GB2144653A

GB2144653A - Methods of preparing Langmuir-Blodgett multilayers

Info

Publication number: GB2144653A
Application number: GB08418919A
Authority: GB
Inventors: Ian Robert Girling; David Robert John Milverton
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1983-08-09
Filing date: 1984-07-25
Publication date: 1985-03-13
Also published as: GB8418919D0

Abstract

A method of preparing Langmuir-Blodgett multilayers on a substrate wherein the substrate is carried on a rotatable member which is partly immersed in a liquid and serves to divide the surface of the liquid into two discrete areas one of which areas carries a monolayer of a material and the other of which carries a monolayer of a different material, or carries no material. On rotation of the member carrying the substrate the substrate repeatedly passes in turn through the two areas forming a non-centrosymmetric multilayer on the substrate if the areas carry monolayers of different materials, or a Z-type film multilayer if only one area carries a monolayer.

Description

SPECIFICATION Methods of Preparing Langmuir-Blodgett Multilayers This invention relates to methods of preparing Langmiur-Blodgett multilayers.

Such multilayers are increasingly finding application in microelectronic devices for use, for example, as insulating layers, resists and waveguides in optoelectronic devices.

A standard method of preparing such multilayers comprises forming a monolayer of a material on a liquid surface and repeatedly passing a substrate on which the multilayer is to be formed through the surface.

One such method will now be described with reference to Figures 1 to 5 of the accompanying drawings in which: Figures 1 and 2 illustrate different stages in the method, and Figures 3, 4 and 5 illustrate different multilayer structures obtainable by the method.

Referring to Figure 1, a monolayer film of amphiphilic molecules 1 is formed on the surface of an aqueous liquid 3, e.g. water, contained in a trough (not shown), and a substrate 5 having a hydrophobic surface is immersed in the liquid 3 causing a monolayer 7 of the molecules to form on the substrate surface.

On withdrawal of the substrate 5 a further monolayer 9 of the molecules is formed on the substrate, the hydrophilic ends of the molecules in the two monolayers being adjacent, as shown in Figure 2.

Further passes of the substrate 5 into and out of the liquid 3 form further paired monolayers to produce a multilayer structure as illustrated in Figure 3.

Such a method can be time consuming and tedious since it involves a succession of lowering and raising steps. Furthermore, when the multilayer structure is required to be noncentrosymmetric, i.e. comprise films of different materials as illustrated in Figure 5, the method is further complicated by the addition of steps involving the removal or change of the film on the liquid or the use of several troughs.

A similar difficulty can arise when attempting to form high quality Z-type films, as illustrated in Figure 4. By a Z-type film is meant a multilayer film in which the molecules in each layer are similarly orientated.

It is an object of the present invention to provide methods of preparing Langmuir-Blodgett multilayers whereby these difficulties may be alleviated.

According to the present invention in a method of preparing Langmuir-Blodgett multilayers on a substrate; the substrate is carried on, or itself comprises, a member which is partly immersed in a liquid and which forms at least part of a barrier which divides the surface of the liquid into two discrete areas; one only of said areas carries a monolayer of a particular material; and the substrate is caused repeatedly to pass in turn through each of said areas by rotation of said member.

In one particular embodiment of the invention the other of said areas carries a monolayer of a material different from said particular material.

The method then produces a noncentrosymmetric multilayer.

In another particular embodiment of the invention the other of said area carries no material. The method then produces a Z-type film multilayer.

Said member is preferably of such a form as to cause a minimum disturbance to the liquid as it is rotated. Hence, said member suitably comprises a roller or an endless belt, web or filament arranged for rotation about an axis substantially parallel to the surface of the liquid.

Two methods in accordance with the invention will now be described with reference to Figures 6 to 8 of the accompanying drawings in which: Figures 6 and 7 illustrate one method; Figure 8 illustrates the other method; and Figure 9 illustrates a modification of the method of Figure 8.

Referring to Figures 6 and 7, in the first method a substrate 11 having a hydrophobic surface is secured to the curved surface of a tubular roller 13 which is partly immersed in an aqueous liquid 1 5.

The liquid is contained in a trough 17 (see Figure 7) and the roller 1 3 is disposed with its axis lying substantially in the plane of the surface of the liquid and forms a barrier which divides the surface of the liquid 1 5 into two discrete areas 1 9 and 21. One of the areas, area 19 in Figure 6, carries on its surface a monolayer film of amphiphilic molecules 23, the other area being free of any material.

To form a Langmuir-Blodgett multilayer film on the substrate the roller 1 3 is rotated about its axis in an anti-clockwise direction as shown in Figure 6, each rotation through an angle of 360C producing a new layer with the molecules in each layer being similarly orientated so that a Z-type film as illustrated in Figure 4 is produced.

It will be appreciated that by using a substrate having a hydrophilic surface and reversing the direction of rotation of the roller 13, a Z-type multilayer in which the orientation of the molecules in the layers is reversed may be produced.

Referring now to Figure 7, in the second arrangement to be described a substrate 25 having a hydrophilic surface is mounted on the roller 13 and the two discrete areas 19 and 21 of the liquid surface respectively carry monolayer films 27 and 29 of amphiphilic molecules of different materials.

On rotation of the roller 13, in the anticlockwise direction as shown in Figure 8, initially molecules are picked up on the substrate surface only at the side of the roller leaving the liquid, i.e.

molecules from film 29 on liquid surface area 21 only are picked up. However, after the roller 1 3 has completed half a turn, a second layer consisting of molecules from film 27 on liquid surface area 1 9 is deposited on the first layer at the other side of the roller. Thereafter, as rotation of the roller 13 continues, layers in which the molecules are respectively oppositely orientated and are derived from films 27 and 29 are continuously picked up at opposite sides of the roller, thus forming a multilayer structure of two different materials of the form illustrated in Figure 5.

It will be appreciated that a similar structure in which the sequence of the layers is reversed may be produced by using a substrate having a hydrophobic surface instead of a hydrophilic surface.

Similarly, by reversing the direction of rotation of the roller 13 a structure in which the orientation of the molecules of each material and the sequence of the layers is reversed may be produced.

It will be understood that whilst in the methods described above by way of example the rotatable member is in the form of a tubular roller, this is not necessarily the case. For example, as illustrated in Figure 9 the method of Figure 8 may be carried out using a rotatable member is in the form of a flexible belt or web 31 mounted for rotation on a pair of parallel spaced rollers 33 and 35, the substrate 37 in this example having a hydrophobic surface.

It will be appreciated that in a method in accordance with the present invention, as in standard methods of forming Langmuir-Blodgett films, some means of keeping the molecules on the liquid surface compressed together so as to form a continuous layer must be employed, such as a barrier movable across the liquid surface. To this end the rotatable member in a method according to the invention may be arranged to be movable across the liquid surface.

It will be appreciated that whilst in the embodiments of the invention described above, by way of example, the substrate is carried on a rotatable member, in other embodiments of the invention, the substrate may itself constitute the rotatable member.

Claims

1. A method of preparing Langmuir-Blodgett multilayers on a substrate wherein: the substrate is carried on, or itself comprises, a member which is partly immersed in a liquid and which forms at least part of a barrier which divides the surface of the liquid into two discrete areas; one only of said areas carries a monolayer of a particular material; and the substrate is caused repeatedly to pass in turn through each of said areas by rotation of said member.

2. A method according to Claim 1 wherein the other of said areas carries a monolayer of a material different from said particular material.

3. A method according to Claim 1 wherein the other of said areas carries no material.

4. A method according to any one of the preceding claims wherein said member comprises a roller arranged for rotation about an axis substantially parallel to the surface of the liquid.

5. A method according to any one of Claims 1, 2 and 3 wherein said member comprises an endless belt, web or filament arranged for rotation about an axis substantially parallel to the surface of the liquid.

6. A method of preparing Langmuir-Blodgett multilayers substantially as hereinbefore described with reference to Figures 6 and 7, Figure 8 or Figure 9.