C. Westphal

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.

Hafnium silicide formation on Si(100) upon annealing

High dielectric constant materials, such as HfO{sub 2}, have been extensively studied as alternatives to SiO{sub 2} in new generations of Si based devices. Hf silicate/silicide formation has been reported in almost all literature studies of Hf based oxides on Si, using different methods of preparation. A silicate interface resembles close to the traditional Si/SiO{sub 2}. The silicate very likely forms a very sharp interface between the Si substrate and the metal oxide, and would be suitable for device applications. However, the thermal instability of the interfacial silicate/oxide film leads to silicidation, causing a dramatic loss of the gate oxide integrity. Despite the importance of the Hf silicide surface and interface with Si, only a few studies of this surface are present in the literature, and a structural determination of the surface has not been reported. This paper reports a study of the Hf silicide formation upon annealing by using a combination of XPS, LEED, and x-ray photoelectron diffraction (XPD) analyses. Our results clearly indicate the formation of a unique ordered Hf silicide phase (HfSi{sub 2}), which starts to crystallize when the annealing temperature is higher than 550 deg. C.

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...

Surfactant mediated heteroepitaxial growth of Ge/Si(111) probed by X-ray photoelectron diffraction

X-ray photoelectron diffraction (XPD) is used as a tool to investigate the growth of Ge on Si(111) with and without surfactant (Sb) mediation. Structural information is extracted directly from the forward scattering maxima of recorded photoelectron diffraction patterns. The result of a quantitative analysis of the patterns taken for Ge layers of different coverage are used for a structural growth model of Ge on Si(111). Without Sb, a compression of the top Si and the first Ge double layers is found followed by a relaxation of the Ge structure. Under the presence of Sb an intermixed interface is formed followed by compressed Ge double layers and relaxed distances between double layers.

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

THE TRANSITION FROM AMORPHOUS SILICON OXIDE TO CRYSTALLINE SILICON STUDIED BY PHOTOELECTRON DIFFRACTION

{\text{ZrO}}_{2}

Photoelectron diffraction as a tool for the study of a buried interface during heteroepitaxial growth of Sb/Ge/Si(111)

films on clean

Facing the interaction of absorbed silicon nano-ribbons on silver

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

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