koichiro saiki - Academia.edu (original) (raw)
Papers by koichiro saiki
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
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.
Bookmarks Related papers MentionsView impact
Physical Review B, 2003
Bookmarks Related papers MentionsView impact
Physical Review B, 2005
Bookmarks Related papers MentionsView impact
Physical Review B, 2001
Bookmarks Related papers MentionsView impact
Thin Solid Films, 2006
Bookmarks Related papers MentionsView impact
Surface Science, 2007
Bookmarks Related papers MentionsView impact
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
Physical Review Letters, 2008
Bookmarks Related papers MentionsView impact
Physical Review B, 2005
Bookmarks Related papers MentionsView impact
Physical Review B, 2005
Bookmarks Related papers MentionsView impact
Journal of Crystal Growth, 2000
Bookmarks Related papers MentionsView impact
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
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
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
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
Japanese Journal of Applied Physics, 2007
Bookmarks Related papers MentionsView impact
Japanese Journal of Applied Physics, 2003
Bookmarks Related papers MentionsView impact
Chemical Physics Letters, 2006
Bookmarks Related papers MentionsView impact
Applied Surface Science, 2001
Bookmarks Related papers MentionsView impact
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
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.
Bookmarks Related papers MentionsView impact
Physical Review B, 2003
Bookmarks Related papers MentionsView impact
Physical Review B, 2005
Bookmarks Related papers MentionsView impact
Physical Review B, 2001
Bookmarks Related papers MentionsView impact
Thin Solid Films, 2006
Bookmarks Related papers MentionsView impact
Surface Science, 2007
Bookmarks Related papers MentionsView impact
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
Physical Review Letters, 2008
Bookmarks Related papers MentionsView impact
Physical Review B, 2005
Bookmarks Related papers MentionsView impact
Physical Review B, 2005
Bookmarks Related papers MentionsView impact
Journal of Crystal Growth, 2000
Bookmarks Related papers MentionsView impact
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
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
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
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
Japanese Journal of Applied Physics, 2007
Bookmarks Related papers MentionsView impact
Japanese Journal of Applied Physics, 2003
Bookmarks Related papers MentionsView impact
Chemical Physics Letters, 2006
Bookmarks Related papers MentionsView impact
Applied Surface Science, 2001
Bookmarks Related papers MentionsView impact