Surface Structure Dynamics Research Articles

Condensation heat transfer on superhydrophobic surfaces

Abstract

Structural Dynamics at Monolayer–Liquid Interfaces Probed by 2D IR Spectroscopy

Monolayers functionalized with tricarbonyl- 1,10-phenanthroline rhenium chloride (RePhen(CO)3Cl) are studied in the presence of a variety of polar organic solvents (chloroform, tetrahydrofuran, dimethylformamide, acetoni- trile), hexadecane, and water. The headgroup, RePhen- (CO)3Cl, is soluble in the bulk polar organic solvents but not in hexadecane or water. The surface structural dynamics are studied using IR absorption, ultrafast two-dimensional infrared (2D IR) vibrational echoes, and heterodyne-detected transient gratings (HDTG). The headgroup is also studied in the bulk solvents. Immersion in solvent changes the environment of the surface bound RePhen(CO)3Cl as shown by a solvent- dependent symmetric CO stretch absorption frequency and line shape. The 2D IR spectroscopy is sensitive to spectral diffusion, which reports on the structural time dependence. In the absence of solvent (bare surface), the spectral diffusion takes place on a 37 ± 4 ps time scale, whereas in the presence of THF, MeCN, or CHCl3 it occurs on the 25 ± 6 ps time scale. However, in DMF, the spectral diffusion time constant is 15 ± 3 ps. In hexadecane the spectral diffusion slows to 77 ± 15 ps, slower than the bare surface. In D2O, the monolayer CO stretch is split into two bands, indicating distinct local structures, and the spectral diffusion of main band is again slower than the bare surface. HDTG spectroscopy is used to investigate the vibrational lifetime dynamics.

ChemInform Abstract: Metal Nanoparticles in Condensed Media: Preparation and the Bulk and Surface Structural Dynamics

AbstractReview: 302 refs.

Helium atom diffraction measurements of the surface structure and vibrational dynamics of CH3–Si(111) and CD3–Si(111) surfaces

The surface structure and vibrational dynamics of CH(3)-Si(111) and CD(3)-Si(111) surfaces were measured using helium atom scattering. The elastic diffraction patterns exhibited a lattice constant of 3.82 Å, in accordance with the spacing of the silicon underlayer. The excellent quality of the observed diffraction patterns, along with minimal diffuse background, indicated a high degree of long-range ordering and a low defect density for this interface. The vibrational dynamics were investigated by measurement of the Debye-Waller attenuation of the elastic diffraction peaks as the surface temperature was increased. The angular dependence of the specular (θ(i)=θ(f)) decay revealed perpendicular mean-square displacements of 1.0×10(-5) Å(2) K(-1) for the CH(3)-Si(111) surface and 1.2×10(-5) Å(2) K(-1) for the CD(3)-Si(111) surface, and a He-surface attractive well depth of ∼7 meV. The effective surface Debye temperatures were calculated to be 983 K for the CH(3)-Si(111) surface and 824 K for the CD(3)-Si(111) surface. These relatively large Debye temperatures suggest that collisional energy accommodation at the surface occurs primarily through the Si-C local molecular modes. The parallel mean-square displacements were 7.1×10(-4) and 7.2×10(-4) Å(2) K(-1) for the CH(3)-Si(111) and CD(3)-Si(111) surfaces, respectively. The observed increase in thermal motion is consistent with the interaction between the helium atoms and Si-CH(3) bending modes. These experiments have thus yielded detailed information on the dynamical properties of these robust and technologically interesting semiconductor interfaces.

3D initial sediment distribution and quantification of mass balances of an artificially-created hydrological catchment based on DEMs from aerial photographs using GOCAD

The spatial distribution and properties of parent material components form the starting point for any soil and ecosystem. Initial phases of ecosystem development are predominantly characterized by the redistribution of sediment components. To improve the understanding of soil-landscape development, the initial sediments need to be quantified in space and time. This study aims at developing and testing methods for the quantification of initial sediment mass balances in the three dimensions of space and in time. The initial mass balance and composition of parent material in an artificially-created hydrological catchment were quantified from a 3D-model of the catchment’s water storage layer. Multi-date digital elevation models (DEMs) were constructed from photogrammetrically derived elevation data after the assessment and improvement of elevation data quality. Three-dimensional models of volume change were constructed from the digital elevation models. Regions of significant volume change were identified. Mass changes were calculated from the volume changes in combination with bulk density information. Based on information about the catchment’s construction, mass changes were separately analyzed in subregions of the models. Terrain attributes were computed to characterize surface structure and to examine correlations with mass change. From the 3D-model, an initial sediment volume of 122,608 m 3 was quantified. A variation of about ±12,300 m 3, due to uncertainty in DEMs from aerial photographs, was calculated. The 3D-model indicates differences in sediment properties between the western and eastern part of the catchment, which are most probably resulting from the dumping of two separate material deliveries during the construction. Models of volume and mass change are constructed for three time periods of catchment evolution. Spatial variations in volume and mass change are observed. The total mass balance reveals a considerable mismatch between the detected amounts of erosion and sedimentation, which gives reason to closely examine the quality of the DEMs. Terrain attributes of four elevation models reflect the diversification of surface structures. Correlations between volume change and surface structures show that erosion processes are dependent on initial surface structures and that these structures, in turn, are enhanced by the processes of sediment redistribution. Although there is a considerable uncertainty in the observed mass changes, the 3D-modelling approach allows a first approximation of the initial, mostly erosion-affected, surface structural dynamics of the artificial catchment. The comparison of multi-date elevation data allows a critical evaluation of the quality of models of change obtained from repeated topographical surveys.

Study on dynamics of surface structure by rapid and time‐resolved X‐ray photoelectron diffraction

AbstractIt took several hours to obtain one X‐ray photoelectron diffraction (XPED) pattern because XPED measurement requires repeated acquisition of XPS as a function of emission angle. The measurement time using our previous XPED system was too long to clarify the dynamics of epitaxial growth and catalytic reaction. In the present study, in order to minimize the measurement time, we improved the software used to control the XPED system. Then, by using the improved system, we obtained information on the structural changes during the heating process of an ion‐bombarded silicon surface. Copyright © 2008 John Wiley & Sons, Ltd.

Dynamics and durability

The durability of glasses and minerals in water has traditionally been predicted using models that ignore the molecular details. Now the surface structure dynamics are shown to play an integral role in their aqueous corrosion.

Single-molecule nanocatalysis reveals heterogeneous reaction pathways and catalytic dynamics

Nanoparticles are important catalysts for many chemical transformations. However, owing to their structural dispersions, heterogeneous distribution of surface sites and surface restructuring dynamics, nanoparticles are intrinsically heterogeneous and challenging to characterize in ensemble measurements. Using a single-nanoparticle single-turnover approach, we study the redox catalysis of individual colloidal Au nanoparticles in solution, using single-molecule detection of fluorogenic reactions. We find that for product generation, all Au nanoparticles follow a Langmuir-Hinshelwood mechanism but with heterogeneous reactivity; and for product dissociation, three nanoparticle subpopulations are present that show heterogeneous reactivity between multiple dissociation pathways with distinct kinetics. Correlation analyses of single-turnover waiting times further reveal activity fluctuations of individual Au nanoparticles, attributable to both catalysis-induced and spontaneous dynamic surface restructuring that occurs at different timescales at the surface catalytic and product docking sites. The results exemplify the power of the single-molecule approach in revealing the interplay of catalysis, heterogeneous reactivity and surface structural dynamics in nanocatalysis.

Vacuum-annealing induced band bending in phosphorus-doped (111) diamond

High-temperature annealing effects on hydrogen (H)-terminated phosphorus (P)-doped diamond (111) surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and reflection high energy electron diffraction (RHEED) experiments. Thermally activated, surface band bending was observed, which is clearly attributed to surface structural changes and adsorbates dynamics. The XPS results are compared between boron (B)- and P-doped diamond surfaces and an energy band model has been introduced to the P-doped diamond surface. The annealing process induces downward band bending (to a maximum of 1.3 eV) in B-doped diamond whereas it reduces the internal barrier height (by about 1 eV) in P-doped diamond and finally, the surface bands are pinned in the middle of the band gap. The depletion layer widths are calculated for both diamond surfaces. The band bending imposed by the annealing process can be effective in tuning the surface barrier height.

Characterization of Surface Structure and p47phox SH3 Domain-Mediated Conformational Changes for Human Neutrophil Flavocytochrome b

The heterodimeric, integral membrane protein flavocytochrome b (Cyt b) is the catalytic core of the phagocyte NADPH oxidase and generates superoxide which plays a critical role in host defense. To better define the activation of superoxide production by this multisubunit enzyme complex, Cyt b-specific monoclonal antibodies (mAbs) and the p47phox SH3 domains (p47SH3AB) were used in the present study as probes to map surface structure and conformational dynamics in human neutrophil Cyt b. In pull-down and co-immunoprecipitation studies with detergent-solubilized Cyt b, the oxidase-inhibitory mAb CS9 was shown to share an overlapping binding site with p47SH3AB on the C-terminal region of the p22phox subunit. Similar studies demonstrated a surprising lack of overlap between the mAb 44.1 and CS9/p47SH3AB binding sites, and they indicated that the oxidase-inhibitory mAb NL7 binds a region physically separated from the p22phox C-terminal domain. Resonance energy transfer and size exclusion chromatography confirmed the above results for functionally reconstituted Cyt b and provided evidence that binding of both mAb CS9 and p47SH3AB altered the conformation of Cyt b. Further support that binding of the p47phox SH3 domains modulates the structure of Cyt b was obtained using a cell-free assay system where p47SH3AB enhanced superoxide production in the presence of a p67phox (1-212)-Rac1(Q61L) fusion protein. Taken together, this study further characterizes the structure of human neutrophil Cyt b in both detergent micelles and reconstituted membrane bilayers, and it provides evidence that the cytosolic regulatory subunit p47phox modulates the conformation of Cyt b (in addition to serving as an adapter protein) during oxidase activation.

Surface Structure and Interface Dynamics of Alkanethiol Self-Assembled Monolayers on Au(111)

Scanning tunneling microscopy (STM) and high-resolution electron energy loss spectroscopy (HREELS) were used to examine the structural transitions and interface dynamics of octanethiol (OT) self-assembled monolayers (SAMs) caused by long-term storage or annealing at an elevated temperature. We found that the structural transitions of OT SAMs from the c(4 x 2) superlattice to the (6 x square root 3) superlattice resulting from long-term storage were caused by both the dynamic movement of the adsorbed sulfur atoms on several adsorption sites of the Au(111) surface and the change of molecular orientation in the ordered layer. Moreover, it was found that the chemical structure of the sulfur headgroups does not change from monomer to dimer by the temporal change of SAMs at room temperature. Contrary to the results of the long-term-stored SAMs, it was found that the annealing process did not modify either the interfacial or chemical structures of the sulfur headgroups or the two-dimensional c(4 x 2) domain structure. Our results will be very useful for a better understanding of the interface dynamics and stability of sulfur atoms in alkanethiol SAMs on Au(111) surfaces.

Cover Picture: Ultrafast Electron Crystallography of Surface Structural Dynamics with Atomic‐Scale Resolution (Angew. Chem. Int. Ed. 20/2004)

Surface structural dynamics are determined with unprecedented spatial and temporal resolution by ultrafast electron crystallography. The dynamics are initiated by a femtosecond laser pulse, and transient surface structures are imaged by an ultrashort electron pulse: A diffraction snapshot is obtained at a given time, δt, and allows the real‐time observation of surface structural dynamics with atomic‐scale resolution. For more details see the Communication by A. H. Zewail and co‐workers on page 2705 ff.

Ultrafast Electron Crystallography of Surface Structural Dynamics with Atomic‐Scale Resolution

A formidable contender to X-ray diffraction is ultrafast electron crystallography. Whereas the former is more suited to investigate the bulk of the substrate, the time, length, and sensitivity scales of electron crystallography provide powerful and complementary information on atomic-scale structural dynamics at the surface (see diffraction image of GaAs crystal).

Ultrafast Electron Crystallography of Surface Structural Dynamics with Atomic‐Scale Resolution

Ultrafast Electron Crystallography of Surface Structural Dynamics with Atomic‐Scale Resolution

Temperature-dependent surface structure and lattice dynamics of NiO(001)

Temperature-dependent surface relaxation and rumpling of NiO(001) were determined by high-resolution medium energy ion scattering. We found that the top-layer Ni plane is displaced toward the vacuum side relative to the top-layer O plane at temperature below 420 K. This is consistent with the ab initio calculation but contradicts the shell model calculation using pair potentials. However, at a temperature above 500 K (close to the N\'eel temperature), relative positions of the O plane to the Ni plane in the top and second layers are reversed. This result suggests that the surface structure is very sensitive to even a slight change of the bulk lattice. We also measured temperature dependent bulk and enhanced thermal vibrations (TVAs) of the top-layer atoms. The Debye temperatures for Ni and O estimated from the bulk TVAs of Ni and O using the simple Debye model are consistent with those derived from the heat capacity measurement. The bulk TVA gradually increases with increasing temperature, while the enhancement of the TVA of the top-layer Ni in the surface normal direction suddenly drops at 500 K. Such a dramatic change may be related to the reversal of the rumpling of the top layer. In contrast to alkali halide crystals, there are no correlations between the first nearest neighbor atoms in the [001] and [101] strings. The present result claims that pair potentials are not applicable to the NiO crystal which has, in part, covalent bonding.

In situ X-ray studies of vapor phase epitaxy of PbTiO 3

As part of a program to understand and control the structure of ferroelectric thin films grown by metal organic vapor phase epitaxy (MOVPE), we have used X-ray scattering to observe the surface structure of PbTiO 3 films during and following growth. Moderately high energy (24 keV) X-rays are used to penetrate the chamber walls for in situ measurements in the high-temperature, reactive MOVPE environment. Performing measurements in situ allows us to study the growth process in real time, to control the thickness of the films to sub-unit-cell accuracy, to observe the surface structure in equilibrium with the vapor, and to preserve film stoichiometry during high-temperature study by maintaining an overpressure of PbO. While the higher X-ray energy also permits a large volume of reciprocal space to be mapped, it presents challenges for surface scattering due to the small critical angle. Examples of results will be presented from studies of surface structure dynamics, crystal growth, and ferroelectric stripe domains in thin films.

Rumpled surface structure and lattice dynamics of NiO(001)

Rumpled surface structure and root mean square (rms) thermal vibration amplitudes of NiO(001) were determined by high-resolution medium energy ion scattering. The clean 1\ifmmode\times\else\texttimes\fi{}1 surface was prepared by cleavage in the air and annealing at 500 \ifmmode^\circ\else\textdegree\fi{}C for 40 min in ${\mathrm{O}}_{2}$ pressure of $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ Torr. The interlayer distance between the top and second layer is contracted by 1.44\ifmmode\pm\else\textpm\fi{}0.07% and the top-layer Ni plane is displaced by 0.10\ifmmode\pm\else\textpm\fi{}0.01 \AA{} toward the vacuum side relative to the top-layer O plane. The present result is consistent with the recent ab initio calculation based on the density functional theory using the local spin density approximation. We also determined the rms thermal vibration amplitudes of Ni and O atoms in the bulk and in the top layer. The result obtained is compared with that calculated using the pair potential proposed by Lewis and Catlow.

Surface Structure and Lattice Dynamics of Alkali Halide Crystals Studied by High-Resolution Ion Scattering

The rumpled surface structure and thermal lattice vibrations of KI(001) and RbI(001) were measured directly by high-resolution medium energy ion scattering (MEIS). The relaxation of interlayer distance between the top and second layer and the rumpling of the top and second layers were determined using the ion shadowing effect with an accuracy of 0.01 Å. From the displaced lattice positions determined above, we derived the dipole moments of the top- and second-layer ions self-consistently employing the polarizabilities estimated from the optical refractive index combined with the Clausius–Mossotti relation. The balance between a short-range force and a long-range Coulombic one made it possible to judge the applicability of the short-range pair potentials proposed so far. We also determined the root-mean-square (rms) thermal vibration amplitudes of the bulk and the top-layer ions together with the correlations of the ions in the [001] and [101] strings by taking various kinds of scattering geometries. The results obtained were compared with those calculated from the molecular dynamics (MD) simulations based on a classical model using the dipole moments determined above and the Born–Mayer type pair potential. The present MEIS results are in overall agreement with the MD simulations.

Cellular automata study of high burn-up structures

We propose a new approach, based on the cellular automata, for processing and modeling the structure dynamics of UO 2 at different cross-section averaged burn-ups. Micrographs of the material surface, subjected to both “as-polished” and “as-etched” treatments, with a magnification of 1250× have been used in our study. It has been shown that this approach provides efficient tools for investigation of the surface structure dynamics both at local and global levels.

Surface structure and lattice dynamics of KI(001) studied by high-resolution ion scattering combined with molecular dynamics simulation

The rumpled surface structure and thermal lattice vibrations of KI(001) were studied by high-resolution medium-energy ion scattering (MEIS) and molecular dynamics (MD) simulation. The relaxation of the interlayer distance between the top and second layer and the rumpling of the top and second layers were measured directly by MEIS with an accuracy of 0.01 \AA{}. From the displaced lattice positions determined above, we derived the dipole moments of the top- and second-layer ${\mathrm{K}}^{+}$ and ${\mathrm{I}}^{\ensuremath{-}}$ ions self-consistently using the polalizabilities estimated from the optical refractive index combined with the Clausius-Mossotti relation. The balance between a short-range force and a long-range Coulombic one made it possible to judge the applicability of the short-range pair potentials proposed so far. We also determined the root-mean-square thermal vibration amplitudes of the bulk and top-layer ions together with the correlations between the top- and second-layer ions by means of the ion shadowing effect applied to various kinds of scattering geometries. The results obtained were compared with those calculated from the MD simulations based on a semiclassical model using the dipole moments determined above and a Born-Mayer- or Hellmann-type pair potential. The present results are in overall agreement with the MD simulations employing the pair potential proposed by Catlow et al. [J. Phys. C 10, 1395 (1977)].