Seiichi Sato

Abstract Silicon (Si) nanocrystals with diameters of 2–5 nm were produced through non-equilibrium condensation of Si vapor. Electron diffraction analysis indicated that the nanocrystals formed a bcc structure with eight atoms per primitive cell (BC-8). The optical bandgap energy of the nanocrystals was about 1.6 eV, and photoluminescence was observed in the region of the bandgap energy. The obtained energy is compared with a theoretically predicted value of the BC-8 Si crystal of the present size.

Porous Si films were formed on electrically insulative, semiconductive, and conductive substrates by depositing aqueous and nonaqueous Si nanoparticle inks. In this study, we focused on whether the Si ink deposition resulted in the formation of uniform porous Si films on various substrates. As a result of the experiments, we found that the inks showing better substrate wettabilities did not necessarily result in more uniform film formation on the substrates. This implies that the ink-solvent wettability and the nanoparticle-substrate interactions play important roles in the uniform film formation. As one of the interactions, we discussed the influence of van der Waals interactions by calculating the Hamaker constants. The calculation results indicated that the uniform film formation was hampered when the nanoparticle surface had a repulsive van der Waals interaction with the substrate.

Hole injection barriers at the regioregular-poly-3(hexylthiophene) (RR-P3HT)/metal (Cu or Ag) interface were investigated using the accumulated charge measurement (ACM). Thermal annealing of RR-P3HT at 55 degrees C decreased the injection barrier. RR-P3HT thermally annealed in N-2 forms an ohmic contact with Ag and a Schottky contact with Cu. The obtained values of the injection barriers, phi(B) were well expressed by the Mott-Schottky rule, i. e., phi(B) = IE - W-m', where IE is the ionization energy of RR-P3HT and W-m' is the work function of the metal electrode in air. The effect of the large vacuum level shift, reported in UPS studies conducted under ultrahigh vacuum, was not observed. (C) 2017 Elsevier B.V. All rights reserved.

The effect of the offset bias voltage on the threshold voltage of the hole injection into the organic-semiconductor (OS) layer was examined in detail in the accumulated charge measurement (ACM) for the n-type Si/SiO2/OS/Ag (OS = zinc phthalocyanine [ZnPc] or metal-free phthalocyanine [H2Pc]) capacitor. The threshold highly depends on the offset bias voltages, when the OS layer is in the hole depletion regime. On the contrary, the threshold was nearly constant when the OS layer operated in the hole-accumulation regime. The hole injection barrier of the Ag/OS interface was obtained by the threshold in the accumulation regime. The obtained values were 0.41 and 0.05 eV for H2Pc/Ag and ZnPc/Ag interfaces, respectively. The study revealed that accurate estimation of the injection barrier is possible by examining the offset voltage dependence in the ACM.