The adsorption of the two group-III metals Ga and In on Si(112) has strong influence on the morphology of the intrinsically faceted Si(112) surface. Upon Ga or In adsorption, the Si(112) surface is smoothed, and quasi-1D adsorbate structures along the [110] direction are observed. These structures consist of (Nx1) building blocks of different sizes, the periodicity of which can be controlled by surface coverage and deposition temperature, as revealed by spot profile analysis low-energy electron diffraction. From x-ray standing-wave measurements, building blocks consisting of two parallel rows of adsorbate atoms are identified for both Ga/Si(112) and In/Si(112). One adsorption site is identified as a terrace (substitutional) site and the other one as a step-edge (adatom) site. These experimental results are compared to several relaxed model structural configurations obtained from density functional theory calculations. In the case of Ga/Si(112), a previously reported structural model by Snijders et al. [Phys. Rev. B 72, 125343 (2005)], including two Ga vacancies per unit cell is corroborated, while for In/Si(112), existing models by Gai et al. [Phys. Rev. B 61, 9928 (2000)] and by Bentmann et al. [Phys. Rev. B 80, 085311 (2009)] can be ruled out, and a new structural model including only one In vacancy per unit cell in the step-edge site is concluded on, similar to the Al/Si(112) model introduced by Gupta and Batra [Phys. Rev. B 72, 165352 (2005)].

The preadsorption of Ag on Si(111) drastically changes the growth of Ge. In a temperature range from $400{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ to $650{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, Ag adsorption on Si leads to the formation of a $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-R ${30}^{\ensuremath{\circ}}$ reconstruction that exhibits a maze-like morphology on the mesoscopic scale, as observed by low-energy electron diffraction (LEED) and low-energy electron microscopy. This maze morphology can be attributed to a surface roughening on an atomic scale, induced by the re-arrangement of top layer atoms during the $7\ifmmode\times\else\texttimes\fi{}7$ to $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-R ${30}^{\ensuremath{\circ}}$ transition. The subsequent deposition of Ge results in the formation of a wetting layer, the evolution of which has been found to be governed by the Ag/Si(111)-$\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$-R ${30}^{\ensuremath{\circ}}$ template's maze structure, as the latter offers a high density of heterogeneous nucleation sites. Upon further Ge growth, three-dimensional islands with diameters in the micrometer range are formed, which exhibit a large and flat (111) top facet. X-ray photoemission electron microscopy reveals that during Ge growth, Ag is segregating to the surface very efficiently. Grazing-incidence x-ray diffraction and transmission electron microscopy have been used to study the composition, strain state and defect structure of the Ge islands in dependence of the growth temperature. The strain induced by lattice mismatch is found to be largely relaxed (80--90% relaxation) in the investigated growth temperature range from 400 to $600{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, which is confirmed by high-resolution LEED measurements. As a main relaxation mechanism, the formation of interfacial misfit dislocations has been identified. Interdiffusion of Si into the Ge islands becomes more and more pronounced for increasing growth temperature, whereas the formation of twinned Ge regions can drastically be suppressed at higher temperature.

Adsorption of Al on a Si(113) substrate at elevated temperatures causes a faceting transition of the initially flat surface. The (113) surface decomposes into a quasi-periodic sequence of Al terminated (115)- and (112)-facets. The resulting surface morphology is characterized in-situ by reciprocal space maps obtained with in-situ spot profile analyzing low-energy electron diffraction and ex-situ atomic force microscopy. The periodicity length of the faceted surface increases with adsorption temperature from 7nm at 650°C to 80nm at 800°C. The stability of the Al terminated Si(112) surface is the driving force for the faceting transition.

The change of the Si(112) surface morphology and structure induced by In adsorption, as well as the impact of In preadsorption on the growth kinetics and island morphology in Ge/Si(112) epitaxy, has been investigated by means of low-energy electron microscopy and diffraction. The intrinsically faceted Si(112) surface is smoothed upon In saturation. In contrast to a previously reported (7 × 1) reconstruction (reported in a recent work of Gai et al.), we observe a [(3 + x) × 1] superstructure, with x ≈ 1/2. This is attributed to the coexistence of (3 × 1) and (4 × 1) building blocks with In vacancies. The presence of such vacancy rows is confirmed by the saturation of the [(3 + x) × 1] structure at about 0.8 monolayers. Ge growth on In-saturated Si(112) leads to the formation of 3-D islands, the morphology of which depends on the growth temperature. At 450°C, isotropic and dashlike islands are observed, whereas at 500°C, larger islands with a triangular outline are found. The orientation of the side facets of these triangular islands have been identified to be (111), (013), and (103). The dependence of the island density on the growth temperature indicates an enhanced Ge surface diffusion, as compared with growth on bare Si(112).

The growth of Ge on Ag:Si(111)-√3×√3-R30° has been studied by low-energy electron microscopy (LEEM), low-energy electron diffraction (LEED) and x-ray photoemission electron microscopy (XPEEM). For submonolayer adsorption of Ag at 550°C, the Ag terminated √3×√3-R30° domains decorate the step edges of the substrate. The wetting layer growth and Ge island nucleation on such a step-edge decorated surface is quite similar to Ge growth on bare Si(111)-7×7. During Ge deposition, the √3×√3-R30° domains dissolve and small Ag terminated 3×1 domains are formed that are distributed over the whole surface. Larger 3×1 domains are found only at the circumference of the three-dimensional (3D) Ge islands. From the Ge 3D island morphology, size distribution and density it is concluded that in this submonolayer Ag pre-adsorption scenario there is only little influence of the Ag on the growth kinetics and island geometry. This is completely different for Ge growth on an entirely covered Ag:Si(111)√3×√3-R30° surface. As compared to growth on bare Si(111)-7×7, a strong increase of the diffusion length is observed that leads to a drastic reduction of the island density. Also the island morphology is strongly affected by Ag pre-adsorption in this regime. Instead of triangular islands, we observe huge, irregularly shaped islands that rather resemble a discontinuous Ge film. [DOI: 10.1380/ejssnt.2010.221]

The influence of Ga pre-adsorption on Si(111), Si(113) and Si(112) surfaces on Ge growth has been investigated by low-energy electron diffraction and microscopy as well as X-ray photoemission spectroscopy. On Si(111), step edges and substrate domain boundaries are decorated with Ga at high deposition temperatures, enabling selective growth and alignment of three-dimensional Ge islands on a chemically modulated surface. On Si(113), a morphological modulation is achieved by Ga saturation, as the Si substrate decomposes into an ordered array of (112) and (115) facets. This results in the growth of Ge islands aligned at the facets. These islands exhibit an anisotropy, as they are elongated along [110]. Ga pre-adsorption on Si(112) smoothens the initially faceted bare surface, and subsequent Ge growth leads to the formation of nanoscale Ge wires. The results are discussed in terms of surface chemistry, as well as diffusion and strain relaxation anisotropy. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The pre-adsorption of Ga on Si(112) leads to a drastic change of the morphology of subsequently grown Ge islands. In contrast to the case for Ge growth on bare Si(112), even nanowire growth can be achieved on Ga terminated Si(112). Employing low energy electron microscopy and low energy electron diffraction, the initial phase of Ge nucleation and Ge island growth was systematically analysed for growth temperatures between 420 and 610 °C, both on clean and on Ga terminated Si(112). In both cases the island density exhibits an Arrhenius-like behaviour, from which diffusion barrier heights of about 1.3 and 1.0 eV can be estimated for growth with and without Ga pre-adsorption, respectively. The Ge island shape on the bare Si(112) surface is found to be nearly circular over the whole temperature range, whereas the shapes of the Ge islands on the Ga terminated Si(112) become highly anisotropic for higher temperatures. Ge nanowires with sizes of up to 2 µm along the direction are observed.

The impact of silver pre-adsorption on germanium growth oil Si(113) was investigated using in-situ low-energy electron microscopy (LEEM) as well as low-energy electron diffraction (LEED). The adsorption of silver leads to the formation of a regular pattern of nanofacets along the [1 (1) over bar0] direction. The periodicity of this pattern in [33 (2) over bar] direction was determined to (44 +/- 4) nm. From LEED series at different energies the facets were identified to be of (111) and (115) orientation. While the (111) facets show a (root 3 x root 3)-R30 degrees reconstruction, the (115) facets exhibit a (2 x n) superstructure The subsequent growth of Ge results in the formation of nanoislands that are aligned along the facets. These Ge islands have an anisotropic shape with typical sizes of about 100 nm in [332] direction and 400 nm in [1 (1) over bar0] direction (C) 2009 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim

Magnetization and domain structure of thin cobalt wedges on textured Au substrates were studied by scanning electron microscopy with polarization analysis (SEMPA). In the thickness regime with perpendicular magnetization, as-grown films contain small domains with diameter between 0.3 and 1.5 μm. The small size is connected to the morphology of the film resulting from the textured nature of the Au substrate. Applying a magnetic field gives a distinct dependence of measured polarization on film thickness, most likely caused by variations in coercivity. Results are compared with those obtained for similar films on single crystal Au substrates, in view of the relation between magnetic properties and morphology.

The magnetic structure of wedge-shaped Co/Au(111) films has been analyzed in the thickness range of around five monolayers where a reorientation transition takes place. The detection of two critical thicknesses with an apparently new phase in between them can be understood by evoking general considerations of stability and coexistence of phases. The analysis in terms of thickness-driven evolution in the anisotropy space of the system leads to the determination of the surface anisotropy constants of first and second order in a most direct and consistent manner.

We investigated YBa2(Cu1−zMz)3O7-δ (MNi,Zn) thin films and determined the decrease of Tc and the increase of residual resistivity due to Cu-site substitution, taking into account the CuO-chain contributions to the total conductivity. Although Zn suppresses Tc stronger than Ni by a factor of 2.3 the increase of resistivity differs only slightly. Furthermore the observed resistivities are too high to be explained within scattering from point-like defects. To reconcile these contradictions, we assumed finite size scattering potentials, which lead to scattering phase shifts δl of higher angular momebtum l > 0. Tc-suppression is discussed qalitatively within this picture.

Cu-site substituted thin films of YBa2(Cu1-zMz)3O7-δ (M=Zn,Ni) are reinvestigated. The Tc-suppression and residual resistivities ϱo are measured as a function of the concentration z. We found that for low concentrations z < 4% the substituents occupy preferrably the in-plane Cu sites whereas for higher concentrations the chain sites are also occupied. Although the residual resistivities of Ni and Zn differ only slightly, the Tc-suppression of Zn is 2.3 times larger than that of Ni. To reconcile the measured resistivities with predictions of a two dimensional scattering model, it is necessary to assume a scattering potential of finite range and to take scattering phase shifts] δl of higher angular momentum (l > 0) into account. The different Tc-suppression rates for Zn and Ni are also discussed within this picture.

The magnetic domain structures in thin hcp Co films grown on Au(111) have been investigated by means of scanning electron microscopy with polarization analysis. The domain pattern in films with out-of-plane magnetization were analyzed in the as-grown state and after annealing. The heat treatment causes the morphology and the magnetic microstructure to change drastically. The films become smoother and the domain pattern exhibits a characteristic thickness dependence. A collapse of the domain size near the reorientation transition is found, consistent with micromagnetic theory.

Bragg reflections of YBa2Cu3O7 (YBCO) films with c-axis orientation on (001) SrTiO3, (001) MgO and (110) NdGaO3 substrates prepared by MO-CVD, sputtering techniques and laser ablation were examined with Co Kalpha and synchrotron radiation (lambda = 0.56 angstrom, HASYLAB, Hamburg) using the q-scan technique at four circle diffractometers. One of the specimens was doped with Ni. The evaluation of positions and relative intensities of the splitted reflections shows a strong correlation between the structure of the substrate surface and the twinning geometry of the YBCO layer.Irradiation of the films on SrTiO3 substrate by heavy ions (1.2 GeV Bi-209, 1.4 GeV U-238, UNILAC, GSI Darmstadt) leads to a gradual parallel alignment of a, b, and a, b(f) (subscripts (s) denoting substrate. and (f) film) which is completed for a dose between 10(11) and 10(12) particles/cm2.

The dependence of resistive transitions, thermal activation energies, and critical current densities of YBa/sub 2/(Cu/sub 1-x/Zn/sub x/)/sub x/O/sub 7- delta / and YBa/sub 2/(Cu/sub 1-x/Ni/sub x/)/sub 3/O/sub 7-x/- thin films on B, T, and the angle Theta between the magnetic field and the c-axis is studied. A decrease of the critical temperature T/sub c/ with increasing doping concentration x is observed. For small x an increase of the activation energy is found, with a maximum around 0.2%. This can be explained by a model assuming local pinning potentials due to the impurity atoms, which begin to overlap for higher concentrations. The films exhibit higher j/sub c/ values for small dopant concentrations than without doping. If the angle Theta is changed, a different j/sub c/(B, T, Theta ) behavior is found than in high-quality undoped films, with additional structures in the curves.< >

Ni-doped epitaxial thin YBa2(Cu1-xNix)3O7-delta films have been prepared by high-oxygen-pressure dc sputtering from stoichiometric targets on SrTiO3 substrates. Structural properties of these c-axis-oriented films were not affected by Ni doping up to x = 15%. Inductively measured transition temperatures show a decrease with a rate of -4.5 K/(at. % Ni) for Ni concentrations up to x = 4%. For higher Ni contents the T(c)-depression rate changes to -1.5 K/(at. % Ni). A change in slope is also detectable in the dependence of the resistivity on Ni concentration. These results can be explained in a model based on a concentration-dependent site preference of the Ni atoms. The activation energy for vortex creep (extracted from resistive transitions) and the critical-current density show the pinning effectiveness of the dopant. Scaling laws for the pinning-force density have also been studied. The Hall concentration n(H) shows a slight increase for small x and a decrease for higher values. The slope dn(H)/dT is also lowered for increasing Ni content. Furthermore, the mobility and the Hall angle of the YBa2(Cu1-xNix)3O7-delta films were deduced from experimental data.

Superconductivity in high-T c oxides originates from the presence of (CuO 2 )-planes which lead to highly anisotropic normal and superconducting transport properties. The short coherence length ξ c ≈ 1 to 3Å causes a spatial variation of the order parameter along the c-direction with dramatic consequences on the vortex dynamics. As model systems to study the influence of structural changes we prepared epitaxial YBa 2 ( Cu 1−x TM x ) 3 O 7 films ( TM = Zn and Ni), Bi 2 Sr 2 CaCu 2 O 8 films and coherent YBa 2 Cu 3 O 7 / PrBa 2 Cu 3 O 7 superlattices. Measurements of the critical current density [Formula: see text] clearly reveal the intrinsic pinning mechanism in YBa 2 Cu 3 O 7 for B ⊥ c at low temperatures which disappears approaching T c . Small transition metal dopings act as pinning centers reducing dissipation due to thermally activated flux movement. The decoupling of the (CuO 2 )-layers in the superlattices causes a transition from anisotropic 3d to 2d behavior. Therefore the superconducting properties in external magnetic fields, which resemble closely those of Bi 2 Sr 2 CaCu 2 O 8 films, are dominated by the field component parallel to the c-axis. For B ⊥ c the resistive transitions ρ (B, T) and the critical current density j c (B, T) are nearly field independent.