Naokiyo Koshikawa

Spontaneous construction of nanoperiodic architecture by two-dimensional self-assembly of an amphiphilic peptide-polyethylene glycol conjugate at the solid/water interface.

An amphiphilic peptide derivative, conjugated to polyethylene glycol (PEG) via the C-terminus, spontaneously assembled into nanodot and nanofiber arrays aligned with nanometer periodicity at the solid/water interface. The obtained planar structure was precisely controlled by the β-sheet conformation of the peptide on the surface, while the peptide segment adopted a random-coil in aqueous solution. The peptide and PEG segments were hierarchically segregated after the peptide-PEG conjugate was adsorbed on the substrate, and the peptide segment transitioned from a random-coil to a β-sheet conformation specifically at the solid/water interface. In this 2D self-assembly, the high dispersity of the peptide-PEG molecule in solution such that it exists as single molecules is essential for improving the uniformity of the 2D patterned nanostructures. The secondary structure based on the peptide segment was controlled by pH of the solution. Configuration of the peptide-PEG conjugate was also controlled by the temperature of the solution, which depended on the lower critical solution temperature (LCST) of the PEG segments. The variation in concentration of the peptide-PEG conjugate drastically influenced the morphologies of the 2D nanostructures because of the difference in the adsorbed amounts at equilibrium.

A peptide-PEG conjugate-directed nanoperiodic hierarchical architecture by spatial selective self-assembly at the solid/water interface

A simple and straightforward method for the construction of planar nanoarchitectures was developed. Two-dimensional arrays of nanodots and nanofibers aligned with nanometer periodicity were spontaneously constructed by the self-assembly of a designed peptide-PEG conjugate at the solid/water interface. In this self-assembly, the secondary structure of the peptide segment adopting a random coil conformation transformed into the β-sheet conformation selectively at the interface. The spatially selective dynamic behavior of the monomeric building blocks adsorbed on the solid surface was a decisive factor in the construction of the hierarchically controlled nanoarchitectures.

Excellent compositional homogeneity in In0.3Ga0.7As crystals grown by the traveling liquiduszone (TLZ) method

The influence of convection in a melt on the compositional homogeneity of the TLZ-grown In0.3Ga0.7As crystals has been investigated by growing crystals with various dimensions on the ground. Excellent compositional homogeneity such as 0.3 plus or minus 0.01 in InAs mole fraction for a distance of 25 mm was obtained when the melt diameter was limited to 2 mm and convective flow in the melt was suppressed. On the other hand, when the crystal diameter was increased to 10 mm, both axial and radial compositional homogeneity was deteriorated due to convection in the melt. Comparing with the numerical simulation, convective flow velocity less than 1.4 mm/h may be sufficient for growing homogeneous crystals and it is not so difficult to suppress convective flow velocity below 1.4 mm/h for 10 mm diameter crystals in microgravity. Therefore, larger homogeneous In0.3Ga0.7As crystals are expected to be grown by the TLZ method on board the International Space Station.