Modelling of surfaces. 2. Metallic alloy surfaces using the BFS method

Summary Using the semiempirical method for alloys developed by Bozzolo, Ferrante and Smith (BFS) [Bozzolo, G. et al., Phys. Rev., B45 (1992) 493] we study the surface structure of fcc-ordered binary alloys. We concentrate on the calculation of surface energies and surface relaxations for the L1₀- and L1₂ ordered structures. Different terminations of the low-index faces are studied. Also, we present results for the interlayer relaxations for planes close to the surface, revealing different relaxations for atoms of different species producing a rippled surface layer.     

Towards optimization of patterned superhydrophobic surfaces.

Experimental and theoretical study of wetting properties of patterned Si surfaces with cylindrical flat-top pillars of various sizes and pitch distances is presented. The values of the contact angle (CA), contact angle hysteresis (CAH) and tilt angle (TA) are measured and compared with the theoretical values. Transition from the composite solid-liquid-air to the homogeneous solid-liquid interface is investigated. It is found that the wetting behaviour of a patterned hydrophobic surface depends upon a simple non-dimensional parameter, the spacing factor, equal to the pillar diameter divided by the pitch. The spacing factor controls the CA, CAH and TA in the composite interface regime, as well as destabilization and transition to the homogeneous interface. We show that the assumption that the CAH is a consequence of the adhesion hysteresis and surface roughness leads to the theoretical values of the CAH that are in a reasonably good agreement with the experimental values. By decreasing the spacing factor, the values of CA=170 degrees, CAH=5 degrees and TA=3 degrees are achieved. However, with further decreasing of the spacing factor, the composite interface destabilizes.     

Nanocarbon-induced rapid transformation of polymer surfaces into superhydrophobic surfaces

We present a facile method for fabricating superhydrophobic polymer surfaces by solubility modulation and nanocarbon (NC)-induced crystallization of polycarbonate (PC). The method consists of dipping polymer sheets in a solvent in which the polymer is partially soluble and then inducing solution crystallization by dipping the sheet in a poor solvent for several seconds. A solvent mixture of methyl ethyl ketone and isopropyl alcohol (IPA) was optimized to shorten the crystallization time in a poor solvent. Single-walled carbon nanotubes, multiwalled carbon nanotubes (MWNTs), and graphene sheets were used to nucleate PC crystallization. In particular, monolayer graphene sheets were prepared by reducing graphene oxide with hydrazine. Crystalline micro- and nanostructures rapidly formed upon dipping of the PC sheets in the solution containing NCs, followed by immersion in IPA. The structures depended on the dimensions of the NCs. Especially, in the MWNT solution, dipping for 10 s was sufficient to create a superhydrophobic surface. Crystallization of PC and the incorporation of NCs during crystallization were characterized by Raman spectroscopy.     

Slender planing surfaces

A theory for slender planing surfaces of general shape at high Froude number was formulated by Casling (J Eng Math (1978) 12:43–57). Although this theory was later extended by Casling and King (J Eng Math (1980) 14:191–205), it remains somewhat distant from application to actual planing vessel design. The present paper is an attempt to move the Casling theory a little in that direction. A modified formula connecting underwater hull shape and wetted planform is suggested here, which may be more suitable for numerical computation. Spraysheets and forces are also discussed, and a sprayless example hull is provided.     

Defects on surfaces

A brief review of various types of defects on surfaces and their role in surface reactions is presented. Particular emphasis is given on defects like steps/kinks and additives (promoters and poison).     

Scattering-reduction effect with overcoated rough surfaces: theory and experiment.

We show that a scattering-reduction effect is obtained by coating a rough surface with an antireflection layer. This research is a generalization of Amra's [J. Opt. Soc. Am. A 10, 365-374 (1993)] study of smooth surfaces conducted with a first-order theory to the case of rough surfaces. We show that the differential method with the R matrix algorithm can be used to study scattering from multilayered rough surfaces. A comparison between numerical and experimental results is given.     

Rough and vicinal surfaces of helium-4 crystals. Mobility measurements

By studying the transmission coefficient of ultrasonic waves perpendicular to the solid-liquid interface, we have measured the mobility of vicinal surfaces of⁴He crystrals for different crystallographic orientations and in the temperature range from 0.38 K to 1 K. The results show an angular dependency of the vicinal mobility as predicted by theory. Further, in comparison with rough interfaces, a spectacular decrease for the mobility of vicinal surfaces due to the decreasing number of moving sites is in good agreement with preceeding results for the phonon term. It has been observed for the first time for the roton term.     

Micrometer dimension derivatization of biosensor surfaces using confocal dynamic patterning.

Using laser scanning confocal optics in conjunction with avidin/biotin technology, micrometer-sized patterns of biomolecules were fabricated on glassy-carbon and fused-silica surfaces. Photoactive biotin was immobilized using the 325-nm line of a Helium-Cadmium laser, which was focused through a 25x or 100x quartz microscope objective. A three-dimensional piezoelectric micromanipulator was used to position the sample surface in the focal plane of the microscope objective and to create patterns on the focused surface. Biotin patterns with line widths of 5-20 microns were produced by varying the scan speed of the micromanipulator while exposing the surface to the laser. The integrity of the immobilized biotin was confirmed by subsequent derivatization with fluorescently labeled avidin. Fluorescence microscopy with a cooled charge coupled device (CCD) imaging system was used to visualize the distribution of biotin and fluorescent avidin within the patterns created by the laser.     

Rem and reels characterization of MgO (100) surfaces. A Technique for studying the cleaving mechanisms and reactions of crystal surfaces

Reflection electron microscopy (REM) is used as a technique for imaging MgO surfaces cleaved by different methods. Several distinct surface structures of MgO (100) have been observed, and the possibility of relating the surface structure images with the breaking mechanisms of the surfaces has been shown. The surface atomic inner-shell excitations have been observed with reflection electron energy-loss spectroscopy (REELS), and the structure modulation of the near-edge fine structure of the O K and Mg K edges is considered to be due to changes in the surface density of states. The REM imaging is capable of providing the nucleation processes of the reaction products on the surfaces in the solid-liquid reactions and the associated relations with the surface structures.     

Modification and coating of biomaterial surfaces by glow-discharge processes. A review

Glow-discharge treatment processes offer a range of specific advantages for the modification of biomaterial surfaces: Versatility with respect to the substrates, geometric conformality, adherence and impermeability of coatings and a wide range of compositions available, to name the most important. After a concise introduction into the generation, properties and uses of glow-discharges, the presentation will give an overview of several reports on glow-discharge-based processes applied to biomaterial surfaces. Examples to be covered include the reduction of platelet reactivity of surfaces, enhancement of cell growth and the reduction of protein adsorption.     

Modelling of oxide surfaces

Ab initio methods have led to very rapid recent progress in the modelling of oxide surfaces. They have made important contributions to knowledge of three areas: equilibrium surface structure; the energetics and structures associated with oxidation and reduction; and the energetics of adsorption and dissociation of simple molecules such as H₂O and HCOOH.     

A calculation of the diffusion energies for adatoms on surfaces of F.C.C. metals

The activation energies for diffusion were determined for gold, platinum and iridium adatoms on (110) and (311) Pt surfaces and were found to be in good agreement with the measurements reported by Bassett and Webber. The Lennard-Jones pair potentials were used to model the interatomic forces, and relaxation of the substrate atoms in near proximity to the adatom was considered in detail. The present calculations clarify the mechanism of the observed two-dimensional diffusion of platinum and iridium atoms on a (110) Pt surface. The results are compared with those obtained using Morse potential functions and different relaxation techniques.