CA2045980A1 - Process for the preparation of high-purity, homogeneous, monomolecular, ultrathin layers on solid supports - Google Patents

Process for the preparation of high-purity, homogeneous, monomolecular, ultrathin layers on solid supports

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Publication number
CA2045980A1
CA2045980A1 CA002045980A CA2045980A CA2045980A1 CA 2045980 A1 CA2045980 A1 CA 2045980A1 CA 002045980 A CA002045980 A CA 002045980A CA 2045980 A CA2045980 A CA 2045980A CA 2045980 A1 CA2045980 A1 CA 2045980A1
Authority
CA
Canada
Prior art keywords
purity
homogeneous
impurities
meniscus
preparation
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
CA002045980A
Other languages
French (fr)
Inventor
Hans Riegler
Karl Spratte
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hoechst AG
Original Assignee
Hoechst AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Hoechst AG filed Critical Hoechst AG
Publication of CA2045980A1 publication Critical patent/CA2045980A1/en
Abandoned legal-status Critical Current

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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B05SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05DPROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00Processes for applying liquids or other fluent materials
    • B05D1/18Processes for applying liquids or other fluent materials performed by dipping
    • B05D1/20Processes for applying liquids or other fluent materials performed by dipping substances to be applied floating on a fluid
    • B05D1/202Langmuir Blodgett films (LB films)
    • CCHEMISTRY; METALLURGY
    • C30CRYSTAL GROWTH
    • C30BSINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/60Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
    • C30B29/64Flat crystals, e.g. plates, strips or discs
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00Nanotechnology for materials or surface science, e.g. nanocomposites
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00Manufacture or treatment of nanostructures

Abstract

Abstract of the disclosure Process for the preparation of high-purity, homogeneous, monomolecular, ultrathin layers on solid supports Process for the preparation of high-purity, homogeneous, monomolecular layers by the Langmuir-Blodgett method.
Contaminant concentrations formed at the end of the meniscus are removed parallel to the three-phase line, for example by a controlled lateral, local flow of a gas across the water surface or dilution of the floating monolayer by expansion. The removal of impurities can be maintained simultaneously during transfer.

Description

HOECHST ARTIENGESELLSCHAFT HOE 90/F 198 Dr. DS/P1 Description ~ ?1$~

Proces~ for the preparation of high-purity, homogeneou~, monomolecular, ultrathin layers on solid supports.

~ he invention relates to a process for the preparation of high-purity, homogeneous, monomolecular layers on solid supports by the Langmuir-Blodgett method, in which contaminant concentrations formed during the transfer process are removed or dilu~ed by selective and con-trolled, lateral, local surface convection or by selec-tive compres~ion/expansion cycles.

Coated supports are increasingly use~ in industrialtechnology.
~:' Thus, supports coated by the LB method can be used, for example, for communication technology as electronically lS and optoelectronically active truc~ural elements. The films are also suitable as active elements or passive matrix in the area of sensor technology. Furthermore, the mechanical or chemical surface properties of substrates can be adapted to a desired purpose by coating their surface, for example for reducing friction. However, the films can also serve as protective films for the support ~` surface underneath in order to preserve its specific -` surface propertieæ.
.~
For these applications, it i8 necessary to prepare well-defined, ultrathin, in some cases al~o multi-layer, coat-ings of high purity, few defects and homogeneity.

Homogeneous, ultrathin, organic, ordered film and film ~ystems which are low in impurities and are, as far as po~sible, free of defects are, for example~ of great intere~t individually for the following applications:
. .
a) Optical applications: directional, guided light trans-mission with low attenuation losses due to absorption or :,, ~: , . - . , , `:
, light scattering, such as, for example, opti ~ wave-guides with nonlinear optical properties.

b) Electrical applications: electric conductors of high anisotropy, for example one-dimensional or two-dimensional conductors (for e~ample molecular elec-tronics).

c) Active elements or "host lattices" for dafined incor-poration o~ sensor elements in the area of sensor tech-nology (for example pyroelectronic detectors of minimum heat capacity or highly specific biosensor~ based on selective ~urface bonding of functional groups or mole-cules).
, d) Protective films as surface barriers against chemical, mechanical or electxical effects (for exEmple lubrication films, corrosion protection, insulating films).

To prepare ordered ultrathin organic films and film syatems, the Langmuir-Blodgett (LB) method i9 preferably used. In thi~ method, suitable molecules are spread on a water surface. By changing the area per molecule it is possible to determine the packing den~ity and structure and orientation of the molecules as a result of the change in the total surface area. Typically, the floating monomolecular layer is then transferred to a solid sub-strate by immersing and/or withdrawing the latter ~hile keeping the area per molecule con~tant. Per dipping ; operation, one monomolecular layer i8 transferred to the ; support. By immersing and withdrawing the same support repeatedly, it is thus possible also to prepare multi-layer systems.

LB films are mainly constructed using water-in oluble amphiphilic molecules. These molecules have a hydrophilic end ~"head'l) and a hydrophobic end ("tail") and align themselves on the water surface with the hydrophilic side pointing toward the water subpha~e. Apart from -, , :, . , , . ~
.

amphiphilic monomers, amphiphilic polymers and long-chain, purely hydrophobic molecule~ are also suitable for constructing LB films.

The preparation of thin films by the LB method has S already been described many times tDE-A 3,843,194;
DE-A 3,911,929).

A central problem when preparing and using LB filmq i~
the purity and homogeneity of the layer~.

When the monolayer spread on the water ~urface i8 trans-ferred to the solid support, it can be observed that a selectively stronger attractive layer/substrate inter-action takes place between the more tightly packed condensed areas of the monolayer compared with the liquid, less ordered matrix of the monolayer. This selec-tive interaction results, for example, in the directly observable ~elective attraction of the ~loating domains of coexisting pha~es by the solid substrate. Furthermore, it can be observed that the support acts as nucleation and condensation area for the monolayer molecules, i.e.
the monolayer is preferentially ad~orbed on the support as a more highly ordered condensed matrix.

The selective interaction of the condensed floating domains and the conden~ation of the monolayer at the tLme of transfer initially leads to the transfer of a con densed layer which i~ low in impuritie6 at the beginning of the LB transfer (beginning of withdrawal of the support), while the impurities simultaneously concentrate in the still floating li~uid film zone directly at the three-phase borderline (i.e. the area where the monolayer touches the ~upport). This phase æeparation i~ a re~ult of the film condensation and the selective attraction of the condensed domains. ~he condensed regions are much more highly ordered than the more liquid regions and contain considerably fewer impurities, since the latter disrupt the order. The fact that the purer sub~tance i~

'' ' `

~)L~

selected for transfer leads to an increase in the con-taminant concentration at the end of the meniscus in the still floating, not yet ~ransferred monolayer. After an initially increasing phase separation, caused by transfer S of the ~urer substance to the support and the increase of contaminant concentration in the still floating boundary zone, a (dynamic) equilibrium is rapidly reached. This equilibrium situation with respect to the local con-taminant concentration and its profile i5 determined by several factors, such as, for example temperature and rate of transfer. An eguilibrium is reached because with increasing contaminant concentration during the transfer the point is necessarily reached at which the selectivity of the substrate/layer interaction is no longer suffici-ent for the condensed matrix and impurities are al~otransferred. For reasons of material conservation, the dynamic equilibrium thus ultLmately leads to the transfer of a layer having the same contaminant concentration as that of the floating film. This is the typical situation with the LB transfer as practised today. The contamina-tion zone is localized because the removal (dilution) of the impurities at the end of the meniscus is only diffusion-controlled due to a lack in convection and therefore virtually without effect for reasonable rates of transfer.
.~
The buildup and stabilization of the higher contaminant concentration at the end of the meniscus can be observed directly ~y increasing the solidification pres~ure (Raoult's law) and thus as a domain-depleted or domain-free zone at the end of the meniscu~. The monolayer to betransferred is always moved through the contamination zone shortly before transfer to the solid 6ubstrate and thus exposed to the conditions of higher contaminant concentration.
, ~
Hitherto, hardly any proce~ses for the direct selective modification of the layer to be transferred by substrate/
layer interactions have been described in the literature.

J

Most processes mentioned relate to the modification of the layer properties of the film still floating on the planar water surface.

One process (Thin Solid Films, 179 (1989) 233-238) describes the electrochemical modification of films during the LB transfer. A low voltage (< 1 volt) applied between the substrate and the subphase results in elec-trochemical oxidation or reduction of the monolayer to be transferred during transfer. The e~periments described are limited to the electrochemical modification of the molecules and their effects on the layer structure.
Physical layer modifications are exclusively explained by the chemical modification of the layer molecules.

Another process (Thin Solid Films, 178 (1989) 183-189) describes the preparation of monolayers which are low in ; impurities by means of local melting on the water sur-face. ~he monolayer is heated locally, i.e. melted, at constant surface pressure by means of a local heat source (for example heating rod) and then again cooled 20; (condensed). The recrystallization pushes the impurities out of the ordered phase. In this method, a heating xod is moved slowly at a suitable distance over the mono-layer, resulting in local melting and subsequent recrys-tallization.

A further process (DE-A 4,010,201) utilizes the healing of defects caused by certain compression/expansion cycles for preparing monolayers on the water which are low in defects.
' The processes described for the physico-structural layer modification are limited to the improvement of monolayers on the water surface. However, investigations have shown that the film properties ~homogeneity, defect density, purity, and the like) change significantly during trans-fer. Since Yirtually all industrial applications require the use of thin organic films on solid supports, the .:

- 6 _ 2 quality of the films transferrad is ultimately the decisive factor. In the hi~herto customary standaxd LB
transfer (continuous transfer at fixed parameters such as pressure, temperature, rate of transfer, and the like), this quality is by no means satisfactory with respect to homogeneity and low number of defects. Thus, in the case of substances having first-order phase transitions, no continuous condensed matrix can be transferred. Com-pression on the water only leads to ~ormation of domains having ordered, pure regions in a liquid, more highly contaminated matrix. ~hese structures are further modi-fied during transfer as a result of layer/substrate interactions, ~o that overall a distinctly heterogeneous film is transferred.

Accordingly, there was the object of developing a process which enables high-purity, monomolecular layers which are low in defects to be obtained on solid support~ by the LB
method.

This object is achieved by the process according to the invention, in which high-purity, homogeneous, mono-molecular ultrathin layers are prepared by the Langmuir-Blodgett method, in which the contaminant concentration formed at the end of the meniscus, which prevents trans-fer of a highly ordered, high-purity matrix, is removed parallel to the three-phase line by sur~ace con~ectionO
.
In a preferred case, the impurities formed at the end of ~ the meniscus can be removed by allowing a suitable gas - to flow across the water surface in a controlled manner (for example lateral laminar flow). Examples of suitable gases of this type are the noble gases but also nitrogen and air. A particular advantage of this process is that it is possible to maintain the removal of the Lmpurities simultaneously during transfer, thus ensuring a con-tinuous procedure.

In a further preferred case, the removal of the . ~ .
.

~f~ f,~ r~ ~

impurities at the end of the meniscus can also be effected or enhanced by suitable compr2ssion/expansion cycles. This i5 typically done by transferring the layer to the support by withdrawal of the latter until, as a result of the continuously increasing contaminant con-centration at the end of the meni3cus, there is a risk of contaminated transfer. Before this occurs, transfer of the monolayer i8 stopped, and the floating film is expanded. This rQsults in dilution of the monolayer floating on the water and in removal of the impurities at the end of the meniscus. After recompression, a portion of high quality layer can then be transferred again to the support. If appropriately done, this result3 in a seamless, homogeneous, high purity, condensed layer.

It is particularly advantageous to lower ~he coated area of the support before film expansion to below the equilibrium level of the meniscus. This avoids undesired, uncontrolled coating (pressure coating) of the support with the hiyhly contaminated layer during expansion or - 20 recompression.

A typical coating sequence for preparing a continuous, homogeneous, high-purity coating is as follows:

1. Slow coating (coating pressure ~ = constant) while monitoring the increase in contaminant concentration at the end of the meniscus.
~ , 2. Stopping the coat ng by halting the withdrawal of the support.
3. Reimmersion of the support at ~ = constant. ~he end of the meni~cus remains fixed on the support but moves relative to the subphase, i.e. the profile of ;~ the meniscus is changed. After lowering the meniscus level (= level of the end of the meniscus relative to the planar subphase surface) by several 100 ~m, ~ the support is halted.

;;' , ' .
.
4. The floating monolayer i8 fully expanded. This removes and dilutes the impurities at the end of the meniscus.
5. The monolayer is recompressed until it reaches the `~ 5 transfer pressure.
6. The support i8 (slowly) withdrawn, and the desired homogeneous high-purity coating is obtained from the suitable meniscus level (eguilibrium level) onwards, -~ while the impurities are simultaneously concentrated at the floating end of the meniscus. ~he coating ~; process is now again repeated starting with 1.

In crder to ensure ef~ective selection of the more highly ordered layer fragments at the end of the meniscus, a comparably slow rate of coating (~ 10 ~m~sec) i8 advantageous.

The process according to the invention is based on the difference in the dipole density of different monolayer ;~ regions. In heterogeneous films (i.e., for example, in contaminated or selectively doped films) it is virtually always possible to achieve local phase sepaations (for example via pressure or temperature), which can then be selected during transfer due to their difference in dipole den~ity. The process according to the invention càn therefore be applied to many different substances.
.
:
The monomolecular layerG prepared by the process accord-~ ing to the invention are di~tinguished by high purity and - high lateral structural ho~oseneity. A particular ad-vantage is that it i6 possible to selectively ad~u~t the purity or sven the degree of doping of the layers.
~' .
~amples Dipalmitoylphosphatidylcholine monolayers were prepared by the process according to the invention. The layers , , , - ~ . ' ` ~ ' ' ; ~

:, ~ ; , ,.,- .

-l~ 9 ~
were first applied by the standard LB method, during which the selective substrate/layer interactions dea-cribed were observed. After initial coating with a zone - low in impurities (~ 50 ~m wide), the contaminant content at the end of the meniscus increases to such an extent that the layer transferred is inhomogeneous and con-taminated. A fluorescent dye added in small amount~
t~ 1 mol-~), which itself acts as impurity and can be localized ~y means of a suitable tran~fer fluorescence microscope, ~erves a~ indicator for the contEmination.
The layers prepared by the customary LB method display a heterogeneous structure.

The result of continuous slow coating with removal of the impurities by convection is shown in Fig.1. The support was first 310wly withdrawn without convection.
This transfers the light, highly contaminated, heterogeneous region (left half Fig. 1 ). Then, without interrupting the withdrawal a constant flow of argon, which achieves the removal of the impurities, was applied. The layer transferred by this method is shown on the righthand side of Fig. 1. It can be seen that the layer prepared by convection contains much less dye (= fewer impurities) than the layer applied under other-~' wise identical conditions but without selective convection. The layer is much lower in impurities and also more homogeneous.

~ Fig. 2 illustrates a ~equential, highly homogeneous -~ coating with few Lmpurities, using suitable compre~sion~
expansion and immersion~withdrawal cycles to remove the accumulated impurities. It can be ~een tha~ it is po~-sible to coat continuous homogeneous zones of various - width and low in impurities (dark) (lower half of Fig.2). The wider of the three dark zones is composed of two successive coating sequences and is intended to show that continuous, homogeneous, high-purity monolayers of any desired length can be transferred by suitable individual coating cycles. The light heterogeneous areas ~:~ between the three dark zone~ are formed by insufficient removal of the accumulating impurities ~here fluorescent dye). The experiments listed for improving the layer quality of DPPC monolayers were also carried out with dimyristoylphosphatidylethanolamine (DMPE) films. For this material, the same ~electivity of the substrate/
: layer interaction with respect to the molecular packing density and orientation was observed.

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., , ~ .

Claims (6)

1. A process for the preparation of high-purity, homogeneous, monomolecular layers by the Langmuir-Blodgett method, which comprises removing contaminant concentrations formed at the end of the meniscus parallel to the three-phase line by surface convection.
2. The process as claimed in claim 1, wherein the impurities are removed by a controlled, lateral, local flow of a gas across the water surface.
3. The process as claimed in claim 2, wherein the gas is a noble gas, nitrogen or air.
4. The process as claimed in claim 1, wherein the removal of the impurities is maintained simul-taneously during transfer.
5. A process for the preparation of high-purity, homogeneous, monomolecular layers by the Langmuir-Blodgett method, which comprises diluting and removing the contaminant concentration formed at the end of the meniscus by expanding the floating monolayer.
6. The process as claimed in claim 5, wherein the removal of the impurities is effected sequentially during suitable immersion/withdrawal and compression/expansion cycles and the coated area of the support is lowered to below the equilibrium level of the meniscus before the film expansion.
CA002045980A 1990-07-02 1991-06-28 Process for the preparation of high-purity, homogeneous, monomolecular, ultrathin layers on solid supports Abandoned CA2045980A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE4021197A DE4021197A1 (en) 1990-07-02 1990-07-02 METHOD FOR PRODUCING HIGH-PURITY, HOMOGENEOUS, MONOMOLECULAR, ULTRADUENER LAYERS ON SOLID CARRIERS
DEP4021197.5 1990-07-02

Publications (1)

Publication Number Publication Date
CA2045980A1 true CA2045980A1 (en) 1992-01-03

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ID=6409589

Family Applications (1)

Application Number Title Priority Date Filing Date
CA002045980A Abandoned CA2045980A1 (en) 1990-07-02 1991-06-28 Process for the preparation of high-purity, homogeneous, monomolecular, ultrathin layers on solid supports

Country Status (6)

Country Link
EP (1) EP0464640A3 (en)
KR (1) KR920002829A (en)
CA (1) CA2045980A1 (en)
DE (1) DE4021197A1 (en)
FI (1) FI913167A (en)
IE (1) IE912306A1 (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19733731A1 (en) 1997-08-04 1999-02-25 Siemens Ag Integrated electrical circuit with passivation layer
DE10326864B3 (en) * 2003-06-14 2005-02-03 Fritz Hockemeyer Process for curing crosslinkable silicones in coating technology

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS60216840A (en) * 1984-04-10 1985-10-30 Canon Inc Film-forming device
FI77679C (en) * 1987-02-23 1989-04-10 K & V Licencing Oy Film aggregate and process for its preparation.
DE3828836A1 (en) * 1988-08-25 1990-03-01 Hoechst Ag METHOD AND DEVICE FOR PRODUCING THIN LAYERS

Also Published As

Publication number Publication date
EP0464640A3 (en) 1992-02-26
DE4021197A1 (en) 1992-01-16
FI913167A (en) 1992-01-03
IE912306A1 (en) 1992-01-15
FI913167A0 (en) 1991-06-28
EP0464640A2 (en) 1992-01-08
KR920002829A (en) 1992-02-28

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