Hideyuki Murata - Academia.edu (original) (raw)
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Papers by Hideyuki Murata
Physical Review B, 1990
We present the results of spectroscopic studies of the electronic structure of the conjugated pol... more We present the results of spectroscopic studies of the electronic structure of the conjugated polymer poly(2, 5-thienylene vinylene). Photoexcitation above the band gap at 1.8 eV gives rise to two transient absorption peaks at 0.44 and 1.0 eV that are associated with bipolarons that live for times of order a few milliseconds at 80 K. Photoluminescence, comparable in intensity to the Raman scattering, is found at energies above the band edge, and we assign this to a hot recombination process. We also report the Raman spectrum, and make a preliminary assignment of the main vibrational modes. Three of the four main peaks disperse as the excitation wavelength is varied. We discuss these results and compare them with those previously reported for a related polymer, poly-(pphenylene vinylene).
Science and Technology of Advanced Materials, 2004
MRS Bulletin, 2012
Organic photovoltaic cells that use small molecules post record-high effi ciencies, prompting mat... more Organic photovoltaic cells that use small molecules post record-high effi ciencies, prompting materials researchers to take a new look.
Journal of Electron Spectroscopy and Related Phenomena, 2001
The work function of commercially available indium tin oxide (ITO) films on glass substrates was ... more The work function of commercially available indium tin oxide (ITO) films on glass substrates was measured using photoemission spectroscopy (PES) and ultra-high vacuum (UHV) Kelvin probe in direct comparison. Absolute Kelvin probe work function values were determined via calibration of the measured contact potential difference (CPD) using an in situ sputtered Au reference sample. The Kelvin probe data confirmed that ultraviolet photoemission spectroscopy (UPS) measurements change the work function of ITO surfaces previously exposed to ambient environment, when measured without in situ surface cleaning procedures. The results also demonstrate that both Kelvin probe and PES yield virtually identical work function values, as long as the Kelvin probe data are calibrated against a known standard. As a consequence, previously reported higher work function values determined with Kelvin probe as compared to values obtained with UPS on similar samples are likely related to a photochemically generated surface dipole during UPS measurements. Comparison between Kelvin probe and low intensity X-ray photoemission spectroscopy (LIXPS) work function measurements demonstrated that accurate work function measurements on ITO previously exposed to the ambient are possible with PES.
Chemical Physics Letters, 2006
Studies on the intrinsic degradation of organic light-emitting devices (OLEDs) based on tris(8-hy... more Studies on the intrinsic degradation of organic light-emitting devices (OLEDs) based on tris(8-hydroxyquinolinolato) aluminum (III) (Alq 3) revealed that the operation stability of the OLEDs depends on the process pressure during device fabrication. Lowering of the pressure resulted in stable devices. In sharp contrast, differences in the initial device characteristics were marginal in all devices. Analyses with a quadrupole mass spectrometer indicated that the primary difference in the pressure during device fabrication was attributable to the amount of residual water. The results show that the degradation of OLEDs is associated with the electrochemical reaction of Alq 3 with water.
Chemical Communications, 2008
Applied Physics Letters, 2011
A blue phosphorescent organic light emitting device fabricated under the ultra high vacuum (UHV) ... more A blue phosphorescent organic light emitting device fabricated under the ultra high vacuum (UHV) condition of 6.5 × 10−7 Pa decreases the initial luminance drop upon lifetesting under a constant dc current of 15 mA/cm2 by 3 times compared to a device fabricated under a high vacuum (HV) condition of 7.6 × 10−6 Pa resulting in a 23% increase in half lifetime. We calculate a water content of 10−4 mol. % in the UHV device emissive layer (EML) and 10−2 mol. % in the HV device EML. We discuss the effects of water on luminance loss and voltage rise for the devices.
The Japan Society of Applied Physics, 2016
The Japan Society of Applied Physics, 2016
The Japan Society of Applied Physics, 2018
The Japan Society of Applied Physics, 2016
Analysis of degradation mechanisms in phosphorescence organic light-emitting diode with steady-st... more Analysis of degradation mechanisms in phosphorescence organic light-emitting diode with steady-state and time-resolved photoluminescence measurements 大山 詩歩 ,久保 友明 ,杉本 和則 ,吉岡 俊博 ,大畑 浩 ,宮口 敏 ,筒井 哲夫 , 酒井 平祐 ,村田 英幸 1 (1.北陸先端大マテリアル,2.CEREBA) Shiho Oyama, Tomoaki Kubo, Kazunori Sugimoto, Toshihiro Yoshioka, Hiroshi Ohata, Satoshi Miyaguchi, Tetsuo Tsutsui, Heisuke Sakai, Hideyuki Murata (1.JAIST, 2.CEREBA) E-mail: murata-h@jaist.ac.jp
IEICE Transactions on Electronics, 2017
We integrate a pressure sensing capacitor and a low operation voltage OFET to develop a pressure ... more We integrate a pressure sensing capacitor and a low operation voltage OFET to develop a pressure sensor. The OFET was used as a readout device and an external pressure was loaded on the sensing capacitor. The OFET operates at less than 5 V and the change in the drain current in response to the pressure load (100 kPa) is two orders of magnitude.
Applied Physics Express, 2017
We simultaneously achieved low voltage operation (-5 V) and large drain current (I D) modulation ... more We simultaneously achieved low voltage operation (-5 V) and large drain current (I D) modulation in a dual-gate organic pressure sensor in which a piezoelectric layer was stacked on a low voltage organic field-effect transistor (OFET). During testing, the I D changed from 3.9×10-9 A to 2.5×10-11 A when a 300 kPa pressure load was applied, and the I D clearly responded to the pressure load and release. An endurance cycle test of the device was performed using a pressure load of 100 kPa, and the I D modulation was consistently reproduced throughout the test.
Extended Abstracts of the 2011 International Conference on Solid State Devices and Materials, 2011
Extended Abstracts of the 2013 International Conference on Solid State Devices and Materials, 2013
We report the synthesis and characterization of two novel semiconducting polymers based on naphth... more We report the synthesis and characterization of two novel semiconducting polymers based on naphthodithiophene and their applications to bulk heterojunction solar cells and transistors. The naphthodithiophene based copolymers exhibit a low optical bandgap of ̴ 1.35 eV with the high field-effect hole motility of 2.77 10-2 cm 2 /(Vs). The solar cells made from the polymers yielded power conversion efficiencies of 3.09% and 3.29% under AM 1.5 G irradiation (100mW/cm 2) for PNDTD12 and PzNDTD12 respectively.
SPIE Proceedings, 2008
Current density-voltage (J-V) characteristics of hole-only devices using indium tin oxide (ITO) a... more Current density-voltage (J-V) characteristics of hole-only devices using indium tin oxide (ITO) anode and N,N'- diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (α-NPD) layer were measured with various thicknesses of a molybdenum oxide (MoO3) buffer layer inserted between ITO and α-NPD. The device with a 0.75-nm-thick MoO3 layer forms Ohmic hole injection at the ITO/MoO3/α-NPD interfaces and J-V characteristics of this device are controlled by a space-charge-limited current. Results of X-ray photoelectron and ultraviolet/visible/near-infrared absorption studies revealed that this Ohmic hole injection is attributable to electron transfers from ITO to MoO3 and from α-NPD to MoO3. Moreover, we demonstrated that the Ohmic hole injection is realized at the interfaces of ITO/rubrene and ITO/N,N'-di(m-tolyl)-N,N'-diphenylbenzidine (TPD) using an ultrathin MoO3 layer as well.
Thin Solid Films, 2009
We realize a nonvolatile and rewritable memory effect in an organic field-effect transistor (OFET... more We realize a nonvolatile and rewritable memory effect in an organic field-effect transistor (OFET) structure using polymethylmethacryrate (PMMA) dispersed with 10-methyl-9-phenylacridinium perchlorate (MPA + ClO 4-) as a gate dielectric. Applying a voltage between a top source-drain electrode and a bottom gate electrode induces electrophoresis of two ions of MPA + and ClO 4 toward the corresponding electrodes in the memory devices. The drain currents of the memory devices markedly increase from 10-9 A to 10-2 A under no gate voltage condition due to the strong space charge polarization effect. Our memory devices have excellent electrical bistability and retention characteristics, i.e. the memory on/off ratio reached 10 7 and the drain current maintained 40% of the initial value after 10 4 s.
J. Mater. Chem. C, 2014
We present a single step, solution based method to deposit polymer films with uniaxial orientatio... more We present a single step, solution based method to deposit polymer films with uniaxial orientation and demonstrate its potential by fabricating polarization sensitive photovoltaic devices.
Materials Letters, 2008
A novel electrospinning process of uniaxially aligned submicron fibers was developed. The number ... more A novel electrospinning process of uniaxially aligned submicron fibers was developed. The number of the fibers was precisely controlled by changing biased collector, and the diameter of the fiber was varied by post-deposition stretching process. This method realized the formation of number-controlled aligned poly[2-methoxy-5-(2´-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/poly(ethylene oxide) (PEO) fibers with the systematic control of the diameter ranging from micrometer to submicrometer. Significant improvement of the uniformity of the fiber diameter was also observed by the stretching process.
Physical Review B, 1990
We present the results of spectroscopic studies of the electronic structure of the conjugated pol... more We present the results of spectroscopic studies of the electronic structure of the conjugated polymer poly(2, 5-thienylene vinylene). Photoexcitation above the band gap at 1.8 eV gives rise to two transient absorption peaks at 0.44 and 1.0 eV that are associated with bipolarons that live for times of order a few milliseconds at 80 K. Photoluminescence, comparable in intensity to the Raman scattering, is found at energies above the band edge, and we assign this to a hot recombination process. We also report the Raman spectrum, and make a preliminary assignment of the main vibrational modes. Three of the four main peaks disperse as the excitation wavelength is varied. We discuss these results and compare them with those previously reported for a related polymer, poly-(pphenylene vinylene).
Science and Technology of Advanced Materials, 2004
MRS Bulletin, 2012
Organic photovoltaic cells that use small molecules post record-high effi ciencies, prompting mat... more Organic photovoltaic cells that use small molecules post record-high effi ciencies, prompting materials researchers to take a new look.
Journal of Electron Spectroscopy and Related Phenomena, 2001
The work function of commercially available indium tin oxide (ITO) films on glass substrates was ... more The work function of commercially available indium tin oxide (ITO) films on glass substrates was measured using photoemission spectroscopy (PES) and ultra-high vacuum (UHV) Kelvin probe in direct comparison. Absolute Kelvin probe work function values were determined via calibration of the measured contact potential difference (CPD) using an in situ sputtered Au reference sample. The Kelvin probe data confirmed that ultraviolet photoemission spectroscopy (UPS) measurements change the work function of ITO surfaces previously exposed to ambient environment, when measured without in situ surface cleaning procedures. The results also demonstrate that both Kelvin probe and PES yield virtually identical work function values, as long as the Kelvin probe data are calibrated against a known standard. As a consequence, previously reported higher work function values determined with Kelvin probe as compared to values obtained with UPS on similar samples are likely related to a photochemically generated surface dipole during UPS measurements. Comparison between Kelvin probe and low intensity X-ray photoemission spectroscopy (LIXPS) work function measurements demonstrated that accurate work function measurements on ITO previously exposed to the ambient are possible with PES.
Chemical Physics Letters, 2006
Studies on the intrinsic degradation of organic light-emitting devices (OLEDs) based on tris(8-hy... more Studies on the intrinsic degradation of organic light-emitting devices (OLEDs) based on tris(8-hydroxyquinolinolato) aluminum (III) (Alq 3) revealed that the operation stability of the OLEDs depends on the process pressure during device fabrication. Lowering of the pressure resulted in stable devices. In sharp contrast, differences in the initial device characteristics were marginal in all devices. Analyses with a quadrupole mass spectrometer indicated that the primary difference in the pressure during device fabrication was attributable to the amount of residual water. The results show that the degradation of OLEDs is associated with the electrochemical reaction of Alq 3 with water.
Chemical Communications, 2008
Applied Physics Letters, 2011
A blue phosphorescent organic light emitting device fabricated under the ultra high vacuum (UHV) ... more A blue phosphorescent organic light emitting device fabricated under the ultra high vacuum (UHV) condition of 6.5 × 10−7 Pa decreases the initial luminance drop upon lifetesting under a constant dc current of 15 mA/cm2 by 3 times compared to a device fabricated under a high vacuum (HV) condition of 7.6 × 10−6 Pa resulting in a 23% increase in half lifetime. We calculate a water content of 10−4 mol. % in the UHV device emissive layer (EML) and 10−2 mol. % in the HV device EML. We discuss the effects of water on luminance loss and voltage rise for the devices.
The Japan Society of Applied Physics, 2016
The Japan Society of Applied Physics, 2016
The Japan Society of Applied Physics, 2018
The Japan Society of Applied Physics, 2016
Analysis of degradation mechanisms in phosphorescence organic light-emitting diode with steady-st... more Analysis of degradation mechanisms in phosphorescence organic light-emitting diode with steady-state and time-resolved photoluminescence measurements 大山 詩歩 ,久保 友明 ,杉本 和則 ,吉岡 俊博 ,大畑 浩 ,宮口 敏 ,筒井 哲夫 , 酒井 平祐 ,村田 英幸 1 (1.北陸先端大マテリアル,2.CEREBA) Shiho Oyama, Tomoaki Kubo, Kazunori Sugimoto, Toshihiro Yoshioka, Hiroshi Ohata, Satoshi Miyaguchi, Tetsuo Tsutsui, Heisuke Sakai, Hideyuki Murata (1.JAIST, 2.CEREBA) E-mail: murata-h@jaist.ac.jp
IEICE Transactions on Electronics, 2017
We integrate a pressure sensing capacitor and a low operation voltage OFET to develop a pressure ... more We integrate a pressure sensing capacitor and a low operation voltage OFET to develop a pressure sensor. The OFET was used as a readout device and an external pressure was loaded on the sensing capacitor. The OFET operates at less than 5 V and the change in the drain current in response to the pressure load (100 kPa) is two orders of magnitude.
Applied Physics Express, 2017
We simultaneously achieved low voltage operation (-5 V) and large drain current (I D) modulation ... more We simultaneously achieved low voltage operation (-5 V) and large drain current (I D) modulation in a dual-gate organic pressure sensor in which a piezoelectric layer was stacked on a low voltage organic field-effect transistor (OFET). During testing, the I D changed from 3.9×10-9 A to 2.5×10-11 A when a 300 kPa pressure load was applied, and the I D clearly responded to the pressure load and release. An endurance cycle test of the device was performed using a pressure load of 100 kPa, and the I D modulation was consistently reproduced throughout the test.
Extended Abstracts of the 2011 International Conference on Solid State Devices and Materials, 2011
Extended Abstracts of the 2013 International Conference on Solid State Devices and Materials, 2013
We report the synthesis and characterization of two novel semiconducting polymers based on naphth... more We report the synthesis and characterization of two novel semiconducting polymers based on naphthodithiophene and their applications to bulk heterojunction solar cells and transistors. The naphthodithiophene based copolymers exhibit a low optical bandgap of ̴ 1.35 eV with the high field-effect hole motility of 2.77 10-2 cm 2 /(Vs). The solar cells made from the polymers yielded power conversion efficiencies of 3.09% and 3.29% under AM 1.5 G irradiation (100mW/cm 2) for PNDTD12 and PzNDTD12 respectively.
SPIE Proceedings, 2008
Current density-voltage (J-V) characteristics of hole-only devices using indium tin oxide (ITO) a... more Current density-voltage (J-V) characteristics of hole-only devices using indium tin oxide (ITO) anode and N,N'- diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (α-NPD) layer were measured with various thicknesses of a molybdenum oxide (MoO3) buffer layer inserted between ITO and α-NPD. The device with a 0.75-nm-thick MoO3 layer forms Ohmic hole injection at the ITO/MoO3/α-NPD interfaces and J-V characteristics of this device are controlled by a space-charge-limited current. Results of X-ray photoelectron and ultraviolet/visible/near-infrared absorption studies revealed that this Ohmic hole injection is attributable to electron transfers from ITO to MoO3 and from α-NPD to MoO3. Moreover, we demonstrated that the Ohmic hole injection is realized at the interfaces of ITO/rubrene and ITO/N,N'-di(m-tolyl)-N,N'-diphenylbenzidine (TPD) using an ultrathin MoO3 layer as well.
Thin Solid Films, 2009
We realize a nonvolatile and rewritable memory effect in an organic field-effect transistor (OFET... more We realize a nonvolatile and rewritable memory effect in an organic field-effect transistor (OFET) structure using polymethylmethacryrate (PMMA) dispersed with 10-methyl-9-phenylacridinium perchlorate (MPA + ClO 4-) as a gate dielectric. Applying a voltage between a top source-drain electrode and a bottom gate electrode induces electrophoresis of two ions of MPA + and ClO 4 toward the corresponding electrodes in the memory devices. The drain currents of the memory devices markedly increase from 10-9 A to 10-2 A under no gate voltage condition due to the strong space charge polarization effect. Our memory devices have excellent electrical bistability and retention characteristics, i.e. the memory on/off ratio reached 10 7 and the drain current maintained 40% of the initial value after 10 4 s.
J. Mater. Chem. C, 2014
We present a single step, solution based method to deposit polymer films with uniaxial orientatio... more We present a single step, solution based method to deposit polymer films with uniaxial orientation and demonstrate its potential by fabricating polarization sensitive photovoltaic devices.
Materials Letters, 2008
A novel electrospinning process of uniaxially aligned submicron fibers was developed. The number ... more A novel electrospinning process of uniaxially aligned submicron fibers was developed. The number of the fibers was precisely controlled by changing biased collector, and the diameter of the fiber was varied by post-deposition stretching process. This method realized the formation of number-controlled aligned poly[2-methoxy-5-(2´-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/poly(ethylene oxide) (PEO) fibers with the systematic control of the diameter ranging from micrometer to submicrometer. Significant improvement of the uniformity of the fiber diameter was also observed by the stretching process.