The interpretation of highly resolved elemental maps is not straightforward: one has to consider the quantum mechanical nature of the scattering process as well as the influence of the microscope. Existing calculations of the contrast in elemental maps are based on a non-relativistic approach, while in most of the currently installed electron microscopes, the electrons penetrate the specimen with relativistic energies >/= 200 keV. Therefore, we have recalculated the intensity distribution in elemental maps based on a fully relativistic theory. Using the concept of contrast transfer functions, the simulations account for lens aberrations as well as the defocus. Surprisingly, the results exhibit considerable deviations between the relativistic and non-relativistic calculations even in the region of low acceleration voltages such as 100 kV. These differences increase with increasing acceleration voltage and are strongly dependent on aperture and energy loss. Quantitative simulations and evaluations of highly resolved elemental maps should therefore make use of a fully relativistic theory.

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We have compared anodically and rapid-thermally oxidized thin SiGe epitaxial layers on silicon. X-ray photoelectron, Auger, and Fourier transform infrared spectroscopies show the existence of SiO 2 and Si-O-Ge for anodic oxides, whereas thermally grown oxides consist of pure SiO 2 . The spatially resolved distribution of the elements in the layer has been investigated by electron energy loss spectroscopy images at microtomed samples. Thermal oxidation leads to a pile-up of Ge at the oxide/SiGe interface and Ge outdiffusion into the Si substrate. The Ge profile in the strained SiGe lattice of epitaxial layers is not affected by applying the electrochemical oxidation treatment. This leads to a significant increase of the photoluminescence intensity due to a decrease of nonradiative recombination, i.e. to a decrease of defect states at the interfaces.Low thermal budget passivation of single crystals or thin epitaxial layers of SiGe is of great interest for device applications such as metal oxide semiconductors 1 or hetero field effect transistors. 2,3 Thermal oxidation leads to a relaxation of the strained epitaxially grown SiGe layer on Si substrate and to a segregation of Ge. 4,5 Furthermore, it has been found that Ge migration to the oxide/ semiconductor interface still occurs at 500°C. 6 Several processes exist which have the potential to suppress this effect. Among those are thermal oxidation at about 500°C at high pressure ͑50-70 bar͒, 7 plasma-assisted oxidation, 8 ion beam deposition, 9 and anodic oxidation. 5 This paper presents a comparative study of oxides grown on epitaxial layers of SiGe by rapid thermal oxidation ͑RTO͒ at 1000°C in dry oxygen atmosphere for 3 min and by anodic oxidation. ExperimentalThe anodic oxidation was performed in 0.04 M KNO 3 /0.3% H 2 O/ethylene glycol solution at room temperature up to a potential of 50 V between the sample and the platinum counter electrode. 5,10,11 The oxide thickness is defined by the applied voltage for a constant concentration of water ͑about 4-5 Å/V for 0.3% water 11 ͒. Afterward, the samples were annealed in forming gas at 450°C. The epitaxially grown strained SiGe layer was deposited at 550°C, had a thickness of about 46 nm, a Ge content of nominally 26%, and was protected by a 5 nm thick Si cap which was removed prior to the oxidation. The oxide thicknesses were on the order of 20 nm. The oxidized SiGe samples were characterized by high resolution transmission electron microscopy ͑HRTEM, Philips CM 30͒ electron spectroscopic imaging ͑ESI, JEOL 3010 with gatan imaging filter͒, Fourier transform infrared ͑FTIR, Perkin Elmer 2000͒, and pulsed photoluminescence spectroscopies. 12

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