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We report on interferometric structures in fluorescence from a thin slab crystal of 5,5'-bis(4'-methoxybiphenyl-4-yl)-2,2'-bithiophene. These structures observed in the relative delay time with 10 ps between double pulses were discussed in terms of coherent dynamics.

Enhanced spontaneous emission of a quantum emitter by sub-wavelength quasi-periodic metamaterials is proposed and demonstrated. Strong enhancement of spontaneous emission of quantum dots was observed. This arises from the semi-localized mode inherent for quasi-periodic structures.

We have studied circular dichroism (CD) in the visible region of composite and double-layer films consisting of a transparent chiral molecule, glucose, and an absorptive achiral dye, rhodamine. Composite and double-layer films show an absorption-induced CD response caused by chirality of glucose at 540 nm, where the rhodamine exhibits absorption. More importantly, in double layers, the polarity of the ellipticity in CD signals is found to be reversed when the incident direction is reversed. We discuss the origin of the polarity reversal, which is very similar to the magneto-optical effect, at the chiral meta-interface without magnetic field.

Epitaxial growth of C60 was found in vapor‐deposited crystals on the KI (001) cleavage surface. C60 molecules deposited on the KI surface, which was preheated at 400 °C, then kept at 195 °C during deposition, crystallized in the face‐centered cubic form with two types of morphologies. Truncated pyramidal crystals epitaxially grew along the KI 〈110〉 directions, taking its C60 (001) face parallel to the KI (001) surface. This epitaxial nucleation occurred at a corner of the crossing steps along the KI 〈100〉 directions which were caused by thermal etching of the KI surface. Molecular mechanics and dynamics calculations revealed that a three‐dimensional (2×2) commensurate lattice matching between the C60 {100} planes and the KI {100} faces at the step corner attributed to the epitaxial nucleation of the pyramidal crystal, in spite of the lower stability of the monolayer interaction of the C60 (001) face with the KI (001) surface. On the other hand, platelike crystals grew, with the C60 (111) face parallel to ...

Structure-dependent electrochromism was investigated with vapor-deposited thin films of zinc and vanadyl naphthalocyanines (ZnNc and VONc). The amorphous ZnNc film deposited on an indium tin oxide (ITO) coated glass electrode exhibited an irreversible electrochromic oxidation in 0.1 M KCl. This reaction gave rise to swelling of the film surface due to expansion of grains caused by incorporation of charge-compensating anions between the aggregated molecules. Epitaxially oriented films were prepared by deposition onto the (001) cleavage surface of NaCl and then transferred onto the ITO electrode. The epitaxial ZnNc film, in which the planar molecules are piled up in columns taking on the face-to-face, eclipsed stacking, exhibited both electrochromic reduction and oxidation. This electrochromic activity was attributed to a reversible incorporation of counterions through hollow channels between the molecular columns, which was accompanied with rearrangement in the molecular stacking. By contrast, no electroch...

Dye-sensitization processes for the (001) surface of n-type titanium oxide (n-TiO2) single crystal coated with vacuum-deposited titanylphthalocyanine (TiOPc) were investigated by means of photoelectrochemical measurements and X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS). The electrode of n-TiO2 coated with TiOPc exhibited two photooxidation current bands in an aqueous electrolyte including hydroquinone (H2Q), due to direct excitation of n-TiO2 below 420 nm and electron transfer from TiOPc to n-TiO2 under the Q-band absorption of TiOPc at 600−800 nm, respectively. The former photocurrent process due to n-TiO2 excitation was remarkably decreased by presence of surface states, which originated from defects of oxygen induced by Ar ion bombardment of the n-TiO2 surface. The photooxidation process sensitized by the latter was evaluated from the determined energy levels of electronic bands for n-TiO2 and TiOPc. The LUMO level of TiOPc was located 0.3 eV above that of n-TiO2, which enabled electron...

N,N'-ジメチルペリレン-3,4:9,10-テトラカルボン酸ジイミド(Me-PTC)をインジウム-スズ酸化物(ITO)ガラス,ポリ(テトラフルオロエチレン)(PTFE)コーティングガラスおよびKBr(001)へき開面上に真空蒸着した。ITOガラス上の膜は無配向多結晶膜から形成されていた。一方,PTFEコーティングガラスおよびKBr上に蒸着した膜は配向膜から形成され,100℃ あるいは150℃ に保った基板上で次の関係で配向成長した :[010](001)Me-PTC//[001](100)PTFE-150℃, [010](001)Me-PTC//[110](001)KBr-100℃, (102)Me-PTC//(001)KBr-150℃ および [010]Me-PTC//[110]PTFE-150℃=±15°. ITO上の膜はそのまま,また,PTFEコーティングガラスおよびKBr上の膜は基板からはく離したのちITOガラス上にすくいとって薄膜電極とし,湿式電池(ITO/Me-PTC/0.5mMI2, 0.1M KI/Pt)を作製した。Me-PTCの導電型は溶液中のI2のドーピングによりn型からp型に変化した。配向膜を用いた電池の性能パラメーターは,無配向膜を用いた電池の値と比較して約3倍向上した。Me-PTC薄膜を用いた太陽電池の性能向上には膜中の分子配列制御とともに粒子径の制御が重要であることがわかった。

Organic field-effect transistors with narrow channels were fabricated using a focused ion beam (FIB) technique. The top-contact source-drain channel of 0.5–3.0 µm length was formed by FIB etching of a gold electrode (200 µm width) deposited onto a vapor-grown pentacene layer on top of a SiO2/Si gate. The hole mobility was increased by reducing the channel length to be smaller than the grain diameter of the pentacene film. The FIB treatment decreased the threshold voltage but increased the off current due to the doping of the irradiated Ga+ ions.

Spectrally narrowed light emission based on stimulated resonance Raman scattering has been observed for epitaxially grown needle crystals of a biphenyl-capped thiophene oligomer. Under optical pumping with a wavelength-tuned pulse laser, the crystals emitted a couple of sharp lines (full width at half maximum ∼0.3 nm) along the direction of the needle axis. In particular, the intense line with a Raman shift of 1435 cm−1 appeared at low excitation energy of a few μJ/pulse. This Raman line was assigned as the symmetric in-plane stretching mode of the molecule. The observed Raman-associated lasing suggests the presence of polaritonic interaction between the uniaxially ordered molecular excitons and emitted photons.

We demonstrate a chiral meta-molecule in the ultraviolet (UV) and visible (VIS) regions using a complex of Au nanoparticles (NPs) and rod-shaped tobacco mosaic virus (TMV). Au NPs five nm in diameter are uniformly formed on peptide-modified TMV. The peptide-modified TMV with uniform-sized Au NPs has improved dispersion in solution. A negative circular dichroism (CD) peak is produced around 540 nm, at plasmonic resonance wavelength of Au NPs. Additionally, modification of a CD peak in the UV region is observed. Attaching NPs to a virus causes the enhancement and modification of CD peaks in both the UV and VIS regions. Our results open a new avenue for the preparation of three dimensional chiral metamaterials at optical frequencies.

Photovoltaic properties of two-layer organic p/n junction solar cells were studied for vacuum-deposited films of p-type phthalocyanine derivatives having different π-electron conjugating macrocycles and n-type N,N′-substituted 3, 4:9, 10-perylenebis(dicarboximide) having different peripheral groups. The power conversion efficiency was optimized by controlling the film thickness, morphology and contact with top-electrodes. The film morphology of the perylene derivatives changed depending on their peripheral alkyl groups, and higher photocurrents were obtained for the cell with a homogeneous layer of perylene derivatives. The molecular modification in p-type phthalocyanine derivatives changed the cell photovaltage. A substitution with electron-withdrawing groups, which lowered the highest occupied molecular orbital (HOMO) energy of the p-type molecules, increased the photovoltage. On the other hand, an extention of the macrocyclic ring from phthalocyanine to naphthalocyanine lowered the photovoltai...

Strong exciton-photon coupling has been observed in a highly oriented organic single crystal microcavity. This microcavity consists of a thiophene/phenylene co-oligomer (TPCO) single crystal laminated on a high-reflection distributed Bragg reflector. In the TPCO crystal, molecular transition dipole was strongly polarized along a certain horizontal directions with respect to the main crystal plane. This dipole polarization causes significantly large anisotropies in the exciton transition and optical constants. Especially the anisotropic exciton transition was found to provide the strong enhancement in the coupling with the cavity mode, which was demonstrated by a Rabi splitting energy as large as ∼100 meV even in the “half-vertical cavity surface emitting lasing” microcavity structure.

A simple “cast-capping” method is adopted to prepare single-crystal perovskites of methyl ammonium lead bromide (CH3NH3PbBr3). By capping a CH3NH3PbBr3 solution casted on one substrate with another substrate such as glass, mica, and distributed Bragg reflector (DBR), the slow evaporation of solvent enables large-size cubic crystals to grow between the two substrates. Under optical pumping, edge-emitting lasing is observed based on Fabry–Perot resonation between parallel side facets of a strip-shaped crystal typically with a lateral cavity length of a few tens of μm. On the other hand, vertical-cavity surface-emitting lasing (VCSEL) is obtained from a planar crystal grown between two DBRs with a cavity thickness of a few μm. Simultaneous detection of those edge- and surface-emissions reveals that the threshold excitation fluence of VCSEL is higher than that of the edge-emitting lasing due to thickness gradient in the planar crystal.

Organic electroluminescence (EL) devices were fabricated with bilayered thiophene/phenylene co-oligomer (TPCO) derivatives: p-type 5,5′-bis(4-biphenylyl)-2,2′-bithiophene (BP2T) and n-type 5,5′-bis(4′-cyanobiphenyl-4-yl)-2,2′-bithiophene (BP2T-CN). Two types of EL device, Al:Li/BP2T-CN/BP2T/ITO (device A) and Au/BP2T/BP2T-CN/ITO (device B), were investigated using vapor-deposited films of BP2T and BP2T-CN by changing the order of deposition onto the indium–tin-oxide (ITO)/glass substrate. The EL performance was significantly improved for device B in which the two molecules had a lying orientation suitable for efficient carrier injection and transport as well as surface emission. In device A, on the other hand, the standing BP2T orientation resulted in much lower current density and EL intensity.

We have investigated the stimulated resonance Raman scattering from single crystals of a thiophene/phenylene co-oligomer. The very narrow lines [full width at half maximum (FWHM)=11–20 cm−1] are observed in the same spectral regions where the spectrally narrowed emissions (FWHM≈300 cm−1) occur upon excitation with intense laser pulse. We related these modes to the stimulated resonance Raman scattering. Two lines of Raman shifts of 1466 and 1605 cm−1 are of molecular origin. Another line with an energy shift of ∼1260 cm−1 from excitation energy, on the other hand, implies the presence of the coherence of crystal origin. The associated split lines accompanying this mode are thought to constitute the longitudinal modes in the Fabry–Perot cavity naturally formed in the crystals.

Gold nanoparticles are generally considered to be biologically inactive. However, in this study we show that the addition of 1.4 nm diameter gold nanoparticle induces the remodeling of the ring-shaped protein TRAP into a hollow, capsid-like configuration. This structural remodeling is dependent upon the presence of cysteine residues on the TRAP surface as well as the specific type of gold nanoparticle. The results reveal an apparent novel catalytic role of gold nanoparticles.

Vertical-cavity organic lasers are fabricated with melt-grown crystals of a cyano-substituted thiophene-phenylene co-oligomer. Due to lying molecular orientation, surface-emitting lasing is achieved even in the half-cavity crystal grown on a distributed Bragg reflector (DBR) under optical pumping at room temperature. Anticrossing splits in angle-resolved photoluminescence spectra suggest the formation of exciton-polaritons between the cavity photons and the confined Frenkel excitons. By constructing the full-cavity structure sandwiched between the top and bottom DBRs, the lasing threshold is reduced to one order, which is as low as that of the half cavity. Around the threshold, the time profile of the full-cavity emission is collapsed to a pulsed shape accompanied by a finite turn-on delay. We discuss these observed characteristics in terms of a polariton contribution to the conventional photon lasing.

Photoelectrochemical properties of Zn-naphthalocyanine (ZnNc) and its modified compound, Zn-2,3-tetraquinoxalinotetraazaporphyrin (ZnTQP) were investigated in thin films. The ZnNc electrode vacuum-deposited on an indium tin oxide (ITO) substrate exhibited almost an ohmic I-V curve in the dark and small cathodic photocurrents under illumination, which was typical for the p-type semiconduction of the ZnNc layer, in a photoelectrochemical cell. The drop-casted film electrode of ZnTQP, on the other hand, showed rectified I-V characteristics in the dark and high anodic photocurrents under illumination, which was attributed to the n-type semiconducting character of the ZnTQP layer. These different photoelectrochemical behaviors were characterized by photocurrent action spectra and ultraviolet photoelectron spectroscopy. The substitution with quinoxalino groups into the Nc macrocyclic system gave rise to lowering of the HOMO energy level for the TQP molecule. This electronic energy shift generated donor electron states in the band gap after contact with the substrate or electrolyte and enabled the photooxidation at the valence band edges corresponding to the Soret-and Q-band excitations. 55 refs., 10 figs.

Structure dependence of electrical properties was investigated for amorphous and epitaxial thin films of chloroaluminumphthalocyanine vacuum deposited on both glass and KCl. The extrinsic conductivity in the dark was improved by elevating substrate temperatures, depending on the morphological change from granular, discontinuous films deposited at a substrate temperature of 25 °C to uniform, continuous ones at 250 °C. The photocurrents under monochromatic light illumination increased in proportion to the amount of adsorbed O2 in the amorphous films on glass. A regular doping form of O2 in the epitaxial film on KCl could enhance photocarrier generation. The granular, discontinuous morphology in the films caused a frequent charge‐carrier recombination at the grain boundaries and defect sites. In the intrinsic region the amorphous films exhibited a higher dark conductivity due to the π‐electron interaction between the randomly arranged molecules and gave a moderate activation energy for conduction. The epitaxial film with a regular orientation exhibited a significantly higher activation energy for intrinsic dark conduction because of a weak molecular interaction between the standing molecular columns.

Photovoltaic solar cells were constructed by successive vacuum deposition of chloroaluminum phthalocyanine (AlPcCl) and Au on a single‐crystal n‐Si wafer. By controlling the thickness and morphology of the AlPcCl deposits in the Au/AlPcCl/n‐Si cells, an improved photovoltaic efficiency was obtained as compared to the Au/n‐Si Schottky‐type cell. The cell with a homogeneous, ultrathin (10 nm thickness) AlPcCl film, which was prepared by deposition on an n‐Si substrate kept at −20 °C, exhibited a high photovoltage (Voc=0.45 V) and strongly sensitized photocurrents in the Q‐band absorption region (600–800 nm) of AlPcCl chromophore. This improved photoresponse was attributed to a space‐charge layer generated inside the AlPcCl film, where the intervening AlPcCl layer prevented the n‐Si surface from forming surface states because of noncontact with the Au top electrode. When discontinuous island crystallites of AlPcCl were formed on the n‐Si surface kept at 200 °C, the Au/AlPcCl/n‐Si cell also exhibited an impro...

Electrochromism of cobalt and zinc naphthalocyanines (CoNc, ZnNc) was investigated in thin films vacuum-deposited on indium tin oxide substrates. The CoNc film exhibited color changes from original green to purple both upon reduction and oxidation, and the ZnNc film exhibited a color change from green to brown only upon oxidation. The electrochromic reduction was a reversible process depending on an electroactivity of the central Co metal, and the electrochromism was attributed to a transition from a reduced state related to the Co(I) center to a π * -state of the Nc-ligand. On the other hand, the electrochromic oxidation irreversibly occurred at the Nc-ring ligand

Response-variable organic photosensors were fabricated using electrochemically synthesized polyphenylene films on an indium-tin-oxide (ITO) substrate as the charge-trapping layer and a vapor-deposited perylene film as the charge-generating layer. The ITO/polyphenylene/perylene/Al cells exhibited differential and/or linear photocurrent responses depending on the voltage bias. At low voltages, negative and positive photocurrent peaks appeared when light incidence was on and off, respectively. This differential response was attributed to trapping of holes photoexcited in the perylene layer by electrolyte ions doped in the polyphenylene film. Application of higher voltages resulted in linear photocurrent responses due to charge separation of photogenerated excitons.

Organic electroluminescence from epitaxially oriented needle crystals of a thiophene/p-phenylene co-oligomer was studied. The crystals grown by vapor deposition on a KCl (100) surface were confined in a p-sexiphenyl (p-6P) layer. After deposition of an Al cathode the film was wet transferred onto an indium tin oxide (ITO) coated glass. At a low bias voltage, this cell exhibited homogeneous blue light emission from the p-sexiphenyl layer due to carrier recombination in the ITO/p-6P/Al region. With an increase of the voltage, the electroluminescence band shifted to the longer wavelengths corresponding to the green spectrum of the co-oligomer. This emission was concentrated on the needle crystals and suggested that the injected holes were confined inside this low-dimensional structure and recombined with electrons injected from the p-6P layer.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in APPLIED PHYSICS LETTERS. 80(4):544-546 (2002) and may be found at https://doi.org/10.1063/1.1435797 ., Article, APPLIED PHYSICS LETTERS. 80(4):544-546 (2002)

Optically pumped lasing of epitaxially oriented molecular crystals is presented. Needle-like crystals of a thiophene/phenylene co-oligomer is grown along the [110] direction of a KCl substrate. The fluorescence light is one-dimensionally confined and amplified by the self-waveguiding effect in the elongated needles. The Fabry-Perot resonation by the terminated ends results in laser oscillations corresponding to the needle length.

This Letter reports a convenient method of fabricating a polymer-based microlaser array. Laterally aligned plastic micropillars equipped with an optical resonator were fabricated by using a lithographic technique with an organic-dye-doped photopolymer, which operated as a laser element with a vertical cavity. Under optical pumping, very fine emission spectra showing a Fabry–Perot-type lasing oscillation were observed. Using this technique, integrated laser cavities with desired operation wavebands can be produced easily.

We have used scanning probe microscopy and transmission electron microscopy (TEM) to investigate the molecular orientation of cobalt naphthalocyanine (CoNc) vacuum deposited onto a NaCl substrate. Atomic force microscopy observations taken on CoNc deposited at room temperature reveal mostly amorphous grains with only few regions showing columnar structure. For CoNc films deposited at 250 °C, scanning tunneling microscopy and TEM showed domains of columnar structure arranged in various orientation. The periodicity of the columnar structure was determined to be 1.5 and 0.34 nm from x‐ray and electron diffraction and indicates that the molecules are standing with their planes perpendicular to the underlying NaCl substrate surface.

Epitaxial thin films of naphthalocyanines (Nc’s) were prepared on the (001) surface of alkali halide (AX) by a vacuum‐deposition technique. Two types of molecular stacking and orientation were found depending on the molecular structure. Metal‐free Nc(H2Nc) and divalent zinc Nc(ZnNc) took the face‐to‐face, eclipsed stacking, P orientation, in which their molecular planes came into a parallel contact to the substrate surface. Trivalent chloroaluminum Nc(AlNcCl) and fluorogallium Nc(GaNcF), and tetravalent vanadyl Nc(VONc) took the eclipsed, slipped stacking, I orientation, holding their molecular planes slightly inclined to the substrate surface. In the latter orientation an unexpected face‐to‐face stacking caused a stacking defect structure. The tetragonal lattice of the Nc crystals demonstrated five types of commensurate matchings to the ionic lattice of AX, depending on the lattice parameters of the Nc and AX crystals. On NaCl unidirectional AX(001)(4×4)R+45°‐Nc was a predominant orientation, and on KCl ...

The denaturation of pseudomonas-cytochrome c 551 at the air-water interface was studied using scanning tunneling microscopy (STM). The STM images indicate that the native secondary and tertiary structures of this protein has been virtually lost at such interface. The polypeptide chains of the unfolded protein are nearly fully extended, and highly aggregated in a localized region, forming a crystalline or a twisted rope-like structure. Our observation demonstrates the capability of STM in studying the unfolding of proteins, and also suggests the possibility of using STM to directly sequence the amino acid residues of a protein.

In view of practical handling of single-walled carbon nanotubes (SWNTs), here we present cutting procedures and spontaneous ordering of SWNTs deposited on highly oriented pyrolytic graphite (HOPG). Purified SWNTs were cut by ultrasonication in H2SO4/HNO3 mixture and further in de-ionized water. Thus, prepared short SWNTs were resuspended in methanol and dropped on a freshly cleaved HOPG surface. Scanning tunneling microscopy under a vacuum revealed that the short tubes of 20–100 nm in length were aligned along the basal axis of the HOPG lattice. Tunneling spectroscopy obtained from the oriented tubes indicated a semiconducting behavior, which was characterized in relation to their helical structure. The observed orientation of SWNTs was attributed to their one-dimensional electronic nature along the tube axis with the HOPG lattice.

1.3 µm solid-state plastic lasers were fabricated using fluorinated-polyimide as the host matrix of the active waveguide doped with near-infrared organic dye, IR26. DFB lasing oscillation as well as FP mode one is realized using photo-nanoimprint lithography.

We have conducted experimental and numerical studies on resonant photon transport through ${\text{Ag-SiO}}_{2}\text{-Ag}$ multilayers with varying ${\text{SiO}}_{2}$ gap-layer thickness due to its application toward the development of a metamaterial superlens. Photon-transport spectra that have been measured using a double-prism system with a $p$-polarized He-Ne laser show a resonant photon tunneling (RPT) peak in the total reflection region and an additional peak in the propagating region. Calculated dispersion curves and electric field profiles reveal that the RPT peak is brought about by antisymmetrically coupled surface-plasmon polaritons (SPPs), very similar to the long-range SPPs in a single-metal film. The additional peak, however, is caused by TM guided modes with symmetrically coupled SPPs. We demonstrate that the ${\text{TM}}_{0}$ guided modes move continuously from the total reflecting region to the propagating region as the gap-layer thickness decreases. This will enable us to realize a device which converts evanescent waves into propagating waves of light, opening the possibility of an alternative type of hyperlens.

5,10,15,20-tetra (4-pyridyl) porphyrin thin films were vacuum-evaporated onto a KCl (001) surface. The orientation of the thin film was investigated by electron microscopy, and X-ray and electron diffractions. The film was composed of crystallites which have orthorhombic lattice with dimensions of a = 2.12 nm, b = 0.68 nm, and c = 2.18 nm. The crystal grew epitaxially on a KCl (001) surface with its (001) plane parallel to the KCl (001) plane. A column structure observed by high-resolution electron microscopy showed molecules packed in thin crystals. The molecular planes of the porphyrin were oriented almost perpendicularly to the KCl (001) plane. The crystals grew along three different directions against the KCl direction, the angles between the column axis and the KCl [100] direction were 0°, 27°, and 45°.

Thin films of polymeric phthalocyanines 4a–c were prepared by in-situ syntheses from oxy-and phenoxy-bridged diphthalonitriles 3a–c with copper layers deposited on Ti plates and KCI crystals. The structure of the polymers was characterized by VIS, IR and photoelectron spectra, and scanning electron microscopy. The most uniform structure was obtained for polymer 4c, in which phthalocyanine rings were linked two-dimensionally by flexible bridges of phenoxy groups. Polymers 4a and 4b are structurally not uniform, and formation of phthalocyanine rings was incomplete especially in polymer 4a. Photoelectrochemical properties of polymeric phthalocyanine electrodes were investigated in Ti/4a–c/Fe(CN)63−/4−/Pt cells. The electrode of 4a shows n-type semiconducting behavior under illumination. The current-voltage curve for the electrode of 4b did not show remarkable rectification or photocurrents. On the other hand, cathodic photocurrents were obtained for the electrode of 4c, indicating a p-type semiconducting behavior under illumination. The photoelectrochemical properties were related to the structural uniformity of the polymers.

Epitaxial growth of 5,10,15,20-tetraphenylporphyrin metal complexes (MTPP; M = Zn, Mg, Co, VO) and their photoelectrochemical properties were investigated. MTPP crystals grew epitaxially on a KC1 (001) surface by a physical vapor deposition method. All the crystals belong to the tetragonal system. The (100) plane of MTPP crystals is parallel to the KC1 (001) plane, and the [100] axis is parallel to the KC1 (120) axis. Photoelectrochemical properties were measured in the indium-tin oxide(ITO)/MTPP/Ia-,I-/Pt system.

An orientation-controlled thin film of AlPcCl was prepared by vacuum deposition on a (001) surface of a KCl substrate. In the epitaxially grown film on KCl AlPcCl molecules stack cofacially, staggering around the Al-Cl-Al bonds and holding the molecular planes parallel to the KCl surface. At a low substrate temperature the deposit was a uniform and closely oriented thin film. As the substrate temperature increased, the film became rugged and cracked due to growth of a large size of crystallites

Photocurrent responses of sol-gel films of silica/titania doped with oxacarbocyanine dye were investigated with a sandwich-type photocell constructed with polymer electrolyte membrane and indium-tin-oxide glass electrodes. At an equilibrium and positive bias voltages, a typical photocell exhibited negative and positive current peaks when the visible light illumination was on and off, respectively. The wavelength dependence of the photocurrent responses well matched to the absorption band of the doped dye. This differential photocurrent response was attributed to trapping of carriers photoexcited in the dye molecules at the defect states in the matrix film. At negative bias voltages, on the other hand, the cell exhibited constant, negative photoelectrochemical currents under illumination. These differential and linear photocurrent responses were affected by the SiO2/TiO2 matrix structures depending on the Si : Ti ratio.

Loss is a critical parameter in metamaterials because it determines the resolution of a super-lens made of metamaterials. The super-lensing effect observed in alternative multi-layer metamaterials consisting of metal and dielectric layers is derived from the resonant photon tunneling (RPT) via surface plasmon polaritons (SPPs). Here we demonstrates that the losses in the metamaterials can be estimated by simultaneous measurements of attenuated total reflection (ATR) and RPT. RPT through silver (Ag)/SiO 2 metamaterials is studied experimentally. A shift of the RPT peak away from the ATR dip is observed; the shift variation in an Ag/SiO 2 system is smaller than that in an aluminum/MgF 2 system. This indicates that the shift is caused by the imaginary part of permittivity, i.e., intrinsic losses, of metamaterials.

Fluorescence micropatterns of rhodamine dye were fabricated in silica/titania sol−gel films by photogeneration of gold nanoparticles. Local reduction of Au(III) ions included in the film enabled us...

Highly polarized and self-waveguided blue light emission was observed in oriented organic crystals of p-sexiphenyl (6P). The 6P molecules were epitaxially grown in needlelike crystals with a submillimeter length by mask-shadowing vapor deposition on the KCl (001) surface. In the crystals, the molecular axes are oriented parallel to the [110] direction of the KCl substrate and perpendicular to the needle axis of the crystal. Under ultraviolet excitation, the blue light emission was confined within the crystal and self-waveguided along the needle axis with the transverse-electric mode, then radiated from the tips of the needles. This self-waveguided emission in the crystal was based on the uniaxially oriented transition dipoles which lay on the KCl surface and were aligned perpendicular to the needle axis in the crystal.

Dark- and photo-electrochemical properties of an orientation-controlled thin film of 5,10,15,20-tetraphenylporphyrin (TPP) were investigated in the indium–tin oxide(ITO)/TPP/I3−,I−/Pt system. The oriented film exhibited a photocurrent quantum yield three times as great as the polycrystalline film. This enhancement in quantum yield may be attributable to the standing molecular orientation of TPP on the ITO substrate.

The crystal growth and the orientation of thin films of 5,10,15,20-tetraphenylporphyrin (H 2 TPP) vacuum-evaporated onto substrates of a KCl (001) surface and a semitransparent A1 electrode film have been investigated by electron microscopy and electron diffraction. The films deposited on a KCI (001) surface show epitaxial growth in which the crystals take a four-directional orientation, and the molecular plane of HzTPP stands perpendicular to the substrate surface. The H 2 TPP crystals with a morphology of rectangular islands grow on the KCI surface kept at 200 ° C, while a continuous thin film totally covers the KCI surface kept at 20 ° C with an identical epitaxial orientation. When H 2 TPP is deposited on a KCI (001) surface coated partially with a small number of Al particles, the crystals take the same orientation. This epitaxial orientation decreases with increasing the coverage of the A1 particles on the KCI surface, and the H 2 TPP film deposited on a semitransparent A1 film shows a random orientation of needle-like crystals. The growth of the thin film with oriented crystals depends on the electrostatic interaction of the H 2 TPP molecules with ionic charges on the KCI surface.

Zinc oxide (ZnO) nanorod arrays for inorganic/organic hybrid solar cells were electrochemically deposited on indium tin oxide (ITO) substrates with a rotating disk electrode setup. The addition of a ZnO seed layer on the ITO prior to electrochemical deposition improved the morphology of the nanorods, resulting in nanorods with smaller and homogenous diameters as well as a higher degree of vertical orientation on to the substrate. The ZnO films deposited on the seeded ITO substrates had higher optical transmittance and lower concentration of defects. Chronoamperometric transient curves show that nucleation and coalescence occurred later for bare ITO substrates, indicating lower densities of initial nuclei, resulting in the growth of nanorods with larger diameters. The solar cell characteristics of the devices fabricated from the seeded ITO substrates were better. The seed layer also acts as a hole-blocking layer, preventing the direct contact between the hole-transporting polymer material and the ITO.

Epitaxial structuring of blue light-emitting molecules, p-phenylene oligomers (p-nP, n=3,4,5,6), was investigated in thin crystals vapor deposited on the (001) surface of a KCl single crystal. Their molecular orientation and morphology changed depending on the molecular length and substrate temperatures during deposition. As the length of p-nP was longer and the substrate temperature was lower, the orientation of the molecular axis changed from standing to lying on the KCl surface due to an increase of molecule–substrate interactions. p-terphenyl (3P) hardly adsorbed on the KCl (001) surface, but a portion of the standing molecules stuck along the step edge of KCl and formed a walllike structure. Long needlelike crystals of p-hexaphenyl (6P) epitaxially grew in two orthogonal KCl [110] directions taking lying orientation even at a higher substrate temperature. In these epitaxial needles, the transition dipoles parallel to the molecular axis gave rise to blue fluorescence sharply polarized along the KCl [1...

Single-crystal cavities of p-sexiphenyl (p-6P) are prepared by precipitation from a solution phase. A typical p-6P crystal has a thin quasi-lozenge shape with a size of several hundreds of μm and a thickness of a few μm. Under optical pumping with a pulsed laser, blue fluorescence is gain-narrowed to amplified spontaneous emission (ASE) due to light confinement inside the slab-type crystal cavity. With increasing excitation fluence, the time profiles of photoluminescence change from an exponential decay of spontaneous regime to a pulsed one typical for stimulated emission. Furthermore, multimode laser oscillations are obtained when a pair of parallel facets of the crystal cavity function as feedback mirrors.

Organic electroluminescent (EL) behaviors were investigated with epitaxially oriented and disordered polycrystalline films of emissive p -sexiphenyl (6P) molecules. In comparison to the disordered polycrystalline 6P film, the epitaxial 6P film in which the molecular axis possessed lying orientation remarkably exhibited a high EL intensity at lower driving voltages, whereas the epitaxial 6P film with standing orientation emitted a weak intensity even at higher voltages.