EUV FELWS nishikino 1211pf...R. Kato, EUVL workshop 2016 “The Design and Development of a 10-kW...

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Transcript of EUV FELWS nishikino 1211pf...R. Kato, EUVL workshop 2016 “The Design and Development of a 10-kW...

Page 1: EUV FELWS nishikino 1211pf...R. Kato, EUVL workshop 2016 “The Design and Development of a 10-kW Class EUV-FEL Project in Japan “ 2nd EUV-FEL WORKSHOP 2017.12.12 The EUV source

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2nd EUV-FEL WORKSHOP 2017.12.12

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2nd EUV-FEL WORKSHOP 2017.12.12

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CollaboratorsM. Ishino, Thanh-Hung Dinh, N. Hasegawa (QST)

S. Ichimaru, M. Hatayama, T. Haga�NTT-AT�

K. Sakaue, M. Washio�Waseda Univ.�

H. Hara, T. Higashiguchi�Utsunomiya Univ.�

T. Itani, Julius Joseph Santillan (EIDEC)

T. Kozawa�Osaka Univ.� K. Okamoto�Hokkaido Univ.�

Anatoly Faenov, Tatiana Pikuz�Osaka Univ., RAS�

H. Kinoshita�Univ. of Hyogo� T. Hatano(Tohoku Univ.�

T. Suemoto �Toyota Physical and Chemical Research Inst.�

A. Kon, Y. Inubushi�JASRI� S. Owada�Riken�

Nikita Medvedev (IPP, Czech) Beata Ziaja (DESY)

The XFEL experiments were performed at the BL1 of SACLA with the approval of JASRI (Proposal No. 2016B8006, 2017A8026, and 2017B8004).

2nd EUV-FEL WORKSHOP 2017.12.12

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Contents

1. Introduction� Motivation.for.the.understanding.of.EUV.laser.ablation

2.-Interaction-with-SXFEL� SXFEL.ablation.(Al.&.Si)� SXFEL.damage.(Mo/Si.&.Resist)� SXFEL.exposure.and.SXFEL.direct.processing

3.-Summary

2nd EUV-FEL WORKSHOP 2017.12.12

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Motivation.for.the.understanding.of.EUV.laser.ablation

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Interaction with EUV laser pulse (ps-XRL)

Faenov,(Appl.(Phys.(Lett.(94,(231107((2009)

Photon&energy&of&pump&light&(eV)

Flue

nce&&(J/cm

2 )

�����

����

���

��

� � �

�� � � �

��� � � �

����

1053nm2&ns&pulse

1ps

0.4&ps&pulse

46.9nm&XRL1.7&ns&(Italy)

LiF

Si

Low&ablation&threshold

13.9nm(XRL7ps(pulse(JAEA)

M. Ishino et al., J. Appl. Phys. 109, 013504 (2011).

M. Ishino et al., Appl. Phys. A 110, 179 (2013).

Al

Au Si

NanoMscale&surface&structure

2nd EUV-FEL WORKSHOP 2017.12.12

The(law(ablation(threshold(of(a(material(for(an(XRL(beam(has(a(possibilityof(efficient(machining(by(a(lithography(process(and(an(ablation(process.(

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Requirement.for.High.power.EUV.source

EUVL DEVELOPMENT

EUV source power

EUV exposure system

250~ W

semiengineering.com

500~1000 W(for HVM)

Next generation photon source for EUVL ?

R. Kato, EUVL workshop 2016“The Design and Development of a 10-kW Class EUV-FEL Project in Japan “

2nd EUV-FEL WORKSHOP 2017.12.12

The EUV source power is need further improvement to HVM requirements.

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Challenge.for.high.performance.EUV.mirror

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collaborated with NTT-AT

Interaction with EUV laser pulse (ps-XRL)

Motivation.for.the.understanding.of.EUV.laser.damage

High power EUV source

Highly-durable EUV optics

Compressed Mo/Si structure around damage

XRL damage spot

Compressed structure around damage

Mo/Si&ML&mirror&ablation

Lurking structure in bottom

Damage(ablation) risk-Multilayer mirror-

-Pellicle--Resist-

Mo/Si Nb/Si

2nd EUV-FEL WORKSHOP 2017.12.12

The Nb/Si multilayer has potential for higher resistance of High power EUV light source.

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2.-Interaction-with-SXFELSXFEL.ablation.(Al.&.Si)

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G & 3-‐‑‒f F f frvx r±kn f s

IUV KISM [XNIKM TVLQNQKI QVU IUL NVXTI QVU QUL[KML J [S XI PVX VN XI SI MX [S MG &,2-‐‑‒BF65 z in f s4PISSMUOQUO [X M VN 5 XMTM S XI QVSM Q PVOXI P QUO BF65 BV[XKMG &,3-‐‑‒ )5 E r±knBF65 c s r lxAM MIXKP VU QU MXIK QVU VN BF65 ]Q P TI MX NVX 5 E [S XI XMKQ QVU UIUV NIJXQKI QVU

2nd EUV-FEL WORKSHOP 2017.12.12

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We.have.started.the.comparison.study.of.pulse.duration.dependence.using.the.two.EUV.lasers..

SXFEL & LP-XRL

(-Wavelength : 13.9nm (89.2eV)Energy: ~0.5 µJPulse width : ~10 psDivergence: < 1mrad

0 0

-( (

Laser plasma(30-50 µmf x 5~ mm)

0.2mrad7 ps

PlasmaEUVlaser

EUVlaser

) (

Double target (Ag)!

EUV$laser$

Glass laser!

01 SXFEL

) ( ) ( ( Wavelength : 13.5nm (92eV)Energy: ~80 µJDivergence: < 1mrad

Fig.1 Experimental setup @ SACLA-BL1, Dec 2016 and Jun 2017

Photon energy: 92 eV (Δλ = 4 eV)Pulse energy: 80 µJ/pulse (±15%)Pulse duration: 200 fs (100- 300 fs)

X-ray filtersZr & Si

Target

KB mirror

CCD energy monitor

X-ray filters

Gas energy monitor

Irradiation condition

Focal spot size at FWHM (typical):Horizontally: 10.5µmVertically: 8.5 µm

Fluence: 5 – 1000 mJ/cm2

Target: Si with a thickness of 0.34 mm

CCD image

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ü Pulse energy on target was evaluated by a CCD energy monitor. It alsowas recorded shot-by-shot by a gas energy monitor during the ablationexperiment.

ü Transmittance of x-ray filters, and sensitivity of the CCD camera werecalibrated by using synchrotron lightof the Photon Factory in Japan.

ü From images of the CCD monitor, the spatial profile of FEL spot ontarget is expected to be a gaussian one.

SACLA-BL1

SACLA-BL1(SXFEL)

Discussion

1. Fluctuation of the FEL

During the experiment, only pulse energy of the FEL was recorded by the gasmonitor in Fig. 1. Other parameters of the FEL such as pulse duration, spectraland spatial profile was not monitored at the same time.

In general, the fluctuation in spectral profile and its influence to theexperimental result are usually small. On the other hand, the fluctuation inspatial profile may cause a large fluctuation in the ablation experiment. Fig. 3(b) and (c) indicate a good and a bad single shot spatial profile of recorded bythe CCD camera in Fig. 1, respectively. Such bad spatial profile was observedat a rate of ~20%.

A this time, it is difficult to measure the pulse duration of the FEL. So, we wouldlike to know how the fluctuation in pulse duration influence to the experimentresults from a theoretical calculation.

By XTANT, are there any differences for pulse durations in range for, anexample,<100 fs, 100~300 fs, and >300 fs at 92 eV photon energy?

CCD image

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Fig. 3 Typical spectral (a) and spatial (a, b) profile of the FEL

92nd EUV-FEL WORKSHOP 2017.12.12

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SXFEL & LP-XRL

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We.have.started.the.comparison.study.of.pulse.duration.dependence.using.the.two.EUV.lasers..

2nd EUV-FEL WORKSHOP 2017.12.12

Background : High power & short pulse soft X-ray lasers

K.Togawa etal.,ProceedingsofIPAC2017

SXFEL at SACLA-Bl1

Plasma-based x-ray laser

Ø Photon energy: 20 to 150 eV

(softx-rayregion)

Ø Pulse energy: 100-µJ class

Ø Pulse width: 200 fs (100~300 fs)

Ø Repetition rate: 60 Hz

Ø Photon energy:89eV(13.9nm)

Ø Pulse energy: 100-nJ class

Ø Pulse width: 7 ps

Ø Repetition rate: 0.1 Hz

Study on dependence of pulse duration is enabled

1sttarget

2ndtarget

XRL5-10mradFullyspatialcoherent

Ni-likeSilverSXRL[13.9nm(89eV)]

XRLseeder

XRLamplifier Pumplaser~0.1Hz

Pumplaser~0.1Hz

2017/9/5 The78thJSAPAutumnMeeting,Fukuoka 2

Study on dependence of pulse duration is enable

92 eV & 200~ fs

89 eV & ~10 ps

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Experimental-setup-at-SACLA@BL1SXFEL experiment

112nd EUV-FEL WORKSHOP 2017.12.12

X"ray&filtersZr &&Si

Target

KB&mirror

CCD&energy&monitor

X"ray&filters

Gas&energy&monitor

CCD image

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Photon&energy:&92&eV&(Δλ&=&4&eV)Pulse&energy:&80&µJ/pulse&(±15%)Pulse&duration:&200&fs&(100F 300&fs)

SACLAKBL1

Irradiation.condition.

Focal&spot&size&at&FWHM&(typical):Horizontally:&10.5µmVertically:&8.5&µm

Fluence:&5&– 1000&mJ/cm2

Target:&Al,&&Si,&Mo,&Mo/Si,&Resist&etc…&

Irradiated sample(Al)

Target chamber

SXFEL

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X@ray-filter-&-CCD-camera-were-calibrated-atKEK@PF-BL11D.

SXFEL experiment

122nd EUV-FEL WORKSHOP 2017.12.12

Schematic of a CCD-based beam monitor

X-rayCCDcameraX-rayfilters

Softx-ray

ResponsivitycalibratedatPF-BL11D

TransmittancemeasuredatPF-BL11D&SACLA-BL1

Beam monitor

① Detail report of calibration process

② A practical use of the beam monitor

2017/9/5 The78thJSAPAutumnMeeting,Fukuoka 4

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Spallative.ablation.structures.on.Al.surfaces

SEM.image

8 PQUV M IS 9B2 MM QUOg &,

SXFEL: != 13.5 nm, " = 100–300 fs SXRL: ! = 13.9 nm, " = 7 ps

�Attenuation length : ~40 nm�Rim structure�Nano scale conical structure�Threshold fluence :15~20 mJ/cm2

132nd EUV-FEL WORKSHOP 2017.12.12

#ps-XRL resultsM. Ishino et al., J. Appl Phys (2011)S. V. Starikov et al., Appl. Phys. B 116, 1005 (2014).

Single shot (20~ mJ/cm2) Single shot (~20 mJ/cm2)

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Theoretical.calculation.of.spallation.process

Metal

152nd EUV-FEL WORKSHOP 2017.12.12

(a) Nucleation of interatomic size form(b) + (c) Inflation of the foams(d) Run away of the spallative layerFinally Appearance of surface nano-relief

M. Ishino et al., J. Appl. Phys. 109, 013504 (2011).

Spallation is long term process in comparison with SXRL pulse width.

Process duration >> Pulse width(more than 100 ps) (7 ps)

Al attenuation length: ~40 nm

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Deep.hole.on.Si.surfaces

LSM.SEM.AFM.image

SXFEL: λ = 13.5 nm, τ = 100–300 fs SXRL: λ = 13.9 nm, τ = 7 ps

�Attenuation lengty : ~600 nm�Melting-like deep hole�Threshold fluence :300~400 mJ/cm2

152nd EUV-FEL WORKSHOP 2017.12.12

#ps-XRL resultsM. Ishino et al., Appl Phys A(2013)

1shot (~500 mJ/cm2)

Single shot (~20 mJ/cm2)

TalyMap Platinum

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水平距離 2.493 µm

垂直高さ 675.799 nm

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Comparison.of.Simulation.resultSi.ablation

Evaluation from simulation resultTHERMAL AND NONTHERMAL MELTING OF SILICON . . . PHYSICAL REVIEW B 91, 054113 (2015)

FIG. 10. (Color online) Damage threshold fluences for siliconcorresponding to the low-density liquid and high-density liquidformation as a function of photon energy.

incoming photon energy. Thus, by converting the dose per atominto the units of incoming fluence with one-photon absorptioncross section from Refs. [55–57], we obtain the damagethreshold predictions shown in Fig. 10. They can be directlyverified experimentally. No effects of thermal diffusion andparticle diffusion were taken into account for the predictionsfrom Fig. 10. They can play a role for the case of small skindepth (the minimum around 20 eV on the picture). Due tothese effects, and possible resolidification governed by theenergy flows out of the laser spot, at such photon energies ourcalculations might underestimate the experimentally measureddamage thresholds.

C. Purely nonthermal melting of silicon

Finally, for comparison we show the predictions for siliconmelting obtained after excluding the nonadiabatic effects(electron-phonon coupling). Within the adiabatic (Born-Oppenheimer) scheme the calculated damage threshold fornonthermal melting of silicon appears to be at the absorbeddose of 2.1 eV/atom. This corresponds to 9% of electronsexcited from the valence to the antibonding states of theconduction band. This threshold value of the electron densityis in an excellent agreement with earlier works [1,2], based onthe adiabatic scheme.

The atomic snapshots shown in Fig. 11 demonstrate thefinal state to be an amorphous high-density liquid [58]. Thetransition to that state proceeds on sub-picosecond time scalesat which thermal effects—if included—would play a role. Theintermediate LDL phase can be identified by the collapsedband gap and increased volume of the modeled supercell (de-creased density) prior to the final contraction to the HDL phase.

As discussed above, the model of nonthermal meltingof silicon based on the Born-Oppenheimer approximationdoes not allow for electron-phonon coupling; i.e., the excitedelectrons do not exchange energy with atoms. The damagethen occurs as a purely nonthermal effect of weakening theinteratomic bonds due to electron excitation. This resultsin much higher damage threshold than that obtained with

FIG. 11. (Color online) Nonthermal phase transition: snapshotsof atomic positions in silicon irradiated with 10 fs laser pulse of!ω = 1 keV photon energy at the absorbed dose of 2.5 eV/atom: (a)t = 0 fs, (b) t = 300 fs, (c) t = 0.5 ps, and (d) t = 1 ps. X, Y, and Zaxes are shown (left bottom of each panel).

a nonadiabatic approach. These findings also indicate thatthermal models such as [11–13,17] can be accurately appliedfor silicon irradiated with laser pulses of low fluences, whenthe nonthermal effects do not play a significant role.

IV. CONCLUSION

In the present work, we studied phase transitions in siliconunder a femtosecond irradiation with an x-ray laser. In orderto account both for thermally and nonthermally triggeredtransitions, we have extended our recently developed hybridmodel [19,20] by including nonadiabatic electron-phononcoupling. In this way heating of a material due to theelectron-phonon coupling can also be treated. The developedscheme is general and can be used in any ab initio moleculardynamics model.

We demonstrated that for silicon under a femtosecondx-ray irradiation, the nonadiabatic energy exchange triggersa phase transition into low-density liquid phase above thethreshold of ∼0.65 eV per atom in terms of the absorbeddose. This semimetallic state is characterized by a closedband gap, with the local order present in atomic structure.At higher doses above ∼0.9 eV/atom, silicon melts into high-density liquid phase with amorphous atomic arrangement. Themodeled phase transition occurs within ∼300−500 fs, in goodagreement with the time scales observed in experiments. Wehave also predicted the damage threshold fluence in silicon asa function of the incoming photon energy.

The transition into high-density liquid phase proceeds as aresult of the interplay between nonthermal and thermal effects.Weakening of interatomic bonds and heating of the lattice byexcited electronic subsystem triggers ultrafast amorphizationof silicon. Neglecting electron-phonon coupling results in asignificant overestimation of the phase transition threshold,which then is ∼2.1 eV/atom. This threshold discrepancy

054113-7

N. Medvedev PRB91, 054113 (2015)

300 mJ/cm2

18

THERMAL AND NONTHERMAL MELTING OF SILICON . . . PHYSICAL REVIEW B 91, 054113 (2015)

FIG. 10. (Color online) Damage threshold fluences for siliconcorresponding to the low-density liquid and high-density liquidformation as a function of photon energy.

incoming photon energy. Thus, by converting the dose per atominto the units of incoming fluence with one-photon absorptioncross section from Refs. [55–57], we obtain the damagethreshold predictions shown in Fig. 10. They can be directlyverified experimentally. No effects of thermal diffusion andparticle diffusion were taken into account for the predictionsfrom Fig. 10. They can play a role for the case of small skindepth (the minimum around 20 eV on the picture). Due tothese effects, and possible resolidification governed by theenergy flows out of the laser spot, at such photon energies ourcalculations might underestimate the experimentally measureddamage thresholds.

C. Purely nonthermal melting of silicon

Finally, for comparison we show the predictions for siliconmelting obtained after excluding the nonadiabatic effects(electron-phonon coupling). Within the adiabatic (Born-Oppenheimer) scheme the calculated damage threshold fornonthermal melting of silicon appears to be at the absorbeddose of 2.1 eV/atom. This corresponds to 9% of electronsexcited from the valence to the antibonding states of theconduction band. This threshold value of the electron densityis in an excellent agreement with earlier works [1,2], based onthe adiabatic scheme.

The atomic snapshots shown in Fig. 11 demonstrate thefinal state to be an amorphous high-density liquid [58]. Thetransition to that state proceeds on sub-picosecond time scalesat which thermal effects—if included—would play a role. Theintermediate LDL phase can be identified by the collapsedband gap and increased volume of the modeled supercell (de-creased density) prior to the final contraction to the HDL phase.

As discussed above, the model of nonthermal meltingof silicon based on the Born-Oppenheimer approximationdoes not allow for electron-phonon coupling; i.e., the excitedelectrons do not exchange energy with atoms. The damagethen occurs as a purely nonthermal effect of weakening theinteratomic bonds due to electron excitation. This resultsin much higher damage threshold than that obtained with

FIG. 11. (Color online) Nonthermal phase transition: snapshotsof atomic positions in silicon irradiated with 10 fs laser pulse of!ω = 1 keV photon energy at the absorbed dose of 2.5 eV/atom: (a)t = 0 fs, (b) t = 300 fs, (c) t = 0.5 ps, and (d) t = 1 ps. X, Y, and Zaxes are shown (left bottom of each panel).

a nonadiabatic approach. These findings also indicate thatthermal models such as [11–13,17] can be accurately appliedfor silicon irradiated with laser pulses of low fluences, whenthe nonthermal effects do not play a significant role.

IV. CONCLUSION

In the present work, we studied phase transitions in siliconunder a femtosecond irradiation with an x-ray laser. In orderto account both for thermally and nonthermally triggeredtransitions, we have extended our recently developed hybridmodel [19,20] by including nonadiabatic electron-phononcoupling. In this way heating of a material due to theelectron-phonon coupling can also be treated. The developedscheme is general and can be used in any ab initio moleculardynamics model.

We demonstrated that for silicon under a femtosecondx-ray irradiation, the nonadiabatic energy exchange triggersa phase transition into low-density liquid phase above thethreshold of ∼0.65 eV per atom in terms of the absorbeddose. This semimetallic state is characterized by a closedband gap, with the local order present in atomic structure.At higher doses above ∼0.9 eV/atom, silicon melts into high-density liquid phase with amorphous atomic arrangement. Themodeled phase transition occurs within ∼300−500 fs, in goodagreement with the time scales observed in experiments. Wehave also predicted the damage threshold fluence in silicon asa function of the incoming photon energy.

The transition into high-density liquid phase proceeds as aresult of the interplay between nonthermal and thermal effects.Weakening of interatomic bonds and heating of the lattice byexcited electronic subsystem triggers ultrafast amorphizationof silicon. Neglecting electron-phonon coupling results in asignificant overestimation of the phase transition threshold,which then is ∼2.1 eV/atom. This threshold discrepancy

054113-7

MD simulation

2nd EUV-FEL WORKSHOP 2017.12.12

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2.-Interaction-with-SXFELSXFEL.ablation.(Mo/Si.&.Resist)

192nd EUV-FEL WORKSHOP 2017.12.12

Collaboration withNTT-AT, Waseda Univ., Utsunomiya Univ., and EIDEC

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Damage.induced.by.psKXRLMo/Si.mirror.damage

202nd EUV-FEL WORKSHOP 2017.12.12

S. Ichimaru et al., Proc. ICXRL 2016 (will be published).

Ablation threshold of Mo/Si multilayers evaluated by EUV lights・~45 mJ/cm2: FEL (FLASH), λ = 13.5 nm, τ = 10 fs [A. R. Khorsand et al., Opt. Express 18, 700 (2010).]・~200 mJ/cm2: Plasma source, λ = 13.5 nm, τ = 8.8 ns [M. Müller et al., Appl. Phys. A 108, 263 (2012).]

ps-XRL: Single shot (20~ mJ/cm2) Normal incidence

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Experimental-setup-at-SACLA@BL1SXFEL experiment

242nd EUV-FEL WORKSHOP 2017.12.12

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332nd EUV-FEL WORKSHOP 2017.12.12

Summary

NanoKscale.surface.modificationsTWe.show.the.surface.ablation/modifications.formed.on.Al.and.Si.induced.by.single.or.multiple..SXFEL.pulse.irradiations.TSurface modification thresholds of SXFEL pulse for materials are essentially lower than thoseof optical lasers.TThe MD simulation developed for soft xKray ablation reveals the spallation process for surfacemodifications.

EUV.lithography.components.testTWe.started.the.EUV.damage.test.on.multiKlayered.mirrors.and.EUV.lithography.components.TThe surface damage are occurred in essentially lower fluence than those ofnsKplasma xKray source.TThere.is.a.possibility.that..the.exposure.sensitivity.is.also.lower.than.a.ablation.threshold.

ACKNOWLEDGEMENTS This work was partly supported by Grant-in Aid for Scientific Research (25390103, 25289244, 26286078 16K04989, 16K05030

and 16F16019) from the Japan Society for the Promotion of Science and the Russian Foundation for Basic Research (RFBR) Grant No. 12-02-00947a. This work was also supported by the Japan Society for the Promotion of Science (JSPA) and Russian Academy of Sciences (RAS) under the JSPS-RAS Joint Research Program (RFBR Grant No. 14-02-92107).