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Understanding the correlation between the morphological and functional properties of particulate materials is crucial across all fields of physical and natural sciences. This manuscript reports on the investigation of the effect of polyethylene glycol (PEG) employed as a capping Agent in the synthesis of SrTiO3 crystals. The crucial influence of PEG on both the shape and size of the strontium titanate particles is revealed, highlighting the effect on the photocurrents measured under
UV–Vis irradiation.
As one of the widely used analytical methods for the analysis of elemental composition of solid matter, energy dispersive X-ray spectroscopy (EDS) has recently gained significant importance regarding its application to the chemical analysis of nanoparticles, especially in conjunction with the use of a scanning electron microscope (SEM) and the use of the transmission operation mode of SEM (STEM-in-SEM). This development was mainly driven by the technological progress with highly sensitive EDS detectors, such that individual nanoparticles can be quickly inspected with EDS at a SEM. Qualitative information on elemental composition with about 10 nm spatial resolution can be achieved complementary to the high-resolution information of the sample surface morphology within the same scanned area as provided by the electron microscope. Representative examples with successful EDS analysis on nanoparticles are presented, but also limitations of the method are described.
An energy dispersive X-ray spectrometer operating with a semiconductor detector should be specified in compliance with the ISO standard 15632 [1]. Requirements for specification are: a) a general description of the spectrometer to evaluate its performance, b) the energy resolution with corresponding dead time, c) the P/B ratio in the Fe55 spectrum and, finally, d) the L/K intensity Ratio in a Ni or Cu spectrum to estimate spectrometer efficiency at low energies. Items b) to d) can be easily checked by the user. Related procedures are recommended in the annexes of the standard.
Checking the performance of energy dispersive X-ray spectrometers as well as validation of the results obtained with energy dispersive X-ray spectrometry (EDX) at a scanning electron microscope (SEM) involve the use of (certified) reference and dedicated test materials. This paper gives an overview on the test materials mostly employed by SEM/EDX users and accredited laboratories as well as on those recommended in international standards. The new BAM reference material EDS-CRM, which is currently in the process of certification, is specifically designed for the characterization of EDS systems at a SEM through calibration of the spectrometer efficiency in analytical laboratories in a simple manner. The certification of the spectra by means of a reference EDS is described. The focus is on the traceability of EDS efficiency which is ensured by measurements of the absolute detection efficiency of silicon drift detectors (SDD) and Si(Li) detectors at the laboratory of the PTB using the electron storage ring BESSY II as a primary X-ray source standard. A new test material in development at BAM for testing the performance of an EDS in the energy range below 1 keV is also briefly presented.
To compare the performance of different energy dispersive X-ray spectrometers (EDS), it is important to define characteristic spectrometer parameters. The ISO 15632 standard defines parameters like energy resolution as FWHM for the Kα lines of carbon, fluorine and manganese. The quantum efficiency, which is the ratio of the detected photons divided by the number of incoming photons for different energies, is another significant spectrometer property. It is important for the light element and low energy line detection sensitivity as well as for higher photon energies above 10 keV. A striking EDS feature, provided and marketed by many manufactures, is the active area of the detector, although actually, the solid angle available for photon collection is the more relevant geometrical parameter. It is defined as: Ω = A /r2 with A being the active area of a spherical detector and r being the distance between the point of the radiation origin and the center of the surface of the active detector chip. A more accurate calculation should be used for large flat detector areas. One should note that the solid angle Ω is not an intrinsic spectrometer property. It can only be defined for a specific detector in combination with a specific system (e.g. SEM, EPMA or TEM). Thus, the minimal possible distance r is determined by the particular geometry e.g. a possible interference with the pole piece or other detectors/components in the chamber of a microscope. New EDS technologies use e.g. integrated SDD chips or inclined chips in thinner detector fingers which can be placed closer to the sample with the final result of larger real solid angles. Therefore, the knowledge of the real solid angle is one of the crucial parameters of an EDS microscope combination. A straightforward way to estimate the real solid angle is to simply determine A and r. If respective data are not provided by the manufacturer, this approach can be difficult.
Need for large-area EDS detectors for imaging nanoparticles in a SEM operating in transmission mode
(2014)
The accurate knowledge of the properties of polycapillary X-ray semi-lenses has a significant influence on the quantitative results in a widespread field of applications involving microfocus X-ray beams. A routine procedure for the characterisation of a polycapillary X-ray semi-lens with a scanning electron microscope (SEM) having attached an energy dispersive spectrometer (EDS) is presented in this paper. A key issue of the procedure consists of fitting the semi-lens in front of the EDS for spectra acquisition. Relevant semi-lens parameters such as focal distance, full width at half maximum (FWHM) of the acceptance area, and transmission are determined in parallelising mode of the semi-lens. Special attention has been paid to the calculation of the transmission.
Determination of the efficiency of an energy dispersive X-ray spectrometer up to 50 keV with a SEM
(2009)
Both electron and polychromatic photon excitations (micro-focus X-ray source) at a scanning electron microscope (SEM) are used to determine the efficiency of an energy dispersive X-ray spectrometer up to 50 keV by means of a calibrated X-ray spectrometer and reference materials (RM) specially selected for this purpose.