Methods
Micro-contactprinting
Monolayer
UV mask
Micro-lithography
Limited by wavelength
X ~ m
~ 10nm
Nano-writing
Phase separated Langmuir-Blodgett Films
Oriented block co-polymers
Intermolecular interaction
X~ nm
Nanoisland
matrix
Chemical Functionalities Differing in size and type
Examples: CH3-, NH2-, CF3-, COOH-, halide, ethylene oxide
Island Surfaces are Formed By Using SAMs with Two Different Functional Groups
Substrate
Terminal FunctionalityAnchoring Functional-
ity
Surfactant type B
Surfactant typeA
Temp : 220C
OTS
Dehydrated Substrate
In 1.1 mM APhMS 60 sec
rinse in toluene
In 1.1 mM OTS soln60 min
CHCl3 rinse15 min 8 Å
Recessed Islands of APhMSIn OTS Background by Backfilling
0 5 P-Aminophenyltrimethoxy silane
m
Silicon waferOHOH OHOH OHOH OHOH
OTS
Ht difference :15 Å
Temp : 220C
Dehydrated Substrate
In 1.1 mM APhMS 60 sec
rinse in toluene
In 1.1 mM OTS soln60 min
CHCl3 rinse15 min 0 5
Recessed Islands of APhMSIn OTS Background by Backfilling
octadecyltrichlorosilanem
Silicon wafer
Method B: Co-Adsorption
Mixed monolayer of OTS and APS(NH2C3H6SiCl3)
Silicon wafer
CH3
23Å
6.5Å
30nmamine
APhMSOTS
octadecyltrichlorosilanes (OTS) P-aminophenyltrimethoxysilanes (APhMS)
Island Formation of Co-Adsorbed Self-assembling
SurfactantsAPhMS islands in OTS Matrix
0
5
10
15
20
25
30
10 13 15 18 22 25 28 31 34 37 40 43 50
Diameter (nm)
35 islands/µm2, average diameter: 28 nm,distribution width: 10 nm
3:1 OTS:APhMS; Chloroform
2mM total concentration of silane
Effect of Composition2 mM CHCl3 solution, deposition time; 2 hrs
OTS/APMS=1:3 OTS Pillars
OTS/APMS=3:1 APhMS islands
OTS/APMS=1:1 OTS Pillars
Contact Angles: 80 Contact Angles: 41
Solvent Effect2 mM solution (OTS/APhMS=1:1), deposition time: 2 hrs,
CHCl3Toluene
CCl4 THF
Contact Angles: 103 Contact Angles: 98
Effect of Solvent on Composition
Monolayer Composition in Mixed Adsorption is a balance between
• relative affinity of surfactants to the depositing solvent
• interfacial energy between the film formed and the depositing solution
Sequential Adsorption for Mixed Monolayers
Partial OTS monolayers with desired islands Low density surrounding OTS islands at100C.
SOLVENT
SUBSTRATE
OTS SOLUTION
SUBSTRATE
SECOND SILANE SOLUTION
Rinse
Fill surrounding with second silane
Temperature Effect
100C
~220CReduced Secondary growth at low temperatures
Control of Morphology and Chemical Functionality at
Nanometer Scale
Mixed monolayer of OTS and BrUTS(BrC11H22SiCl3)
Silicon wafer
CH3
23Å
15Å
30nm to 10 µm Br
10 2
Height HeightFriction Friction
Control of Morphology at Angstrom Scale
Mixed monolayer of OTS and DTS(C10H21SiCl3)
Silicon wafer
CH3
23Å
14Å
30nm to 10 µm
10
Height Friction
Nano-dots
5
Low OTS concentration & low deposition time
pH 8. . .
Imaging at loads of ~ 1.5 GPa (70 nN). . .3 scans
unworn unwornworn. . . leads to rapid pit formation and facile dissolution
pH 5. . . Imaging at loads of ~ 0.7 GPa (58 nN). . .10 scans
. . . friction appears to be decreasing. . . surface roughens by ~ 0.5 Å
. . . charging followed by surface atom abstraction is observed
nativeIn wear
pH 5. . . Imaging at loads of ~ 1.6 GPa (96 nN). . . 10 scans
pH 3. . . Imaging at loads of ~ 0.7 GPa (56 nN). . .83 scans!
. . . no wear to be found, even with increased loads!
. . . no charging due to low [OH-].
Studies of Lubricant Films: Functionalization of AFM tip and Particle Surface
CH3(CH2)17-Si(OCH2CH3)3
(OTE)
Functionalization with organosilanes:
Si(100)
Contact angle with water on OTE modified particle films
- Forms self-assembled monolayers on silica.- Have been used in MEMS devices.
AFM Tip
Thiols on Au…
Salmeron and Liu
Nanopatterning of Surfaces
AFM STM
Liu et al, Acc. Chem. Res. 33 (2000) 457.
C18S/Au
C18S implanted in a C10S/Au
Mirkin dip-pen lithography
Allows fab in air!
Amro et al, Langmuir 16 (2000) 3006.