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

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

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

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

8. 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 RT
Sputter Gas
2.7 mT Ar
2.7 mT Ar mT H2
Neutral sputtered atoms
Two separate targets:
Ti or Ni
plasma
magnetic field
lines -V
Growth rate: 0.4 Å /sec
Bi-layer spacing: ~80 Å

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

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

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

12. Auger Electron Spectroscopy Measurements of Atomic Concentration
20 ML w/o H (new Ti target)
20 ML w/o H (old Ti target)
20 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.
20 ML w/o H (old Ti target)
20 ML w/H

13. Correction to Theoretical 1st Order Peak Reflectivity

14. Temperature Programmed Desorption Measurements of Hydrogen Concentration
TiH2 powder
500 A Ti
40 ML
2 ML
Concentration of hydrogen
proportional to area under curve.
Sample
[H]/[Ti]
500 A
2.0
40 ML w/H
20 ML w/H
2.2
10 ML w/H
1.5
6 ML w/H
2.5
4 ML w/H
1.7
2 ML w/H
40 ML w/o H
0.7
20 ML w/o H
0.8
10 ML w/o H
1.0
6 ML w/o H
4 ML w/o H
0.9
2 ML w/o H
1.2
0.4
0.3

15. 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.
Munter et al., Physica B 221 (1996) 500.
Substitution of Be for Ni +
Addition of H to Ti

16. NBS Reactor LH2 Cold Source
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
20 ML
w/o H
10 ML
w/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