Gebruikerscommissie-bijeenkomst STW-project...
Transcript of Gebruikerscommissie-bijeenkomst STW-project...
Gebruikerscommissie-bijeenkomst STW-project VAF5804
‘Metal-hydrides for smart coatings’
Vaste Stof fysica, FEW, VU, De Boelelaan 1081
22 January 2004, 1100-1500 hr, S207
Program
1100 hr Coffee1115 hr Project summary Ronald Griessen1130 hr New understanding of the Wiebke Lohstroh/
switching of Mg2NiH4 Ronald Griessen1150 hr Optimization of optical
properties by using sputteredcompositional gradient films Bernard Dam
1210 hr Labtour1245 hr Lunch1400 hr H-diffusion in ZrO2 Beatriz Noheda1420 hr Discussion1500 hr Tea
Gebruikerscommissie
Paul van der Sluis (PRL)John Kelly (UU)WWim van Helden (ECN)Gert Jan Kramer (Shell)Beatriz Noheda (VU/STW)Dana Borsa (VU/STW)Bernard Dam (VU)Ronald Griessen (VU)Leo Korstanje
Metal-hydrides for smart coatings (combi-solar collectors)
V
Solar collector
PhotovoltaicVAREM
H2O H2O
Purpose of the project “Metal-hydrides for smart coatings”
optimise optical properties optimise switching kinetics optimise the structural stability of the Mg-Ni VAREM incorporate the optimised VAREM in a switchable device
History of the project
Idea: Summer 2001Start: 25 September 2002 Sputter apparatus: Sept. 2003One Postdoc: Beatriz NohedaNew postdoc: Dana BorsaTo hire: 1 OIO +1 TWAIO
Wiebke Lohstroh
New Understanding of the Switching of Mg2NiHx
Thin FilmsWiebke Lohstroh
vrije Universiteit amsterdam
1st generation switchable mirrors
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.51E-5
1E-4
1E-3
x=[H]/[Y]
Res
istiv
ity [m
Ωcm
]
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Transmission [V
]
H2Y Y YH3
Huiberts et al. Nature 380 (1996) 231
Switchable Mirrors
1st generation:
Huiberts, Amsterdam (1996)
RE-Hx (YHX)
2nd generation:
Van der Sluis, PHILIPS (1997)
RE-Mg-Hx (GdMgHX)
3rd generation:
Richardson, Berkeley (2001)
RE free-Hx (Mg2NiHX)Black state
The Mg2Ni - H system
J.J. Reilly and R.H. WiswallInorganic Chemistry 7 (1968), 2254
Mg2Ni ↔ Mg2NiH4
3.6 wt% H
Advantages of Thin Films• Transport properties
• Reflection & Transmission
~200nm
Pd
Mg2NiHx
Glass
Outline of this talk
The black state in Mg2NiHx
What is so special about itOptical measurementsSelf-organized layeringImplications for this STW project
This talk
The black state in Mg2NiHx
The Mg2Ni - H system
Mg2Ni Mg2NiH4
H2metallicsolid solutionMg2NiH0.3
insulatorEg~1.7eVMg2+[NiH4]4-
LT monoclinic
hexagonal~32%vol
HT>510Kcubic
10002000
30004000
50006000
3.0 2.5 2.0 1.5 1.0
-0.5-0.4-0.3-0.2-0.10.00.10.20.30.40.50.60.7
Ref
lect
ance
Loading time (s)
Photon energy (eV) Isidorsson et al. APL80 (2002) 2350
220nm Mg2.17Ni 3nm PdRT / up to 1bar H2
1.01.5
2.02.5
2000
4000
60008000
0.00
0.01
0.02
0.03
0.04
0.05Tr
ansm
issi
on
Time [
s]Energy [eV]H2
220nm Mg2.17Ni 3nm PdRT / up to 1bar H2
10002000
30004000
50006000
3.0 2.5 2.0 1.5 1.0
-0.5-0.4-0.3-0.2-0.10.00.10.20.30.40.50.60.7
Ref
lect
ance
Loading time (s)
Photon energy (eV)
0 1000 2000 3000 4000 5000 60000.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Res
istiv
ity (m
Ωcm
)
Ref
lect
ance
/ Tra
nsm
ittan
ceat
1.2
4 eV
Time (s)
0.1
1
10
Mg2Ni Mg2NiH≈ 4
Black state
Mg2NiH~0.7
Hall Effect & H - concentration
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00
1
2
3
4
5
6
7
8
x = [H]/[Mg2Ni]
Nef
f [10
22/c
m3 ] @
100k
The black state is not due to an abrupt change in charge carrier concentration
Garcia et al. PRB 59(1999) 11 746
1 H removes1 electron
This talk
The black state in Mg2NiHx
What is so special about it
10002000
30004000
50006000
3.0 2.5 2.0 1.5 1.0
-0.5-0.4-0.3-0.2-0.10.00.10.20.30.40.50.60.7
Ref
lect
ance
Loading time (s)
Photon energy (eV)
Fig. 4: Optical reflectance spectra of the same film as in Fig.3 during slow hydrogen uptake atroom temperature. The hydrogen gas pressure is successively increased from a few millibar to 1bar. The contour plot shows that the minimum reflectance occurs for all photon energies atessentially the same hydrogen composition, i.e. Mg2NiH0.3. This implies that the film is blackover the entire visible spectrum.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.00.0
0.1
0.2
0.3
0.4
0.5
0.64.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
Photon energy (eV)
Ref
lect
ance
For a film with d=220 nm we need κ > 2 to explain T<0.0001
dceTκω2−
≅
Lambert-Beer
( )( ) 22
22
11
κκ
+++−
≅nnR
n: refractive indexκ: extinction coefficient
0.0
0.1
0.2
0.3
0.4
0.5
0.6
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.00.0
0.1
0.2
0.3
0.4
0.5
0.64.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
Photon energy (eV)
Ref
lect
ance
Rthen R > 0.4 !
T
The Absorbing State of Mg2.1NiHx
Isidorsson et al. APL80 (2002) 2350
1000 2000 3000 4000 5000 6000
3.0
2.5
2.0
1.5
1.0
Time (s)
Phot
on E
nerg
y (e
V)
0 1000 2000 3000 4000 5000 60000.0
0.1
0.2
0.3
0.4
0.5
Ref
lect
ance
Time (s)
3.0
2.5
2.0
1.5
1.0
0.0 0.1 0.2 0.3 0.4 0.5
Reflectance
Ener
gy (e
V)
The impossible black state in Mg2NiHx
T
(n, κ)3 nm Pd
220 nmMg2NiHx
quartz
calculate R & T
compare it with experiment
R
0 1 2 3 4 50
1
2
3
4
5
6
κ
n
(n,κ)
No solution for a
homogeneous sample
T
R
The impossible black state in Mg2NiHx
no metallic reflection from the substrate side
H-gradient ?
H-rich
H-poor
Inhomogeneous ?
grain size ~30nmno diffuse scattering
This talk
The black state in Mg2NiHx
What is so special about itOptical measurements
The black state
The black state viewed from two sidesH2 200nm Mg2Ni / 5nm Pd on sapphire
substrate Pd
H loading starts close to substrate
This talk
The black state in Mg2NiHx
What is so special about itOptical measurementsSelf-organized layering
0.1
1
Res
istiv
ity
Energy [eV]
250nm Mg1.69Ni / 7.3nm Pd
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
Photon energy (eV)
Log
Res
istiv
ityReflection from the substrate-side
H
Reflection from the Pd-side
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
Photon energy (eV)
Log
Res
istiv
ity
250nm Mg1.69Ni / 7.3nm Pd
Res
istiv
ity
Energy [eV]
Two Layer ModelPd
Mg2NiH4
Pd
Mg2NiH0.3
Mg2NiH4
Pd
Mg2NiH0.3
Mg2NiH4
PdMg2NiH0.3
Mg2NiH4
Details of the black state
Mg2NiH0.3
Pd
<ε>
Pd
Mg2Ni
Pd
Mg2NiH4Mg2NiH0.3
Pd
Mg2NiH4
Reversibility
0.1
1
Res
istiv
ity [m
Ωcm
]
0.1
energy [eV]
unloading
reversiblesymmetric
H2
This talk
The black state in Mg2NiHx
What is so special about itOptical measurementsSelf-organized layeringImplications for this STW project
Implications
Mg2NiHx is a complicated systemInfra-red properties are favorableComposition is crucialOptimization is possibleSputtered gradient samples are the key to success
That’s all,
for this time