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Journal Articles

High spatial resolution ZnO scintillator for an in situ imaging device in EUV region

Arita, Ren*; Nakazato, Tomoharu*; Shimizu, Toshihiko*; Yamanoi, Kohei*; Empizo, M.*; Hori, Tatsuhiro*; Fukuda, Kazuhito*; Minami, Yuki*; Sarukura, Nobuhiko*; Maruyama, Momoko; et al.

Optical Materials, 36(12), p.2012 - 2015, 2014/10

 Times Cited Count:7 Percentile:38.97(Materials Science, Multidisciplinary)

A single shot image of a ZnO crystal excited by the EUV laser of Kansai Photon Science Institute was captured. The evaluated EUV beam waist radii from the ZnO emission pattern along the horizontal and vertical axes are 5.0 and 4.7$$mu$$m, respectively. The expected focal spot size of EUV laser and the spatial resolution of the magnifier (including the Schwarzschild objectives and lenses) are however 1 and 4$$mu$$m, respectively. The discrepancy on the spatial resolutions is attributed to exciton diffusion. We estimated the ZnO exciton diffusion length from the effective decay time which is shortened by exciton-exciton collision quenching and which is dependence on excitation energy density. Our results indicate that the short lifetime of ZnO is required to improve the spatial resolution.

Journal Articles

Evaluation of soft X-ray laser with ${it in situ}$ imaging device of high spatial resolution ZnO scintillator

Nakazato, Tomoharu*; Shimizu, Toshihiko*; Yamanoi, Kohei*; Sakai, Kohei*; Takeda, Kohei*; Nishi, Ryosuke*; Minami, Yuki*; Cadatal-Raduban, M.*; Sarukura, Nobuhiko*; Nishimura, Hiroaki*; et al.

Japanese Journal of Applied Physics, 50(12), p.122202_1 - 122202_4, 2011/12

 Times Cited Count:8 Percentile:37.66(Physics, Applied)

We demonstrate the potential of a hydrothermal method-grown ZnO as a high-spatial resolution imaging device for in-situ soft X-ray laser diagnostics by characterizing the exciton emission patterns. By plotting the emission pattern radii at each position, we estimated the evolution of the beam radius around the focal point. The beam profile of the Ni-like Ag ion plasma laser was estimated from the waist radii as 29 and 21$$mu$$m, the divergence angle as 7.2 and 11 mrad and the M2 factor as 47 and 50 in the horizontal- and vertical-axis, respectively. Spatial resolution of the magnifier was estimated to be 6$$mu$$m and is expected to improve by optimizing the optics of the magnifier and using a telescope. Our results would enhance the use of ZnO as an imaging device that would play a crucial role in the development and application of soft X-ray light sources.

Journal Articles

Development of the X-ray interferometer and the method of spatial and temporal synchronization of XRL and optical pulse

Hasegawa, Noboru; Ochi, Yoshihiro; Kawachi, Tetsuya; Terakawa, Kota*; Tomita, Takuro*; Yamamoto, Minoru; Nishikino, Masaharu; Oba, Toshiyuki; Kaihori, Takeshi; Imazono, Takashi; et al.

X-Ray Lasers 2010; Springer Proceedings in Physics, Vol.136, p.353 - 358, 2011/12

The understanding of the dynamics of the initial process is important for the micro processing and welding by the ultra-short laser pulse. The X-ray laser is suitable for probing this initial process because it has short wavelength (Ni-like Ag, 13.9 nm) and short duration (7 ps). For this investigation, the origin of time of the pumping pulse is quite important. In this study, we used the scintillation plate and the plasma gate technique to realize the spatial and temporal synchronization of the pump and probe pulses. For the spatial alignment, a CsI scintillation plate that was set at the sample position was illuminated by both the X-ray laser pulse, and the fluorescence light were detected by the CCD camera. For the temporal synchronization, we set a thin foil at the sample position. We measured the transmission of the X-ray laser while changing a temporal delay of the pumping laser with respect to the time of X-ray laser pulse to obtain the origin of the irradiation time.

Journal Articles

Evaluation of ZnO fast scintillator spatial resolution using the FZP-focused X-ray laser

Tanaka, Momoko; Nakazato, Tomoharu*; Shimizu, Toshihiko*; Yamanoi, Kohei*; Sakai, Kohei*; Sarukura, Nobuhiko*; Nishikino, Masaharu; Oba, Toshiyuki; Kaihori, Takeshi; Ochi, Yoshihiro; et al.

JAEA-Conf 2011-001, p.126 - 128, 2011/03

The spatial resolution of hydrothermal method grown zinc oxide (ZnO) scintillator was evaluated using X-ray laser focused with Fresnel zone plate. The fluorescence image of the ZnO scintillator was measured to be less than 10um using CCD camera coupled with a Schbartzchild expander mirror. The availability of large size ZnO crystal up to 3-inch is quite attractive for future lithography and imaging applications.

Journal Articles

X-ray imaging by using ZnO crystal

Sarukura, Nobuhiko*; Nakazato, Tomoharu*; Shimizu, Toshihiko*; Yamanoi, Kohei*; Sakai, Kohei*; Ehrentraut, D.*; Fukuda, Tsuguo*; Tanaka, Momoko; Nishikino, Masaharu; Kawachi, Tetsuya

Reza Kenkyu, 39(3), p.193 - 196, 2011/03

Development of light sources in the soft X-ray/X-ray region, such as laser induced plasma emission and XFEL, is in demand for applications in various fields of science, medicine, and industry, among others. To promote this endeavor, development of imaging devices as diagnostic tools in this wavelength region is required. ZnO is a prominent candidate material for high spatial and temporal resolution imaging devices because of its emission at 380 nm, lifetime of less than 1 ns, and availability of large and cheap but high quality crystals. We obtained a single shot image of ZnO emission pattern excited by an X-ray laser at the Advanced Photon Research Center, Japan Atomic Energy Agency. The spatial resolution was estimated to be around 10 $$mu$$m. This result shows that ZnO can be used as a powerful imaging device for applications such as EUV lithography.

Journal Articles

Hydrothermal-method-grown ZnO single crystal as fast EUV scintillator for future lithography

Nakazato, Tomoharu*; Furukawa, Yusuke*; Tanaka, Momoko; Tatsumi, Toshihiro*; Nishikino, Masaharu; Yamatani, Hiroshi*; Nagashima, Keisuke; Kimura, Toyoaki*; Murakami, Hidetoshi*; Saito, Shigeki*; et al.

Journal of Crystal Growth, 311(3), p.875 - 877, 2009/01

 Times Cited Count:24 Percentile:87.06(Crystallography)

The temperature dependence of scintillation properties of a hydrothermal-method-grown zinc oxide (ZnO) emission is investigated using a nickel-like silver laser emitting at 13.9 nm. A broad peak at 386 nm with a full-width at half-maximum (FWHM) of 15 nm at room temperature (298 K) is obtained. The peak position tends to be blue shifted while the FWHM becomes narrower when the crystal temperature is decreased to 25 K. Streak images fitted by a double exponential decay reveal that the measured emission decay at 105 K was $$tau$$$$_{1}$$ = 0.88 ns and $$tau$$$$_{2}$$ = 2.7 ns. This decay time of a few nanoseconds is suitable for lithographic applications and is sufficiently short for the characterization of laser plasma extreme ultraviolet (EUV) sources with nanosecond durations.

Journal Articles

Time-resolved fluorescence spectrum of wide-gap semiconductors excited by 13.9 nm X-ray laser

Tanaka, Momoko; Furukawa, Yusuke*; Nakazato, Tomoharu*; Tatsumi, Toshihiro*; Murakami, Hidetoshi*; Shimizu, Toshihiko*; Sarukura, Nobuhiko*; Nishikino, Masaharu; Kawachi, Tetsuya; Kagamitani, Yuji*; et al.

X-Ray Lasers 2008; Springer Proceedings in Physics Series, Vol.130, p.501 - 505, 2009/00

We measured the time-resolved fluorescence spectra of ZnO and GaN single crystals excited by an X-ray laser operating at 13.9 nm and evaluated their scintillation properties for EUV excitation as compared with UV excitation case. For ZnO, a clear fluorescence peak of excitonic origin was observed at around 380 nm and the decay lifetime of less than 3 ns is found to be almost similar to the UV excitation case. The fluorescence at 380 nm is ideal for scintillator device design in the EUV and further applications. For GaN, the lifetimes are much longer than ZnO and the temporal profile of the EUV-excited fluorescence differs with the UV excitation case. As such, the EUV scintillation properties of ZnO is said to be more favorable than GaN. Finally, it is also demonstrated that an X-ray laser is an excellent tool for spectroscopic characterization of materials intended for next-generation lithography applications.

Journal Articles

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

Furukawa, Yusuke*; Tanaka, Momoko; Nakazato, Tomoharu*; Tatsumi, Toshihiro*; Nishikino, Masaharu; Yamatani, Hiroshi; Nagashima, Keisuke; Kimura, Toyoaki; Murakami, Hidetoshi*; Saito, Shigeki*; et al.

Journal of the Optical Society of America B, 25(7), p.B118 - B121, 2008/07

 Times Cited Count:24 Percentile:74.95(Optics)

Using EUV laser operated at 13.9 nm ZnO and GaN are shown to be excellent scintillators in this wavelength region. Especially ZnO has short response time of 3 ns and prominent peak fluorescence from excitation at 380 nm.

Oral presentation

Single-shot focal spot image of EUV laser using a ZnO scintillator

Nakazato, Tomoharu*; Shimizu, Toshihiko*; Yamanoi, Kohei*; Takatori, Satoru*; Estacio, E.*; Cadatal, M.*; Sarukura, Nobuhiko*; Nishimura, Hiroaki*; Mima, Kunioki*; Tanaka, Momoko; et al.

no journal, , 

We have observed the single shot, focused image of a EUV laser through the emission of a ZnO scintillator. An estimated EUV laser focal spot size of 50$$times$$88 micrometer is reasonable considering the long focal length of the spherical mirror. This work reports a feasible method to perform single-shot beam diagnostics for EUV laser sources using a ZnO crystal scintillator. Furthermore, since the ZnO fluorescence is at 380 nm wavelength, the imaging optics for the diagnostics can all be placed outside the vacuum chamber; thereby making experiments less cumbersome. Having a capability in fast and efficient beam profiling of EUV laser sources with acceptable resolving power is very important in future lithography applications.

Oral presentation

Evaluation of ZnO fast scintillator spatial resolution using the FZP-focused EUV laser

Nakazato, Tomoharu*; Shimizu, Toshihiko*; Yamanoi, Kohei*; Sakai, Kohei*; Sarukura, Nobuhiko*; Ehrentraut, D.*; Fukuda, Tsuguo*; Tanaka, Momoko; Nishikino, Masaharu; Yamatani, Hiroshi*; et al.

no journal, , 

no abstracts in English

Oral presentation

Fluorescence from Ar$$_2$$ excimer using EUV free electron laser

Nishi, Ryosuke*; Minami, Yuki*; Yamanoi, Kohei*; Nakazato, Tomoharu*; Shimizu, Toshihiko*; Sarukura, Nobuhiko*; Iwayama, Hiroshi*; Shigemasa, Eiji*; Harries, J.; Nagasono, Mitsuru*

no journal, , 

no abstracts in English

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