The relaxation of ultrathin polymethyl methacrylate (PMMA) films, which were spin-coated on SiO2 and SiOH substrates, was examined with different film thicknesses. In the glassy state, several relaxation processes revealed temporal variations in thicknesses. In sharp contrast to bulk PMMA in which the monotonic volume reduction was expected, the ultrathin films exhibited thickness variations, which would be classified into at least four types: (1) a slow increase in the thickness with time, where the thickness, h, is less than the radius of gyration, R g (h < R g); (2) scattered, fluctuating temporal variation (h ∼ R g); (3) contraction in film thickness, followed by expansion for the films with h ∼ 2.6R g; and (4) scattered temporal variation eventually leading to bulk relaxation (h > 3R g). Such a complex relaxation phenomenon could have originated from the interaction of the substrate with the heterogeneous out-of-equilibrium configurations of the polymer molecules that were confined to a quasi-2-D geometry.

Electrical conductance of thin Ni films, deposited on insulating SiO2 substrates, was investigated for the initial stage of magnetron sputtering for the purpose of optimize control of catalyst particles sizes of carbon nanotubes. The conductance was not proportional to the deposition time in the early phase of deposition. The conductance rapidly increased, after a period of near-insulating behavior from the start of deposition, and thereafter the increase of conductance was almost proportional to the total deposition duration. The period of near-insulating behavior and the rapid increase of conductance in the early deposition phase were attributed to growth of island structures in the initial deposition and formation of a continuous film through the connection of islands. The effect of base vacuum pressure prior to sputtering deposition also was investigated by conductance measurements. It was demonstrated that measuring electrical conductance during sputtering deposition was a convenient tool to examine the structures in the deposited film.

No abstract

Imine‐based covalent organic frameworks (COFs) are crystalline porous materials with prospective uses in various devices. However, general bulk synthetic methods usually produce COFs as powders that are insoluble in most of the common organic solvents, arising challenges for the subsequent molding and fixing of these materials on substrates. Here, we report a novel synthetic methodology that utilizes an electrogenerated acid (EGA), which is produced at an electrode surface by electrochemical oxidation of a suitable precursor, acting as an effective Brønsted acid catalyst for imine bond formation from the corresponding amine and aldehyde monomers. Simultaneously, it provides the corresponding COF film deposited on the electrode surface. The COF structures obtained with this method exhibited high crystallinities and porosities, and the film thickness could be controlled. Furthermore, such process was applied for the synthesis of various imine‐based COFs, including a three‐dimensional (3D) COF structure.

No abstract