self-assembly seminar ppt

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.


Fabrication of Arrayed LEDs by Self-Assembly


Arrayed polymer micro lenses used in imaging


Organic thin film transistors (OTFT) for flexible electronic devices

Rollable OTFT based display


Lipid molecules and cell membranes


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

self-assembly seminar ppt

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