Co/Cu superlattices with total thicknesses ranging from 10 nm to 60 nm and with periodicities of 1.6–8.5 nm were sputtered on single-crystalline sapphire (1120)-substrates. Sputtering with low rates at room temperature yields samples of high epitaxial and crystalline quality. By careful choice of the sputtering parameters, either the fee [100] or the fcc [111] orientation can be selected as growth direction on one and the same substrate orientation. The preference for a particular film orientation appears to be kinetically driven. In all cases, the average lattice spacings d and the appearance of satellite reflections in x-ray Bragg-scans point to coherent growth up to thicknesses of 30 nm. X-ray small angle reflectivity measurements reveal clear oscillations and satellites indicative for smooth interfaces. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations supplement the characterization of the films.

In the present study fluorescence microscopy is used in order to investigate the light-induced shape transitions of giant unilamellar vesicles. Therefore pyrene was solubilized in the lipophilic core of the bilayer which allows the transformation of the shape of unilamellar vesicles upon UV irradiation. It turns out that tubular vesicles tend to collapse after illumination forming a string of nearly monodisperse spherical pearls. Giant unilamellar spherical vesicles with small excess areas can be changed reversibly into elliptical aggregates after irradiation with UV light.

In the present study the influence of toluene on the bending elastic modulus k(c), of dimyristoylphosphatidylcholine (DMPC) vesicles in the L-alpha phase is investigated using videomicroscopy. For giant unilamellar DMPC vesicles, a mean value of k(c) = (1.42 +/- 0.21) x 10(-19) J is determined at 30 degrees C. Addition of toluene, which is predominantly incorporated in the lipophilic core of the bilayer. induces a lowering of the bending elastic modulus with increasing concentration up to a plateau value of k(c) = (0.36 +/- 0.10) x 10(-19) J. This effect seems to be dominated by the mobility of the nonpolar molecules in the lipophilic part of the bilayer. Vesicles near the maximum solubilization capacity exhibit an anomalous increase of the bending elastic constant because of the formation of small hydrophobic dusters of phase-separated toluene. In the case of complete membrane saturation, these clusters can be clearly visualized in the vesicle membrane region. Thermally induced undulations vanish as a consequence of the reduction of the excess area a. Microscopy investigations of the temperature dependence of the bending elastic modulus were performed for both pure DMPC and toluene containing DMPC vesicles. Further analysis of the isobaric thermal area expansion coefficient beta indicates a reduced thermal expansivity for vesicles containing toluene. The values of beta vary from (6.9 +/- 0.8) x 10(-3) K-1 for DMPC vesicles to (1.6 +/- 0.3) x 10(-3) K-1 in the presence of toluene.

Ultra thin buried InAs layers on GaAs (001) crystals prepared by molecular beam epitaxy are structurally characterized using synchrotron radiation. Grazing incidence X-ray reflectivity and crystal truncation rods were utilized to determine the average layer thickness, interface roughness, and the stoichiometry of the layers. From X-ray standing wave experiments the In lattice site and vertical distribution are determined. We discuss our results in view of the structural transition of the layer system with In deposition from 1.0 to 2.1 ML.

We have investigated the magnetic structure of thin [001] oriented Cr films using neutron and X-ray diffraction experiments to measure their spin density waves and the strain waves, respectively. For epitaxial Cr films with thicknesses between 1000 and 4000Å grown on Nb films on sapphire substrates, we provide phase diagrams including incommensurate transverse and longitudinal spin-density waves (SDW) as well as commensurate antiferromagnetic spin structures. The results show that for Cr(001) on Nb a single domain SDW prevails with a wave vector Q perpendicular to the surface. At low temperatures the SDW is longitudinal and becomes mostly transverse between 150 and 250K, higher than in bulk Cr where the spin–flip transition occurs at 123K. Furthermore, the magnitude of Q is increased as compared to bulk Cr. These effects decrease with increasing film thickness. With neutron scattering we have also observed a commensurate antiferromagnetic phase with spins pointing out of the plane. The commensurate phase occurs at a temperature between 250 and 305K and persists up to at least 340K, far above the bulk Néel temperature of 311K for the incommensurate phase.

For thin epitaxial Cr(001) films capped with a ferromagnetic Fe layer a transverse spin density wave (SDW) is expected which propagates in the out-of-plane direction with the Cr spins aligned parallel to the film plane in the direction of the Fe magnetization vector. Synchrotron and neutron scattering experiments show, however, that the SDW wave propagates parallel to the film plane with spins oriented out-of-plane. In addition, a commensurate antiferromagnetic phase is found. The re-orientation of the SDW is caused by a frustrated Fe–Cr exchange coupling introduced by monoatomic steps at the Fe–Cr interface. Complete re-orientation takes place over some distance close to the interface reducing severely the coherence length of the SDW structure. With the surface scattering method we have measured the coherence length of the SDW as a function of depth. Furthermore, we have investigated the role of the commensurate antiferromagnetic phase near the Fe–Cr interface. We find no scattering from a commensurate order, implying a layering of the two phases with the incommensurate phase on top.

Medium energy ion scattering, X-ray standing waves and measurements of crystal truncation rods were used to show that it is possible to prepare spatially well confined Bi doping layers (δ-doping layers) on Si(001) with a Bi doping level of 3 × 1021cm−3 by a combination of Bi molecular beam epitaxy and low temperature deposition of a Si top layer with subsequent annealing (solid phase epitaxy). The Bi concentration exceeds the equilibrium Bi solubility by more than three orders of magnitude. The Bi atoms are incorporated into the Si host lattice on substitutional sites. The Bi doping profile exponentially decays into the top Si layer with an attenuation length ranging from 40 to 6Åand a fraction of Bi atoms in substitutional lattice sites of up to 96%, depending on the annealing conditions.

We have investigated proximity effects of Fe layers on the spin density waves (SDW) and the concomitant charge density waves or strain waves in thin epitaxial Cr[001] films using synchrotron and neutron scattering. Unlike in bulk Cr we observe a strong anisotropic occupation of the three possible SDWs with their wave vectors Q pointing along the {001} directions. In a pure 3000 Å thick Cr[001] film, the SDW exhibits an almost complete out-of-plane orientation, whereas in a Cr film of the same thickness capped by a 20 Å Fe layer the SDW becomes completely reoriented with Q now propagating in the plane. This SDW is preserved over the entire temperature range from 10 K up to the Néel temperature of about 311 K.

High fluence implantation of 95-keV Fe-ion in epitaxial Ag/Fe 200 Å/Ag-(001)-multilayers were performed to induce structural modifications. The correlation between structural quality and magnetic properties was investigated by measurements with ferromagnetic resonance (FMR) and out-of-plane x-ray-diffraction techniques (XRD). The FMR results show for fluences up to 1015 cm−2 a decrease of the crystalline- and perpendicular-uniaxial anisotropies, which are attributed to strain relaxation due to the ion-irradiation detected with XRD. From these results the magnetoelastic coefficient B1 is determined to −3×106 J/m3. At higher fluences of 1016 cm−2 we observe a strong reduction of the perpendicular-uniaxial anisotropy and a change of the crystalline anisotropy from cubic towards that of a tetragonal symmetry. Further, increasing fluences lead to a lattice widening above the Fe-bulk value and an increase of the interface roughness.

Ion beam mixing in epitaxial Ag/Fe/Ag-(001)-layers by 95 keV-Fe-ions at room temperature has been investigated by means of ferromagnetic resonance (FMR) and out-of-plane x-ray-diffraction (XRD). The XRD-data show for fluences less than 10(15) cm(-2) a strain relaxation of the Fe-layer and interface roughness of 1-3 monolayers. The influence on the magnetic parameters can be well described by a magnetoelastic effect due to the strain relaxation indicating rearrangements and demixing at the interfaces. At a fluence of 10(16) cm(-2) we observe a strong reduction of the perpendicular-uniaxial-anisotropy and a change of the crystalline-anisotropy from cubic towards that of a tetragonal symmetry. Simultaneously a lattice widening above the Fe-bulk value and an increase of the interface roughness occur.

We have investigated proximity effects of Fe layers on the spin density waves (SDW) in thin epitaxial Cr[0 0 1] films with neutron scattering. Unlike in bulk Cr we observe a strong anisotropic occupation of the three possible SDWs. In pure Cr[0 0 1] films the SDWs exhibit an almost complete out-of-plane propagation with spins parallel to Q. With only 20 A Fe on top of these Cr films, the SDW becomes completely re-oriented with Q now propagating in the plane but the Cr-spins still point out of the plane. This implies that the Fe and Cr moments are ooriented perpendicular to each other.

We present the observation of charge density waves and strain waves in thin epitaxial Cr(001) films by means of scattering with synchrotron radiation. The Cr films were grown by molecular beam epitaxial techniques on MgO(001) substrates and on Al2O3 (11¯02) substrates with a Nb(001) buffer layer. The ratio between the amplitudes of both modulations can be derived from the measured intensities. From the data a substrate induced change of this ratio and of the modulation wavelength as compared to the bulk value can be infered.

We have grown by molecular-beam-epitaxy thin Cr(110) films on Nb(110) buffer layers on sapphire Substrates. Films ranging from 50 Angstrom to 1100 Angstrom in thickness exhibit a single-domain structure. Using extensive x-ray characterization methods, we find a pronounced in-plane expansion of the Cr layers which relaxes as the film thickness increases, while the out-of-plane lattice spacing remains constant and bulklike over the entire thickness range. The in-plane lattice relaxation can be described by an isotropic strain relaxation model. In contrast, the out-of-plane behavior is highly anomalous, which may be due to strain density waves.

We have prepared Co/Cu(111) superlattices by molecular-beam-epitaxy methods on sapphire (1120BAR) substrates with a Nb buffer layer. The structural properties with various superlattice periodicities and layer thicknesses have been thoroughly analyzed by high-resolution x-ray Bragg-scattering and surface-scattering methods. The characterization includes the structural coherence lengths and mosaic distributions parallel and perpendicular to the film plane, the epitaxial relation to the Nb buffer, the stacking sequence, and in particular the interfacial roughness. These parameters are crucial for the interpretation of magnetic data concerning the exchange coupling in the Co/Cu superlattice. For all the superlattices studied we find that they are coherently strained with complete in-plane matching and corresponding out-of-plane Poisson response. The stacking is always completely fcc-like, with no hcp contribution even for a Co/Cu thickness ratio of 2/1. The interfacial roughnesses as obtained from fits to low- and high-angle x-ray reflectivity data are 14 and 6 angstrom, respectively. These parameters are discussed within the framework of random and correlated roughness effects.

A quantitative simulation is carried out in order to test the political outcome of ABM and MIRVs. Technical variables serve as input: number of ICBMs, of ABMs, hit probabilities, etc. Strategic positions result as output: mutual second strike capability, effective defense of one power only, etc. The conclusion is that MIRVs, especially in com bination with ABMs, represent an extreme threat to equilibrium.