Research Equipment
The following is a description of our Electron Probe Micro Analyzer (EPMA), housed in the New Materials Center Analysis & Measurement Room.
Electron Probe Micro Analyzer
JXA-8900R, JEOL Ltd.
First of all, what exactly is an Electron Probe Micro Analyzer (EPMA)?
If one wants to determine the chemical composition of solid materials on a microscopic scale, an effective method is to stimulate an area of the target sample, and then to observe what comes out. With an Electron Probe Micro Analyzer (EPMA), incident electrons are the stimulant and the things that come out are X-rays with characteristic energy. As the sample is bombarded by a focused electron beam, electron-sample interactions take place and they yield both derivative electrons and x-rays from the sample. Via different processes giving rise to different types of signals, one can learn that each of which carries information about some property of the sample. EPMA is a fully qualitative and quantitative method of non-destructive elemental analysis of micron-sized volumes at the surface of materials in vacuum. Analyses can be performed automatically at microscopic points or over small areas of the sample surface to produce compositional maps.
What is its minimum field of analysis, and how precise is it?
EPMA is used for non-destructive elemental analysis of micron-sized volumes at the surface of materials. The electron optics of an EPMA allow much higher resolution images to be obtained than can be seen using visible-light optics, with sensitivity at the level of ppm. Routine quantification to 1% reproducibility is obtained over several days.
Are there any limitations as to what elements can be analyzed in a sample?
Yes. Liquids and gasses cannot be analyzed since measurement must be conducted under vacuum with the device. There are two methods of analysis available when using an EPMA to analyze X-ray energy. The first involves the use of a Bragg reflection from a dispersive crystal. Wavelength Dispersive X-ray Spectroscopy (WDS) is used to separate and detect a wavelength (energy), and since the resolution is high (up to 10 eV), and the background level is low, elements releasing characteristic X-rays with similar energy are also distinguished. A micro area can be analyzed with this method. However, an X-ray intensity is lost from the sample when using a spectrometer and this must be compensated for by applying a lot of electron beams to it. This leads to several demerits for this method, such as damaging the sample or needing extra time to perform measurements. Elements that can be analyzed with this method range from Be to U. The other method is called Energy Dispersive X-ray Spectroscopy (EDS). This involves separating X-ray energies with a semiconductor X-ray detector, and producing signals which correspond to the resulting intensity. The merits and demerits of this method are completely opposite of those for the WDS method. Elements that can be analyzed with this method range from B to U. So, one must choose a method that either a) tends to damage the sample by the application of electron beams, or b) is used according to the difference in characteristic X-ray energy between elements to be analyzed.
Finally, how is the Electron Probe Micro Analyzer being used at JAIST?
When performing synthesis of advanced materials and characterizing their novel physical properties, the EPMA is indispensable for nondestructively determining chemical composition of macroscopic as well as nanoscopic materials synthesized. At JAIST the EPMA is used for analyzing the chemical composition of advanced materials including glass, high-temperature superconductors, hetero-epitaxial oxide thin films of semiconductors, biochemistry, and so on.
