Surface Chemistry of cyclic olefins on 2×1 and modified Si(100) surfaces

Qiang Li and K.T. LeungDepartment of Chemistry, University of Waterloo

Waterloo, Ontario N2L 3G1, Canada

E-mail=qli@uwaterloo.caWebsite=http://leung.uwaterloo.ca

Outline

• Introduction• Purpose ; Design ; Experimental

• Example: TDS study for styrene/Si(100)• Conclusion

Acknowledgements

WEPIL group: X. Zhou, Z. He, S. Mitlin

Funding: NSERC

Introduction

• Organic semiconductor• Design in my work

– Substrate (Si(100)2x1 surface)– Adsorbate (cyclic olefins)– Surface analytical techniques

• Experimental– LEED & AES– TDS

The first organic FET

( Ref: A. Tsumura et al., Appl. Phys., 49(18), 1986 )

Diamond structure of Si

Ref: Charles Kittel, Introduction to Solid State Physics

Si(100) 2x1

Ideal bulk geometry

Reconstruction

Surface dimer model

( Ref: C729 education materials:http://www.chembio.uoguelph.ca/educmat/chm729/chm729.htm )

Chosen adsorbates

• Benzene

• Toluene

• Pyridine

• Styrene

• Xylene– p-xylene

– m-xylene

– o-xylene

Cycloaddition

Si(100)2x1

Si(100)1x1-H

Clusters of SiC after annealing

50 100 150 200 250 300

SiC (x25)

Si

Der

ivat

ive

elec

tron

yiel

d, N

'(E)

Electron energy, E (eV)

AES Results

0

5

1 0

1 5

2 0

2 50 1 0 2 0 3 0 4 0 5 0 6 0

Styrene Exposure (L)

Benzene Exposure (L)0 5 1 0 1 5 2 0 2 5 3 0

8%

20%

C(K

LL)/S

i(LVV

) (%

)

Toluene coverage > benzene coverageθBenzene ~ 1/4 ML (or 1 molecule/2 dimers)θToluene = θBenzene • (20% / 8%) • (6 / 8)

= 1.875 θBenzene ~ 50 %

Carbon concentration after annealing to different temperatures

Moleculardesorption

200 400 600 800 1000 1200 1400

20

40

60

80

100

100% = 100 L toluene

AES C(KLL)/Si(LVV)

Car

bon

Con

cent

ratio

n (%

)

Temperature (K)

30%10%Molecularadsorption

Dissociativedesorption plus...

100% = 1/4 monolayer

60%90%

350-600 K 800-1000 K

3 features in TDS

• Masses– What

• Peak temperature– Energy– What– Thermal dynamic

• Profile of the peak– How much– Desorption mechanism (0th, 1st,

2nd...)

TDS set-up

Temperature Programmed Desorption

QMS PC

Si(100) sample Temp. detector

Power Distributor

DSP

MOD3

PID Control

35 40 45 50 55 60 65 70 75 80 85 90 950.0

0.2

0.4

0.6

0.8

1.0

Toluene Gas Mass Cracking Pattern

Abu

ndan

ce (r

atio

to 9

1 am

u)

MCR (amu)

RT adsorption at various exposures

300 500 700 900 11000

500

(a) 0.5 L C8D8N / Si(100)2x1 Mass 112 Mass 28 Mass 4

Temperature (K)

0

1000

2000

3000

(b) 4 L C8D8N / Si(100)2x1

Rel

ativ

e In

tens

ity

0

2000

4000

6000

(c) 100 L C8D8N / Si(100)2x1

Exposure dependant of H evolution

mHHCHCsitesActivieHCHC m +→÷ −32563256 _

θ (1-θ)n 0 0

θ - x (1-θ)n- mx x mx

X < θ and mx < (1-θ)n, which gives

+>−<

+≤<

nmnθ ),θ1(

nmnθ θ,

mnx

x

Then, the ratio of dissociation product

P = xmax =

+>−

+≤

nmnθ if ),θ1(

nmnθ if θ,

mn

So that when θ < n / (m+n), P increases with θ. But when θ becomes higher than

n / (m+n), P decreases as θ increases. When θ = n / (m+n), P reaches the maximum.

nmnP+

=max

Ring vs Vinyl group

300 500 700 900 11000

1

2

3

4

Mass 112 (x10) Mass 28 Mass 4

(a) 4 L styrene-d8 / Si(100)2x1

Temperature ( K )

0

1

2

3

4

5

Mass 109 (x10) Mass 28 Mass 4 Mass 2

(b) 10 L styrene-ring-d5 Si(100)2x1

Relat

ive I

nten

sity

Electron bombardment on styrene / Si(100)

300 500 700 900 11000

1

2

3

(a) 10 L styrene-ring-d5 / Si(100)2x1 0.20 mA 80 eV for 30 min

Temperature ( K )

0

1

2

3

4

Mass 109 (x10) Mass 28 Mass 4 Mass 2

(b) 10 L styrene-ring-d5 Si(100)2x1

Relat

ive I

nten

sity

Surface conditions

300 500 700 900 11000

1

2

3

4

5(a) Styrene-ring-d5 on sputtered Si(100)

Mass 109 (x10) Mass 28 Mass 26 Mass 4 Mass 2 (x0.1)

Relat

ive I

nten

sity

Temperature (K)

0

1

2

3

4

5

6

(b) Styrene-ring-d5 on oxidized Si(100)

Mass 109 (x10) Mass 83 (x10) Mass 28 Mass 4

Hydrogenation of styrene/Si(100)

300 500 700 900 11000

10

20

30(a) Hydrogenation on styrene-d8/Si(100)2x1

Mass 32 Mass 28 Mass 4 Mass 2

Temperature (K)

0

10

20

30

40

50 (b) Hydrogenation on styrene-d5/Si(100)2x1

Mass 28 Mass 27 Mass 4 Mass 2

Relat

ive I

nten

sity

0.0

0.1

0.2

0.3

(c) Hydrogenation on styrene-d5/Si(100)2x1

Mass 109 Mass 83 Mass 54

Take-home Message

• Molecular desorption is minor pathway:– Majority from vinyl attachment state (>85%)

through cycloaddition adsorption– A little from the ring attachment state (<15%)

through cycloaddition adsorption

• Hydrogen evolution– RT dehydrogenation from vinyl group– Further dehydrogenation during dissociative

thermal desorption (* the remaining attach to Si(100) through substitution adsorption with the aromatic ring)

– Decomposed from the ring at the temperature higher than that for the typical H desorption from Si(100)

• Electron-induced polymerization• Surface conditions

– Versatile surface chemistries: hydrogenation, dehydrogenation, dissociation, polymerization, etc.