Page 32 - ILL Annual Report 2019

MATERIALS SCIENCE
Max Wolff. German/Swedish Department of Physics and Astronomy, Uppsala University, Sweden
‘I am a lecturer in neutron scattering at Uppsala University, Sweden, I am interested in functional materials, with an emphasis on energy materials, magnetic liquids and
polymers. Neutron scattering techniques provide unique and decisive information in all these areas.’
Nuclear spin-incoherent neutron scattering from quantum well resonators
Reflectometer for the analysis of materials SuperADAM
The high penetration of neutrons allows for the study of buried interfaces, while the energy of cold neutrons makes them an excellent probe of dynamics. However,
the limited brilliance of neutron sources makes the combination of reflectometry and spectroscopy challenging. This is especially true for thin films containing hydrogen, which scatters mainly nuclear spin-incoherent.
On the one hand this scattering allows probing tracer diffusion but is, on the other hand, often seen as background signal in studies at low momentum transfer Q. We have quantified the nuclear spin incoherent scattering from a 100 nm thick metal hydride film, paving the way towards studies of surface dynamics using neutrons.
AUTHORS
M. Wolff (Uppsala University, Sweden)
A. Devishvili (ILL)
B.P. Toperverg (Petersburg Nuclear Physics Institute, Russia)
ARTICLE FROM
Phys. Rev. Lett. (2019)—doi: 10.1103/PhysRevLett.123.016101
REFERENCES
[1] M. Wolff, EPJ Web of Conferences 188 (2018) 04002
[2] W.A. Hamilton, G.A. Klein, G.I. Opat and P.A. Timmins, Phys. Rev.
Lett. 58 (1987) 2770
[3] F. Pfeiffer, V. Leiner, P. Høghøj and I. Anderson, Phys. Rev. Lett. 88
(2004) 055507
[4] S.A. Holt, A.P. Le Brun, C.F. Majkrzak, D.J. McGillivray, F. Heinrich,
M. Lösche and J.H. Lakey, Soft Matter 13 (2009) 2576
[5] M. Wolff, A. Devishvili, J.A. Dura, F.A. Adlmann, B. Kitchen,
G.K. Palsson H. Palonen, B.B. Maranville, Ch.F. Majkrzak and B.P. Toperverg, Phys. Rev. Lett. 123 (2019) 016101
Together with grazing-incidence neutron and X-ray scattering, surface science has advanced enormously. Nevertheless, many scientific questions remain unresolved. These include spin-wave dispersions, as well as dynamics of glass formers and self-assembled monolayers. An important aspect in biology is the dynamics of water close to membranes, while understanding the dynamics of lithium and protons in thin films is crucial for developing energy storage and conversion materials.
With neutrons, the density profile across an interface is extracted from specular reflectivity. Fewer studies probe in- plane structures [1] and almost none dynamics [2], since the brilliance of neutron beams is limited. One way to enhance surface signals is by using quantum resonators [3]. We combine this method with magnetic contrast variation [4] to gain additional control of the neutron wave field.
Figure 1 shows the scattering length density (SLD) profile
of neutrons impinging under grazing incidence onto a 100 nm-thick vanadium hydride resonator sandwiched between iron layers. The film is grown epitaxially on MgO and covered by palladium and aluminium oxide to prevent oxidation. For
10
-2 10
-3 10
-4 10
10-5
10 100 10 11
Data/Mo+de+l Spinstate
-1-1 0
Pd
12 12 Fe Fe
VH
10 10
-1
10
10 / – + 8
0.75 nm 0.75 nm
V/VO x
10-2 10- - 8 10
4
15.7 nm 15.7 nm
Fe Fe
6
-3
d
m
V V
1 10
10- - / – + + – 6
Iron
10
3
-3
0
2
0
10
-3 4 10-
-4
Å)
4
10 4 10- 10
4
108.1 nm 108.1 nm
0
10-5
200
0.05 0.1
0.15
0.2 0.25
15.7 nm Fe 0.756 nm V
ANNUA-6L REPORT 2019
10-6 10
0.00
0.05 0.10 -1 0.15
0.20
0.25
10
-4
5 2 2 10-
5 10-
10
Figure 1
The SLD profile of a vanadium hydride resonator. The colour map represents the wave field for different incident wave numbers of the neutron. The panel to the right is a sketch of the sample structure.
10
2 10 -2
2 χ norm
-5
-1
n
-2
Vanadium
1 / –+ 8
Iro
7.28 nm Al2O3
24
10 22
10 0
2
0 Distance from surface [Å]
-5
Data/Mo+de+l Spinstate / ++
2
χ = 4.098
8 6 - 10- χ = 4.098 0 0 0 Vanadium
m
3
0
2
0
/ – –V
/ – –/ – – +1+1
1
χnorm
+
/ – + + –8
Iro
n
Iron
7.28 nm
Al2O3
22
Va
–
–10 0.5
e
H
e
. = 4–.098 4
+
V/VOx
26
. = 4–.098 4
2
1
2
0
0
m
10-4 0 0 0 200 40.005 0 6000.10 800 0.15 1000 102.20 0 14000.25 15.7 nm Fe
40.005 0 6000.10
800
-1
1000
102.20 0 14000.25 0.2 0.25
0.7M56gOnm V MgO
0.05 dista0n.c1e froQmzin[tÅe Qz(A )
-1 distance froQmzin[tÅerfa]ce (Å) Distance from interface (Å)
2
FeFe Fe Fe
1.3 nm 1.3 nm
100.5
F
F
8
0
0
0
0
0
00
4
2
0 surface [Å]
04
06
08
01
01
00
1 r0fa.1]ce5(Å)
(0A.15)
-1
Q
-
z
0
00
4
04
00
6
Di
distance from interface (Å)
00
Vanad
0
s
00
6
ist
06
t
a
a
00
8
nce
fr
n
0
00
8
c
om
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f
i
n
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adiu
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1
rf
r
ac
0
00
1
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0
2
0
1
0
00
0
2
0
1
01
01
20
0
0
1
20
0
4
0
1
01
4
4
4
Normalized Reflectivity Normalized Reflectivity
SLD (10-6 Å-2)
SLD (10-6 Å-2)
Reflectivity
Normalized Reflectivity
Reflectivity
Normalized Reflectivity
SLDSL[D1(10-6-Å6-2)Å-2] SLDSL[D1(10-6-Å6-2)Å-2]