11

Thermal and LowThermal and Low--energy Ionenergy Ion--mediated Surface Chemistry of mediated Surface Chemistry of

Halocarbons on Si(111)7Halocarbons on Si(111)7××7 and 7 and SiOSiO22Zhenhua He

Department of Chemistry

22

OutlineOutlineIntroduction

• Si(111) surface• Experimental• Motivation• Halocarbons

• Present work• Modification of Si(111)7x7 and SiO2 surfaces by low-energy

Ion-mediated surface reactions of three fluorocarbons

• Formation of novel adstructures and functionalization of Si(111) surfaces using thermal evolutions of six-member family of chloroethylenes

Summary & Outlook

33

Introduction Introduction –– Si(111) substrateSi(111) substrate• Diamond structure of Si

• Si(111)7x7 surface

Reconstruction

7x7

• Silicon is the predominant material in the semiconductor industry

• Ideal platform for studying site-specific surface reactions on Si(111)7x7 template

1x1

44

Present work Present work -- ProcedureProcedureIon-mediated surface reactions• Low-energy (50 eV) fluorocarbon ionsChemisorption at RT• A family of six chloroethylenes• Adsorption Properties (by vibrational EELS)• Surface structure (by LEED)Thermal desorption• Adsorption Energy & geometry (by DFT)• Surface chemistry (by temperature dependent

EELS, TDS)Surface condition• Si(111)7x7• Vitreous SiO2• Ar+ sputtered Si (more defects)

55

IntroductionIntroductionExperimental & theoretical methodsExperimental & theoretical methods

Experimental• UHV chamber (P

66

Experimental: EELSExperimental: EELSPrinciple:∆E = hω = E impact – E scattered

MonochromatorAnalyzer

Monoenergeticelectron beam

Overall energy resolution

FWHM ∆E1/2 =

Sqrt [(∆E1/2M)2+ (∆E1/2A)2+ (∆E1/2non-ideal)2]

Great efforts are needed to get better resolution

Tuning the EELS system very time-consuming

77

Experimental: EELSExperimental: EELS

820

150

2900

(b) H2C=CF2 10000 L

1201360 (c) H2C=CH2

1000 L

Cou

nts

of S

catte

red

Ele

ctro

ns

Si(111)7x7x50

1070

0 1000 2000 3000 4000 5000

135 1510

2980

1050

510

(a) H2C=CCl2 100 L

Energy Loss (cm-1)

Principle: Energy Loss∆E = hω = E impact – E scattered

Three frequency ranges

Dipole Scattering Selection Rules

Active Inactive

Scattering Modes:• Dipole mode--dominated at specular direction• Impact mode--better resolved at off-specular

direction

88

Experimental: TDS setupExperimental: TDS setup

20 30 40 50 60 70 80 90 100 1100

20

40

60

80

100

Rel

ativ

e In

tens

ity

m/z

Wepil NIST

Cracking pattern H2C=CCl2

0 100 200 300 400 500 6000

200

400

600

800

1000

Tem

pera

ture

(K)

Time (s)

Cracking pattern for a specific molecule

Temperature ramps as a linear function of time

• Intensities for different masses →amount of desorbed species

• Desorption temperature → bonding energy & adsorption geometry

• Shape of TDS profiles → reaction order

400 600 800 1000

H2

C2H2

HCl

C2H2Cl2

100 L H2C=CCl2 on Si(111)7x7

X 0.2

X 0.5

X 0.02

Rel

ativ

e In

tens

ity

Temperature (K)

SiCl2

99

Experimental Experimental -- LEEDLEED

Si(111)7x7 100 L iso-DCE/Si(111)7x7

• Structure of the near-surface region

• Changes of surface structure when exposed to different types/amounts gases

1010

Fluorocarbons: Objective & MotivationFluorocarbons: Objective & Motivation

• To study the interaction of low-energy fluorocarbon ions with Si(111)7x7 and vitreous SiO2 at molecular level (mechanisms and reaction pathways)

• Scientific reasons• Halo Silicon Surface Chemistry• Ion Surface Chemistry

• Practical reasons• To understand the fundamental processes in plasma

etching and film deposition. • New inter-metal dielectric films :

• Halonated SiO2• Halocarbonated-SiO2

1111

Introduction Introduction ––Halocarbons PlasmaHalocarbons Plasma• Schematic diagram of Plasma etching system

• Our simple ion gun

• High aspect ratio etch

MEMS example

• Halocarbon gas of interest is cracked and ionized by electrons inside the ion gun• Postive halocarbon ion beam with high energy (>500 eV) is formed by the lenses • Low-energy ions are obtained by the floating voltage on the sample

1212

Vibrational frequencies (in cmVibrational frequencies (in cm--11) of reference silicon ) of reference silicon and related systemsand related systems

Vibrational mode This work Ref. [21] Ref. [22] Ref. [23,24,25,26]

Si−F bendSi−F2 bendSi−F3 bend 337Si−F4 bend 380

Si−C stretch 810-850 750-950Si−F stretch 850 825

Si−F2 stretch827,a 870a,

920,b 965b 920

Si−F3 stretch 838,a 1015b 965

Si−H stretch 2080-2180 2088-2120

C−H stretch 2860 2860-3000

C−H2 stretch

C−H3 stretch2879-2955

780-885

300340

Fluorocarbon ions: exposure on 7x7Fluorocarbon ions: exposure on 7x7

0 1000 2000 3000 4000 5000

2095

2080

2110

850

830

(a) 1 kL (b) 2.2 kL (c) 5 kL (d) 10 kL

180

3710

2130

2860

810

340

(d)(c)(b)(a)

Si(111)7x7 CH2F2 at 50 eV

x20

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)

0 1000 2000 3000 4000 5000

(e) 10 kL, 50 eV 2100

29001360

810

850

(d) 5 kL, 50 eV

x50

120

(a) 10 kL, 0 eV

(b) 1 kL, 50 eV

(c) 2 kL, 50 eV

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)

Si(111)7x7H2C=CF2

0 500 1000 1500 2000 2500

160

870

845

780

885340

(d)(c)(b)(a)

Si(111)7x7 CF4 at 50 eV

x20(a) 1 kL (b) 2.5 kL (c) 5 kL (d) 10 kL

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)

CF4 CH2F2 C2H2F2

νSi–Fx = 780-885νSi–C = 810-850

cm-1

δSi–Fx300-380 νCH

νCHνSiH

νSiH

C2H2F2+ (30%)C2H2F+ (20%)CF+ (15%)CH2F+ (12%)C2HF+ (11%)

CH2F+ (38%)CHF2+ (37%)CF+ (11%)CHF+ (4%)

CF3+ (78%)CF2

+ (10%)CF+ (3%)

Fluorocarbon ions: Si(111) Fluorocarbon ions: Si(111) vs.vs. SiOSiO22

0 500 1000 1500 2000 2500

950

385

385 710

(e) sample (c) annealed to 900 K

(d) sample (c) annealed to 700 K

(c) 10 kL CF4 at 50 eV

(b) 5 kL CF4 at 50 eV

(a) Vitreous SiO2180

960

1040

1040

840

385

Vitreous SiO2

x10

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)

0 500 1000 1500 2000 2500

180

810

865

885

810

340

(d)

(c)

(b)

(a)

Si(111)7x7

x5 (a) 10 kL CF4 at 50 eV(b) annealed to 700 K(c) annealed to 900 K(d) annealed to 1100 K

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)

CF3+ incident on 7x7 CF3+ incident on SiO2

νSiC

δSi–Fx

νSi-O-SiSymmetric 710Asymmetric 1040

δSi–O-Si

• More SiFx, and fewer SiC on SiO2

Fluorocarbon ions: CHFluorocarbon ions: CH22FF22 vs.vs. CC22HH22FF22the effect of C=C bondthe effect of C=C bond

0 1000 2000 3000 4000 5000

850

385710

1040

(f) 900 K

(e) 830 K

(d) 780 K

(c) 700 K

(b) 10 kL CH2F2 at 50 eV

(a) Vitreous SiO2

2180

180

1040

920

2860

790

385

Vitreous SiO2

x10

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)0 1000 2000 3000 4000 5000

2185

1050

770

385

690

840

2920

(g) 900 K

(f) 810 K

(e) 730 K

(d) 20 kL

(c) 10 kL

(b) 2 kL

(a) SiO2

x20

160

Vitreous SiO2H2C=CF2 at 50 eV

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)

νSi-O-Si

• Fewer SiFx on SiO2 produced by ion-irradiation in C2H2F2

Fluorocarbon ions: TDSFluorocarbon ions: TDSCF4 and CH2F2 C2H2F2

300 400 500 600 700 800 900 1000 1100

0

1

2

0

1

2

3

4

5

6

(a) mass 66

Temperature (K)

Si(111)7x7 Vitreous SiO2

10 kL C2H2F2 at 50 eV(b) mass 85

10 kL C2H2F2 Si(111)7x7 Vitreous SiO2

Rel

ativ

e In

tens

ity0

1

2

300 400 500 600 700 800 900 10000

1

2

0

1

2

3

4

5

6

7

8

9

10

11

(b) mass 66

(a) mass 47

Temperature (K)

Si(111)7x7 Vitreous SiO2

10 kL CH2F2 at 50 eV

(c) mass 85

10 kL CF4 at 50 eV Si(111)7x7 Vitreous SiO2

Rel

ativ

e In

tens

ity

• Fewer desorption of SiF2 and SiF4from SiO2 ion-irradiated in C2H2F2than from si(111)7x7

• More desorption of SiF2 and SiF4from SiO2 ion-irradiated in CF4 or CH2F2

1717

Fluorocarbon ions (50 eV): SummaryFluorocarbon ions (50 eV): Summary

Carbon state transition plus

Reaction layer = SiFx and

carbonaceous layer

SiC alloyand/or

Hydrocarbonfragments

SiF2 and/or H2

Bombardment...

350-700 K

SiF4

desorption

700-1000 K

Silicon carbideCarbon diffusion

into bulk

CHxFy+ or C2HxFy+

• CFx layer is only formed at sufficiently high dose of CF3+ ion incidence (>3x1016cm-2, H. Toyoda, H. Morishima, R. Fukute, Y. Hori, I. Murakami, and H. Sugai, J. Appl. Phys. 95 (2004) 5172)

• In our case, the estimated dose of CF3+ ion incident on the sample surface is ~1016 cm-2 for 10,000 L exposure of CF3+ ions

• Ion current ~ 200nAcm-2 at 1x10-6 Torr ion dose ~ 1x1016cm-2 for 10,000 L of CF3+ ions

1818

Fluorocarbon ions (50 eV): SummaryFluorocarbon ions (50 eV): Summary• The resulting surface products on Si(111)7x7 and

vitreous SiO2 obtained by the irradiation of low-energy fluorocarbon ions from three fluorocarbons with different F-to-C ratio have been examined systematically

• On Si(111)7x7, the ion-irradiation in the three fluorocarbons produced similar reaction layer: fluorosilyl (SiFx) and carbonaceous cluster (SiC and/or hydrocarbon fragments)

• On vitreous SiO2, more fluorosilyl (SiFx) formed than on 7x7 surface when the surfaces exposed to the same dose of ion-irradiation generated in CF4 or CH2F2

• But, the same dose of ion-irradiation generated in C2H2F2 produced a smaller amount of fluorosilyl (SiFx) on Si(111)7x7 than on vitreous SiO2

• The presence or absence of a C=C bond in the sputtering gas and the F-to-C ratio of a sputtering gas are found to play important roles

1919

Introduction Introduction –– ChloroethylenesChloroethylenes

• Adsorbates of interest

• Common industrial chemicals for processing and treatment of silicon wafers

• An ideal platform for studying geometric isometric effects and the effects of halogen substitution on organosilicon chemistry

• Competition among several plausible reaction mechanisms: cycloaddition to “diradical” on surface, and formation of surface vinyl via cleavage of C–Cl bonds as well as dative bonding resulting from the inductive effect of Cl atoms

MCE PCETCE

iso- trans- cis-DCE

• Cl content• isometric • Si9H12 cluster

• diradical

4.6 Å

4.3 Å

2.4 Å

2.9

Å

3.3 Å

2020

Si(111)7x7Si(111)7x7

2121

Chloroethylene chemisorption: Cl content effectChloroethylene chemisorption: Cl content effect

820

150

2900510

(b) H2C=CHCl

820

1201360

(c) H2C=CH2

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Si(111)7x7x50

1070

0 1000 2000 3000 4000 5000

135 1510

29801050

510

(a) H2C=CCl2

Energy Loss (cm-1)

•• DechlorinationDechlorinationPrimary channel for 2 and Primary channel for 2 and

more Cl substitutionmore Cl substitution

•• CycloadditionCycloaddition

νC=C

νCH2

C sp3

C sp2

νSi–Cl = 510 cm-1

2222

Chloroethylene Chloroethylene -- isometric effectisometric effect

AA

Different adstructuresChlorovinyl and vinylidene

Low saturation exposure for molecules with =CCl2 group

Steric effect between cis-DCE and trans-DCE

0 1000 2000 3000 4000 5000

115082

010

5078

074

0

1510

160

120

135

130

x50

1360

2980

510

(d) trans - C2H2Cl2

(c) cis-C2H2Cl2

(b) iso-C2H2Cl2

(a) C2HCl3

Si(111)7x7

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)

1150

0 200 400 600 800 10000.0

0.2

0.4

0.6

0.8

1.0

TCE

iso-DCE

cis-DCE

trans-DCE

Rel

ativ

e In

tens

ity

Nor

mal

ized

to th

e El

astic

Pea

k (%

)

Exposure (L)

C−H stretch2980 cm-1

the relative intensity of EELS feature →Saturation exposure

ClH

Si

H

Cl

H

Si

H

HCl

Si

HH

SiSi

H

ClCl

Si

H

HCl

Si

Cl

νSi–Cl = 510 νC=C=1510 νCH=2980Si

Cl

2323

Chloroethylene: thermal desorptionChloroethylene: thermal desorption

H300 K

2

Cl

HCl Si

+

Cl

Si

ClH

(V)

Si

H

H300 K

2

+

ClCl Si

+Cl

Si

ClH

Si

H

(IV)

H

2

>450 K

Si

>450 KCl

SiH

H+ 2

Cl

2 Si

H

SiSi

H

(VI)

>580 K

hydrocarbonfragmentsor SiC

+

H

Si2

2 + H

HSi

400 600 800 1000 1200

x 0.2

(f) mass 98

(e) mass 96

x 0.05

(d) mass 63

(c) mass 36

(b) mass 26

(a) mass 2

1000 L cis-C2H2Cl2 on Si(111)7x7

x 0.02

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Temperature (K)

IIIII

SiCl2

HCl

H2

350 K

+

+

+300 K

(VI)

H

ClCl

H

Si

H

ClCl

H

SiSi

Si

Si

Si

Cl

Si

Cl

Si H

Cl

H

Cl

H

H I

Three states of acetylene desorption

• Desorption from di-σ bonded vinylene

• Low temperature desorption• Resulting from β-Cl elimination of 2-chlorovinyl

2424

Novel adstructure Novel adstructure -- vinylidenevinylidene• First observation of vinylidene

on semiconductor surface produced by RT adsorption of iso-dichloroethylene on Si(111)7x7• The presence of the νC=C EELS

feature• Supported by DFT calculations

D2

0 1000 2000 3000 4000 5000

880

x25

(i) 950 K

(h) 890 K

(g) 840 K

(f) 770 K1360

1050

2080

2980

510

1510

135

(e) 720 K

(d) 670 K

(c) 580 K

(b) 450 K

(a) 100 L

Si(111)7x7H2C=CCl2

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)

820

νC=C

νCH2

δ ρCH2νSi–Cl = 510 cm-1 ΔE=- 510.2 kJ mol-1

2525

Trichloroethylene Trichloroethylene –– thermal evolutionthermal evolution• First observation of acetylide on

semiconductor surface produced by RT adsorption of iso-dichloroethylene on Si(111)7x7• The presence of the νCH EELS

feature at 3300 cm-1

0 1000 2000 3000 4000 5000

(i ) 970 K

(h) 920 K

820

1150

2080 2900

510

1510

120

(g) 850 K

(f ) 700 K

(e) 580 K(d) 450 K

(a) 100 L

Si(111)7x7Cl2C=CHCl

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)

(b) 350 K

(c) 400 K

3300

2980

x25

Mono-σ bonded Si-C≡CH

(d)

H

HCl

2

+

300 K

2

hydrocarbonfragmentsand/or SiC

2 +

2

3

+

+ Si

H

>580 K

Cl

Cl

Cl

Si

Cl H

Si

Cl

Si

Si

Cl

H

Si Si

Cl

Si

Si

(VII) (X)

+ (IX)

Cl

Si32

+Cl

>450 KSi

ClCl

Si

H

Si(VI)

Cl

Si

Cl

>450 K

+

H

Si

Cl

SiSi

(VIII)

di-σ bonded chlorovinylene (Hċ=ċCl)mono-σ bonded chlorovinyl (Clċ=CHCl)

νCH2

νC=C

2626

Cycloaddition, dechlorination and dative adsorptionCycloaddition, dechlorination and dative adsorption

Summary of geometries found in the room-temperature adsorption of Chloroethylenes

300 K+

SiSi

Cl

ClCl

ClCl

ClCl

Cl

SiSi

• Dechlorination occurs for all the chloroethylenes

• [2+2] cycloaddition found in monochloroethylene on Si(111)7x7

• Dative adsorption involving the chlorine (Cl) for all chloroethylenes on Si(111)

H 2 +Cl

Cl

H

Si

ClH

+H

Si

ClCl

Si

H

SiSi

H

300 K

2 Si 2 Si

H

H

+

300 K

2H

Cl

Si

Cl

Si

Si

H

HH

HH

SiSi

H

Cl

(I)

(II)

2727

Summary Summary • First systematic study of thermal evolution of a family of

chloroethylenes on Si(111)7x7 surface• Dechlorination occurs for all the chloroethylenes; [2+2]

cycloaddition found monochloroethylene/Si(111); Dative adsorption involving the Cl for all chloroethylenes/Si(111)

• First observation of novel adstructures formed by chemisorption of chloroethylenes: in particular, di-σbonded vinylidene on semiconductor surface

• First comprehensive study of the interactions of low fluorocarbon ions with Si(111) and SiO2 surfaces using more-surface sensitive technique: vibrational EELS

• The presence or absence of a C=C bond in the sputtering gas and the F-to-C ratio of a sputtering gas are found to play important roles on the resulting surface products obtained by the irradiation of low-energy fluorocarbon ions

2828

Outlook Outlook • Further studies of surface chemistry mediated

by the low-energy fluorocarbons ions using more chemical-sensitive techniques (e.g. AES, electronic EELS, XPS)

• Extend the current study of chloroethylenes on Si(111)7x7 to bromoethylenes and iodoethylenes on Si(111)7x7 to explore the site-specific surface reactions of Si(111)7x7 surface

• Study post adsorption of lager hydrocarbons with unsaturated bonds (e.g. styrene) on silicon surface with the vinyl and vinylidene to explore the further functionalization of silicon surface for molecular electronics

2929

Thank youThank you• Dr. K.T. Leung

• Dr. Dan Thomas, Dr. Pu Chen and Dr. Qing-Bin Lu

• Dr. Qiang Li and Xiaojin Zhou • Xiang Yang and Sergey Mitlin• Dr. Michael Thiam, Dr. Nina Heinig• Dr. Hui Yu

• Entire staff of the Science Shops

We, the willingLed by the unknowing

Are doing the impossibleFor the ungrateful

We have done so muchfor so long

With so littleWe are now qualified

To do anythingWith nothing

3030

Chemisorption theory: searching an elephantChemisorption theory: searching an elephant

E. Shustorovich, Accounts of Chemical Research, 21 (1988)183.

3131

Si(111)7x7: DAS modelSi(111)7x7: DAS model

3232

Trichloroethylene Trichloroethylene –– thermal evolutionthermal evolution• First observation of acetylide on

semiconductor surface produced by RT adsorption of iso-dichloroethylene on Si(111)7x7• The presence of the νCH EELS

feature at 3300 cm-1

0 1000 2000 3000 4000 5000

(i ) 970 K

(h) 920 K

820

1150

2080 2900

510

1510

120

(g) 850 K

(f ) 700 K

(e) 580 K(d) 450 K

(a) 100 L

Si(111)7x7Cl2C=CHCl

Rel

ativ

e In

tens

ity (a

rbitr

ary

units

)

Energy Loss (cm-1)

(b) 350 K

(c) 400 K

3300

2980

x25

Si-C≡CH

(c)

H

Cl

Cl

350 K

+

+ Cl

+300 K

(V)

SiH

ClCl

Cl

Si

H

ClCl

Cl

SiSi

Si

Cl

Cl

H

Si

SiSi

Cl

(d)

H

HCl

2

+

300 K

2

hydrocarbonfragmentsand/or SiC

2 +

2

3

+

+ Si

H

>580 K

Cl

Cl

Cl

Si

Cl H

Si

Cl

Si

Si

Cl

H

Si Si

Cl

Si

Si

(VII) (X)

+ (IX)

Cl

Si32

+Cl

>450 KSi

ClCl

Si

H

Si(VI)

Cl

Si

Cl

>450 K

+

H

Si

Cl

SiSi

(VIII)

3333

Si(111)7x7Si(111)7x7

3434

• In our case, the estimated dose of CF3+ ion incident on the sample surface is ~1016 cm-2 for 10,000 L exposure of CF3+ ions

• Ion current ~ 200nAcm-2 at 1x10-6 Torr ion flux ~ (2x10-7 Cs-1cm-2)/(1.6x10-19 C) =1.25x1012cm-2s-1ion dose ~ 1.25x1012cm-2 for 1L of exposure of CF3+ ions ion dose ~ 1x1016cm-2 for 10,000 L of CF3+ ions

3535

Fluorocarbon ions (100 eV): A related workFluorocarbon ions (100 eV): A related work• At the small dose of CF3+ ions (3x1016cm-2 ), a balance between the C atom supplied by CF3+incidence and the C atom lost by CFx radical desorption is established, while F atoms on the surface approach a steady state determined by CF3+ ion incidence and the SiFx radical desorption.

• CFx layer is only formed at sufficiently high dose of CF3+ ion incidence

• In our case, the estimated dose of CF3+ ion incident on the sample surface is ~1016 cm-2

• H. Toyoda, H. Morishima, R. Fukute, Y. Hori, I. Murakami, and H. Sugai, J. Appl. Phys. 95 (2004) 5172.

Surface analysis techniquesSurface analysis techniques

3737

Low Energy Electron DiffractionAuger Electron Spectroscopy

Electro

n Ener

gy Loss

Spectr

oscopy

Thermal Desorption Spectrometry

Ion Gun

Electron gun• In our case, the estimated dose of CF3+ ion incident on the sample surface is ~1016 cm-2 for 10,000 L exposure of CF3+ ions

• Ion current ~ 200nAcm-2 at 1x10-6 Torr ion flux ~ (2x10-7 Cs-1cm-2)/(1.6x10-19 C) =1.25x1012cm-2s-1ion dose ~ 1.25x1012cm-2 for 1L of exposure of CF3+ ions ion dose ~ 1x1016cm-2 for 10,000 L of CF3+ ions

Diamond structure of SiPresent work - ProcedureIntroduction Experimental & theoretical methodsExperimental: EELSExperimental: EELSExperimental: TDS setupExperimental - LEEDFluorocarbons: Objective & MotivationIntroduction –Halocarbons PlasmaVibrational frequencies (in cm-1) of reference silicon and related systemsFluorocarbon ions: exposure on 7x7Fluorocarbon ions: Si(111) vs. SiO2Fluorocarbon ions: CH2F2 vs. C2H2F2 the effect of C=C bondFluorocarbon ions: TDSFluorocarbon ions (50 eV): SummaryIntroduction – ChloroethylenesSi(111)7x7Chloroethylene chemisorption: Cl content effectChloroethylene - isometric effectChloroethylene: thermal desorptionNovel adstructure - vinylideneTrichloroethylene – thermal evolutionCycloaddition, dechlorination and dative adsorptionSummaryOutlookThank youChemisorption theory: searching an elephantSi(111)7x7: DAS modelTrichloroethylene – thermal evolutionSi(111)7x7Fluorocarbon ions (100 eV): A related workSurface analysis techniques