Addition of Hydrogen to Ni-Ti Multilayers:

1. Addition of Hydrogen to Ni-Ti Multilayers: Implications for Neutron Monochromator and Supermirror Performance Brent J. Heuser Dept. Nuclear, Plasma, & Radiological Engineering University of Illinois at Urbana-Champaign • Outline • Introduction—neutron monochromators, supermirrors, & guides • Sample preparation—magnetron sputtering (Ar or Ar+H2 gas) • Experimental results—NR, XRD, AFM, AES, TPD analysis • Discussion—effect of H; correlation between NR, AFM, & AES Supported by the DOE INIE Program

2. Acknowledgements Hyunsu Ju (NPRE UIUC) Sungkyun Park (IPNS ANL) Rick Goyette (SNS ORNL) UIUC FS-MRL staff: Tony Banks Nancy Finnegan Scott MacLaren Vania Petrova Mauro Sardela

3. Cold Neutron Guide Halls Orphée Reactor & Guide Hall at the LLB, Saclay Neutron guides transport long wavelength neutrons far from reactor containment where neutron and gamma-ray backgrounds are much lower. Guides are based on total external reflection and must be very efficient. NIST Reactor & Guide Hall

4. Neutron Guides Scattering Instrument Vacuum Reflective coatings Neutron Guides Evacuated channels with coatings on top, bottom, and sides that reflect neutrons. Cold Source LH2 or CH4 ~4-25 K

5. q fixed R l lc Multilayer films R Ni (Nb = 9.40 x 10-6 A-2) Interdiffusion barrier d Ti (Nb = -1.95 x 10-6 A-2) Q Review of Basic Neutron Optical Elements Single-layer films R l fixed q or Q qc or Qc

6. Review of Basic Neutron Optical Elements Total External Reflection q Bare Si Substrate q q Qc Substrate + Nickel Coating Substrate + Ni-58 Coating guide monochromator q Substrate + Ni-Ti Multilayer Coating

7. Supermirror films Continuous distribution of d-spacing values extends critical edge R l=8.8Å Q Hino et al., NIMB, 529 (2004) 54. Must be able to accept larger angular divergence or use shorter wavelength neutrons Internal coating Natural Ni Ni-58 (Gain~1.5) Ni-Ti Supermirror (Gain~m2) Neutron guides Review of Basic Neutron Optical Elements NiC-Ti

8. Substrate @ RT Sputter Gas 2.7 mT Ar 2.7 mT Ar + 0.3 mT H2 Neutral sputtered atoms plasma magnetic field lines Two separate targets: Ti or Ni -V Fabrication of Ni-Ti Multilayer Films Using Magnetron Sputtering Samples ~500 Å Ni ~500 Å Ti 1 Ni-Ti BL 2 Ni-Ti BL 4 Ni-Ti BL 6 Ni-Ti BL 10 Ni-Ti BL 15 Ni-Ti BL 20 Ni-Ti BL 40 Ni-Ti BL Growth rate: 0.4 Å /sec Bi-layer spacing: ~80 Å

9. R vs. Q—measurements and fits R vs. BL Number 40 BL 20 BL w/H w/H w/o H w/o H 10 BL 6 BL w/H Reflectivity Ratio w/H w/o H w/o H 4 BL 2 BL w/H w/H w/o H w/o H Neutron Reflectivity Measurements—POSY 2 @ IPNS-ANL

10. 6 BL 6 BL Fits to the Neutron Reflectivity Measurements Fits not unique!

11. 2 BL w/o H 6 BL w/o H 4 BL w/o H Ra=1.4 Å Ra=1.6 Å Ra=1.8 Å 10 BL w/o H 20 BL w/o H 40 BL w/o H Ra=5 Å Ra=7 Å Ra=9 Å 500 Å Ni 500 Å Ti 500 Å TiH2 Ra=4 Å Ra=15 Å Ra=11 Å Atomic Force Microscopy Measurements of Surface Roughness Gradual increase in roughness of top surface is observed that is consistent with degradation of reflectivity for BL > 6.

12. 20 ML w/o H (new Ti target) 20 ML w/o H (old Ti target) 20 ML w/o H (old Ti target) 20 ML w/H 20 ML w/H Auger Electron Spectroscopy Measurements of Atomic Concentration Oxygen content at noise level; oscillations in oxygen signal in 20 w/H ML sample have same period as Ti and Ni oscillations, but correlated to Ti. Concentration profiles for Ti in the with-hydrogen ML samples are flat indicating uniform hydrogen concentration within Ti layers. Ti and Ni signal oscillations in ML samples dampen away from the film-substrate inter- face, consistent with increase surface roughness for high BL number observed with AFM.

13. Correction to Theoretical 1st Order Peak Reflectivity

14. Concentration of hydrogen proportional to area under curve. 500 A Ti TiH2 powder 40 ML 2 ML Temperature Programmed Desorption Measurements of Hydrogen Concentration

15. Substitution of Be for Ni + Addition of H to Ti Munter et al., Physica B 221 (1996) 500. Conclusion Addition of hydrogen to Ti works—increase in 1st order diffraction peak reflectivity observed. Gains in on-sample intensity of 2-3 should be possible without too much effort. Degradation in 1st order peak reflectivity with BL value consistent with surface roughening observed with AFM. Larger interfacial roughness as BL value increases was observed with AES, consistent with AFM.

16. Orphee Reactor—LLB Saclay NBS Reactor LH2 Cold Source NIST

17. Auger Electron Spectroscopy Measurements of Atomic Concentration 40 ML w/H Oxygen content at noise level; oscillations in oxygen signal in 20 w/H ML sample have same period as Ti and Ni oscillations, but correlated to Ti. Concentration profiles for Ti in the with-hydrogen ML samples are flat indicating uniform hydrogen concentration within Ti layers. Ti and Ni signal oscillations in ML samples dampen away from the film-substrate inter- face, consistent with increase surface roughness for high BL number observed with AFM. Bulk Ni 20 ML w/H Bulk Ti 10 ML w/H 20 ML w/o H

19. Addition of Hydrogen to Ni-Ti Multilayers: Implications for Neutron Supermirror Performance Brent J. Heuser, UIUC Hyunsu Ju, UIUC Sungkyun Park (ANL), Rick Goyette (ANL), Tony Banks (UIUC), Nancy Finnegan (UIUC), Scott MacLaren (UIUC), Vania Petrova (UIUC) Mauro Sardela (UIUC) Neutron optics—monochromators and supermirrors Sample preparation. Experimental results—NR, XRD, AFM, AES, TPD analysis Supported by the DOE INIE Program