nitrogen cooled ED-system, specified resolution 138 eV, standard Be-window, element range Na-U.
• Specimen stage: The minimum step size is 0.5 µm. Accommodation of a wide range of samples sizes, including 40mm round, 48*28mm, 30*30mm, but the standard size being either 1 inch (25.4mm) round or 28 x 48 mm sized thin sections; maximum specimen size 75*50*25 mm. A maximum of 6 samples/standards of the standard size (1in) can be loaded at the same time.
• Optical microscope: reflected and transmitted light optics and polariser. The magnification is fixed to 400. An attached color CCD camera provides an image on the computer screen.
• Vacuum system: Cameca standard vacuum system.
• Anticontamination: Equipment comprising a liquid nitrogen cold finger near the point of impact of the electron beam, and an oxygen jet to burn off carbon contamination.
• Instrument control via a SUN SPARCstation5 running under Solaris 2.5.1. The instrument is fully automated for unattended overnight operation, including a Z-axis autofocus system.
• Edwards Auto 306 sputter-coater for carbon coating of non-conductive specimens to facilitate a stable electron beam.
• A second SUN workstation with Cameca SX software running in dummy mode for offline data processing, image analysis and software training.
A variety of standard materials that cover most geological and materials science applications is available. The original file format of analysis data is ASCII, which is easily converted to Excel 5. Possible image formats are "Cameca" (ASCII), Sun Raster or TIFF. Only the Cameca format contains information about analysis conditions. Data transfer by floppy, CD-R, CIP or ftp.
For further questions please contac Mrs. Dr. Hiltrud Müller-Sigmund . 