California Volcano Observatory

Menlo Park SEM and Electron Microprobe

Building 11, contact Dawn Ruth

A computer screen and keyboards sit on a table next to a tall boxy electron microscope, flanked by long detector tubes

Scanning Electron Microscopy lab, Menlo Park California.

(Credit: Jessica Ball, CalVO. Public domain.)

The Electron Microbeams Facility is located at the USGS Menlo Park and is run by CalVO. The facility hosts two instruments with overlapping but complementary approaches for chemical analyses, the scanning electron microscope (SEM) and the electron probe microanalyser (EPMA). Both approaches use a focused electron beam to excite the surface of materials. Upon excitation, the material emits x-rays that can reveal its chemical makeup.

The Scanning Electron Microscope (SEM) is designed for rapid analysis of a wide range of areas (< 1 µm to several mm), providing an immediate assessment of the chemistry of geologic materials. The SEM is also optimized for high spatial resolution sample imaging. Research includes, but is not limited to:

  • Qualitative chemical mapping of methane hydrates
  • Imaging and qualitative chemical analyses of minerals and microbes associated with soil development

The SEM is actually a combination of several instruments and detectors that combine multiple approaches for detailed geochemical, textural, and crystallographic analysis.

  • Tescan Vega3 Tungsten Filament Scanning Electron Microscope
  • 2 Oxford X-MaxN 150 mm2 energy dispersive spectrometers
  • Oxford Symmetry Electron Backscatter Diffraction detector
  • Gatan cryo-stage for low temperature and low vacuum analyses
  • TESCAN Motorized Retractable Extended Spectral Range Panchromatic Cathodoluminescence Detector (185-850 nm spectral range)

Many researchers use the SEM as a reconnaissance tool to help guide their work on the EPMA. The EPMA is designed for high precision analyses, allowing the user to analyze low concentration elements at high spatial resolution (≥1 µm to 10s µm). Research includes, but is not limited to:

  • Analysis of tephra collected from the seafloor to study volcanic and marine sediment processes along the Gulf of Alaska
  • Analysis of experimental petrology samples to decipher magmatic processes within the deep crust
A boxy microprobe with multiple electron-producing tubes sits next to a desk with two wide monitors and two empty chairs

The full setup for the electron microprobe in Menlo Park, CA, including a computer with JEOL, Thermo, and Probe for EPMA software. 

(Credit: Dawn Ruth, USGS. Public domain.)

The Electron Probe MicroAnalyzer (EPMA) is also a combination of multiple instruments and detectors, optimized for high spatial resolution, quantitative, geochemical analysis. Our new (as of March 2021) instrument is a JEOL JXA 8530 F+ Electron Probe Microanalyzer with the following specifications:

  • 5 Spectrometer configuration:
    • Spectrometer 1 (4 crystal, standard size): TAP, PET, LDE1, LDE2
    • Spectrometer 2 (2 crystal, large size):  TAP L, LDE6 L
    • Spectrometers 3-5 (2 crystal, large size):  PETL, LIFL
  • Thermo Energy Dispersive Spectrometer
  • JEOL Panchromatic Cathodoluminescence Detector
  • ibss GVX10 DS Asher Source plasma cleaner
  • LN2 cold finger

In addition to JEOL and Thermo software, the lab also uses Probe for EPMA.

The Electron Microbeams Facility is a user facility open to all USGS scientists and outside researchers interested in chemical analysis at high spatial resolution. Interested users should contact Dawn Ruth ( for information about instrument availability and pricing.


Dawn CS Ruth, PhD

Research Geologist and Electron Microbeam Lab Director
Volcano Science Center
Phone: 650-329-4935