A coincidence transmission electron microscope with digital waveform measuring system for analytical microscopy

We have been developing a new analytical transmission electron microscope (TEM), called a coincidence TEM, which in principle enables elemental mapping images to be observed at a high signal‐to‐noise (S/N) ratio under very low dose radiation conditions. In this paper, we report the development of a coincidence TEM with a digital waveform measuring system for obtaining a coincidence elemental mapping image. In this system, analog signals detected by a Si(Li) detector and a multianode, position‐sensitive photomultiplier (PSPM) are continuously converted into 12‐bit digital waveform data at a rate of 100 MHz, and transferred to a PC. From the transferred digital waveform data, information on X‐ray photon energy, electron incident position, and detection times of both X rays and electrons are calculated by digital waveform measurement, which lead to the observation of a successful coincidence elemental mapping image. Copyright © 2005 John Wiley & Sons, Ltd.     

Electron holography with a Cs-corrected transmission electron microscope.

Cs correctors have revolutionized transmission electron microscopy (TEM) in that they substantially improve point resolution and information limit. The object information is found sharply localized within 0.1 nm, and the intensity image can therefore be interpreted reliably on an atomic scale. However, for a conventional intensity image, the object exit wave can still not be detected completely in that the phase, and hence indispensable object information is missing. Therefore, for example, atomic electric-field distributions or magnetic domain structures cannot be accessed. Off-axis electron holography offers unique possibilities to recover completely the aberration-corrected object wave with uncorrected microscopes and hence we would not need a Cs-corrected microscope for improved lateral resolution. However, the performance of holography is affected by aberrations of the recording TEM in that the signal/noise properties ("phase detection limit") of the reconstructed wave are degraded. Therefore, we have realized off-axis electron holography with a Cs-corrected TEM. The phase detection limit improves by a factor of four. A further advantage is the possibility of fine-tuning the residual aberrations by a posteriori correction. Therefore, a combination of both methods, that is, Cs correction and off-axis electron holography, opens new perspectives for complete TEM analysis on an atomic scale.     

Local and surface analysis within an analytical electron microscope

Analytical transmission electron microscopes have the ability to display at very high spatial resolution both the structural information of solid specimens prepared as thin films and the spectroscopic information related either to electronic properties or to the elemental composition. An example of study, by electron energy loss spectroscopy, of small spherical silicon particles is given as an illustration of the performances of the technique.     

A piezoelectric goniometer inside a transmission electron microscope goniometer

Piezoelectric nanoactuators, which can provide extremely stable and reproducible positioning, are rapidly becoming the dominant means for position control in transmission electron microscopy. Here we present a second-generation miniature goniometric nanomanipulation system, which is fully piezo-actuated with ultrafine step size for translation and rotation, programmable, and can be fitted inside a hollowed standard specimen holder for a transmission electron microscope (TEM). The movement range of this miniaturized drive is composed of seven degrees of freedom: three fine translational movements (X, Y, and Z axes), three coarse translational movements along all three axes, and one rotational movement around the X-axis with an integrated angular sensor providing absolute rotation feedback. The new piezoelectric system independently operates as a goniometer inside the TEM goniometer. In situ experiments, such as tomographic tilt without missing wedge and differential tilt between two specimens, are demonstrated.     

High-resolution analytical transmission electron microscopy of semiconductor quantum structures

Analytical transmission electron microscopy was applied to characterize the size, shape, real structure, and, in particular, the composition of different semiconductor quantum structures. Its potential applicability is demonstrated for heterostructures of III-V semiconducting materials and II-VI ones, viz. (In,Ga)As quantum wires on InP and (In,Ga)As quantum dots on GaAs both grown by metal organic chemical vapor deposition, and CdSe quantum dots on ZnSe grown by molecular beam epitaxy. The investigations carried out show that the element distribution even of some atomic layers can be detected by energy-dispersive X-ray spectroscopy, however, exhibiting a smeared profile. Contrary to that, sub-nanometre resolution has been achieved by using energy-filtered transmission electron microscopy to image quantum dot structures.     

Investigations on thin solid layers by analytical transmission electron microscopy

Summary Among the instruments for solid state characterization working with a free electron probe, the Transmission Electron Microscope (TEM) has the best lateral resolution. The application is restricted, however, by the demand that the samples need to be suitably thinned. TEMs operating in the scanning mode yield several advantages. Equipped additionally with spectrometers, the TEM becomes an Analytical TEM. Energy Dispersive X-ray Spectroscopy (EDXS) and Electron Energy Loss Spectroscopy (EELS) allow the chemical analysis of the observed details of structure; the EELS permits additionally investigations on the electron configuration and on binding relations. Technical developments have increased considerably the information possibilities, such as lateral resolution or detection sensitivity. Recently two new types of instruments are in development, the dedicated Scanning-TEM with a field emission gun, supplying scanning images and analyses up to the nanometer range, and the energy filtering (stationary beam-) microscope which yields images and diffraction diagrams with a sharpness in contrast not previously reached. In the future the construction of an aberration-free objective lens promises a further advance into the atomic dimension.     

Transmission electron microscope and scanning auger investigations of temper-embrittled 12% Cr steel

Summary Reversible temper-embrittlement of 12% Cr martensitic steel was investigated. It was observed by SEM that morphology of the carbides found on the smooth intercrystalline fracture facets of the embrittled sample is much different from M₂₃C₆ carbides observed by TEM on the former austenite grain boundaries. Morphology of the carbides on the smooth facets matches TEM data for the M₇C₃ carbides formed during the embrittlement treatment in some distance from the former austenite grain boundaries. Associated SAM analysis data suggest that phosphorus tends to concentrate within stress fields formed around M₇C₃ carbides.

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Untersuchungen von Versprödungseffekten in Cr-Iegierten Stählen mit Transmissionelektronenmikroskopie und Auger-Spektroskopie

     

Imaging modes for scanning confocal electron microscopy in a double aberration-corrected transmission electron microscope.

Aberration correction leads to reduced focal depth of field in the electron microscope. This reduced depth of field can be exploited to probe specific depths within a sample, a process known as optical sectioning. An electron microscope fitted with aberration correctors for both the pre- and postspecimen optics can be used in a confocal mode that provides improved depth resolution and selectivity over optical sectioning in the scanning transmission electron microscope (STEM). In this article we survey the coherent and incoherent imaging modes that are likely to be used in scanning confocal electron microscopy (SCEM) and provide simple expressions to describe the images that result. Calculations compare the depth response of SCEM to optical sectioning in the STEM. The depth resolution in a crystalline matrix is also explored by performing a Bloch wave calculation for the SCEM geometry in which the pre- and postspecimen optics are defocused away from their confocal conditions.     

Nanostructure manipulation device for transmission electron microscopy: application to titania nanoparticle chain aggregates.

Experimental difficulties in studying nanostructures stem from their small size, which limits the use of traditional techniques for measuring their physical properties. We have developed a nanostructure manipulation device to apply tension to chain aggregates mounted in a transmission electron microscope. A 1-mm-long slit was cut in the center of a lead-tin alloy disc, measuring 3 mm in diameter and 200 microm in thickness. The disc was heated to about 140 degrees C before it was pressed between two quartz slides. The disc was then thinned by mechanical dimpling and ion milling until holes developed around the slit. The edges of the slit were 0.2 to 3 microm in thickness while the gap between them was up to a few microns. This disc was bonded to the two plates of a cartridge. The slit could be widened or narrowed at controlled speeds of 0.5 to 300 nm/s. The system was tested using titania (TiO2) nanoparticle chain aggregates (NCA) deposited across the slit. The ends of the NCA remained attached to the edges of the slit, which was widened at about 0.7 nm/s. In this way, the NCA was stretched up to 176% of its initial length before breaking.     

Low-energy electron capture by 6-Aza-2-thiothymine: investigations by electron attachment and electron transmission spectroscopies

The interaction of low-energy (0-10 eV) electrons with 6-aza-2-thiothymine is investigated in the gas phase by studies of sharp structure in the total electron scattering cross section and by mass analysis of the stable or long-lived negative ions produced by electron attachment. The most efficient fragmentation process, occurring at 0.15 eV, involves the ejection of a closed-shell neutral molecule (CH3CN). Ab initio calculations support our proposal that this process leads to ring closure to form a stable four-member heterocyclic anion. A long-lived parent anion with an approximate lifetime of 75 microseconds is observed near zero electron energy, and evidence is also seen for the slow decay of this anion by ejection of CH3CN. Near 3.3 eV, an anion of m/e 41 is produced that is likely to be a metastable valence anion of bent CH3CN, but the dipole-bound anion cannot be ruled out.     

Characterization of Fe/Cr multilayers by analytical transmission electron microscopy

Different techniques of analytical TEM were used to investigate Fe/Cr multilayers. These multilayers show a dependence of their electrical resistance as a function of the magnetic field. This effect called giant magnetoresistance can be utilized for example in magnetic recording heads. Typical dimensions of the single layer thickness are in the nanometer region. Therefore the microstructure of this material has been investigated by transmission electron microscopy (TEM). To get additional analytical information energy dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS) can be used. Received: 15 July 1997 / Revised: 5 February 1998 / Accepted: 6 February 1998     

Automated grain mapping using wide angle convergent beam electron diffraction in transmission electron microscope for nanomaterials

The grain size statistics, commonly derived from the grain map of a material sample, are important microstructure characteristics that greatly influence its properties. The grain map for nanomaterials is usually obtained manually by visual inspection of the transmission electron microscope (TEM) micrographs because automated methods do not perform satisfactorily. While the visual inspection method provides reliable results, it is a labor intensive process and is often prone to human errors. In this article, an automated grain mapping method is developed using TEM diffraction patterns. The presented method uses wide angle convergent beam diffraction in the TEM. The automated technique was applied on a platinum thin film sample to obtain the grain map and subsequently derive grain size statistics from it. The grain size statistics obtained with the automated method were found in good agreement with the visual inspection method.     

Application of analytical transmission electron microscopy to the characterization of interlayers in fibre-reinforced composites with ceramic and glass matrices

The microchemistry of interfaces and corresponding interlayers in different fibre-reinforced ceramic and glass composite systems has been investigated by using a dedicated scanning transmission electron microscope demonstrating the potential applicabilities of such an instrument to this large field of materials science. Energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy were used to determine the materials composition on a nanometre scale. Besides analyses performed in the spot mode of the electron probe the distributions of the elements present in the interface region were measured as line profiles across the relevant interface structure by X-ray spectroscopy with a lateral resolution of about 5 nm, even for the detection of a light element as carbon. Moreover, in the composite systems under investigation the two-dimensional element distribution was also attained by energy-filtered imaging. In addition, first results of energy loss near edge structure analyses are presented indicating variations of the chemical bonding of silicon at the interface in a Nicalon fibre/Duran glass composite.     

Identification of respirable asbestos fibres by quantitative x-ray microanalysis with a scanning transmission electron microscope (STEM)

Summary Quantitative X-ray microanalysis of respirable asbestos fibres, based on the ratio method, enables the identification of different asbestos varieties in the submicrometre diameter range. A new identification scheme is proposed and applied for samples from an asbestos-cement factory and from a mining site. STEM analysis is compared with other methods of single particle analysis.

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Identifizierung von lungengängigen Asbestfasern mittels quantitativer Röntgenmikroanalyse mit einem Rastertransmissionselektronenmikroskop

Zusammenfassung Die quantitative Röntgenmikroanalyse von lungengängigen Asbestfasern im Submikrometerbereich nach der Verhältnismethode ermöglicht die Identifizierung der verschiedenen Asbestarten. Ein Schema zur Identifizierung von Asbestfasern wird vorgeschlagen und zur Charakterisierung von zwei Asbestproben angewendet. Vorteile und Nachteile der Methode in Vergleich mit anderen Methoden werden diskutiert.

     

Electron microscope investigations on the morphology of aluminium hydroxides

Summary The results are given of an investigation by means of the electron microscope and electron diffraction of the morphology of amorphous aluminium hydroxide and boehmite. The ageing process of amorphous aluminium hydroxide prepared from aluminium nitrate, ammonium alum and amalgamated aluminium was studied.

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Zusammenfassung Untersuchungen im Elektronenmikroskop und mit Elektronenbeugung über die Morphologie vom amorphen Aluminiumhydroxyd und B?hmit werden beschrieben. Die Alterung von amorphem Aluminiumhydroxyd, hergestellt aus Aluminiumnitrat, Ammoniumalaun und amalgamiertem Aluminium wurde untersucht.

     

Quantitative trace analysis with X-ray fluorescence in the scanning electron microscope

The potential of a scanning electron microscope will be enhanced markedly by adapting the X-ray fluorescence for material analysis. The illuminating system röntgenbox enables the analyst to execute analyses in the concentration range from 100 percent down to the low ppm range without time consuming preparation steps. X-ray intensities of traces are measured for different anodes in the elemental range fromZ=11 to 90 (sodium to thorium).