self-assembly seminar ppt
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SELF-ASSEMBLYNANOMATERIALS
Contents
1. Introduction
2. Self-assembly
3. Self-assembled monolayer (SAM)
4. Self-assembly by chemisorption
5. Electrostatic self-assembly
6. Microcontact printing of SAM
7. Microdisplacement printing of SAM
8. Conclusions
9. References
Introduction
Nanomaterials and its fabrication
Dimension
Zero-Dimensional
One-Dimensional
Two-Dimensional
Nucleation
Homogeneous
Heterogeneous
Introduction contd..
Nanostructure fabrication techniques
Top-down approach
Bottom-up approach
Film growth methods
Vapour-phase
Liquid-phase
Filament growth modes
Island growth
Layer growth
Island-Layer growth
Self-assembly
Definition: Self-Assembly (SA) is the spontaneous
organization of molecules or objects into well defined
aggregates via non covalent interactions (or forces)
Forces:
Chemisorption
Electrostatic force
Hydrophobicity and hydrophilicity
Capillary force
Features of SA nanostructures
Self-assembled structures are capable of
self-correcting and self-healing
Complex structures with fewer defects
Self-assembled structures are robust
Fabrication in inaccessible spaces
Repetitive or reconfigurable structures
Simple, parallel, low-cost processing
Self-assembled monolayer (SAM)
SA surfactant molecule
1. Headgroup
2. Surface group
3. Alkyl or derivatized alkyl
group
Self-assembled surfactant molecule
SAM contd..
Arrangement of SA molecules
Self-assembly by chemisorption
Self-assembly methods
Organosilicon or alkylsilane
derivatives on Si
Alkanethiols on gold, silver
Dialkyl sulfides on gold
Alcohols and amines on platinum
Carboxylic acids on aluminium
oxide and silver silane
Organosilicon group
Alkanethiols group
Silane (Silicon hydride)
Self-assembled monolayers of alkylsilane
SAM on Si substrate
Surfactant:
Alkyltrichlorosilane (C3H5Cl3Si)
10–3M concentration
Organic solvent:
Mixture of 80/20 Isopar-G/CCl4
Reaction time: 2–3 mins
Washed using methanol
R - Si - X3Alkylsilane
SAM on Si substrate
SAM of alkylsilane contd..
Self-assembled multilayer structure
SA of alkanethiol monolayer on gold
Alkanethiol solution (20μM – 0.1mM)
Gold substrate – 0.5×0.5cm
Immersion time – 24h
Ethanol to wash
The adsorption process
Sulfur adsorption (10s)
Orientation ordering (≈10h)
S-H bond with the gold surface
Alkanethiol
SAM on gold contd..
Alkanethiol monolayer on gold
STM topograph of an octanethiol monolayer on Au
Core–shell structures
Definition
Types:
Novel metal–oxide (Gold-Silica)
Novel metal–polymer (Silver-polystyrene)
Oxide–polymer (Silica-polypyrrole)
Gold-silica core-shell structure
Using alkylsilane (APS) SAM
(3-aminopropyl trimethoxysilane)
Gold is vitreophobic
Colloidal solution of gold (15nm) –
500ml; pH- 2 to 3
Silica sol (Na2SiO3), pH- 10 to11
Vigorous stirring for 24 hours
(NH2-(CH2)3-Si-(OCH3)3 )
(APS)
Silane (Silicon hydride)
Fig. 2: TEM Images of silica-coated gold particles. shell thicknesses are (a, top left) 10 nm, (b, top right) 23 nm, (c, bottom left) 58nm, and (4 bottom right) 83nm.
Fig. 1: (a) Formation of monosized gold particles (b) Introducing SAM on gold(c) Deposition of silica shell.
Electrostatic self-assembly
Principle:
Two oppositely charged particles,
suspended in a fluid, will attract
Gold discs
Alkanethiol 1 mM
Silicon substrate
PDMS stamp
(Poly-dimethylsiloxane) Inks
Photoresist
HS(CH2)11NH3+Cl- +
HS(CH2)15COOH –
Step 1: Fabrication of patterned surfaces
Step 2: Fabrication of charged gold microstructures
Step 3: Assembly of particles
Fig.: SEMs of patterns of disks (or stars) after electrostatic self-assembly in ethanol:
Microcontact printing of SAM
Photolithographic techniques
Elastomeric stamp – Polydimethylsiloxane (PDMS)
Ink – Alkanethiol (0.1–1.0 mM)
Gold films – 50 to 2000 A° thick
Silicon - Substrate
Titanium – Adhesion provider b/w Au and Si
Fig.: Schematic of the procedure for microcontact printing of alkanethiol SAMs on Au coated Si
Microdisplacement printing of SAM
Pre-assembled monolayer- 1-
adamantanethiolate (AD)
PDMS stamp
Gold substrate
Schematic depicting microdisplacement printing
Applications
Manufacturing of ICs, transistors, chips and other electronic
circuit components.
Semiconducting oxide nanorods, and nanoribbons.
Current research in nanoscale semiconducting nanowires for
devices applications span from field-effect transistors,
bio/chemical sensors, ultra-violet lasers, light emitting
diodes, and photo-detectors.
Nanoscale self-assembly of thin-film molecular materials for
electro-optic switching.
Applications contd..
Improved self-assembly of nanomaterials may
enhance solar cells
Self-assembly in magnetic nanowire arrays and
microarrays production.
Applications contd..
Fabrication of Arrayed LEDs by Self-Assembly
Applications contd..
Arrayed polymer micro lenses used in imaging
Applications contd..
Organic thin film transistors (OTFT) for flexible electronic devices
Rollable OTFT based display
Applications contd..
Lipid molecules and cell membranes
Applications contd..
Tobacco mosaic virus
Conclusions
Self-assembled structures are capable of self-correcting and
self-healing resulting in fewer defect.
Two strategies have received significant research attention –
“Self-Assembled Monolayers (SAMs) and Electrostatic Self-
Assembly (or layer- by-layer assembly)” due to the easiness in
processing.
Self-assembly has big role to play in future in synthesis of
many perfect and cost-effective nanostructures
References
A book titled “Nanostructures and nanomaterials” by Guozhong Cao, 2004 edition.
Technical papers and presentations:
Microfabrication through electrostatic self-assembly by Joe Tien, Andreas Terfort, and
George M. Whitesides, 1997.
Microcontact printing of self-assembled monolayers: applications in microfabrication by
James L Wilbur, Amit Kumar, Hans A Biebuyck, Enoch Kim and George M Whitesidesy,
1996.
Microdisplacement printing by A. A. Dameron, J. R. Hampton, R. K. Smith, T. J. Mullen, S.
D. Gillmor, and P. S. Weiss, 2005.
Self-assembled monolayers on gold substrate made from functionalized thiols and
dithiols by Michaela Georgeta Badin, 2007.
Molecular self-assembly by Sigma-Aldrich, Volume 1 and 2, 2006.
Websites: www.wikipedia.com and www.wapedia.com
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