"Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

Albert Einstein

"It was during my enchanted days of travel that the idea came to me, which, through the years, has come into my thoughts again and again and always happily - the idea that geology is the music of the earth."

Hans Cloos











Electron microprobe laboratory - JEOL-8600

Question, comments? Contact the microprobe manager (Julien).
You may also consult the electron microprobe database for reservation request and more!

    General information

    An electron microprobe is an electron microscope designed for the non-destructive x-ray microanalysis and imaging of solid materials. It is capable of high spatial resolution (1 µm beam size) and relatively high analytical sensitivity. The analytical facilities' JEOL JXA-8600 can acquire digital secondary-electron and backscattered-electron images as well as elemental x-ray maps. It is equipped with 4 wavelength-dispersive spectrometers and an energy-dispersive spectrometer. Most of the periodic table can in principle be analyzed (Be through U), subject to several important considerations.

    Analysis quality

    The quality of analyses performed depends essentially on the quality of sample preparation, character of the sample material, and availability of appropriate primary and secondary calibration standards for the desired elements. A precision usually less than 0.5% relative depending on element abundance, and accuracy as good as 1-2% can be obtained with this instrument.

    The analytical sensitivity ranges from a low of ~50 parts per million for optimum cases, to a typical detection limit of several hundred ppm, but can be as high as several weight percent for problem elements. The volume sampled is typically a few cubic microns, corresponding to a weight of a few picograms.

    Samples

    Samples must be prepared as flat (planar on a micron scale), polished to 0.05 um final polish, solid mounts up to 1 inch in diameter or standard thin-sections (see image below), and must be clean and stable in a 10-5 to 10-6 torr vacuum environment. After preparation, samples are made electrically conductive with a layer of carbon using the carbon evaporator. Your samples should be completely polished, coated, and mounted (if applicable and reasonable) before the beginning of your session. The microprobe laboratory is equipped with a vacuum carbon sputter coater. Advise the manager of the facility ahead of time, if you need to coat your sample in our laboratory.

    Samples (thin-sections or solid mounts) can be prepared at CU Boulder. Contact for further information.

    Hardware

    The JEOL JXA-8600 electron microprobe is a fully-automated, customized instrument that has met the most rigorous delivery specifications for an electron microprobe to date. The microprobe has a total of 4 wavelength-dispersive spectrometers, of which three are equipped with two analyzing crystals, and one with four.

    Spectrometer Crystal Inventory

       (SP 1) TAP PET LDEC LDEB (extended-range)
       (SP 2) TAP LDE1
       (SP 3) LIF PET
       (SP 4) PET LIF

    The table aside lists the elements that each crystal can be used to detect. Note that in practice element analytical lists are set up in advance for most routine materials, and judgement based on experience is used to select a particular x-ray line and crystal for a given application.

    Crystals & detectable elements

    Crystal Element Range
    LIF
    (4.0267 Å)
    Kα lines, Ca to Rb
    Lα lines, Sb to U
    PET
    (8.742Å)
    (*)
    Kα lines, Si to Cr
    Lα lines, Rb to Eu
         (Kr to Eu on SP 1)
    Mα lines, Lu to Bi and Th to U
    TAP
    (25.757 Å)
    Kα lines, F to Si
         (O to Si on SP 1)
    Lα lines, Cr to Zr
    Mα lines, La to Pt
    LDE1
    (60 Å)
    Kα lines, C to Ne
         (optimum for O & F)
    Lα lines, Ca to Ni
    LDEC
    (98 Å)
    Kα lines, Be to O
         (optimum for C & N)
    LDEB
    (147 Å)
    Kα lines, Be to C
         (optimum for Be & B)

    (*) Three PET crystals, two of which are PET-J (high reflectivity crystals).

    A movie showing the crystal & detector movement is also available, check this here!

    The microprobe has a PGT Avalon energy-dispersive spectrometer (EDS) and a Geller dPict x-ray analyzer that is used to simultaneously acquire x-rays over a wide energy range. The EDS system is equipped with a beryllium window and can identify major to minor (ca. >1 wt-%) elements from sodium (Na) to heavier elements. This EDS detector can be used to perform energy-dispersive quantitative analysis of major elements if so desired.

    Software

    Our Jeol JXA-8600 currently uses the Geller dQuant spectrometer and stage automation system. dQuant for Windows and related programs store their data in Microsoft Access database files. All standard compositions are maintained in a standard database, and read in by dQuant for Windows during correction. dQuant for Windows performs all spectrometer and stage automation activities, and handles all operations during an automated microprobe run, including matrix correction.

    Geller Microanalytical Lab

    Analytical Capabilities

    Our microprobe is nominally capable of analyzing a wide range of elements (from Be through U), at concentrations typically above 100 parts per million. This instrument has very good electronic and analytical stability, vacuum cleanliness, and capability to perform analyses with high precision and accuracy as demonstrated by a history of applications. The volume excited by the electron beam is a few cubic micron (depending on material density), corresponding to a sample size of a few picograms. The primary advantage of microprobe analysis is that the analysis is non-destructive, although some material must be consumed in making a polished mount, and that a very small amount of material is sampled for a measurement. It is the ideal technique for analyzing crystals that are zoned, or samples that are made up of intimately-mixed phases where one needs to spatially resolve the phases being studied. The analytical sensitivity does depend on the matrix of other elements present, and the material properties of the compound to be analyzed.

    Imaging Capabilities

    Digital imaging (secondary-electron or backscattered-electron) and x-ray element mapping can be acquired using the Geller dPict software. This program allows one to simultaneously acquire wavelength-dispersive and energy-dispersive x-ray maps as well as secondary-electron or backscattered-electron images. X-ray maps can be acquired at a full 16-bit count resolution, which enables a large dynamic count range to be sampled. Two basic x-ray mapping modes are available, digital mapping, which is essentially a multiple-scan averaging mode that produces a binary image based on x-ray detection at each pixel (i.e. a noise suppressed dot-mapping technique), and counter-mode mapping, which is a slower but higher resolution pixel-by-pixel map acquisition mode. The digital mapping mode allow for relatively fast acquisition to discriminate phases with large chemical difference, whereas the counter-mode mapping is a slower acquisition to discriminate phases with smaller chemical difference.

    Digital images are saved in TIFF format, and can be printed out on either the Optra S1250 or an HP 970 CSE color inkjet printer. Image processing can be perfomed using dPict, ImagePro (Media Cybernetics), or Photoshop (Adobe). The dPict program has several advanced capabilities, like mosaic images using relative registration, so that images collected manually can be combined to form a mosaic master image.

    Here are a few examples of imaging using our microprobe; click on a picture to view them, there are images in the gallery than the thumbnails shown here!

    Precision

    The precision of measurements on the electron microprobe is a function of x-ray counting statistics, which depend on the total number of x-ray counts collected on both the standard used for calibration, and also on the counts collected on the sample. The minimum precision attainable on the instrument is in the vicinity of 0.5% relative, as determined by replicate measurements on wafer standards involving extensive spectrometer movement. Spectrometer mechanical reproducibility is considered to be the limiting factor in precise measurements on our instrument. Therefore, at low total counts collected, counting statistics errors dominate, and at high total counts collected, instrumental reproducibility dominates. Precision also depends on the chemical homogeneity of both the standard used for calibration, and also that of the sample. Some beam sensitive material, such as glass or carbonate, might require lower current for the analysis or larger beam size (analysis volume), which will reduce the precision or the spatial resolution, respectively.

    Accuracy

    The accuracy of measurements on the electron microprobe depends on accurate knowledge of the composition of the primary calibration standard, and the "correctness" of the algorithm used to convert from x-ray intensity to concentration units (i.e. matrix correction: "ZAF" or "φρz" procedure). A global accuracy statement cannot be made. However, the accuracy is typically better than 5%, but may be worse for elements subject to peak interferences, or where there is a large compositional difference between the standard and sample and a large correction factor is observed (i.e. x-ray absorption, for example). At CU Boulder, we do our best to have the "perfect" standard for your analysis. Check our microprobe database for a list of currently available standards.

    The bullseye representation:
    Schematic representation of accuracy and precision. Naturally, at our facility we aim for both accuracy and precision (lower-right image)...


    JEOL JXA-8600

    Use policy

    Time availability

    There are two time slots available for use of the microprobe:
       - Day: 8 AM to 5 PM
       - Evening: 5 PM to 8 AM the next day (*).

    Anyone using the microprobe must be trained, and must know the theory of x-ray diffraction and electron microprobe in general. Contact the manager of the facility for more information about possible training.

    (*) Only experienced user are allowed to use the probe during the evening and overnight, as no support is guaranteed past 6 PM.


    Minimum Use and Cancellation Policy

    When you sign up to use the microprobe, you agree to use the instrument at that time, for a minimum of 1 hour per session. Cancellation is possible if advised a week before and if a valid excuse is given, Past this delay, cancellation is no longer an option and a two hour minimum will be charged (per day). You should sign up for time only if your sample(s) will be ready and you have no other schedule conflicts.

    Priority

    Priority for use of the probe is as follows:
       1. Maintenance
       2. Lab business and submitted jobs
       3. All other users

    Refer to the microprobe database for the online agenda and online reservation request. Any reservation request must be approved by the manager of the facility.


    Guarantee

    You deserve the best possible results from the instrumentation and the manager of the facility, within the limits of the techniques involved and human nature. If you have any problems whatever, feel free to discuss these issues with the manager of the facility. We all want this laboratory to operate in an efficient and productive fashion!

    Pricing and confitions

    We are open to in-house and outside researchers!

    Contact the facility manager for pricing and conditions.

    Concluding remarks

    Only advanced / trained users may work without assistance. For some basic work, a couple hours of training might be sufficient, providing you do know the theory, the basic principles of an electron microprobe, and the software/hardware controlling our microprobe (Geller system: dQuant, dSspec, dPict).

    The manager of the facility is usually available for any concern from Monday to Friday, from 8 or 9 AM to 5 or 6 PM (at least), unless otherwise stipulated (official holidays, vacation, illness...).

    Maintenance service

    The facility JEOL JXA-8600 Superprobe is continuously maintained under ongoing contract by JEOL engineers. High priority is given to WDS spectrometer alignment, spectrometer reproducibility, detector counting system deadtime calibration and correction. Specific procedures are followed that exceed the specifications of the instrument manufacturer, in terms of spectrometer calibration and reproducibility testing. Our instrument is maintained to a high standard not achieved at a number of other facilities. We can demonstrate as good as 2-3% reproducibility over a one year period on our instrument.

    Writeup summary

    On the right, you will find a summary of the instrument hardware, software, standards, and correction scheme used for typical analytical runs. You may consider using a similar summary in your publication, if you have used our electron microprobe facility. Refer also to the microprobe database or ask the manager of the facility for more details, as your run may entail the use of non-standard analytical protocols.

    "Analyses are performed on a JEOL JXA-8600 electron microprobe equipped with 4 wavelength-dispersive spectrometers, and a PGT energy-dispersive spectrometer. Analyses are acquired using the dQuant for Windows operating system, interfaced to the Geller microprobe automation. Typical operating conditions are 15 KV accelerating potential and 20 nA probe current. Standards used in the analytical facility range from simple silicate and oxide end-member compounds to primary silicate standards recognized throughout the analytical community. A wide range of standards appropriate to specific analytical problems may also be used. X-ray intensity measurements are converted to concentration units using dQuant correction package developed at Caltech (CITZAF) (see CALTECH website for a document reference)."


Julien M. Allaz (University of Colorado Boulder) © 2012
Background picture: View on the southern Alps from Pizzo Forno (Ticino, Switzerland; J. Allaz © 2008).