Nano Structured Interface between Nano Structured Interface between - - PowerPoint PPT Presentation

12/3/2005 ICNT-2005, San Francisco 1

International Congress on Nanotechnology (ICNT 2005) International Congress on Nanotechnology (ICNT 2005) October 31 October 31-

• November 4, 2005, San Francisco, USA

November 4, 2005, San Francisco, USA

Nano Structured Interface between Nano Structured Interface between Gold Nanoparticles and Oxide and Gold Nanoparticles and Oxide and the the Role in CO oxidation Role in CO oxidation

• L. Guczi
• L. Guczi, A. Beck and K. Frey

, A. Beck and K. Frey Chemical Research Center, Hungarian Academy of Chemical Research Center, Hungarian Academy of Sciences Sciences Institute of Isotopes, P. O. Box 77, H Institute of Isotopes, P. O. Box 77, H-

• 1525 Budapest,

1525 Budapest, HUNGARY HUNGARY

12/3/2005 ICNT-2005, San Francisco 2

• Unique

electronic and chemical properties are Unique electronic and chemical properties are known to develop in solid when known to develop in solid when its its dimensions dimensions reach the reach the nanoscale nanoscale. .

• C

Changes hanges including discrete electronic structures, including discrete electronic structures, modified physical structures and altered chemical modified physical structures and altered chemical reactivit reactivity y, manifest themselves as new physical and , manifest themselves as new physical and chemical properties not observed in chemical properties not observed in ‘ ‘bulk bulk’ ’ form of form of the material. the material.

BACKGROUND BACKGROUND

12/3/2005 ICNT-2005, San Francisco 3

• xidic support

catalyst model catalyst single crystal

• xide layer

conducting substrate active phase

Why to Use Model Catalysts ? Why to Use Model Catalysts ?

12/3/2005 ICNT-2005, San Francisco 4

Long range ordering: single crystals Short range ordering : nanoscale metal particles

12/3/2005 ICNT-2005, San Francisco 5

How to fabricate model nanoparticles ?

Using pulsed laser deposition on a Si(100) single crystal Using pulsed laser deposition on a Si(100) single crystal ( („ „bottom up bottom up” ” approach) approach) Partial destroying thin films by e.g. implantation Partial destroying thin films by e.g. implantation ( („ „to top p down down” ” approach) approach)

12/3/2005 ICNT-2005, San Francisco 6

MAIN GOAL MAIN GOAL

The present work is aimed at The present work is aimed at model modeling ing the the Au/ Au/FeO FeOx

x

interface to find out whether interface to find out whether  FeO FeOx

x/SiO

/SiO2

2/Si(100) substrate promotes Au nano

/Si(100) substrate promotes Au nano-

• particles through the Au/FeO

particles through the Au/FeOx

x interface, or

interface, or  the burried interface also affects the burried interface also affects iron oxide iron oxide by Au by Au particles. particles.  the electron structure, morphology and the electron structure, morphology and CO CO

• xidation are investigated
• xidation are investigated

Nanosized gold particles Nanosized gold particles interfaced with interfaced with Fe Fe2

2O

O3

3

is is highly active catalyst for CO highly active catalyst for CO

• xidation.
• xidation.

12/3/2005 ICNT-2005, San Francisco 7

Pulsed Laser Deposition (PLD) Pulsed Laser Deposition (PLD) Pulsed Laser Deposition (PLD)

• J. Phys. Chem., (1997
• J. Phys. Chem., (1997)

)

Sample Sample preparation preparation

Guczi et al. Topics in Catal., 29 (2004) 129

• J. Phys. Chem. B., 101 (1997) 9973

12/3/2005 ICNT-2005, San Francisco 8

Sample Sample preparation (I) preparation (I)

• J. Phys. Chem. B, 104 (2000) 3183

SiO SiO2

2/Si(100)

/Si(100) FeO FeOx/SiO /SiO2/Si(100) /Si(100) nano Au/FeO nano Au/FeOx

x/SiO

/SiO2

2/Si(100)

/Si(100) PLD of Fe PLD of Fe + O + O2 PLD of Au PLD of Au

12/3/2005 ICNT-2005, San Francisco 9

12/3/2005 ICNT-2005, San Francisco 10

12/3/2005 ICNT-2005, San Francisco 11

Composition and core level characteristics of PLD sample

water O 1s: 533.1

• OH

O 1s: 531.5 (4.00.5)1015 Fe-O O 1s: 529.9 Fe3+ Fe 2p3/2: 710.9 Au0 Au 4f7/2: 84.0

Au surface

• conc. (at/cm2)

Possible chemical state Binding Energy (eV)

12/3/2005 ICNT-2005, San Francisco 12

Catalytic activity of PLD in CO oxidation at 523 K Catalytic activity of PLD in CO oxidation at 523 K

2.2 Reduced in H2 35.2 Oxidized 13.7 As prepared Activity of PDL(I) mol CO2/mgAu/ min Treatment

Oxidation converts FeO(OH) species on the surface at the Oxidation converts FeO(OH) species on the surface at the gold/iron oxide interface (perimeter) FeO according to the gold/iron oxide interface (perimeter) FeO according to the following equations: following equations: 4 FeO(OH) 4 FeO(OH)   4 FeO + + 2 H 4 FeO + + 2 H2

2O

O(g)

(g) + O

+ O2 (g)

(g)

(1) (1) Fe Fe2+

2+ +

+ O + + O2

2 (g) (g) 

 Fe Fe3+

3+ + O

+ O2

• (s)

(s)

(2) (2) where means an oxygen vacancy on the surface. where means an oxygen vacancy on the surface.

12/3/2005 ICNT-2005, San Francisco 13

 Reaction (1) does not require

• xidative

atmosphere to remove water.  Reaction (2) occurs in the vicinity of the gold particles. Reactions (1) and (2) take place along the perimeter of the gold/iron oxide interface: XPS results show that FeO species are created when after the oxidation the gold particles is partially covered by support species.  O2

• (s) species formed interact with

iron ions formed in the vicinity of the gold particles O2

• + Au+  O2 + Au

(3) Evidences Evidences

• Heating

Heating in He in place of in He in place of O O2

2 the Au/FeO(OH) shows

the Au/FeO(OH) shows no phase transition, only no phase transition, only some water desorption. some water desorption. No change in activity is No change in activity is found although Au found although Au – vacancy pairs are vacancy pairs are generated. generated.

• If the support (FeO(OH))

If the support (FeO(OH)) alone is treated in O alone is treated in O2

2

there is no changes there is no changes neither in the Fe 2p B.E., neither in the Fe 2p B.E., nor in the catalytic nor in the catalytic activity. activity.

12/3/2005 ICNT-2005, San Francisco 14

Bulk: Fe O + FeOOH

2 3

Fe

3+

Au BE = 83.9 eV

O2(g)

e

• e
• O2

Surface: Fe

2+ Au/FeO perimeter

x

This effect is a consequence of the interface created during the treatment along the Au/Fe2O3 perimeter.

Catal Letter, 67, (2000) 117 Catal Letter, 67, (2000) 117

12/3/2005 ICNT-2005, San Francisco 15

• The reactivity of the samples in the

The reactivity of the samples in the CO CO oxidation

• xidation decreases

decreases in the sequence of in the sequence of Au Au/ /FeO FeOx

x/SiO

/SiO2

2/

/Si Si(100)> (100)>FeO FeOx

x/SiO

/SiO2

2/

/Si Si(100)> (100)> > >Au Au/SiO /SiO2

2/

/Si Si(100)> (100)>Si(100). Si(100).

• It was

It was established that in developing the catalytic activity established that in developing the catalytic activity the the gold gold is is metallic metallic and the and the support support is is amorphous amorphous with Fe with Fe 2p 2p B.E. of B.E. of 71 710 0. .8 8 eV eV B.E; B.E;

• reaction occurs at

reaction occurs at Au/FeOx interface along Au/FeOx interface along the perimeter of the perimeter of gold particles. gold particles.

Conclusion on A Conclusion on Au nanoparticles deposited u nanoparticles deposited

• nto Fe
• nto Fe2

2O

O3

3/SiO

/SiO2

2/Si(100)

/Si(100) by PLD by PLD

• J. Phys. Chem. B.,
• J. Phys. Chem. B., 104 (

104 (2000 2000) 3183 ) 3183

12/3/2005 ICNT-2005, San Francisco 16

SiO2/Si(100) 80nm Au/SiO2/Si(100) 10nm Au/SiO2/Si(100) nano Au/SiO2/Si(100) e e-

• beam evaporation

beam evaporation e e-

• beam evaporation

beam evaporation Implantation by Implantation by Ar Ar ions ions

Effect of gold particle size Effect of gold particle size alone alone ? ?

10 nm thick film was treated using 10 nm thick film was treated using implantation by Ar+ ions implantation by Ar+ ions at 40 keV energy at 40 keV energy and 10 and 1015

15 atom/cm

atom/cm2 dose (incident angle is 90 degree). dose (incident angle is 90 degree). 80 nm thick film was 80 nm thick film was used as reference used as reference

• J. Am. Chem. Soc.,
• J. Am. Chem. Soc., 125

125, 4332 (2003) , 4332 (2003)

12/3/2005 ICNT-2005, San Francisco 17

1 2 3 4 5 6 7 8 9 1000 2000 3000 4000 5000 6000 sec µmol/cm2 "implanted" Au/SiO2/Si(100) "as deposited" Au/SiO2/Si(100)

Rate of CO oxidation on Au/SiO2/Si(100) substrate: small Au nano paticles are more active.

CO oxidation as test reaction over CO oxidation as test reaction over 10 nm Au 10 nm Au film film and Au nanoparticles and Au nanoparticles on SiO

• n SiO2

2/Si(100)

/Si(100)

12/3/2005 ICNT-2005, San Francisco 18

Sample CO/O2 : 10/20 Torr Initial reaction rate T = 803 K μmol.s-1.cm-2 SiO2/Si(100) 4.7x10-4 Au/SiO Au/SiO2

2/Si(100

/Si(100) ) (implanted) (implanted) 1.5x10 1.5x10-3

3

Au/SiO Au/SiO2

2/Si(100) (implanted) 2

/Si(100) (implanted) 2nd

nd reaction

reaction 2.0x10 2.0x10-

• 4

4

Fe Fe2

2O

O3

3 deposited on Au/SiO

deposited on Au/SiO2

2/Si(100) sample

9.5x10 /Si(100) sample 9.5x10-

• 2

2

after 2 after 2nd

nd reaction

reaction Fe Fe2

2O

O3

3 deposited on SiO

deposited on SiO2

2/Si(100)

/Si(100) 2.3x10 2.3x10-

• 2

2

CO oxidation CO oxidation (initial rates) (initial rates)

• J. Am. Chem. Soc.,
• J. Am. Chem. Soc., 125

125, 4332 (2003) , 4332 (2003)

12/3/2005 ICNT-2005, San Francisco 19

Decoration of Decoration of gold gold nanoparticles nanoparticles by by Fe Fe2

2O

O3

3/

/Au Au interface creates active interface creates active sites with enhanced sites with enhanced catalytic activity catalytic activity. . Model experiments is required to Model experiments is required to compare the effect

• f

compare the effect

• f

“ “direct direct” ” Au/Fe Au/Fe2

2O

O3

3

and and “ “inverse inverse” ” Fe Fe2

2O

O3

3/Au

/Au interface. interface.

12/3/2005 ICNT-2005, San Francisco 20

SiO2 Si(100) Au 80nm Au nano FeOx FeOx FeOx Si(100) Au 80nm SiO2 FeOx Au nano SiO2 Si(100)

Ar+ impl. e

• b
• m

b . e- bomb.

Pulsed Laser Deposition

Modelling Modelling „ „inverse inverse” ” Fe Fe2

2O

O3

3/Au system

/Au system -Fe2O3 PLD

12/3/2005 ICNT-2005, San Francisco 21

Structure of gold particles and film Structure of gold particles and film

12/3/2005 ICNT-2005, San Francisco 22

Si 2p XPS Si 2p XPS Si 2p XPS Si ToF SIMS Si ToF SIMS Si ToF SIMS

96 98 100 102 104 106 108 110 Binding energy, eV

Intensity, a.u.

1 2 Si 2p

a

50000 100000 150000 200000 250000

27.5 28 28.5 Mass number

Intensity, counts

Si+ C2H4

+

1 2

b

12/3/2005 ICNT-2005, San Francisco 23

• 5

5 10 15 20 25

1000 2000 3000

Signal intensity, a.u. Binding energy, eV

x10

80 nm Au 10 nm Au

80 nm Au/SiO 80 nm Au/SiO2

2/Si(100) is

/Si(100) is used as a reference used as a reference.

Valence band spectra of gold Valence band spectra of gold Valence band spectra of gold

• 2

2 4 6 8 10 12 14 16 18 20 Binding energy, eV Intensity, a.u.

1 2 3 x8 4 5 x5

nano nano Au/SiO Au/SiO2/Si(100 /Si(100) )

XPS XPS

x1 x8 x1 x5

12/3/2005 ICNT-2005, San Francisco 24

Bulk or nanoparticles ? Bulk or nanoparticles Bulk or nanoparticles ? ? Au Au 4f 4f core level B.E. core level B.E.

bulk

nano nano

80 82 84 86 88 90 92 Binding energy, eV

Intensity, a.u.

1 3 x10 2

Au 4f

12/3/2005 ICNT-2005, San Francisco 25

Structure of iron oxide layer Structure of iron oxide layer

12/3/2005 ICNT-2005, San Francisco 26

FeOx/Au/SiO2/Si(100) FeO FeOx

x/Au/SiO

/Au/SiO2

2/Si(100)

/Si(100)

Au nanoparticles/SiO2/Si(100)

SIMS AFM

100 1000 10000 100000 194 195 196 197 198 199 200 Mass number Intensity, counts AuSi1 FAS-4 FASR-3

Au+

Au/Si FeOx/Au/Si

12/3/2005 ICNT-2005, San Francisco 27

before after

12/3/2005 ICNT-2005, San Francisco 28

80 82 84 86 88 90

Intensity, a.u. Binding energy

80 nm Au/SiO2/Si(100) 10 nm Au/SiO2/Si(100)

x10 x10 FeOx/80nm Au/SiO2/Si(100)

Au 4f

12/3/2005 ICNT-2005, San Francisco 29

CO oxidation over CO oxidation over FeO FeOx

x covered

covered Au Au nanoparticles on deposited on nanoparticles on deposited on SiO SiO2

2/Si(100)

/Si(100)

Au nanoparticles

0.00E+00 5.00E-03 1.00E-02 1.50E-02 2.00E-02 2.50E-02 1 2 3 4

samples

ro/mol cm-2s-1

SiO2/Si(100) Au/SiO2/Si(100) FeOx/Au/SiO2/Si(100) FeOx/SiO2/Si(100)

12/3/2005 ICNT-2005, San Francisco 30

80 nm Au

0.00E+00 5.00E-03 1.00E-02 1.50E-02 2.00E-02 2.50E-02

1 2 3 4 samples

ro/mol.cm-2.s

• 1

SiO2/Si(100) Au/SiO2/Si(100) Fe2O3/Au/SiO

2/Si(100)

Fe2O3/SiO2/Si(100)

CO oxidation over CO oxidation over FeO FeOx

x covered 80 nm thick

covered 80 nm thick Au Au film on deposited on film on deposited on SiO SiO2

2/Si(100)

/Si(100)

12/3/2005 ICNT-2005, San Francisco 31

Effect of temperature used in CO

• xidation on the surface

Effect of temperature used in CO Effect of temperature used in CO

• xidation
• xidation on the surface
• n the surface

AFM AFM after 5 min reaction

after 5 min reaction

After heating up in reaction the FeOx surface is roughening.

before reaction after reaction

12/3/2005 ICNT-2005, San Francisco 32

XPS on FeOx/Au/SiO2/Si(100) sample XPS on FeO XPS on FeOx

x/Au/SiO

/Au/SiO2

2/Si(100) sample

/Si(100) sample

Fe Fe2

2O

O3

3 (Fe

(Fe3+

3+),

), FeOOH FeOOH (Fe (Fe3+

3+),

), FeO FeO (Fe (Fe2+

2+),

),

before reaction after reaction

12/3/2005 ICNT-2005, San Francisco 33

S Sites ites in the CO oxidation are located on in the CO oxidation are located on the iron oxide itself the iron oxide itself promoted by Au promoted by Au underneath. underneath.

Similar effects were

• bserved

in Similar effects were

• bserved

in the the CO

• xidation
• n

CO

• xidation
• n

Pt(111)/CeO Pt(111)/CeO2

• 2. If the CeO

. If the CeO2

2 coverage

coverage is around 1.3 is around 1.3– –10 ML (no 10 ML (no exposed Pt), the activity is higher exposed Pt), the activity is higher than on Pt(1 1 1) or CeO than on Pt(1 1 1) or CeO2

2 alone.

alone. The authors concluded that The authors concluded that the reaction occurred at the surface of the reaction occurred at the surface of the thin oxide film the thin oxide film whose properties were radically altered by the whose properties were radically altered by the presence of the presence of the underlying fully encapsulated Pt. underlying fully encapsulated Pt.

.

C.

• C. Hardacre

Hardacre, , et al., et al., J. Phys. Chem. 98 (1994)

• J. Phys. Chem. 98 (1994) 10901

10901

.

12/3/2005 ICNT-2005, San Francisco 34

The The FeO FeOx

x deposited on

deposited on Au Au nanoparticles nanoparticles is more is more active active than that on 80 nm Au layer, than that on 80 nm Au layer, we advance the we advance the hypothesis of the occurrence of a hypothesis of the occurrence of a strong electronic strong electronic „ „coupling through coupling through’’ ’’ effect at the effect at the FeO FeOx

x/

/Au Au nanoparticle nanoparticle interface interface due to the size reduction due to the size reduction. .

Presence

• f

Presence

• f
• xide
• xide
• verlayer
• verlayer

clearly clearly confirm confirms s the absence of an Au/ the absence of an Au/FeO FeOx

x

interface interface exposed to exposed to the the surface. surface.

12/3/2005 ICNT-2005, San Francisco 35

Morphology of gold (nano vs layer) affects the Morphology of gold (nano vs layer) affects the chemical composition and chemical composition and the structure of the the structure of the iron oxide iron oxide, consequently, its reativity. , consequently, its reativity.

This is analogous of V This is analogous of V2

2O

O5

5 deposited on Au(111) or Au

• r Au

foil (Somorjai). U foil (Somorjai). Under nder vacuum conditions oxygen vacuum conditions oxygen was found to was found to desorb desorb and and after hydrogen after hydrogen treatment treatment some oxygen was removed as H some oxygen was removed as H2

2O resulting in

O resulting in surface segregation of bulk oxygen. surface segregation of bulk oxygen. Similarly, when iron Similarly, when iron oxide is deposited on Pt(111)

• xide is deposited on Pt(111)

and Pt(100) the and Pt(100) the chemical chemical reactivity is strongly reactivity is strongly influenced by the substrate orientation influenced by the substrate orientation. .

12/3/2005 ICNT-2005, San Francisco 36

• When

When an an “ “inverse inverse” ” Au/Fe Au/Fe2

2O

O3

3

i is fabricated by s fabricated by Fe Fe2

2O

O3

3

deposition onto deposition onto either either Au/SiO Au/SiO2/Si(100) /Si(100) nano nano-

• particles or 80

particles or 80 nm reference sample nm reference sample, , the the catalytic activity in the CO catalytic activity in the CO

• xidation is enhanced compared to
• xidation is enhanced compared to both

both Au/SiO Au/SiO2

2/Si(100) and

/Si(100) and Fe Fe2

2O

O3/SiO /SiO2

2/Si(100).

/Si(100).

• Increas

Increasing ing the the thickness of iron oxide thickness of iron oxide vanishe vanishes the effect of s the effect of gold gold on the active sur

• n the active surface.

face.

• The activity enhancement is larger for

The activity enhancement is larger for nano nano-

• type Au/Fe

type Au/Fe2

2O

O3 than for bulk than for bulk-

• type Au/Fe

type Au/Fe2O O3 co co-

• operation. The gold effect
• peration. The gold effect

can be indirect, can be indirect, because because Au Au is is not exposed to the surface not exposed to the surface and it and it modifies the catalytically working Fe modifies the catalytically working Fe2O O3

We can conclude that We can conclude that

12/3/2005 ICNT-2005, San Francisco 37

The support from COST D15/005/99 and National The support from COST D15/005/99 and National Science and Research Fund (grant # 34920 and Science and Research Fund (grant # 34920 and 30427) are acknowledged. 30427) are acknowledged.

Acknowledgments Acknowledgments

12/3/2005 ICNT-2005, San Francisco 38

• 2

2 4 6 8 10 12

• 500

500 1000 1500 2000 2500 3000 3500

Intensity Binding energy TiO2/Si TiO2/Au/Si különbség

Valence band

• 2

2 4 6 8 10 1000 2000 3000 4000 5000

Intensity Binding energy difference nano Au bulk Au TiO2/Au/Si TiO2/Si valence band

Effect of gold on TiO Effect of gold on TiO2

2 valence band

valence band

difference

12/3/2005 ICNT-2005, San Francisco 39

1000 2000 3000 4000 20 40 60 80

CO2 formed, mol/cm2 reaction time, s 8nmAu/SiO2/Si(100) TiO2/8nmAu/SiO2/Si(100) TiO2/SiO2/Si(100)

1000 2000 3000 4000 10 20 30 40 50 60 70 80

CO2formed, mol/cm2 reaction time, s 60nmAu/SiO2/Si(100) TiO2/60nmAu/SiO2/Si(100) TiO2/SiO2/Si(100)

Effect of gold on activity of TiO Effect of gold on activity of TiO2

2

12/3/2005 ICNT-2005, San Francisco 40

• 2

2 4 6 8 10 12

• 1000

1000 2000 3000 4000 5000 6000 7000 8000

Intensity Binding energy x4 FeOx/filmAu/Si FeOx/Si

valence band

difference

12/3/2005 ICNT-2005, San Francisco 41

FeOx/Au/SiO2/Si(100) Effect of thickness on rate FeO FeOx

x/Au/SiO

/Au/SiO2

2/Si(100)

/Si(100) Effect of thickness on rate Effect of thickness on rate

500 1000 1500 2000 5 10 15 20 25 30

CO2, mol/cm2 reakcióido,s

5 5 nm FeO nm FeOx/ /Au Au/SiO /SiO2

2/

/Si Si(100 (100) ) 40 40 nm FeO nm FeOx/ /Au Au/SiO /SiO2

2/

/Si Si(100) (100) 40 nm FeOx/SiO2/Si(100)

time, (s)

12/3/2005 ICNT-2005, San Francisco 42

Valence band spectra of FeOx covered gold ? Valence band spectra of FeO Valence band spectra of FeOx

x covered

covered gold gold ? ?

• 2

2 4 6 8 10 12 14 16 18 20 Binding energy, eV Intensity, a.u.

1 2 3 x8 4 5 x5

FeO FeOx

x/nano

/nano Au/SiO Au/SiO2/Si(100) /Si(100) FeO FeOx

x/film

/film Au/SiO Au/SiO2

2/Si(100)

/Si(100)

XPS XPS

x1 x8 x1 x5

12/3/2005 ICNT-2005, San Francisco 43

Experiments xperiments carried out carried out on

• n TiO

TiO2

2/Au model systems

/Au model systems built on built on a Pt a Pt foil foil shows a shows a fundamental difference between fundamental difference between both samples in both samples in terms of preparation. terms of preparation. TiO TiO2

2 film was prepared under in situ

film was prepared under in situ conditions by evaporating Ti in oxygen atmosphere, conditions by evaporating Ti in oxygen atmosphere, whereas in whereas in the present case the present case stoichiometric stoichiometric Fe Fe2O O3 was was sputtered onto the sputtered onto the gold film or gold film or nano nano-

• particles.
• particles. Nevertheless, they showed that Au is

Nevertheless, they showed that Au is visible after evaporation (AES) and O visible after evaporation (AES) and O2

2 activation occurs on Au

activation occurs on Au nanoparticles. nanoparticles.

Z.M. Liu, M.A. Vannice, Catal. Lett. 43 (1997) 51

12/3/2005 ICNT-2005, San Francisco 44

Freund and Freund and coworkers coworkers prepared gold particles prepared gold particles with a mean diameter of 3 nm deposited on Al with a mean diameter of 3 nm deposited on Al2

2O

O3

3,

, FeO FeO and Fe and Fe3

3O

O4 model supports and found these model supports and found these particles to adsorb CO quite strongly and more or particles to adsorb CO quite strongly and more or less independent of the support. Furthermore, the less independent of the support. Furthermore, the role of the oxide support was ascribed to oxygen role of the oxide support was ascribed to oxygen activation and stabilisation of very small gold activation and stabilisation of very small gold particles particles

Shaikhutdinov et al., Catal. Lett., 86 (2003) 211.

12/3/2005 ICNT-2005, San Francisco 45

Why is the large difference in activity among the Why is the large difference in activity among the Au/Fe Au/Fe2

2O

O3 CP, PLD created Au/FeO CP, PLD created Au/FeOx

x/SiO

/SiO2/Si(100) /Si(100) & FeO & FeOx

x/Au/SiO

/Au/SiO2

2/Si(100) samples ?

/Si(100) samples ?

It is believed that amorphicity of the iron oxide is It is believed that amorphicity of the iron oxide is

• ne of the reasons causing such differences. This
• ne of the reasons causing such differences. This

decreases in sequence of decreases in sequence of CP > Fe in O CP > Fe in O2

2 evaporation >

evaporation >  -

• Fe

Fe2

2O

O3

3 evaporation

evaporation

12/3/2005 ICNT-2005, San Francisco 46