"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."
CU Boulder – Electron Microprobe Laboratory - JEOL JXA-8230
An electron microprobe (EMP) is an electron microscope designed for the non-destructive
X-ray microanalysis and imaging of solid materials. It provides precise and accurate
chemical composition (for elements Be to U) at the micron-scale of a large variety of solid
materials such as minerals, glasses, alloys, and ceramics. The primary advantage of EMP
analysis is the non-destructive and in-situ character of the analysis. All you need is a
well-polished, flat sample, such as a regular petrographic thin section or an epoxy mount.
EMP is the ideal technique for analyzing chemically zoned crystals, for testing a material's
homogeneity, for sampling delicately intermixed phases, or for identifying and
characterizing phases (chemistry, size, shape). As it is an in-situ technique, information
on texture and deformation can be preserved.
The purchase of the JEOL-8230 would not have been possible without the help many
researchers throughout Colorado and beyond that supported our proposal. We are extremely
thankful to them. We also acknowledge financial support from NSF-EAR grant #1427626 (PIs
Mahan, Allaz and Farmer; 2014-2017) and from the University of Colorado (30% cost-share
and laboratory renovation).
The NEW Electron Microprobe (2016)
The department of Geological Sciences at the University of Colorado Boulder was awarded a
Major Research Instrumentation grant in Summer 2014 to replace the 30-year old JEOL-8600
(*). In Spring 2016, a new 5-spectrometer JEOL JXA-8230
Superprobe equipped with LaB6 electron gun was installed. This new instrument uses only
dry pumps (cleaner vacuum), has very good analytical stability, and delivers high quality
data. Compared to the older instrument, this new EMP offers:
- Enhanced spatial resolution (LaB6 electron gun: beam size ca. 0.2-0.7 um);
- Five wavelength dispersive spectrometers (WDS), four of which are
equipped with large-area monochromators for higher sensitivity (2 to 3x gain);
- Faster acquisition capability, for example 10 elements in a couple of minutes,
with detection limits around 50 to 200 ppm;
- Trace element analysis capability with detection limits around 10 ppm or better;
- A silicon-drift energy dispersive spectrometer (EDS) from Thermo Scientific
with an ultra-thin window to detect light elements (Be to F);
- A panchromatic cathodoluminescence detector from JEOL;
- Numerous software improvements for better and faster analyses.
As usual, we welcome work from external researchers and private corporations.
Contact the lab manager for more information.
(*) Not retired! The venerable JEOL-8600 has been relocated to Auburn University (Alabama)
and will soon be operational again.
The new JEOL-8230 electron microprobe and its detectors
Samples must be solids, prepared flat (planar on a micron scale), very well-polished
(0.05 um final polish), and must be clean and stable under high vacuum (10-4 Pa). Advise the
lab manager if your sample is water- or alcohol-soluble as these liquids are used for fine
polishing and cleaning. We strongly recommend samples be either mounted on a petrographic
thin-section (27 x 46 mm) or a 1-inch round glass slide, or embedded in a 1 or 1 1/4 inch
diameter epoxy disk (see image aside). Samples of irregular or non-conventional size could
be mounted, but at the cost of complications and possible inaccurate results.
Thin-sections or epoxy mounts can be prepared at CU Boulder. Contact Paul Boni
(paul.boni [at] colorado.edu) for further information.
Example of perfectly suitable samples for use on our microprobe JEOL-8230.
Carbon and metal coating
To ensure conductivity and identical analytical conditions between our standards and
your unknowns, samples are usually carbon-coated (ca. 15 nm thin-film). A fully
refurbished Edwards Auto306 dual-coater is available in our laboratory, and can coat
up to 6 thin sections at once with carbon and/or metal (e.g., Al, Au, Ag). Whereas
most applications only require carbon-coating, some specific applications such as
monazite dating or beam-sensitive materials will likely require the use of metal
coating for enhanced precision and accuracy. We are currently working on developing
an adequate protocol for quantitative analysis with metal-coating. Advise the manager
of the facility ahead of time if you need to coat your sample in our laboratory.
Fully refurbished Edwards Auto 306 coater: Dual carbon and metal evaporation system,
high vacuum with dry pumps only, up to 6 thin sections (or 8 one-inch round mounts)
coated at once.
Wavelength Dispersive Spectrometers
The JEOL JXA-8230 electron microprobe is fully-automated, and has 5 wavelength-dispersive
spectrometers (WDS), one of which is equipped with four monochromators for low-energy
X-ray analysis (including light elements, Be to F), and four are equipped with
large-area monochromators that reach 2 to 3 times higher count rate. The latter
is key for our ability to excel in trace element analysis, and for outperforming many
other microprobe laboratories. The spectrometer configuration is as follows:
The periodic table below lists which element can be detected with which monochromator.
If necessary, the lab manager will assist you in choosing the most optimum setup for you work.
Periodic table of major X-ray lines (Ka, La and Ma) that can be analyzed with
our instrument. Click on the image to see an interactive version of this periodic
table (will open in a new page).
JEOL software & Probe for EPMA
Users of the JEOL JXA-8230 can choose to use either the JEOL software, or the more
advanced “Probe for EPMA” (ProbeSoftware, Inc.) for their quantitative analysis work.
Both software has their advantages, and the choice is made depending on the needs.
The JEOL software is easier to use and totally appropriate for easy and quick
analysis of a few elements. It has some unique features such as automatic peak
identification on WDS scans, fast imaging capability, and quantitative mapping using
point analysis as a calibration point.
Probe for EPMA offers greater versatility,
which comes at the price of greater complexity. It is recommended for experienced
users, or for special applications to ensure higher precision and accuracy. It offers
unique capabilities, such as:
- Quick analysis (10 elements in a minute) using the Mean Atomic Background correction;
- Time-dependent intensity correction to counteract beam damage effects in carbonate, glass, alkali-rich phases, phosphate, etc.;
- Multipoint background correction for accurate trace element analysis in complex matrix;
- Full quantitative element mapping;
- Improved correction routine for peak interferences;
- Versatility in correction matrix;
- Combined EDS-WDS analysis: use EDS for major elements, and WDS for minor and traces;
Energy Dispersive Spectrometer (EDS)
A new Thermo Scientific UltraDry energy-dispersive spectrometer (EDS) detector was
installed with the new EMP. This silicon-drift detector has an ultra-thin window
capable of detecting low energy X-rays, and thus light elements (Be to F). The
optimum energy resolution at Mn Ka is 125 eV with the longest time constant (6.4
microseconds; see chart below). Major elements (and some minor) can be detected
within seconds even at low current. Its ability to reach a million counts per second
before saturation allows for high beam current applications. With all that,
hyperspectral mapping using our EDS is also possible! Standard-based quantification
and EDS hyperspectral mapping for major and minor elements is also available.
The latest EDS software “Pathfinder 1.1” from Thermo is used for analysis by EDS only.
This advanced software notably offers a point and shoot option for quick phase
identification in a sample area and a hyperspectral mapping for quick phase
identification. It has never been so easy and fast to identify the unknown!
Full-width at half-maximum (FWHM) of several major X-ray lines measured on our
EDS system. Compare to an older SiLi detector, our new EDS can detect light elements
(Be to F) and an improved energy resolution (126 eV at Mn Ka versus 160 eV on a SiLi
BSE, SE and CL
The EMP is equipped with a Secondary Electron (SE), BackScattered Electron (BSE), and
panchromatic CathodoLuminescence (panCL) detectors. SE is used for relief effect, BSE
for density contrast and CL to capture visible light photons emitted by some
materials. Instead of a tungsten filament, our instrument is equipped with a LaB6
cathode, which offers a higher brightness, a smaller beam size (ca. 0.2-0.7 um), and
ultimately better image resolution. Image resolution will of course depend on the
beam current, and acceleration voltage (see FIGURE). The maximum field of view at the
minimum magnification (40x) is around 3 mm, and mosaic imaging can be used to cover
larger areas if necessary.
The new BSE detector can acquire perfect images even in materials of high density
contrast, without problem of under- or over- saturation. The enhanced dynamic range
allows for high contrast images to reveal subtle variations in composition of less
than 0.1 average atomic number (e.g., between alpha-beta brasses). The panCL detector
does not replace a high-quality monochromator CL, yet it provides decent images of
zircon, quartz, fluorite, and other cathodoluminescent minerals that can become
helpful for quick localization of an area-of-interest. Variations of CL intensity
might correspond to crystal defects (e.g. irradiation damage) or to variation of
composition, often at the trace element level.
Comparison of images obtained at variable current and voltage in a small area
(FOV 12 um). Optimum imaging resolution is achieved at high voltage (25 keV) and low
current (< 10 nA). Due to a more limited electron penetration depth, more surface
details can be seen at low voltage. Most analytical work is done at 15 keV and 10 to
50 nA. Trace element analyses requires the use of high beam current (> 100 nA) to the
cost of spatial resolution (beam size ca. 0.7 um at 200 nA).
X-ray element mapping is possible with both the EDS detector (hyperspectral mapping)
and the five WDS detectors.
The EDS hyperspectral mapping option acquires a complete EDS spectrum on each
scanned pixel. In minutes, a data-cube is created that can be used to identify
chemically-distinct phases. To some extent, major variation of composition within a
phase can be identified.
WDS element mapping is limited to 5 elements per pass. However, such a detector has
an unbeatable sensitivity compared to EDS, which makes it ideal for mapping small
variations of composition, or for minor or trace elements. WDS element mapping can
also be used to map an entire thin section quickly to specifically look for accessory
minerals (e.g., monazite, zircon, apatite).
WDS mapping can be done either in beam scanning mode for a small area (< 50-100 microns),
or in stage scanning mode for a larger area. We can now provide the user with fully quantified
WDS element maps with incredible quality! As of January 2017, EDS mapping is
limited to beam scanning mode only (maximum field-of-view ca. 3 mm), and combined
EDS-WDS mapping only works in beam scanning mode. We are working with Thermo, JEOL,
and Probe Software to implement combined EDS-WDS stage mapping.
Mapping time for WDS or EDS depends on the desired spatial and analytical resolution,
and on the type of material to be mapped. Quick EDS or small-area WDS maps can be
done in a few minutes, but larger area maps or mapping for minor to trace elements
will likely require several hours. See the example of applications section for some
Resulting images can be exported as TIF or Bitmap file format. Quantitative maps
acquired with Probe Image can be exported in grid files to be treated with third
party software such as Surfer from Golden Software, Inc.
Example of a fully quantitative X-ray element mapping in calcite (shell debris, courtesy K. Chin, CU Boulder).
You deserve the best
The quality of analyses performed depends essentially on the quality of sample
preparation, the character of the sample material, and the availability of
appropriate primary and secondary standards for the desired elements. We are
dedicated to providing users with the best results, and if necessary, we will work
together to develop new and optimum analysis routines to cover your needs. Regular
testing, calibration, and a service contract with JEOL guarantees the instrument is
always performing at its optimum.
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 the sample. The new instrument can attain precision
better than 0.3% (relative) on major elements, as determined by numerous replicate
analysis of primary and secondary standards over an extended period. Beam current,
counting time, overvoltage and the geometry of the system can affect the X-ray count
rate, and thus the precision. To reach acceptable precision (ideally better than
2-5%), trace element analysis requires both high current (> 100 nA) and long counting
time (several minutes).
Beam sensitive materials
The dense package of highly energetic electrons thrown at a solid material can locally
produce significant heat, which can potentially damage the material and yield
inaccurate results. Hydrous materials, glasses, carbonates, phosphates, and
alkali-rich phases (among others) are more prone to devolatilization,
diffusion, or even amorphization (melting) or ablation. In such materials, it is
often necessary to use a lower current (lower precision) and/or to increase the
electron beam size (lower spatial resolution). To improve accuracy, Probe for EPMA
can correct for potential beam damage using a time-dependent intensity correction on
the first 5 analyzed elements. In the near future, we will be testing the use of
metal coating instead of carbon to minimize beam damage effects (e.g., aluminum
coating for monazite U-Th-Pb dating, silver or aluminum on carbonate).
The accuracy of measurements on the electron microprobe depends on accurate knowledge of
the composition of primary standards, and the exactitude of the matrix correction
used (so-called ZAF or φ(ρz) procedure) and other corrections (e.g., peak
interference correction). A general accuracy statement cannot be made, although it is
typically better than 2%. Accuracy can be affected by peak interferences if not
properly accounted for. When analyzing trace elements, peak interference corrections
become crucial, as does the accuracy of the background correction.
The detection limit varies depending on the analyzed element and the monochromator used.
For most elements, the new EMP can achieve detection limits on the order of 50 to 100
ppm within a couple minutes. The aggregation of multiple spectrometers, use of higher
current (> 100 nA), and long counting time (10’ or more) permits the reaching of a
higher sensitivity and detection limit around 1 to 10 ppm.
In most cases, the analytical volume is in the range of a few cubic microns or less
(~picograms). The exact volume analyzed chiefly depends on (a) the acceleration
voltage used (higher voltage = higher volume), (b) the X-ray energy line targeted
(higher energy = smaller volume), (c) the density of the analyzed material (lower
density = larger volume), and (d) the electron beam diameter. A Monte-Carlo simulation
program such as Casino and Win X-ray can help researchers to evaluate the volume.
Standards and Reference Materials
Excellent standards and reference materials are crucial to insure accuracy of microprobe
analysis. Our collection of standards and reference materials (synthetic and natural
materials) has recently been completed, and now fully covers the need for most
applications (silicate, REE-minerals, sulfides, carbonate, metal alloys, etc.). We
will continue to improve it further depending on the analytical needs. Check our
database (De-MA) for a list of currently available standards. For
more information on standards, you can also visit the Focused Interest Group on
Microanalytical Standards (https://figmas.org)
created by Julien Allaz (CU Boulder), Anette von der Handt (University Minnesota) and Owen K. Neill
(Washington State University) in 2016, under the umbrella of the Microanalytical Society
and the Microscopy Society of America.
Learning more about the microprobe
The new instrument and lab will be incorporated into a variety of teaching activities
including a graduate level course on analytical methods (taught by Dr. Allaz) and
several undergraduate courses. Activities for the latter will be facilitated by
technological enhancements such as a large wall-mounted monitor for viewing of
activities by standing groups of 6-8 students, a web-cam for remote viewing of lab
activities during lecture classes, and remote access to one of the operational
computers for viewing of activities during lecture classes. In the future, we
anticipate designing an intensive 3-day workshop to train students and other
researchers on the use of the new instrument. This workshop will permit students and
researchers to use the instrument with minimal assistance from the laboratory
manager. The online laboratory access will also permit external students to easily
access the instrument without being physically present, thus enlarging the impact on
STEM students and minority students that could not otherwise use such an instrument.
EarthScope - Award for Geochronology Student (AGeS) Research Program
Our Electron Microprobe Laboratory is a participating laboratory for the AGeS program
(Awards for Geochronology Student Research) from EarthScope. Our laboratory offers in
situ monazite and xenotime geochronology by electron microprobe analysis. More
information on the EarthScope AGeS program website (click the banner below).
Online resources on SEM, EPMA, and related detectors
Google is your friend to look for valuable information and learn more about SEM and EPMA.
For researchers and student who would like to know more about the technique, the
following website are all good starting points. Thanks to Anette von der Handt (U.
Minnesota) for sharing with me most of these links.
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. See the
Teaching tab for more information.
(*) Only experienced users can use the probe during the
evening and overnight, as no support is guaranteed past 6 PM.
Reservation, Minimum Use, and Cancellation Policy
Users should sign up for time only if their samples are ready and if they have no
other schedule conflicts. If more than one day of analysis is required, it is highly
recommended to reserve consecutive days. When sending a reservation request, the
researcher is required to specify what materials and what elements will be analyzed
to help the lab manager or his assistant to prepare the instrument. 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 notified a week ahead of time and if
a valid excuse is given. With less than a week's notice, cancellation is no longer
an option and a two-hour minimum will be charged (per day).
Priority for use of the probe is as follows:
2. Lab business and submitted jobs
3. All other users
You deserve the best possible results from the instrument and the manager of the
facility, within the limits of the techniques involved and human nature. If you have
any problems whatsoever, feel free to discuss these issues with the manager of the
facility. We all want this laboratory to operate in an efficient and productive
Pricing and conditions
We are open to in-house and outside researchers! The manager of the facility is
usually available to assist Monday to Friday, from 8 or 9 AM to 5 or 6 PM, unless
otherwise stipulated (official holidays, vacation, illness...).
Untrained users will receive assistance to obtain their analysis. Only advanced and
trained users may work without assistance, and thus may benefit from the unassisted
rate. A quick training can be given on the first day of the analysis session
(additional charges apply). Contact the facility manager for pricing and
For some basic work, a couple hours of training might be sufficient, providing the
user knows the theory, the basic principles of an electron microprobe, and the
software controlling the instrument (JEOL and Thermo EDS programs, and if required
Probe for EPMA and Probe Image).