EP0819185B1 - Method for preparing a film consisting of an oxide or hydroxide of an element in columns ii or iii of the periodic table, and composite structures including such a film - Google Patents

Method for preparing a film consisting of an oxide or hydroxide of an element in columns ii or iii of the periodic table, and composite structures including such a film Download PDF

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Publication number
EP0819185B1
EP0819185B1 EP96911017A EP96911017A EP0819185B1 EP 0819185 B1 EP0819185 B1 EP 0819185B1 EP 96911017 A EP96911017 A EP 96911017A EP 96911017 A EP96911017 A EP 96911017A EP 0819185 B1 EP0819185 B1 EP 0819185B1
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process according
film
chosen
oxide
metal
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EP0819185A1 (en
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Daniel Lincot
Sophie Peulon
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Centre National de la Recherche Scientifique CNRS
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D9/00—Electrolytic coating other than with metals
    • C25D9/04—Electrolytic coating other than with metals with inorganic materials

Definitions

  • the present invention relates to a preparation process a film of a metal oxide or a metal hydroxide an element from columns II or III of the classification, deposited on a substrate.
  • Thin film metallic oxides are materials very important in various technological fields of made of their optical, electrical and catalytic characteristics. Among their many applications, we can cite for example the use of zinc oxide for the preparation conductive and transparent electrodes in the batteries solar.
  • Thin layers of metal oxide are generally obtained by vacuum deposition techniques such as sputtering, or chemical sputtering in vapor phase, or by depositing successive layers by molecular beam epitaxy (MLE). All these processes use expensive equipment.
  • Switzer (supra) and R. T. Coyle, et al., (US-A-4,882,014) further describe the preparation of oxide powders and of metal hydroxides, as precursors of ceramics. These powders are formed by precipitation in the vicinity of the cathode of an electrochemical cell, caused by the reduction of nitrate ions. These powders are then dried and sintered at high temperature to obtain the materials ceramics. Any deposits formed on the cathode are scraped off to be recovered as a powder. The goal therefore is the obtaining of powder, and neither the obtaining direct of an oxide or hydroxide film on a substrate, nor its use as such is described. In addition, no mention is made of a reduction reaction oxygen for the formation of an oxide or hydroxide film.
  • the object of the present invention is to provide a method which does not have the disadvantages of the the prior art, to obtain a film of a metal oxide or a metal hydroxide on an electrochemical support, said film with good mechanical strength and good adhesion to the support.
  • the method is characterized in that dissolves oxygen in the electrolyte and a cathode potential is imposed on the electrochemical cell lower than the oxygen reduction potential and greater than the metal M deposit potential in the electrolyte considered.
  • the process of the present invention can be implemented works to prepare a film of a single metal compound. he can also be used to prepare a film of a mixed compound containing at least two metallic elements.
  • we introduce in the electrolyte at least one precursor salt of each of the desired metallic species and the potential imposed on the electrochemical cell is greater than the potential for deposits metallic in the considered bath.
  • the process of the present invention can be implemented work for the preparation of a film of a compound of at least a metal M chosen from the metallic elements of the columns II and III of the periodic table, and more specifically for the preparation of a film of a zinc compound, cadmium, gallium or indium.
  • the electrochemical cell used for the implementation of the process of the invention comprises an electrode which works as a cathode and serves as a support for the film of compound of M electrodeposited, a counter electrode and a reference electrode.
  • the electrode consists of any conductive material which can be used as a cathode material.
  • metallic materials such as for example iron, steels, copper or gold, conductive metallic oxides such as for example tin oxide SnO 2 , oxide d indium In 2 O 3 , mixed indium tin oxide (ITO) or titanium oxide TiO 2 , or semiconductor materials such as silicon, GaAs, InP, Cu (In, Ga ) (S, Se) 2 or CdTe.
  • conductive metallic oxides such as for example tin oxide SnO 2 , oxide d indium In 2 O 3 , mixed indium tin oxide (ITO) or titanium oxide TiO 2
  • semiconductor materials such as silicon, GaAs, InP, Cu (In, Ga ) (S, Se) 2 or CdTe.
  • the counter electrode can be an unassailable electrode such as for example a platinum or gold electrode, or of a material coated with these metals. It can also be an electrode constituted by the metal M of the compound of which seeks to form a film. In this case, the oxidation of the metal M of the counter-electrode keeps the concentration constant metal M of the electrolyte.
  • the reference electrode is chosen from the electrodes usually used as such, especially the electrode mercury sulfate (ESM) or the chloride electrode mercury (ECS).
  • ESM electrode mercury sulfate
  • ECS chloride electrode mercury
  • the corresponding potentials are respectively of +0.65 V and +0.25 V with respect to the normal electrode with hydrogen (ENH).
  • the electrolyte contains at least one precursor salt of at least minus one metallic species M and one solvent.
  • the solvent of the electrolyte is chosen from water and polar nonaqueous solvents commonly used in electrochemical cells, among which we can cite alcohols, more particularly isopropanol, acetonitrile, dimethyl sulfoxide and propylene carbonate. Water is a particularly preferred solvent.
  • the precursor salt of the metallic element M can be chosen from the salts soluble in the solvent used for the electrolyte.
  • these salts mention may be made of inorganic salts such as halides, sulfates, nitrates and perchlorates, and organic salts such as acetates.
  • the electrolyte may optionally contain at least one second salt, known as support salt.
  • This second salt is a dissociable salt in the solvent used and has for main function ensure good electrical conductivity of the electrolyte, especially in the case where the concentration of the precursor salt of metal M is weak.
  • This salt can be chosen from the salts sodium, potassium or ammonium, the anion of which will not cause not precipitation of an insoluble compound with the metal cation M.
  • inorganic salts such as halides, sulfates, nitrates and perchlorates, or organic salts such as acetates, lactates and formates.
  • this second salt is advantageously potassium chloride, preferably at a concentration about 0.1 mole / l.
  • the electrolyte may also contain, in addition or at the place of the second salt, a complexing compound with respect to cation M, to adapt the conditions of formation of the compound from M to the window allowed by the reduction of oxygen.
  • a complexing compound with respect to cation M
  • the addition complexing agents chosen for example from oxalates, citrates, fluorides, chlorides, iodides and bromides, makes it possible to dissolve the precursor salt of the metal by weakly acid medium (pH ⁇ 5-4).
  • the electrolysis is carried out in the presence of oxygen dissolved in the electrolyte.
  • the oxygen concentration is fixed between very low values, of the order of 10 -5 mole / l, and the solubility limit of oxygen in the electrolyte, (of the order of 10 -3 mole / l in aqueous medium).
  • Oxygen can be dissolved advantageously by introducing into the electrolyte a gas mixture consisting of oxygen and a neutral gas.
  • the neutral gas can be argon or nitrogen.
  • a suitable choice of the oxygen concentration of the gas mixture and the gas flow in the electrolyte makes it possible to impose a predetermined concentration of oxygen in the electrolyte.
  • the oxygen / neutral gas volume ratio is between 1 and 2.
  • the potential imposed on the electrochemical cell is maintained constant at a predetermined value between the potential of depositing the metal M in the electrolyte considered and the oxygen reduction potential.
  • the deposit potential of metal M in the considered electrolyte can be easily determined by the skilled person by noting the intensity in potential function in an analog electrochemical cell to that in which the process of the invention is put in use, in the absence of oxygen.
  • the reduction potential oxygen is provided by the literature.
  • the potential for the deposition of a zinc oxide film on a SnO2 cathode can be fixed between -0.75 V and -0.1 V vs ENH and for depositing a film of cadmium hydroxide on a gold cathode between -0.24 V and -0.05 V vs ENH.
  • the implementation of the process according to the invention produces generally a linear growth in the thickness of the deposit as a function of time.
  • the thickness of a film can therefore be predetermined by adjusting the amount of electricity used for filing. Thicknesses from a few nm to a few ⁇ m can be obtained.
  • the filing speed particularly favorable is between about 0.5 and 1 ⁇ m / h.
  • the nature of the compound constituting the film deposited on the electrochemical cell electrode can be chosen by appropriately setting the reaction conditions.
  • the process of the invention should be carried out under conditions in which the oxide is thermodynamically more stable than the hydroxide.
  • favorable conditions are obtained with relatively low deposition rates and high temperatures. Therefore, for obtaining oxides from aqueous solutions, low concentrations of M (i) will be used.
  • a Zn (II) concentration is preferably used, less than 10 -2 mole / l, more particularly less than 5.10 - 3 mole / l, a temperature at least equal to 50 ° C, and an oxygen concentration lower than the saturating concentration in the solution.
  • the process of the invention should be carried out with a relatively high deposition rate and at a relatively low temperature. These conditions are met when using high M (i) concentrations.
  • a concentration of Zn (II) greater than 2.10 -2 mole / l is used, a temperature less than 50 ° C and an oxygen concentration less than or equal at saturating concentration.
  • the process of the invention leads the deposition of oxide layers.
  • the anion A is the anion introduced into the electrolyte by the precursor salt of the metal M, or else the anion of the second dissociable salt introduced into the electrolyte to increase its conductivity.
  • the anion A is chosen as a function of its propensity to form compounds defined with the metal M and with the hydroxyl ions, and as a function of the properties expected for the film deposited. Thus, it may be advantageous to obtain zinc oxide films doped with halides.
  • the films obtained by the process of the invention are very adherent to the substrate, which is a criterion fundamental for applications.
  • their structure can vary from a very open made of the growth of crystals separated from each other whose crystal quality is, moreover, remarkable, a dense structure made of coalesced grains.
  • a type particular structure can be obtained by choosing to appropriately the site density setting of nucleation on the substrate, and the potential electrolysis parameter. The lower the density of nucleation sites, the more the structure will be open. Conversely, the higher the density the higher the nucleation sites, the more structure compact. In addition, the more negative the potential, the more the structure will be compact.
  • a treatment electrochemical prior to the substrate in the absence of metal ions, by reduction of oxygen for example, allows for more compact deposits.
  • Another process to activate the substrate is to deposit an undercoat of very fine metal M, of the order of a few nanometers, by application for a very short time (e.g. around 30 seconds) of a more cathodic potential, before to apply the deposition potential of the compound of M.
  • the method of the present invention makes it possible to obtain a multilayer structure constituted by a conductive support layer and a film of oxide or hydroxide M (OH) x A y , which constitutes another object of the present invention.
  • the composite structure has various applications.
  • Multilayer structures comprising a compact film are generally useful for applications requiring continuous layers. Such structures can be used for example as a chemical or electrochemical sensor or as a catalyst.
  • the composite structures can also be used as a transparent electrode in solar cells, in flat luminescent devices, and more generally, in various optoelectronic devices.
  • the support layer consists of a thin layer of a material chosen from iron, steels, copper or gold, conductive metal oxides such as for example oxide tin SnO 2 , indium oxide In 2 O 3 , mixed indium tin oxide (ITO) or titanium oxide TiO 2 , semiconductor materials such as silicon, GaAs, InP, Cu (In, Ga) (S, Se) 2 or CdTe.
  • the support layer consists of a thin layer of one of the preceding materials, deposited on a glass plate.
  • Multi-layer structures comprising a structured film open are used for applications requiring large developed areas.
  • applications include chemical sensors or electrochemicals, and catalysts.
  • the device used comprises an electrolysis tank, an electrode, a counter electrode and a reference electrode, all three being connected to a potentiostat.
  • Tank of electrolysis is provided with a stirring system and means to introduce a gas mixture with a predetermined flow rate argon / oxygen having a predetermined composition. Temperature is kept constant at 80 ° C using a bath of water.
  • the electrode consists of a film of SnO 2 deposited on glass.
  • the counter electrode consists of a platinum plate.
  • the reference electrode is a mercury sulfate electrode.
  • the SnO 2 electrode was subjected to a treatment which consists in maintaining it for 20 minutes under a potential of -1.3 V / ESM included in the oxygen reduction field, in a KCl solution (0.1 mol / l) not containing the metallic element of which the oxide is to be deposited, in the presence of dissolved oxygen at saturation.
  • an electrolyte is introduced consisting of an aqueous solution of KCl (0.1 M) and zinc chloride (5.10 -3 M).
  • the gas mixture is continued to bubbled through the electrolyte and the cell is applied to a potential of -1.3 V relative to the reference electrode (corresponding to a potential of -0 , 65 V vs ENH).
  • the reaction is stopped after 1 h 30, and the film obtained has a thickness of 1 ⁇ m, determined using a mechanical profilometer. This thickness is related to the amount of electricity consumed during the deposit ( ⁇ 7 C for 5 cm 2 ).
  • the oxide film obtained was characterized according to different methods.
  • X-ray diffraction diagram of oxide film zinc obtained preferably oriented along the ⁇ 002> axis, presents only the characteristic lines of the phase hexagonal zinc oxide (20.1 °) and lines corresponding to the substrate.
  • the infrared spectrum of the zinc oxide film obtained shows the band lying around 450-550 cm -1 , characteristic of ZnO. No characteristic band of the hydroxyl ions is visible.
  • the film obtained is compact, transparent, smooth and homogeneous.
  • transmission is high, in agreement with the transparency of the film to the eye.
  • Capacitive measurements carried out in an electrolytic medium have shown that the ZnO film obtained was conductive, of n type, and that the apparent doping rate is high, of the order of 10 18 -10 19 cm -3 .
  • the method of the invention was implemented under conditions analogous to those of Example 1, but omitting the prior treatment of the SnO 2 electrode, the latter being simply degreased.
  • the oxide deposit obtained consists of a multitude of needles with a hexagonal section, the bases of which are fixed to the substrate. These needles are well separated from each other and therefore constitute an open structure having a large developed surface.
  • the height of the needles can reach several ⁇ m for a base surface of the order of ⁇ m 2 . It increases with the duration of the deposit.
  • the device used is analogous to that used for the preparation of an oxide film and the operating conditions are identical, except as regards the composition of the electrolyte.
  • the electrolyte is an aqueous solution of KCl (0.1 M) and zinc chloride (3.10 -2 M).
  • the film obtained has a thickness of 0.5 ⁇ m, determined at using a mechanical profilometer. This thickness is related the amount of electricity consumed during the deposit.
  • the hydroxide film obtained was characterized according to different methods.
  • the X-ray diffraction diagram of the hydroxide film has a preferential orientation along the 6.5 ° line of the compound Zn 5 (OH) 8 Cl 2 .
  • the infrared spectrum of the zinc hydroxide film obtained has a dominant band located around 3500 cm -1 , characteristic of hydroxyl ions.
  • the characteristic band of the Zn-O bonds of the oxide around 500 cm -1 is not present.
  • the film obtained is covering and consists of hexagonal grains well defined.
  • the film obtained has a thickness of 0.3 ⁇ m, determined under electron microscopy.
  • the hydroxide film obtained was characterized according to different methods.
  • the film obtained has an open structure.
  • the film obtained has a thickness of 0.4 ⁇ m, determined under electron microscopy.
  • the complex hydroxide film obtained has a covering structure.
  • the composition Cd (OH) x Cl 1-x was confirmed by an X-ray analysis and by an analysis by electron spectroscopy.
  • the film obtained after one hour has a thickness of 0.5 ⁇ m, determined under electron microscopy. It is transparent and covering.
  • the Ga / O stoichiometric ratio determined using a Ga 2 O 3 standard is 0.324.
  • the gallium compound obtained therefore corresponds to gallium hydroxide Ga (OH) 3 or to hydrated gallium oxide Ga 2 O 3 .3H 2 O.

Description

La présente invention concerne un procédé de préparation d'un film d'un oxyde métallique ou d'un hydroxyde métallique d'un élément des colonnes II ou III de la classification, déposé sur un substrat.The present invention relates to a preparation process a film of a metal oxide or a metal hydroxide an element from columns II or III of the classification, deposited on a substrate.

Les oxydes métalliques en couche mince sont des matériaux très importants dans divers domaines technologiques du fait de leurs caractéristiques optiques, électriques et catalytiques. Parmi leurs nombreuses applications, on peut citer par exemple l'utilisation d'oxyde de zinc pour l'élaboration d'électrodes conductrices et transparentes dans les piles solaires.Thin film metallic oxides are materials very important in various technological fields of made of their optical, electrical and catalytic characteristics. Among their many applications, we can cite for example the use of zinc oxide for the preparation conductive and transparent electrodes in the batteries solar.

Les couches minces d'oxyde métalliques sont généralement obtenues par des techniques de dépôt sous vide telles que la pulvérisation cathodique, ou "sputtering", le dépôt chimique en phase vapeur, ou par dépôt de couches successives par épitaxie par jets moléculaires (EJM). Tous ces procédés mettent en oeuvre des appareillages coûteux.Thin layers of metal oxide are generally obtained by vacuum deposition techniques such as sputtering, or chemical sputtering in vapor phase, or by depositing successive layers by molecular beam epitaxy (MLE). All these processes use expensive equipment.

Un autre procédé pour la préparation de couches minces d'oxydes est la pulvérisation chimique réactive, qui est réalisée sous atmosphère ordinaire, sans enceinte fermée. Cependant, les températures de dépôt sont très élevées, de l'ordre de 400-500°C.Another process for the preparation of thin layers of oxides is reactive chemical spraying, which is carried out under ordinary atmosphere, without closed enclosure. However, deposition temperatures are very high, around from 400-500 ° C.

Divers travaux ont été entrepris pour réaliser des dépôts pour voie électrolytique. Par exemple, Jay A. Switzer, Electrochemical Synthesis of Ceramic Films and Powders, Am. Ceram. Soc. Bull. 66, [10] 1521-24 (1987), décrit la préparation d'un film d'oxyde sur l'anode d'une cellule électrochimique par oxydation d'un ion métallique dissous, suivie d'une hydrolyse et d'une calcination, le procédé étant illustré par la préparation d'oxyde de thallium. Ce procédé reposé sur une augmentation du degré d'oxydation de l'ion métallique en solution, avec formation et dépôt sur un substrat d'un oxyde insoluble. Ce procédé ne peut toutefois être mis en oeuvre que pour préparer l'oxyde d'un métal qui a au moins deux degrés d'oxydation stables dans le milieu réactionnel. J.A. Switzer (précité) et R. T. Coyle, et al., (US-A-4,882,014) décrivent en outre la préparation de poudres d'oxydes et d'hydroxydes de métaux, en tant que précurseurs de céramiques. Ces poudres sont formées par précipitation au voisinage de la cathode d'une cellule électrochimique, provoquée par la réduction d'ions nitrates. Ces poudres sont ensuite séchées et frittées à haute température pour obtenir les matériaux céramiques. Les dépôts éventuellement formés sur la cathode sont grattés pour être récupérés sous forme de poudre. Le but visé est par conséquent l'obtention de poudre, et ni l'obtention directe d'un film d'oxyde ou d'hydroxyde sur un substrat, ni son utilisation en tant que tel ne sont décrites. En outre, aucune mention n'est faite d'une réaction de réduction d'oxygène pour la formation d'un film d'oxyde ou d'hydroxyde.Various works have been undertaken to carry out electrolytic deposition. For example, Jay A. Switzer, Electrochemical Synthesis of Ceramic Films and Powders, Am. Ceram. Soc. Bull. 66, [10] 1521-24 (1987), describes the preparation of an oxide film on the anode of an electrochemical cell by oxidation of a dissolved metal ion, followed by hydrolysis and calcination, the process being illustrated by the preparation of thallium oxide. This process rests on a increasing the degree of oxidation of the metal ion to solution, with formation and deposition on an substrate of an oxide insoluble. However, this process cannot be implemented that to prepare the oxide of a metal that has at least two stable oxidation states in the reaction medium. J.A. Switzer (supra) and R. T. Coyle, et al., (US-A-4,882,014) further describe the preparation of oxide powders and of metal hydroxides, as precursors of ceramics. These powders are formed by precipitation in the vicinity of the cathode of an electrochemical cell, caused by the reduction of nitrate ions. These powders are then dried and sintered at high temperature to obtain the materials ceramics. Any deposits formed on the cathode are scraped off to be recovered as a powder. The goal therefore is the obtaining of powder, and neither the obtaining direct of an oxide or hydroxide film on a substrate, nor its use as such is described. In addition, no mention is made of a reduction reaction oxygen for the formation of an oxide or hydroxide film.

Le but de la présente invention est de fournir un procédé qui ne présente pas les inconvénients des procédés de l'art antérieur, pour obtenir un film d'un oxyde métallique ou d'un hydroxyde métallique sur un support par voie électrochimique, le dit film présentant une bonne tenue mécanique et une bonne adhérence sur le support.The object of the present invention is to provide a method which does not have the disadvantages of the the prior art, to obtain a film of a metal oxide or a metal hydroxide on an electrochemical support, said film with good mechanical strength and good adhesion to the support.

La présente invention a pour objet un procédé pour le dépôt sur un support, d'un film d'un oxyde métallique ou d'un hydroxyde métallique de formule M(OH)xAy, M représentant au moins une espèce métallique au degré d'oxydation i choisie parmi les éléments des colonnes II ou III de la classification, A étant un anion dont le nombre de charges est n, 0<x≤i et x+ny=i, dans une cellule électrochimique qui comprend une électrode constituée par le dit support et fonctionnant en tant que cathode, une contre-électrode, une électrode de référence et un électrolyte constitué par une solution conductrice d'au moins un sel du métal M. Le procédé est caractérisé en ce qu'on dissout de l'oxygène dans l'électrolyte et on impose à la cellule électrochimique un potentiel de cathode inférieur au potentiel de réduction de l'oxygène et supérieur au potentiel de dépôt du métal M dans l'électrolyte considéré.The subject of the present invention is a method for depositing on a support, a film of a metal oxide or a metal hydroxide of formula M (OH) x A y , M representing at least one metallic species in degree d oxidation i chosen from the elements of columns II or III of the classification, A being an anion whose number of charges is n, 0 <x≤i and x + ny = i, in an electrochemical cell which comprises an electrode constituted by said support and operating as a cathode, a counter electrode, a reference electrode and an electrolyte consisting of a conductive solution of at least one salt of the metal M. The method is characterized in that dissolves oxygen in the electrolyte and a cathode potential is imposed on the electrochemical cell lower than the oxygen reduction potential and greater than the metal M deposit potential in the electrolyte considered.

Lorsque l'on impose à la cellule électrochimique un potentiel tel que défini ci-dessus, il se produit une réduction de l'oxygène et la formation d'oxyde ou d'hydroxyde M(OH)xAy du métal M qui se dépose sur la cathode.When a potential as defined above is imposed on the electrochemical cell, there is a reduction in oxygen and the formation of oxide or hydroxide M (OH) x A y of the metal M which is deposited on the cathode.

Dans la suite du texte, l'expression "composé de M" est utilisée pour désigner indifféremment l'oxyde métallique pur, l'hydroxyde M(OH)i ou l'hydroxyde complexe M(OH)xAy.In the remainder of the text, the expression “compound of M” is used to denote either the pure metal oxide, the hydroxide M (OH) i or the complex hydroxide M (OH) x A y .

Le procédé de la présente invention peut être mis en oeuvre pour préparer un film d'un composé d'un seul métal. Il peut également être mis en oeuvre pour préparer un film d'un composé mixte contenant au moins deux éléments métalliques. Lorsque l'on prépare un film d'un composé mixte, on introduit dans l'électrolyte au moins un sel précurseur de chacune des espèces métalliques souhaitées et le potentiel imposé à la cellule électrochimique est supérieur au potentiel des dépôts métalliques dans le bain considéré.The process of the present invention can be implemented works to prepare a film of a single metal compound. he can also be used to prepare a film of a mixed compound containing at least two metallic elements. When preparing a film of a mixed compound, we introduce in the electrolyte at least one precursor salt of each of the desired metallic species and the potential imposed on the electrochemical cell is greater than the potential for deposits metallic in the considered bath.

Le procédé de la présente invention peut être mis en oeuvre pour la préparation d'un film d'un composé d'au moins un métal M choisi parmi les éléments métalliques des colonnes II et III de la classification périodique, et plus spécialement pour la préparation d'un film d'un composé de zinc, de cadmium, de gallium ou d'indium.The process of the present invention can be implemented work for the preparation of a film of a compound of at least a metal M chosen from the metallic elements of the columns II and III of the periodic table, and more specifically for the preparation of a film of a zinc compound, cadmium, gallium or indium.

La cellule électrochimique utilisée pour la mise en oeuvre du procédé de l'invention comprend une électrode qui fonctionne en tant que cathode et qui sert de support au film de composé de M électrodéposé, une contre-électrode et une électrode de référence.The electrochemical cell used for the implementation of the process of the invention comprises an electrode which works as a cathode and serves as a support for the film of compound of M electrodeposited, a counter electrode and a reference electrode.

L'électrode est constituée par tout matériau conducteur utilisable comme matériau de cathode. A titre d'exemple, on peut citer les matériaux métalliques tels que par exemple le fer, les aciers, le cuivre ou l'or, des oxydes métalliques conducteurs tels que par exemple l'oxyde d'étain SnO2, l'oxyde d'indium In2O3, l'oxyde mixte d'indium et d'étain (ITO) ou l'oxyde de titane TiO2, ou des matériaux semi-conducteurs tels que le silicium, GaAs, InP, Cu(In,Ga) (S,Se)2 ou CdTe. Ces matériaux peuvent être utilisés sous forme de plaque, ou sous forme d'un film mince déposé sur un support isolant tel que le verre par exemple.The electrode consists of any conductive material which can be used as a cathode material. By way of example, mention may be made of metallic materials such as for example iron, steels, copper or gold, conductive metallic oxides such as for example tin oxide SnO 2 , oxide d indium In 2 O 3 , mixed indium tin oxide (ITO) or titanium oxide TiO 2 , or semiconductor materials such as silicon, GaAs, InP, Cu (In, Ga ) (S, Se) 2 or CdTe. These materials can be used in the form of a plate, or in the form of a thin film deposited on an insulating support such as glass for example.

La contre-électrode peut être une électrode inattaquable telle que par exemple une électrode de platine ou d'or, ou d'un matériau revêtu de ces métaux. Elle peut également être une électrode constituée par le métal M du composé dont on cherche à former un film. Dans ce cas, l'oxydation du métal M de la contre-électrode permet de maintenir constante la concentration en métal M de l'électrolyte.The counter electrode can be an unassailable electrode such as for example a platinum or gold electrode, or of a material coated with these metals. It can also be an electrode constituted by the metal M of the compound of which seeks to form a film. In this case, the oxidation of the metal M of the counter-electrode keeps the concentration constant metal M of the electrolyte.

L'électrode de référence est choisie parmi les électrodes utilisées habituellement comme telles, notamment l'électrode de sulfate mercureux (ESM) ou l'électrode au chlorure mercureux (ECS). Les potentiels correspondants sont respectivement de +0,65 V et +0,25 V vis à vis de l'électrode normale à hydrogène (ENH).The reference electrode is chosen from the electrodes usually used as such, especially the electrode mercury sulfate (ESM) or the chloride electrode mercury (ECS). The corresponding potentials are respectively of +0.65 V and +0.25 V with respect to the normal electrode with hydrogen (ENH).

L'électrolyte contient au moins un sel précurseur d'au moins une espèce métallique M et un solvant.The electrolyte contains at least one precursor salt of at least minus one metallic species M and one solvent.

Le solvant de l'électrolyte est choisi parmi l'eau et les solvants non aqueux polaires utilisés habituellement dans les cellules électrochimiques, parmi lesquels on peut citer les alcools, plus particulièrement l'isopropanol, l'acétonitrile, le diméthylsulfoxyde et le carbonate de propylène. L'eau est un solvant particulièrement préféré.The solvent of the electrolyte is chosen from water and polar nonaqueous solvents commonly used in electrochemical cells, among which we can cite alcohols, more particularly isopropanol, acetonitrile, dimethyl sulfoxide and propylene carbonate. Water is a particularly preferred solvent.

Le sel précurseur de l'élément métallique M peuvent être choisi parmi les sels solubles dans le solvant utilisé pour l'électrolyte. Parmi ces sels, on peut citer les sels inorganiques tels que les halogénures, les sulfates, les nitrates et les perchlorates, et les sels organiques tels que les acétates.The precursor salt of the metallic element M can be chosen from the salts soluble in the solvent used for the electrolyte. Among these salts, mention may be made of inorganic salts such as halides, sulfates, nitrates and perchlorates, and organic salts such as acetates.

L'électrolyte peut éventuellement contenir au moins un second sel, dit sel support. Ce second sel est un sel dissociable dans le solvant utilisé et a pour fonction principale d'assurer une bonne conductivité électrique de l'électrolyte, notamment dans le cas où la concentration du sel précurseur du métal M est faible. Ce sel peut être choisi parmi les sels de sodium, de potassium ou d'ammonium, dont l'anion ne provoquera pas la précipitation d'un composé insoluble avec le cation métallique M. A titre d'exemple, on peut citer les sels inorganiques tels que les halogénures, les sulfates, les nitrates et les perchlorates, ou les sels organiques tels que les acétates, les lactates et les formiates. Pour le dépôt d'un film d'un composé du zinc, ce second sel est avantageusement le chlorure de potassium, de préférence à une concentration d'environ 0,1 mole/l.The electrolyte may optionally contain at least one second salt, known as support salt. This second salt is a dissociable salt in the solvent used and has for main function ensure good electrical conductivity of the electrolyte, especially in the case where the concentration of the precursor salt of metal M is weak. This salt can be chosen from the salts sodium, potassium or ammonium, the anion of which will not cause not precipitation of an insoluble compound with the metal cation M. By way of example, mention may be made of inorganic salts such as halides, sulfates, nitrates and perchlorates, or organic salts such as acetates, lactates and formates. For the deposit of a film of a zinc compound, this second salt is advantageously potassium chloride, preferably at a concentration about 0.1 mole / l.

L'électrolyte peut également contenir, en plus ou à la place du deuxième sel, un composé complexant vis à vis du cation M, pour adapter les conditions de formation du composé de M à la fenêtre permise par la réduction de l'oxygène. Par exemple, pour les composés de gallium ou d'indium, l'addition de complexants, choisis par exemple parmi les oxalates, les citrates, les fluorures, les chlorures, les iodures et les bromures, permet de solubiliser le sel précurseur du métal en milieu faiblement acide (pH ≈ 5-4).The electrolyte may also contain, in addition or at the place of the second salt, a complexing compound with respect to cation M, to adapt the conditions of formation of the compound from M to the window allowed by the reduction of oxygen. Through example, for gallium or indium compounds, the addition complexing agents, chosen for example from oxalates, citrates, fluorides, chlorides, iodides and bromides, makes it possible to dissolve the precursor salt of the metal by weakly acid medium (pH ≈ 5-4).

L'électrolyse est effectuée en présence d'oxygène dissous dans l'électrolyte. La concentration de l'oxygène est fixée entre des valeurs très faibles, de l'ordre de 10-5 mole/l, et la limite de solubilité de l'oxygène dans l'électrolyte, (de l'ordre de 10-3 mole/l en milieu aqueux). L'oxygène peut être dissous de manière avantageuse en introduisant dans l'électrolyte un mélange gazeux constitué par de l'oxygène et un gaz neutre. Le gaz neutre peut être l'argon ou l'azote. Un choix approprié de la concentration en oxygène du mélange gazeux et du débit gazeux dans l'électrolyte permet d'imposer une concentration prédéterminée d'oxygène dans l'électrolyte. De préférence, le rapport en volume oxygène/gaz neutre est compris entre 1 et 2.The electrolysis is carried out in the presence of oxygen dissolved in the electrolyte. The oxygen concentration is fixed between very low values, of the order of 10 -5 mole / l, and the solubility limit of oxygen in the electrolyte, (of the order of 10 -3 mole / l in aqueous medium). Oxygen can be dissolved advantageously by introducing into the electrolyte a gas mixture consisting of oxygen and a neutral gas. The neutral gas can be argon or nitrogen. A suitable choice of the oxygen concentration of the gas mixture and the gas flow in the electrolyte makes it possible to impose a predetermined concentration of oxygen in the electrolyte. Preferably, the oxygen / neutral gas volume ratio is between 1 and 2.

Lors de la mise en oeuvre du procédé de l'invention, le potentiel imposé à la cellule électrochimique est maintenu constant à une valeur prédéterminée comprise entre le potentiel de dépôt du métal M dans l'électrolyte considéré et le potentiel de réduction d'oxygène. Le potentiel de dépôt du métal M dans l'électrolyte considéré peut être aisément déterminé par l'homme de métier en relevant l'intensité en fonction du potentiel dans une cellule électrochimique analogue à celle dans laquelle le procédé de l'invention est mis en oeuvre, en l'absence d'oxygène. Le potentiel de réduction de l'oxygène est fourni par la littérature. A titre d'exemple, le potentiel pour le dépôt d'un film d'oxyde de zinc sur une cathode de SnO2 peut être fixé entre -0,75 V et -0,1 v vs ENH et pour le dépôt d'un film d'hydroxyde de cadmium sur une cathode d'or entre -0,24 V et -0,05 V vs ENH.When implementing the method of the invention, the potential imposed on the electrochemical cell is maintained constant at a predetermined value between the potential of depositing the metal M in the electrolyte considered and the oxygen reduction potential. The deposit potential of metal M in the considered electrolyte can be easily determined by the skilled person by noting the intensity in potential function in an analog electrochemical cell to that in which the process of the invention is put in use, in the absence of oxygen. The reduction potential oxygen is provided by the literature. For exemple, the potential for the deposition of a zinc oxide film on a SnO2 cathode can be fixed between -0.75 V and -0.1 V vs ENH and for depositing a film of cadmium hydroxide on a gold cathode between -0.24 V and -0.05 V vs ENH.

La mise en oeuvre du procédé selon l'invention produit généralement une croissance linéaire de l'épaisseur du dépôt en fonction du temps. L'épaisseur d'un film peut par conséquent être prédéterminée en réglant la quantité d'électricité utilisée pour le dépôt. Des épaisseurs de quelques nm à quelques µm peuvent être obtenues. La vitesse de dépôt particulièrement favorable se situe entre environ 0,5 et 1 µm/h.The implementation of the process according to the invention produces generally a linear growth in the thickness of the deposit as a function of time. The thickness of a film can therefore be predetermined by adjusting the amount of electricity used for filing. Thicknesses from a few nm to a few µm can be obtained. The filing speed particularly favorable is between about 0.5 and 1 µm / h.

La nature du composé constituant le film déposé sur l'électrode de la cellule électrochimique peut être choisie en fixant de manière appropriée les conditions réactionnelles.The nature of the compound constituting the film deposited on the electrochemical cell electrode can be chosen by appropriately setting the reaction conditions.

Pour l'obtention d'un film d'oxyde, il convient de mettre en oeuvre le procédé de l'invention dans des conditions dans lesquelles l'oxyde est thermodynamiquement plus stable que l'hydroxyde. Dans ce cas, en milieu aqueux, des conditions favorables sont obtenues avec des vitesses de dépôt relativement faibles et des températures élevées. De ce fait, pour l'obtention d'oxydes à partir de solutions aqueuses, on utilisera des concentrations en M(i) faibles. Par exemple, pour obtenir un film d'oxyde de zinc à partir d'une solution contenant KCl comme sel support, on utilise une concentration en Zn(II) de préférence inférieure à 10-2 mole/l, plus particulièrement inférieure à 5.10-3 mole/l, une température au moins égale à 50 °C, et une concentration en oxygène inférieure à la concentration saturante dans la solution.To obtain an oxide film, the process of the invention should be carried out under conditions in which the oxide is thermodynamically more stable than the hydroxide. In this case, in an aqueous medium, favorable conditions are obtained with relatively low deposition rates and high temperatures. Therefore, for obtaining oxides from aqueous solutions, low concentrations of M (i) will be used. For example, to obtain a zinc oxide film from a solution containing KCl as a support salt, a Zn (II) concentration is preferably used, less than 10 -2 mole / l, more particularly less than 5.10 - 3 mole / l, a temperature at least equal to 50 ° C, and an oxygen concentration lower than the saturating concentration in the solution.

Pour obtenir un dépôt d'hydroxyde en milieu aqueux, il convient de mettre en oeuvre le procédé de l'invention avec une vitesse de dépôt relativement élevée et à une température relativement basse. Ces conditions sont remplies lorsqu'on utilise des concentrations en M(i) élevées. Par exemple, pour obtenir un film de composé Zn(OH)xAy, on utilise une concentration en Zn(II) supérieure à 2.10-2 mole/l, une température inférieure à 50°C et une concentration en oxygène inférieure ou égale à la concentration saturante.To obtain a hydroxide deposition in an aqueous medium, the process of the invention should be carried out with a relatively high deposition rate and at a relatively low temperature. These conditions are met when using high M (i) concentrations. For example, to obtain a film of compound Zn (OH) x A y , a concentration of Zn (II) greater than 2.10 -2 mole / l is used, a temperature less than 50 ° C and an oxygen concentration less than or equal at saturating concentration.

En milieu non aqueux, le procédé de l'invention conduit au dépôt de couches d'oxydes. In a nonaqueous medium, the process of the invention leads the deposition of oxide layers.

Dans un film de M(OH)xAy, l'anion A est l'anion introduit dans l'électrolyte par le sel précurseur du métal M, ou bien l'anion du second sel dissociable introduit dans l'électrolyte pour augmenter sa conductivité. L'anion A est choisi en fonction de sa propension à former des composés définis avec le métal M et avec les ions hydroxyles, et en fonction des propriétés attendues pour le film déposé. Ainsi, il peut être intéressant d'obtenir des films d'oxyde de zinc dopés par les halogénures.In a film of M (OH) x A y , the anion A is the anion introduced into the electrolyte by the precursor salt of the metal M, or else the anion of the second dissociable salt introduced into the electrolyte to increase its conductivity. The anion A is chosen as a function of its propensity to form compounds defined with the metal M and with the hydroxyl ions, and as a function of the properties expected for the film deposited. Thus, it may be advantageous to obtain zinc oxide films doped with halides.

Les films obtenus par le procédé de l'invention sont très adhérents au substrat, ce qui constitue un critère fondamental pour les applications. En fonction des conditions de dépôt, leur structure peut varier d'une structure très ouverte faite de la croissance de cristaux séparés entre eux dont la qualité cristalline est au demeurant remarquable, à une structure dense faite de grains coalescés. Un type particulier de structure peut être obtenu en choisissant de manière appropriée le paramètre densité de sites de nucléation sur le substrat, et le paramètre potentiel d'électrolyse. Plus la densité de sites de nucléation sera faible, plus la structure sera ouverte. Inversement, plus la densité de sites de nucléation sera élevée, plus la structure sera compacte. En outre, plus le potentiel est négatif, plus la structure sera compacte. Il faut noter également qu'un traitement électrochimique préalable du substrat, en l'absence d'ions métalliques, par réduction de l'oxygène par exemple, permet d'obtenir des dépôt plus compacts. Un autre procédé pour activer le substrat consiste à déposer une sous-couche de métal M très fine, de l'ordre de quelques nanomètres, par application pendant un temps très court (par exemple de l'ordre de 30 secondes) d'un potentiel plus cathodique, avant d'appliquer le potentiel de dépôt du composé de M.The films obtained by the process of the invention are very adherent to the substrate, which is a criterion fundamental for applications. Depending on the conditions of deposit, their structure can vary from a very open made of the growth of crystals separated from each other whose crystal quality is, moreover, remarkable, a dense structure made of coalesced grains. A type particular structure can be obtained by choosing to appropriately the site density setting of nucleation on the substrate, and the potential electrolysis parameter. The lower the density of nucleation sites, the more the structure will be open. Conversely, the higher the density the higher the nucleation sites, the more structure compact. In addition, the more negative the potential, the more the structure will be compact. It should also be noted that a treatment electrochemical prior to the substrate, in the absence of metal ions, by reduction of oxygen for example, allows for more compact deposits. Another process to activate the substrate is to deposit an undercoat of very fine metal M, of the order of a few nanometers, by application for a very short time (e.g. around 30 seconds) of a more cathodic potential, before to apply the deposition potential of the compound of M.

Le procédé de la présente invention permet d'obtenir une structure multi-couche constituée par une couche conductrice support et un film d'oxyde ou d'hydroxyde M(OH)xAy, qui constitue un autre objet de la présente invention. Suivant la nature de la couche conductrice support et du film, la structure composite a diverses applications. The method of the present invention makes it possible to obtain a multilayer structure constituted by a conductive support layer and a film of oxide or hydroxide M (OH) x A y , which constitutes another object of the present invention. Depending on the nature of the conductive support layer and the film, the composite structure has various applications.

Les structures multi-couches comprenant un film compact sont intéressantes, de manière générale, pour les applications nécessitant des couches continues. De telles structures peuvent être utilisées par exemple comme capteur chimique ou électrochimique ou comme catalyseur. Les structures composites peuvent également être utilisées comme électrode transparente dans les cellules solaires, dans les dispositifs luminescents plats, et de manière plus générale, dans divers dispositifs optoélectroniques. Dans un mode de mise en oeuvre particulier, la couche support est constituée par une couche mince d'un matériau choisi parmi le fer, les aciers, le cuivre ou l'or, les oxydes métalliques conducteurs tels que par exemple l'oxyde d'étain SnO2, l'oxyde d'indium In2O3, l'oxyde mixte d'indium et d'étain (ITO) ou l'oxyde de titane TiO2, les matériaux semi-conducteurs tels que le silicium, GaAs, InP, Cu(In,Ga)(S,Se)2 ou CdTe. Dans un mode de réalisation préféré, la couche support est constituée par une couche mince de l'un des matériaux précédents, déposée sur une plaque de verre.Multilayer structures comprising a compact film are generally useful for applications requiring continuous layers. Such structures can be used for example as a chemical or electrochemical sensor or as a catalyst. The composite structures can also be used as a transparent electrode in solar cells, in flat luminescent devices, and more generally, in various optoelectronic devices. In a particular embodiment, the support layer consists of a thin layer of a material chosen from iron, steels, copper or gold, conductive metal oxides such as for example oxide tin SnO 2 , indium oxide In 2 O 3 , mixed indium tin oxide (ITO) or titanium oxide TiO 2 , semiconductor materials such as silicon, GaAs, InP, Cu (In, Ga) (S, Se) 2 or CdTe. In a preferred embodiment, the support layer consists of a thin layer of one of the preceding materials, deposited on a glass plate.

Les structures multi-couches comprenant un film à structure ouverte sont utilisées pour des applications nécessitant des surfaces développées importantes. A titre d'exemple de telles applications, on peut citer les capteurs chimiques ou électrochimiques, et les catalyseurs.Multi-layer structures comprising a structured film open are used for applications requiring large developed areas. As an example of such applications include chemical sensors or electrochemicals, and catalysts.

La présente invention est décrite ci-après plus en détails par des exemples concrets de mise en oeuvre du procédé de l'invention, donnés à titre illustratif, l'invention n'étant bien entendu pas limitée à ces exemples.The present invention is described below in more details by concrete examples of implementation of the process of the invention, given by way of illustration, the invention of course not being limited to these examples.

EXEMPLE 1EXAMPLE 1 PREPARATION D'UN FILM D'OXYDE DE ZINCPREPARATION OF A ZINC OXIDE FILM

Le dispositif utilisé comprend une cuve d'électrolyse, une électrode, une contre-électrode et une électrode de référence, toutes trois étant reliées à un potentiostat. La cuve d'électrolyse est munie d'un système d'agitation et de moyens pour introduire avec un débit prédéterminé un mélange gazeux argon/oxygène ayant une composition prédéterminée. La température est maintenue constante à 80°C à l'aide d'un bain d'eau. The device used comprises an electrolysis tank, an electrode, a counter electrode and a reference electrode, all three being connected to a potentiostat. Tank of electrolysis is provided with a stirring system and means to introduce a gas mixture with a predetermined flow rate argon / oxygen having a predetermined composition. Temperature is kept constant at 80 ° C using a bath of water.

L'électrode est constituée par un film de SnO2 déposé sur verre. La contre-électrode est constituée par une plaque de platine. L'électrode de référence est une électrode de sulfate mercureux.The electrode consists of a film of SnO 2 deposited on glass. The counter electrode consists of a platinum plate. The reference electrode is a mercury sulfate electrode.

Préalablement à la mise en oeuvre du procédé, l'électrode SnO2 a été soumise à un traitement qui consiste à la maintenir pendant 20 minutes sous un potentiel de -1,3 V/ESM compris dans le domaine de réduction de l'oxygène, dans une solution KCl (0,1 mole/l) ne contenant pas l'élément métallique dont on veut déposer l'oxyde, en présence d'oxygène dissous à saturation.Prior to the implementation of the method, the SnO 2 electrode was subjected to a treatment which consists in maintaining it for 20 minutes under a potential of -1.3 V / ESM included in the oxygen reduction field, in a KCl solution (0.1 mol / l) not containing the metallic element of which the oxide is to be deposited, in the presence of dissolved oxygen at saturation.

Dans la cuve d'électrolyse munie de l'électrode ainsi traitée, on introduit un électrolyte constitué par une solution aqueuse de KCl (0,1 M) et de chlorure de zinc (5.10-3 M). On fait ensuite barboter à travers l'électrolyte pendant une heure, un mélange gazeux oxygène-argon (rapport en volume oxygène/argon = 1,4) afin que la solution soit bien en équilibre avec le mélange gazeux. Lorsque l'équilibre est atteint, on continue de faire barboter le mélange gazeux dans l'électrolyte et on applique à la cellule à un potentiel de -1,3 V par rapport à l'électrode de référence (correspondant à un potentiel de -0,65 V vs ENH). La réaction est arrêtée après 1 h 30, et le film obtenu a une épaisseur de 1 µm, déterminée à l'aide d'un profilomètre mécanique. Cette épaisseur est liée à la quantité d'électricité consommée durant le dépôt (≈ 7 C pour 5 cm2).In the electrolysis tank provided with the electrode thus treated, an electrolyte is introduced consisting of an aqueous solution of KCl (0.1 M) and zinc chloride (5.10 -3 M). An oxygen-argon gas mixture is then bubbled through the electrolyte for one hour (oxygen / argon volume ratio = 1.4) so that the solution is well in equilibrium with the gas mixture. When equilibrium is reached, the gas mixture is continued to bubbled through the electrolyte and the cell is applied to a potential of -1.3 V relative to the reference electrode (corresponding to a potential of -0 , 65 V vs ENH). The reaction is stopped after 1 h 30, and the film obtained has a thickness of 1 μm, determined using a mechanical profilometer. This thickness is related to the amount of electricity consumed during the deposit (≈ 7 C for 5 cm 2 ).

Le film d'oxyde obtenu a été caractérisé selon différentes méthodes.The oxide film obtained was characterized according to different methods.

Analyse aux rayons XX-ray analysis

Le diagramme de diffraction des rayons X du film d'oxyde de zinc obtenu, orienté préférentiellement suivant l'axe <002>, présente uniquement les raies caractéristiques de la phase hexagonale de l'oxyde de zinc (20,1°)et les raies correspondant au substrat.X-ray diffraction diagram of oxide film zinc obtained, preferably oriented along the <002> axis, presents only the characteristic lines of the phase hexagonal zinc oxide (20.1 °) and lines corresponding to the substrate.

Analyse par spectroscopie d'électrons (EDS)Electron spectroscopy (EDS) analysis

Cette analyse a été effectuée en mesurant les rayons X émis sous bombardement électronique dans un microscope à balayage. Les énergies sont caractéristiques des atomes. Sur le spectre EDS du film obtenu, on note l'absence de pic à 2,830 keV, ce qui permet de conclure à l'absence d'ions chlorures dans le produit obtenu et confirme que le produit obtenu est l'oxyde et non pas d'un hydroxyde complexe.This analysis was carried out by measuring the X-rays emitted under electron bombardment in a scanning microscope. The energies are characteristic of atoms. On the spectrum EDS of the film obtained, we note the absence of a peak at 2.830 keV, which which makes it possible to conclude that there are no chloride ions in the product obtained and confirms that the product obtained is oxide and not a complex hydroxide.

Analyse par infrarougeInfrared analysis

Le spectre infra-rouge du film d'oxyde de zinc obtenu présente la bande se situant vers 450-550 cm-1, caractéristique de ZnO. Aucune bande caractéristique des ions hydroxyles n'est visible.The infrared spectrum of the zinc oxide film obtained shows the band lying around 450-550 cm -1 , characteristic of ZnO. No characteristic band of the hydroxyl ions is visible.

La structure du filmThe structure of the film

Le film obtenu est compact, transparent, lisse et homogène. Sur la courbe de transmission optique directe du film d'oxyde de zinc obtenu, pour les longueurs d'onde du domaine visible (> 400 nm), la transmission est élevée, en accord avec la transparence du film à l'oeil. Vers les courtes longueurs d'onde, il apparaít un front d'absorption abrupt, qui indique le caractère semi-conducteur du film et la présence d'une bande interdite qui correspond à celle de ZnO à environ 3,4 eV.The film obtained is compact, transparent, smooth and homogeneous. On the direct optical transmission curve of the film zinc oxide obtained, for the wavelengths of the domain visible (> 400 nm), transmission is high, in agreement with the transparency of the film to the eye. Towards short lengths wave, there appears a steep absorption front, which indicates the semiconductor character of the film and the presence a band gap which corresponds to that of ZnO at approximately 3.4 eV.

Des mesures capacitives effectuées en milieu électrolytique ont montré que le film ZnO obtenu était conducteur, de type n, et que le taux de dopage apparent est élevé, de l'ordre de 1018-1019 cm-3.Capacitive measurements carried out in an electrolytic medium have shown that the ZnO film obtained was conductive, of n type, and that the apparent doping rate is high, of the order of 10 18 -10 19 cm -3 .

EXEMPLE 2EXAMPLE 2 PREPARATION D'UN FILM D'OXYDE DE ZINC A STRUCTURE OUVERTEPREPARATION OF AN OPEN-STRUCTURED ZINC OXIDE FILM

On a mis en oeuvre le procédé de l'invention dans des conditions analogues à celles de l'exemple 1, mais en omettant le traitement préalable de l'électrode de SnO2, celle-ci étant simplement dégraissée.The method of the invention was implemented under conditions analogous to those of Example 1, but omitting the prior treatment of the SnO 2 electrode, the latter being simply degreased.

Dans ces conditions, le dépôt d'oxyde obtenu est constitué d'une multitude d'aiguilles à section hexagonale dont les bases sont fixées au substrat. Ces aiguilles sont bien séparées les unes des autres et constituent par conséquent une structure ouverte présentant une grande surface développée. La hauteur des aiguilles peut atteindre plusieurs µm pour une surface de base de l'ordre du µm2. Elle augmente avec la durée du dépôt. Under these conditions, the oxide deposit obtained consists of a multitude of needles with a hexagonal section, the bases of which are fixed to the substrate. These needles are well separated from each other and therefore constitute an open structure having a large developed surface. The height of the needles can reach several µm for a base surface of the order of µm 2 . It increases with the duration of the deposit.

EXEMPLE 3EXAMPLE 3 PREPARATION D'UN FILM DE Zn(OH)xCl1-x PREPARATION OF A FILM OF Zn (OH) x Cl 1-x

Le dispositif utilisé est analogue à celui utilisé pour la préparation d'un film d'oxyde et les conditions opératoires sont identiques, sauf en ce qui concerne la composition de l'électrolyte. L'électrolyte est une solution aqueuse de KCl (0,1 M) et de chlorure de zinc (3.10-2 M).The device used is analogous to that used for the preparation of an oxide film and the operating conditions are identical, except as regards the composition of the electrolyte. The electrolyte is an aqueous solution of KCl (0.1 M) and zinc chloride (3.10 -2 M).

Le film obtenu a une épaisseur de 0,5 µm, déterminée à l'aide d'un profilomètre mécanique. Cette épaisseur est liée à la quantité d'électricité consommée durant le dépôt.The film obtained has a thickness of 0.5 μm, determined at using a mechanical profilometer. This thickness is related the amount of electricity consumed during the deposit.

Le film d'hydroxyde obtenu a été caractérisé selon différentes méthodes.The hydroxide film obtained was characterized according to different methods.

Analyse aux rayons XX-ray analysis

Le diagramme de diffraction des rayons X du film d'hydroxyde présente une orientation préférentielle suivant la raie à 6,5 ° du composé Zn5(OH)8Cl2.The X-ray diffraction diagram of the hydroxide film has a preferential orientation along the 6.5 ° line of the compound Zn 5 (OH) 8 Cl 2 .

Analyse par spectroscopie d'électrons (EDS)Electron spectroscopy (EDS) analysis

Cette analyse a été effectuée comme précédemment. Elle montre la présence d'un pic à 2,83 keV, caractéristique des ions chlorures.This analysis was carried out as previously. She shows the presence of a peak at 2.83 keV, characteristic of the ions chlorides.

Analyse par infrarougeInfrared analysis

Le spectre infra-rouge du film d'hydroxyde de zinc obtenu présente une bande dominante se situant vers 3500 cm-1, caractéristique des ions hydroxyles. La bande caractéristique des liaisons Zn-O de l'oxyde aux environs de 500 cm-1 n'est pas présente.The infrared spectrum of the zinc hydroxide film obtained has a dominant band located around 3500 cm -1 , characteristic of hydroxyl ions. The characteristic band of the Zn-O bonds of the oxide around 500 cm -1 is not present.

Structure du filmStructure of the film

Le film obtenu est couvrant et constitué de grains hexagonaux bien définis.The film obtained is covering and consists of hexagonal grains well defined.

EXEMPLE 4EXAMPLE 4 PREPARATION D'UN FILM D'HYDROXYDE DE CADMIUMPREPARATION OF A CADMIUM HYDROXIDE FILM

Le dispositif utilisé est analogue à celui utilisé pour la préparation d'un film d'oxyde de zinc et les conditions opératoires sont identiques, sauf en ce qui concerne les points suivants :

  • le potentiel appliqué à la cathode est de -0,9 V /réf. (-0,3 V vs ENH) ;
  • l'électrolyte est une solution aqueuse contenant NaClO4 (0,1 M) et CdCl2 (5.10-4 M), saturée en oxygène, à une température de 80 °C ;
  • la durée de la réaction est d'une heure.
The device used is analogous to that used for the preparation of a zinc oxide film and the operating conditions are identical, except as regards the following points:
  • the potential applied to the cathode is -0.9 V / ref. (-0.3 V vs ENH);
  • the electrolyte is an aqueous solution containing NaClO 4 (0.1 M) and CdCl 2 (5.10 -4 M), saturated with oxygen, at a temperature of 80 ° C;
  • the reaction time is one hour.

Le film obtenu a une épaisseur de 0,3 µm, déterminée sous microscopie électronique.The film obtained has a thickness of 0.3 μm, determined under electron microscopy.

Le film d'hydroxyde obtenu a été caractérisé selon différentes méthodes.The hydroxide film obtained was characterized according to different methods.

Analyse aux rayons XX-ray analysis

On constate la présence de la raie caractéristique de Cd(OH)2 sur le diagramme de diffraction des RX.We observe the presence of the characteristic line of Cd (OH) 2 on the X-ray diffraction diagram.

Analyse par spectroscopie d'électronsElectron spectroscopy analysis

Cette analyse a été effectuée comme précédemment. On constate l'absence des raies caractéristiques du chlore.This analysis was carried out as previously. We aknowledge the absence of the characteristic lines of chlorine.

Structure du filmStructure of the film

Le film obtenu présente une structure ouverte.The film obtained has an open structure.

EXEMPLE 5EXAMPLE 5 PREPARATION D'UN FILM DE Cd(OH)xCl1-x PREPARATION OF A FILM OF Cd (OH) x Cl 1-x

Le dispositif utilisé est analogue à celui utilisé pour la préparation d'un film d'oxyde de zinc et les conditions opératoires sont identiques, sauf en ce qui concerne les points suivants :

  • le potentiel appliqué à la cuve est de -0,15 V vs ENH.
  • l'électrolyte est une solution aqueuse contenant KCl (0,1 mole/l) et CdCl2 (10-2 mole/l), saturée en oxygène, à une température de 50 °C ;
The device used is analogous to that used for the preparation of a zinc oxide film and the operating conditions are identical, except as regards the following points:
  • the potential applied to the tank is -0.15 V vs ENH.
  • the electrolyte is an aqueous solution containing KCl (0.1 mole / l) and CdCl 2 (10 -2 mole / l), saturated with oxygen, at a temperature of 50 ° C;

Le film obtenu a une épaisseur de 0,4 µm, déterminée sous microscopie électronique.
Le film d'hydroxyde complexe obtenu a une structure couvrante.
La composition Cd(OH)xCl1-x a été confirmée par une analyse aux rayons X et par une analyse par spectroscopie d'électrons.The film obtained has a thickness of 0.4 μm, determined under electron microscopy.
The complex hydroxide film obtained has a covering structure.
The composition Cd (OH) x Cl 1-x was confirmed by an X-ray analysis and by an analysis by electron spectroscopy.

EXEMPLE 6EXAMPLE 6 PREPARATION D'UN FILM DE COMPOSE DE GALLIUMPREPARATION OF A GALLIUM COMPOUND FILM

Le dispositif utilisé est analogue à celui utilisé pour la préparation d'un film d'oxyde de zinc et les conditions opératoires sont identiques, sauf en ce qui concerne les points suivants :

  • le potentiel appliqué à la cuve est de -0,65 V vs ENH.
  • l'électrolyte est une solution aqueuse à pH 3 contenant du chlorure de potassium (0,1 mole/l), du sulfate de gallium (7,7x10-3 mole/l) et de l'oxalate de sodium (6x10-3 mole/l) saturée en oxygène, à une température de 50 °C ;
The device used is analogous to that used for the preparation of a zinc oxide film and the operating conditions are identical, except as regards the following points:
  • the potential applied to the tank is -0.65 V vs ENH.
  • the electrolyte is an aqueous solution at pH 3 containing potassium chloride (0.1 mole / l), gallium sulfate (7.7x10 -3 mole / l) and sodium oxalate (6x10 -3 mole / l) saturated with oxygen, at a temperature of 50 ° C;

Le film obtenu après une heure a une épaisseur de 0,5 µm, déterminée sous microscopie électronique. Il est transparent et couvrant.The film obtained after one hour has a thickness of 0.5 µm, determined under electron microscopy. It is transparent and covering.

L'analyse par rayons X montre la présence majoritaire de gallium et d'oxygène. Le rapport stoechiométrique Ga/O déterminé grâce à un étalon de Ga2O3 est de 0,324. Le composé de gallium obtenu correspond par conséquent à l'hydroxyde de gallium Ga(OH)3 ou à l'oxyde de gallium hydraté Ga2O3.3H2O.X-ray analysis shows the majority of gallium and oxygen. The Ga / O stoichiometric ratio determined using a Ga 2 O 3 standard is 0.324. The gallium compound obtained therefore corresponds to gallium hydroxide Ga (OH) 3 or to hydrated gallium oxide Ga 2 O 3 .3H 2 O.

Claims (23)

  1. Process for depositing a film of a metal oxide or of a metal hydroxide of formula M(OH)xAy, M representing at least one metallic species in the oxidation state i chosen from the elements in Groups II and III of the Periodic Table, A being an anion whose number of charges is n, 0 < x ≤ i and x + ny = i, on a substrate in an electrochemical cell which includes an electrode consisting of said substrate and working as the cathode, a counterelectrode, a reference electrode and an electrolyte consisting of a conducting solution of at least one salt of the metal M, said process being characterized in that oxygen is dissolved in the electrolyte and a cathode potential of less than the reduction potential of oxygen and greater than the potential for deposition of the metal M in the electrolyte in question is imposed on the electrochemical cell.
  2. Process according to claim 1, characterized in that M is chosen from Zn, Cd, Ga and In.
  3. Process according to claim 1, characterized in that the solvent of the electrolyte is chosen from water and polar solvents.
  4. Process according to claim 1, characterized in that the salt of the metal M is chosen from halides, sulfates, nitrates, perchlorates and acetates.
  5. Process according to claim 1, characterized in that the oxygen dissolved in the electrolyte is supplied by a mixture of inert gas and oxygen.
  6. Process according to claim 1, characterized in that the counterelectrode is an electrode consisting of the metal M.
  7. Process according to claim 1, characterized in that the electrolyte contains at least one dissociable supporting salt chosen from organic and inorganic, sodium, potassium and ammonium salts, the anion of which will not cause precipitation of an insoluble compound with the metal cation M.
  8. Process according to claim 7, characterized in that the supporting salt is chosen from halides, sulfates, nitrates, perchlorates, acetates, lactates, formates, oxalates and citrates.
  9. Process according to claim 1, for the preparation of an oxide film, characterized in that an aqueous medium containing KCl is used in which the Zn(II) concentration is less than 10-2 mol/l, the temperature is at least equal to 50°C and the oxygen concentration is less than the saturation concentration in the solution.
  10. Process according to claim 9, characterized in that the Zn(II) concentration is less than 5 x 10-3 mol/l.
  11. Process according to claim 1, for the preparation of a Zn(OH)xAy film, characterized in that an aqueous medium containing KCl is used in which the Zn(II) concentration is greater than 2 × 10-2 mol/l, the temperature is less than 50°C and the oxygen concentration is less than or equal to the saturation concentration.
  12. Process according to claim 1, characterized in that the electrolyte contains at least one precursor salt of different metallic species M.
  13. Process according to claim 1, characterized in that the electrode consists of a metallic material, chosen from iron, steels, copper and gold, a conductive metal oxide, such as, for example, tin oxide SnO2, indium oxide In2O3, mixed indium tin oxide (ITO) or titanium oxide TiO2, or a semiconductor material such as silicon, GaAs, InP, Cu(In,Ca)(S,Se)2 or CdTe.
  14. Process according to claim 13, characterized in that the metallic material or the semiconductor material is in the form of a thin film deposited on an insulating substrate.
  15. Process according to claim 14, characterized in that the insulating substrate is transparent.
  16. Process according to claim 1, characterized in that the electrolyte contains at least two metal salts, M representing more than one metallic species.
  17. Process according to claim 1, characterized in that the electrolyte contains, in addition to or in place of the second salt, a compound which complexes with the cation M.
  18. Process according to claim 17, characterized in that, in the case of gallium compounds or indium compounds, the complexing agent is chosen from oxalates, citrates and fluorides, chlorides, bromides and iodides.
  19. Multilayer structure consisting of a substrate layer supporting a film of a metal oxide or of a metal hydroxide of formula M(OH)xAy, M representing at least one metallic species in the oxidation state i chosen from the elements in Groups II and III of the Periodic Table, A being an anion whose number of charges is n, 0 < x ≤ i and x + ny = i, the substrate layer being a layer of a conductive material chosen from iron, steels, copper, gold, conductive metal oxides and semiconductor materials.
  20. Multilayer structure according to claim 19, characterized in that the layer of conductive material or of semiconductor material is supported by an insulating plate.
  21. Multilayer structure according to claim 19, characterized in that the conductive metal oxide is chosen from tin oxide SnO2, indium oxide In2O3, mixed indium tin oxide (ITO) and titanium oxide TiO2.
  22. Multilayer structure according to claim 19, characterized in that the semiconductor material is chosen from silicon, GaAs, InP, Cu(In,Ga)(S,Se)2 and CdTe.
  23. Electrode for a photocell, consisting of a multilayer structure according to claim 19.
EP96911017A 1995-04-06 1996-04-02 Method for preparing a film consisting of an oxide or hydroxide of an element in columns ii or iii of the periodic table, and composite structures including such a film Expired - Lifetime EP0819185B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR9504088A FR2732696B1 (en) 1995-04-06 1995-04-06 PROCESS FOR PREPARING AN OXIDE OR HYDROXIDE FILM OF AN ELEMENT OF COLUMNS II OR III OF THE CLASSIFICATION, AND THE COMPOSITE STRUCTURES INCLUDING SUCH A FILM
FR9504088 1995-04-06
PCT/FR1996/000495 WO1996031638A1 (en) 1995-04-06 1996-04-02 Method for preparing a film consisting of an oxide or hydroxide of an element in columns ii or iii of the periodic table, and composite structures including such a film

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DE69611162T2 (en) 2001-06-07
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US6030517A (en) 2000-02-29
FR2732696B1 (en) 1997-06-20
FR2732696A1 (en) 1996-10-11

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