Surface structure of In/Si(1 1 1) studied by reflection high-energy positron diffraction

We have investigated a quasi-one-dimensional structure of In/Si(1 1 1) surface using reflection high-energy positron diffraction (RHEPD), which is sensitive to the topmost surface structure under the total reflection condition. From the rocking curves, we found that In atoms are located at two different vertical positions, i.e., 0.99 Å and 0.55 Å from the Si zigzag chain in both 4 × 1 (210 K) and 8 × 2 (60 K) phases.     

Experimental study on forced convective heat transfer of flowing gaseous solid suspension at high temperature

The results of an experimental study of the forced convective heat transfer to helium-graphite suspension at high temperatures up to 1173K are presented. Entering gas Reynolds number ranges from 1.0 x 10⁴ to 2.0 x 10⁴ and the particle loading ratio reaches about 4. The ratio of the Nusselt number of the suspension to that of gas alone increases considerably in a range of high loading ratios as the wall temperature increases. Subsequently, two kinds of turbulence promoters (200 and 400 mm pitch twisted tapes) are inserted in the flowing gaseous solid suspensions to make use of the large inertia forces of particles. The current results show that the local heat fluxes with use of the tapes increase significantly with the rise in the wall temperature owing to the radiative effect of the particulate phase.     

Atomic structure of two-dimensional binary surface alloys: Si(111)-√21 × √21 superstructure

The atomic structures of Au and Ag co-adsorption-induced √21 × √21 superstructure on a Si(111) surface, i.e., (Si(111)-√21 × √21-(Au, Ag)), where the Si(111)-5 × 2-Au surface is used as a substrate, have been investigated using reflection high-energy positron diffraction (RHEPD) and photoemission spectroscopy. From core-level spectra, we determined the chemical environments of Ag and Au atoms present in the Si(111)-√21 × √21-(Au, Ag) surface. From the rocking curve and pattern analyses of RHEPD, we found that the atomic coordinates of the Au and Ag atoms were approximately the same as those of the Au and Ag atoms in other Si(111)-√21 × √21 surfaces with different stoichiometries. On the basis of the core-level and RHEPD results, we revealed the atomic structure of the Si(111)-√21 × √21-(Au, Ag) surface.     

Synthesis and Surface Chemical Properties of Adhesive Protein of the Asian Freshwater Mussel,Limnoperna fortunei

The adhesive polydecapeptide poly(Lys‐Pro‐Thr‐Gln‐Tyr‐Ser‐Asp‐Glu‐Tyr‐Lys) (average repeating number, n = 5), which is the consensus sequence of the Asian freshwater mussel Limnoperna fortunei adhesive protein (Lffp), has been synthesized by the polycondensation of the active esters. The surface chemical experiments revealed the following characteristics of the freshwater adhesive protein: (i) wettability of the Lffp solution is affected by the polar component value (γ_s^p) of the surface free energy of the substrate, and a substrate having a γ_s^p less than 10 mJ·m^–2 exhibits a reduced wettability of the Lffp solution; (ii) the comparison of wettability of native Lffp with synthetic Lffp suggests that the decapeptide sequence, ‐Lys‐Pro‐Thr‐Gln‐Tyr‐Ser‐Asp‐Glu‐Tyr‐Lys‐, contributes to the interaction with the underwater surface; (iii) the Lffp tends to adsorb on nonpolar surfaces that have a low γ_s^p value; and (iv) the adsorption ability of the freshwater adhesive protein is less than that of the marine adhesive protein because of the higher hydrophilicity of the freshwater adhesive protein. An antifouling examination indicated that a γ_s^p value of the substrate surface of less than 10 mJ·m^–2 should achieve a higher antifouling effect towards the L. fortunei attachment. These results are the first findings for the development of a freshwater antifouling strategy based on the molecular mechanism underlying the attachment of L. fortunei.     

Convection-Flow-Assisted Preparation of a Strong Electron Dopant,Benzyl Viologen,for Surface-Charge Transfer Doping of Molybdenum Disulfide

Transition metal dichalcogenides (TMDCs) have received attention as atomically thin post-silicon semiconducting materials. Tuning the carrier concentrations of the TMDCs is important, but their thin structure requires a non-destructive modulation method. Recently, a surface-charge transfer doping method was developed based on contacting molecules on TMDCs, and the method succeeded in achieving a large modulation of the electronic structures. The successful dopant is a neutral benzyl viologen (BV⁰); however, the problem remains of how to effectively prepare the BV⁰ molecules. A reduction process with NaBH₄ in water has been proposed as a preparation method, but the NaBH₄ simultaneously reacts vigorously with the water. Here, a simple method is developed, in which the reaction vial is placed on a hotplate and a fragment of air-stable metal is used instead of NaBH₄ to prepare the BV⁰ dopant molecules. The prepared BV⁰ molecules show a strong doping ability in terms of achieving a degenerate situation of a TMDC, MoS₂. A key finding in this preparation method is that a convection flow in the vial effectively transports the produced BV⁰ to a collection solvent. This method is simple and safe and facilitates the tuning of the optoelectronic properties of nanomaterials by the easily-handled dopant molecules.