WO2008111850A2

WO2008111850A2 - Synthesis of molecular metalorganic compounds

Info

Publication number: WO2008111850A2
Application number: PCT/NO2008/000099
Authority: WO
Inventors: Ola Nilsen; Helmer FJELLVÅG
Original assignee: Universitetet I Oslo
Priority date: 2007-03-15
Filing date: 2008-03-14
Publication date: 2008-09-18
Also published as: WO2008111850A3

Abstract

A process for the preparation of thin films of a molecular metalorganic nature comprising growing with a gas phase deposition technique preferable the ALCVD (atomic layer chemical vapour deposition) technique. As an example, trimethylaluminium (TMA), titanium tetrachloride (TiCl4), diethyl zinc (DEZ), and 8-hydroxyquinoline (q) have been used as precursors to fabricate thin films of aluminium tris 8-hydroxyquinoline, titanium tetra 8-hydroxyquinoline, and zinc bis 8-hydroxyquinoline constructing a molecular hybrid type film. These films can be used as emittive materials in organic light emitting diodes (OLED) applications and as n-type conducting materials. In addition, films of aluminium benzoate have been fabricated using TMA, benzoic acid, and water or ozone.

Description

Synthesis of molecular metalorganic compounds

The present invention relates to a process for preparation of thin films of molecular metalorganic compounds, thus producing a thin film, a thin film, substrates comprising such thin films, and the use of the thin films.

Today metalorganic compounds are used within different technical fields, but especially within the field of electronics have they received much attention lately. These compounds may function as n-type semiconducting materials and thus be useful in different electronic components. As an example metal quinoline type materials are used as emitting layers in organic light emitting diodes devices.

Today thin films comprising metalorganic compounds can be produced through different processes. Thin films of metal quinoline type materials can be produced by many different means such as wet chemical routes, sol-gel spin coating, and physical processes such as thermal evaporation, and gas phase deposition processes such as chemical vapour deposition. These techniques have some drawbacks when it comes to covering uneven surfaces and large surfaces. Some of the techniques also have restriction when it comes to thermal conditions; some techniques require that the substrates can sustain high temperatures.

The aim of the present invention is to provide an alternative preparation method for production of molecular metalorganic compounds, which may provide a relatively even layer on even as well as uneven surfaces. The method should further be applicable for covering large surfaces. Further it is an aim to provide a method where the composition and the thickness of the film of metalorganic compounds more easily can be adapted for different purposes.

ALCVD (= atomic layer chemical vapour deposition, also known as ALE = atomic layer epitaxy, and ALD = atomic layer deposition) is a thin film technique that utilizes only surface reactions, and is described in prior art, see e.g. M. Ritala, M. LeskelS, in: H.S. Nalwa (Ed.), Handbook of Thin Film Materials, vol. I, Academic Press, San Diego, CA, 2001, p. 103.

A thin film is produced by the ALCVD technique by using different types of precursors. The precursors are pulsed sequentially into the reaction chamber where it reacts with all surfaces present; each pulse is followed by a purging time with an inert gas. In this way gas phase reactions are eliminated and film is constructed by precursor units in the order that they are pulsed. This technique makes it possible to change building units at the resolution of one monolayer, and therefore enables production of artificial structures of hybrid films with different types of organic and inorganic building units. Traditional the ALCVD process leads to materials comprising a three-dimensional network.

It has now surprisingly been found that this technique can be utilized to construct thin films of molecular metalorganic compounds such as materials belonging to the class of metal quino lines and metal benzoates.

One aspect of the present invention is a process for preparation of a thin film comprising molecular metalorganic compounds on a substrate characterised by using an atomic layer gas phase deposition technique comprising the following steps: a) contacting the substrate with a pulse of an inorganic precursor selected from a group consisting of metal alkyls, metal cycloalkyls, metal aryls, metal amines, metal silylamines, metal halogenides, metal carbonyls and metal chelates, where the metal is selected from the group comprising Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Te, Po, alkali metals, alkaline earth metals, 3d-insertion metals, 4d- insertion metals, 5d-insertion metals, lanthanides and actinides; b) reacting the inorganic precursor with an organic compound present on at least one surface of the substrate or adsorbing the inorganic precursor on at least one surface of the substrate; c) removing non-adsorbed or non-reacted inorganic precursor and reaction by- products if any; d) contacting the inorganic precursor on the surface of said substrate with a pulse of an organic precursor with at least one functional group capable of a chemical reaction with an inorganic precursor, e) reacting the organic precursor with the inorganic compound adsorbed on the 5 surface, or adsorbing the organic precursor on the surface; f) removing non-adsorbed or non-reacted organic precursor and reaction byproducts if any; g) optionally repeating step a) to f) until the wanted film thickness is achieved; o where either step b) or step e) comprises a reaction forming a layer of molecular metalorganic compounds.

Another aspect of the present invention is a thin film comprising hybrid monolayers comprising molecular metalorganic compounds held together by physical forces such ass van der Waals forces or dipole forces.

Further the present invention provides a substrate characterised by comprising a thin film coating produced by the process according to the present invention or a thin film according to the present invention. 0

A further aspect of the present invention is the use of a thin film produced by the process according to the present invention or a thin film according to the present invention as an emittive layer in OLED applications, as an n-type semiconducting material. S

Other embodiments of the present invention are described in the subclaims.

The inventors surprisingly found that synthesis of metal quinolines by the ALCVD technique provide materials that are of a typical molecular-solid-type material and noto of the traditional three-dimensional network-type commonly associated with materials produced by this technique. The surprisingly additional effect that the ALCVD technique brings into this field is the possibility to use alternating highly reactive types of precursors in order to produce metalorganic compounds of different types. The ALCVD technique has the advantage over the other mentioned techniques in that it can coat surfaces of intricate shape in a conformal fashion without producing pinholes. The material can also be produced at relatively low temperatures enabling thermal sensitive substrates to be used.

In the present invention the term "inorganic precursor" is considered to mean any compound comprising an inorganic moiety, where the inorganic precursor comprises one or more reactive groups for reaction with a different precursor.

By the term "inorganic moiety" is meant a moiety that contains at least one metal atom. For instance it may be a compound that is metal organic, organometallic, a halogen compound, carbonyl or any other compound that is able to bring the metal into the gas phase at a suitable process temperature.

hi the present invention the term "organic precursor" describes an organic compound with at least one functional group available for reaction with the inorganic precursor.

The process, according to present invention, comprises applying alternate pulses of inorganic and organic precursors, which react and form metalorganic compounds. It must be understood that which precursor, organic or inorganic, is used first can be freely selected. However, the first precursor should have the ability to be either physically or chemically adsorbed on the surface, so that the first precursor is available for reaction with the second precursor after the first purge. Further, the reacted second precursor should provide the possibility for subsequent physical and/or chemical adsorption of a new pulse of the first precursor. So, depending on the choice of the first pulse, the inorganic or organic precursor should either have the ability of being chemically or physically adsorbed on the surface or form a surface on which the other precursor may be adsorbed. By the term "oxygen comprising precursor" is meant a small oxygen comprising compound such as H₂O, H₂O₂, O₃, O₂, D₂O, N₂O, NO, NO₂, N₂O₄, HO-C_1-6 alkyl etc. preferably H₂O, H₂O₂, O₃, and O₂.

s In the present invention the term "organic precursor comprising a quinoline backbone" is considered to mean any compound comprising a quinoline ring and at least one functional group substituent.

The ALCVD technique can be viewed as a controlled sequential chemical reaction I₀ technique. The film is built by letting a functional group on a gas molecule react with a suitable site on a surface. The gas molecules that react should leave a site on the surface that will function as a reactive site for a following type of gas molecules in order to produce a continuous film. However, as now seen by growth of metal quinolines and metal benzoate, it may be sufficient that the site left on the surface is of a type where is subsequent physical adsorption may take place.

This type of growth is exemplified in the growth OfAIq₃, Tiq₄₎ Znq₂ and aluminium benzoate type of films, which will be described in more detail below.

20 Some inorganic precursors that may take part in the process according to the invention are described below. All the suggested reactions are only illustrations of possible reactions and are not to be interpreted as limitations. Other inorganic precursors that can take part in the process are for instance described in J. Appl. Phys. 97, 121301 (2005).

2₅ Metal alkyls

Metal alkyls and metal cycloalkyls are rather reactive and hence undergo reaction with most organic functional groups. This is exemplified by production of thin films by trimethyl-aluminium (TMA) and hydroxides. Examples of possible metal alkyls are: A1(CH₃)₃, Zn(Et)₂, Zn(Me)₂ , MgCp₂; where Cp stands for cyclopenthyl.

30

Metal halogenides

Some electropositive metal halogenides are rather reactive and undergo reaction with many organic functional groups. The halogen may be F, Br, Cl or I. Some examples are AlCl₃, TiCl₄, SiCl₄, SnI₄, Si(CH₃)₂Cl₂. Metal carbonyls

Metal carbonyls are also reactive, and some examples are: Fe₂(CO)₉, Mn(CO)_x

Metal chelates

Examples of reactive metal chelates are: VO(thd)₂, Mn(HMDS)₂, Fe(HMDS)₂,

TiO(thd)₂, Pt(thd)₂.

Thd (=2,2,6,6-tetramethylheptane-3,5-dione) is a chelating compound from which compounds with elements as Ti, V, and several more can be made. HMDS stands for hexamethyl-disilazane

Other possible chelates are beta-ketones such as acetylacetonates, fluorinated thd- compounds and ethylene-diamine-tetra acetic acid (EDTA).

Metal aryls

Examples of applicable metal aryls are BiPh₃ and PbPh₃ where Ph stands for phenyl.

Metal amines

Metal amines can i.e. be the compounds like Hf(NEt₂)₄ and Zr(NEt₂)₄ where Et stands ethyl.

Metal silylamines Examples of applicable metal silylamines are Mn(HMDS) and Mg(HMDS), where HMDS stands for hexamethyldisilazane.

Metals

The metal for the inorganic precursor is selected from the group consisting of Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Te, Po, alkali metals, such as Li, Na, K, Rb, Cs; alkaline earth metals, such as Be, Mg, Ca, Sr, Ba; 3d-insertion metals, such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn; 4d-insertion metals, such as Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd; 5d-insertion metals, such as La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, lanthanides such as Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and actinides such as Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr. Some of the more interesting metals are Al, Si, Sn, Zn, Mg, Ti, V, Mn, Fe, Co, Cr, Cu, or Pt.

The organic precursor as defined above is an organic compound with one functional group able to react with an inorganic precursor. The organic backbone can be any organic compound selected from alkanes, alkenes, alkynes, cycloalkanes, aryls, aromatic or non-aromatic, heterogenic or non-heterogenic ring structures, where the heterogenic compound comprises one or more heterogenic atoms selected among N, O, P and S. Where the organic backbone in each may comprise between 1 and 30 carbon atoms, preferably between 1 and 12 and more preferred between 3 and 9 carbon atoms.

The term "functional group" as used here means any organic rest which will react with the reactive group on the inorganic precursors according to the present invention, where the reaction will led to a bond between the organic and inorganic moieties and where any by-product created by this reaction is preferably non-reactive under the prevailing conditions and can easily be removed from the surface by purging. With the term "bond" is meant both strong covalent bonds and weaker bonds such as interactions between electro file elements and electron rich areas such as electron lone pairs or aromatic systems. Examples of functional groups comprise, but are not limited to, -OH, -COOH, -0-(C_1-6 alkyl), -NH₂, -NH-R, etc.

For the process according to the present invention to lead to the inventive layer of molecular metalorganic compounds it is expected that if the organic compound comprises more than one reactive site like the lone pair and the functional group in 8- hydroxyquinoline, these sites most likely must have an orientation so that they will all react with the same inorganic moiety. Further, after reaction with an inorganic moiety the organic group should not react and form strong bonds with the inorganic precursors in the next pulse, thus forming a network.

One group of metalorganic compounds of special interest is metal quinolines. Metal quinolines are condensed phases where the central metal is chelated by the same or different types of quinolines. The structural backbone of quinoline, together with the structure of aluminium tris 8-hydroxyquinoline is given below. The quinolines that are of particular interest in this application are those that in addition to the lone pair of electrons on the nitrogen atom have at least a functional group present which can react with the metal atom, such as the 8-hydroxyquinoline.

The structure of the quinoline backbone is as follows:

Quinoline

The metal organic molecule aluminium tris 8-hydroxyquinoline (= AIq₃) has the following structure:

Aluminium tris 8-hydroxyquinoline (= AIq₃)

Metal quinoline type films may be used for different types of purposes. Metal quinoline type materials are used as emitting layers in OLED (organic light emitting diodes) devices. They may function as n-type semiconducting materials and may thus enter into such electronics, however, it is most recognised as an emitting material in OLED (organic light emitting diode) applications where it also serves as an n-type semiconducting material. Aluminium tris-8-hydroxyquinoline is also known as a triple emitter. The surfaces that are coated by metal-quinoline type material may take any physical form as long as it is a solid or liquid stable during the deposition conditions. One may use flat substrates or powder or surfaces with complex geometries.

Due to the large number of possible quinolines and metals that may be imagined used in constructing such metal-quinoline type material, there is an almost unlimited imagined outcome in possible properties that may be produced. Some of these constructions may involve several layers of different metals and quinoline materials in order to construct the desired properties. The motivation of this work has been to demonstrate that the ALCVD method may extend the different possibilities one has to produce metal quinolines.

The present invention will be described in further detail referring to the enclosed figures. Where the figures illustrates the following:

Fig. 1: The effect of the pulse and purge parameters on the growth of zinc bis 8- hydroxyquinoline at a reactor temperature of 125 °C and with an inherent pulse/purge scheme of 1 s Zn(CH₂CH₃)₂ - I s purge - 3 s 8-hydroxyquinoline - 2 s purge.

Fig. 2: hi situ measurement of mass change by quarts crystal microbalance during deposition of zinc bis 8-hydroxyquinoline at a reactor temperature of 125 ⁰C.

Fig. 3: Growth rate of zinc bis 8-hydroxyquinoline as function of reactor temperature for a pulse/purge scheme of 1 s Zn(CH₂CH₃)₂ - I s purge - 3 s 8-hydroxyquinoline - 2 s purge.

Fig. 4: In situ measurement of mass change by quarts crystal microbalance during deposition of aluminium tris 8-hydroxyquinoline at a reactor temperature of 85 ⁰C.

Fig. 5: Growth rate of aluminium tris 8-hydroxyquinoline as function of reactor temperature for a pulse/purge scheme of 1 s A1(CH₃)₃ - I s purge - 3 s 8-hydroxyquinoline - 2 s purge. Fig. 6: In situ measurement of mass change by quarts crystal microbalance during deposition of titanium tetra 8-hydroxyquinoline at a reactor temperature of 85 °C.

Fig. 7: Growth rate of titanium tetra 8-hydroxyquinoline as function of reactor temperature for a pulse/purge scheme of 1 s TiCl₄ - I s purge - 3 s 8-hydroxyquinoline - 2 s purge.

Fig. 8: Infrared transmittance analysis of films deposited at 125 ⁰C on silicon and for powdered 8-hydroxyquinoline embedded in a KBr matrix. Znq₂ = zinc bis 8- hydroxyquinoline, AIq₃ = aluminium tris 8-hydroxyquinoline.

Fig. 9: Infrared transmittance analysis of films deposited at 100 °C on silicon using the pulsing schemes: H₂O + benzoic acid + TMA, O₃ + benzoic acid + TMA, and for film of Al₂O₃ formed by pulsing H₂O + TMA.

Fig. 10: Photoluminescence at room temperature OfAIq₃, Znq₂, and Tiq₄ films by excitation of radiance with a wavelength of 375 nm. The intensity scale is normalized to the maximum intensity.

Using the ALCVD technique, it will for instance be possible to produce quinoline chelated compounds comprising a range of different metals and quino lines. The precursor materials will then be of a volatile metal compound with suitable reactivity and a quinoline with the desired properties. Typical metal compounds suitable as precursor for such synthesis are the metal alkyls, metal halogenides, metal cyclopentadienyls, metal β-ketonates etc. The basic quinoline comprises a nitrogen group in an aromatic ring. In order to make a reaction scheme according to the traditional ALD type of growth, it is necessary with an additional functional group, e.g. an alcohol, and that the two (or more) functional groups forms bridging constructions between different metals in the structure. However, we have now shown that it is indeed possible to deposit materials where the functional groups bond to the same metal by the ALD technique, and thus chelate this metal. At present one of the more interesting quinolines from a technological point of view is the 8-hydroxyquinolines where the dentates are the lone pairs on the oxygen and the nitrogen in the compound. For such quinolines it is expected that the hydroxyl group is important for the ALD reaction mechanism. The procedure can be explained through an example:

0) The overall initial step is to treat the native surface with the reactive metal precursor, e.g. Al(CHs)₃. This will react with hydroxyl (-OH) groups present

. on the surface and form metal precursor fragments, e.g. -0-Al(CH₃) _!_₂. The reaction will then stop due to lack of reactive surface sites. The surface will then form a basis as an active surface for the next reaction step.

1) The reaction chamber is purged for excess A1(CH₃)₃ and by-products in order to prevent any gas phase reactions from taking place.

2) The next step is introduction of the hydroxyl-quinoline. The hydroxyl groups of these quinolines will react with the methyl groups of the active surface and form Al-O-quinoline bonds.

3) The reaction chamber is purged for excess quinoline and by-products in order to prevent any gas phase reactions from taking place.

4) A1(CH₃)₃ is then introduced. It will react with all surfaces present which by now should be saturated with quinoline. One should inherently believe that at this point there were no more reactive sites present for reaction with

A1(CH₃)₃. However, experiments have shown this to not be the case and A1(CH₃)₃ does in deed react with the surface.

Steps 1-4 are then repeated until the film has gained the desired thickness.

The exact reaction mechanism is unsolved at the moment but one hypothesis is that it involves a reaction step where either the metal compound or the chelating compound is physically adsorbed to the surface. Alternatively, it might be hypothesised in the case of quinoline, that one quinoline chelate in the metal quinoline compound opens up when additional inorganic precursor is pulsed and forms bond to both its native metal atom and the new metal atom. The molecular structure of the compound is restored when additional quinoline chelate is introduced in the next pulse. Alternatively it may also be hypothesised that the 8-hydroxyquinoline upon insertion into the chamber may take part in a two step reaction scheme, where it first reacts with the methyl groups of the A1-(CH₃)_X fragments on the surface. Secondly, additional 8- hydroxyquinoline may form relatively strong weak bonds between the aromatic ring structures in the quinolines and as such appear as a dimer with an additional functional group exposed for subsequent reactions with the next TMA pulse. In the hypothesis TMA is used only as an example and the hopythesis may be equally valid for other metal precursors such as DEZ and TiCl₄.

Examples

The films have been deposited using a F- 120 Sat (ASM Mirochemistry) reactor by using trimethylaluminium, hereafter termed TMA, (EMF Chemicals Ltd. 99,999%), diethyl zinc (Crompton, technical quality), hereafter termed DEZ, titanium tetrachloride (Fluka, >99%) , 8-hydroxyquinoline, hereafter referred to as q (Aldrich, >98%) as precursors. The temperature of the TMA, TiCl₄, and DEZ precursors was held at 20 °C during film growth whereas 8-hydroquinoline was sublimed at 80 °C.

Nitrogen was produced in house using a Schmidlin Nitrox 3001 generator (99.999% as to N₂+ Ar) and used as purging and carrier gas. The pressure of the reactor during growth was maintained at 2 mbar by employing an inert gas flow of 300 cm³ min^"1.

The pulse and purge parameters of the film growth was investigated by using a quarts crystal microbalance (QCM, sometimes also named quarts crystal monitor), by using two 6 MHz gold or silver coated crystal sensors and a Matex MT-400 crystal monitor connected to a computer. This constellation made it possible to sample two sensors at the same time with a 10 Hz recording rate.

A Siemens D5000 diffractometer in θ-θ mode, equipped with a Gδbel mirror producing parallel Cu Ka radiation, was used for x-ray reflectivity thickness measurements. IR analysis was performed on films deposited on both sides of double polished Si(IOO) substrates and using a blank Si(IOO) substrate as reference. A Perkin Elmer FT-ER System 2000 was used for this purpose.

The films were deposited on soda lime and Si(IOO) substrates by sequentially pulsing of TMA, TiCl₄, or DEZ and 8-hydroxyquinoline.

The substrate material is not limited to the type of materials used here but can be any material reactive towards at least one of the precursors.

The reaction mechanism for formation of zinc bis 8-hydroxyquinoline from diethyl zinc (DEZ) and 8-hydroxyquinoline (q) has been investigated using quarts crystal microbalance (QCM) and thickness measurements using x-ray reflectivity (XRR). The QCM results for films deposited at 125 °C are given in Fig. la-d, Fig. 2, and Fig. 3. These findings show that the growing surfaces are rapidly saturated when DEZ is introduced, but that most of this is reevaporated during the purging time. The surfaces were not saturated completely with 8-hydroxyquinoline under the given experimental conditions, but this layer seems to be stable towards thermal reevaporation. There seems to be little or no so-called ALCVD window for the growth as function of reactor temperature, and the growth has almost ceased completely for reactor temperatures above some 200 ⁰C.

Similar investigations on the growth of aluminium tris 8-hydroxyquinoline (AIq₃) by the ALCVD technique at 85 °C has shown a somewhat different type of reaction scheme, see Fig. 4. For this reaction scheme it seems that the TMA saturates the surface in a lesser extent than the quinoline compounds under the experimental conditions used. However both surfaces seem to be stable towards thermal reevaporation. It is not clear whether an ALCVD-window for the growth as a function of reactor temperature can be found in the region 100 - 125 ⁰C, see Fig. 5. At increased temperatures the growth is notably reduced. Similar investigations on the growth of titanium tetra 8-hydroxyquinoline (Tiq₄) at 85 °C by the ALCVD technique has shown a more normal type of ALD growth, see Fig. 6. For this reaction scheme it is evident that TiCl₄ has an excess physically adsorbed layer which is removed during purging. Both the TiCl₄ and the q materials seem to reach saturation during their pulses and seem to be stable towards thermal reevaporation. There seems to be little or no so-called ALCVD window for the growth as function of reactor temperature, and the growth is reduced for increased temperatures, as shown on Fig. 7.

The phase composition of Znq₂, Tiq₄ and AIq₃ films have been investigated by infrared absortion measurments (FT-IR), these are visible on Fig. 8. These show that a significant amount of the characteristic absorption bands for 8-hydroxyquinoline are found in the deposited films as well. Infrared absorption measurements have also been performed on commercial powedered samples of Znq₂ (Aldrich > 99%) and AIq₃ (Aldrich > 99.995%) and show identical patterns as what is found for the respective films.

Films OfAIq₃, Znq₂, and Tiq₄ have been analysed by AFM (atomic force microscopy, Digital Instruments, type Dimension 3100 in tapping mode). The results are presented in Table 1 and show that the films have a low roughness even for relatively thick films.

Table 1:

Type Film thickness / nm Rougness / RMS (root mean square) nm

AIq₃ 17.5 0.3 Znq₂ 26.0 0.4 Znq₂ 225 2.0 TJq₄ 40X) 04

The photoluminescence of films OfAIq₃, Znq₂, and Tiq₄ were analysed at room temperature by excitation with a laser with wavelength of 375 nm. These show that the AIq₃ and Znq₃ are well luminescent with maxima of 523 and 531 nm, respectively. The films with Tiq₄ were also somewhat photoluminescent with a maximum at 560 nm, however, the intensity was much less. This can be seen in the scattering of the data

We have also surprisingly found it possible to produce films of organic- inorganic hybrid molecular compound nature with benzoic acid and TMA forming an aluminium benzoate type of compound. The films have been produced by using a pulsing scheme OfH₂O + benzoic acid + TMA, and also from O₃ + benzoic acid + TMA, where the individual precursors are pulsed sequentially and separated by a purge with inert gas.

No detectable film is formed when only benzoic acid and TMA are pulsed in an alternating fashion. However, by introduction of a pulse of O₃ or H₂O prior to the pulse of benzoic acid, the film forms easily. Table 2 gives the growth rates for the different experiments performed at a reactor temperature of 100 ⁰C, showing that a dramatic increase in growth rate results from introduction of O₃ or H₂O prior to the pulse of benzoic acid. Investigations with IR spectroscopy (Fig. 9) prove that the films do contain benzoic acid. The exact reaction mechanism leading to such film growth is at present unknown.

Table 2. Growth rate at 100 °C for different pulsing schemes in growth of aluminium benzoate and aluminium oxide. The individual precursors are pulsed sequentially and separated by a purge with inert gas.

Sequence Growth rate (nm/cycle)

H₂O + benzoic acid + TMA 1.455

O₃ + benzoic acid + TMA 0.316

H₂O + TMA 0.120

O₃ + TMA 0.100 benzoic acid + TMA 0.0

Claims

C l a i m s

1.

Process for preparation of a thin film comprising molecular metalorganic compounds on a substrate characterised by using an atomic layer gas phase deposition technique comprising the following steps: a) contacting the substrate with a pulse of an inorganic precursor selected from a group consisting of metal alkyls, metal cycloalkyls, metal aryls, metal amines, metal silylamines, metal halogenides, metal carbonyls and metal chelates, where the metal is selected from the group comprising Al, Ga, hi, Tl, Si, Ge, Sn, Pb,

As, Sb, Bi, Te, Po, alkali metals, alkaline earth metals, 3d-insertion metals, 4d- insertion metals, 5d-insertion metals, lanthanides and actinides; b) reacting the inorganic precursor with an organic compound present on at least one surface of the substrate or adsorbing the inorganic precursor on at least one surface of the substrate; c) removing non-adsorbed or non-reacted inorganic precursor and reaction byproducts if any; d) contacting the inorganic precursor on the surface of said substrate with a pulse of an organic precursor with at least one functional group capable of a chemical reaction with an inorganic precursor, e) reacting the organic precursor with the inorganic compound adsorbed on the surface, or adsorbing the organic precursor on the surface; f) removing non-adsorbed or non-reacted organic precursor and reaction byproducts if any; g) optionally repeating step a) to f) until the wanted film thickness is achieved;

where either step b) or step e) comprises a reaction forming a layer of molecular metalorganic compounds.

2.

Process according to claim 1 , characterised in that the steps a) to c) are repeated one or more times before the steps d) to g) are performed.

3.

Process according to claim 1 , characterised in that the process further comprises performing the steps d) to f) one or more times before the steps a) to g) are performed.

4.

Process according to any one of the claims 1-3, characterised in that it further comprises the steps cl) to c3) after step c) where these steps are cl) contacting the surface of said substrate with a pulse of an oxygen comprising precursor; c2) reacting the oxygen comprising precursor with the surface; c3) removing non-reacted oxygen comprising precursor and reaction by-products if any.

5.

Process according to claim 4, characterised in that the organic precursor comprises a benzene backbone.

6. Process according to any one of the claims 1-4, characterised in that the organic precursor comprises a quinoline backbone.

7.

Process according to any one of the claims 1-5, characterised in that the metal in the inorganic precursor is an electro positive metal and that the organic precursor is an organic compound selected from the group comprising a quinoline backbone.

8.

Process according to any one of the claims 1-7, characterised in that removing of non- reacted precursors and by-products in step c) and f) and optionally c3) is performed by purging with an inert, gas preferably nitrogen.

9.

Process according to any one of the claims 1-8, characterised in that the substrate comprises a monolayer of an organic precursor according to claim 1 bound to the surface, before step a) is performed for the first time.

10.

Process according to any one of the claims 1-9, characterised in that the inorganic precursor comprises an electropositive metal selected from the group comprising Al, Si, Sn, Zn, Mg, Ti, V, Mn, Fe, Co, Cr, Cu and Pt and that the organic precursor is an organic compound comprising a quinoline or a benzene backbone.

11.

Process according to any one of the claims 1-10, characterised in that the inorganic precursor is 8-hydroxyquinoline.

12.

Process according to any one of the claims 1-11, characterised in that the thin film comprises monolayers of molecular aluminium tris 8-hydroxyquinoline.

13.

Process according to any one of the claims 1-11, characterised in that the thin film comprises monolayers of molecular zinc bis 8-hydroxyquinoline.

14.

Process according to any one of the claims 1-11, characterised in that the thin film comprises monolayers of molecular titanium tetra 8-hydroxyquinoline.

15. Process according to any one of the claims 1-11, characterised in that the thin film comprises monolayers of molecular aluminium tris benzoate.

16.

Thin film comprising hybrid monolayers comprising molecular metalorganic compounds held together by physical forces such as van der Waals forces or dipole s forces.

17.

Substrate characterised by comprising a thin film coating produced by the process according to any one of the claims 1-15 or a thin film according to claim 16. 0

18.

Use of a thin film produced by the process according to any one of the claims 1-15 or a thin film according to claim 16 as an emittive layer in OLED applications, as an n-type semiconducting material. 5

19.

Use according to claim 18, where the hybrid thin film produced by ALCVD is used for producing an OLED display or a lighting source.