[en] In order to improve the electrical behaviour of metal-insulator-metal capacitors with ZrO_2 insulator grown by Atomic Layer Deposition, the influence of the insertion of interfacial Cr layers between Pt electrodes and the zirconia is investigated. An improvement of the α-voltage coefficient of capacitance as low as 567 ppm/V"2 is achieved for a single layer of Cr while maintaining a high capacitance density of 10.7 fF/μm"2 and a leakage current of less than 1.2 × 10"−"8 A/cm"2 at +1 V. The role of the interface is discussed by means of X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy showing the formation of Zr stabilized chromia oxide phase with a dielectric constant of 16.

[en] Since the availability of monochromators in transmission electron microscopes (TEMs), electron energy loss spectrometry (EELS) is widely used to determine band gaps and the dielectric properties of semiconductors on a nano-metre scale. Nevertheless, three physical effects hamper straightforward analysis: (a) relativistic energy losses, (b) the delocalization of the energy loss which is in the 10 nano-metreer range for valence losses, and (c) the presence of interface plasmons. When reducing the operation voltage of the TEM one can kill two birds with one stone: (a) the relativistic losses will disappear as soon as v_e< c₀/n(with v_e as the speed of the electron, c₀ as the vacuum speed of light and n as the refractive index of the investigated sample) and (b) the delocalization will decrease, because it also depends on the energy of the incident electron probe. The determination of the optical properties of quantum structures is discussed in the case of GaP/GaAs interface at 200 keV and 20 keV beam energy, respectively. Further, the influence of the delocalization of the energy loss signal is discussed theoretically and experimentally.

[en] Since monochromated transmission electron microscopes have become available, the determination of bandgaps and optical properties using electron energy loss spectrometry (EELS) has again attracted interest. The underlying idea is very simple: below the bandgap energy no transitions can contribute to the valence EELS signal. However, the bandgap cannot be directly read out from the recorded data. Therefore the optical properties cannot be determined correctly from the low loss using the Kramers-Kronig relations. We will discuss under which conditions relativistic effects may be surpressed. It is demonstrated that scanning TEM (STEM) geometry is not applicable for most bandgap measurements

[en] According to theory, x-ray magnetic circular dichroism in a synchrotron is equivalent to energy loss magnetic chiral dichroism (EMCD) in a transmission electron microscope (TEM). After a synopsis of the development of EMCD, the theoretical background is reviewed and recent results are presented, focusing on the study of magnetic nanoparticles for ferrofluids and Heusler alloys for spintronic devices. Simulated maps of the dichroic strength as a function of atom position in the crystal allow evaluating the influence of specimen thickness and sample tilt on the experimental EMCD signal. Finally, the possibility of direct observation of chiral electronic transitions with atomic resolution in a TEM is discussed.

[en] A transmission electron microscopy study of a tempered bainitic nuclear reactor pressure vessel steel was carried out. Cross-section thin foils from nickel electroplated Charpy V-notch specimens fractured in impact and quasi static loading at -30 deg. C were prepared in the ductile tearing and cleavage regions of the fracture surface. In the ductile tearing zone, the microstructure was very heterogeneous. Dislocation cells, shear bands, and fine heavily deformed subgrains were found. The deformation in the impact specimen was localized only in the vicinity of the fracture surface, where long thin subgrains situated along the fracture surface were often observed. In the quasi static three-point bend specimen, the strain localization was found also in deeper areas under the fracture surface. There were shear bands (bundles of long thin subgrains) mostly aligned in parallel to the fracture surface. Numerous areas of the shear band intersections (at ∼45^o to the main shear band direction) were also observed. In the vicinity of cleavage zones of both types of specimens, no significant differences in the microstructure with respect to the bulk material were observed. Only an increased dislocation density was found

[en] The recently discovered EMCD technique (energy loss magnetic chiral dichroism) can detect atom specific magnetic moments with nanometer resolution, exploiting the spin selectivity of electronic transitions in energy loss spectroscopy. Yet, direct imaging of magnetic moments on the atomic scale is not possible. In this paper we present an extension of EMCD that can overcome this limit. As a model system we chose bcc Fe. We present image simulations of the L₃ white line signal, based on the kinetic equation for the density matrix of the 200 kV probe electron. With actual progress in instrumentation (high brightness sources, aberration corrected lenses) this technique should allow direct imaging of spin moments on the atomic scale.

[en] Retardation effects such as Cerenkov losses and waveguide modes alter the valence electron energy-loss spectrum of semiconductors and insulators as soon as the speed of the probing electron exceeds the speed of light inside the probed medium. This leads to the dilemma, that optical properties from these media cannot be determined correctly using electron energy-loss spectrometry (EELS) if no corrections are applied. In this work we present two ways out of this dilemma: a reduction of the beam energy and the application of an off-line correction. We demonstrate the accuracy of these two methods by using two similar layers of Si_x:H having slightly different refractive indices and discuss the impact of the normalization parameter during Kramers-Kronig analysis (KKA) on the obtained dielectric properties. We further demonstrate that KKA can be applied without the use of standard specimens, if thickness determination using transmission electron microscopy and EELS is accurate enough

[en] Electron vortex beams were only recently discovered and their potential as a probe for magnetism in materials was shown. Here we demonstrate a method to produce electron vortex beams with a diameter of less than 1.2 Angst . This unique way to prepare free electrons to a state resembling atomic orbitals is fascinating from a fundamental physics point of view and opens the road for magnetic mapping with atomic resolution in an electron microscope.

[en] The aluminium induced layer exchange process is used for growing crystalline Si films on amorphous substrates like glass, which are further epitaxially thickened and can be used for photovoltaic applications. In this work we investigated Al₂O₃ membranes separating the Al and Si layer during the layer exchange by means of high-resolution transmission electron microscopy and studied the influence of the membranes' structure on crystallization of Si. We observed a phase transformation of the membrane from the amorphous state to γ-Al₂O₃ at exchange temperatures at above 450 deg. C. At higher temperatures this transformations induces cracks into the thin membrane. We further discuss the influence of this phase transformation on the preferential orientation of the growing Si grains

[en] The measurement of circular dichroism in the electron microscope is a new, emerging method and, as such, it is subject to constant refinement and improvement. Different ways can be envisaged to record the signal. We present an overview of the key steps in the energy-loss magnetic chiral dichroism (EMCD) experiment as well as a detailed review of the methods used in the intrinsic way where the specimen is used as a beam splitter. Lateral resolution up to 20-30 nm can be achieved, and the use of convergent beam techniques leads to an improved S/N ratio. Dichroic effects are shown for Ni and Co single crystal; as a counterexample, measurements were carried also for a non-magnetic (Ti) sample, where no dichroic effect was found