Norihisa Mino

Vibrational sum-frequency generation (VSFG) spectra of n-alkyltrichlorosilanes chemisorbed on quartz plate

Abstract Organic thin films prepared by chemical adsorption of n -alkyltrichlorosilanes (CH 3 (CH 2 ) m SiCl 3 ; m =6,7,13,17,18) on quartz plates were investigated by vibrational sum-frequency generation (VSFG) spectroscopy. The vibrational resonances by CH stretch bands of methyl and methylene groups were examined taking advantage of the fact that the bands associated with methylene groups in the trans conformation do not contribute to the VSFG signal. The density of adsorbed molecules and that of all- trans conformational sequences of alkyl chains decreased when the substrates were pretreated by oxygen plasma indicating the depletion of surface hydroxyls, which are the adsorption sites. The g-t conformation sequences on the plasma-treated substrates were found to increase by the length of the alkyl chain and the total number of gauche conformations exceeded that of adsorbed molecules when the number of CH 2 groups in an alkyl chain is around 8.

Thin film characteristics of fluorine-substituted monolayers prepared by chemical adsorption from solution

Abstract Monolayers containing a fluorine-substituted carbon chain were prepared by the chemical adsorption (CA) technique. Characteristics of the monolayers were evaluated by spectroscopy, copper decoration technique, current-voltage characteristics (current density and resistivity), measurement of the contact angle, and friction tests. By the copper decoration technique, the CA monolayer was more pinhole free and uniform than a Langmuir-Blodgett film. The characteristics (such as the leakage current density, resistivity, critical surface tension and coefficient of kinetic friction) of the fluorine-substituted monolayers depended markedly on the number of substituted fluorine atoms.

Solution Growth of Rubrene Single Crystals Using Various Organic Solvents

To fabricate organic field-effect transistors (OFETs) with high carrier mobility, we attempted to grow 5,6,11,12-tetraphenylnaphthacene (rubrene) single crystals from solution and to improve their quality. Investigations into solvents in which rubrene was highly soluble proved that its solubility depended on the presence or absence of aromatic rings and chloro groups rather than on the polarity of the solvents. Rubrene crystals were grown from aromatic solvents, specifically from toluene, p-xylene, and aniline solvents, as well as from 1,2-dichloroethane (DCE) solvent. As a result, rubrene single crystals larger than 1 mm were obtained. Powder X-ray diffraction (XRD) analysis showed that the crystals obtained from the p-xylene and toluene solvents were rubrene, and 1H-nuclear magnetic resonance (1H-NMR) measurement proved that the crystals had not incorporated the solvent at the detection level. In addition, atomic force microscopy (AFM) confirmed that the rubrene crystals grown from the p-xylene and aniline solvents had flat faces and that the crystal from the p-xylene solvent had monomolecular steps on parts of the surfaces. Rubrene single crystal OFETs with graphite electrodes and parylene as an insulator showed carrier mobilities of ~0.75 cm2 V-1 s-1.

Photopolymerization of monomolecular films with diacetylene bonds on an aqueous subphase

Abstract The photoreactivity of monomolecular films of a diacetylene derivative (10,12-pentacosadiynoic acid (PDA)) under UV irradiation has been investigated at the air-water interface. With decreasing molecular area, the reactivity of the Langmuir film (the Langmuir film is the monomolecular film on an aqueous subphase) decreased, and the colour transition of the Langmuir film polymerized by the UV irradiation was from blue to red. Furthermore, the colour transition (blue to red) was also caused by heating the polymerized Langmuir-Blodgett (LB) films at about 60°C. The colour transition of the polymerized PDA Langmuir film exhibited reversibility at the air-water interface when the condition of the subphase was changed, but that of the LB films did not exhibit reversibility. In the differential scanning calorimetry diagrams, the PDA LB films had an endothermal peak a 67°C, but the polymerized film had two peaks at about 70 and 200°C. These results indicate that the photoreactivity of the PDA monomolecular film at the air-water interface was affected by the molecular arrangement and density, and the colour transition of the PDA polymer may be caused by the structural disorder of the side-groups joined to the polymer backbone.

Control of Pretilt Angles of Liquid Crystal Molecules in a Liquid Crystal Cell Using a Chemically Adsorbed Monolayer as an Alignment Film

Using chemically adsorbed monolayers with two surfactants as an alignment film for a liquid crystal cell, liquid crystal cells were structured. The monolayers showed a fair degree of alignment effects without rubbing. By changing the composition ratio of the mixture of the surfactants having a long hydrocarbon chain and a short hydrocarbon chain, the pretilt angles of the liquid crystal molecules could be controlled. The molecular density or the molecular arrangements in the chemically adsorbed monolayers may strongly affect the pretilt angles. To interpret the experimental results, possible model structures in the monolayer were proposed.

Fabrication of self-assembled monolayer patterns by selective electron beam irradiation and a chemical adsorption technique

Abstract Self-assembled monolayer patterns have been fabricated on silicon dioxide/silicon substrates by a chemical adsorption (CA) technique from 18-nonadecenyltrichlorosilane, 9-(heptadecafluorodecyl-dimethylsilyl) nonyltrichlorosilane etc. and a selective electron beam irradiation in a nitrogen atmosphere through an SUS mask. The fabrication of CA monolayer patterns was well confirmed by an X-ray photoelectron spectroscopy measurement, a contact angle measurement and film thickness measurement. A fine line and space pattern are fabricated in this study.

Applications of a Chemically Adsorbed Monomolecular Layer Having a Fluorocarbon Chain as an Anti-Contamination Film

Monomolecular layers having a fluorocarbon chain were developed and made suitable for practical use as anti-contamination films for glasses, such as front door window glass plates of automobiles and window glass plates of electric ovens or microwave ovens, and also for stainless steel applications, such as covers of electric rice cookers, by using a chemical adsorption technique for the first time in the world. The layer was anchored to the substrate surface through covalent bonds. Thus the layer did not peel off and was durable against rubbing and scratching. As the film thickness was from about 1 to 2 nm, the layer was also optically transparent and the luster and color tone of the substrates was maintained. The lowest surface tension obtained was 8.2 mN/m, which is about a half that of Teflon. Although thermo-durability was a little low in comparison with that of Teflon, the production cost was lower. Thus this anti-contamination film should be very useful in the field of anti-contamination surface treatment.

Electrical evaluation of ultrathin organic films on solid substrates

Abstract We established two evaluation methods for monolayer-order organic films on solid substrates and evaluated various kinds of films, i.e. Langmuir-Blodgett films of monoalkyl lipids, dialkyl lipids, dialkylsilane, and fluorocarbon, and chemically adsorbed films of three kinds of trichlorosilane compounds. One method is the measurement of the electroplating current during copper decoration, and the other the measurement of I–V characteristics using a micromanipulating mercury probe. Electrical characterization of the films with monolayer-order thickness is possible by using both types of liquid top electrodes, and a clear dependence of the electrical properties on monolayer number has been found quite reproducibly.

Preparation of multilayers using chemical adsorption and electron-beam irradiation

Abstract Multilayers of ω-nonadecenyl-trichlorosilane (V-NTS) have been prepared on SiO 2 /Si substrate by repeated cycles of chemical adsorption (CA) of V-NTS from a nonaqueous solution and electron-beam (EB) irradiation in air. The thickness of the multilayers was increased by a fixed value at every CA cycle. The molecular density and degree of arrangement of the V-NTS monolayer were higher than that of a ω-tricosenic acid (ωTSA) monolayer transferred onto a substrate by the Langmuir-Blodgett (LB) method. The vinyl group of V-NTS disappeared and hydroxyl, aldehyde, and/or carboxyl groups were formed when the irradiation was carried out in oxygen atmosphere, whereas imino and/or amino groups were formed when the irradiation was carried out in nitrogen atmosphere. Using this method, multilayers of high molecular density can be obtained easily.

Control of the reactivity of chemically adsorbed monolayers of polydiacetylene derivatives exposed to UV irradiation

Abstract Polydiacetylene derivative monolayers have been prepared on SiO 2 /Al/glass substrates by a chemical adsorption (CA) technique from the mixture of 18,20-heneicosadiynoxytrichlorosilane (18-DATS) and propyltrichlorosilane (PTS) or 7,9-tetradecadinyloxy-propyltrichlorosilane (7-DATS) and PTS of different composition ratios dissolved in a nonaqueous solvent (CA solution), and then polymerized by ultraviolet (UV) light irradiation in a nitrogen atmosphere. By changing the composition ratio of DATS and PTS in the solution, polymerized monolayers of blue and/or red phase were obtained.