Yusuke Furukawa

Electronic absorption and Raman studies of BF4−-doped polythiophene based on the spectra of the radical cation and dication of α-sexithiophene

Abstract The electronic absorption and Raman spectra of as-polymerized BF 4 − -doped polythiophene have been analyzed on the basis of the spectra of the radical cation and dication of α-sexithiophene, viewed as models of a positive polaron and a positive bipolaron, respectively. The Raman spectra taken with laser lines between 632.8 and 1064 nm have been attributed to positive polarons existing in doped polythiophene. The Raman results confirm that the two-band feature observed in the electronic absorption spectra of doped polythiophene is attributable to polarons.

Hydrothermal method grown large-sized zinc oxide single crystal as fast scintillator for future extreme ultraviolet lithography

The scintillation properties of a hydrothermal method grown zinc oxide (ZnO) crystal are evaluated for extreme ultraviolet (EUV) laser excitation at 13.9nm wavelength. The exciton emission lifetime at around 380nm is determined to be 1.1ns, almost identical to ultraviolet laser excitation cases. This fast response time is sufficiently short for characterizing EUV lithography light sources having a few nanoseconds duration. The availability of large size ZnO crystal up to 3in. is quite attractive for future lithography and imaging applications.

Efficient ejection of H3+ from hydrocarbon molecules induced by ultrashort intense laser fields

The ejection processes of hydrogen molecular ion H(3)(+) from 12 kinds of hydrocarbon molecular species, methanol, ethanol, 1-propanol, 2-propanol, acetone, acetaldehyde, methane, ethane, ethylene, allene, 1,3-butadiene, and cyclohexane, induced by intense laser fields (approximately 10(14) W/cm(2)) have been investigated by time-of-flight mass spectroscopy. The observation of the H(3)(+) production with the kinetic energy range of 3.5-5.0 eV from doubly ionized ethylene, allene, 1,3-butadiene, and cyclohexane, which have no methyl groups, showed the existence of the ultrafast hydrogen migration processes that enables three hydrogen atoms to come together to form H(3)(+) within a hydrocarbon molecule.

Two-body Coulomb explosion and hydrogen migration in methanol induced by intense 7 and 21fs laser pulses

Two-body Coulomb explosion with the C-O bond breaking of methanol induced by intense laser pulses with the duration of Delta t=7 and 21 fs is investigated by the coincidence momentum imaging method. When Delta t=7 fs, the angular distribution of recoil vectors of the fragment ions for the direct C-O bond breaking pathway, CH(3)OH(2+)-->CH(3) (+)+OH(+), exhibits a peak deflected from the laser polarization direction by 30 degrees -45 degrees , and the corresponding angular distribution for the migration pathway, CH(2)OH(2) (+)-->CH(2) (+)+H(2)O(+), in which one hydrogen migrates from the carbon site to the oxygen site prior to the C-O bond breaking, exhibits almost the same profile. When the laser pulse duration is stretched to Delta t=21 fs, the angular distributions for the direct and migration pathways exhibit a broad peak along the laser polarization direction probably due to the dynamical alignment and/or the change in the double ionization mechanism; that is, from the nonsequential double ionization to the sequential double ionization. However, the extent of the anisotropy in the migration pathway is smaller than that in the direct pathway, exhibiting a substantial effect of hydrogen atom migration in the dissociative ionization of methanol interacting with the linearly polarized intense laser field.

Temperature dependence of scintillation properties for a hydrothermal-method-grown zinc oxide crystal evaluated by nickel-like silver laser pulses

The scintillation properties of a hydrothermal-method-grown zinc oxide (ZnO) crystal in the extreme ultraviolet region are evaluated using a nickel-like silver laser with an emission wavelength of 13.9 nm. The temperature dependence of the scintillation properties of the ZnO emission at a wavelength of ~380 nm is investigated. The emission exhibits a broad peak at 386 nm with a full width at half-maximum (FWHM) of 15 nm at room temperature (298 K). Decreasing the ZnO crystal temperature to 25 K causes the peak position to be blueshifted by 12 nm while the FWHM becomes narrower by 9 nm as compared with the room temperature case.

Ejection dynamics of hydrogen molecular ions from methanol in intense laser fields

The ejection of hydrogen molecular ions from two-body Coulomb explosion processes of methanol (CH3OH, CD3OH and CH3OD) in an intense laser field (800 nm, 60 fs, 0.2 PW cm−2) is investigated by a coincidence momentum imaging method. From the coincidence momentum maps, the ejection processes of hydrogen molecular ions, CH3OH2+→ Hm+ + CH(3−m)OH+(m = 2, 3), CD3OH2+→ Dm+ + CH(3−m)OH+(m = 2, 3) and CH3OD2+→ Hm+ + CH(3−m)OD+(m = 2, 3), are identified. Based on the results obtained with isotopically substituted methanol, the isotope effect on the ejection process of hydrogen molecular ions is discussed. Furthermore, the ejection of H/D exchanged hydrogen molecular ions (HD+, HD2+ and H2D+) is identified, and the timescales for the H/D exchanging processes are estimated from the extent of anisotropy in the ejection directions.

Direct observation of an attosecond electron wave packet in a nitrogen molecule.

Attosecond electron wave packet in a molecule is captured by the pump-probe method with a-few-pulse attosecond pulse train. Capturing electron motion in a molecule is the basis of understanding or steering chemical reactions. Nonlinear Fourier transform spectroscopy using an attosecond-pump/attosecond-probe technique is used to observe an attosecond electron wave packet in a nitrogen molecule in real time. The 500-as electronic motion between two bound electronic states in a nitrogen molecule is captured by measuring the fragment ions with the same kinetic energy generated in sequential two-photon dissociative ionization processes. The temporal evolution of electronic coherence originating from various electronic states is visualized via the fragment ions appearing after irradiation of the probe pulse. This observation of an attosecond molecular electron wave packet is a critical step in understanding coupled nuclear and electron motion in polyatomic and biological molecules to explore attochemistry.

Orientation dependence of the Schottky barrier height for La0.6Sr0.4MnO3/SrTiO3 heterojunctions

The authors report on the crystallographic orientation dependence of the Schottky properties for heterojunctions between a half-metallic ferromagnet La0.6Sr0.4MnO3 (LSMO) and Nb-doped SrTiO3 semiconductor. The Schottky barrier height determined by in situ photoemission measurements is independent for the substrate orientations (001) and (110), while the magnetic properties of LSMO (110) films are more enhanced than for (001) films. These results suggest that the performance of magnetic devices based on ferromagnetic manganite is improved by using (110)-oriented substrates.

Resolving vibrational wave-packet dynamics of D2+ using multicolor probe pulses

We demonstrate the generation and real-time observation of the vibrational wave packet of D(2)(+) by using a sub-10-fs extreme UV high-harmonic pump pulse and a three-color probe laser pulse whose wavelength ranges from near-IR to vacuum UV. This multicolor pump-probe scheme can provide us with a powerful experimental tool for investigating a variety of wave packets evolving with a time scale of ~20 fs.

Development of Vacuum Ultraviolet Streak Camera System for the Evaluation of Vacuum Ultraviolet Emitting Materials

Details of the design and development of a bright vacuum ultraviolet Seya–Namioka type spectrometer and streak camera system with reflection-type input optics is presented. The Seya–Namioka spectrometer has a 40 mm by 45 mm holographic grating with a groove density of 600 grooves/mm, linear dispersion of 8 nm/mm, and effective F-number of 4.2. To eliminate loss of light by absorption, the streak camera imaging unit uses Al and MgF2 coated imaging optics with at least 80% reflection from 125–850 nm and has an effective F-number of 4. It is equipped with a synchronized scan unit that can be tuned to 82 MHz and a slow scan speed unit that can measure up to 2-MHz single event. Temporal response of the system at the 20-ns scanning range is evaluated to be around 260 ps.