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.

Appearance and structure – LaBAppearance and structure – LaB66

Unit cell of LaB6

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

Hydrogen Atom SourceHydrogen Atom Source

Filament

Ceramic Shield

Copper Leads Ceramic

Insulators

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.

LEED Pattern of LaBLEED Pattern of LaB66 (111) (111)

After annealing to 1363 K

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

Questions?Questions?

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