Microprobe

To request instrument time or discuss potential projects, please contact Jim Eckert via email or phone (203-432-3181). All users should expect to provide compensation to the laboratory for all research time on the machine.

For users who wish an introduction to the instrument to become familiar with its capabilities, a demonstration session (~1 hour) can be scheduled at no charge.

If training is required while performing initial analyses for your research, Jim Eckert will bring you up to speed on the machine and oversee the initial analyses of your specimens during this instruction; time shall be charged only at the standard rate throughout any training period, including oversight of all initial specimen analyses without an additional charge for "technical/operator assistance."

All users should expect to provide compensation to the laboratory for all research time on the machine. The only exception to the foregoing is that small laboratory projects for Geology & Geophysics courses, which utilize the microprobe, are encouraged. Students who are properly trained or who make arrangements for operator assistance may use the equipment for such projects for up to 5 hours without charge. 

To make optimal use of the facility, we encourage use by both academic and corporate institutions.

A note on scheduling

Since installation in April 2009 of the JEOL JXA-8530F microprobe (funded by the NSF [EAR-0744154] and Yale University), operation continues primarily in a fairly normal mode; in most cases we eventually are able to accomplish most needed tasks (including a 33-element oxide setup, incorporating all REE with overlaps and interferences).

Unfortunately we no longer can provide a URL with reliably updated instrument-schedule info, resulting from a change in website execution, storage, and editing that ITS imposed a while ago. We attempt to accommodate all interest, but the schedule can be full for days to weeks in advance. Also, some ongoing instrument testing may be needed with little or no advance notice. 

If at all possible, making arrangements at least several days in advance (as many as possible) always is recommended. Also, when submitting a request for microprobe time, please include some indication what type of analysis you expect to need (e.g., EDS-qualitative and/or semi-quantitative, primarily imaging, or WDS-quantitative), along with appropriate sample details. For WDS-quantitative work, ideally this information should include at least the primary elements of interest. All scheduling must be arranged directly with Jim Eckert. 

An electron microprobe is a versatile instrument that bombards a small sample with a beam of high-energy electrons. Specimens usually are polished (especially for quantitative analysis) and must be coated with a thin film of carbon or metal to prevent the buildup of an electrical charge (unless they are electrically conductive). This electron beam excites the specimen to produce physical effects that can be used to extract various types of microscale information. These effects range from atomic density (indicated by an effect known as “backscattered electrons”) to elemental abundance. 

The concentration of an element can be shown in a map of the specimen or can be quantified by comparison to standards with known amounts of the element. For quantitative analysis, the excited area of the specimen can be as small as about 1 micron in diameter; a micron is 1/1000 of a millimeter. Thus, very small areas can be analyzed chemically and those areas can be linked to the distribution of elements throughout the specimen. 

This detailed information can be applied to science and engineering fields as diverse as geology, archeology, materials science, metallurgy, chemistry, physics, gemology, electronics, biology, medicine, dentistry, environmental science and engineering, and forensics, to name a few.  

The microprobe also can function fully as a scanning electron microscope (SEM), with most of the imaging capabilities thereof. Although the Yale JEOL 8530F laboratory concentrates primarily on quantitative microscale chemical analysis, secondary and backscattered electron imaging play an important role in evaluating the textural relationships of analyzed areas. In addition, some of the research in the lab uses primarily the SEM imaging capabilities.

Since the microprobe functions also as a scanning electron microscope (SEM), in addition to element maps of a specimen, images from secondary electrons (SEI) and back-scattered electrons (BSE, a.k.a. COMPO or BEI) also can be produced. The Yale JXA-8530F can routinely apply magnifications over 250,000X. This capability, coupled with the quantitative analysis described below, permits detailed microscale assessment of a specimen.  

Uses of the microprobe: Qualitative analysis — Quantitative analysis — Element mapping

Qualitative analysis

Qualitative and semi-quantitative microscale chemistry can be assessed rapidly using EDS spectrometry. This can benefit phase identification and recognition of compositional variability in a sample. This allows rapid imaging and compositional mapping, as well as storage of images and data in readily transferable formats. With either the native JEOL acquisition software or with Probewin, we also can accommodate integration of EDS data into the quantitative-analysis package. [Back to top]

Quantitative analysis

Quantitative microscale chemical analysis, using wavelength dispersive spectrometry (WDS), requires both a stable, well-tuned instrument and standards for comparison that are both well characterized and appropriate for a given specimen. The JXA-8530F has proven to be a stable instrument most of the time, and the Yale suite of available standards is quite diverse and extensive (silicates, oxides, sulfides, sulfates, carbonates, phosphates, phosphides, fluorides, chlorides, chlorates, borates, nitrides, tellurides, arsenides, iodides, selenides, aluminides, native elements, and metals). Typical operating conditions for the electron beam are an accelerating voltage of 10-15 kV, beam currents of 5 to 20 nanoamps, and beam diameter of 1 to 10 microns. However, these parameters can be varied widely (0.5 - 30 kV, ~10 pA to ~3000 nA, beam diameter from focused to ~25 microns {maximum for spectrometer focusing geometry}) to address various questions. Many of the Yale standards, a collection begun by Horace Winchell in the 1960's, are appropriate representatives of their mineral group. These generally high-quality standards, which include both synthetic and naturally occurring varieties, have been graciously provided by a wide variety of esteemed scientists over several decades. Nonetheless, alternative standards for less traditional projects also can be applied.

Quantitative analysis can address all elements heavier than beryllium (boron and higher). Each analysis takes several minutes to count the X-rays and perform related calculations. Ultimate WDS detection limits for sodium and heavier elements are about 50 to 100 ppm (0.005 to 0.01 wt%, elemental); for lighter elements, the instrument is somewhat less sensitive. For most major elements, these truly quantitative microscale chemical measurements typically have accuracy and precision on the order of 1%. Comprehensive setups applied heretofore include a 33-element oxide setup, incorporating all REE with overlaps and interferences. Automated analysis allows the operator to assign locations for analysis during a session, then acquire data automatically (unattended) at those stored locations. Thus, the operator may concentrate on other tasks while the time-consuming X-ray counting and data reduction are completed. Data can be transferred via network or USB connections for rapid accommodation into reports and manuscripts. [Back to top]

Element mapping

Areal distribution of elements can be obtained by acquiring X-ray intensities with step resolutions as small as ~1 micron. These can differentiate various phases and/or show internal compositional zonation within single grains. In some cases these are critical for choosing locations to perform quantitative analysis. Up to 5 WDS elements and 37 EDS elements can be acquired in a single pass, in addition to SEI and BSE images. A monochromatic cathodoluminescence (CL) detector also can be applied during element mapping. [Back to top]

Appropriate specimens for microprobe imaging and analysis can be geological, biological, or technical materials of various compositions and textures. To be appropriate, specimens must be:

• Solid and dry with a clean surface.
• Stable in a vacuum and under a high-voltage electron beam (some less stable materials can be evaluated under less intense voltage and current, though this limits quantitative potential).
• Polished on the flat upper surface (for quantitative analysis) — this can be completed in the lab here, if needed.
• Mounted on either:
  1. 25.4 mm (1") diameter cylindrical blocks, plates, or discs;
  2. 27 mm wide (standard petrographic {U.S.}) glass slides or thin (~1 mm) plates up to 80 mm long (45 mm standard); or
  3. Another substrate no more than 100 mm X 100 mm and 25 mm thick (high).
• Able to conduct an electrical current or to be coated with a thin layer of conductive carbon (coating ideally performed in the lab here).

Backscattered electron image (BSE): High-energy electron image more sensitive to composition at mean atomic number (MAN).  

Characteristic X-ray: X-ray emitted at a wavelength/energy specific to the shell and characteristic of a specific element.

Continuum X-ray: X-ray emitted within a continuous spectrum (noise).

Electron microprobe (a.k.a. electron probe microanalyzer [EPMA]): Instrument using an electron beam (as in SEM) for observation/analysis of samples, including WDS quantification.

Energy dispersive spectrometry (EDS): "Quick" acquisition and display of X-ray data in a single spectrum with low spectral resolution

Scanning electron microscope (SEM): Instrument that applies an electron beam for observation/analysis of samples, including imaging by SEI and BSE; some have EDS.

Secondary electron image (SEI): Low-energy electron image more sensitive to surface features.

Wavelength dispersive spectrometry (WDS): Most sensitive acquisition of X-ray data for quantitative analysis; slower than EDS but more accurate and precise.

Phase: Physically and chemically separable part of a system, such as a mineral in a rock

Shells (electron, X-ray): Atomic electron energy levels from which electrons are ejected to produce X-rays.  In order of decreasing energy, the most useful are:

• K: Innermost shell
• L: Next outer shell
• M: Next outer shell

Spectrum: Range of X-ray wavelength/energy, within which peaks represent characteristic X-rays.

Please acknowledge us in your publications using the following language:

"Electron images and X-ray data were collected on the JEOL JXA-8530F field-emission-gun (FEG) electron microprobe in the Yale University Department of Earth and Planetary Sciences. Installation of this instrument was funded by the NSF(IF/EAR-0744154) and Yale University."