Biomedical subjects

Mutsuyoshi Matsumoto

Publications and source records attributed to Mutsuyoshi Matsumoto.

9 recordsLinked to original sources

PubMed2005

Alkyl chain conformation and the electronic structure of octyl heavy chalcogenolate monolayers adsorbed on Au(111).

Adsorption states of dioctyl dichalcogenides (dioctyl disulfide, dioctyl diselenide, and dioctyl ditelluride) arranged on Au(111) have been studied by X-ray photoelectron spectroscopy (XPS), infrared-visible sum-frequency generation (SFG), and ultraviolet photoelectron spectroscopy (UPS). XPS measurements suggest that dioctyl dichalcogenides dissociatively adsorbed on Au(111) surfaces to form the corresponding monolayers having chalcogen-gold covalent bonds. The elemental compositions of octanechalcogenolates on Au(111) indicate that the saturation coverages of the octyl heavy chalcogenolate (OcSe, OcTe) monolayers are lower than that of the octanethiolate (OcS) self-assembled monolayers (SAMs). The SFG observations of the CH(2) vibrational bands for the heavy chalcogenolate monolayers strongly suggest that a discernible amount of gauche conformation exists in the monolayers, while OcS SAMs adopt highly ordered all-trans conformation. The intensity ratio of the symmetric and asymmetric CH(3) stretching vibration modes measured by SFG shows that the average tilt angle of the methyl group of the OcSe monolayers is greater than that of the OcS SAMs. The larger tilt angle of the methyl group and the existence of a discernible amount of gauche conformation in the OcSe monolayers are due to the lower surface coverage of the OcSe monolayers compared with the OcS SAMs. The smaller polarization dependence in the angle-resolved UPS (ARUPS) spectra of the OcSe monolayers than that of the OcS SAMs is caused by the more disordered structures of the alkyl chain in the former. XPS, SFG, and ARUPS measurements indicate a similar tendency for the OcTe monolayers. The density of states (DOS) observed by UPS at around 1.3 eV for OcS adsorbed on Au(111) is considered to be the antibonding state of the Au-sulfur bond. Similar DOS is also observed by UPS at around 1.0 eV for the OcSe monolayers and at approximately 1.6 eV for the OcTe monolayers on Au(111).

Journal Article↗

PubMed2005

Correlation of the number of thiophene units with structural order and carrier mobility in unsubstituted even- and odd-numbered alpha-oligothiophene films.

We investigate the correlation of the number of thiophene units with the structural order and carrier mobility of the films through studies on thin-film transistors (TFTs) based on alpha-quinquethiophene (5T), alpha-sexithiophene (6T), and alpha-septithiophene (7T). The X-ray diffraction (XRD) data of the nT films deposited at low substrate temperatures present obviously different structural orders depending on the parity of the number of thiophene units. Although even-numbered nT films present well-ordered structures and large carrier mobilities, odd-numbered nT films present two different crystalline polymorphs and vastly low carrier mobilities reflecting the coexistence of two crystalline polymorphs. However, the XRD data of both even- and odd-numbered nT films deposited at high substrate temperatures indicate that the nT molecules form single well-ordered structures. Those ordered TFTs exhibit large carrier mobilities accompanying an increase in the number of thiophene units, 0.05, 0.08, and 0.13 cm2 V(-1) s(-1) for 5T, 6T, and 7T, respectively. The parity of the number of thiophene units affects the structural order intrinsically in grown thin films, and affects carrier mobilities extrinsically in their TFTs.

Journal Article↗

PubMed2005

Adsorption states of dialkyl ditelluride autooxidized monolayers on Au(111).

Organic ditellurides (R2Te2 where R = n-butyl (C4), n-octyl (C8), and n-cetyl (C16)) were synthesized, and their adsorption states after oxidation on Au(111) surfaces were studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), theoretical analyses, near-edge X-ray absorption fine structure (NEXAFS) measurements, contact angle measurements, and atomic force microscopy (AFM). The obtained results show that dialkyl ditellurides form autooxidized monolayers (AMs) on the surfaces under ambient conditions and that the oxidation process is accelerated by ambient light. XPS, UPS, and theoretical analyses suggest that the autooxidized ditelluride species consist of polymers or oligomers with Te-O-Te-O network structures stabilized by oxygen bridges between tellurium molecules following the cleavage of tellurium-gold bonds. NEXAFS and contact angle measurements indicate that the average tilt angles of the alkyl chains from the surface normal are smaller for the AMs of dialkyl ditellurides having longer alkyl chains. AFM measurements show defects and roughness features around a few angstroms in height on the surfaces of the dialkyl ditelluride AMs.

Journal Article↗

PubMed2004

Control of photoreaction of amphiphilic spiropyran/n-alkane Langmuir and Langmuir-Blodgett films using the phase transition of n-alkane.

The structures and photoreactions of Langmuir and Langmuir-Blodgett (LB) films of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-1'-octadecyl-8-(docosanoyloxymethyl)spiro[2H-1-benzopyran-2,2'-(2H)-indole] (SP), mixed with n-alkane are investigated. The mixing ratio was fixed at 1/2 for SP/n-alkane. The surface pressure-area isotherms of SP/octadecane are categorized into two regimes: a low-temperature regime where octadecane is packed with the alkyl chains of SP, and a high-temperature regime where the addition of octadecane does not influence the isotherms significantly. The temperature dividing the two regimes is related with the melting point of the n-alkane mixed with SP in the bulk. UV irradiation of the Langmuir film in the high-temperature regime gives rise to light-induced J-aggregation, whereas that in the low-temperature regime causes only the isomerization of SP to the corresponding merocyanine, indicating that J-aggregation is hindered by the presence of n-alkane in the low-temperature regime. IR external reflection spectroscopy of the Langmuir films shows that n-alkane is released from the film during J-aggregation. The structural changes of the mixed Langmuir and LB films during J-aggregation are almost the same with those of the films of pure SP.

Alkanes↗

PubMed2004

Template-directed patterning using phase-separated Langmuir-Blodgett films.

The structures of the mixed Langmuir-Blodgett (LB) films of conventional amphiphiles (CAs) and amphiphilic silane-coupling agents (SCAs) were investigated using IR spectroscopy, atomic force microscopy, and friction force microscopy. By using CAs having hydrogenated alkyl chains and SCAs having perfluorinated alkyl chains, phase-separated structures were formed with domains consisting of CAs surrounded by SCAs. The size and shape of the domains depended strongly on the mixed components, the mixing ratios, and the subphase temperature. In particular, usage of a CA having hydrogenated and perfluorinated portions in the hydrophobic group as one of the components led to the formation of nanothreads. When the phase-separated mixed LB films were heated, SCAs formed covalent bonds with the substrates having silanol groups whereas CAs did not have such ability. Rinsing the heat-treated LB films with ethanol selectively removed CAs with the SCA regions intact, resulting in the fabrication of templates. The structures of the templates reflected those of the original phase-separated LB films. LB transfer of amphiphiles on the templates led to the confinement of the amphiphiles in regions with the size and shape delineated by the templates. These results demonstrate that a variety of amphiphiles can be confined two-dimensionally in a designed manner.

Journal Article↗

PubMed2004

Brewster angle microscopic observations of the Langmuir films of amphiphilic spiropyran during compression and under UV illumination.

The structure of the Langmuir film of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-l'-octadecyl-8-(docosanoyloxyme thyl)spiro[2H-1-benzopyran-2,2'-(2H)-indole] (SP), is investigated using Brewster angle microscopy (BAM). The BAM observations show that the Langmuir film of SP can be roughly categorized into three regimes: a low-temperature regime at 7-13 degrees C; a medium-temperature regime at 23-30 degrees C; a high-temperature regime at 40 degrees C. The low-temperature regime is characterized both by the domains that are formed just after the spreading and by the onset of the surface pressure when the domains are merged together to form continuous trilayers. In the medium-temperature regime, a continuous monolayer film is formed after the solvent evaporation, followed by the growth of "embryos" with compression. Around the phase transition point, the "embryos" serve as the "nucleation sites" of the circular trilayer domains. The characteristic features of the high-temperature regime are similar to the ones of the medium-temperature regime except for the absence of a steep rise in surface pressure after the plateau region and the absence of the circular trilayer domains. UV illumination of the Langmuir films leads to the isomerization of SP into merocyanine (MC). However, J-aggregates of MC are formed only when the circular trilayer domains are present. On the basis of the above results, we present a phase diagram of the Langmuir film of SP. The structure and photoreaction depend strongly on the phase of the Langmuir film, indicating that the area/molecule is not the only decisive parameter.

Benzopyrans↗

PubMed2004

Thermal hysteresis in the photoresponsivity of a langmuir film of amphiphilic spiropyran.

We have found a thermal hysteresis in the photoresponsivity of a Langmuir film for the first time. The Langmuir film of an amphiphilic spiropyran, 1',3'-dihydro-3',3'-dimethyl-6-nitro-1'-octadecyl-8-(docosanoyloxymethyl)spiro[2H-1-benzopyran-2,2'-(2H)-indole] (SP) was fabricated at 13 degrees C at 10 mN m-1, followed by heating to a given temperature. UV irradiation of this film caused only the isomerization of SP to the corresponding merocyanine (MC) up to 29 degrees C. Light-induced J-aggregation of MC occurred at 30 degrees C. On the other hand, once the film was heated to 30 degrees C, light-induced J-aggregation was observed down to 27 degrees C. The hysteresis should be related with the phase transitions that occur in the bulk of SP at similar temperatures. No significant morphological change occurred by light-induced J-aggregation in the Langmuir-Blodgett (LB) film of SP by the present method, in contrast to the case of the LB films fabricated under isothermal conditions at 30 degrees C. This feature enabled us to pattern the LB film with J-aggregate of MC by UV irradiation through a photomask of lines with a width of 5 mum each.

Journal Article↗

PubMed2003

Phase switching of a single isomeric molecule and associated characteristic rectification.

Variations in molecular electronic structures related to conformational change are exceedingly attractive because of their key role in the understanding and development of functional processes in molecular electronics and biology. We observed, for the first time, the novel phase switching of a photoactive isomeric molecule, N-(2-mercaptoethyl)-4-phenylazobenzamide (Azo molecule) at a single-molecule level, which exhibits a distinctive change in the conductive characteristic under scanning tunneling microscope (STM) measurement. In comparison with the results obtained by the measurement of photoactive isomerization of the isolated Azo molecule, which was performed also for the first time, the observed characteristics are attributed to the results of the trans and cis phase transformation of the Azo molecule, under the condition of an external electric field and current flow. A specific point is that the potential landscape of the system is controllable by the electric field and provides a conformational stability with asymmetric bias dependence resulting in rectification.

Journal Article↗

PubMed2002

Effective insulating properties of autooxidized monolayers using organic ditellurides.

Dialkyl ditellurides adsorb on Au(111) surfaces by wet deposition to form highly resistive autooxidized monolayers (AMs) due to the automatic formation of oxidized tellurium species after the adsorption of ditellurides on the surfaces under air in contrast to the case of the lighter dichalcogenides such as disulfides and diselenides. The ditelluride AMs could be applied to the selective fabrication of effective resistance, ferroelectric layers, piezoelectric parts, and/or new imaging systems using the feature of tellurium oxide in small device circuits.

Journal Article↗