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We studied a surface modification technique for indium tin oxide (ITO) anodes without precleaning and resist banks for manufacturing organic light-emitting diodes (OLEDs) by inkjet printing. The ITO surface modified by inductively coupled plasma (ICP) with an optimized CF4/O2 (7:3) gas mixture improved both its hydrophilicity and its work function, while the resist surface treated by the plasma became hydrophobic. The resist and ITO surfaces treated by plasmas of various gas mixtures (i.e., CF4, CF4/Ar (1:2), CF4/O2 (x:1; x=1, 7/3, 4, and 9) were analyzed by X-ray photoelectron spectroscopy (XPS) of the C 1s, F 1s, O 1s, and In 3d5/2 core levels. On the uncleaned ITO surfaces modified by CF4/O2 plasmas, organic contaminants were removed more efficiently and the deposition of CFx on the remaining contaminants decreased with increasing oxygen. The amount of F in the form of InFx increased using the CF4/O2 (7:3) plasma in comparison with that using the CF4/Ar and CF4 plasmas. We investigated the effect of adding oxygen to CF4 on the change in gaseous species produced in the plasma chamber by mass spectrometry. In the CF4/O2 (7:3) plasma, the peak intensities of F+, HF+, F2+, O+, and O2+ were higher than those in the CF4 plasma. The results suggest that In2O3 was generated by the oxidation of indium with O, and InFx was generated by the fluoridation of indium with HF. By introducing InFx onto ITO surfaces using the CF4/O2 plasma, the hole-injection energy barrier could be reduced.

It was reported recently that the diamine-terminated molecules show two sets of single molecular conductance peaks in the conductance histogram. Although we found another set of conductance value of 1,4-diaminobutane in a lower current range, it was difficult to determine the conductivity definitely because the compound has different conformations with different gauche contents within its molecular chain. To make it easier to determine and analyze a single molecular conductance we measured here the conductance of 1,4-phenylenediamine, whose conformation cannot be changed in terms of the gauche contents. As a result, new sets of conductance other than those reported recently [L. Venkataraman, J.E. Klare, C. Nuckolls, M.S. Hybertsen, M.L. Steigerwald, Nature 442 (2006) 904] were observed.

In this study, we fabricated glass substrates covered with hydrophilic and hydrophobic silanes to investigate the effect of wettability of these surfaces on DNA molecular combing. As the hydrophilic and the hydrophobic silane, a mercapto-terminated (HS(CH 2 ) 3 Si(OCH 3 ) 3 ) and a methyl-terminated one (CH 3 (CH 2 ) 3 Si(OCH 3 ) 3 ) were used, respectively. The wettability was controlled by changing the molar ratio of the two components in the mixed monolayer. From the results of the DNA molecular combing, it was shown that the mercapto terminals on the surfaces were hardly dissociated into S - groups in aqueous buffers with pH 5.5 and 8.0. In addition, it was found that the length of the immobilized DNA molecules on the hydrophilic surfaces was shorter than that on the hydrophobic ones.

An efficient computational method to calculate NMR chemical shifts of large biomolecular systems is proposed. The method is based on the fragment molecular orbital (FMO) method combined with the gauge-including atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) methods. It accurately reproduced the conventional ab initio NMR values for a 10-residues peptide. The method was also applied to ubiquitin (76 amino-acid residues), and the calculated chemical shifts agree well with experimentally measured shifts. The proposed method requires a much lower computational cost than the conventional ab initio methods to calculate chemical shifts of large systems.

The effect of the binding modes of two amino terminal groups present on two gold protrusions on currents passing through a single molecular junction of Au/1,4-diaminobutane/Au was studied via the repeated formation of a break junction using a scanning tunneling microscope (STM) under nitrogen at room temperature. In addition to the two reported (high and low) values of the single molecular conductance of diaminobutane, another lower conductance was found through a careful analysis of histograms in a low-current range (0–0.3 nA). The techniques used here to improve the determination of the values of single molecular conductance were the selection of valid i–s curves with current steps and the use of the robust statistical method to correct for the contribution of the background tunneling currents to the current histograms. These three single molecular conductance values are attributed to three different binding modes of the two terminal amino groups giving the three different contact resistances at room temperature. That is, each amino terminal group is likely to be bound to one or the other gold protrusion through a more or a less conductive contact mode. Thus, a single molecular junction between two gold electrodes has three different contact modes, i.e., i) more–more, ii) more–less (or less–more), and iii) less–less conductive contact modes at the two ends.

We first observed a unique pyrene (Py) emission from 10-(1-(6-hexyl)pyrenyl)decanoic acid (1,6-HPDA) Langmuir-Blodgett (LB) films. In the fluorescence spectra of the 1,6-HPDA LB films, the normal bands of monomer and excimer emission of Py were absent but the new structured emission band with peaks at 422, 448, and 473 nm was observed. Besides the intensity, the shape of the characteristic structured emission band at shorter wavelengths than normal excimers did not changed essentially on lowering the Py concentration in the LB monolayer from 100 to 1 mol%. The spectroscopic studies on HPDA LB films of a variety of Py concentrations suggested that a novel excimer responsible for the structured new emission would be efficiently formed by photo-excitation of a Py-Py pre-associated dimer in different manners than those of normal excimer formations. (c) 2005 Elsevier B.V. All fights reserved.

Transient absorption measurements of an acceptor-sensitizer-donor (A-S-D) triad molecule (ASD) that contained viologen, pyrene, and ferrocene as the A, S, and D moieties, respectively, were made in benzonitrile and aqueous micellar solutions, and in a Langmuir-Blodgett (LB) monolayer assembly. Intramolecular electron transfer reactions were initiated by photo-excitation of the S moiety, which gave rise to the long-lived final charge-separated A(center dot-)-S-D center dot+ state. The rate of the backward electron transfer from A(center dot-) to D center dot+ was determined from the absorption decay of the viologen cation radical monitored at 600-700 nm. The estimated lifetime of the final charge-separated state was ca. 60 ns, based on measurements of the solutions. Extremely slow decay (much longer than 600 Vs) of the transient absorption of the viologen cation radical was observed for a mixed ASD LB film with 22-tricosenoic acid (TA). This slow decay observed on a LB film at higher ASD concentrations may be explained by lateral charge migration between adjacent molecules in the monolayer plane. (c) 2005 Elsevier B.V. All rights reserved.

The efficiency of the lateral photo-induced electron transfer between cyanine (electron donor) and viologen (electron acceptor) amphiphiles (Cy and V, respectively) was examined by observing the absorption and emission spectra of V doped Cy LB films. The sharp J-band observed in the absorption and fluorescence spectra indicated the efficient formation of J-aggregate of the cyanine chromophore even in the mixed LB monolayers with V The fluorescence intensities of the J-band decreased monotonously with the increase of V concentration but the dependence of the electron transfer efficiency on the film composition was rather complicated. The efficiency of the lateral electron transfer estimated at the composition region of the lower V ratios, where V molecules are expected to disperse homogeneously into the Cy monolayer, was such that ca. 90 molecules of Cy would be quenched by one center molecule of V. (c) 2005 Elsevier B.V. All rights reserved.

We investigated the interaction between DNA and n-alkylsilanized glass surfaces at pH 8 using fluorescence microscopy and atomic force microscopy (AFM). The surface densities of DNA molecules deposited on the glass surfaces with or without n-alkylsilanes were measured by fluorescence microscopy. In order to clarify the interaction between the DNA molecule and the substrate surface, forces in various buffer solutions (pH 2.0–9.0) between a cleaned Si3N4 tip and each substrate surface were measured by AFM. The repulsive forces were measured at pH 8 between the cleaned Si3N4 tip and all of the substrate surfaces, when they were separated in the buffer solution. The repulsive forces can be attributed to observation that the Si3N4 tip and all of the substrate surfaces were charged negatively at pH 8. The repulsive electrical double layer (EDL) forces against the bare glass surface and the surface silanized with n-propyltrimethoxysilane (C3), however, were higher than that against the surface with n-hexadecyltrimethoxysilane (C16). The adhesive forces, which are partially due to van der Waals forces, between the tip and the substrate surface were much higher on the surface with C16 than on those with C3 and of the bare glass substrate. It is important to note that both DNA and the Si3N4 tip at pH 8 were charged negatively. The higher repulsive EDL and the lower adhesive forces observed on the surfaces with C3 and of the bare glass substrate at pH 8 rationalized the fluorescence microscopic observation that the DNA molecules hardly adsorbed on these two surfaces. On the contrary, the higher adhesive force as well as the lower repulsive EDL force on the surface with C16 at pH 8 rationalized why the DNA molecules adsorbed well on this surface.

Photo-induced charge separation in mixed Langmuir–Blodgett (LB) films containing oriented A–S–D triads and inert matrix molecules was studied by using scanning Maxwell stress microcopy. A, S, and D stand for electron acceptor, sensitizer, and electron donor moieties of the triad, respectively. The change in surface potentials upon photo-excitation corresponded well with creation and disappearance of photo-induced dipole moments in the LB films due to the photo-induced charge separation in the oriented A–S–D triads followed by charge recombination. The observed lifetime of the separated charges in the LB films, however, was longer by several orders of magnitude than that of isolated A–S–D triads in solution observed by transient absorption spectroscopy. The magnitude of the photo-induced surface potentials, i.e. the content of the separated charges with the longer lifetime decreased drastically with the decrease in the concentration of A–S–D triads in the mixed LB films. Therefore, we concluded that the separated charges with the longer lifetime were created by lateral diffusion of photo-produced anion (electrons) and cation radicals (holes) among neighboring A and D moieties, respectively, in the LB films. We also found that addition of a second donor (D′) monolayer next to a layer of D end moieties of the mixed A–S–D monolayer in multilayered LB films enhanced the photo-induced charge separation with the long lifetime. When light harvesting (H) molecules acting as antenna was mixed with the A–S–D triads in place of the inert matrix molecules, the photo-induced charge separation was observed under irradiation of photons, which were absorbed by the H moieties.

Biodevices composed of biomolecular layer have been developed in various fields such as medical diagnosis, pharmaceutical screening, electronic device, photonic device, environmental pollution detection device, and etc. The biomolecules such as protein, DNA and pigment, and cells have been used to construct the biodevices such as biomolecular diode, biostorage device, bioelectroluminescence device, protein chip, DNA chip, and cell chip. Substantial interest has focused upon thin film fabrication or the formation of biomaterials mono- or multi-layers on the solid surfaces to construct the biodevices. Based on the development of nanotechnology, nanoscale fabrication technology for biofilm has been emerged and applied to biodevices due to the various advantages such as high density immobilization and orientation control of immobilized biomolecules. This review described the nanoscale fabrication of biomolecular film and its application to bioelectronic devices and biochips.

Alignment behavior of a discotic liquid crystalline triphenylene (C8OBTP) on substrates coated with self-assembled monolayers (SAMs) of alkanethiol and asymmetrical alkyl disulfide was investigated by polarized microscopy. Discotic nematic (ND) and rectangular columnar (Colr) phases of C8OBTP shows a different alignment behavior depending on the element of SAMs. C8OBTP exhibits a fan-shaped texture on an alkanethiol SAM in Colr phase, while it has a tendency to show a planar alignment on asymmetrical alkyl disulfide SAM. The different elements of the SAM could influence the alignment behavior of discotic liquid crystal distinctly even in columnar mesophase which has highly self-cohesive forces of systems.

It is important to understand an electronic property of an interface between an organic material and a metal electrode. In the present work, we measured current–voltage ( I – V ) curves of self-assembled monolayers (SAMs) on Au(1 1 1) using a conducting atomic force microscope (AFM) with chemically modified Au-coated AFM tips. This contact resulted in a bilayer junction between the Au(1 1 1) substrate covered with one SAM and the Au-coated tip with the other SAM. An alkanethiol (octanethiol) and benzenemethanethiols with various terminal groups (–H, –CH 3 , –Cl, –CF 3 ) were used as the adsorbates. The shapes of the I – V curves depended on the terminal groups. This phenomenon was attributed to the change in the work function of gold due to different permanent dipole moments of the terminal groups.

To study interaction between a single atom protrusion and molecules in a self-assembled monolayer during non-contact atomic force microscopy (nc-AFM), we attempted molecular dynamics (MD) simulation using a monolayer consisting of united CH 3 atoms with a mass ( m 0 ). The interaction of a single gold atom tip with the united atoms and a continuum gold substrate was treated explicitly in terms of microscopic potentials under temperature control with Berendsen’s thermostat. On the other hand, the probe tip with an artificial reduced mass of ca. 600 m 0 was bound to a cantilever spring in order to measure its macroscopic nc-AFM behavior. Energy dissipation as a function of temperature was also studied.

Lambda bacteriophage deoxyribonucleic acid (DNA) molecules stained with YOYO-1 were deposited and stretched on chemically modified Si(1 0 0) wafer and cover glass substrates. The Si(1 0 0) wafer with a natural oxide layer and the cover glass surface were first chemically modified by vapor phase chemisorption with mixed two organosilanes. DNA molecules were then aligned on the substrate surfaces by chemical and physical adsorption from an aqueous solution during molecular combing. The aligned DNA molecules were observed by Kelvin probe force microscopy and intermittent contact-mode atomic force microscopy (AFM) as well as fluorescence microscopy. Interaction between the stretched DNA molecules and the chemically modified Si(1 0 0) substrate surface was examined using these AFMs.

The motion of single conjugated molecules inserted in a self-assembled monolayer (SAM) matrix composed of a spherical bicyclo[2.2.2]octane derivative was observed using scanning tunnelling microscopy at room temperature. Two kinds of conjugated molecules, i.e. benzenemethanethiol and 4-biphenylmethanethiol, were inserted in the SAM matrix. It was revealed that the isolated single molecules exhibited two types of motions. One was the change in tilt of the molecular axis at a fixed position, and the other was lateral motion in the SAM matrix. These motions of the single molecules due to thermal energy at room temperature were most likely caused by large and mobile vacancies of single molecular defects in the SAM matrix.

Origins of peak broadening in a histogram of measured adhesive forces were studied. The adhesive forces were measured in water by pulsed-force-mode atomic force microscopy. One sample was prepared by a microcontact printing method on a sputtered gold film with fine grains, on which CH 3 - and COOH-terminated regions were produced. Gold surfaces of other samples were chemically modified homogeneously by a self-assembling method in solution. Their surfaces were, however, topographically different, i.e. (i) an Au(1 1 1)-terrace-rich gold film prepared by vacuum vapor deposition at high temperature and (ii) sputtered gold films on cover glass with different grain sizes obtained by different deposition time. These sample surfaces and the probe tip surface were all CH 3 -terminated by self-assembled monolayers with CH 3 (CH 2 ) 19 SH. The main origin of peak broadening in the histogram was the topographic effect. Namely, the change in the grain sizes and the change in multiplicity of contacts between the tip and convexities of the grains resulted in the distribution of the observed adhesive forces.

A bioelectronic device consisting of protein-adsorbed hetero-Langmuir–Blodgett (LB) films was investigated. Four kinds of functional molecules, cytochrome c , viologen, flavin, and ferrocene, were used as a secondary electron acceptor (A 2 ), a first electron acceptor (A 1 ), a sensitizer (S), and an electron donor (D), respectively. To fabricate the cytochrome c adsorbed hetero-LB film, poly- l -aspartic acid was used as the bridging molecule. The hetero-LB film was fabricated by subsequently depositing ferrocene, flavin, and viologen onto the pretreated ITO glass. Cytochrome c -adsorbed hetero-LB films were prepared by the adsorption of cytochrome c onto the poly- l -aspartic acid treated-LB films by intermolecular electrostatic attraction. Finally, the MIM (metal/insulator/metal) structured molecular device was constructed by depositing aluminum onto the surface of the cytochrome c -adsorbed hetero-LB films. Hetero-LB films were analyzed by Atomic Force Microscopy (AFM), and cytochrome c adsorption onto the films confirmed. The photoswitching function was achieved and the photoinduced unidirectional flow was in accordance with the rectifying characteristics of the molecular device. The direction of energy flow was in accordance with the energy level profile across molecular films. Based on the measurement of the transient photocurrent of the molecular device efficient directional flow of photocurrent through the redox potential difference was observed. The photodiode characteristics of the proposed bio-electronic device were verified and the proposed molecular array mimicking the photosynthetic reaction center could be usefully applied as a model system for the development of the bio-molecular photodiode.

An amphiphilic A2+-S-D triad molecule and its reference compounds, S−D, A2+-S, and S type molecules, were synthesized and studied using time-resolved transient absorption spectroscopy. The three moieties in the triad, i.e., an electron acceptor moiety (A2+, viologen), a sensitizer moiety (S, perylene), and an electron donor moiety (D, ferrocene), were linearly combined by sigma-bonded tunneling bridges. Intramolecular electron transfer reactions were initiated by photoexcitation of the S moiety to 1S*, and the long-lived final charge separated state, A•+-S-D•+, was formed. Although the yield of the initial charge separated state, A•+-S•+-D, was very high (0.93), the overall yield of the final charge separated state was ca. 0.2. The rate of the backward electron transfer from A•+ to S•+ was observed to be two times lower than that of the forward electron transfer from 1S* to A2+, suggesting that with suitable molecular engineering, the yield of long-lived charge separation in such triads could be improved.

In studies of molecular devices, it is very important to estimate the electric conductivity of single molecules. This subject has recently been studied in various ways. Weiss and co-workers (J. Am. Chem. Soc. 120 (1998) 2721) estimated transconductance of a single molecule embedded in a self-assembled monolayer (SAM) using scanning tunneling microscopy (STM). In the present work, we studied the transconductance of various single molecules embedded in SAM matrices such as alkanethiolate and biphenylmethanethiolate derivatives. We formed one-component SAMs of decanethiolate (DT) and biphenylmethanethiolate (BPMT) on Au(111), and then inserted 4-carboxyterphenyl-4′-methanethiol (CTPMT) in the one-component SAMs of DT and BPMT. In addition, BPMT used as one of the matrices above was inserted as isolated single molecules in the other one-component SAM of DT. These SAMs enabled us to measure the transconductance of the isolated single molecules using STM. All the STM images of these three types of the mixed SAMs showed that the isolated single molecules were scattered in the one-component SAMs. The STM topographic height differences between the isolated single molecules and the matrices depended on differences in their electronic tunneling conductivities.

Molecular pattern formation using chemically modified cytochrome c and green fluorescent protein (GFP) was presented for the application as a bioelectronic device. A protein conjugate was synthesized by the formation of disulfide bridges. In order to make molecular assembly onto the gold-coated substrate, cytochrome c was cross-linked with N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP). After the modification of cytochrome c, it was spontaneously deposited, so that it could be adsorbed onto the gold-coated substrate by self-assembly (SA) technique. Using the cellulose membrane, cytochrome c molecules were deposited onto the gold-coated substrate with the spatial resolution of ca. 0.2 μm. In order to verify the modified cytochrome c, UV absorption spectrum was measured. GFP was adsorbed onto the cytochrome c monolayer by electrostatic force. Fluorescence emission spectrum was investigated to verify the existence of the GFP molecule onto the cytochrome c monolayer. To verify the adsorption of cytochrome c molecules onto the gold-coated substrate and GFP molecules onto the cytochrome c monolayer, the atomic force microscopy and lateral force microscopy investigations were performed. Molecular pattern formation of cytochrome c and GFP molecules were successfully performed by chemical means and electrostatic force.

Photoinduced electron transfer in biomolecular photodiode consisting of protein-adsorbed hetero-Langmuir–Blodgett (LB) films was investigated. Four kinds of functional molecules, cytochrome c, viologen, flavin, and ferrocene, were used as a second electron acceptor, a first electron acceptor, an electron sensitizer, and an electron donor, respectively. The hetero-LB film was fabricated by subsequently depositing ferrocene, flavin, and viologen onto the pretreated ITO glass. Cytochrome c-adsorbed hetero-LB films were prepared by soaking the hetero-LB films into the phosphate buffer solution containing cytochrome c. To verify the optimal adsorption conditions of cytochrome c molecules onto the viologen LB layers, the UV-absorption spectrum and atomic force microscopy observations of LB films were performed. Finally, the metal/insulator/metal structured molecular device was constructed by depositing aluminum onto the surface of the cytochrome c-adsorbed hetero-LB films. For photoelectric response properties, the current–voltage characteristic and photoswitching effect of the proposed molecular photodiode were investigated. To verify the charge shift, transient photocurrent of the molecular photodiode was measured.

The light-harvesting function of the J-aggregate of the cyanine dye, N,N′-dioctadecyloxacyanine (Cy), in Langmuir–Blodgett (LB) monolayers containing the amphiphilic perylene derivative (Pe) as an energy acceptor was examined by varying the Cy:Pe molar ratio from 10:1 to 2000:1. A characteristic J-band considerably red-shifted from the corresponding monomer absorption band of Cy was intensely observed in the absorption spectra of the mixed Cy LB monolayers with Pe with the molar mixing ratios Cy:Pe=200:1, 500:1, 1000:1, and 2000:1. Although the contents of Pe in the mixed LB monolayers are such small fractions, the emission from excited Pe induced by energy transfer (ET) from photo-excited Cy was observed clearly. The highest sensitized emission intensity of Pe was observed on the mixed LB monolayer with the molar mixing ratio Cy:Pe=50:1 in which all excited energies of Cy were transferred to Pe. In this molar ratio, however, the ET from monomer or dimer Cy to Pe seemed to be dominant, and the antenna effect of Cy in this state is as low as ca. 50. In contrast, the antenna effect of J-aggregated Cy estimated for the mixed LB monolayers with low Pe ratios (Cy:Pe=500:1, 1000:1, and 2000:1) was such that ca. 250 molecules of Cy would harvest light for excitation of one Pe molecule. This can be attributed to the high rate of exciton migration in the J-aggregates, by which ET probability was increased.

Polyion complexed mixed LB films of amphiphiles with long FC chains (PFECA [CF 3 (CF 2 ) 8 (CH 2 ) 2 O(CH 2 ) 2 COOH] or perfluorodecanoic acid (PFDA) [CF 3 (CF 2 ) 8 COOH]) and those with long hydrocarbon (HC) chains, 3-, 6-, 9- or 12-(9-anthroyloxy) stearic acids (3-, 6-, 9- or 12-ANSTAs) deposited on Si substrates were characterized by atomic force microscopy/friction force microscopy (AFM/FFM). AFM/FFM images of 1:1 mixed LB films of PFDA and 6-, 9-, or 12-ANSTA showed phase separated structures, while those of PFDA and 3-ANSTA did not. AFM/FFM images of 1:1 mixed LB films of PFECA and 3-, 6-, or 9-ANSTA did not show phase separated structure. These results show that the amphiphile molecules with long HC chain which have a bulky probe unit at the position in the methylene chain close to head group (e.g. 3-ANSTA) can mix well with the amphiphile molecules with long fluorocarbon (FC) chains (PFDA or PFECA). Similar results were also observed in the mixed LB films of PFDA (or PFECA) and doxylstearic acids. According to the π – A isotherms for these amphiphiles with bulky probe unit, the molecular sectional area in the monolayers for these amphiphile molecule increased as the position of the probe unit approached to the head group. Since the cohesion energy for molecules decrease with the increase in the inter-molecular distance, the molecular mixing between the amphiphile with FC chain and that with HC chain which have a bulky probe unit at the position closer to head group can be attributed to the decrease of cohesion energy due to the increase in the inter-molecular distance. In the AFM/FFM image for 1:1 mixed LB films of PFDA and 12-ANSTA, the following interesting phenomenon were observed. After a scanning with large load over the part of an island composed of 12-ANSTA, which is higher than the sea area before these scanning, the height of the whole area of the island became lower than the sea area. From this result, it was confirmed that this mixed LB film has a ‘side by side’ structure.

The photoinduced electron transfer rate in hetero-Langmuir–Blodgett (LB) films, composed of electron sensitizing protein and electron accepting organics, was investigated. The hetero-LB film was fabricated by sequentially depositing green fluorescence protein (GFP), viologen, and TCNQ, which functioned as an electron sensitizer, a relay, and an acceptor, respectively. To verify the hetero-LB film formation, surface morphologies of the GFP film and viologen/TCNQ LB film were observed by atomic force microscopy (AFM). The fast charge separation of the molecular interface was investigated by analyzing the time-resolved fluorescence decays of GFP homo-, GFP/viologen hetero- and GFP/viologen/TCNQ hetero-LB film using a time-correlated single photon counting (TCSPC) method. In GFP/viologen hetero-films, the fluorescence decay of excited GFP was faster than that in the GFP homo-film. Based on the decay of fluorescence the charge separation rates of excited GFP were calculated. The fluorescence lifetime and charge separation rate of the GFP/viologen/TCNQ hetero-LB film increased slightly compared to that of the GFP/viologen hetero-LB film as a result of the addition of the TCNQ layer, electron acceptor. On the basis of its molecular interface charge separation behavior, the proposed molecular array can be used as a component of the molecular photodiode.

We report here a theoretical study with quantum chemical calculations based on experimental results to understand highly efficient reduction of CO2 to formic acid by using zinc under hydrothermal conditions. Results showed that zinc hydride (Zn–H) is a key intermediate species in the reduction of CO2 to formic acid, which demonstrates that the formation of formic acid is through an SN2-like mechanism.

Photoinduced electron transfer in the molecular electronic device consisting of protein-adsorbed hetero Langmuir-Blodgett (LB) film was investigated. Three kinds of functional molecules, cytochrome c, viologen, and green fluorescent protein (GFP) were used as an electron acceptor, a mediator, and a sensitizer, respectively. The hetero-LB film was fabricated by subsequently depositing cytochrome c and viologen onto the pretreated ITO or quartz glass. GFP adsorbed hetero-LB films were prepared by soaking the hetero-LB films into the buffer solution containing GFP. The MIM (metal/insulator/metal) structured molecular device was constructed by depositing aluminum onto the surface of the GFP-adsorbed hetero LB films. Due to the excitation by irradiation with a 460 nm monochromic light source, the photoinduced unidirectional flow of electrons in the MIM device could be achieved and was detected as photocurrents. The photoswitching function was achieved and the rectifying characteristic was observed in the molecular device. Based on the measurement of transient photocurrent of molecular device, the unidirectional flow of electrons was verified.

We investigated the adsorption processes of terphenyl (TP) derivatized thiols, [1,1‘:4‘,1‘ ‘-terphenyl]-4-thiol (TP0), which form self-assembled monolayers (SAMs) on Au(111). Scanning tunneling microscopy observation revealed that the adsorption process is dependent on the solvent in which the TP0 molecules can dissolve. When methylene chloride was used as a solvent, the TP0 molecules nucleate anisotropically along 〈112〉 directions with a 3-fold symmetry at the initial stage. At 1 min of immersion, a phase-separated image was taken. In the topographically lower region, molecular lattices (a = 0.65 ± 0.05 nm, b = 1.3 ± 0.05 nm) appeared, where the TP0 molecules were arranged parallel to the Au surface. After more than 5 min of immersion, the molecular lattices disappeared and larger striped patterns with a spacing of ca. 8 nm were observed. On the other hand, when ethanol was used as a solvent, the adsorption process of the TP0 molecules completely changed, and such larger striped patterns were not observe...

The optimal fabrication condition of cytochrome c Langmuir-Blodgett (LB) film was investigated. To verify the pH dependence of cytochrome c film formation, the various π-A isotherms were obtained at pH 6.0, 7.0, 8.0, 9.0, and 10.0, respectively. The cytochrome c LB films were then fabricated onto the quartz substrate, and the deposition of cytochrome c LB films was investigated by UV-visible spectroscopy.

Photoinduced electron transfer in molecular hetero- Langmuir-Blodgett (LB) films consisting of Green fluorescent protein (GFP)/viologe/TCNQ was investigated. In this work, charge transfer process in the molecular hetero-films has been investigated by femto-second transient absorption spectroscopy. Based on the transient absorption in the GFP/viologen/TCNQ series hetero-films, charge transfer from excited GFP to viologen (TCNQ) was observed with subpicosecond time resolution.

The charge transfer characteristics of molecular homo-films composed of green fluorescence protein (GFP) were investigated by time-resolved fluorescence measurement. In this work, time-resolved fluorescence decay of GFP homo film was measured to investigate the solid-state fluorescence lifetime and to observe the charge transfer by using time-correlated single photon counting method (TCSPC).

The charge transfer characteristics of molecular hetero-LB films composed of green fluorescence protein (GFP), viologen, and cytochrome-c were investigated by transient fluorescence measurement. In this work, transient fluorescence decay of GFP homo film and GFP/viologen/cytochrome-c hetero films were measured to investigate the charge separation rate and transport mechanism by using time-correlated single photon counting method (TCSPC).

Ferrocene(1-1′-ferrocene-N-dioctadecyl carboxamide), flavin(7,8-dimethly-10-dodecylisoalloxazine), viologen [N-allyl-N7′-[3-propylamidoN″,N″-di(n-octadecyl)]-4,4′bipyridiumdibromide), and cytochrome c were used as an electron donor (D), sensitize (S), the first electron acceptor (A1), and the second electron acceptor (A2), respectively in fabricating molecular device. Malonic acid or poly-L-aspartic acid were used as a bridging molecule for the adsorption of A2 molecules onto A1 layers. In order to confirm the electron transfer, Scanning tunneling microscopy(STM) investigation was performed.

To make a molecular assembly of cytochrome c onto the Au substrate, the cytochrome c was modified using the 2-succinimidyl-3-(2-pyridyldi-th-io)propionate(SPDP), so the functional group on the cytochrome c surface was modified. And the modified cytochrome c was adsorbed onto the Au substrate. The modified cytochrome c was examined by using UV-visible spectroscopy and FT-IR. Also, the morphology of cytochrome c adsorbed onto the Au substrate was analyzed by Atomic Force Microscopy(AFM).

In order to improve the power efficiency of standard multilayered organic electroluminescent (EL) devices, i.e. ITO/HTL/ETL/M, enhanced electron and enhanced hole injection at an ETL/M and an ITO/HTL interface, respectively, were attempted, as well as enhanced electron–hole recombination at an HTL/ETL interface, by designing proper charge injection at these interfaces. Here, ITO, HTL, ETL, and M are abbreviations for an indium-tin oxide anode, a hole-transport layer, an electron-transport layer, and a metal cathode. The HTL and ETL materials used were N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) and tris(8-hydroxyquinoline)–aluminum (Alq3) respectively, whereas a vapor-deposited aluminum (Al) electrode was used as the metal cathode M. In order to enhance the charge injection at both electrodes, lowering the barrier heights and thinning the barrier thickness were attempted by controlling the work functions of the ITO and the Al electrode and doping the HTL and the ETL, respectively. For lowering the work function of the Al cathode and doping the Alq3 ETL, the reaction of hot Al atoms with alkali metal carboxylates during Al vapor deposition was utilized. To increase the work function of the ITO and doping the TPD HTL, the use of thin TPD films doped with various oxidizing reagents was examined at the ITO/HTL interface. The enhancement of the charge recombination at HTL/ETL was attained by increasing the interfacial areas, i.e. introducing a mixed layer of TPD and Alq3, or inserting a thin film of rubrene with a higher recombination efficiency.

The effect of alkali metal (Li + , Na + , K + , Rb + , and Cs + ) acetates and fluorides at an aluminum/tris(8-hydroxyquinoline) aluminum (Alq 3 ) interface on performance of organic electroluminescent (EL) devices is described. We also studied the effect of acetates with different metals, such as Mg 2+ and Al 3+ , on the performance of the EL devices. EL characteristics of the devices with Al/alkali metal acetates were compared with those of devices with Al/alkali metal fluorides or an Al cathode itself. We found that the bilayer cathodes with alkali metal acetates exhibited better device performance than the bilayer cathodes with alkali metal fluorides. The improvement can be attributed to lowering of the work function of the Al cathode and doping of Alq 3 with alkali metals that were formed by the higher reactivity of alkali metal acetates than alkali metal fluorides with hot Al atoms impinging on these salts during the vapor deposition. The enhanced electron injection resulted in more balanced charge-carrier injection and thus higher EL efficiencies.

Patterned self-assembled monolayers (SAMs) were formed on gold films and observed by friction force microscopy (FFM) and adhesive force mapping with pulsed-force mode atomic force microscopy (PFM–AFM). The substrate gold films were prepared by sputtering gold on flat surfaces of osmium-coated cover glass with surface roughness, R a , of 0.3 nm. The patterned samples with the CH 3 and COOH terminated regions were prepared using the Langmuir–Blodgett (LB) method, partial removal of the LB film by ultrasonication, and SAM formation. The CH 3 and COOH terminated regions of the patterned SAMs in air and in water were observed by mapping friction and adhesive forces with FFM and PFM–AFM, respectively, using gold-coated AFM tips chemically modified with a thiol compound terminating in CH 3 or COOH. The adhesive forces measured in air increased in the order of CH 3 /CH 3 , CH 3 /COOH (or COOH/CH 3 ), and COOH/COOH, while those in water increased in reverse order. The enormous high adhesive force observed in water for CH 3 /CH 3 was attributed to hydrophobic interaction between the CH 3 tip and the CH 3 terminated sample surface. With CH 3 tip, the lower friction force was observed, however, in water on the CH 3 terminated region than on the COOH terminated region. This experimental finding raises a question as to what is the effective normal load in friction measurements in water.

We have studied electrical conduction of conjugated molecules with phenyl rings embedded into alkanethiol self-assembled monolayers (SAMs), to investigate the molecular structural effect on the electrical conduction. Scanning tunneling microscope (STM) images of this surface revealed that the conjugated molecules with phenyl rings adsorbed mainly on defects and domain boundaries of the pre-assembled alkanethiol (nonanethiol C9) SAM and formed conjugated domains. In the case of conjugated molecules with one or three methylene groups between the sulfur and phenyl rings, the measured height of the conjugated molecular domains depended on their lateral sizes, while a strong dependence was not observed in the case of conjugated molecules without a methylene group. By analyzing size dependence on the height of the conjugated molecular domain, we could evaluate the electronic conductivity of the molecular domains. As a result of the analysis, to increase the vertical conduction of the molecular domains, one meth...

We have investigated an insertion process of conjugated molecules, 4-biphenylmethanethiol (BP) and [1,1′:4′,1″-terphenyl]-4-methanethiol (TP) into preassembled n-alkanethiol self-assembled monolayers on Au(111) using scanning tunneling microscopy (STM). Ex situ STM observation revealed that the insertion process is dependent on an organic solvent in which the conjugated molecules dissolve. The insertion of conjugated molecules with three phenyl rings (TP) was faster than that with two phenyl rings (BP). By analyzing the STM images, the lower limits of resistances for single BP and TP molecules were obtained as 22±5 and 36±5 GΩ, respectively.

Pulsed-force-mode atomic force microscopy (PFM-AFM), with functionalized probe tips, was applied to discrimination of chemical functionalities of a binary system of mixed self-assembled monolayers (SAMs) consisting of CH 3 - and COOH-terminating alkane thiols. PFM-AFM enabled simultaneous imaging surface topography and distribution of adhesive forces between the tip and sample surfaces. Since the adhesive forces were directly related to interaction between the chemical functional groups on the tip and sample surfaces, we combined the adhesive force mapping by PFM-AFM with the chemically modified tips to accomplish imaging the sample surface with the chemical sensitivity. The adhesive force mapping by PFM-AFM with the CH 3 -modified tips in pure water clearly discriminated the hydrophobic CH 3 -terminating domains embedded in the COOH-terminating SAM matrix.

Mixed self-assembled monolayers (SAMs) of biphenylmethanethiol derivatives with CH 3 and COOH terminal groups and those of 1-decanethiol and a biphenylmethanethiol derivative with a CH 3 or a COOH terminal group were prepared on Au(111) surfaces. The resulting mixed SAMs were imaged by scanning tunneling microscopy (STM). These mixed SAMs can be used to study chemical force microscopy (CFM) by noncontact atomic force microscopy (nc-AFM). Namely, the CH 3 and COOH terminal groups of the SAMs can be recognized by different surface interactions with a surface functional group on a gold-coated AFM tip derivatized with the same thiol compound with a CH 3 or a COOH terminal group. The present result also suggests that these SAMs can be used to study CFM using nc-AFM with simultaneous tunneling current measurement. By this method, for example, a molecular location of a biphenylmethanethiol derivative with a COOH terminal group in an alkanethiol matrix observed by nc-AFM can be confirmed by the tunneling current measurement due to lower tunneling barrier height of the biphenylmethanethiol than that of the alkanethiol derivative.

The phase separation and orientation of molecules in mixed Langmuir–Blodgett (LB) films of hydrocarbon (HC) and fluorocarbon (FC) amphiphilic compounds were studied using scanning surface potential microscopy (SSPM) and friction force microscopy (FFM). The LB films were formed with a monolayer on an aqueous subphase containing calcium cations as the counter ions for the common carboxylate anions of the two types of amphiphilic compounds. It was found that the structure of the phase-separated LB films was different from that of previously studied HC–FC mixed LB films complexed with polymer cations. Namely, the structure of the present LB films was a “side-by-side” structure, while that of the previous ones was an “on-top” structure. In addition, it was found from SSPM that differences in surface potentials between the two separated phases were small for all the mixed LB films prepared with various HC/FC molar ratios. In other words, compositions were similar between these two phases: the rich component of one phase was at a slightly higher concentration than that of the other phase. The similarity in the compositions explained the low contrast in friction between these two phases as observed by FFM.

In this paper the reductive desorption for homogeneously mixed self-assembled monolayers (SAMs) on Au(111) electrodes formed from an asymmetrical disulfide, i.e. butyl hexadecyl disulfide [C 4 H 9 -S-S-C 16 H 33 ; H4H16] or decyl 2-(perfluorohexyl)ethyl disulfide [C 10 H 21 -S-S-(CH 2 ) 2 (CF 2 ) 5 CF 3 ; H10F8] was studied by cyclic voltammetry. Peak potentials of electrochemical desorption waves for the SAMs of these asymmetrical disulfides were different from those of SAMs containing only one of the constituent chains. The peak potential deviation from those of the single component SAMs suggests mixing of the two constituent chains in molecular dimensions. The ratio of the two constituent chains of the asymmetrical disulfide in each of the SAMs was considered to be exactly 1:1 when the homogeneously mixed SAMs were prepared under favorable conditions with respect to reaction concentration and temperature. We will discuss features of cyclic voltammograms in terms of the structure of the SAMs.

We have studied the phase-separation of self-assembled monolayers (SAMs) of dialkyl disulfides on Au surface. Initially, the heat-induced phase-separation of SAMs consisting of unsymmetric disulfide molecules (CF 3 (CF 2 ) 5 (CH 2 ) 2 SS(CH 2 ) 7 CH 3 ) of hydrocarbon and fluorocarbon chains was investigated. We proved that the dimer structure cleaved on the Au surface. Subsequently, we formed one-dimensional nanostructures utilizing an anisotropic phase-separation of SAMs consisting of a mixture of the above unsymmetric disulfide and a symmetric disulfide of hydrocarbon (CH 3 (CH 2 ) 7 SS(CH 2 ) 7 CH 3 ). The wire-like structure with a width of 5 nm and a length ≈100 nm was observed by scanning tunneling microscopy.

We have used high-resolution X-ray photoelectron spectroscopy (XPS) to investigate the molecular dependence on sulfur chemical states of organosulfur monolayers of alkanethiol, dialkyl disulfide, m...

We have succeeded in the formation of one-dimensional wire-like structure in the self-assembled monolayers (SAMs) made from the mixture of an unsymmetric disulfide consisting of hydrocarbon and fluorocarbon chains and a symmetric disulfide of hydrocarbon chains on Au(111). By focusing on co-adsorption process of the above two disulfide molecules onto the Au surface, it is found that an exchange reaction should take place and a part of the symmetric disulfide molecules was replaced by the unsymmetric disulfides during immersion in the solution. The molecules having fluorocarbons were also found to replace hydrocarbons on Au surface.

Electric conductivity of organic molecules was estimated with molecular resolution using self-assembled techniques and scanning tunneling microscopy (STM). Conjugated molecules of [1,1‘:4‘,1‘ ‘-terphenyl]-4-methanethiol (TP) were embedded in self-assembled monolayers of insulative n-alkanethiols, and when observed by STM, TP molecules appeared as protruding domains. The apparent height of the TP domains increases as the lateral size of the domains grows from 1 to 10 nm, reflecting the increase in the vertical conductance of the domains due to the lateral, intermolecular interaction. We assumed that the molecules are connected to each other with resistors for estimating the effect of intermolecular interaction on the conductance and calculated the height of conducting disks with various radii, which should roughly reproduce the size-dependent height of the TP domains observed by STM. The estimated resistance of the single TP molecule was less than 40 GΩ, and the effective lateral conductivity corresponding...

Fluorescence and absorption spectra were measured on Langmuir–Blodgett (LB) films containing acceptor–sensitizer (A–S) dyads. In the dyads, the length of hydrocarbon bridges interconnecting acceptor (viologen) and sensitizer (pyrene) were synthetically changed. In the LB films, the accumulation of viologen cation radical which can quench the excited pyrene moiety as an energy acceptor was observed during UV irradiation under N 2 . The rate constant of photoinduced intramolecular electron transfer in the LB films was estimated from the fluorescence intensities by taking the energy transfer quenching into consideration.