Preliminary characterization of first multilayer mirrors for the soft X-ray water-window

Transcription

1 Preliminary characterization of first multilayer mirrors for the soft X-ray water-window Gianfelice Cinque, Augusto Marcelli, Antonio Grilli and Agostino Raco INFN, Laboratori Nazionali di Frascati, via E. Fermi 40, I Frascati, Italy Valentino Rigato, Alessandro Patelli and Valentina Mattarello INFN, Laboratori Nazionali di Legnaro, viale dell Università 2, I Legnaro, Italy Giannantonio Cibin IMONT, Piazza dei Caprettari 70, I Roma, Italy Design and test of high reflectivity devices for soft X-rays at quasi-normal incidence: Synchrotron Radiation soft X-ray microscopy of organic systems and X-ray microprobe. Multilayer mirrors for almost monochromatic X-rays in the low energy range, and quasinormal incidence to fully exploit the angular aperture. Design and deposition of multilayer at the INFN Legnaro Laboratories: first Ni/Ti and Ni/TiO 2 multilayers with Λ > nm and number of layers from 150 to 300. High Vacuum compatible reflectometer set-up at the INFN Frascati Laboratories: characterization of the multilayer reflectivity by SR beam below 1 kev at DAΦNE.

2 X-ray microscopy in reflection: an example ~10 mm Spherical Reflecting optics ~20 mm X-ray fan angle of incidence F t a b horizontal divergence 5 mrad vertical divergence 5-3 mrad Object F s DAΦNE@LNF SR source Image in collaboration with A.Faenov, T.Pikuz and A.Reale L Aquila Univ. M. Sanchez del Rio et al., A novel imaging x-ray microscope based on spherical crystal, Rev. Sci. Inst. 72(8) (2001) 3291.

3 Normal incidence multilayer mirrors ni = 1 δ i m 2δ λ = 2Λsinϑm 1 2 sin ϑ m δ = ( d 1 δ1 + d 2δ 2 ) /( d1 + d 2 ) Λ = d absorber + d Λ δλ Γ = 10 spacer d d abs tot m = 1 90 ϑ 1 δ i <<1 2Λ λ

4 Multilayer material: selection for the X-ray water-window 2 χ r r λ n π () () () ( ) 0 r = ε r = + χ r 1 + = 1 ρ()( r f if ) = 1 δ iβ Low absorption from spacer and absorber Max contrast from the absorber Spacer material sets the working range Sharp interfaces Ni/Ti Water window Astrophysics FEL A.V. Vinigradov and B.Ya. Zeldovich, "X-ray and far UV multilayers mirrors", Appl. Optics., 16, 89 (1977)

5 Mo/Si and Ni/Ti(O x ) deposition set-up at the LNL Chamber 3 sputtering cathodes RF(13.56MHz)-driven Process gas: Ar, Xe, O 2 DC biasable sample-holder ( V) Helmoltz coils (0 60G) Quartz micro-balances quadrupole mass spectrometer Cylindrical Langmuir probe Computer control Up to 500 Ni/TiOx bi-layers Shutters position Sample-holder position DC sample-holder bias cathodes applied power Helmoltz coils current O 2 gas admission base pressure < mbar operating Ar pressure mbar

6 First Ni/Ti and Ni/TiO x multilayers deposition at LNL Multilayer Ni/TiOx 3 multilayers deposited in the Work on nickel titanium oxide: NT015 project of 150 periods of Ni/TiO 2 on Si(100) substrate Nominal values: TiO thickness 8.6Å Ni thickness 6.0Å Multilayer Ni/Ti 4 multilayers deposited in the work on nickel titanium: NT012 project of 300 periods Ni/Ti on Si(100) substrate

7 Normalized Yield First Ni/Ti and Ni/TiO x multilayers: characterization by RBS Multilayer Sam ple NNi/Ti T 010 NT012 project 300 periods Ni/Ti on Si(100) substrate E n e r g y (M e V ) 5 A r Ti N i C h a n n e l RBS: α-beam a 2.2, 2.0 and 1.8 MeV scattering angle Spectrum: no sample contamination by Ar values: Ti thickness 5.5Å Ni thickness 7.6 Å

8 Soft X-ray reflectometer at LNF double-crystal monochromator DAΦNE e - ring Wiggler SR source beamline multilayer UHV exp. chamber and detector The Wiggler source gives a continuous SR spectrum of softer X- rays with critical energy ~300 ev. Bragg diffraction by a couple of KAP(100) crystals (2d=26,6Ǻ) is used for the X-ray energy selection down to 480eV. A double goniometer allows ω scans and θ 2θ scans under vacuum with an angle precision/accuracy better than 1/2000 degrees in closed-loop.

9 DAΦNE as Synchrotron Radiation source The electron ring of the DAΦNE collider has unique characteristics as Synchrotron Radiation source: since the low energy, 0,51 GeV, and the high circulating current, routinely over 1 A, an intense photon flux spectrally peaked in the lower energy range is provided. ph/(s mrad 2 ) Δλ/λ=0.1% 1E15 1E14 1E13 1E12 1E11 1E10 1E9 1E8 1E7 Wiggler SR at 1 A KAP(100) 4390 ev 1800 ev 5600 ev Si(111) Ge(111) SiO 2 (1010) KTP(011) ev ev ev1960 ev ev 2000 ev X-rays Wiggler critical energy ~300eV X-ray fan 5 x 2 mrad 2 (h x v) θ = 1/γ = 1 mrad

10 Boomerang monochromator and KAP crystals KAP(100) crystal n.4 2d=2.51nm ΔE/E=1/200 XRD by Cu Kα 1 line [cps] Huber θ 2θ goniometer 8048 kv 8 ma X-rays SR ω [degrees] Double-crystal fixed-exit movement spanning Bragg angles from 15 to 75 KAP(100) crystals tested by a Cu source and a θ 2θ diffractometer XRD by Claudio Veroli and Giorgio Cappuccio CNR-ICSM

11 HV experimental chamber and θ 2θ goniometer 2 Micos Precision Rotation Stage PRS UHV VG magnetic rotary feedthrough 2-phase-micro-step endless motors contactless limit-reference switches optical rulers for absolute positioning Rotation Range ( ) 360 endless Accuracy ( ) +/ Repeatability ( ) +/ Reversal Error ( ) Resolution: Open-Loop ( ) Closed-Loop ( ) Micos CORVUS 2 axes Microstep Controller + manual Joystick/Display ADC Input 12 bit for signal 0-10V LabVIEW code for ω scan and θ 2θ scans Absolute photodiode AXUV100EUT Area 10x10 mm² UHV preamp 10V/nA +/-1% SR SR

12 Preliminary tests on a Si/Mo multilayer at LNF: Characterization of the reflectometer set-up by an ω-scan 8 7 Si/Mo Λ = 64 Å 40 bilayers optimized for eV@8deg Si(1-1-1)@2,8keV detector S [V] whitebeam SR ω scan@45deg multilayer@550ev (50%) +825eV (33%) +965eV (16%) 1 upward scan downward scan 0 average-background ω [degrees]

13 Preliminary measurements on Ni/Ti multilayers at LNF: characterization of the reflectivity by an ω-scan Ni/Ti 300 bilayers 4 1 st scan upward 2 nd scan downward S [V] SR 670eV ω scan 3 rd scan upward 4 th scan downward average-background (x4) ω [degrees]

14 Ni/Ti multilayer test by XRD and XRR: XRD by Claudio Veroli and Giorgio Cappuccio CNR-ICSM Ni/Ti 300 layers XRD by Cu Kα 1 line Huber θ 2θ goniometer kv 30 ma max deg fwhm/peak=1/ [cps] [cps] ω [deg] ω [deg] XRR Cu k α line (0.154 nm) - Padova Univ. Ni/Ti 300 layers Λ = ± 0.07Å Ni/TiO x 150 layers Λ = ± 0.18 Å

15 from XRR measurements: Ni/Ti and Ni/TiO x now: Λ Ni/Ti = ± 0.07Å Λ Ni/TiOx = ± 0.18 Å from XRD intensity comparison: R Ni/Ti = 1/8 R Si/Mo (72%) R Ni/Ti ~ 9 % from SR ω-scan reflectivity comparison: R Ni/Ti = 1/15 R Si/Mo (72%) R Ni/Ti ~5% R Ni/Ti ~ 7 % Future Ideal multilayers taylored for the water-window: energy scan simulation of ideal Ni/Ti and Ni/TiO 2. Reflectivity (%) R max 425.8eV α =1 M u ltilayer N i/tio 2 N=500 Γ =0.39 Λ =14.6 Å M u ltilayer N i/ti N =500 Γ =0.39 Λ =14.6 Å R max 426eV Incident Energy (ev)

16 Conclusions: The spectral region from 24 to 300 Å is strategical for fundamental research in astrophysics, for projection nano-lithography and for applications of future FEL. In the so-called water-window between O and C K-edges, the X-ray microscopy on organic systems, cells and organelles, becomes important as well as the X-ray microprobe spectroscopy by Synchrotron Radiation. INFN Gr.V supports the experiment ARCHIMEDE (ARCHItects of Mirror Euv Devices) between LNL and LNF: => tayloring and deposition of multilayers at LNL => HV soft X-rays reflectometer set-up at LNF. a special thanks to: Giacomo Viviani and Marco Pietropaoli - INFN-LNF Giorgio Cappuccio and Claudio Veroli CNR-ISMN

17 Soft X-ray beamline at DAΦNE slits UHV window monochromator G. Cinque et al., The Soft X-ray Beamline at Frascati, SPIE Proc (2005) 448.

18 ML mirrors in astrophysics EIT SUN DISK IMAGE: EMISSION from Fe IX, X at 171 Å (SOHO Mission NASA Goddard Space Flight Center) Solar disk and corona emission