Ulf Berges

Structure of the interface between ultrathin SiO{sub 2} films and 4H-SiC(0001)

The interface between ultrathin SiO{sub 2} films and 4H-SiC(0001) has been studied by x-ray photoelectron spectroscopy (XPS) and photoelectron diffraction. The investigation was performed for two different films. An ordered silicate layer showed a clear ({radical}(3)x{radical}(3))R30 deg. reconstruction, whereas a second film showed no long-range order. The comparison of the photoelectron diffraction data from these two films reveals that the local atomic environments of the Si atoms at the interface are very similar in both films. Further, a comparison of the experimental data with simulation calculations within a comprehensive R-factor analysis shows that also the local environments around near-interface Si atoms inside the SiO{sub 2} film are similar, but some modifications to the model are necessary. The use of the cluster radius as a fitting parameter in the simulation allowed to estimate the size of locally ordered regions in the film without long-range order to be about 4.5 to 5.0 A ring . It turns out that the transition from SiC to SiO{sub 2} is abrupt and therefore the occurrence of defects in the SiO{sub 2} film near the interface is probable. These defects may be oxygen vacancies, oxygen dangling bonds or silicon interstitials.

Investigation of carbon contaminations in SiO2 films on 4H-SiC(0001)

SiO2 films can be grown on SiC by oxidation of the clean SiC surfaces. During the oxidation process carbon atoms have to leave the crystal. This occurs by outdiffusion of CO molecules from the reaction front through the growing film. Carbon atoms remaining at the interface or in the oxide film lead to an increased density of states in the band gap, and therefore lower the quality of the SiO2∕SiC interface. In this work photoemission spectroscopy and photoelectron diffraction were used to study the carbon contamination in ultrathin SiO2 films on 4H-SiC(0001). The contaminations were produced during oxidation at high temperatures and low oxygen pressure. Due to their chemical shift carbon atoms from the contaminations and from the substrate can be distinguished in the C 1s photoemission spectrum. A combined photoelectron spectroscopy and photoelectron diffraction study shows that these carbon agglomerations are similar to carbon enrichments observed after heating of clean SiC surfaces and that they are eith...

Detection of the Magnetocrystalline Anisotropy in X-Ray Magnetic Linear Dichroism Reflection Spectra Across the Fe 3p and 2p Edges

The magnetocrystalline anisotropy of X-ray magnetic linear dichroism (XMLD) reflection spectra measured on single-crystalline bcc Fe films across the 3p and 2p edges are presented. The XMLD spectra were obtained from a series of reflection spectra by aligning the electric field vector of linearly polarized undulator radiation with respect to the crystal axes. Our results show the presence of a huge magnetocrystalline anisotropy in the XMLD reflection spectra. The XMLD signal is further investigated as a function of the Fe film thickness in Au/Fe/Ag/GaAs layered systems. Simulations of the reflection spectra reveal the influences of interference effects, which can enhance or diminish the XMLD signals. The measured spectra are in good agreement with ab initio calculated spectra.

Hard x-ray photoemission spectroscopy on the trilayer system MgO/Au/Fe using standing-wave excitation

The trilayer system MgO/Au monolayer/Fe was investigated by hard x-ray photoemission experiments in combination with the standing-wave technique. The insertion of the Au layer into the Fe/MgO tunnel junction provides an additional handle to influence the properties of the interface. The recently explored method of standing-wave excited hard x-ray photoemission was used to investigate both the structural properties and chemical states of the interfacial layers in one experiment. The results show that the Au monolayer does not grow as a closed layer, but intermixes strongly with the Fe below. This behaviour results in a very sharp interface between the Au/Fe and the MgO layer on top. However, the XPS spectra show no hint for a formation of FeO at the interface.

Thermal stability of ultrathin ZrO{sub 2} films and structure determination of ZrSi{sub 2} islands on Si(100)

The temperature dependence of ultrathin

Facing the interaction of absorbed silicon nano-ribbons on silver

{\text{ZrO}}_{2}

Photoemission Electron Microscopy and Scanning Electron Microscopy of Magnetospirillum magnetotacticum’s Magnetosome Chains

films on clean

Photoemission Electron Microscopy as a Tool for Studying Steel Grains

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Structure of the interface between ultrathinSiO2films and4H−SiC(0001)

-reconstructed Si(100) was studied by means of x-ray photoelectron spectroscopy and photoelectron diffraction (XPD).

Determination of layer-resolved composition, magnetization, and electronic structure of an Fe/MgO tunnel junction by standing-wave core and valence photoemission

{\text{ZrO}}_{2}