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The order-disorder transition in a 170 A thick Cu3Au(111) epitaxial alloy film is examined using x-ray diffraction techniques. Below the transition temperature T0, a disordered surface layer of thickness l is detected. This layer exhibits wetting behavior, i.e., l increases, obeying a logarithmic growth law on approach to T0. We show by a detailed analysis of the order parameter profiles that the stiffness of the order-disorder interface is temperature dependent, resulting in a nonuniversality of the wetting transition.

We present a novel surface phenomenon found in the investigation of the ordering kinetics near the surface of Cu{sub 3}Au(001). Monitoring different classes of Fourier components of the ordered L1{sub 2} structure by time-resolved x-ray scattering, we found a giant anisotropy in the relaxation behavior. The layered structure normal to the surface relaxes ultrafast while lateral ordering occurs much more slowly ({tau}{sup -1}{sub {perpendicular}}{gt}20{tau}{sup -1}{sub {parallel}}). We argue that the recently discovered oscillating segregation profile acts as a two-dimensional nucleating sheet for ordering wave vectors normal to the surface. {copyright} {ital 1997} {ital The American Physical Society}

We demonstrate that crystal truncation rod scattering can ideally be applied to extract detailed information on surface segregation profiles in multicomponent systems. We present an x-ray study of the surface segregation at C${\mathrm{u}}_{3}$Au(001) at various temperatures above the order-disorder transition temperature. It exhibits a pronounced exponentially decaying, oscillatory behavior versus depth. The associated decay length $\ensuremath{\Lambda}$ is found to obey $\ensuremath{\Lambda}\ensuremath{\sim}{t}^{\ensuremath{-}\ensuremath{\nu}}$, with $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.49\ifmmode\pm\else\textpm\fi{}0.04$ and $t\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}({T\ensuremath{-}T}_{\mathrm{SP}})/T$, and, thus, is related to the bulk order parameter fluctuations and the bulk spinodal temperature ${T}_{\mathrm{SP}}$.

A Comment on the Letter by Sudeshna Chattopadhyay et al., [Phys. Rev. Lett. 105, 037803 (2010)]. The authors of the Letter offer a Reply.

We report direct experimental evidence for a layer-dependent step-edge barrier in organic thin film growth, investigating di-indenoperylene on SiO_{2} as an archetypical system. In particular, we show that a noticeable Ehrlich-Schwöbel effect emerges only beyond the 3rd molecular layer, accompanied by mass step-upward diffusion. We further disclose that this thickness dependence of the interlayer transport is directly related to molecular reorientations during the first stages of the growth. This is ultimately responsible for a morphological transition from layer-by-layer growth to surface rapid roughening. These experimental findings should compel further development of molecular-scale models for organic thin film growth.

The existence of surface and interfacial melting of ice below 0 deg. C has been confirmed by many different experimental techniques. Here we present a high-energy x-ray reflectivity study of the interfacial melting of ice as a function of both temperature and x-ray irradiation dose. We found a clear increase of the thickness of the quasiliquid layer with the irradiation dose. By a systematic x-ray study, we have been able to unambiguously disentangle thermal and radiation-induced premelting phenomena. We also confirm the previously announced very high water density (1.25 g/cm{sup 3}) within the emerging quasiliquid layer.

The surface sensitivity was achieved by exploiting the effect of total reflection. The radial distribution of the critical diffuse intensity around a superlattice reflection exhibits a cusplike shape at the critical temperature T c . From this distribution we determined for the first time the critical surface exponent ηη=1.52±0.04 which agrees well with the prediction for the ordinary transition of a semi-infinite Ising system

We present an extended synchrotron x-ray scattering study of the structure of thin manganite films grown on SrTiO3(001) substrates and reveal a new kind of misfit strain relaxation process which exploits twinning to adjust lattice mismatch. We show that this relaxation mechanism emerges in thin films as one-dimensional twinning waves which freeze out into a twin domain pattern as the manganite film continues to grow. A quantitative microscopic model which uses a matrix formalism is able to reproduce all x-ray features and provides a detailed insight into this novel relaxation mechanism. We further demonstrate how this twin angle pattern affects the transport properties in these functional films.

Using a high-energy x-ray transmission-reflection scheme we have studied the density profile of solid-liquid Schottky contacts close to the interface. We found a massive disturbance of the electronic system on the liquid metal side at different interfaces with pronounced density anomalies on a new length scale. The liquid metal at the interface forms a strongly compressed layer followed by a density depleted layer. The experimental evidence points to a charge transfer phenomenon in the metallic system. Control experiments performed at a metal-insulator interface confirm this picture.

We report the self-organization of organic nanodots with high crystallinity during the growth of organic heterostructures of Di-indenoperylene (DIP) onto copper-hexadecafluorophthalocyanine (F16CuPc), donor and acceptor molecules, respectively. The process is related to the Stranski-Krastanov growth mode, which is accompanied by a novel type of structural reconstruction of the underlying organic film. This reconstruction affects three monolayers adjacent to the organic interface. In spite of the close resemblance to the formation of semiconductor nanostructures for inorganic heteroepitaxy, the present results conclusively demonstrate a distinctly different growth mechanism for organic heteroepitaxy whose understanding demands further theoretical studies.

The structure of the oxygen-induced $p(4\ifmmode\times\else\texttimes\fi{}4)$ reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.

We present an extended synchrotron x-ray scattering study of the structure of thin manganite films grown on SrTiO3(001) substrates and reveal a new kind of misfit strain relaxation process which exploits twinning to adjust lattice mismatch. We show that this relaxation mechanism emerges in thin films as one-dimensional twinning waves which freeze out into a twin domain pattern as the manganite film continues to grow. A quantitative microscopic model which uses a matrix formalism is able to reproduce all x-ray features and provides a detailed insight into this novel relaxation mechanism. We further demonstrate how this twin angle pattern affects the transport properties in these functional films.

The structure of the oxygen-induced p(4 x 4) reconstruction of Ag(111) is determined by a combination of scanning tunneling microscopy, surface x-ray diffraction, core level spectroscopy, and density functional theory. We demonstrate that all previous models of this surface structure are incorrect and propose a new model which is able to explain all our experimental findings but has no resemblance to bulk silver oxide. We also shed some light on the limitations of current density functional theories and the potential role of van der Waals interactions in the stabilization of oxygen-induced surface reconstructions of noble metals.

Physical review letters 95(23), 235703 (2005). doi:10.1103/PhysRevLett.95.235703, Published by APS, College Park, Md.

We report pronounced smecticlike ordering in a ferrofluid adjacent to a ${\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ wall. In the presence of small magnetic fields perpendicular to the interface, ordered layers of magnetite nanoparticles form that can extend up to 30 layers. We also show that short ranged ordered structures emerge when the magnetic field direction is parallel to the interface; however, the layering is strongly perturbed. These results have been obtained by in situ neutron reflectometry which gives a detailed microscopic picture of these ordering phenomena. They also reveal the formation of a wetting double-layer which forms the magnetic template for the observed ordering sheets. The implications of these findings are discussed.

We report pronounced smecticlike ordering in a ferrofluid adjacent to a SiO2 wall. In the presence of small magnetic fields perpendicular to the interface, ordered layers of magnetite nanoparticles form that can extend up to 30 layers. We also show that short ranged ordered structures emerge when the magnetic field direction is parallel to the interface; however, the layering is strongly perturbed. These results have been obtained by in situ neutron reflectometry which gives a detailed microscopic picture of these ordering phenomena. They also reveal the formation of a wetting double-layer which forms the magnetic template for the observed ordering sheets. The implications of these findings are discussed.

The physical behavior of condensed matter can be drastically altered in the presence of interfaces. Using a high-energy x-ray transmission-reflection scheme, we have studied ice-SiO2 model interfaces. We observed the formation of a quasiliquid layer below the bulk melting temperature and determined its thickness and density as a function of temperature. The quasiliquid layer has stronger correlations than water and a large density close to rho(HDA)=1.17 g/cm(3) of high-density amorphous ice suggesting a structural relationship with the postulated high-density liquid phase of water.

The oxidation of the Pd(100) surface at oxygen pressures in the 10^-6 to 10^3 mbar range and temperatures up to 1000 K has been studied in-situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the (T,p) environmental conditions we either observe a thin sqrt(5) x sqrt(5) R27 surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K., 4 pages including 4 figures, Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.html

We report a new type of short-range order correlations at the (001) surface of Cu 3 Au which no longer produces the 2k F -splitting characteristic for the bulk short-range order scattering. We present the temperature dependence of this phenomenon and a theoretical interpretation of its origin. We argue that this new surface effect is caused by a drastic change of the strain-induced interactions at the surface.

We report a new type of short-range order correlations at the (001) surface of Cu3Au which no longer produces the 2k(F)-splitting characteristic for the bulk short-range order scattering. We present the temperature dependence of this phenomenon and a theoretical interpretation of its origin. We argue that this new surface effect is caused by a drastic change of the strain-induced interactions at the surface.

The scaling exponents alpha, beta, and 1/z in thin films of the organic molecule diindenoperylene deposited on SiO2 under UHV conditions are determined. Atomic-force microscopy, x-ray reflectivity, and diffuse x-ray scattering were employed. The surface width displays power law scaling over more than 2 orders of magnitude in film thickness. We obtained alpha = 0.684+/-0.06, beta = 0.748+/-0.05, and 1/zeta = 0.92+/-0.20. The derived exponents point to an unusually rapid growth of vertical roughness and lateral correlations. We suggest that they could be related to lateral inhomogeneities arising from the formation of grain boundaries between tilt domains in the early stages of growth.

We present a theoretical and experimental study of the effect of lattice distortions on the short-range order and the energetics of ordering binary alloys. Applying a reciprocal space approach which accounts for the elastic response of the lattice, the diffuse scattering of the model system Cu(83)Mn(17) can be explained with only a few physical parameters. The model calculations point to a nonanalytic diffuse intensity at q = 0. X-ray scattering experiments are presented providing clear evidence for this phenomenon which carries detailed information on the strain-induced interaction.

We have combined x-ray diffraction studies with first-principles calculations to study the interplay between segregation and ordering at the (110) surface of ${\mathrm{Ni}}_{90}{\mathrm{Al}}_{10}$. We find a ${L1}_{2}$-ordered monolayer at the surface. The observed ordering as well as recently reported Al segregation at the surface are explained in a consistent picture. A delicate competition between the tendency for Al segregation and ordering in the Ni-Al system induced by the symmetry break at the surface stabilizes a long-range ordered surface in the entire concentration range ${c}_{\mathrm{Ni}}g0.75$.

We have combined x-ray diffraction studies with first-principles calculations to study the interplay between segregation and ordering at the (110) surface of Ni(90)Al(10). We find a L1(2)-ordered monolayer at the surface. The observed ordering as well as recently reported Al segregation at the surface are explained in a consistent picture. A delicate competition between the tendency for Al segregation and ordering in the Ni-Al system induced by the symmetry break at the surface stabilizes a long-range ordered surface in the entire concentration range c(Ni)0.75.

We present a theoretical and experimental study of the effect of lattice distortions on the short-range order and the energetics of ordering binary alloys. Applying a reciprocal space approach which accounts for the elastic response of the lattice, the diffuse scattering of the model system Cu(83)Mn(17) can be explained with only a few physical parameters. The model calculations point to a nonanalytic diffuse intensity at q = 0. X-ray scattering experiments are presented providing clear evidence for this phenomenon which carries detailed information on the strain-induced interaction.

The order-disorder transition in a 170 A thick Cu3Au(111) epitaxial alloy film is examined using x-ray diffraction techniques. Below the transition temperature T0, a disordered surface layer of thickness l is detected. This layer exhibits wetting behavior, i.e., l increases, obeying a logarithmic growth law on approach to T0. We show by a detailed analysis of the order parameter profiles that the stiffness of the order-disorder interface is temperature dependent, resulting in a nonuniversality of the wetting transition.