Post on 26-May-2015
Self Assembled Monolayers (SAMs)
Tutorial
SAMs: 2-D Self-Assembly at Atomic Level
• Self-assembly in liquid or vapor phase driven by amphiphilic character of the molecules
• Ordered molecular 2D assemblies formed spontaneously by the chemisorption of the head group to a substrate.
substrate
Head group
Tail
Functional group(e.g., -CH3, -COOH, -OH)
• Head group– Affinity to substrate to induce
chemisorbed surface reactions– High energy chemical bound (100 kJ/mol)
provides molecular stability (thermal, chemical, biological)
• Tail group– Closed-packed structure driven by Van
der Waals interaction between alkyl chains
• Functional group– Defines properties of monolayer, e.g.,
hydrophobicity/hydrophilicity, affinity to anchor with biological entities
SAMs precursors
• Key selection criteria– Head group determined by substrate
• Silanes for (trichlorosilane, alkylsilane) for oxides • Thiols (organosulfurs) for metals:
– Functional group• Non-polar hydrophobic: e.g., -CH3
• Polar hydrophilic: -OH, -COOH
Thiols for SAMs on Au surfaces Silanes for SAMs on oxide surfaces
DiBenedetto, S.A., et al., Adv. Mater., 2009. 21(14-15): 1407-1433.
Applications
• Permeation coating for flexible electronics• Nanostructure functionalization• Organic thin film transistor (gate dielectrics,
contacts)• Anti-stiction for MEMS and NEMS • Cell adhesion / protein adsorption• Large surface area surface coating for permeation
/ wettability control
Herrmann et al.,J.Micromech. and Microeng, 2005. 15(5): p. 984-992.
Teshima, K., et al., Langmuir, 2003. 19(20): p. 8331-8334.
Hydrophobic SAM on oxide
Biological assays Gas permeation barrier
Gurard-Levin, et al.. Annual Rev. of Analyt. Chem., 2008. 1: p. 767-800.
Asay and al., Tribol. Lett., 2008. 29(1): p. 67-74.
MEMS lubrication coating
Hydrophobic coating on Al2O3
85
90
95
100
105
110
0.25s 1s 5s
Cont
act a
ngle
[deg
res]
Pulse time [s]
60s
300s
600s
Source @ 105°CReactor @ 105°C
Expo time[s]
• Precursor: Dodecyltricholorosilane (DTS)• Source @ 100-120°C, Reactor 100-120°C
• Sample: Silicon with 200 nm thermal ALD Al2O3
• Sample prep: none• Result: 110° contact angle achieved with 1s pulse, 600s expo
Contact angles following DTS coatings on Al2O3 coated samples in Savannah 200
600 s DTS exposure
200 nm Al2O3 surface.
Combining ALD and SAMs
PEG hydrophilic coating on Nylon
• Precursor: 2Methoxy(polyethyleneoxy)propyl)trimethoxylsilane• Source @ 100°C, Reactor 50°C• Sample: Nylon12• Sample prep: Al2O3 ALD seed layer deposited at 50°C
• Result: nylon made more hydrophilic by combination of ALD+ polyethylene glycol coating
Tuning coating performance by combining ALD and SAMs
Oleophobic coatings
• Comment– Contact angle for oil increases
from 15 to 50 deg after 600 s expo on metal
• Precursor– Tridecafluoro 1,1,2,2
tetrahydrooxtyl)trichlorosilane
• Samples– Oxide:Si+25 nm Al2O3– Metal: Si+10 nm Ni
• Recipe– 75C source, 120C reactor– 1x 1s pulse, 600 s expo
2011.01.18_run 12 _DSC707
• Comment– Top view of samples from
previous slide– Notice oleophilicity of metal
surface and significant improvement after SAM expo
Oleophobic coating expo time
• Comment– 900 s expo appears optimal
• Samples– Si+10 nm Ni
• Recipe– 75C source, 120C reactor– 5x 1s pulses, 300 to 1800 s expos
Textiles
Wool fabric coated with ALD TiO2EDS X-ray map of the wool
Market for performance Textiles is large – domestic, to industrial
•Spill resistant fabrics – SAMs hydrophobic coatings•High moisture absorbancy fabric (sportswear) – SAMs Hydrophilic coating• Abrasion resistant fabrics – Al2O3 coatings