Tsuyohiko Fujigaya

Electrically Biased Nanolithography with KOH-Coated AFM Tips

This letter provides the first study aimed at characterizing the desorption and nanolithographic processes for SAM-coated, gold-coated silicon substrates oxidatively patterned with an AFM with a tip under potential control. The process either results in recessed patterns where the monolayer has been removed or raised structures where the monolayer has been removed and silicon oxidation has taken place. Eleven different SAMs have been studied, and the type of pattern formed depends markedly upon SAM chain length, end functional group, and applied bias. We show how local pH and choice of monolayer can be used to very effectively control the type of pattern that is ultimately formed. Interestingly, we show that hydroxide anion accessibility to the substrate surface is one of the most significant factors in determining the pattern topography. Moreover, control over the pattern topography can be achieved by controlling the concentration of the KOH in the water meniscus formed at the point of contact between tip and surface in the context of a bias-controlled DPN experiment with a KOH-coated tip. The work provides important insight into the factors that control SAM desorption and also ways of controlling the topography of features made in a potential-controlled scanning probe nanolithographic process.

Electrospinning of poly(vinylpyrrodine) template for formation of ZrO2 nanoclusters for enhancing properties of composite proton conducting membranes

ABSTRACT Nanosized ZrO2 clusters were prepared by electrospinning a poly(vinylpyrrodine) (PVP)/ZrO2 mixture for calcination to remove PVP template and sizing. The morphological, chemical, structural, and thermal resistance changes during preparation stages were investigated using scanning electron microscope, energy-dispersive X-ray spectroscopy, transmission electron microscope, X-ray diffraction, and thermogravimetric analysis. The obtained ZrO2 clusters were used for preparation of nanocomposite membranes by dispersion in 2,6-pyridine polybenzimidazole (2,6-Py-PBI) matrix at 5 wt% content followed by phosphoric acid (PA) doping. The ZrO2 nanoclusters were found to be uniformly distributed in 2,6-Py-PBI/PA matrix leading to a remarkable increase in the PA doping level and proton conductivity of the obtained composite membrane. GRAPHICAL ABSTRACT

Single-Walled Carbon Nanotubes as a Molecular Heater for Thermoresponsive Polymer Gel Composite

The structural stiffness, effective optical absorption ranging from UV to IR region and efficient photothermal conversion of the carbon nanotubes (CNTs) are attractive feature as a molecular heater, which can be useful for therapy, actuator and so on. Dai et al. reported that the near-IR (NIR) irradiation to a living HeLa cell after uptaking a CNTs/DNA composite caused death of the cells (Kam, et al., 2005) due to the intense local heating triggered by the NIR irradiation. We have described that pulsed-NIR irradiation of CNTs wrapped by an anthracenependanted polymer allowed the dissociation of the polymer from the CNTs surface followed by aggregation of the CNTs, in which the CNTs act as a “molecular heater” that triggers removal of the polymer from the SWNT surface.(Narimatsu, et al., 2006) On the other hand, thermoresponsive polymer gels, which show phase transitions, are of interests in wide areas of science and technology from the aspects of both fundamental (experimental and theory) and applications (Bohidar, et al., 2003). Poly(Nisopropylacrylamide) (PNIPAM) (Hirotsu, et al., 1987; Schild, 1992) and its derivatives are well-known thermoresponsive materials, which show a phase transition triggered by external stimuli such as the solvent composition, (Katayama, et al., 1984) pH, (Tanaka, et al., 1980) ionic strength, (Tanaka, et al., 1980) electric field (Tanaka, et al., 1982) and light. (Ishikawa, et al., 1993; Juodkazis, et al., 2000; Mamada, et al., 1990; Nayak & Lyon, 2004; Suzuki & Tanaka, 1990) Among the various light sources, NIR laser light is a fascinating stimulus especially from a biomedical point of view, because biomedical tissues have a slight absorption in the NIR region, (Weissleder, 2001) which enable remote stimulation of the NIR absorbent in the body from the outside. The combination of CNTs with PNIPAM would expect to trigger the phase transition of PNIPAM with NIR irradiation through photothermal conversion of CNTs. In this article, we propose the utilization of single-walled carbon nanotubes (SWNTs) as a photon antenna that serves as an effective “molecular heater” around the NIR region.