International Conference on Ultrafast Phenomena, 2010
ABSTRACT Coherent vibrational relaxation is investigated for CH and OH stretch modes in PVA film ... more ABSTRACT Coherent vibrational relaxation is investigated for CH and OH stretch modes in PVA film by femtosecond coherent anti-Stokes Raman spectroscopy. The vibrational relaxation for CH mode is found faster than that for OH mode.
2011 International Quantum Electronics Conference (IQEC) and Conference on Lasers and Electro-Optics (CLEO) Pacific Rim incorporating the Australasian Conference on Optics, Lasers and Spectroscopy and the Australian Conference on Optical Fibre Technology, 2011
ABSTRACT We have performed femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CAR... more ABSTRACT We have performed femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) to study the vibrational dynamics of Polyvinyl alcohol (PVA) film. We observed CARS signal beats between vibrational modes in PVA and measured the coherent vibrational relaxation rates of CH and OH stretch modes. We found that the coherent vibrational relaxation of anti-symmetric CH stretch mode in PVA is much faster than that of symmetric mode, probably due to faster resonant vibrational energy transfer to adjacent CH groups in a polymer chain.
ABSTRACT A novel method for fabrication of the quantum wire structures has been investigated by w... more ABSTRACT A novel method for fabrication of the quantum wire structures has been investigated by which a quantum wire has been successfully fabricated on top of a (111)B facet structure with a very sharp ridge. Electron microscope study has shown that GaAs wires with the effective lateral width of 16–18 nm and with the thickness of 6–9 nm are formed at the ridge top. Photoluminescence and cathodoluminescence measurements indicate that ID quantum confinement of electrons is realized at the ridge top and its blue shift agrees with the quantum confined energy calculated for the observed wire structure.
ABSTRACT An edge quantum wire (EQWI) structure with a feature width of 120 nm was successfully pr... more ABSTRACT An edge quantum wire (EQWI) structure with a feature width of 120 nm was successfully prepared on (111)B micro facets; the structure was fabricated by an ensemble of several growth modes in molecular beam epitaxy (MBE) on a patterned (001) substrate without resorting to any advanced lithographic technique. A clear deviation from the linear relationship is observed in a Landau plot of magnetoresistance at low magnetic fields, providing the first evidence of magnetic depopulation of one-dimensional subbands in a facet EQWI. The sheet electron concentration measured is 5.4 × 1011cm−2 which corresponds to the linear concentration of 4.8 × 106cm−1, and the mobility is 3 × 104cm2V−1s−1 or higher. These values indicate a high crystal quality of the facet EQWI thus prepared.
ABSTRACT The radiative decay of one-dimensional (1D) excitons is studied in novel GaAs quantum wi... more ABSTRACT The radiative decay of one-dimensional (1D) excitons is studied in novel GaAs quantum wires (QWI's) prepared by molecular beam epitaxy. The temperature dependence of the radiative lifetime tau(T) is measured, and is compared with that of 2D excitons in quantum wells (QW's): tau(T) of 1D excitons grows much more slowly with T than that of 2D excitons, resulting in shorter lifetime for T>20 K. This is ascribed to thermalization in the concentrated 1D density of states in QWIs. Analysis based on a theory has revealed that tau(T) is expressed as 92&surd;T ps K-1/2 in QWIs and as 24T ps K-1 in QWs.
... Jpn. J. Appl. Phys., 45 (2006), p. 3652. [14] H. Miyagawa, S. Koshiba, K. Takao, K. Fujii, M.... more ... Jpn. J. Appl. Phys., 45 (2006), p. 3652. [14] H. Miyagawa, S. Koshiba, K. Takao, K. Fujii, M. Mizumaki, O. Sakata, S. Kimura, R. Ueji and N. Sumida. Jpn. J. Appl. Phys., 45 (2006), p. 3548. [15] RL de Kronig and WJ Penney. Proc. R. Soc. London Ser. A, 130 (1930), p. 499. ...
We evaluate the shape of ridge quantum wires (RQWIs) with nm-scale resolution by using SEM and ul... more We evaluate the shape of ridge quantum wires (RQWIs) with nm-scale resolution by using SEM and ultra-high-vacuum (UHV) AFM system which is connected to MBE chamber. This MBE-AFM system provides us a detailed information about the evolution of size and uniformity of ridges grown under various conditions. In this report, we investigate systematically how the growth temperature Ts and As flux affect the width and morphology of GaAs ridge structure. The results show that a very sharp and uniform GaAs ridge structures (W < 10 nm) can be obtained. On the basis of this understanding, we fabricated the ridge quantum wire of 10 nm width.
Mechanisms of molecular beam epitaxy have been investigated for GaAs and AlAs by growing and anal... more Mechanisms of molecular beam epitaxy have been investigated for GaAs and AlAs by growing and analyzing the shapes of facet structures consisting of an (001) top surface and two (111)B side surfaces. It is found that all of the Ga flux on the three facet planes is incorporated into the film, but the growth rates on (111)b AND (001) depend
InGaAs and GaAs layers and GaAs/AlAs superlattice (SL) structures were grown by MBE on (757)B GaA... more InGaAs and GaAs layers and GaAs/AlAs superlattice (SL) structures were grown by MBE on (757)B GaAs substrates and their corrugated growth fronts induced by the step bunching process were closely investigated by scanning transmission electron microscope (STEM). Cross-sectional images obtained from the [101¯] direction have revealed asymmetries and other features of strongly corrugated InGaAs layers and a smoothing process in
InGaAs and GaAs layers and GaAs/AlAs superlattice (SL) structures were grown by MBE on (757)B GaA... more InGaAs and GaAs layers and GaAs/AlAs superlattice (SL) structures were grown by MBE on (757)B GaAs substrates and their corrugated growth fronts induced by the step bunching process were closely investigated by scanning transmission electron microscope (STEM). Cross-sectional images obtained from the [101¯] direction have revealed asymmetries and other features of strongly corrugated InGaAs layers and a smoothing process in
International Conference on Ultrafast Phenomena, 2010
ABSTRACT Coherent vibrational relaxation is investigated for CH and OH stretch modes in PVA film ... more ABSTRACT Coherent vibrational relaxation is investigated for CH and OH stretch modes in PVA film by femtosecond coherent anti-Stokes Raman spectroscopy. The vibrational relaxation for CH mode is found faster than that for OH mode.
2011 International Quantum Electronics Conference (IQEC) and Conference on Lasers and Electro-Optics (CLEO) Pacific Rim incorporating the Australasian Conference on Optics, Lasers and Spectroscopy and the Australian Conference on Optical Fibre Technology, 2011
ABSTRACT We have performed femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CAR... more ABSTRACT We have performed femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) to study the vibrational dynamics of Polyvinyl alcohol (PVA) film. We observed CARS signal beats between vibrational modes in PVA and measured the coherent vibrational relaxation rates of CH and OH stretch modes. We found that the coherent vibrational relaxation of anti-symmetric CH stretch mode in PVA is much faster than that of symmetric mode, probably due to faster resonant vibrational energy transfer to adjacent CH groups in a polymer chain.
ABSTRACT A novel method for fabrication of the quantum wire structures has been investigated by w... more ABSTRACT A novel method for fabrication of the quantum wire structures has been investigated by which a quantum wire has been successfully fabricated on top of a (111)B facet structure with a very sharp ridge. Electron microscope study has shown that GaAs wires with the effective lateral width of 16–18 nm and with the thickness of 6–9 nm are formed at the ridge top. Photoluminescence and cathodoluminescence measurements indicate that ID quantum confinement of electrons is realized at the ridge top and its blue shift agrees with the quantum confined energy calculated for the observed wire structure.
ABSTRACT An edge quantum wire (EQWI) structure with a feature width of 120 nm was successfully pr... more ABSTRACT An edge quantum wire (EQWI) structure with a feature width of 120 nm was successfully prepared on (111)B micro facets; the structure was fabricated by an ensemble of several growth modes in molecular beam epitaxy (MBE) on a patterned (001) substrate without resorting to any advanced lithographic technique. A clear deviation from the linear relationship is observed in a Landau plot of magnetoresistance at low magnetic fields, providing the first evidence of magnetic depopulation of one-dimensional subbands in a facet EQWI. The sheet electron concentration measured is 5.4 × 1011cm−2 which corresponds to the linear concentration of 4.8 × 106cm−1, and the mobility is 3 × 104cm2V−1s−1 or higher. These values indicate a high crystal quality of the facet EQWI thus prepared.
ABSTRACT The radiative decay of one-dimensional (1D) excitons is studied in novel GaAs quantum wi... more ABSTRACT The radiative decay of one-dimensional (1D) excitons is studied in novel GaAs quantum wires (QWI's) prepared by molecular beam epitaxy. The temperature dependence of the radiative lifetime tau(T) is measured, and is compared with that of 2D excitons in quantum wells (QW's): tau(T) of 1D excitons grows much more slowly with T than that of 2D excitons, resulting in shorter lifetime for T>20 K. This is ascribed to thermalization in the concentrated 1D density of states in QWIs. Analysis based on a theory has revealed that tau(T) is expressed as 92&surd;T ps K-1/2 in QWIs and as 24T ps K-1 in QWs.
... Jpn. J. Appl. Phys., 45 (2006), p. 3652. [14] H. Miyagawa, S. Koshiba, K. Takao, K. Fujii, M.... more ... Jpn. J. Appl. Phys., 45 (2006), p. 3652. [14] H. Miyagawa, S. Koshiba, K. Takao, K. Fujii, M. Mizumaki, O. Sakata, S. Kimura, R. Ueji and N. Sumida. Jpn. J. Appl. Phys., 45 (2006), p. 3548. [15] RL de Kronig and WJ Penney. Proc. R. Soc. London Ser. A, 130 (1930), p. 499. ...
We evaluate the shape of ridge quantum wires (RQWIs) with nm-scale resolution by using SEM and ul... more We evaluate the shape of ridge quantum wires (RQWIs) with nm-scale resolution by using SEM and ultra-high-vacuum (UHV) AFM system which is connected to MBE chamber. This MBE-AFM system provides us a detailed information about the evolution of size and uniformity of ridges grown under various conditions. In this report, we investigate systematically how the growth temperature Ts and As flux affect the width and morphology of GaAs ridge structure. The results show that a very sharp and uniform GaAs ridge structures (W < 10 nm) can be obtained. On the basis of this understanding, we fabricated the ridge quantum wire of 10 nm width.
Mechanisms of molecular beam epitaxy have been investigated for GaAs and AlAs by growing and anal... more Mechanisms of molecular beam epitaxy have been investigated for GaAs and AlAs by growing and analyzing the shapes of facet structures consisting of an (001) top surface and two (111)B side surfaces. It is found that all of the Ga flux on the three facet planes is incorporated into the film, but the growth rates on (111)b AND (001) depend
InGaAs and GaAs layers and GaAs/AlAs superlattice (SL) structures were grown by MBE on (757)B GaA... more InGaAs and GaAs layers and GaAs/AlAs superlattice (SL) structures were grown by MBE on (757)B GaAs substrates and their corrugated growth fronts induced by the step bunching process were closely investigated by scanning transmission electron microscope (STEM). Cross-sectional images obtained from the [101¯] direction have revealed asymmetries and other features of strongly corrugated InGaAs layers and a smoothing process in
InGaAs and GaAs layers and GaAs/AlAs superlattice (SL) structures were grown by MBE on (757)B GaA... more InGaAs and GaAs layers and GaAs/AlAs superlattice (SL) structures were grown by MBE on (757)B GaAs substrates and their corrugated growth fronts induced by the step bunching process were closely investigated by scanning transmission electron microscope (STEM). Cross-sectional images obtained from the [101¯] direction have revealed asymmetries and other features of strongly corrugated InGaAs layers and a smoothing process in
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Papers by S. Koshiba