Search

The Langmuir-Blodgett (LB) films based on BEDOTTF-C10TCNQ (bisethylenedioxytetrathiafulvalene-decyltetracyanoquinodimethane) complex have an essentially metallic nature. Physical properties of the LB films are briefly summarised in addition to those of the monolayers at the air-water interface.

Conductivity switching was observed in the LB films of supermolecules having phenylazonaphthalene, alkyl chains, and pyridinium(TCNQ)2 as switching, transmission, and working units. respectively. The utilization of phenylazonaphthalene shifts the wavelength of the control light for the conductivity switching toward a longer wavelength region compared with the case of azobenzene as a switching unit.

Luminescence spectra and their variation with temperature have been investigated for solid films of poly(methylphenylsilane) and its branched analogs. Introduction of branching points to the polymers enhances the broad luminescence band in the visible region while suppressing the sharp UV luminescence band due to the resonant recombination of the exciton. The intensity of the visible luminescence is observed to keep on increasing with decreasing temperature in contrast with the nearly temperature‐independent intensity of the resonant luminescence. The behavior is interpreted in terms of phonon‐assisted tunneling between luminescence centers and nonradiative ones.

An amphiphilic C 60 molecule with a substituent having a hydrophilic carboxylic group at the end was found to form a monolayer at the air-water interface and the structure of the Langmuir-Blodgett (LB) film (Z-type) was elucidated. The shortest distance between the C 60 was estimated to be 0.95 nm using a limiting area per molecule of 0.78 nm 2 at the air-water interface, assuming the close packing of the C 60 moiety in two dimensions. Adjacent C 60 moieties have an electronic interaction which was shown in the red-shift of the characteristic bands in the UV/vis absorption spectrum of the LB film compared with that of a solution spectrum. Several lines of evidence suggested that the molecule has an oblique orientation in the LB film and exists in a pairwise manner due to the dimer formation of the carboxylic groups within a monolayer, not between the adjacent monolayers. The AFM observations revealed that the surface of a single-layer LB film, which consists of domains of ca. 0.1 μm in diameter, is rather smooth and that the undulation is ±1 nm for most of the surface except for defects such as vacancy and bilayer regions. The area fractions of the monolayer, the vacancy, and the bilayer regions were estimated to be 88 ± 7, 7 ± 5, 5 ± 3%, respectively. The layer structure was also confirmed using X-ray diffraction analyses which indicate the repeat distance of ca. 2.6 nm along the surface normal of the multilayer LB film.

The third-order nonlinear-susceptibility ${\mathrm{\ensuremath{\chi}}}^{(3)}$(-2\ensuremath{\omega};\ensuremath{\omega},\ensuremath{\omega},0) spectrum has been investigated for thin films of linear-Si-chain compounds, poly(dihexylsilane), by measurements of electric-field-induced second-harmonic generation (EFISHG). In the ${\mathrm{\ensuremath{\chi}}}^{(3)}$ spectrum for EFISHG, two-photon resonance structures to the first and second levels of one-dimensional excitons were observed. The observed ${\mathrm{\ensuremath{\chi}}}^{(3)}$ spectrum can be accounted for by considering multiple optical processes in the one-dimensional excitonic series characteristic of the Si-chain system.

Recognition properties of the monolayers of amphiphilic cyclodextrins (CDs) at the air-water interface were investigated by using the Langmuir-Blodgett technique. The CD having amino groups interacted with water-soluble azobenzene, exhibiting an increase in area per molecule with repeated compression and expansion of the monolayer. By introducing one or three isomers of water-soluble azobenzene into the subphase after the formation of the CD monolayers, the amounts of the incorporated azobenzene were obtained by the subsequent transfer of the monolayers. The results indicate that the CD cavity is not the only binding site for azobenzene and that the amounts of the incorporated azobenzene are governed not just by the relationship between the cavity size and the shape of the azobenzene molecule.

Langmuir-Blodgett (LB) films of a long-chain pyridinium-(TCNQ) 2 salt (where TCNQ denotes tetracyanoquino-dimethane), APT(8–12), exhibit a photoinduced conductivity change associated with the trans-cis isomerization of the azobenzene group in the molecule. Recently the development of a one-dimensional (1D) columnar structure in the LB films of a similar long-chain pyridinium-(TCNQ) 2 salt, C 22 PT, was indicated through quantitative analyses of the temperature-dependent spin susceptibility and the angular-dependent electron spin resonance line shape. The application of these methods to the APT(8–12) films has provided another example of a quasi-1D spin system realized in the LB film system.

A novel principle of molecular architecture for monolayers containing azobenzene moieties is presented which allows the chromophores to be organized with a high density and with sufficient mobility for photochemical change. This monolayer represents a new medium for a data storage system; each single azobenzene group is in principle capable of storing the information of 1 bit. The physical properties of this monolayer have been investigated at the air-water interface. Data storage in the macrometer range is demonstrated with a single monolayer transferred on glass.

A metallic Langmuir-Blodgett (LB) film which does not require any secondary treatments obtained by using a charge-transfer complex of bis(ethylenedioxy)tetrathiafulvalene (BO) and decyltetracyanoquinodimethane (C 10 TCNQ) was examined. A strong band in the IR region was observed due to the conduction electron. The average charges of the C 10 TCNQ and BO in the LB film were -1 and +0.4, respectively, determined from the shift of the specific bands. The room-temperature conductivity of the film was 10 S/cm. The temperature dependence of conductivity of the film was well fitted by the formula σ=AT -α exp(-E g /2k B T), which is related to an activation-type conduction within the domain boundaries of a granular-structured film. The temperature dependence of the thermoelectric power clearly shows the metallic nature of the film

X-ray-induced ablation of Si-containing polymers is investigated for application to the surface-imaging process in X-ray lithography. Polysilanes, polystyrene, and polymethacrylates are chosen for this study. Ultraviolet (UV) and Fourier-transfer infrared (FTIR) spectra are observed and all of the polymers are found to have positive tone characteristics against soft X-ray exposure. Based on measurements of remaining film thickness after exposure, polymethacrylates are found to have a high self development sensitivity. However, copolymerization gives no improvement in sensitivity. Oxygen reactive ion etching (O2-RIE) rates of these polymers are also measured and found to depend on the Si content of the polymer. A bilayer resist using the polymer as a surface imaging resist is patterned by X-ray exposure and subsequent dry etching. Applicability of Si-containing X-ray resist to self-development is presented.

It was found that rubbing as-cast films of poly(di-n-hexylsilane) (PDHS) with a wiping paper results in films withthe Si-backbone chains are oriented along the rubbing direction. The differences in the structure of the PDHS film before and after the rubbing treatment was investigated. In the oriented film of PDHS with a trans-planar conformation, the n-hexyl side chains stand almost perpendicular to the substrate surface. This rubbing method can also be applied to thin films of other polysilanes and polygermanes

Langmuir-Blodgett (LB) films of the fullerene (C60) were formed with a variety of matrices. The pure C60 formed a collapsed film at the air-water interface and the transferred film had an inhomogeneous surface. By mixing with icosanoic acid, the monolayers were transferred onto substrates with good quality and the resultant LB films had a smooth surface. The 1:1 mixture with dioctadecyldimethylammonium-ClO4 was deposited as Z-type film onto substrates. The film is, however, composed of doughnut-shaped aggregates for a single-layered sample. Multilayered samples had undulations of ca. 100 nm. The absorption spectra of both of the mixed films were in good agreement with those of evaporated films. The LB films with a long-alkyl γ-cyclodextrin were also examined.

The temperature dependent spin susceptibility of the LB films of a TCNQ salt with an alkylpyridinium was found to be explained by the random-exchange Heisenberg antiferromagnetic chain model, indicating the development of 1D spin chains in the system. The ESR spectra of the films at the X and K bands show clear out-of-plane anisotropy. The analysis of these line shapes using the spectrum simulation method reveals that the linewidth anisotropy is dominated by the exchange-narrowed secular dipolar width peculiar to quasi-1D spin systems. This result provides further evidence for the development of the 1D columnar structure of TCNQ molecules, and suggests that the chain axis lies in the film plane. In addition, the analysis yields the orientation of TCNQ molecules, which is consistent with the formation of the columnar structure.

The ESR spectra of conductive Langmuir-Blodgett (LB) films of N-docosylpyridinium-(TCNQ) 2 are observed at the X and K bands. The spectrum simulation method is adopted to analyze these spectra, which show clear out-of-plane anisotropy, in order to obtain information concerning the magnetic and structural properties of the system. The analysis reveals that the linewidth anisotropy is dominated by the exchange-narrowed secular dipolar width peculiar to quasi one-dimensional spin systems. This result is consistent with the temperature dependent spin susceptibility data of the system, which has been found to be explained by the random-exchange Heisenberg antiferromagnetic chain model. These facts indicate the development of one-dimensional spin chains in the LB films. In addition, the orientation of TCNQ molecule is estimated from the spectrum analysis.

We have investigated the ↑ χ (3) (−3 ω ; ω , ω , ω )↑ spectra of polysilane films by means of third-harmonic generation. The fundamental photon energy is scanned from 0.56 to 2.2 eV. The ↑ χ (3) ↑ spectra show three structures, which are assigned to three- and two-photon excitonic resonances. These features indicate that the predominant excited states involved in the non-linear optical response of polysilanes are composed of three levels: the lowest one-photon allowed exciton, a one-photon forbidden exciton, and another higher-lying one-photon allowed state.

Optical spectra (ordinary absorption, photoluminescence, electroabsorption, and two-photon absorption spectra) have been investigated for thin films of polysilanes with a variety of backbone conformations such as trans planar, alternating trans-gauche, helical, and disordered forms. The results observed have revealed new features of one-dimensional exciton states characteristic of each conformation of the polymer backbone

Photoactive and conductive Langmuir-Blodgett films are described utilizing cyclodextrin derivatives, TCNQ radical salts, metal-dmit complexes and fullerenes to form 0,1,2, and 3-dimensional molecular systems.

One-photon and two-photon absorption and photoluminescence spectra have been investigated for thin films of poly(dihexylgermane) (PDHG) for a comparison with those of its Si-backbone analog, poly(dihexylsilane) (PDHS), with similar trans-planar backbones. The electronic structures of trans-planar PDHG and PDHS have been shown to resemble each other, including the energy positions of the $^{1}$${\mathit{B}}_{1\mathit{u}}$ and $^{1}$${\mathit{A}}_{\mathit{g}}$ exciton transitions, which is not in accord with a prediction by band-structure calculations. A significant difference of the exciton absorption peak in Si and Ge backbones is seen only for the gauchelike disordered conformation.

Three types of photochemical swithcing phenomena in LB films were observed using amphiphilic molecules consisting of azobenzene, alkyl chain, and pyridinium(TCNQ) 2 . For two types the conductivity of the LB film changed reversibly with photoisomerization of azobenzene. The third type showed phenomena which are compared to the learning process

We have synthesized helical polysilanes on which the pendant groups are partly substituted by dye molecules. The introduction of a few percent of dye molecules into the substituents enhances the luminescent efficiency of the visible region, by behaving as luminescence centers. We have demonstrated that the excitation energy is transferred efficiently by free excitons on the Si backbones to reach the luminescence centers, where energy transfer occurs from the exciton to the dye molecule, and as a result sensitized luminescence occurs. The exciton transfer is found to occur over 50–100 monomer units on the polysilane backbone. This approach will open the way to fabricating a wavelength-tunable luminous device by utilizing the exciton transport on Si chains.

Hybrid Langmuir–Blodgett (LB) films were fabricated by transferring pure monolayers of an azobenzene derivative having a TCNQ (7,7,8,8-tetracyanoquinodimethane) moiety (APT) and then 1:1 mixed monolayers of cyanine/APT on solid substrates. The hybrid LB films have binary output modes. The alternate irradiation of UV and visible light yielded reversible cis - trans isomerization of APT, which was accompanied by the electrical conductivity switching associated with APT molecules and the change in the optical properties of the films due to the development of the J -band of the cyanine dye (CY). The order of the sequential deposition of the APT pure monolayers and the 1:1 mixed monolayers of CY/APT plays an important role in realizing the hybrid LB films with binary output modes.

A single monolayer of amphiphilic spiropyran was transferred on solid substrates using the Langmuir–Blodgett technique. Two types of circular domains were observed in the LB films: the larger domains with a diameter of 3–4 μm and the smaller ones with a diameter of 1 μm. The morphology changed depending on the concentration of the spreading solution, the subphase temperature and the spreading solvent. On irradiation with UV light, the spiropyran photoisomerized to merocyanine, followed by the J-aggregate formation of the merocyanine. Flower-like three-dimensional structures formed on the top of the larger domains accompanied by the J-aggregate formation. These structures developed until most of the molecules in the affected domains were transported to the structures.

Highly conductive hybrid Langmuir−Blodgett (LB) films of MoS2 and amphiphilic compounds such as alkylammonium halides and alkylamines were fabricated. The interlayer spacing of the LB films depended on the organic species. The lateral conductivity of 10-layer LB films was in the range of 101 to 102 S cm-1 and decreased with an increase in interlayer spacing. The conductivity of 102 S cm-1 is the highest value for LB films reported so far. The conductivity of the LB films increased with the layer number and became constant when the layer number was sufficiently large. The conductivity was stable at room temperature even for single-layer LB films and decreased by less than an order of magnitude during four months.

Vacuum wafer-level packaged two-dimensional optical scanners actuated by vertical electrostatic combs have been developed. A 1 mm-diameter gimbal mirror with high frequency deflection and a surrounding 2.5 × 3 mm movable frame with low frequency deflection are fabricated in a SOI wafer. Wafer-level packaging with anodically bonded borosilicate glass substrates on both sides together with non-evaporable getters fixed on the lower glass substrate allows hermetic sealing in high vacuum. The gimbal mirror and the movable frame are both deflected mechanically ± 12 deg. at a resonant frequency of 25.1 kHz with a driving voltage of 18 V, and at a resonant frequency of 78.6 Hz with a driving voltage of 10 V, respectively. The internal pressure of the device is 20 Pa.

Two-photon-absorption spectra have been investigated for solid films of polysilanes with various Si-backbone conformations such as trans planar, alternating trans-gauche, helical, and disordered forms. In all the polysilanes with ordered backbones, the distinct two-photon-absorption peaks were observed at energies 0.8--1.0 eV above the one-photon-absorption peaks. These one-photon and two-photon transitions are interpreted in terms of the ground and excited states of one-dimensional excitons on the Si backbones.

Switching and memory phenomena were observed of Cu–TCNQ films, triggered by a stimulus with an STM tip. When a 1.5-volt stimulus was given to the film surface for 1 min, a convex image (120 nm in diameter) appeared in the STM image. This image, stable for at least 20 hours at room temperature, was deleted by a heat treatment.

The structure and physical properties of highly conductive Langmuir-Blodgett films of tridecylmethylammonium-Au(dmit) 2 (3C10-Au) are described. The layered structure of the film was revealed by X-ray diffraction method. The d-spacing was 1.9 and 2.7 nm for the film before and after oxidation, respectively. The conductivity of the LB films of 3C10-Au after oxidation was 30 – 50 S/cm at room temperature, showing a metallic temperature dependence down to around 150 K.

Electro-absorption (EA) spectra and their temperature-dependence have been investigated for thin films of poly(dihexylsilane) (PDHS) and poly(dibutylsilane) (PDBS), which show the backbone conformations of the all-trans planar and the 7/3 helical type, respectively. In both of the polysilanes, EA spectra have revealed the field-activated (one-photon forbidden) transitions which are positioned at energies 0.8 eV higher than the lowest singlet exciton states. EA spectra in PDHS have further revealed an exciton state at ca. 5.6 eV characteristic of the all-trans planar conformation, possibly including two-electron excited configurations.

Electro-absorption (EA) spectra have been investigated for thin films of poly(di-n-hexylsilane) which shows the thermochromic phase transition associated with the conformational change in Si-backbones. The EA spectra for the trans-planer polysilanes (low-temperature phase) have revealed the one-photon forbidden A g state at 4.2 eV in addition to the Stark-shifted lowest B u exciton at 3.4 eV. The drastic change in EA spectra is observed on the phase transition, which is interpreted as the influence of the backbone conformation on the extended exciton states.

In the mixed Langmuir–Blodgett (LB) films of a selenium-containing cyanine dye and an azobenzene derivative (molecular ratio=3:1), the azobenzene photoisomerized reversibly by the alternate illumination with UV and visible light. After three cycles of photoisomerization, the J-band of the cyanine dye started to develop and reached a saturated state after 12 h, when the samples were stored in the dark. A drastic change in the morphology of the mixed LB films occurred with the development of the J-band. When the J-band was fully developed, a number of cones protruded from the film surface which should be due to the formation of J-aggregate of the cyanine dye. The size of the largest cones was ca. 250 nm in height and ca. 2000 nm in diameter at the base. The light-induced J-aggregation in the present case is similar in nature to the previously reported case (M. Matsumoto et al., J. Phys. Chem. B 101 (1997) 702). However, the number of cones is smaller, the size larger, and the time necessary for the full development of the cones longer in the present case compared with the previous case.

In the mixed Langmuir−Blodgett films of a cyanine dye and an azobenzene derivative, J-aggregate formation of the cyanine proceeded with the reversible photoisomerization of the azobenzene. AFM obse...

The structures and the photoisomerization of polyion complex Langmuir-Blodgett (LB) films of an amphiphile bearing two azobenzene units were studied. The anionic amphiphile was spread on the aqueous subphases with and without polycations. The area per molecule depended on the polycation species and was larger than that of pure amphiphile for three polycations out of four. It was suggested that the area per molecule is determined by the compromise between the various intermolecular interactions involved in the formation of the monolayer. The LB transfer was possible for all the polyion complex systems and reversible photoisomerization was observed for all the LB films by alternate UV and visible light irradiation. As the area per molecule where the LB transfer was conducted increased, the fraction of the cis isomer at the photostationary state with UV light irradiation increased, suggesting the role of free volume in the trans-to-cis photoisomerization.

Tachibana et al. have developed the series of the charge-transfer complexes (APT materials) of azobenzene-containing alkyl chain pyridiniums and TCNQ, which exhibits marked conductivity change upon the photoisomerization of the azobenzene group, providing a new class of ultrathin organized molecular films. The in situ measurements performed on the APT(8–12) and APT(12–12) films have detected the clear ESR spectral change upon the photoisomerization, indicating the modification of the TCNQ columnar structures. The observed changes in the magnetic parameters are discussed in relation to the possible mechanism of the conductivity change.

Optical properties of silicon‐ and germanium‐based network copolymers, [Si(C6H13)]1−x‐ [Ge(C6H13) ]x, have been investigated for various Si/Ge compositions (x). The backbone Si/Ge atoms are coordinated by the three other Si/Ge backbone atoms in the polymers. These Si/Ge copolymers show the absorption spectra which are typical of amorphous semiconductors. Their color continuously traverses the visible range with x, which is due to the change of the band gap (Tauc gap) energy as well as to the presence of localized subgap states. The Si/Ge copolymer shows a broad band of luminescence in the visible region. The luminescence band maximum was observed to shift by ∼0.5 eV with change of the Si/Ge ratio.

The molecular orientation in Langmuir-Blodgett films of a 3:2 charge-transfer complex of tetramethyltetrathiafulvalene and tetradecyltetracyanoquinodimethane [(TMTTF)3(C14TCNQ)2] is discussed from the observed anisotropic ESR spectra at the K and X bands. Anisotropy of g values shows the existence of in-plane preferential orientation of the complex with the pπ orbital axis and long axis of the TMTTF molecules parallel and perpendicular to the dipping direction of the substrate, respectively. The effect of aging on ESR spectra of the system is also reported. The decrease in the difference in linewidth at the K and X bands observed for the external magnetic field normal to the film plane indicates the reduction in the degree of misorientation of the molecules by aging.

Photochemical switching phenomena are very sensitive to the length of alkyl chain of the transmission unit. Conversion to the cis isomer in the photoisomerization of azobenzene in the switching unit increased with an increase in the length of the transmission unit. Change in conductivity of the LB films, however, showed a complicated behavior with variation in the length of the transmission unit.

Azobenzene derivatives were recognized by amphiphilic cyclodextrins (CDs) in LB films. The amount of ortho isomer of methyl red incorporated in the LB film was very small for any of the CDs used, whereas considerable amounts of the para and meta isomers were kept in the films, most of which were included in the cavity. The size of the cavity of the CDs was reflected in the out-of-plane anisotropy and the peak shift in the polarized absorption spectra of the LB films of the CDs containing the azobenzene derivatives.

The Langmuir-Blodgett (LB) films of the fullerene (C[sub 60]) were formed with and without matrix molecules. The pure C[sub 60] formed a collapsed film at the air-water interface. The surface of the transferred film was inhomogeneous, as observed by atomic force microscopy (AFM). The monolayers of a 1:1 mixture with icosanoic acid were transferred onto substrates with good quality. The LB films had a smooth surface composed of a mixture of C[sub 60] and icosanoic acid dispersed with flat microcrystals of C[sub 60] observed by AFM. The 1:1 mixture with dioctadecyldimethylammonium perchlorate was deposited as Z-type film onto the substrates. The absorption spectra of both of the mixed films were in good agreement with those of evaporated films. These films will be precursors of the molecular systems utilizing the peculiar properties of fullerenes and fullerene anions. 13 refs., 4 figs.

For Langmuir-Blodgett (LB) films of C 16 H 33 -Q3CNQ, both macroscopic and nanoscopic current-voltage measurements reveal asymmetries in the DC electrical conductivity.

We report the optical properties of the thin films of cyclic and linear and polysilanes containing phenyl groups by heat treatments. We observe the shift to a longer wavelength of the absorption edge in UV-visible absorption spectra of the thin films, when the cyclic and linear polysilane films were heated at 500 °C after UV irradiation. This behavior is interpreted in terms of the formation of network siloxene films by the dissociation of phenyl groups from silicon structures and the accompanying incorporation of oxygen into the silicon structures. It is shown that UV irradiation before heating and substituent groups attached to cyclic and linear polysilanes affect the spectral changes by heat treatment.

Electrical and optical properties of Langmuir-Blodgett (LB) films were controlled using photoisomerization of supermolecules having switching, transmission, and working units. Conductivity switching was observed in single-component LB films of the supermolecules on alternate photoirradiation with UV and VIS light. In the mixed LB films with cyanine dye, J-aggregate formation was induced by photoisomerization of the supermolecule. It was suggested that the signal produced by the molecular deformation could be conveyed to the surrounding molecules, causing the cyanine molecules to form J-aggregate.