Unique Analytical Capabilities in FE-SEM Utilizing Soft X-Ray Spectrometer (SXES)

N. Erdman, S. Asahina, Y. Uetake
United States

Keywords: SEM, low voltage, nanostructure, soft X-ray spectroscopy


Successful imaging and characterization of nanomaterials, composites and biological specimens require unsurpassed performance in the low and ultra-low kV range in FEG-SEM for both imaging and analytical modes. The state of the art FEG-SEM nowadays shows superb resolution with various detectors at a wide range of accelerating voltages and has the ability to perform fast and reliable microanalysis at low kV using high probe currents, without loss of spatial resolution and with an ease of operation. Moreover, the analytical performance is becoming a significant factor and of particular interest is not only the ability to identify correctly the compositional differences but also to begin achieving in FE-SEM what has been long a realm of dedicated techniques like Auger or EELS, i.e. identifying the bonding characteristics and the chemical state.. Wavelength dispersive spectroscopy (WDS) has been traditionally the technique of choice in SEM when there was a need to either a) quantify elements with higher precision than EDS; or b) separate individual elements with overlapping peak positions. While the EDS has a resolution of around 127eV, the WDS spectrometer typically has an energy resolution of 16eV, almost an order of magnitude improvement in spectral resolution. A recently developed new soft X-ray spectrometer has been targeted specifically for ultra-low X-rays with energies as low as 50eV to be measured (for example Li Kα line) and up to 700eV. This detector offers enhanced detection sensitivity allowing analysis of Boron at tens of ppm range, with energy resolution of 0.2eV (Al L). The design of the spectrometer utilizes a specialized grating as an X-ray dispersive element, with the wavelength separated X-rays being collected on a CCD device that serves as a detector. The ability of an FE-SEM to deliver high current in a small spot at low kV improves efficiency of the soft X-ray collection. Moreover, because this type of spectrometer has an exceptional energy resolution, distinct peak shapes can be attributed to specific chemical states and density of states of the valence band. This means that for the first time chemical state analysis is available by utilizing an X-ray spectrometer in a common instrument such as SEM. In this paper we will present the results of utilizing this spectrometer for various materials science problems, such as corrosion and solute trapping, solar thin film analysis, trace element analysis of boron, carbon and nitrogen in steel and more. We will also discuss possibilities for analysis of higher atomic number elements as well.