Langmuir blodgett films

Details Langmuir blodgett films Langmuir blodgett films

1987-04-20

1989-10-24

Buffalow, Edith

Stock material or miscellaneous articles

Composite

4274343, B32B 904

Patent

active

048761508

DESCRIPTION:

BRIEF SUMMARY
This invention relates to Langmuir-Blodgett (LB) films, and to devices using such films.
An LB film is generally prepared by depositing a monolayer of a surface-active material onto a water surface, using now well established techniques. The molecules of the surface active material align in the monolayer, the hydrophilic ends remaining in the water, and the hydrophobic end projecting out of the surface. By other known techniques, this monolayer may be transferred essentially intact onto the surface of a solid substrate, and further monolayers deposited on the layer on the substrate to form a film, ie a Langmuir-Blodgett film.
Compounds used in LB films are generally long chain molecules, containing 14 or more carbon atoms in their chain, with a hydrophilic "head" and a hydrophobic "tail," such as long chain carboxylic acids, eg CH.sub.3 (CH.sub.2).sub.14 CO.sub.2 H, where the CO.sub.2 H group constitutes the hydrophilic head.
LB films have properties, which make them useful in certain electronic devices.
Conventional (Y-type) LB films are symmetrical about their layer planes; However one of the most interesting features of the LB technique is the ability it gives to carry out the assembly of complicated molecular systems by depositing successive layers of different materials.sup.2. In particular multilayer films of the general type ABAB . . . where A and B are monolayers of different materials, and are non-centrosymmetric, are expected to show interesting and potentially useful pyroelectric, piezoelectric and second order non-linear optical effects. A two compartment LB trough has been developed which allows the convenient fabrication of ABAB . . . films.sup.3.
Interest in pyroelectrics for thermal detectors is generally increasing because of their wide spectral response, sensitivity and lack of cooling requirements. Thin film pyroelectrics in particular are provoking much interest due to the shorter response times available with low thermal mass, large area capability, and compatibility with electronic readout devices such as the charge coupled device (CCD) or the pyro-FET. Being a low temperature technique the LB technique is compatible with semiconductor materials and large areas of uniform deposition are in principle possible.
To produce a pyroelectric effect a material must possess a spontaneous polarisation P.sub.s (C cm.sup.-2) thus it must also possess a polar axis. This requires that the material be non-centrosymmetric. Normally P.sub.s is not directly observable due to compensation of the surface polarization charge by conduction charges from the material or atmospheric ions. However P.sub.s may be a function of the temperature T, and if T is changed slightly the compensation charges are too slow (since pyroelectrics are dielectrics) to follow the change in P.sub.s and a charge .+-.Q appears on the surface perpendicular to the polar axis; this is the pyroelectric effect.
We define the pyroelectric coefficient by
Generally p is also p(T) but the variation is normally weak except near phase transitions in ferroelectric pyroelectrics. Therefore we can write Q=p.DELTA.T where .DELTA.T is a small change in T. Conventional high performance pyroelectrics have p=3.times.10.sup.-8 C cm.sup.2 K.sup.-1. Nearly all such materials are ferroelectrics operating close to their Curie temperature to obtain the high dPs/dT.
In conventional Y-type LB films the molecular dipole moments of adjacent layers cancel and therefore P.sub.s =0. In an ABAB . . . film the dipole moments of A and B being different do not cancel but add vectorally to give a non zero P.sub.s and a polar axis perpendicular to the film plane. X and Z type films will also show a non-zero Ps; pyroelectricity and piezoelectricity in such films has been reported by Vlinov4,5.
It is an object of the present invention to provide novel LB films which have improved pyroelectric and piezoelectric properties. Other objects and advantages will be apparent from the following description.
According to a first aspect of the invention a Langmuir-Blodgett film of

REFERENCES:
patent: 4536450 (1955-08-01), Garito
L. M. Blinov, Polar Langmuir-Blodgett Films, 1984, vol. 120, Thin Solid Films, pp. 161-170.
M. F. Daniel, Prep of Non-Centrosym, L-B Films . . . , Mol. Cryst. Liq. Cryst. vol. 102, (Letters), pp. 193-198.

Affiliated with

Also associated with

Rating

Langmuir blodgett films does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Langmuir blodgett films, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Langmuir blodgett films will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1588488