koichiro saiki - Academia.edu (original) (raw)

Papers by koichiro saiki

Research paper thumbnail of The influence of source molecule structure on the low temperature growth of nitrogen-doped graphene

Physical Chemistry Chemical Physics, 2015

Doping of heteroatoms such as nitrogen into the lattice structure of graphene can tune and tailor... more Doping of heteroatoms such as nitrogen into the lattice structure of graphene can tune and tailor the overall electronic properties.

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Research paper thumbnail of Radiation-mode optical microscopy on the growth of graphene

Nature communications, 2015

Chemical vapour deposition (CVD) growth of graphene has attracted much attention, aiming at the m... more Chemical vapour deposition (CVD) growth of graphene has attracted much attention, aiming at the mass production of large-area and high-quality specimens. To optimize the growth condition, CVD grown graphene is conventionally characterized after synthesis. Real-time observation during graphene growth enables us to understand the growth mechanism and control the growth more easily. Here we report the optical microscope observation of the CVD growth of graphene in real time by focusing the radiation emitted from the growing graphene, which we call 'radiation-mode optical microscopy'. We observe the growth and shrinkage of graphene in response to the switching on and off of the methane supply. Analysis of the growth feature reveals that the attachment and detachment of carbon precursors are the rate-determining factor in the CVD growth of graphene. We expect radiation-mode optical microscopy to be applicable to the other crystal growth at high temperatures in various atmospheres.

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Research paper thumbnail of Atomic and electronic structure of an unreconstructed polar MgO(111) thin film on Ag(111)

Physical Review B, 2003

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Research paper thumbnail of Metal-induced gap states in epitaxial organic-insulator/metal interfaces

Physical Review B, 2005

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Research paper thumbnail of Heteroepitaxial growth of LiCl on Cu(001)

Physical Review B, 2001

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Research paper thumbnail of Pentacene films grown on surface treated SiO2 substrates

Thin Solid Films, 2006

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Research paper thumbnail of Electronic structure of octane on Cu(1 1 1) and Ni(1 1 1) studied by near edge X-ray absorption fine structure

Surface Science, 2007

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Research paper thumbnail of Highly sensitive reflection high-energy electron diffraction measurement by use of micro-channel imaging plate

Review of Scientific Instruments, 2000

Micro-channel plate (MCP) was used to intensify the image on the fluorescent screen in reflection... more Micro-channel plate (MCP) was used to intensify the image on the fluorescent screen in reflection high-energy electron diffraction. The primary electron current could be reduced by four orders of magnitude to get the image of the same intensity as in the measurement without MCP. The reduction of electron beam enabled observation of ionic crystal surfaces without causing electrolysis and charging effect.

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Research paper thumbnail of Alignment-Induced Epitaxial Transition in Organic-Organic Heteroepitaxy

Physical Review Letters, 2008

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Research paper thumbnail of Electric-field-induced charge injection or exhaustion in organic thin film transistor

Physical Review B, 2005

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Research paper thumbnail of Electronic properties of metal-induced gap states formed at alkali-halide/metal interfaces

Physical Review B, 2005

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Research paper thumbnail of Investigation of the growth mechanism of an InSe epitaxial layer on a MoS2 substrate

Journal of Crystal Growth, 2000

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Research paper thumbnail of Effect of annealing on the mobility and morphology of thermally activated pentacene thin film transistors

Journal of Applied Physics, 2006

Pentacene thin film transistors (TFTs) were fabricated by the organic molecular beam deposition m... more Pentacene thin film transistors (TFTs) were fabricated by the organic molecular beam deposition method. The TFTs were characterized in order to study the effect of thermal annealing on the morphology and carrier mobility of the transistors. For all the TFT samples the mobility exhibited an Arrhenius relationship with temperature, indicating a thermally activated transport that could be explained by the carrier trap and thermal release transport mechanism. Therefore, in order to investigate the annealing effect, we tested the data for a significant period of time after annealing until the temperature recovered to room temperature, so that the thermal activation effect was screened and possible effects of thermal expansion and stress were also ruled out. As a result, we found that only with a temperature below a critical temperature of approximately 45°C could annealing improve the mobility, while annealing with T>50°C would decrease the mobility compared to the value before anneal...

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Research paper thumbnail of Anodization of electrolytically polished Ta surfaces for enhancement of carrier injection into organic field-effect transistors

Journal of Applied Physics, 2005

Electrolytically polished surfaces of Ta sheets were anodized in an aqueous KI solution to form T... more Electrolytically polished surfaces of Ta sheets were anodized in an aqueous KI solution to form Ta2O5 films with a relatively high dielectric constant and a high breakdown electric field. Organic field-effect transistors (OFETs) were fabricated on these Ta2O5∕Ta substrates with a bottom gate configuration. The Ta2O5 films anodized at 100V were about 200nm thick, and the dielectric strength was as high as 5MV∕cm. A p-type pentacene OFET fabricated on this bottom gate showed the good field-effect mobility of 0.35cm2∕Vs. By using this high-k gate substrate, it becomes possible to inject a higher amount of charge carriers into organic active layers than on the SiO2∕Si gate conventionally used in most OFETs.

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Research paper thumbnail of Analysis of charge transport in a polycrystalline pentacene thin film transistor by temperature and gate bias dependent mobility and conductance

Journal of Applied Physics, 2007

The gate bias and temperature dependent field-effect mobility and conductance of a polycrystallin... more The gate bias and temperature dependent field-effect mobility and conductance of a polycrystalline pentacene thin film transistor (TFT) were analyzed to study the charge transport in the material. Since both heating and cooling can obviously change the film morphology, a relatively narrow temperature range was adopted to rule out the possible influence of structure variation on the device characterization. Both mobility and conductance values increased with the gate bias and showed a thermally activated Arrhenius-like behavior, while the threshold voltage deceased with temperature. Several models were compared, and it was found that the observations could only be well interpreted by a multiple trapping model, which suggests that the temperature and gate bias dependences should be attributed to the increased free charge carrier density. The density of trap states in the band gap was evaluated by the field-effect mobility as well as the field-effect conductance data. The results discl...

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Research paper thumbnail of Oriented Growth of Sexithiophene Induced by Edge of Metal Electrodes

Japanese Journal of Applied Physics, 2010

Recently it has been shown that the “graphoepitaxy” of organic semiconductor α-sexithiophene (6T)... more Recently it has been shown that the “graphoepitaxy” of organic semiconductor α-sexithiophene (6T) occurs on artificial periodic grooves fabricated on thermally-oxidized Si substrates. In the present study, similarly oriented growth of 6T thin films was found around the edge of metal electrodes. Using this phenomenon to realize single crystalline organic transistors, substrates with short channel Au electrodes were fabricated by photolithography, and 6T films were grown on these substrates by molecular beam deposition. The {010} planes of 6T crystals tended to face the wall of the channel (electrode edge), probably due to the chemical affinity of Au for S atoms in 6T molecules. The transistor characteristics of the test device were measured, and the results suggested that this orientation control technique using the shape of electrodes would lead to improvements in device performance.

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Research paper thumbnail of Effect of Organic Buffer Layer on Performance of Pentacene Field-Effect Transistor Fabricated on Natural Mica Gate Dielectric

Japanese Journal of Applied Physics, 2007

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Research paper thumbnail of Accumulation and Depletion Layer Thicknesses in Organic Field Effect Transistors

Japanese Journal of Applied Physics, 2003

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Research paper thumbnail of Effect of UV/ozone treatment of the dielectric layer on the device performance of pentacene thin film transistors

Chemical Physics Letters, 2006

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Research paper thumbnail of Electron-energy-loss spectroscopy of K C60 and K-halides: comparison in the K3p excitation region

Applied Surface Science, 2001

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Research paper thumbnail of The influence of source molecule structure on the low temperature growth of nitrogen-doped graphene

Physical Chemistry Chemical Physics, 2015

Doping of heteroatoms such as nitrogen into the lattice structure of graphene can tune and tailor... more Doping of heteroatoms such as nitrogen into the lattice structure of graphene can tune and tailor the overall electronic properties.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Radiation-mode optical microscopy on the growth of graphene

Nature communications, 2015

Chemical vapour deposition (CVD) growth of graphene has attracted much attention, aiming at the m... more Chemical vapour deposition (CVD) growth of graphene has attracted much attention, aiming at the mass production of large-area and high-quality specimens. To optimize the growth condition, CVD grown graphene is conventionally characterized after synthesis. Real-time observation during graphene growth enables us to understand the growth mechanism and control the growth more easily. Here we report the optical microscope observation of the CVD growth of graphene in real time by focusing the radiation emitted from the growing graphene, which we call 'radiation-mode optical microscopy'. We observe the growth and shrinkage of graphene in response to the switching on and off of the methane supply. Analysis of the growth feature reveals that the attachment and detachment of carbon precursors are the rate-determining factor in the CVD growth of graphene. We expect radiation-mode optical microscopy to be applicable to the other crystal growth at high temperatures in various atmospheres.

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Research paper thumbnail of Atomic and electronic structure of an unreconstructed polar MgO(111) thin film on Ag(111)

Physical Review B, 2003

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Research paper thumbnail of Metal-induced gap states in epitaxial organic-insulator/metal interfaces

Physical Review B, 2005

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Heteroepitaxial growth of LiCl on Cu(001)

Physical Review B, 2001

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Pentacene films grown on surface treated SiO2 substrates

Thin Solid Films, 2006

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Electronic structure of octane on Cu(1 1 1) and Ni(1 1 1) studied by near edge X-ray absorption fine structure

Surface Science, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Highly sensitive reflection high-energy electron diffraction measurement by use of micro-channel imaging plate

Review of Scientific Instruments, 2000

Micro-channel plate (MCP) was used to intensify the image on the fluorescent screen in reflection... more Micro-channel plate (MCP) was used to intensify the image on the fluorescent screen in reflection high-energy electron diffraction. The primary electron current could be reduced by four orders of magnitude to get the image of the same intensity as in the measurement without MCP. The reduction of electron beam enabled observation of ionic crystal surfaces without causing electrolysis and charging effect.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Alignment-Induced Epitaxial Transition in Organic-Organic Heteroepitaxy

Physical Review Letters, 2008

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Electric-field-induced charge injection or exhaustion in organic thin film transistor

Physical Review B, 2005

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Electronic properties of metal-induced gap states formed at alkali-halide/metal interfaces

Physical Review B, 2005

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Investigation of the growth mechanism of an InSe epitaxial layer on a MoS2 substrate

Journal of Crystal Growth, 2000

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Effect of annealing on the mobility and morphology of thermally activated pentacene thin film transistors

Journal of Applied Physics, 2006

Pentacene thin film transistors (TFTs) were fabricated by the organic molecular beam deposition m... more Pentacene thin film transistors (TFTs) were fabricated by the organic molecular beam deposition method. The TFTs were characterized in order to study the effect of thermal annealing on the morphology and carrier mobility of the transistors. For all the TFT samples the mobility exhibited an Arrhenius relationship with temperature, indicating a thermally activated transport that could be explained by the carrier trap and thermal release transport mechanism. Therefore, in order to investigate the annealing effect, we tested the data for a significant period of time after annealing until the temperature recovered to room temperature, so that the thermal activation effect was screened and possible effects of thermal expansion and stress were also ruled out. As a result, we found that only with a temperature below a critical temperature of approximately 45°C could annealing improve the mobility, while annealing with T>50°C would decrease the mobility compared to the value before anneal...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Anodization of electrolytically polished Ta surfaces for enhancement of carrier injection into organic field-effect transistors

Journal of Applied Physics, 2005

Electrolytically polished surfaces of Ta sheets were anodized in an aqueous KI solution to form T... more Electrolytically polished surfaces of Ta sheets were anodized in an aqueous KI solution to form Ta2O5 films with a relatively high dielectric constant and a high breakdown electric field. Organic field-effect transistors (OFETs) were fabricated on these Ta2O5∕Ta substrates with a bottom gate configuration. The Ta2O5 films anodized at 100V were about 200nm thick, and the dielectric strength was as high as 5MV∕cm. A p-type pentacene OFET fabricated on this bottom gate showed the good field-effect mobility of 0.35cm2∕Vs. By using this high-k gate substrate, it becomes possible to inject a higher amount of charge carriers into organic active layers than on the SiO2∕Si gate conventionally used in most OFETs.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Analysis of charge transport in a polycrystalline pentacene thin film transistor by temperature and gate bias dependent mobility and conductance

Journal of Applied Physics, 2007

The gate bias and temperature dependent field-effect mobility and conductance of a polycrystallin... more The gate bias and temperature dependent field-effect mobility and conductance of a polycrystalline pentacene thin film transistor (TFT) were analyzed to study the charge transport in the material. Since both heating and cooling can obviously change the film morphology, a relatively narrow temperature range was adopted to rule out the possible influence of structure variation on the device characterization. Both mobility and conductance values increased with the gate bias and showed a thermally activated Arrhenius-like behavior, while the threshold voltage deceased with temperature. Several models were compared, and it was found that the observations could only be well interpreted by a multiple trapping model, which suggests that the temperature and gate bias dependences should be attributed to the increased free charge carrier density. The density of trap states in the band gap was evaluated by the field-effect mobility as well as the field-effect conductance data. The results discl...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Oriented Growth of Sexithiophene Induced by Edge of Metal Electrodes

Japanese Journal of Applied Physics, 2010

Recently it has been shown that the “graphoepitaxy” of organic semiconductor α-sexithiophene (6T)... more Recently it has been shown that the “graphoepitaxy” of organic semiconductor α-sexithiophene (6T) occurs on artificial periodic grooves fabricated on thermally-oxidized Si substrates. In the present study, similarly oriented growth of 6T thin films was found around the edge of metal electrodes. Using this phenomenon to realize single crystalline organic transistors, substrates with short channel Au electrodes were fabricated by photolithography, and 6T films were grown on these substrates by molecular beam deposition. The {010} planes of 6T crystals tended to face the wall of the channel (electrode edge), probably due to the chemical affinity of Au for S atoms in 6T molecules. The transistor characteristics of the test device were measured, and the results suggested that this orientation control technique using the shape of electrodes would lead to improvements in device performance.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Effect of Organic Buffer Layer on Performance of Pentacene Field-Effect Transistor Fabricated on Natural Mica Gate Dielectric

Japanese Journal of Applied Physics, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Accumulation and Depletion Layer Thicknesses in Organic Field Effect Transistors

Japanese Journal of Applied Physics, 2003

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Effect of UV/ozone treatment of the dielectric layer on the device performance of pentacene thin film transistors

Chemical Physics Letters, 2006

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Electron-energy-loss spectroscopy of K C60 and K-halides: comparison in the K3p excitation region

Applied Surface Science, 2001

Bookmarks Related papers MentionsView impact