EP1427678A1

EP1427678A1 - Substrate coated with a composite film, method for making same and uses thereof

Info

Publication number: EP1427678A1
Application number: EP02774836A
Authority: EP
Inventors: Catherine Jacquiod; Jean-Marc Berquier; Sophie Besson; Jean-Pierre Boilot; Christian Ricolleau; Thierry Gacoin
Original assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Priority date: 2001-07-25
Filing date: 2002-07-25
Publication date: 2004-06-16
Also published as: CN1297505C; BR0211413B1; KR100870711B1; KR20040024590A; US7348054B2; MXPA04000722A; JP4184958B2; RU2004105271A; BR0211413A; PL368602A1; RU2288167C2; WO2003010103A1; CN1558877A; ZA200400522B; FR2827854B1; US20040219348A1; JP2004535925A; FR2827854A1

Abstract

The invention concerns a substrate coated with a composite film based on a mesoporous mineral layer containing nanoparticles formed in situ inside the layer. The composite film has a periodic lattice structure in the greater part of the thickness where the nanoparticles are present, structure wherein the nanoparticles are periodically arranged on a scale of domains of at least 4 periods in the thickness of the film. Said structure is obtainable from a mesoporous mineral layer with periodic structure on the scale of domains of at least 4 periods of pores forming a matrix on the substrate, by deposition of at least a precursor in the pores of the matrix layer; and growth of particles derived from the precursor with spatial distribution and dimension control by the structure of the pores of the matrix. The invention is applicable to materials for electronics, non-linear optics, magnetism.

Description

SUBSTRATE COATED WITH COMPOSITE FILM, MANUFACTURING METHOD AND APPLICATIONS

The present invention relates to the field of thin layer materials capable of being applied to substrates to give them various functions or properties, in particular optical, electrical, magnetic, physical, chemical.

It relates more particularly to a substrate coated with a composite film based on a mesoporous mineral layer containing nanoparticles.

The term “nanoparticles” designates solid particles of nanometric dimensions, that is to say of the order of a few nanometers or a few tens of nanometers. These particles are of particular interest insofar as they may have specific properties, in particular optical and electronic, which differ significantly from those of solid material. Thus, particular physical properties are observed for particles of nanometric size, such as increased field effects for metals, quantum confinement for semiconductors and superparamagnetism for magnetic compounds. Obtaining particles of defined size capable of being distributed in space according to a desired arrangement represents a capital challenge in the fields in particular of optoelectronics, nonlinear optics, ...

Some authors report works in which mesoporous materials are used as a growth support for nanocrystals. We hear by "Mesoporous" a porous material whose pores have dimensions between 2 and 50 nm. Below 2 nm, the pores are qualified as micropores; beyond 50 nm, we speak of macropores.

Most of the work relates to powdered mesoporous materials, such as the family of M41s: these are (alumino) silicates materials very close to zeolites and, like the latter, characterized by a periodic network of pores, most often hexagonal or cubic bi-continuous, where the pores have a perfectly defined size of 2 to 10 nm. The structuring of the porous material into a periodic network of pores is linked to the synthesis technique, which consists in condensing the silicate mineral matter in the presence of organic structuring agents which are organized into micelles and crystalline phases. After treatment for removing the structuring agents, a porous material is obtained, the pores of which are the perfect replica of the organic species. Compared to unstructured mesoporous solids such as silica gels for example, the tortuosity of the porous network is low and the developed surface very accessible. This makes it possible to envisage these materials as support hosts for particles.

But even in these structured materials, the synthesized particles are generally distributed randomly in the porous matrix and their size is not well controlled.

Work has also been carried out in the field of thin layers deposited on substrate, in particular for optical applications.

Tang et al., Thin Solid Films, 1998, 321, 76-80 reports the penetration of SiGe particles into a mesoporous silica film deposited on a silicon substrate by a sol-gel process inspired by the mode of synthesis of M41s.

Using the molecular beam epitaxy technique (abbreviated as MBE for molecular beam epitaxy), a layer of SiGe or Ge is deposited and grown on the surface of the mesoporous silica film over a thickness of 6 to 70 nm at a growth rate of 0.1 Â / s which is supposed to allow diffusion of the atoms in the openings of the mesopores. Photoluminescence measurements make it possible to identify the presence of particles which would be localized in the mesoporous layer and whose dimensions correspond to those of the pores of the silica matrix. However, the thickness penetration into the layer is not characterized. In particular, the method used is based on the diffusion of metal atoms in the mesoporous silica layer from the surface layer of SiGe or Ge towards the silica / substrate interface, diffusion which is no longer allowed (despite suitably chosen growth rate) as soon as the pores close to the silica / Ge or SiGe interface are filled. In addition, the presence of the surface layer, which contains particles of different sizes, is a drawback.

On the other hand, Plyuto et al., Chem. Commun., 1999, 1653-1654, describes the synthesis of silver nanoparticles in a mesoporous silica film deposited on Pyrex slides by chemical means by ion exchange with A fNhy followed by a reduction treatment. Particle formation begins with the reduction of Ag ⁺ ions to Ag ° atoms which migrate into the mesoporous silica matrix and gradually aggregate. Under the conditions described, the nanoparticles formed were randomly distributed in the mesoporous matrix and their size was not uniform.

This irregularity in the formation of nanoparticles represents a serious drawback for applications where it is sought to produce a homogeneous effect or property on the surface of the substrate, in particular when the property is linked to the quantity of material, the size or shape of a particle or the arrangement thereof, which is particularly the case with optical properties.

The object of the present invention is to remedy this drawback and to provide a layered material containing nanoparticles of regular structure. This object was achieved with a substrate coated with a composite film based on a mesoporous mineral layer containing nanoparticles formed in situ inside the layer, characterized in that the composite film has a periodic lattice structure in most of the thickness where the nanoparticles are present, structure in which the nanoparticles are arranged periodically on the scale of domains of at least 4 periods in the thickness of the film.

The expression "the composite film has a periodic lattice structure throughout its thickness" means that the nanoparticles and the mineral matter which surrounds them are arranged in a geometric pattern which is repeated by periods in most, preferably all, of the film thickness where the particles are present.

Preferably, the periodic lattice is at least two-dimensional, that is to say that the geometric repeating pattern is two or three dimensions. Preferably, the periodic network of the film is three-dimensional, in particular of the hexagonal, cubic or quadratic type.

This repetition can be oriented identically throughout the volume of the material, with a structure that can be compared to that of single crystals, or can be oriented identically at the domain scale of at least 4 periods. (in general at least about 20 nm) with an overall structure which can be compared to that of polycrystals.

Advantageously, the particles are arranged periodically with at least 5, preferably at least 10 periods per domain. Depending on the size of the particles, the extent of the periodic structure domains can be more or less vast. As an indication, these domains can have a dimension of at least 20 nm in at least one direction.

Advantageously, this periodic structure of the composite film is obtained from a mesoporous mineral layer of periodic structure on the scale of domains of at least 4 pore periods (in general at least about 20 nm) forming a matrix on the substrate, by:

• deposit of at least one precursor in the pores of the matrix layer; and

• growth of particles derived from the precursor with control of the spatial distribution and dimensions by the structure of the pores of the matrix. The invention has thus demonstrated that an ordered structure of mesoporous film is capable of hosting the growth of nanoparticles in all the desired thickness and all the volume, by imposing on the particles a regular shape and dimensions and a periodic arrangement. in the space reproducing the characteristics of the pores that make up the film.

According to this embodiment, a key element consists in generating the particles inside the pores from a precursor which undergoes a chemical modification in place in order to transform into the constituent material of the particle. Compared to the technique based on the diffusion of the material itself even that coalesces or aggregates inside the pores, the problems of occlusion of the pores near the diffusion source are avoided, which limit the penetration of the particles at the heart of the thickness of the mesoporous layer.

Contrary to what Plyuto et al. Have observed, the inventors have shown that a mesoporous layer of periodic structure can be the seat of an ordered growth of particles and limited by the size of the pores, and they have accessed unexpected to a periodically structured composite film.

According to a preferable characteristic, the periodic structure of the composite film is obtained by impregnating the matrix layer with a liquid composition containing at least one precursor and a liquid vehicle, and controlled growth of particles derived from the precursor. The liquid route indeed seems to be the best method for depositing the precursor (s) inside the pores, by having homogeneous access to all the desired volume and in particular the thickness of the basic mesoporous layer, which allows in the next stage a harmonious and regular growth of the particles.

According to the invention, the substrate carrying the coating can be made of various materials of the mineral type such as glass, silica, ceramics or vitroceramics, metal, or of the organic type such as plastics. For certain applications in the optical field, the transparency of the substrate may be desirable.

As examples of glass materials, mention may be made of float glass (or float glass) of conventional soda-lime composition, optionally hardened or tempered by thermal or chemical means, an aluminum or sodium borosilicate. Examples of plastics include (poly (methyl methacrylate) (PMMA), polyvinyl butyral (PVB), polycarbonate (PC) or polyurethane (PU), thermoplastic ethylene / vinyl acetate (EVA) copolymer, poly (ethylene terephthalate) (PET), poly (butylene terephthalate) (PBT), polycarbonate / polyester copolymers, cycloolefinic copolymer of the ethylene / norbornene or ethylene / cyclopentadiene type, ionomer resins, for example an ethylene / acid copolymer ( meth) acrylic neutralized by a polyamine, thermosetting or thermoscrosslinkable such as polyurethane, unsaturated polyester (UPE), ethylene / vinyl acetate copolymer ...). The substrate generally affects an essentially planar or two-dimensional shape with a variable contour, such as for example a plate or a wafer, but can also affect a volume or three-dimensional shape consisting of the assembly of essentially planar surfaces, for example in the form of a cube or a parallelepiped, or not, for example in the form of fibers.

It can be coated with composite film on one or more sides.

The composite film according to the invention has a thickness advantageously between 10 nm and 10 μm (these limit values being included), in particular 50 nm and 5 μm. High quality film structures are produced for film thicknesses from 100 to 500 nm.

The mesoporous mineral layer forming the base of the composite film has a periodic structure at the domain scale of at least 4 periods. As said previously, this means that the layer comprises one or more areas within which the pores are organized according to the same repeating pattern repeated at least 4 times, the orientation of an axis characteristic of the patterns may be different from one area to another. The characteristic dimension of these domains (in general at least about 20 nm) corresponds to a dimension of coherent diffraction domains and can be deduced in a known manner by the Scherrer formula from the width of the main peak of the X-ray diffraction diagram.

The advantage of the relatively large-scale periodicity of the mesoporous basic network lies in the possibility of distributing the particles in an orderly manner with a distance from each other (from center to center) corresponding to the pitch of the repeating pattern with a preferential orientation , for example perpendicular or parallel to the surface of the substrate.

Preferred layers are organized with a periodic structure on the scale of domains of the order of 100 nm, advantageously 200 to 300 nm.

Many chemical elements can be at the base of the mesoporous film: this comprises as essential constituent material at least one compound of at least one of the elements: Si, W, Sb, Ti, Zr, Ta, V, Pb, Mg, Al, Mn, Co, Ni, Sn, Zn, Ce.

The mesoporous mineral layer is preferably based on at least one oxide such as silicon oxide, titanium oxide, etc. For applications in the field of optics, the material constituting the layer may be chosen so that it is transparent at certain wavelengths, in particular in the visible range.

According to an advantageous embodiment, the mesoporous mineral layer is obtained by: • bringing the substrate into contact with a liquid composition comprising at least one oxide precursor and at least one organic agent; and

• precipitation and polycondensation of oxide around the structuring agent.

The metal oxides are capable of being deposited in film by sol-gel route as above, with the possibility of controlling the porosity according to various structures generally monodisperse in size, that is to say in which the size of the pores ( diameter or equivalent diameter) is calibrated to a determined value in the mesoporous domain: we can note in particular a pore network structure of two-dimensional hexagonal symmetry (2D) with porous channels in the form of straight tubes stacked in the hexagonal mode, of tπ ^' -dimensional hexagonal symmetry (3D) with substantially spherical pores stacked in the hexagonal mode, of three-dimensional cubic symmetry possibly deformed. Three-dimensional structures can be useful for establishing isotropic properties of the composite film, while two-dimensional structures give access to anisotropic properties with in particular applications in the field of nonlinear optics or optical filters. Once the layer is filled with particles, the resulting composite film has a periodic lattice structure which retains the same symmetries.

All these structures are accessible by the above method by adapting the coating composition, in particular the choice of the structuring agent. This method will be described in more detail below.

The nanoparticles capable of being included in the composite film of the substrate according to the invention can in particular comprise compounds chosen from:

• metals, for example silver, gold, copper, cobalt, nickel ... the optical or magnetic properties of which can be exploited;

• chalcogenides, in particular sulfides or selenides, of one or more metals, for example derivatives of zinc, lead, cadmium, manganese, in particular ZnS, PbS, (CdMn) S, (CdZn) S, CdSe, ZnSe, the photoluminescence or semiconductor properties of which can be exploited;

• oxides of one or more elements, for example derived from silicon, zinc, zirconium, cerium which can confer improved mechanical properties on the surface layer;

• halides, in particular chlorides, of one or more metals, in particular silver chloride with photochromic properties, or copper chloride which absorbs UV rays;

• phosphides; • but also organic compounds.

The particles may consist of a single material, obtained from a single precursor or of several precursors which react with one another to form a new chemical compound, or of a combination of materials obtained from several precursors which react or not between them to form composite particles. According to a particular embodiment, the nanoparticles consist of a core at the periphery of which is a second material in the form of discrete particles such as crystallites or of a continuous envelope, where the periphery material grows on the core at the inside the pores of the mesoporous material from a corresponding material precursor. The material of the core can be of any organic or mineral type, and the material of the periphery is advantageously chosen from the compounds mentioned above.

In addition to the possibility of ordered distribution of the particles on the surface of the substrate, the invention also makes it possible to optimize the quantity of particles deposited on the substrate, more particularly to maximize this quantity without aggregation of the particles. Thus, the volume fraction occupied by the nanoparticles in the composite film can be of the order of 10 to 70% of the volume of the organized domains, in particular around 50%.

The invention also relates to a method of manufacturing a substrate as described above, which comprises the steps consisting in:

(1) deposit a mesoporous mineral layer on the surface of the substrate,

(2) bringing the mineral layer into contact with a liquid composition containing at least one nanoparticle precursor and a liquid vehicle,

(3) subjecting the layer impregnated with precursor to an energy supply, or to the action of radiation or at least one liquid or gaseous reagent.

According to a preferred embodiment, step (1) of depositing the mesoporous layer successively comprises:

The preparation of a liquid composition comprising at least one precursor of the material constituting the mesoporous layer, and at least one organic structuring agent,

• applying the composition to the substrate,

• the precipitation of the precursor around the organic structuring agent and the growth of molecules derived from the precursor, • the elimination of the organic structuring agent.

For the manufacture of a mesoporous oxide layer, the preparation of the liquid composition advantageously comprises:

• the preparation of an oxide precursor soil in a hydroalcoholic liquid phase, • the maturing of the soil, then

• mixing with the structuring agent.

Indeed, the ripening of the soil allows a preliminary condensation of the oxide precursor which promotes the structuring of the oxide layer condensed on the substrate into large domains. Advantageous conditions for curing include maintaining the soil at a temperature of 40 to 60 ° C for a period of 30 min to 24 hours, the curing time being shorter the higher the temperature.

In this case, the oxide precursor is advantageously a hydrolyzable compound, such as a halide or an alkoxide, the structuring agent is advantageously chosen from cationic surfactants, preferably of the quaternary ammonium type, or nonionic, including the copolymers , preferably based on polyalkylene oxide, in particular di-block or tri-block copolymers based for example on ethylene or propylene oxide.

A particularly favorable embodiment of the process of the invention for the synthesis of a mesoporous layer of silica consists in that the organic structuring agents consist of micelles of cationic surfactant molecules, the precursor of the mesoporous material is a silicon alkoxide, and they are in solution and, optionally, in hydrolyzed form. Particularly advantageously, the cationic surfactant is cetyltrimethylammonium bromide, the precursor of the mesoporous material is a silicon alkoxide in partially or fully hydrolyzed form.

In soil, the molar ratio of the organic structuring agent to silicon can be of the order of 10 ^"4 to 0.5, preferably of 10 ^{" 3} to 0.5, advantageously of 0.01 to 0.1 .

With a cationic structuring agent of quaternary ammonium type, the molar ratio of the structuring agent to silicon is preferably of the order of 0.1; with a nonionic structuring agent of the copolymer type, the molar ratio of the structuring agent to silicon is preferably of the order of 0.01.

This soil can be applied in a variable thickness, in particular by diluting the concentration of the soil. The presence of a diluent, preferably an alcohol, exacerbates the positive effect linked to the evaporation of the solvent, on the homogeneous texturing of the coating. In an embodiment optimized for a mesoporous layer of silica, the mixture is diluted with an alcohol in a volume ratio of 1: 1 to 1: 30, preferably from 1: 1 to 1: 5, in particular from 1: 1 to 1 : 3 for application of a thin layer of the order of 100 to 400 nm.

After deposition of the soil, the substrate is generally subjected to drying in the open air or in nitrogen during which the polymerization of the oxide network around the structuring agents continues.

Then the structuring agents can be removed, for example by calcination, by solvent extraction or by ozonolysis (combined action of oxygen and UVC rays). Non-thermal treatments are preferred when the substrate is organic such as plastic. Step (2) of the method according to the invention consists in impregnating the mesoporous base layer with a liquid composition containing at least one precursor of nanoparticles.

According to a particular embodiment, the nanoparticle precursor is a metal salt or complex soluble in the liquid vehicle: the metal ions penetrate inside the pores of the base layer and can be fixed there by different types of interaction, by example of polar type or by ion exchange with the surface of the pores.

The liquid composition may contain complexing agents to avoid precipitation of the metal, in particular in the form of hydroxides in the medium aqueous. Can be used as complexing agents ammonia, amines or carboxylates.

The impregnation composition is adapted so as not to degrade the mesoporous mineral matrix. For aqueous compositions, an important parameter may be the pH of the impregnating composition.

Indeed, when the mesoporous matrix is based on metal oxide or other element, an excessively basic composition can be harmful to the porous structure by dissolution of the walls of the pores. Preferably, the liquid impregnation composition has a pH less than or equal to 10.

On the other hand, the pH of the composition can be adjusted to optimize the interaction of the precursor with the mesoporous layer, in particular it can be adjusted within a range which promotes the adsorption of the precursor species on the walls of the pores.

The counterions or ligands are chosen to obtain species which are soluble in the preferred pH range.

The impregnation can be carried out by immersion or dipping of the substrate in the liquid composition or by any other method of applying liquid to a solid.

To increase the yield of the impregnation step, in particular in the case where the precursor has a low affinity for the material of the mesoporous mineral layer, the method can comprise an intermediate step (1 ′) in which the mineral layer is treated mesoporous to increase the reactivity of the pores with respect to the precursor (s), in particular by grafting reactive groups on the surface of the pores which interact with the precursor (s) chemically or electrostatically.

Thus, in this intermediate treatment step, complexing groups for the precursors can be grafted onto the surface of the pores. Such treatment can be carried out by liquid or gas.

In the case of a mesoporous layer of mineral oxide, the treatment may consist in reacting the layer with an alkoxide, in particular of silicon, functionalized by a reactive group, or with an alumina precursor functionalized by a reactive group. The impregnation step (2) can be followed by a rinsing step (2 ') to remove excess material, in particular to avoid the accumulation of precursor at the film-air interface which would be susceptible to '' completely block the surface pores. In general, the interactions between the functional groups on the walls of the pores and the precursors, in particular metal cations, are strong enough to retain the precursor in the pore despite rinsing.

Step (3), which consists in reacting the precursor in place in the pores, can use an input of thermal energy or the action of radiation such as ultraviolet rays, or a liquid or gaseous reagent.

Among the reagents, a gaseous reagent is preferable because it generally guarantees instant penetration into all the pores of the material, allowing a transformation of the precursor and a growth of the particles simultaneously throughout the volume of the mesoporous matrix, which avoids the problems of diffusion. species and clogging of pores.

To form the particles of the materials indicated above, the gaseous reagent can be chosen from a chalcogen-based gas, for example based on sulfur, selenium, tellurium, for example H ₂ S, H ₂ Se, based on halide, in particular based on chlorine, for example HCl, Cl ₂ , a reducing gas, for example H ₂ , and an oxidizing gas, for example O ₂ , in particular as a mixture of O ₂ , N ₂ .

In a preferred embodiment, the impregnated layer is treated at a temperature less than or equal to 300 ° C., in particular to 200 ° C., in particular to 150 ° C. A moderate temperature prevents diffusion and aggregation of particles and guarantees the stability of the mesoporous structure during the reactive treatment. Reactive treatments at room temperature are preferred.

During the transformation reaction of the precursor of particles, the chemical species formed does not generally have the same interaction with the surface of the pore, and the site of attachment of the precursor in the pore is released and is accessible to receive a new precursor molecule as long as the particle does not occupy the entire volume of the pore.

Thus, the impregnation (2) and reaction (3) steps can be repeated to reach the desired degree of filling, if necessary until the mesoporous mineral layer is saturated.

The evolution of the filling of the mesoporous layer can be followed by different methods including spectrophotométπ ^e or X-ray diffraction

After a certain number of impregnation-reaction cycles, it is observed that the properties of the composite film obtained no longer change, a sign that the mesoporous layer is completely saturated with particles.

It has been verified that the growth of the particles is controlled by the mesoporosity of the base layer and that the particles formed have dimensions limited by the dimensions of the pores, that is to say that the particles grow with each cycle until a maximum size corresponding to the dimensions of the pores.

In some cases, we can observe a kind of contraction or on the contrary of expansion of the mesoporous layer, so that dimensional parameters of the structure of the composite film are slightly modified (reduced or increased) compared to the dimensional parameters of the structure of the initial mesoporous mineral layer, but without altering the geometry of the network repeat pattern.

Depending on the nature of the particles, the substrate according to the invention can have several applications.

In this regard, the invention also relates to the application of a substrate as described above to the production of solar concentrators in particular for photovoltaic cells, to quantum dots, materials for non-linear optics or magnetism. To this end, the material can be treated or coated with an additional protective or functional layer (s). The following examples illustrate the invention.

EXAMPLE 1 This example describes the manufacture of a layer of silica charged with nanoparticles of cadmium sulfide on a Pyrex glass substrate.

First of all, a silica sol is prepared by mixing TEOS tetraethoxyorthosilicate (or tetraethoxysilane) of formula Si (OC ₂ H ₅ ) with acidified water to pH = 1.25 with HCl and with ethanol in a 1: 5: 3.8 molar ratio. The mixture is subjected to 1 hour ripening at 60 ° C. (The optimum maturing range for a silica sol is generally 30 min to 1 hour at 60 ° C, or equivalent 2 to 6 hours at 40 ° C). A cationic surfactant of the quaternary ammonium type is then added to the colorless and transparent soil mainly composed of silicic acid.

Si (OH) ₄ which is the hydrolysis product of TEOS and low molecular weight oligomers (SiO) _n . The surfactant chosen is cetyltrimethylammonium bromide (CTAB) introduced in an amount such that the CTAB: Si molar ratio is equal to 0.1.

Given its amphiphilic nature, the surfactant forms micellar supramolecular structures. The CTAB: Si molar ratio of 0.1 is optimal for obtaining micellar structures arranged so as to form a periodic structure.

The solution obtained is diluted with ethanol in a volume ratio 1: 1.

The solution is deposited on Pyrex slides of 2.5 cm by 2.5 cm by centrifugation or "spin coating": according to this technique, the sample is rapidly rotating during deposition; this spin coating operation is characterized by a speed of 3000 rpm and a rotation time of the order of 100 s.

The CTAB is then extracted from the film of each sample by calcination in a tubular oven at 450 ° C in air with a rise of 10 ° C / h. The film thus formed is transparent, mesoporous and its thickness, determined with the profilometer, is approximately 300 nm.

With different dilution factors, the thickness of the mesoporous silica film can be varied. Thus, by choosing a volume ratio of 2: 1 to 1: 4, it is possible to obtain layer thicknesses of the order of 400 to 100 nm.

The porous network corresponds to the volume left vacant by the elimination of the CTAB micelles, taking into account the contractions likely to occur during the heating / calcination operations, among others. The pore volume of this layer is 55% relative to the total volume of the film.

The characteristics of the porous network are determined by X-ray diffraction, X-ray scattering in grazing incidence and transmission electron microscopy. These analyzes reveal a three-dimensional hexagonal structure (space group P6 ₃ / mmc with the hexagonal axis of symmetry perpendicular to the plane of the substrate). The pores are substantially spherical with a uniform diameter of the order of 3.5 nm.

Figures 1 and 2 are electron microscopy images in transmission respectively in transverse and flat section.

In FIG. 1, it can be seen that the mesoporous layer 2 has a periodic network structure throughout its thickness from the interface with the substrate 1 to the interface with the air 3. The pores 4 are aligned parallel to the substrate surface.

FIG. 2 reveals the existence of domains 5, 6, 7 of large extent, of dimension greater than 200 nm in all the directions of the plane. Within each domain, the pores are arranged according to the repeating pattern of the hexagonal network over several tens of periods, but the orientation of the repeating axis in the plane of the substrate (a) varies by domain 5 to a neighboring domain 6 or 7. From one domain to another the orientation of the hexagonal axis of symmetry (c) is unchanged, always perpendicular to the surface of the substrate.

This structure is similar to that of a polycrystalline material where all the grains have a common orientation relative to the substrate.

It is said that the mesoporous layer is structured in a periodic network, on the scale of 200 nm domains, and is monodisperse in size.

This structure can also be obtained by immersion and drawing from the silica sol (or "dipcoating"). An impregnation solution based on cadmium nitrate is prepared. To an aqueous solution of 0.1 M cadmium nitrate, one equivalent of ammonia and one equivalent of sodium citrate are added, and the pH is adjusted to 9.5 by addition of ammonia. NH ₃ and citrate act as ligands which complex cadmium nitrate and prevent precipitation of cadmium hydroxide.

The pH of 9.5 is optimal, because the adsorption of cadmium ions on silica is optimal above pH 9 while the dissolution of the silica walls becomes critical above pH 10.

The Pyrex substrate coated with the mesoporous silica layer is immersed in the impregnation solution for approximately one minute, then extracted and washed with deionized water to remove the excess cations, in particular near the surface. During this operation, the metal cations attach to the surface of the silica pores by complexing with SiO ^" groups of the silanols on the surface of the silica. The SiO / Cd interaction resists the operation of wash with water.

The sample is then placed in a primary vacuum enclosure into which hydrogen sulfide gas H ₂ S is slowly injected up to atmospheric pressure at room temperature. The precipitation of CdS sulfide particles by reaction of sulfur with the complexed Cd is instantaneous and takes place locally in the heart of the porous cavity simultaneously in all the pores. The precipitation of the sulfide leads to the regeneration of the SiO ^" sites.

The steps of impregnation and reaction with H ₂ S are repeated several times. The film impregnated with Cd ²⁺ is colorless. After reaction with H ₂ S it becomes slightly yellow and the intensity of the coloration increases with the treatment cycles.

Analysis of the substrate by mass spectrometry with secondary ions (SIMS) shows a homogeneous distribution of CdS in the depth of the layer.

The progress of the filling of the layer is followed by absorption spectrophotometry, illustrated by the spectra of FIG. 3: the absorbance increases with the number of cycles up to a ceiling reached in the eighth cycle, (the curve a shows the spectrum obtained after the first soaking in the cadmium solution, curve b presents the spectrum obtained after the first treatment H ₂ S; curves c, d, e, f, g, present the spectra obtained respectively after 2, 3, 4 , 5, 7 cycles, and the curve h shows the spectra obtained after the gem ^e _and ^e em _C y _C ι _are ςyj _overlap).

After the ninth cycle, the absorbance no longer changes, proving that there is no more CdS in the layer than in the previous cycle. The mesoporous layer is therefore saturated with CdS.

From the correlation curves of the absorption spectra, the size of the aggregates can be determined by the energy of the energy transition. It is concluded that the particle size distribution is very narrow centered on 3.5 nm.

The characterization by X-ray diffraction confirms that the three-dimensional hexagonal structure is preserved.

This is confirmed by an observation with a transmission electron microscope illustrated by the image of FIG. 4 which represents an image in cross section. It can be seen that the mesoporous layer is completely filled with CdS nanoparticles which respect the arrangement of the pores of the initial layer. A composite film is thus obtained containing approximately 50% by volume of CdS particles. EXAMPLE 2

A similar structure of ZnS nanoparticles is produced in a layer of silica on a substrate, by modifying Example 1 as follows.

First of all, as in Example 1, the same layer of mesoporous silica is deposited on a substrate. The impregnation solution this time consists of an aqueous solution of zinc nitrate of 0.1 M concentration to which 1 molar equivalent of sodium citrate is added. The pH is then adjusted to 7.5 by adding ammonia. In general, the adsorption of zinc ions is optimal in a pH range above pH 7. It is advantageously placed in a range of the order of 7 to 10, preferably close to neutrality between 7 and 8 , so that the silica does not suffer from a dissolving effect on the walls of the pores.

The steps of impregnation and treatment with H ₂ S are carried out as in Example 1, with control of the growth of the ZnS particles by UV-visible spectrophotometry, and repeated until no more can be distinguished. two successive absorption spectra.

The composite film obtained after 7 impregnation / treatment cycles has the same periodic lattice structure of particles stacked in the hexagonal mode throughout the thickness of the silica layer.

EXAMPLE 3 This example describes the growth of CdS aggregates in another mesoporous layer of silica.

A silica sol is prepared as in Example 1 by mixing TEOS with acidified water and ethanol in a molar ratio 1: 5: 3.8. The mixture is subjected to maturing for 1 hour at 60 ° C. The structuring agent is a nonionic surfactant consisting of a triblock copolymer of the polyoxyethylene-polyoxypropylene-polyoxyethylene type. We choose the Pluronic PE6800 product of formula E0 ₃ P0 ₂₈ E0 ₃ (EO for ethylene oxide; PO for propylene oxide). It is added to the silica sol in a copolymer: Si molar ratio equal to 0.01. The solution is then diluted with ethanol in a volume ratio of 1: 2. The deposition and calcination steps are the same as in Example 1.

A layer of mesoporous silica 200 nm thick is obtained. With this structuring agent, it is possible to choose a dilution volume ratio of 1: 1 to 1: 2 in order to obtain layers of silica of the order of 400 to 200 nm in thickness.

The porous network which corresponds to the volume left vacant by the elimination of the Pluronic micelles, also has a three-dimensional structure of monodisperse pores in size.

FIG. 5 is a transmission electron microscopy image in cross section which illustrates the periodic distribution of the pores.

The substrate coated with this layer of mesoporous silica is subjected to the same impregnation operations with the cadmium nitrate solution and treatment with H ₂ S as in Example 1. A saturated layer of CdS nanoparticles is obtained after 5 impregnation / treatment cycles. EXAMPLE 4

This example describes the growth of silver nanoparticles in a mesoporous layer of silica with a three-dimensional hexagonal structure.

An impregnating solution based on silver nitrate is prepared. To a 0.1 M aqueous solution of silver nitrate, a molar equivalent of citrate is added; a white precipitate of silver citrate appears. Ammonia is then added until the precipitate has dissolved (pH = 9.5). The pH of 9.5 is optimal, because the adsorption of silver ions on silica is optimal above pH 9 while the dissolution of the silica walls becomes critical above pH 10. The mesoporous silica film deposited on substrate is impregnated for one minute in this solution, rinsed and dried as in Example 1.

Then grafted hexamethyldisilazane (HMDS, of formula (CH ₃ ) ₃ -Si- NH-Si- (CH ₃ ) ₃ ). This molecule makes it possible to limit the diffusion of the silver ions during the subsequent reduction of the silver ⁽¹⁾ and thus avoid the formation of large particles.

The impregnated substrate is placed in a cell containing 200 μl of HMDS and the cell is placed under vacuum and hermetically closed, then heated to a temperature of approximately 70 ° C. for approximately 5 minutes. The cell is then purged to remove excess HMDS. Finally, the Ag ⁺ ions are reduced, which can be carried out under an atmosphere of argon and hydrogen at 100 ° C for 4 hours or under an atmosphere of pure hydrogen for one hour.

The final product is characterized by transmission electron microscopy, where the cross-sectional image reveals a film filled with nanoparticles. This image shows that the particles have a narrow size distribution, and have particle alignments. The size distribution is narrow with an average of 3.4 nm and a standard deviation of 0.64. The diffraction of the image shows that the particles are distributed according to the 3D hexagonal structure of the space group P6 ₃ / mmc.

Claims

CLAIMS 1. Substrate coated with a composite film based on a mesoporous mineral layer containing nanoparticles formed in situ inside the layer, characterized in that the composite film has a periodic lattice structure in most of the thickness where the nanoparticles are present, structure in which the nanoparticles are arranged periodically on the scale of domains of at least 4 periods in the thickness of the film.

2. Coated substrate according to claim 1, characterized in that the periodic network is at least two-dimensional.

3. Coated substrate according to claim 1 or 2, characterized in that, the periodic structure of the composite film is obtained from a mesoporous mineral layer of periodic structure on the scale of domains of at least 4 pore periods forming matrix on the substrate, by: • depositing at least one precursor in the pores of the matrix layer; and

• growth of particles derived from the precursor with control of the spatial distribution and dimensions by the structure of the pores of the matrix.

4. Coated substrate according to claim 3, characterized in that the periodic structure of the composite film is obtained by impregnation of the matrix layer with a liquid composition containing at least one precursor and a liquid vehicle, and controlled growth of particles derived from the precursor.

5. Coated substrate according to any one of claims 1 to 4, characterized in that the substrate consists of a mineral material such as glass, silica, ceramic or organic such as a plastic material.

6. Coated substrate according to any one of claims 1 to 5, characterized in that the composite film has a thickness of 10 nm to 10 μm, in particular from 50 nm to 5 μm.

7. Coated substrate according to any one of the preceding claims, characterized in that the mesoporous mineral layer is based on at least one metal oxide.

8. Coated substrate according to claim 7, characterized in that the mesoporous mineral layer is obtained by: • bringing the substrate into contact with a liquid composition comprising at least one oxide precursor and at least one organic agent; and

• precipitation and polycondensation of oxide around the structuring agent.

9. Coated substrate according to claim 7 or 8, characterized in that the mesoporous mineral layer has a pore network structure of three-dimensional symmetry.

10. Coated substrate according to any one of the preceding claims, characterized in that the nanoparticles comprise compounds chosen from metals, chalcogenides, oxides, halides, phosphides and organic compounds.

11. Coated substrate according to any one of the preceding claims, characterized in that the nanoparticles are composite particles, consisting of a core and a peripheral material.

12. Coated substrate according to any one of the preceding claims, characterized in that the volume fraction occupied by the nanoparticles in the organized domain or domains is of the order of 10 to 70% of the volume of the domain.

13. Method for manufacturing a coated substrate according to any one of the preceding claims, characterized in that it comprises the steps consisting in:

(1) deposit a mesoporous mineral layer on the surface of the substrate,

14. Method according to claim 13, characterized in that the step (1) of depositing the mesoporous layer successively comprises:

• applying the composition to the substrate,

The precipitation of the precursor around the organic structuring agent and the growth of molecules derived from the precursor,

• elimination of the organic structuring agent.

15. Method according to claim 14, characterized in that the preparation of the liquid composition comprises:

• mixing with the structuring agent.

16. The method of claim 15, characterized in that the oxide precursor is a hydrolyzable compound, such as a halide or an alkoxide, and in that the structuring agent is chosen from cationic surfactants, preferably of the type quaternary ammonium, or nonionic ammonium, including the copolymers, preferably of polyalkylene oxide type.

17. The method of claim 16, characterized in that the precursor is a silica precursor, the structuring agent is a cationic surfactant of quaternary ammonium type, the molar ratio of the structuring agent to silicon is of the order of 0 1.

18. The method of claim 17, characterized in that the mixture is diluted with an alcohol in a volume ratio of 1: 1 to 1: 30, preferably from 1: 1 to 1: 5 for application of a layer thin on the order of 100 to 400 nm.

19. Method according to any one of claims 13 to 18, characterized in that the nanoparticle precursor is a metal salt or complex soluble in the liquid vehicle.

20. Method according to any one of claims 13 to 18, characterized in that the liquid impregnation composition is aqueous-based and has a pH adjusted to optimize the interaction of the precursor with the mesoporous layer.

21. Method according to any one of claims 13 to 20, characterized in that it comprises an intermediate step (1 ') in which the mesoporous mineral layer is treated to increase the reactivity of the pores vis-à-vis the precursors.

22. Method according to any one of claims 13 to 21, characterized in that the impregnation step (2) is followed by a rinsing step (2 ').

23. Method according to any one of claims 13 to 22, characterized in that the reagent is chosen from a gas based on chalcogen or halogen, a reducing gas and an oxidizing gas.

24. Method according to any one of claims 13 to 23, characterized in that the impregnated layer is treated at a temperature less than or equal to 300 ° C.

25. Method according to any one of claims 13 to 24, characterized in that the steps of impregnation (2) and of reaction (3) are repeated.

26. Application of a coated substrate according to any one of claims 1 to 12 to the production of solar concentrators in particular for photovoltaic cells, quantum dots, materials for non-linear optics or magnetism.