Interaction of hydrogen with a Interaction of hydrogen with a LaBLaB6 6 (111) surface(111) surface
Advisor: Prof. Michael TrenaryAdvisor: Prof. Michael Trenary
Jenna Cameli
ObjectiveObjective
There is critical need for the development of an alternative energy There is critical need for the development of an alternative energy source to fossil fuel.source to fossil fuel.
A hydrogen based economy presents a feasible alternative.A hydrogen based economy presents a feasible alternative.
To achieve this, a suitable material for hydrogen storage has to be To achieve this, a suitable material for hydrogen storage has to be found.found.
Metal hydrides are one of the most promising materials for hydrogen Metal hydrides are one of the most promising materials for hydrogen storage.storage.
In order to make hydrogen storage, and by extension a hydrogen In order to make hydrogen storage, and by extension a hydrogen economy a reality, basic research on metal hydrides is necessary.economy a reality, basic research on metal hydrides is necessary.
Why Lanthanum hexaboride (LaBWhy Lanthanum hexaboride (LaB66)?)?
Boron hydrides have high weight percentages which come close to the Boron hydrides have high weight percentages which come close to the DOE target of 9% for a suitable material for hydrogen storage.DOE target of 9% for a suitable material for hydrogen storage.
It has been shown that CaBIt has been shown that CaB66 can be hydrogenated to give Ca(BH can be hydrogenated to give Ca(BH44))22..
LaBLaB66 has the same structure as CaB has the same structure as CaB66..
We assume LaBWe assume LaB66 to interact with hydrogen in a similar manner. to interact with hydrogen in a similar manner.
Introduction- Lanthanum hexaboride Introduction- Lanthanum hexaboride (LaB(LaB66))
A refractory ceramic material with a m.p. = 2210 ºC.A refractory ceramic material with a m.p. = 2210 ºC.
Insoluble in water.Insoluble in water.
Stable in vacuum.Stable in vacuum.
Principal use is in hot cathodes.Principal use is in hot cathodes.
Also used in electron microscopes, microwave Also used in electron microscopes, microwave tubes, electron lithography, x-ray tubes and electron tubes, electron lithography, x-ray tubes and electron beam welding.beam welding.
Experimental OutlineExperimental Outline
1) Design and install a hydrogen atom source.
2) Use RAIRS (Reflection Absorption Infrared Spectroscopy) to find out if B-H bonds are formed.
3) Use XPS (X-ray Photoelectron Spectroscopy) to monitor elements present on surface.
4) Use LEED (Low Energy Electron Diffraction) for structure
determination of the surface..
Experimental ApparatusExperimental Apparatus Ultra-High Vacuum (UHV); Pressure: 4.0 x 10Ultra-High Vacuum (UHV); Pressure: 4.0 x 10-11-11 torr torr
Viewport
XPS
LEED
IR Detector
IR Spectrometer
RAIRSRAIRSLaB6 (111) 100 L atomic hydrogen, ~ 300 K
Wavenumber (cm-1)
500 1000 1500 2000 2500 3000 3500 4000 4500
R/R
116
118
120
122
124
126
.02%
Structure of LaBStructure of LaB66 (111) (111)
Top view
Side view
T. Yorisaki, A. Tillekaratne, Q. Ge, C. Oshima, S. Otani, M. Trenary. Surface Science. Submitted.
RAIRSRAIRS
.002%
LaB6 (111)-1000 L atomic hydrogen, 237.5 K
Wavenumber (cm-1)
500 1000 1500 2000 2500 3000 3500 4000 4500
R/R
74.8
75.0
75.2
75.4
75.6
75.8
76.0
XPS before AnnealingXPS before Annealing
0 200 400 600 800 1000 1200-200
0
200
400
600
800841
743
633
534425
246
190106
33
Co
un
ts/s
eco
nd
Binding Energy (eV)
LaB6 (111)
W 4f5/2
W 4d5/2
W 4p3/2La 4d3/2
La 3d5/2
La 3d3/2
B 1s
XPS After AnnealingXPS After Annealing
0 200 400 600 800 1000-200
0
200
400 840
747635
534
427373
246
108
33
Co
un
ts/s
eco
nd
Binding Energy (eV)
LaB6 (111)
W 4f5/2
La 4d 3/2
W 4d 5/2
W 4p3/2
La 3d5/2
La 3d3/2
SummarySummary
XPS and LEED used to examine sample surface
RAIRS used to identify B-H bonds
No B-H bonds seen under any tested conditions
Possible reasons for lack of B-H bonds:
– tungsten blocking boron sites thus preventing hydrogen from reacting
– a lower temperature is required for B-H bond formation
AcknowledgementsAcknowledgements
Thanks to Dr. Trenary and Aashani Tillekaratne for guidance Thanks to Dr. Trenary and Aashani Tillekaratne for guidance throughout the program and to Dr. Takoudis, Dr. Jurisch, and Qian throughout the program and to Dr. Takoudis, Dr. Jurisch, and Qian Tao for all their hard work in organizing the program.Tao for all their hard work in organizing the program.
Special thanks to the NSF and DOD for financial support from grant Special thanks to the NSF and DOD for financial support from grant EEC-NSF Grant # 0755115 and the NSF for grant CMMI-NSF Grant EEC-NSF Grant # 0755115 and the NSF for grant CMMI-NSF Grant # 0925425# 0925425