辻岡 強

Fine metal patterning with a small work function is indispensable to the high integration of organic electronics devices including organic light-emitting devices and organic memories. Selective metal deposition on photochromic surfaces is a promising method to prepare such metal patterns. We found that the surface physical properties of polymer films for metal deposition changed depending on their drying temperature and the photoisomerization state of the doped-photochromic diarylethene (DAE). The Mg deposition property on the DAE-doped polystyrene (PS) film was dramatically switched by light irradiation. Light-controlled selective Mg deposition for poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) was also achieved. Fine metal patterning with a width of 15 mm on DAE5%-doped polymer film with maskless vacuum evaporation was successfully demonstrated. Light-controlled selective metal deposition will contribute to the large scale integration of polymer electronics.

フォトクロミック・ジアリールエテンの新機能として,その異性化状態に依存したメタル蒸着選択機能と,有機エレクトロニクス分野への応用として,レーザー走査による異性化を利用した微細な電極パターン・メタルパターンのマスクレス形成を実証した.

Fine metal patterning was performed by selective Mg deposition on photopolymers. Mg patterns with a minimum width of 5 mu m were obtained by using maskless vacuum evaporation. The selective deposition originates in the difference of glass transition temperature, microscopically, of surface molecular motion between polymerized and nonpolymerized photopolymer surfaces. The difference between photoreactive small molecules and polymers was also discussed. The selective metal deposition method would be applied to a wide range of organic surfaces; this method showed great potential for the preparation of fine wiring for various organic electronic devices.

Selective metal Mg deposition was achieved for a structure with the 8-nm-thick intermediate layer of Alq3 on a photochromic diarylethene (DAE) layer. Selective deposition for a structure with the Alq3 intermediate layer was attributed to uncolored DAE molecules exposed on the surface due to the migration and the aggregation of Alq3 molecules on the uncolored DAE layer. Laser spot irradiation enables both isomerization and an annealing effect on samples with an Alq3 intermediate layer, thereby achieving selective Mg deposition. Selective deposition for a structure with an intermediate layer could be important for the preparation of patterned cathodes in the field of organic electronics.

This paper presents a review of our reported theoretical studies that we performed to identify experimental spectroscopic data (NMR, Raman, IR, and ESR), find applications that utilize transport property (hole and electron), design the environmental field effect around a molecule (polymer and crystal), and to elucidate nonlinear response properties. Moreover, new results on thermal stability and reaction in crystalline state are also included. We put emphasis on how theoretical studies on photochromic systems contributed to an understanding of the experimental data on a molecular level. (C) 2008 Elsevier B.V. All rights reserved.

We developed an electrode/wiring patterning method that does not employ evaporation shadow masks; this method is based on selective metal deposition of photochromic diarylethene (DAE). In the selective Mg deposition based on the photoisomerization of DAE, Mg vapor atoms are deposited only on colored DAE film obtained upon UV irradiation, but not on uncolored film. We demonstrated fine metal Mg patterning with a minimum width of 3 mu m and the preparation of a patterned cathode. The selective metal deposition method has significant potential for preparing fine electrodes/wiring for various organic electronic devices.

Hole-injection recording of organic semiconductor memory with a photochromic diarylethene memory layer was investigated by using a device structure with an electron block layer (EBL). Devices with thicker EBL showed faster current decrease, that is, high isomerization efficiency. The high efficiency of isomerization originating from the long lifetime of a cationic state was achieved by hole injection with low voltage. Hole-isomerization recording has the potential for very low power consumption organic memory.

Device structure dependence of the recording efficiency of organic bistable molecular memory using photochromic diarylethene (DAE) was studied. Devices with a thicker memory layer showed faster current decrease, that is, shorter writing time. This was attributed to effective isomerization at the many carrier traps in the memory layer. The device with an electron transport layer that consisted of a Silole derivative showed fast writing speed. The device with an Alq3 electron transport layer showed electroluminescence. This indicates the holes were transported through the DAE layer without contribution for isomerization. DAE molecules with good receptivity for both carriers should be developed for obtaining high speed memory. (c) 2005 American Institute of Physics.

The new aspect of photochromic memory with electronic function is introduced. Electrical carrier dissociation from photoexcited photochromic diarylethene molecules was observed. It would be applied to nondestructive readout of photon-mode memory. © 2005 Optical Society of America.

This paper presents a principle for a novel electrical molecular memory device using a photochromic diarylethene, which has the potential ability of inexpensive, disposable, extremely high bit-density, and very low power consumption. This device is based on an isomerization reaction of the diarylethene molecule via its excited state by injection of electric carriers, not by photon absorption. The reversible writing by carrier injection is demonstrated. The advantages and applications of the molecular memory are discussed.

The photocurrent characteristics of a diarylethene (DAE) film were investigated. The photocurrents were attributed to the dissociation of electric carriers from the excited molecules in the DAE film. We demonstrated the on-off property of the photocurrent according to the isomerization state. Results reveal that the short-wavelength light corresponding to the high-energy absorption band of the colored DAE film generated higher carrier/photon efficiency than did the long-wavelength light corresponding to the low-energy absorption band. (C) 2004 American Institute of Physics.

Electrical carrier-injection and transport characteristics of photochromic diarylethene thin films were investigated. Injected and transported carriers (injected current) to the diarylethene film were increased with the existence ratio of the closed-ring form, which was one isomerization state of the diarylethene molecule. A dramatic increase was observed at a 12-percent existence ratio of the closed-ring molecules. A lowering effect of the potential barrier, which is caused by a Poole-Frenkel-like effect with a short distance interaction potential for hole transportation by increasing the existence ratio of the closed-ring molecules is proposed as the mechanism behind this phenomenon. (C) 2003 American Institute of Physics.

A principle of organic memory device using a bistable photochromic molecule is presented that allows extremely high bit densities and very low power consumption. This device is based on an isomerization reaction of photochromic diarylethene molecule via its excited state by an electric carrier injection, not by photon absorption. Experimental data show that the reversible writing and nondestructive reading of information by the carrier injection is feasible. The advantages and properties of such an organic semiconductor memory using a bistable molecule are discussed. (C) 2003 American Institute of Physics.

The signal-to-noise ratio (SNR) and possible data-transfer rate of nondestructive photocurrent-detection readout in near-field photochromic memory were calculated theoretically. The photocurrent-detection readout provided a much higher SNR and a higher data-transfer rate than those of conventional transmittance-detection readout. The SNR of the photocurrent-detection readout was dependent on the electric field applied to the medium and the potential barrier height between the photochromic recording layer and the photoabsorbing layer. A sufficient SNR was obtained under the conditions of an electric field of 2.5 V/m and a potential barrier height <0.4 eV in land area. Photocurrent-detection readout is a promising method to achieve high SNR, high data-transfer rate, and ultrahigh recording density with nondestructive-readout capability. (C) 2002 Optical Society of America.

Voltage increases of organic mono layered devices under constant-current operation were investigated in order to clarify the origin of the degradation of organic light emitting devices (OLED). The rate of voltage increase for tris(8-hydroxyquinoline)aluminum (Alq(3)), which is the most popular material for the electron transport layer. was the tar.-est. whereas those for hole transporting materials (4.4',4"-tris(3-methylphenyl-phenylamino)-triphennyl-amine (MTDATA), 4,4'bis[N-(1-naphthyl)-N-phenylamino] biphenyl (NPB). N.N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4.4'-diamine (TPD)) were small. The origin of the recoverable voltage change of the Alq(3) layer was attributed to the electronic characteristic change of the Alq(3) layer, that is, the ionic impurities or the orientation of Alq(3) molecules.

Photochromic diarylethenes with electric carrier (hole) controlling ability for nondestructive readout were investigated. The ionization potential of the photostationary colored diarylethene films was around 5.7-5.8 eV, irrespective of differences in their molecular structures. Good hole injection/transport characteristics were observed for the colored films of diarylethenes with triphenylamine groups.

Conventional solution electrochemiluminescent (SECL) cells have a low luminance. In this paper, we propose an ion conductive assistant dopant (ICAD) system to improve the luminance of SECL cells. The SECL cell is assumed to have a simple structure of [transparent electrode/emitting solution/transparent electrode]. The solution of the cell consists of a mixed solvent (o-dichlorobenzene/acetonitrile = 2/1 (vol/vol)), rubrene used as the emitting material, and 1,2-diphenoxyethane used as the ICAD. When voltage is applied to this SECL cell, the cell achieves a luminance of 183 cd/m(2) and a luminous efficiency of 1.5 cd/A at 8 V with yellow emission. On the other hand, an SECL cell without an ICAD results in a low luminance of 0.3 cd/m(2) at 8 V, corresponding to a conventional SECL cell. The ICAD improves the luminance 600 times by enhancing the ion conduction of rubrene cations in the solution. Furthermore, when the mixed solvent (o-dichlorobenzene/toluene = 2/1 (vol/vol)), which has a high voltage resistance, is used in the SECL cell, the cell obtains a maximum luminance of 986 cd/m(2) at 80 V. The features of the SECL cell are a simple cell structure and a transparent emitting area. SECL cells are expected to be used in unique displays with a see-through function for automobiles, windows, information equipment, and so on.

A solution electrochemiluminescent (SECL) cell is an emitting device that employs one type of emitting solution. In this study, tris(2-phenylpyridine) iridium [Ir(ppy)(3)], a well-known emitting material in organic electroluminescent cells, was used in a SECL cell. The cell had a simple structure of transparent electrode/emitting solution/transparent electrode. The solution consisted of benzonitrile used as the solvent, and Ir(ppy), used as the emitting material. When voltage was applied to this SECL cell, green emission was produced with a peak wavelength of 530 am, which originated from Ir(ppy)3. This SECL cell showed a maximum luminance of 3 cd/m(2) and a luminous efficiency of 0.014cd/A. The features of the SECL cell are a simple cell structure and a transparent emitting area. SECL cells are expected to be used in unique displays with a see-through function for automobiles, windows, information displays, and so forth.

We propose a carrier trapping (CT) dopant method to improve the luminous efficiency of organic light-emitting diodes (OLEDs). The CT dopant did not emit light itself, but adjusted the charge balance in the OLEDs. The cell structure of the OLED in the experiment was as follows: Indium tin oxide (ITO)/hole transport layer (50 nm, 2TNATA)/emitting layer (20 nm, NPB + 5% rubrene)/electron transport layer (30 nm, Alq + 4% CT dopant)/MgIn. (2TNATA: 4,4',4"-Tris(N-(2-naphthyl)N-phenyl-amino)-triphenylamine, NPB; N,N'-Di(naphthalen-1-yl)-N,N'-diphenyl-benzidine). 4,4'-Bis(carbazol-9-yl)-biphenyl (CBP) was used as a CT dopant. This cell had a yellow emission originating from the rubrene with the luminous efficiency of 8.7 cd/A at a Current density of 10 mA/cm(2). On the other hand, when the CT dopant was not used, the luminous efficiency was 7.5 cd/A. The luminous efficiency was improved by the CT dopant method.

Two-step two-photon absorption on a photochromic layer with coherent photons was simulated by the Monte-Carlo method. The simulation indicated that highly localized photons, such as near-field light with a very small aperture, induce an effective two-photon reaction beyond the 2nd-order dependence.

We proposed and demonstrated a nondestructive readout method using photocurrent detection for photon-mode photochromic memory, The principle of this readout method, which utilized the ionization potential change according to photoisomerzation reaction, was confirmed by using a medium with a photochromic diarylethene layer and phthalocyanine photoabsorbing layer, and by using a near-infrared readout light. We demonstrated perfect nondestructive readout operations over 10(6) times. (C) 2001 American Institute of Physics.

The driving duty ratio dependence of the luminance lifetime of various tris(8-hydroxy-quinolinate)aluminium-based organic light-emitting devices (OLEDs) was investigated. High-duty-ratio driven devices with low mean operational voltage had a long lifetime in comparison to DC-driven devices. This indicates voltage-mode degradation was suppressed by high-duty-ratio driving. The long lifetime effected by high-duty-ratio driving became increasingly small in the range of large operational mean current because of accelerated current-mode degradation. The development of high-efficiency OLEDs, therefore, is of prime importance not only to achieve low power consumption but also to obtain long-lifetime OLEDs by high-duty-ratio driving.

Various structures of organic light-emitting devices (OLEDs) including electrophosphorescence were measured for their capacitances. The zero bias capacitances were in inverse proportion to the total thickness of organic layers. Positive bias voltag only affected the capacitances. It is suggested that Joule heating of organic layers caused the dependences of the capacitances on voltage. The maximal capacitances were scattered from 7 to 34 nF/cm2, and in inverse proportion not only to the total thickness, but also to the single layer thickness of Alq. The similarity of these proportionality factors suggested that the dielectric constants of the hole transports and Alq were not so different, and the contribution of Alq layer was dominant for the maximal capacitance. The capacitances of OLEDs were roughly estimated from total thickness without respect to the difference of dielectric constants of whole layers.

The operating current mode dependence of luminescence properties of rubrene-doped yellow organic light-emitting diodes (OLEDs) was investigated. The devices were driven by three types of constant current mode: a simple direct current (DC) mode, a simple alternating current (AC) mode and a pulsed current (PC) mode. The device driven by the AC mode showed low energy efficiency because of the existence of time intervals with no emission in spite of energy consumption. The device driven by the PC mode showed the highest efficiency and better stability compared with the devices driven by the other modes.

The great interest in photochromic materials for high-density optical memory has been increased for the past decade. A super-low power readout method has been proposed to solve a problem about degradation of recorded information by readout process. About 10(6)-time readout was demonstrated by the method, New high-density optical memory, a super-resolution disk with a photochromic mask layer, was introduced, The super-resolution method has enabled us to increase the recording density of conventional optical disks. Ultra-high density near-field photochromic memory as a new innovative storage technology was also discussed.

Near-field optical recording on polystyrene thin films containing photochromic perinaphthothioindigo (NTI) was carried out. NTI underwent a reversible trans/cis photoisomerization in the polystyrene film, and only the trans-form emitted fluorescence. First, polystyrene film containing trans-form NTI molecules was used as the recording medium. Upon irradiation with 633 nm light from a fiber probe tip (aperture diameter similar to 100 nm), the fluorescent trans-forms in a small region were converted into non-fluorescent cis-forms. The recorded small legions were detected as dark spots as small as 110 nm by scanning across the written area. Second, polystyrene film containing cis-form NTI molecules was used as the recording medium. Upon irradiation with ultrasmall 488 nm light (aperture diameter similar to 80 nm), bright spots as small as 50 nm were recorded and read out with scanning 633 nm light. The bright spots were due to the fluorescence of the photogenerated trans-form NTI molecules. Both the dark and bright spots were erased by irradiation with 488 nm and 633 nm light, respectively. The bright spot could also be recorded using a pulse Nd3+:YAG laser (532 nm, pulse width 20 ns).

We propose an emitting assist (EA) dopant system for obtaining organic light-emitting diodes (OLEDs) with pure red emission. The EA dopant (rubrene) did not itself emit but assisted the energy transfer from the host (Alq(3)) to the red emitting dopant (DCM2). The cell structure used was {indium tin oxide/hole injection layer [(20 nm), CuPc/hole transport layer (50 nm), NPB/emitting layer (40 nm), Alq(3)+DCM2 (2%)+rubrene (5 wt %)]/MgIn}. (CuPc: Copper (II) phthalocyanine, NPB: N, N-'-Di(naphthalen-1-yl)-N, N-'-diphenyl-benzidine, DCM2: 4-Dicyanomethylene- 2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-8-yl)vinyl]-4H-pyran). A stable red emission (chromaticity coordinates: x=0.64, y=0.36) was obtained in this cell within the luminance range of 100-4000 cd/m(2). When the cell was not doped with rubrene, the emission color changed from red to orange as the luminance increased. The EA dopant system is a promising method for obtaining red OLEDs. (C) 1999 American Institute of Physics. [S0003- 6951(99)04538-6].

The signal-to-noise ratio (SNR) on the fluorescence readout of a near-field photochromic memory was theoretically studied. Under various conditions the shot-noise-limited SNR was analyzed. SNR by bright spot recording (BSR) that was better than that by dark spot recording (DSR) was obtained under the condition of low writing power or wide bandwidth. Under the condition of bandwidth W = 1 MHz and P-write = 10(-8) W only ESR can attain sufficiently high SNR, and the SNR was greater by as much as 30 dB than that of DSR. It was concluded that BSR is a promising method for high-density near-field photochromic memory with a fluorescence readout. (C) 1999 Optical Society of America.

The data transfer rate of near-held photochromic memory was theoretically studied. The data transfer rate for the medium with the sensitivity epsilon(B) = 10(4) and phi(BA) = 0.1 in the recording process was about 1 kilo bps (bits per second) at the light power density of 10(2) W/cm(2), but it increased to over 1 Mbps at 10(5) W/cm(2). Fluorescence and reflectance detection readout methods of a near-field photochromic optical memory were also theoretically studied. The data transfer rate at the light power of 10(-6) W in the readout process was around 1-10 Mbps. When the average reflectance is high, there is a benefit of using a fluorescence detection method for obtaining a high data transfer rate.

The fluorescence- and transmittance-detection readout methods of a near-field photochromic optical memory by a scanning-probe technique were studied theoretically. Shot noise, as the principal noise, was taken into account in an analysis of the signal-to-noise ratio (SNR). Under most conditions, fluorescence-detection readout yielded a better SNR than did transmittance-detection readout. For a transmittance change of 0.9-1.0 as a result of recording, a readout light power of approximately 100 nW, and a system bandwidth of 1 MHz, only the fluorescence-detection readout method, under the condition that the fluorescent layer of the medium have a fluorescence quantum yield greater than 0.4, can produce a sufficiently large SNR. (C) 1998 Optical Society of America.

The fluorescence- and transmittance-detection readout methods of a near-field photochromic optical memory by a scanning-probe technique were studied theoretically. Shot noise, as the principal noise, was taken into account in an analysis of the signal-to-noise ratio (SNR). Under most conditions, fluorescence-detection readout yielded a better SNR than did transmittance-detection readout. For a transmittance change of 0.9-1.0 as a result of recording, a readout light power of approximately 100 nW, and a system bandwidth of 1 MHz, only the fluorescence-detection readout method, under the condition that the fluorescent layer of the medium have a fluorescence quantum yield greater than 0.4, can produce a sufficiently large SNR. © 1998 Optical Society of America.

The recording density limit of a near-field optical memory that uses a photochromic medium was theoretically studied by use of Shannon's information theory. Shot noise and material noise were taken into account in the analysis of the signal-to-noise ratio. The conventional recording density limit, which is defined by the inverse of the minimum recorded mark area, and Shannon's recording density limit were evaluated. The conventional recording density limit was 10(11)-10(12) bits/cm(2), and Shannon's recording density limit was 10(12)-10(13) bits/cm(2). (C) 1998 Optical Society of America [S0740-3224(98)02203-6].

In order to solve problems of photochromic memory, a superlow power readout method and a crosstalk reduction method for multi-wavelength recording were proposed. In the demonstration of 2-wavelength recording using photochromic diarylethenes, the crosstalk between multiplexed channels, which is caused from broad absorption bands of compounds, was effectively reduced by the method. A new high density optical memory, a super-resolution disk with a photochromic mask layer, was also introduced. The super-resolution method has enabled us to increase the recording density of conventional optical disks. © 1998 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.

The spot shape on super-resolution optical disks with a photon-mode mask layer was theoretically analyzed. The spot shape was found to depend on the lifetime of the bleached state of the dyes, the light power, and the disk rotation speed. When the lifetime is short, the super-resolution spot shape is not produced at high disk speeds. On the other hand, a dye mask layer with long lifetime, such as a photochromic mask, can produce a sharp spot shape in the higher disk speed region, and therefore is suitable for obtaining a super-resolution disk with a high data transfer rate.

The signal-to-noise ratio (SNR) in the photochromic super-resolution readout of optical disks was theoretically analyzed. The shot noise limited SNR, such as that in magnetooptical disks, was improved only for the short recorded mark. However, the media noise limited SNR, such as that in phase change disks, was greatly improved for both short and long recorded marks.

The super-resolution mastering of read-only optical disks using a photoreactive bleachable dye mask layer was theoretically analyzed. Equations have been derived which describe the photoreactions of the resist layer and mask layer. A numerical simulation based on these equations showed that the transmittance of the mask directly affects the quality of the formed pit shape. A high-quality pit shape is obtained by using a low transmittance mask.

The sensitivity (product of molar extinction coefficient and quantum yield) of 2-(1,2-dimethyl-3-indolyl)-3-(2,4,5-trimethyl-3-thienyl)-maleic anhydride is dependent on its concentration in poly(vinyl butyral) film and on the irradiation wavelength (515 nm and 633 nm). Energy transfer from the open-ring to the closed-ring form is suggested as a possible mechanism for the time dependence of the sensitivity in the polymer film containing high chromophore concentration on irradiation with 515 nm light. (C) 1997 Elsevier Science S.A.

Super-resolution readout for read-only optical disks was demonstrated using a photochronic mask layer. Nonlinear transmittance change, which is desirable for effective super-resolution readout, was achieved using a the photochromic mask layer with an optical density of 0.5. The photochromic super-resolution method is expected to increase the recording density of not only read-only disks, but also magneto-optical and phase change disks.

A single GaN-based light emitting diode (LED) induced both coloring and bleaching reactions of photochromic molecules. Coloring reactions of photochromic diarylethenes were performed using light of a short wavelength which was emitted from a GaN-based LED driven by a pulsed current, and bleaching reactions were performed using light of a long wavelength which was emitted from the LED driven by a constant current.

The possibility of a super resolution optical memory using a saturable absorption dye mask layer is theoretically discussed. An equation which estimates the transmittance change of the mask layer has been derived. The numerical simulation shows that an efficient super-resolution is performed when the initial optical density of the mask layer is high.

The possibility of a super-resolution optical memory using a photochromic mask layer was theoretically discussed. An equation which estimates the transmittance change of the mask layer was derived. The numerical simulation based on the equation showed that the reflectance increase of the layer by photo-irradiation is nonlinear when the optical density of the layer is high. The nonlinear response decreased the crosstalk in adjacent recording tracks and improved the MTF (modulation transfer function) characteristics, resulting in a higher recording density.