Langmuir-Blodgett (LB) Film

Langmuir-Blodgett(LB) Film

Centre For Nanoscience and Technology

Course:734- Self Assembly of Nanostructure

Course Instructor: Dr.A.Vadivel Murugan (Associate Prof.)

Presented by-Sanjeeb Limbu, Master of Technology (Second Year)

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Introduction about Langmuir –Blodgett Film

Principle of monolayer formation

Compression of Monolayer

Langmuir-Blodgett Film Deposition

Fabrication of Langmuir –Blodgett Film

Structural characterisation of Langmuir-Blodgett film

Mechanical measurement of Langmuir-Blodgett film

Applications of Langmuir-Blodgett Film

Advantages-Disadvantages of Langmuir-Blodgett film

Conclusion

OVERVIEW

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Introduction about Langmuir –Blodgett Film

Langmuir Film: The two dimensional crystalline arrangement of molecules at the air- water interface is known as Langmuir film. Langmuir-Blodgett (LB) Film(1932): When the mono- or multilayer's of Langmuir films were transferred onto a solid substrate it is called Langmuir-Blodgett (LB) film.

Deposition of Langmuir film onto solid substrate:

There are three deposition schemes commonly used to transfer Langmuir film onto solid substrate to form Langmuir-Blodgett (LB) film.

These are:

Y-Type deposition

X-Type deposition

Z-Type deposition

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An amphiphilic species, dissolved in a volatile organic solvent, is spread onto an aqueous surface.

After evaporation of the organic solvent, the amphiphilic molecules start to reorganize, forming a film in which the nonpolar tails of the amphiphile rise above the aqueous subphase, while the polar head groups remain immersed.

At this point, the molecules are dispersed and the film is not continuous.

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Principle of monolayer formation


The surface is compressed by means of a moving barrier (which is part of the trough). A feedback system, called Wilhelmy plate, controls the position of the barrier, and thus the surface pressure.

Wilhelmy plate

Moving barrier

Free-floating films on the trough surface are called Langmuir films.

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To obtain information about the stability of the film, the reorientation of the molecules, the phase transitions and conformational transformations, pressure-area isotherms must be studied.

Molecular area (nm2/molecule)

Surf

ace

pre

ssure

(m

N/

m)

Gas phase

Liquid phase

Solid phase

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X-Type deposition:(Down stroke)

Z-Type deposition:(Upstroke)

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Hydrophilic-hydrophobic interaction (X & Z type)

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Langmuir-Blodgett Film Deposition

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Schematic of the Langmuir–Blogett deposition process

The amphiphile is dissolved in an organic solvent and subsequently spread at the air–water interface. The solvent evaporates and a monolayer of the amphiphile at the air–water interface remains (a). The monolayer at the air–water interface can be further manipulated by means of a movable barrier allowing control of the area per molecule (b). The Langmuir monolayer can be transferred by an up-stroke on to a hydrophilic surface (c) and via a down-stroke on to a hydrophobic surface. A dual compartment trough enables the simultaneous processing of two different materials (d), while a programmed dipping sequence allows the determination of layer architecture at a molecular level

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The material is dissolved in an appropriate organic ,volatile solvent (e.g, Chloform,Haxane,Toluene) and dispersed on to the surface of an aqueous sub phase

The solvent evaporates within a short time and the molecule then left spread over the hole surface

The monolayer are compressed until the molecules are aligned in a regular momentum

Langmuir-Blodgett film are fabricated by immerging a clean substrate into the monolayer curved aqueous sub phase

Repeated dipping of the substrate result in the deposition of a multilayer structure, which in same case can be hundreds of monolayer


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Structural characterisation of Langmuir-Blodgett film

Once the films are formed, several techniques can be utilized to characterize : Pressure-Area isotherms; provides information on the miscibility of heterogeneous phases. Spectroscopy; provides information on the chemical composition and nature of the aggregation on the films. Once UV-Vis Steady state fluorescence spectroscopy FTIR NMR Raman etc. X-ray diffraction; provides insights as to the arrangement of heterogeneous films. Microscopy; enables to get a visual repr- esentation of the film surface. AFM SEM TEM Other parameters include changes in conductivity, pH & Temperature of sub phase, molefraction, pressure of lifting, thickness etc.…

SEM image CA-SA mixed LB film.

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Applications of Langmuir-Blodgett Film

LB films can be used as passive layers in MIS (metal-insulator-semiconductor) which have more open structure than silicon oxide, and they allow gases to penetrate to the interface more effectively.

LB films also can be used as biological membranes. Lipid molecules with the fatty acid moiety of long carbon chains attached to a polar group have received extended attention because of being naturally suited to the Langmuir method of film production. This type of biological membrane can be used to investigate: the modes of drug action, the permeability of biologically active molecules, and the chain reactions of biological systems.

Also, it is possible to propose field effect devices for observing the immunological response and enzyme-substrate reactions by collecting biological molecules such as antibodies and enzymes in insulating LB films.

Anti-reflective glass can be produced with successive layers of fluorinated organic film.

The glucose biosensor can be made of poly(3-hexyl thiopene) as Langmuir–Blodgett film, which entraps glucose-oxide and transfers it to a coated indium-tin-oxide glass plate.

UV resists can be made of poly(N-alkylmethacrylamides) Langmuir–Blodgett film.

UV light and conductivity of a Langmuir–Blodgett film.

Langmuir–Blodgett films are inherently 2D-structures and can be built up layer by layer, by dipping hydrophobic or hydrophilic substrates into a liquid sub-phase.

Langmuir–Blodgett patterning is a new paradigm for large-area patterning with mesostructured features

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Advantages-Disadvantages of Langmuir-Blodgett film

Advantages:

Centro-Symmetric or non centro symmetric structure

Control of molecular level(20 Angstroms)

Insulator,semiconductors,conductors

Applications: Non-Linear optics, sensing nanotechnology

Disadvantages:

Slow to fabricate thick film-drying time required after each layer

Mechanical and Chemical stability poor

Required clean room

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Conclusion

LB-Film has been proposed for many practical applications covering a wide range

of different areas from bio sensing to anti reflection coating, to all optical processing

units

Significant accomplishments in designing molecules and LB structures with

function have been mode and relationship between the macroscopic and the molecular

structure

LB-techniques remain potentially useful due to its simplicity and the ability to build

molecular assemblies defined on molecular scale

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