Parallel-detection Electron Energy Loss Research Articles

Grooved fluorescent plate for parallel-detection electron energy loss spectroscopy in ultra-high-voltage electron microscopy

The fluorescent plates in parallel-detection electron-energy-loss spectroscopy are studied from the viewpoint of the spatial resolution and the background of spectra. The self-supporting fluorescent plate is proposed in order to reduce the backscattered electrons from the supporting substrate of the fluorescent plate. Many fine grooves are cut on the thin Si plate and are filled with phosphor powder. This “grooved fluorescent plate” is effective to suppress the blur of spectra although the intensity decreases slightly.

Nanoanalysis of impurity precipitation on grain boundaries in polysilicon

Polycrystalline silicon (polysilicon) has been the subject of extensive studies in recent years due to its wide applications in microelectronics and solar cells, see for example references. In most cases of interest impurities segregated to the grain boundaries strongly modify the electronic properties of this material. Understanding the behavior of impurities in polysilicon requires a detailed knowledge of their distribution, phase and thermodynamical stability. In the present study, the structure and chemistry of grain boundaries in polysilicon were characterized by HREM and very high spatial resolution FEG/AEM.The specimen materials are Solarex cast polysilicon used for solar cells, which are manufactured under a proprietary method called the ubiquitous crystallization process. The samples for TEM observations were cut from the ingot perpendicular to its growth direction and then thinned to electron transparency by mechanical polishing and ion milling. HREM was performed at 200kV in an ISI-002B. Microanalysis was done using a Philips 400ST/FEG microscope coupled to a Gatan parallel-detection electron energy loss spectrometer, at 100kV. A liquid nitrogen cooled specimen holder was used for nanoprobe experiments to minimize specimen contamination and local specimen heating.

Parallel EELS as a complementary tool in an Analytical TEM study of metal alloys

The advent of efficient parallel-detection electron energy loss spectrometers (EELS) in analytical transmission electron microscopes (ATEM) promotes rapid elemental characterization of various materials containing light, as well as heavy, elements at high spatial resolution. In the current study, the microstructures of Udimet 520 and HK-25 were investigated to integrate advances in parallel EELS methods with other ATEM techniques.Thin foils of Udimet 520, a nickel based heat-resistant superalloy, were obtained using common ion milling techniques. Precipitates of the HK-25, a heat resistant steel alloy, were obtained by etching (with Marble's reagent) a polished surface, extracting with a replicating Parlodian film, dissolving the film with amyl acetate and dispersing the resulting particles on holey carbon grids. A JEOL 2000FX ATEM fitted with a Gatan Model 666 EELS system was operated at 200 kV for studies of these alloys.

Inelastic Electron Scattering and Total Reflectivity in RHEED

The detailed studies of the electron energy distribution of the specular reflected beam and the total reflectivity for a platinum single crystal (111) surface under a variety of diffraction conditions were carried out on a JEM-2000FX transmission electron microscope equipped with a Gatan 666 paralleldetection electron energy loss spectrometer.Five different diffraction conditions are characterized as D1-D5. With D1, the specular reflected spot falls in an intersection of a parallel Kikuchi line with a parabola; with D2, the specular reflected spot coincides with an intersection of the Kikuchi lines running parallel to and inclined to the crystal surface; with D3, that is pure specular Bragg reflection (the specular reflected spot crosses only the parallel Kikuchi line); with D4, the specular reflected spot intersects only with a parabola; and with D5, the specular reflected spot falls only on the oblique K-lines. A series of specular reflected beam energy loss spectra collected from the first four different diffraction conditions is shown in figure 1, where the spectra 1-4 correspond to conditions D1-D4, respectively.

Towards quantitative analysis of nanometer-sized helium bubbles in irradiated steels using parallel-detection EELS in a STEM

The stress rupture properties of high nickel austenitic alloys and austenitic stainless steels used in the nuclear industry are strongly affected under irradiation by the formation of helium from boron by means of an n-α reaction. As the congregation and growth of helium bubbles (typically 20-50nm diameter) at grain boundaries can cause embrittlement in stressed steels, it is important to gain an understanding of embrittlement mechanisms in the material. Consequently, an accurate measurement of quantities such as bubble pressure and metal surface energy is highly desirable. However, this can only be achieved if the number of helium atoms per unit volume is known. In this work, we report on the use of parallel-detection electron energy loss spectroscopy (PEELS) on a VG HB501 scanning transmission electron microscope (STEM) as a powerful technique for characterising helium bubbles in irradiated steels. In addition, we suggest a simple analytical process that could be used to quantify the amount of helium present in each bubble.

Parallel detection electron energy loss spectroscopy for microanalysis in transmission electron microscopy

Parallel detection electron energy loss spectroscopy for microanalysis in transmission electron microscopy

Fine structure of inner shell electron energy loss edges of manganese oxides

Rask et al. showed that electron energy loss spectroscopy (EELS) may be used to identify oxidation states of polyvalent cations. For the case of manganese, differences in oxidation state are reflected in the shape and position of the edges in the EELS spectrum due to inelastic scattering of incident electrons by the inner shells of manganese and oxygen. We have used a scanning transmission electron microscope (STEM) with a cold field emission gun (FEG) and a parallel-detection EELS system to re-investigate the variations in energy loss fine structure of EELS spectra of various manganese oxides with a significantly improved energy resolution.Spectra were recorded at 100 kV using a VG HB501 STEM with post-specimen lenses, and a Galan Model 666 parallel-detection electron energy loss spectrometer. The operation and performance of this system are discussed elsewhere in these proceedings. For the inner shell edges, the energy dispersion produced by the spectrometer was set to give 0.05 eV per channel. so that a complete spectrum of 1024 channels sampled a range of energy loss of 50 eV. The energy resolution, of the order of 0.4 eV, was therefore not limited by the spatial resolution of the photodiode array in the spectrometer. The oxygen K and manganese L2,3 edges were recorded separately.

Progress in parallel-detection electron energy loss spectroscopy

Parallel-detection electron energy loss spectrometers improve the detection efficiency by several hundred times compared to the traditional serial-detection spectrometers, but they have their own set of difficulties, such as the limited dynamic range of solid state detectors, the possibility of stray reflections of the intense zero loss beam giving rise to spurious background, and channel-to-channel gain variation. Fortunately, none of these difficulties is turning out to be insoluble. Here we report on improvements of the Gatan 666 parallel detection electron spectrometer in the areas of increasing the dynamic range of the detector, and in eliminating stray reflections.The increase in the dynamic range of the detector was needed especially for low energy losses (high spectral intensities), which usually saturated the detector even at the minimum acquisition time of 12 msecs. Accordingly, we have developed an electron attenuator which uses a magnetic dipole to sweep the spectrum across the detector perpendicular to the dispersion direction (Fig. 1).

Parallel detection electron spectrometer using quadrupole lenses

The design and performance of a parallel detection electron energy loss spectrometer utilizing several new design elements are described. The system uses three electromagnetic quadrupole lenses to transform the electron energy spectrum produced by a single magnetic sector spectrometer into a magnified spectrum suitable for parallel detection, and detects the spectrum with a single-crystal YAG scintillator, which is fiber-optically coupled to either a 512-channel or a 1024-channel photodiode detector. The photodiode is interfaced to a computer via direct memory access, and it is possible to read out entire spectra in 6.1 ms. The photodiode is cooled to -30°C, and the noise due to the dark current only begins to limit the detector performance for integration times longer than 100 s. The system is capable of achieving detective quantum efficiencies higher than 0.25 over eight decades of electron intensities of interest to EELS carried out in a transmission electron microscope. The optimum operation of the system is described and the theoretical limits of the system performance are discussed. Examples of results from several standard EELS test specimens are given, and the most probable future uses for parallel detection are briefly described.

High spatial resolution analysis using parallel detection EELS

The application of parallel detection electron energy loss spectroscopy to the characterization of small particles or interfaces is demonstrated. Data are presented that show variations of low energy loss plasmons, Al L 23 edge near edge fine structure, and oxygen concentration with spatial resolution better than 10 nm. The use of this technique for chemical and electronic structure measurements from very small specimen volumes is discussed.