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Our in situ X-ray study shows that a silicon substrate in contact with an undersaturated In(Ge) solution is wetted by an approximately 1 nm thin germanium film, which does not grow any thicker. The results can be understood by the use of thickness-dependent correlated interfacial energies. This near-equilibrium heterogeneous interface structure marks the initial stage of crystal growth before the formation of bulk material, which can only form under conditions of supersaturation. This finding uncovers a fundamental aspect of the thermodynamics at solid-liquid interfaces relevant for understanding the transition from equilibrium to supersaturation and is of importance for nanoscale solution growth methods.

European accelerator-based X-ray facilities came together in 2017 in a consortium that will use their combined expertise to accelerate discoveries, secure funding and guide policy. A year and a half later, the chair of the consortium Helmut Dosch reflects on the ambition and opportunities of this type of cooperation.

We report Raman scattering measurements on azimuthally ordered thin films of F16CuPc, prepared by organic molecular beam deposition on A-plane sapphire substrates. The observed peak frequencies have been compared both to the results of a model calculation for the vibrational modes of the free molecule and to those reported by other authors in related materials. This analysis provides a plausible identification of the modes responsible for the strongest spectral features. Detailed evaluation of the spectra reveals that some observed modes, which correspond to vibrations of the macrocycle inner ring, largely retain the intramolecular character and their polarisation properties can be used to study the orientation and stacking configuration of the molecules. We provide structural parameters deduced either in molecular or crystal symmetry considering the simpler possibilities, i.e. a single column molecular stacking and a herringbone-like structure. The results suggest that the thicker and most ordered film is structurally close to the recently reported crystal organisation of bulk ribbon samples of this compound. The crystalline quality of the ordered films is mainly reflected in some other Raman peaks which are related to the motion of peripheral atoms and dominate the high wavenumber part of the spectra. These modes are affected by intermolecular interactions inducing Davydov splittings that are unequivocally identified by the observed Raman selection rules. The performed analysis also provides quantitative estimates of the degree of in-plane ordering. Copyright © 2013 John Wiley & Sons, Ltd.

25 pages, 5 figures, 2 tables., The rapidly increasing power conversion efficiencies of organic solar cells are an important prerequisite towards low cost photovoltaic fabricated in high throughput. In this work we suggest indane as non-halogenated replacement for the commonly used halogenated solvent o-dichlorobenzene. Indane was blended with the higher volatile solvents chloroform or toluene or o-xylene in order to improve wettability and to reduce drying time. The combination of high volatile solvents with the less volatile host solvent indane allows for an increased fabrication speed due to a reduction of the overall drying time and provides films with good light absorption behavior and high polymer crystallinity. For the solvent mixture toluene-indane, solar cell performance is comparable to the o-dichlorobenzene reference device indicating this mixture as a suitable replacement for increased productivity without drawbacks in nanomorphology as investigated by atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD). This study provides a fundamental understanding on solvent mixture drying kinetics and can aid the ink formulation., The presented work was funded by the German Research Foundation (DFG) within the Priority Program 1355. We thank Ralf Weigel for his support in the MPI-MF beamline at ANKA. We acknowledge the European Synchrotron Radiation Facility for provision of synchrotron radiation facilities and Alexei Vorobiev for his support at ESRF. We further thank Hendrik Hölscher and the Karlsruhe Nano Micro Facility (KNMF) for the access to the AFM. This work was carried out in the framework of Holst Centre’s shared research programs. B.S.H. thanks the Karlsruhe House of Young Scientists (KHYS) for financial support.

We report an in situ X-ray investigation of the composition dependence on the structural evolution during drying of doctor-bladed blends of poly-(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). This study enables an observation of the microstructure evolution in real time during blend crystallization. P3HT:PCBM blends with ratios of 1:0.5, 1:0.8, and 1:2 exhibit differing structural evolution during the course of solvent evaporation resulting in a different microstructure of the blends upon solidification. Large excess of PCBM over the eutectic composition impedes the π−π packing of P3HT chains and leads to a not yet observed diffraction feature with an associated spacing of 12.6 A, which might originate from a disordered phase of intimate mixed P3HT and PCBM molecules. This work provides a microscopic understanding of the composition dependence of the film formation from solution. The structural results are discussed in relation to the composition dependence of photovoltai...

Interfaces are inherent in and essential to organic electronic devices. At every interface, both organic/organic and organic/inorganic, the potential to utilize nanostructuring to control device performance is very high. In this paper, we focus on one example of nanostructuring at the donor/acceptor heterojunction in organic photovoltaics, with the purpose of modifing efficiency by four orders of magnitude. We show that the length of the exciton dissociating interface can be tuned by changing the substrate temperature for small molecule heterojunction photodiodes based on crystalline DIP/C60 mixtures. Due to the tuneable interface morphology, the performance of such devices can be changed from poor performing planar heterojunctions to higher efficiency ordered nanoscale bulk heterojunction structures. In this way, highly crystalline DIP can be thought of as a natural “bulk” heterojunction.

In this combined atomic force microscopy and X-ray diffraction study, we explore the microscopic origin of the scaling properties of the growth of organic−organic heterostructures formed here by F16CoPc and diindenoperylene (DIP) molecules as representative systems for electron and hole transporting materials. We evaluate the influence of the morphological properties of the first organic layer (DIP) on further temporal evolution of the morphology and structure of F16CoPc films. From the derived scaling exponents, we conclude that the morphology evolution is dominated by mound formation. The microscopic origin of such morphology is ascribed to structural changes occurring during the first stages of F16CoPc growth as revealed by grazing incidence X-ray diffraction (GIXD). The microstructure of organic materials should be taken into account, the challenging task of modeling growing surfaces and interfaces of organic materials.

The density deficit of water at hydrophobic interfaces, frequently called the hydrophobic gap, has been the subject of numerous experimental and theoretical studies in the past decade. Recent experiments give values for the interfacial depletion that consistently correspond to less than a monolayer of water. The main question which remained so far unanswered is its origin and the mechanisms affected by the chemistry and molecular geometry of a particular hydrophobic coating. In this work, we present a combined high-energy X-ray reflectivity and molecular dynamics simulation study of the water depletion at a perfluorinated hydrophobic interface with a spatial resolution on the molecular scale. A comparison of our experimental and computational results elucidates the underlying mechanisms that affect the extent of the interfacial depletion. The complex interplay between surface chemistry and topography precludes the existence of a direct and universal relation between the macroscopic contact angle and the nanoscopic water depletion.

We report a detailed study of the self-assembly process of di-indenoperylene (DIP) on Cu(1 0 0) surfaces, investigated by variable temperature scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. During the initial growth stages a preferred nucleation at the step edges is revealed. Subsequently, large ordered 2D islands grow from the step edges, while smaller 2D islands form on the terrace sites. The equilibrium fluctuation of these 2D clusters has been monitored in real-time, thereby obtaining a direct insight into the temperature dependence of the molecular surface diffusion. The substrate–adsorbate interactions determine the azimuthal molecular orientation, finally lead to the formation of highly ordered chiral domains which are commensurate with the substrate.

A crystalline nanoporous molecular network was tailored by supramolecular assembly of pentacene and F 16 CuPc on Cu(100). The structure and self-assembly mechanisms of the pure and binary layers were analyzed by STM. F 16 CuPc films and mixed layers of pentacene/F 16 CuPc in a ratio of 2:1 show two enantiomorphic chiral domains with high structural order in contrast to pentacene which exhibits no long-range order in pure films. A model of the epitaxial relationship on Cu(100) is given, which suggests C-F...H bonding as a possible driving force for the bimolecular self-assembly in addition to the still strong interaction between the substrate and the organic bilayer.

The formation of ultrathin oxide layers on the facets of MgO(0 0 1) supported Rh nanoparticles is revealed by high-resolution transmission electron microscopy (HRTEM) and spatially-resolved electron energy-loss spectroscopy (EELS). An O–Rh–O trilayer surface oxide has been observed on both {1 1 1} and (0 0 1) facets, which is confirmed by image simulation using the atomic model of a two-dimensional surface oxide obtained by density functional theory (DFT). The spacing between the oxide layer and the Rh {1 1 1} facet is however markedly smaller, indicating a variation of interface bonding in the case of nanoparticles. When the oxide layer is slightly thicker with two Rh planes, the structure of the surface oxide is different from corundum Rh2O3 bulk oxide, and the trilayer surface oxide persists as terminating layer. The spacing between the oxide layer and the Rh(1 1 1) facet is found to vary, being smaller in the middle of the oxide layer. It is also found that oxidation is more pronounced at the intersections of the nanoparticles’ facets.

We have investigated the structure and composition of the model catalyst system Pd/MgO(0 0 1) during oxidation, CO reduction and CO oxidation at near atmospheric pressures by a combination of in situ X-ray diffraction and ex situ transmission electron microscopy and spectroscopy techniques. From the in situ X-ray experiments, we find: (a) the Pd nanoparticles with 9 nm in diameter transform into epitaxial PdO above 10−1 mbar O2 pressure at 570 K, (b) the oxidation process can be reverted by CO exposure, recovering Pd nanoparticles in their initial orientation, and (c) during CO oxidation in a mixture of 50 mbar O2 and 50 mbar CO a new phase is evolving with lattice constant close to the MgO substrate value, which we assign to expanded Pd nanoparticles forming upon carbon incorporation. Ex situ transmission electron microscopy and different spectroscopy techniques uncover the CO2 induced growth of a disordered overlayer containing C, Mg and O, which forms during CO oxidation and leads to an overgrowth of Pd nanoparticles thereby deactivating the catalyst.

Diffuse X-ray scattering has been an important tool for understanding the atomic structure of binary systems for more than 50 years. The majority of studies have used laboratory-based sources providing 8 keV photons or synchrotron radiation with similar energies. Diffuse scattering is weak, with the scattering volume determined by the X-ray absorption length. In the case of 8 keV photons, this is not significantly different from the typical extinction length for Bragg scattering. If, however, one goes to energies of the order of 100 keV the scattering volume for the diffuse scattering increases up to three orders of magnitude while the extinction length increases by only one order of magnitude. This leads to a gain of two orders of magnitude in the relative intensity of the diffuse scattering compared with the Bragg peaks. This gain, combined with the possibility of recording the intensity from an entire plane in reciprocal space using a two-dimensional X-ray detector, permits time-resolved diffuse scattering studies in many systems. On the other hand, diffraction features that are usually neglected, such as multiple scattering, come into play. Four types of multiple scattering phenomena are discussed, and the manner in which they appear in high-energy diffraction experiments is considered.

Combining atomic force microscopy, X-ray specular reflection, and grazing incidence X-ray diffraction experiments provides a thorough characterization of the structural properties of PTCDI-C8 films on native silicon dioxide as a function of both growth and post-annealing temperatures. We disclose that monomolecular islands and terraces are polycrystalline with lateral sizes of only ∼280 A. While the lateral size of the crystallites remains unaffected by an increase of the growth temperature, the ordering along the surface normal is greatly enhanced, thereby reducing the density of topographical grain boundaries. Similarly, optimal post-annealing temperatures cause a better vertical ordering of the multilayer. From a detailed analysis of the X-ray reflectivity as obtained for the best ordered film, we provide accurate information on the vertical structure in the thin film and determine the tilt of the perylene cores.

By a combined AFM/X-ray study, we unveil a reconstruction at the organic interface accompanying the Stranski−Kranstanov growth of di-indenoperylene (DIP) deposited on fluorinated cobalt-phthalocyan...

An extensive search for possible structural models of the (2 × 1)-reconstructed rutile TiO 2 (0 1 1) surface was carried out by means of density functional theory (DFT) calculations. A number of models were identified that have much lower surface energies than the previously-proposed ‘titanyl’ and ‘microfaceting’ models. These new structures were tested with surface X-ray diffraction (SXRD) and voltage-dependent STM measurements. The model that is (by far) energetically most stable shows also the best agreement with SXRD data. Calculated STM images agree with the experimental ones for appropriate tunneling conditions. In contrast to previously-proposed models, this structure is not of missing-row type; because of its similarity to the fully optimized brookite TiO 2 (0 0 1) surface, we call it the ‘brookite (0 0 1)-like’ model. The new surface structure exhibits two different types of undercoordinated oxygen and titanium atoms, and is, in its stoichiometric form, predicted to be rather inert towards the adsorption of probe molecules.

The microscopic insight into how and why catalytically active nanoparticles change their shape during oxidation and reduction reactions is a pivotal challenge in the fundamental understanding of heterogeneous catalysis. We report an oxygen-induced shape transformation of rhodium nanoparticles on magnesium oxide (001) substrates that is lifted upon carbon monoxide exposure at 600 kelvin. A Wulff analysis of high-resolution in situ x-ray diffraction, combined with transmission electron microscopy, shows that this phenomenon is driven by the formation of a oxygen–rhodium–oxygen surface oxide at the rhodium nanofacets. This experimental access into the behavior of such nanoparticles during a catalytic cycle is useful for the development of improved heterogeneous catalysts.

By combining in-situ X-ray diffraction and atomic force microscopy, we investigate the structure and morphology of organic heterostructures formed by deposition of pentacene onto fluorinated copper-phthalocyanine (F 16 CuPc) films grown with two different molecular orientations. Well ordered pentacene films grow upon deposition on top of standing-up F 16 CuPc molecules ( s -structure) and finally form homogeneous films. When pentacene is deposited on lying-down F 16 CuPc ( l -structure), laterally small and high crystallites form. The pentacene preserves the same thin-film structure and excellent alignment along the surface normal in either case, with mosaicities of only 0.015 ± 0.001°. We demonstrate in this work how thin organic buffer layers can be employed to tailor the growth of ordered organic heterostructures.

We present a comparative study of the growth of the technologically highly relevant gate dielectric and encapsulation material aluminum oxide in inorganic and also organic heterostructures. Atomic force microscopy studies indicate strong similarities in the surface morphology of aluminum oxide films grown on these chemically different substrates. In addition, from X-ray reflectivity measurements we extract the roughness exponent β of aluminum oxide growth on both substrates. By renormalising the aluminum oxide roughness by the roughness of the underlying organic film we find good agreement with β as obtained from the aluminum oxide on silicon oxide ( β = 0.38 ± 0.02), suggesting a remarkable similarity of the aluminum oxide growth on the two substrates under the conditions employed.

The diffuse scattering of body-centered cubic β-Ti–V was measured using high-energy synchrotron X-rays and two-dimensional detectors. The study included in situ experiments of the equilibrium β-phase and room temperature measurements of the quenched metastable state. The kinematical X-ray scattering revealed details in reciprocal space that could not be detected by the electron diffraction employed in previous studies. The signal was analyzed using a statistical thermodynamic approach based on physically motivated parameters. The characteristic features attributed to an ω-like structure or a “diffuse ω-phase” in the past are explained by static lattice distortions due to atomic size mismatch.

F 16 CuPc deposited on pentacene is characterized by the coexistence of two different configurations: F 16 CuPc is found in the standing up phase (“ s -configuration”) on top of pentacene terraces and in a lying down phase (“ l -configuration”) at pentacene step edges. By combining AFM and grazing incidence X-ray diffraction we show that the ratio between F 16 CuPc in l - and s -configurations increases with thickness of the pentacene substrate film, demonstrating the role of the pentacene steps as nucleation centers for the F 16 CuPc l -configuration. Experiments performed with ultra-thin pentacene thicknesses disclose that the F 16 CuPc l -configuration does not grow on top of the first and second pentacene layers, pointing to the action of long-range interactions with the substrate.

We report a detailed in situ X-ray diffraction study of the influence of chloride on the atomic structure evolution at the solid-electrolyte interface during the selective dissolution of Cu from a Cu3Au(111) surface immersed in 0.1 M H2SO4. We disclose that the formation of the initial ultrathin Au-rich (111) with an inverted stacking sequence, as recently observed at Cu3Au(111) in contact with pure 0.1 M H2SO4, is strongly influenced by adding 5 mM HCl. The main finding is a negative shift of about 150 mV of the critical potential at which the ultra-thin Au-rich layer transforms into thicker Au islands. The presented results support the view that it is not a thermodynamic driving force, but rather the rate of surface diffusion that dominates the formation of the structures of the metallic layer. Keywords: X-ray diffraction, Solid-electrolyte interface, Surface diffusion, Corrosion

We have investigated the interaction of oxygen with the (100) surface of the noble metal Ag in a wide O2 pressure range, in situ, by surface X-ray diffraction. At 370 K and 10-2 mbar oxygen pressure, we observe a strong change in the diffraction signal, which is in line with the formation of oxygen induced Ag vacancies, up to a concentration of 25% in the topmost Ag layer. We argue that these vacancies are associated with local fluctuations of the p(2√2 × √2)R45° missing row reconstruction in a highly dynamical oxygen adsorption−desorption process. A detailed structural model is derived from the X-ray data and the observed stability of the structure as a function of temperature and oxygen pressure is compared to recent ab initio thermodynamic calculations. Finally, at 440 K and 1 mbar oxygen pressure, we did not observe noticeable subsurface oxygen formation (

Combining atomic force microscopy (AFM) and in situ grazing incidence X-ray diffraction (GIXD) we study the morphology and in-plane structure of diindenoperylene (DIP) on SiO 2 in the early stages of the growth. We unravel noticeable strain relaxation phenomena in the in-plane structure during the growth of the first layers, concomitant with a transition from layer-by-layer growth to rapid roughening at a certain critical thickness of about five monolayers.

The oxidation behavior of Ag(1 1 1) was studied by means of in situ surface X-ray diffraction at atmospheric oxygen pressure. Exposure to 1 bar oxygen at 773 K reveals a competing growth of three different oxygen-induced structures on Ag(1 1 1), namely the well-known p (4 × 4) reconstruction, a surface oxide in a p (7 × 7) coincidence structure and the bulk oxide Ag 2 O in ( 1 ¯ 1 ¯ 1 ¯ ) orientation. The latter two exhibit the same honeycomb on hexagon arrangement of the Ag sublattice with respect to the Ag(1 1 1) surface. An inverted stacking of Ag planes in the bulk oxide islands is observed as compared to the Ag(1 1 1) substrate, which sheds new light on the Ag 2 O formation process. Finally, we present a structural model of the p (7 × 7) reconstruction, based on a three-layer O–Ag–O slab of Ag 2 O(1 1 1).

The oxidation in air of NiAl(110) was investigated in the temperature range from 870 °C–1200 °C by in situ x-ray diffraction and transmission electron microscopy. Oxidation at 870 °C and 1 bar oxygen leads to the formation of an epitaxial layer of γ-alumina showing an R30° orientation relationship with respect to the underlying substrate. At oxidation temperatures between 950 °C and 1025 °C, we observed a coexistence of epitaxial γ- and polycrystalline δ-Al2O3. The α-Al2O3starts to form at 1025 °C and the complete transformation of metastable phases to the stable α-alumina phase takes place at 1100 °C. The fcc-hcp martensitic-like transformation of the initial γ-Al2O3to epitaxial α-Al2O3was observed. X-ray diffraction and cross-section transmission electron microscopy proved the existence of a continuous epitaxial α-Al2O3layer between the substrate and the polycrystalline oxide scale, having a thickness of about 150 nm. The relative orientation relationship between the epitaxial alumina and the underlying substrate was found to be NiAl(110) || α-Al2O3(0001) and [110] NiAl || [1120].

The surface structure of Cu(100) modified by chloride and iodide has been studied in an electrochemical environment by means of in-situ scanning tunneling microscopy in combination with in-situ surface X-ray diffraction with a particular focus on adsorbate and potential dependent surface relaxation phenomena. For positive potentials close to the on-set of the copper dissolution reaction, the X-ray data disclose an extraordinarily large Cu-Cl bond length of 2.61 A for the c(2 x 2)-Cl phase. This finding points to a largely ionic character of the Cu-Cl interaction at the Cu(100) surface, with chloride particles likely to retain their full charge upon adsorption. Together with the positive surface charging at these high potentials, this ionic Cu-Cl bond drives the observed 2.2% outward relaxation between the first two copper layers. These results indicate that the bond between the first and the second copper layer is significantly weakened which appears as the crucial prerequisite for the high surface mobility of copper-chloride species under electrochemical annealing conditions at these high potentials. With 2.51 A the Cu-I bond is 4% shorter than the Cu-Cl bond implying that the nature of the Cu-I bond is mainly covalent. Accordingly, we observe a significant inward relaxation of the top Cu layers upon substituting chloride by iodide at the same electrode potential, which suggests that the iodide adsorption involves charge transfer from the halide to the copper substrate.

We demonstrate that the growth of F16CuPc 1-D nanostructures can be directed by templates of gold nanoparticles. The growth occurs via vapor-phase transport, whereby the gold nanoparticles act as nucleation sites for F16CuPc molecules and promote their anisotropic growth. The F16CuPc 1-D structures adopt diameters of approximately 15-30 nm independent of the nanoparticle size. This approach enables a technologically simple and inexpensive fabrication of very uniform organic 1-D structures (aspect ratio of approximately 30) and precise control of their location and packing density.

We present an experimental study on the first stages of the thin film growth of the organic molecule F(16)CuPc (hexadecafluoro-copper-phthalocyanines) on SiO(2). By means of in situ X-ray reflectivity, in situ grazing incidence X-ray diffraction (GIXD), and ex situ atomic force microscopy (AFM), we provide a detailed picture of the film growth mode and its structural evolution at the nanometer scale. We discovered the formation of a low-density layer of molecular aggregates with heights between 5 and 10 A at the interface with the SiO(2) and show that, on top of this interfacial layer, the nucleation and two-dimensional growth of elongated islands of upright standing molecules take place. Structural changes are observed, pointing to significant relaxations of the lattice parameters within the first layers of standing molecules.

We have investigated the oxidation behavior of Pd nanoparticles grown epitaxially on MgO(1 0 0) single crystal substrates. We find that the interaction of oxygen with octahedral Pd nanoparticles at 500 K can be subdivided in three stages: above 10−6 mbar O2 pressure, the particles start to flatten; above 10−3 mbar, the particles begin to shrink laterally and to be less truncated at the corners. The formation of epitaxial bulk PdO sets in at oxygen pressures above 0.1 mbar, which is accompanied by a continuous shrinkage of the Pd particles. Our results point to a novel nanoparticle oxidation mechanism: the Pd particles act as dissociation centers for O2 and serve at the same time as source for Pd atoms resulting in epitaxial PdO growth on MgO(1 0 0).

Diindenoperylene (DIP) thin films deposited on SiO 2 -surfaces by organic molecular beam deposition in ultra-high vacuum at room temperature have been investigated by atomic-force-microscopy and X-ray scattering as a function of film thickness. We observe the evolution of two distinct molecular orientations; the long axis of the DIP molecule is pointing either along the surface normal (σ-orientation) or along the surface ( λ -orientation). Initially, the films exhibit predominantly σ-orientated islands. Increasing the film thickness, elongated, fibrous λ -orientated islands nucleate on top of the σ-oriented islands and dominate the growth front due to their fast 3D growth mode. Upon annealing at 150 °C, the fibers disappear. We argue that these observations can be understood as a competition between surface energy (favoring the σ-orientation) and growth kinetics (favoring the λ -orientation).

We present a detailed study of the thermal stability of organic thin films of diindenoperylene encapsulated by sputtered aluminum oxide layers. We studied the influence of capping layer thickness, stoichiometry, and heating rate on the thermal stability of capped films and their eventual breakdown. Under optimized encapsulation conditions (thick and stoichiometric capping layer), the organic films desorb only at temperatures 200 °C above the desorption of the uncapped film. Moreover, the capped organic films retain their crystalline order at these elevated temperatures, whereas they would normally (i.e., uncapped) be in the gas phase. This study therefore also shows a way of studying organic materials under temperature conditions normally inaccessible. Considering results from complementary techniques, we discuss possible scenarios for the eventual breakdown. The results have implications for the performance and long-term stability of organic devices for which stability against elevated temperatures as well as against exposure to ambient gases is crucial.

The great power of the cluster-expansion method for atomistic simulations of the ground state properties and the thermodynamic properties of multi-component solids is highlighted. In the first part of the paper some recently developed combinations of this method with other atomistic simulation techniques (N-body potentials and cluster functionals) are discussed. In the second part the ab-initio cluster expansion method is used to investigate the ground-state structures for bulk FexCo1–x, the Ni90%–Al(110) surface and for adatom configurations on Mo(112), and the phase diagram for the system Ni–Fe–Al. Finally, an outlook for future applications of this calculational technique is given. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrochemical deposition of Cu and Co in monolayer amounts on hydrogen terminated Si(1 1 1) was studied ex situ and in situ by X-ray techniques. The X-ray beam was found to have a strong effect on the deposit causing desorption under the beam. Cu deposition on GaAs(0 0 1) from UHV is compared with electrodeposited Cu on the same surface, elucidating similarities and differences of electrochemical and UHV deposition. Roughening due to corrosion of Cu3Au(1 1 1) is observed by crystal truncation scattering. The observed behaviour of passivation of this surface is explained by the formation of Au clusters, increasingly covering the surface at higher oxidation potential.

A dedicated beamline for the Max-Planck-Institut fur Metallforschung was recently taken into operation at the Angstro/mquelle Karlsruhe (ANKA). Here we describe the layout of the beamline optics and the experimental end-station, consisting of a heavy duty multiple circle diffractometer. For both a new design was realized, combining a maximum flexibility in the beam properties [white, pink, (focused) monochromatic, energy range 6–20 keV] with a special diffractometer for heavy sample environments up to 500 kg, that can be run in different geometrical modes. In addition the angular-reciprocal space transformations for the diffractometer in use are derived, which allows an operation of the instrument in the convenient six circle mode. As an example, results from surface x-ray diffraction on a Cu3Au(111) single crystal are presented.

The late growth stages and the post-growth diffusion of crystalline organic thin films have been investigated for 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on Ag(111), a model system in organic epitaxy. In situ x-ray measurements at the anti-Bragg point during the growth show intensity oscillations followed by a time-independent intensity which is independent of the growth temperature. At T > 350 K, the intensity increases after growth up to a temperature-dependent saturation value due to a post-growth diffusion process. The time-independent intensity and the subsequent intensity recovery have been reproduced by models based on the morphology change as a function of the growth temperature. The morphology found after the post-growth diffusion processes has been studied by specular rod measurements., 9 pages, 8 figures, accepted for publication in Surface Science

We show that the thermal stability of thin films of the organic semiconductor diindenoperylene (DIP) can be strongly enhanced by aluminum oxide capping layers. By thermal desorption spectroscopy and in-situ X-ray diffraction we demonstrate that organic films do not only stay on the substrate, but even remain crystalline up to 460C, i.e. 270 deg. above their desorption point for uncapped films (190C). We argue that this strong enhancement of the thermal stability compared to uncapped and also metal-capped organic layers is related to the very weak diffusion of aluminum oxide and the structurally well-defined as-grown interfaces. We discuss possible mechanisms for the eventual breakdown at high temperatures.

We studied the self-organization process of F16CuPc films (20–30 ML) on stepped Al2O3 (1120) substrates. X-ray diffraction measurements revealed a highly ordered layered structure with the molecules in a nearly upright configuration. The morphology, investigated by atomic force microscopy, consisted of long (several microns) and narrow (20–100 nm) needlelike terraces unidirectionally aligned along one of the main crystallographic directions of the Al2O3 (1120) surface. High resolution atomic force microscopy images revealed in-plane molecular order with the molecular stacking direction parallel to the needlelike terraces. Such anisotropic morphology is the result of a self-organization process of F16CuPc in elongated crystallites driven to a preferential orientation by the interaction with the substrate. Spectroscopic ellipsometry showed that these films exhibit anisotropic optical properties correlated with the molecular arrangement.

The magnetic and thermodynamic properties of iron–cobalt alloys have been investigated by means of first-principles density-functional calculations. A cluster expansion (CE) bridged the quantum and the statistical mechanics, providing a set of magnetically implicit effective cluster interactions (ECIs). Our results show that magnetism is crucial to the ordering tendencies in iron–cobalt: A non-spin-polarized calculation predicts Fe–Co as a phase separating system. This is also true in the case of atomic defects for the B2 (CsCl) phase of FeCo, where magnetism stabilizes the system against a spontaneous formation of antistructure atoms. As a by-product, our analysis helps to elucidate the origin of the controversy on the existence of a low-temperature Fe 3 Co ordered phase.

Thin films of hexadecafluorophthalocyanine (F16CuPc) were grown by organic molecular beam deposition (OMBD) under ultra high vacuum (UHV) conditions on oxidized Si(0 0 1) substrates. The film thicknesses ranged from 120 to 450 A and the substrate temperature was varied from −150 to 300 °C. X-ray diffraction and atomic force microscopy (AFM) were used to characterize the structure and morphology of the layers. Spectroscopic ellipsometry was employed to determine the dielectric properties and to locate characteristic transitions between 1.4 and 3.7 eV. The correlation of the electronic properties with the molecular packing in the films is discussed. The results are compared to the case of F16CuPc films grown on stepped sapphire surfaces, which differ in their lateral ordering behavior.

We present a real-time X-ray scattering study of the growth modes in organic molecular-beam epitaxy. We have studied the model system 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) on Ag(111) and find a temperature-dependent transition from layer-by-layer growth to islanding. The transition smears out for low substrate temperatures, T, implying that the degree of the layer-by-layer growth of the wetting layer decreases with decreasing T. This behavior has been analyzed quantitatively and reproduced by kinetic Monte Carlo simulations. The implications and consequences of our findings for the understanding of the organic molecular-beam epitaxy are discussed.

Nanometer sized Au clusters deposited on a silicon substrate forming Au–SiO2–Si structure are important for the development of contacts in nanotechnology. Systematic x-ray reflectivity, scanning probe microscopy, and scanning tunneling spectroscopy measurements were done to understand the relationship between morphology and electrical transport properties of this nanostructural metal–insulator–semiconductor system. The presence of an interfacial layer at the metal–insulator interface dictates the tunneling current through this structure and exhibits a gap leading to a suppression of current. Local density of states and electron density/thickness of the interfacial layer have been extracted from the measurements to understand the evolution of metallicity of this Au–SiO2–Si structure.

We present a route for the preparation of cross-sectional TEM specimens of crystalline organic thin films which minimizes the mechanical, chemical and thermal load of the organic film during preparation and allows to take TEM images with molecular resolution. A typical example of a thin film of diindenoperylene capped with a thin layer of gold is shown to demonstrate the application of the technique for the investigation of metal-organic interfaces.

c ¨ Abstract The formation of small gold clusters at the initial stage of the metal growth on a thin film of the conjugated organic semiconductor diindenoperylene (DIP) leads to charging during ultraviolet photoemission spectroscopy (UPS) investigations. Additional irradiation of the sample with visible light was successfully applied to re-establish charge neutrality on the sample surface. By varying the light energy, we demonstrate that the optical formation of excitons and yor polarons results in efficient electron transfer from DIP to the positively charged Au clusters and thus the elimination of charging in UPS. This allows the collection of reliable information on the interface electronic structure. 2003 Elsevier Science B.V. All rights reserved.

The thermal stability and dewetting effects of crystalline organic thin films on inorganic substrates have been investigated for a model system for organic epitaxy, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on Ag(111). The thin films deposited under a variety of growth conditions have been annealed stepwise and studied by in situ x-ray diffraction and noncontact atomic force microscopy. It has been found that comparatively smooth films deposited at temperatures T(g)less than or similar to350 K are metastable, while films deposited at T(g)greater than or similar to350 K are stable against annealing on a time scale of several hours. The thermal expansion of thin PTCDA films and bulk samples has been determined. (C) 2003 American Institute of Physics.

We present a new experimental scheme for the high-resolution X-ray study of deeply buried interfaces, as they occur in novel functional nanomaterials and in nature. Our experimental approach is based on the preparation and the use of high energy X-ray microbeams and on stable and high-resolution mechanical diffraction stages. We discuss the principle of this technique and demonstrate its future potential for the study of functional interfaces by way of several proof-of-principle experiments which have been carried out at a prototype setup at the European Synchrotron Radiation Facility.