Marrying organic molecules onto Silicon surface
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Marrying Marrying organic molecules organic molecules onto onto Silicon surfaces Silicon surfaces Xiaojing Zhou, K.T. Leung Watlabs, Department of Chemistry University of Waterloo Waterloo, Ontario N2L 3G1 Canada
Transcript of Marrying organic molecules onto Silicon surface
Marrying Marrying organic moleculesorganic molecules onto onto Silicon surfacesSilicon surfacesXiaojing Zhou, K.T. Leung
Watlabs, Department of ChemistryUniversity of WaterlooWaterloo, Ontario N2L 3G1Canada
•• MotivationMotivation•• Silicon surfacesSilicon surfaces•• How to design the manipulation How to design the manipulation
through different organic moleculesthrough different organic molecules•• How to characterize their propertiesHow to characterize their properties•• My experimental setup, results and My experimental setup, results and
discussiondiscussion•• AcknowledgementsAcknowledgements
Outline
27 percent of the Earth's crust
The starting material for nearly all the microelectronic "chips
(Circuits per chip) = 2 (year-1975)/1.5
We are seeing the end of traditional microelectronic technology“By 2017, device features will have shrunk past a critical lengthwhere the device will no longer work under its current design”
Microelectronics miniaturization will depend on functionality of individual molecules and atoms.
Logic gates Si dimers
Using silicon dimers as memory bits
Ian Appelbaum, Tairan Wang, Shanhui Fan, J. D. Joannopoulos and V. Narayanamurti, Nanotechnology 12 (2001) 391
The modification of organic molecules on silicon surface provides variety of new capabilities in optical, electronic, mechanical , chemical and biological activities.
S.F. Bent / Surface Science 500(2002) 879
1300-1400 K
Si(100)
Si(100)2x1Si(111)7x7
A puzzle for Si(100)2x1: titled or flat dimer structure
+ -2.28 A1.7o tilted75+5 kcal/mol
[2+2] cycloaddition
[2+4] cycloaddition(Diels-Alder addition)
C2H4 C2H2 C4H6 (1,3-butadiene)
HOMO
LUMO
1.57 A
-43.2 kcal/mol
1.35 A
-60.2 kcal/mol -67.5 kcal/mol -41.9 kcal/mol
Woodward-Hoffmann selection rules for cycloaddition reaction:
[2+2] cycloaddition [2+4] cycloadditionSuprafacial bond formation
Antarafacial bond formation
ethylene
p T C
(b) benzene
C-F=132 kcal/mol C-Cl= 95 kcal/mol C-Br=67 kcal/mol C-H=105 kcal/mol
Br BrSi
Ca Ca
Si
HH
BrCa
Cb
Si
Br
Si
H
H
(a) Vinylene (b) Vinyl Bromide
Insertion reaction:
Si-Si breakage
X.J Zhou, Q. Li, Z.H. He, X. Yang and K.T. Leung, Surface Science Letter 543 (2003) L668.
Surface characterization for adsorbates:
o Scanning tunnelling microscopy
o Scanning tunnelling spectroscopy
o Atomic force microscopy
o Low-energy electron diffraction
o X-ray photoelectron spectroscopy
o Auger electron spectroscopy
o Infrared spectroscopy
o Electron energy loss spectroscopy
o other surface analytical techniques
My experiments
Desorption: Temperature programmed desorption (TPD)
XPS
polymethylmethacrylateKE = hv – BE
NOTE - the binding energies (BE) of energy levels in solids are conventionally measured with respect to the Fermi-level of the solid, rather than the vacuum level. This involves a small correction to the
equation given above in order to account for the work function (φ) of the solid.
TPD
Rdes = ν . Nx exp ( - Eades / R T )
Eades - activation energy for
desorption
x - kinetic order of desorption (typically 0,1 or 2)
Rdes - desorption rate ( = -dN/dt )
TPD provides information about the desorption kinetics such as desorption order, desorption activation energy etc.
Intensity ratio: 4:5:1
(a) Trichlorovinyl, ΔE=−63.3 kcal/mol (b) Cross-dimer-bridge, ΔE=−77.8 kcal/mol
(e) H-bridge, ΔE=−194.5 kcal/mol
(d) Out-of-plane dimer-bridge, ΔE=−97.7 kcal/mol(c) In-plane dimer-bridge, ΔE=−114.1 kcal/mol
B3LYP/6-31G(d) with fixing the bottom two layers of silicon and hydrogen atoms
3.2 A
3.75 A
C2H2
HCl
SiCl
TPD profiles indicates chlorine atoms leave surface above 800 K as either HCl or SiCl2
Summary
• Halogenated ethylenes react with Si(100)2x1 dissociatively at RT, following predominately insertion mechanism.
• Tetrachloroethylene molecules modify Si(100) surface with C2 dimer bridge, protected by four chlorine atoms.
• Chlorine atoms can be used in the further development in term of making devices.
Acknowledgements
Delaware surface theoretician Barriocanal (left) and Doren.
Stanford cycloaddition group
CNRC researchers
Wisconsin chemists University of Minnesota
self-assembled monolayers
North Carolina, surface chemists
