EP0819185A1 - 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

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Publication number
EP0819185A1
EP0819185A1 EP96911017A EP96911017A EP0819185A1 EP 0819185 A1 EP0819185 A1 EP 0819185A1 EP 96911017 A EP96911017 A EP 96911017A EP 96911017 A EP96911017 A EP 96911017A EP 0819185 A1 EP0819185 A1 EP 0819185A1
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EP
European Patent Office
Prior art keywords
oxide
chosen
film
metal
electrolyte
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Granted
Application number
EP96911017A
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German (de)
French (fr)
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EP0819185B1 (en
Inventor
Daniel Lincot
Sophie Peulon
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Centre National de la Recherche Scientifique CNRS
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Centre National de la Recherche Scientifique CNRS
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Classifications

    • 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 process for preparing a film of a metal oxide or a metal hydroxide of an element of columns II or III of the classification, deposited on a substrate.
  • Metallic oxides in thin layers are very important materials in various technological fields because of their optical, electrical and catalytic characteristics. Among their many applications, one can quote for example the use of zinc oxide for the development of conductive and transparent electrodes in solar cells.
  • the thin metal oxide layers are generally obtained by vacuum deposition techniques such as sputtering, or "sputtering", chemical vapor deposition, or by deposition of successive layers by molecular beam epitaxy (E-JM ). All of these methods use expensive equipment.
  • JA Switzer (cited above) and RT Coyle, et al. (US-A-, 882, 014) further describe the preparation of metal oxide and hydroxide powders as ceramic precursors. 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 ceramic materials. Any deposits formed on the cathode are scraped off to be recovered in the form of powder. The aim is therefore to obtain powder, and neither the direct obtaining of an oxide or hydroxide film on a substrate, nor its use as such are described. Furthermore, no mention is made of an oxygen reduction reaction for the formation of an oxide or hydroxide film.
  • the object of the present invention is to provide a process which does not have the drawbacks of the methods of the prior art, in order to obtain a film of a metal oxide or of a metal hydroxide on a support by electro-chemical means. , the said film having good mechanical strength and good adhesion to the support.
  • the method is characterized in that oxygen is dissolved in the electrolyte and a cathode potential is imposed on the electrochemical cell lower than the oxygen reduction potential and greater than the deposit potential of the metal M in the considered electrolyte.
  • the process of the present invention can be used to prepare a film of a single metal compound. It can also be used to prepare a film of a mixed compound containing at least two metallic elements. When a film of a mixed compound is prepared, at least one precursor salt of each of the desired metal species is introduced into the electrolyte and the potential imposed on the electrochemical cell is greater than the potential of the metallic deposits in the bath considered.
  • the process of the present invention can be used for the preparation of a film of a compound of at least one metal M chosen from the metallic elements of columns II and III of the periodic table, and more particularly for preparing a film of a zinc, cadmium, gallium or indium compound.
  • the electrochemical cell used for implementing the process of the invention comprises an electrode which functions as a cathode and which 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 Sn0 2 , indium ln 2 0 3 , mixed indium tin oxide (ITO) or titanium oxide Ti0 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 Sn0 2 , indium ln 2 0 3 , mixed indium tin oxide (ITO) or titanium oxide Ti0 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 it is sought to form a film. In this case, the oxidation of the metal M of the counter-electrode makes it possible to keep the metal concentration M of the electrolyte constant.
  • the reference electrode is chosen from the electrodes usually used as such, in particular the mercurous sulfate electrode (ESM) or the mercurous chloride electrode (ECS).
  • ESM mercurous sulfate electrode
  • ECS mercurous chloride electrode
  • the corresponding potentials are respectively +0.65 V and +0.25 V with respect to the normal hydrogen electrode (ENH).
  • the electrolyte contains at least one precursor salt of at least one metallic species M and a solvent.
  • the solvent of the electrolyte is chosen from water and the nonaqueous polar solvents usually used in electrochemical cells, among which there may be mentioned alcohols, more particularly isopropanol, acetonitrile, dimethyl sulfoxide and carbonate. propylene. 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. Among 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, called the support salt.
  • This second salt is a salt disso ⁇ ciable in the solvent used and has the main function of ensuring good electrical conductivity of the electrolyte, especially in the case where the concentration of the precursor salt of the metal M is low.
  • This salt can be chosen from sodium, potassium or ammonium salts, the anion of which will not cause the 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 advantageous. sow potassium chloride, preferably at a concentration of about 0.1 mole / l.
  • the electrolyte can also contain, in addition to or in place of the second salt, a complexing compound with respect to the cation M, in order to adapt the conditions for the formation of the compound of M to the window permitted by the reduction of oxygen.
  • a complexing compound chosen for example from oxalates, citrates, fluorides, chlorides, iodides and
  • L 1 electrolysis is carried out in the presence of dis ⁇ oxygen in the electrolyte.
  • the oxygen concentration is fixed between very low values, of the order of
  • the oxygen can be dissolved advantageously intro ⁇ reducing in the electrolyte a gas mixture consisting of oxygen and a neutral gas.
  • the neutral gas can be argon
  • the oxygen concentration of the gas mixture and the gas flow rate 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 kept constant at a predetermined value between the potential for deposition of the metal M in the electrolyte considered and the reduction potential d 'oxygen.
  • 3 ⁇ metal M in the electrolyte considered can be easily determined by a person skilled in the art by raising the intensity as a function of the potential in an electrochemical cell analogous to that in which the process of the invention is implemented, in the absence of oxygen.
  • Oxygen is provided by the literature.
  • the potential for depositing a zinc oxide film on a SnO2 cathode can be set 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 method according to the invention generally produces 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 the deposit. Thicknesses from a few nm to a few ⁇ m can be obtained.
  • the particularly favorable deposition rate is between approximately 0.5 and 1 ⁇ m / h.
  • the nature of the compound constituting the film deposited on the electrode of the electrochemical cell 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 concentration is used in Zn (II) preferably less than 10 "2 mol / 1, more particularly less than 5.10 ⁇ 3 mole / 1, 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 / 1 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 to the deposition of layers of oxides.
  • 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.
  • the films obtained by the process of the invention are very adherent to the substrate, which constitutes a fundamental criterion for the applications.
  • Another method for activating the substrate consists in depositing a very thin metal sublayer M, of the order of a few nanometers, by application for a very short time (for example of the order of 30 seconds) of a potential more cathodic, before applying the deposition potential of the compound of M.
  • the method of the present invention makes it possible to obtain a multi-layer structure consisting of a conductive support layer and an oxide or hydroxide film M (0H) x A y , which constitutes another object of the present invention. .
  • the composite structure has various applications. Multi-layer structures comprising a compact film are advantageous, in general, 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 Sn0 2 , indium oxide ln 2 0 3 , mixed indium tin oxide (ITO) or titanium oxide Ti0 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 film with an open structure are used for applications requiring large developed surfaces. Examples of such applications include chemical or electrochemical sensors, and catalysts. The present invention is described below in more detail 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.
  • the device used comprises an electrolysis tank, an electrode, a counter electrode and a reference electrode, all three being connected to a potentiostat.
  • the electrolysis tank is provided with a stirring system and means for introducing with a predetermined flow rate an argon / oxygen gas mixture having a predetermined composition.
  • the temperature is kept constant at 80 ° C. using a water bath.
  • the electrode consists of a film of Sn ⁇ 2 deposited on glass.
  • the counter electrode consists of a platinum plate.
  • the reference electrode is a mercury sulfate electrode.
  • the Sn0 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 field of reduction of the oxygen, in a KC1 solution (0.1 mole / 1) not containing the metallic element whose oxide is to be deposited, in the presence of dissolved oxygen at saturation.
  • an electrolyte is introduced consisting of an aqueous solution of KC1 (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 linked to the quantity of electricity consumed during the deposit ( ⁇ 7 C for 5 cm 2 ).
  • the oxide film obtained was characterized by different methods.
  • X-ray analysis The X-ray diffraction diagram of the zinc oxide film obtained, preferably oriented along the ⁇ 002> axis, shows only the lines characteristic of the hexagonal phase of zinc oxide (20, 1 ° ) and the lines corresponding to the substrate.
  • the infrared spectrum of the zinc oxide film obtained presents 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.
  • the transmission is high, in agreement with the transparency of the film to the eye.
  • an abrupt absorption front appears, which indicates the semiconductor character of the film and the presence of a forbidden band which corresponds to that of ZnO at around 3.4 eV.
  • Capacitive measurements carried out in an electrolytic medium have shown that the film ZnO obtained was conductive, of type n, 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 similar to those of Example 1, but omitting the preliminary treatment of the SnO 2 electrode, the latter being simply degreased. Under these conditions, the oxide deposit obtained is made up of a multitude of needles with a hexagonal section, the bases being 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
  • the film obtained has a thickness of 0.5 ⁇ m, determined using a mechanical profilometer. This thickness is related to 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 line to
  • the infrared spectrum of the zinc hydroxide film obtained has a dominant band located around 3500 cm --'-, characteristic of hydroxyl ions.
  • the characteristic band of the Zn-0 bonds of the oxide around 500 cm ⁇ 1 is not present.
  • the film obtained is covering and consists of well-defined hexagonal grains.
  • 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 NaC10 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.
  • the film obtained has a thickness of 0.3 ⁇ m, determined under electron microscopy.
  • the hydroxide film obtained was characterized according to different methods. X-ray analysis We observe the presence of the characteristic line of Cd (OH) 2 on the X-ray diffraction diagram. Electron spectroscopy analysis
  • the film obtained has an open structure.
  • the apparatus used is similar 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 KC1 (0.1 mole / 1) and CdCl 2 (10 "2 mole / 1), saturated with oxygen, at a temperature of 50 ° C;
  • the film obtained has a thickness of 0.4 ⁇ m, determined under electron microscopy.
  • the complex hydroxide film obtained has a covering structure.
  • composition Cd (OH) x Cl 1 . x was confirmed by X - ray analysis and by electron spectroscopy analysis.
  • the device used is analogous to that used for the preparation of a zinc oxide film and the conditions The operating procedures 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 / 1), gallium sulfate (7.7xl0 ⁇ 3 mole / 1) and sodium oxalate (6xl0 ⁇ 3 mole / 1) saturated with oxygen, at a temperature of 50 ° C;
  • the film obtained after one hour has a thickness of 0.5 ⁇ m, determined under electron microscopy. It is transparent and covering.
  • the stoichiometric ratio Ga / 0 determined using a Ga 2 0 3 standard is 0.324.
  • the gallium compound obtained therefore corresponds to gallium hydroxide Ga (OH) 3 or to hydrated gallium oxide Ga 2 0 3 .3H 2 0.

Abstract

A method enabling a film consisting of an oxide or hydroxide of a species selected from the elements in columns II or III of the periodic table to be deposited on a substrate in an electrochemical cell that includes an electrode consisting of said substrate. According to the method, oxygen is dissolved in the electrolyte, and a cathode potential lower than the oxygen reduction potential and higher than the deposition potential of metal M in the electrolyte in question is imparted to the electrochemical cell. The method is suitable for preparing composite structures that are particularly useful as transparent electrodes in photovoltaic cells.

Description

Procédé de préparation d'un film d'oxyde ou d'hydroxyde d'un élément des colonnes II ou III de la classification, et les structures composites comprenant un tel film. Process for the preparation of an oxide or hydroxide film of an element from columns II or III of the classification, and composite structures comprising such a film.
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 process for preparing a film of a metal oxide or a metal hydroxide of an element of columns II or III of the classification, deposited on a substrate.
Les oxydes métalliques en couche mince sont des maté¬ riaux très importants dans divers domaines technologiques du fait de leurs caractéristiques optiques, électriques et cata- lytiques. 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. 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 (E-JM) . Tous ces procédés mettent en oeuvre des appareillages coûteux.Metallic oxides in thin layers are very important materials in various technological fields because of their optical, electrical and catalytic characteristics. Among their many applications, one can quote for example the use of zinc oxide for the development of conductive and transparent electrodes in solar cells. The thin metal oxide layers are generally obtained by vacuum deposition techniques such as sputtering, or "sputtering", chemical vapor deposition, or by deposition of successive layers by molecular beam epitaxy (E-JM ). All of these methods use expensive equipment.
Un autre procédé pour la préparation de couches minces d'oxydes est la pulvérisation chimique réactive, qui est réa¬ lisée sous atmosphère ordinaire, sans enceinte fermée. Cepen¬ dant, 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 an ordinary atmosphere, without a closed enclosure. However, the deposition temperatures are very high, of the order of 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 prépara- tion d'un film d'oxyde sur l'anode d'une cellule électrochi¬ mique 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- , 882, 014) décrivent en outre la préparation de poudres d'oxydes et d'hydroxydes de métaux, en tant que précurseurs de cérami¬ ques. 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'obten¬ tion directe d'un film d'oxyde ou d'hydroxyde sur un subs¬ trat, 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. Le but de la présente invention est de fournir un pro¬ cédé 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 électro¬ chimique, le dit film présentant une bonne tenue mécanique et une bonne adhérence sur le support.Various works have been undertaken to make deposits for the electrolytic route. 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 is based on an increase in the degree of oxidation of the metal ion in solution, with the formation and deposition on an substrate of an insoluble oxide. This process can however only be used to prepare the oxide of a metal which has at least two stable oxidation states in the reaction medium. JA Switzer (cited above) and RT Coyle, et al. (US-A-, 882, 014) further describe the preparation of metal oxide and hydroxide powders as ceramic precursors. 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 ceramic materials. Any deposits formed on the cathode are scraped off to be recovered in the form of powder. The aim is therefore to obtain powder, and neither the direct obtaining of an oxide or hydroxide film on a substrate, nor its use as such are described. Furthermore, no mention is made of an oxygen reduction reaction for the formation of an oxide or hydroxide film. The object of the present invention is to provide a process which does not have the drawbacks of the methods of the prior art, in order to obtain a film of a metal oxide or of a metal hydroxide on a support by electro-chemical means. , the said film having 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(0H)xAy, M représentant au moins une espèce métallique au degré d'oxydation i choisie parmi les éléments des colonnes II ou III de la classifica¬ tion, 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, une contre-élec¬ trode, une électrode de référence et un electrolyte 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 present invention relates to a process for the deposition on a support, of 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, a counterelectrode, a reference electrode and an electrolyte constituted by a conductive solution of at least one salt of the metal M. The method is characterized in that oxygen is dissolved in the electrolyte and a cathode potential is imposed on the electrochemical cell lower than the oxygen reduction potential and greater than the deposit potential of the metal M in the considered electrolyte.
Lorsque l'on impose à la cellule électrochimique un potentiel tel que défini ci-dessus, il se produit une réduc- tion 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 tion of oxygen and the formation of oxide or hydroxide M (OH) x Ay 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)j^ ou 1 '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) j ^ or 1 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. 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 spéciale¬ ment 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 used to prepare a film of a single metal compound. It can also be used to prepare a film of a mixed compound containing at least two metallic elements. When a film of a mixed compound is prepared, at least one precursor salt of each of the desired metal species is introduced into the electrolyte and the potential imposed on the electrochemical cell is greater than the potential of the metallic deposits in the bath considered. The process of the present invention can be used for the preparation of a film of a compound of at least one metal M chosen from the metallic elements of columns II and III of the periodic table, and more particularly for preparing a film of a zinc, cadmium, gallium or indium compound.
La cellule électrochimique utilisée pour la mise en oeu¬ vre 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 implementing the process of the invention comprises an electrode which functions as a cathode and which 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 Sn02, l'oxyde d'indium ln203, l'oxyde mixte d'indium et d'étain (ITO) ou l'oxyde de titane Ti02, 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 Sn0 2 , indium ln 2 0 3 , mixed indium tin oxide (ITO) or titanium oxide Ti0 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 con- centration 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 it is sought to form a film. In this case, the oxidation of the metal M of the counter-electrode makes it possible to keep the metal concentration M of the electrolyte constant.
L'électrode de référence est choisie parmi les électro¬ des utilisées habituellement comme telles, notamment l'élec¬ trode de sulfate mercureux (ESM) ou l'électrode au chlorure mercureux (ECS) . Les potentiels correspondants sont respec i- vement 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, in particular the mercurous sulfate electrode (ESM) or the mercurous chloride electrode (ECS). The corresponding potentials are respectively +0.65 V and +0.25 V with respect to the normal hydrogen electrode (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 one metallic species M and a 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 1 ' isopropanol, l'acéto- nitrile, le diméthylsulfoxyde et le carbonate de propylène. L'eau est un solvant particulièrement préféré. 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 inorga¬ niques tels que les halogenures, les sulfates, les nitrates et les perchlorates, et les sels organiques tels que les acé- tates.The solvent of the electrolyte is chosen from water and the nonaqueous polar solvents usually used in electrochemical cells, among which there may be mentioned alcohols, more particularly isopropanol, acetonitrile, dimethyl sulfoxide and carbonate. propylene. 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. 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 disso¬ ciable 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 1 ' anion ne provo¬ quera 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 halogenures, 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 avantageu- sèment le chlorure de potassium, de préférence à une concen¬ tration d'environ 0,1 mole/1.The electrolyte may optionally contain at least one second salt, called the support salt. This second salt is a salt disso¬ ciable in the solvent used and has the main function of ensuring good electrical conductivity of the electrolyte, especially in the case where the concentration of the precursor salt of the metal M is low. This salt can be chosen from sodium, potassium or ammonium salts, the anion of which will not cause the 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 deposition of a film of a zinc compound, this second salt is advantageous. sow potassium chloride, preferably at a concentration of 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 5 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 lesThe electrolyte can also contain, in addition to or in place of the second salt, a complexing compound with respect to the cation M, in order to adapt the conditions for the formation of the compound of M to the window permitted by the reduction of oxygen. For example, for gallium or indium compounds, the addition of complexing agents, chosen for example from oxalates, citrates, fluorides, chlorides, iodides and
10 bromures, permet de solubiliser le sel précurseur du métal en milieu faiblement acide (pH « 5-4) .10 bromides, makes it possible to dissolve the precursor salt of the metal in a weakly acidic medium (pH “5-4).
L1électrolyse est effectuée en présence d'oxygène dis¬ sous dans l'électrolyte. La concentration de l'oxygène est fixée entre des valeurs très faibles, de l'ordre deL 1 electrolysis is carried out in the presence of dis¬ oxygen in the electrolyte. The oxygen concentration is fixed between very low values, of the order of
15 10"5 mole/1, et la limite de solubilité de l'oxygène dans l'électrolyte, (de l'ordre de 10~3 mole/1 en milieu aqueux) . L'oxygène peut être dissous de manière avantageuse en intro¬ duisant dans l'électrolyte un mélange gazeux constitué par de l'oxygène et un gaz neutre. Le gaz neutre peut être l'argon15 10 "5 mole / 1, and the solubility limit of oxygen in the electrolyte, (of the order of 10 ~ 3 mole / 1 in aqueous medium). The oxygen can be dissolved advantageously intro ¬ reducing in the electrolyte a gas mixture consisting of oxygen and a neutral gas. The neutral gas can be argon
20 ou l'azote. Un choix approprié de la concentration en oxygène du mélange gazeux et du débit gazeux dans l'électrolyte per¬ met d'imposer une concentration prédéterminée d'oxygène dans l'électrolyte. De préférence, le rapport en volume oxy¬ gène/gaz neutre est compris entre 1 et 2.20 or nitrogen. An appropriate choice of the oxygen concentration of the gas mixture and the gas flow rate 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.
25 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 poten¬ tiel de dépôt du métal M dans l'électrolyte considéré et le potentiel de réduction d'oxygène. Le potentiel de dépôt du25 During the implementation of the method of the invention, the potential imposed on the electrochemical cell is kept constant at a predetermined value between the potential for deposition of the metal M in the electrolyte considered and the reduction potential d 'oxygen. The deposit potential of
3α 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 analo¬ gue à celle dans laquelle le procédé de l'invention est mis en oeuvre, en l'absence d'oxygène. Le potentiel de réduction3α metal M in the electrolyte considered can be easily determined by a person skilled in the art by raising the intensity as a function of the potential in an electrochemical cell analogous to that in which the process of the invention is implemented, in the absence of oxygen. The reduction potential
35 de l'oxygène est fourni par la littérature. A titre d'exem¬ ple, le potentiel pour le dépôt d'un film d'oxyde de zinc sur une cathode de Sn02 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.Oxygen is provided by the literature. As an example, the potential for depositing a zinc oxide film on a SnO2 cathode can be set 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 consé¬ quent être prédéterminée en réglant la quantité d'électricité utilisée pour le dépôt. Des épaisseurs de quelques nm à quel¬ ques μm peuvent être obtenues. La vitesse de dépôt particu¬ lièrement favorable se situe entre environ 0,5 et 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 réactionnel- les.The implementation of the method according to the invention generally produces 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 the deposit. Thicknesses from a few nm to a few μm can be obtained. The particularly favorable deposition rate is between approximately 0.5 and 1 μm / h. The nature of the compound constituting the film deposited on the electrode of the electrochemical cell can be chosen by appropriately setting the reaction conditions.
Pour l'obtention d'un film d'oxyde, il convient de mét¬ tre 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 condi¬ tions 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 KC1 comme sel support, on utilise une concentration en Zn(II) de préférence inférieure à 10"2 mole/1, plus parti- culièrement inférieure à 5.10~3 mole/1, une température au moins égale à 50 °C, et une concentration en oxygène infé¬ rieure 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 film of zinc oxide from a solution containing KC1 as a support salt, a concentration is used in Zn (II) preferably less than 10 "2 mol / 1, more particularly less than 5.10 ~ 3 mole / 1, 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/1, 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 / 1 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. Dans un film de M(OH)xAy, l'anion A est l'anion intro¬ duit dans l'électrolyte par le sel précurseur du métal M, ou bien l'anion du second sel dissociable introduit dans l'élec¬ trolyte 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 halogenures. 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'élec- trolyse. 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 trai- tement 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.In a nonaqueous medium, the process of the invention leads to the deposition of layers of oxides. In a film of M (OH) x Ay, 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 constitutes a fundamental criterion for the applications. Depending on the deposition conditions, their structure can vary from a very open structure made of the growth of crystals separated from each other, the crystal quality of which is, moreover, remarkable, to a dense structure made of coalesced grains. A particular type of structure can be obtained by appropriately choosing the density parameter of nucleation sites on the substrate, and the potential parameter of electrolysis. The lower the density of nucleation sites, the more the structure will be open. Conversely, the higher the density of nucleation sites, the more compact the structure. In addition, the more negative the potential, the more compact the structure. It should also be noted that a prior electrochemical treatment of the substrate, in the absence of metal ions, by reduction of oxygen for example, makes it possible to obtain more compact deposits. Another method for activating the substrate consists in depositing a very thin metal sublayer M, of the order of a few nanometers, by application for a very short time (for example of the order of 30 seconds) of a potential more cathodic, before applying 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(0H)xAy, qui cons¬ titue un autre objet de la présente invention. Suivant la nature de la couche conductrice support et du film, la structure composite a diverses applications. Les structures multi-couches comprenant un film compact sont intéressantes, de manière générale, pour les applica¬ tions nécessitant des couches continues. De telles structures peuvent être utilisées par exemple comme capteur chimique ou électrochimique ou comme catalyseur. Les structures composi¬ tes peuvent également être utilisées comme électrode transpa¬ rente dans les cellules solaires, dans les dispositifs lumi¬ nescents plats, et de manière plus générale, dans divers dis¬ positifs 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 cui¬ vre ou l'or, les oxydes métalliques conducteurs tels que par exemple l'oxyde d'étain Sn02, l'oxyde d'indium ln203, l'oxyde mixte d'indium et d'étain (ITO) ou l'oxyde de titane Ti02, 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 pla¬ que de verre. Les structures multi-couches comprenant un film à struc¬ ture 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. La présente invention est décrite ci-après plus en détails par des exemples concrets de mise en oeuvre du pro¬ cédé de l'invention, donnés à titre illustratif, l'invention n'étant bien entendu pas limitée à ces exemples.The method of the present invention makes it possible to obtain a multi-layer structure consisting of a conductive support layer and an oxide or hydroxide film M (0H) 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. Multi-layer structures comprising a compact film are advantageous, in general, 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 Sn0 2 , indium oxide ln 2 0 3 , mixed indium tin oxide (ITO) or titanium oxide Ti0 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. Multi-layer structures comprising a film with an open structure are used for applications requiring large developed surfaces. Examples of such applications include chemical or electrochemical sensors, and catalysts. The present invention is described below in more detail 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 1 PREPARATION D'UN FILM D'OXYDE DE ZINCEXAMPLE 1 PREPARATION OF A ZINC OXIDE FILM
Le dispositif utilisé comprend une cuve d' électrolyse, une électrode, une contre-électrode et une électrode de réfé¬ rence, 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 tempé¬ rature est maintenue constante à 80°C à l'aide d'un bain d' eau. L'électrode est constituée par un film de Snθ2 déposé sur verre. La contre-électrode est constituée par une plaque de platine. L'électrode de référence est une électrode de sulfate mercureux. Préalablement à la mise en oeuvre du procédé, l'élec¬ trode Sn02 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 KC1 (0,1 mole/1) ne contenant pas l'élément métalli- que dont on veut déposer l'oxyde, en présence d'oxygène dissous à saturation.The device used comprises an electrolysis tank, an electrode, a counter electrode and a reference electrode, all three being connected to a potentiostat. The electrolysis tank is provided with a stirring system and means for introducing with a predetermined flow rate an argon / oxygen gas mixture having a predetermined composition. The temperature is kept constant at 80 ° C. using a water bath. The electrode consists of a film of Snθ2 deposited on glass. The counter electrode consists of a platinum plate. The reference electrode is a mercury sulfate electrode. Prior to the implementation of the method, the Sn0 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 field of reduction of the oxygen, in a KC1 solution (0.1 mole / 1) not containing the metallic element whose 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 electrolyte constitué par une solu¬ tion aqueuse de KC1 (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, dé¬ terminée à l'aide d'un profilomètre mécanique. Cette épais- seur 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 KC1 (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 linked to the quantity of electricity consumed during the deposit (≈ 7 C for 5 cm 2 ).
Le film d'oxyde obtenu a été caractérisé selon différentes méthodes. Analyse aux rayons X 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,l°)et les raies correspondant au substrat. Analyse par spectroscopie d'électrons (EPS)The oxide film obtained was characterized by different methods. X-ray analysis The X-ray diffraction diagram of the zinc oxide film obtained, preferably oriented along the <002> axis, shows only the lines characteristic of the hexagonal phase of zinc oxide (20, 1 ° ) and the lines corresponding to the substrate. Electron spectroscopy (EPS) 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. Analyse par infrarougeThis 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, the absence of peak at 2.830 keV is noted, which makes it possible to conclude that there is no chloride ions in the product obtained and confirms that the product obtained is the oxide and not a hydroxide complex. Infrared analysis
Le spectre infra-rouge du film d'oxyde de zinc obtenu pré¬ sente la bande se situant vers 450-550 cm-1, caractéristique de ZnO. Aucune bande caractéristique des ions hydroxyles n'est visible. La structure du filmThe infrared spectrum of the zinc oxide film obtained presents the band lying around 450-550 cm -1 , characteristic of ZnO. No characteristic band of the hydroxyl ions is visible. The structure of the film
Le film obtenu est compact, transparent, lisse et homo¬ gène. 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 lon¬ gueurs d'onde, il apparaît 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. Des mesures capacitives effectuées en milieu électroly- tique 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.The film obtained is compact, transparent, smooth and homogeneous. On the direct optical transmission curve of the zinc oxide film obtained, for the wavelengths of the visible range (> 400 nm), the transmission is high, in agreement with the transparency of the film to the eye. Towards the short wavelengths, an abrupt absorption front appears, which indicates the semiconductor character of the film and the presence of a forbidden band which corresponds to that of ZnO at around 3.4 eV. Capacitive measurements carried out in an electrolytic medium have shown that the film ZnO obtained was conductive, of type n, and that the apparent doping rate is high, of the order of 10 18 -10 19 cm -3 .
EXEMPLE 2 PREPARATION D'UN FILM D'OXYDE DE ZINC A STRUCTURE OUVERTEEXAMPLE 2 PREPARATION 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 Sn02, celle-ci étant simplement dégraissée. Dans ces conditions, le dépôt d'oxyde obtenu est consti¬ tué d'une multitude d'aiguilles à section hexagonale donr les bases sont fixées au substrat. Ces aiguilles sont bien sépa¬ rées 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. EXEMPLE 3The method of the invention was implemented under conditions similar to those of Example 1, but omitting the preliminary treatment of the SnO 2 electrode, the latter being simply degreased. Under these conditions, the oxide deposit obtained is made up of a multitude of needles with a hexagonal section, the bases being 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. EXAMPLE 3
PREPARATION D'UN FILM DE Zn(OH)xCl1_χ Le dispositif utilisé est analogue à celui utilisé pour la préparation d'un film d'oxyde et les conditions opératoi- res sont identiques, sauf en ce qui concerne la composition de l'électrolyte. L'électrolyte est une solution aqueuse dePREPARATION OF A FILM OF Zn (OH) x Cl 1 _ χ 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
KC1 (0,1 M) et de chlorure de zinc (3.10-2 M) .KC1 (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 using a mechanical profilometer. This thickness is related to 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 àThe X-ray diffraction diagram of the hydroxide film has a preferential orientation along the line to
6,5 ° du composé Zn5(OH)8Cl2.6.5 ° of the compound Zn 5 (OH) 8 Cl 2 .
Analyse par spectroscopie d'électrons (EPS)Electron spectroscopy (EPS) 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. It shows the presence of a peak at 2.83 keV, characteristic of chloride ions.
Analyse par infrarougeInfrared analysis
Le spectre infra-rouge du film d'hydroxyde de zinc obtenu présente une bande dominante se situant vers 3500 cm--'-, caractéristique des ions hydroxyles. La bande caractéristique des liaisons Zn-0 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 --'-, characteristic of hydroxyl ions. The characteristic band of the Zn-0 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. EXEMPLE 4The film obtained is covering and consists of well-defined hexagonal grains. EXAMPLE 4
PREPARATION D'UN FILM D'HYDROXYDE DE CADMIUM 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 NaC104 (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. Le film obtenu a une épaisseur de 0,3 μm, déterminée sous microscopie électronique.PREPARATION OF A CADMIUM HYDROXIDE FILM 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 NaC10 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. 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. Analyse aux rayons X On constate la présence de la raie caractéristique de Cd(OH)2 sur le diagramme de diffraction des RX. Analyse par spectroscopie d'électronsThe hydroxide film obtained was characterized according to different methods. X-ray analysis We observe the presence of the characteristic line of Cd (OH) 2 on the X-ray diffraction diagram. Electron spectroscopy analysis
Cette analyse a été effectuée comme précédemment. On constate l'absence des raies caractéristiques du chlore. Structure du filmThis analysis was carried out as previously. We note the absence of the characteristic lines of chlorine. Structure 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)χCl1_χ 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 KC1 (0,1 mole/1) et CdCl2 (10"2 mole/1) , saturée en oxygène, à une température de 50 °C ;PREPARATION OF FILM Cd (OH) Cl χ 1 χ _ The apparatus used is similar 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 KC1 (0.1 mole / 1) and CdCl 2 (10 "2 mole / 1), saturated with oxygen, at a temperature of 50 ° C;
Le film obtenu a une épaisseur de 0,4 μm, déterminée sous microscopie électronique.The film obtained has a thickness of 0.4 μm, determined under electron microscopy.
Le film d'hydroxyde complexe obtenu a une structure couvrante.The complex hydroxide film obtained has a covering structure.
La composition Cd(OH)xCl1.x a été confirmée par une analyse aux rayons X et par une analyse par spectroscopie d' électrons .The composition Cd (OH) x Cl 1 . x was confirmed by X - ray analysis and by electron spectroscopy analysis.
EXEMPLE 6 PREPARATION D'UN FILM DE COMPOSE DE GALLIUMEXAMPLE 6 PREPARATION 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/1), du sulfate de gallium (7,7xl0~3 mole/1) et de l'oxalate de sodium (6xl0~3 mole/1) 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 conditions The operating procedures 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 / 1), gallium sulfate (7.7xl0 ~ 3 mole / 1) and sodium oxalate (6xl0 ~ 3 mole / 1) 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/0 déterminé grâce à un étalon de Ga203 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 Ga203.3H20. X-ray analysis shows the majority of gallium and oxygen. The stoichiometric ratio Ga / 0 determined using a Ga 2 0 3 standard is 0.324. The gallium compound obtained therefore corresponds to gallium hydroxide Ga (OH) 3 or to hydrated gallium oxide Ga 2 0 3 .3H 2 0.

Claims

REVENDICATIONS
1. 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 nom¬ bre de charges est n, 0<x≤i et x+ny=i, dans une cellule élec¬ trochimique qui comprend une électrode constituée par le dit support, une contre-électrode, une électrode de référence et un electrolyte constitué par une solution conductrice d'au moins un sel du métal M, ledit procédé étant caractérisé en ce qu'on dissout de l'oxygène dans l'électrolyte et on impose à la cellule électrochimique un potentiel de cathode infé¬ rieur au potentiel de réduction de l'oxygène et supérieur au potentiel de dépôt du métal M dans l'électrolyte considéré.1. 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 with the degree of 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 electro-chemical cell which comprises an electrode constituted by the said support, a counter electrode, a reference electrode and an electrolyte consisting of a conductive solution of at least one salt of the metal M, said method being characterized in that oxygen is dissolved in the electrolyte and imposes on the electrochemical cell a cathode potential lower than the oxygen reduction potential and greater than the deposit potential of the metal M in the electrolyte considered.
2. Procédé selon la revendication 1, caractérisé en ce que M est choisi parmi Zn, Cd, Ga ou In.2. Method according to claim 1, characterized in that M is chosen from Zn, Cd, Ga or In.
3. Procédé selon la revendication 1, caractérisé en ce que le solvant de l'électrolyte est choisi parmi l'eau et les solvants polaires.3. Method according to claim 1, characterized in that the solvent of the electrolyte is chosen from water and polar solvents.
4. Procédé selon la revendication 1, caractérisé en ce que le sel du métal M est choisi parmi les halogenures, les sulfates, les nitrates, les perchlorates et les acétates.4. Method according to claim 1, characterized in that the salt of the metal M is chosen from halides, sulfates, nitrates, perchlorates and acetates.
5. Procédé selon la revendication 1, caractérisé en ce que l'oxygène dissous dans l'électrolyte est apporté par un mélange de gaz neutre et d'oxygène.5. Method according to claim 1, characterized in that the oxygen dissolved in the electrolyte is provided by a mixture of neutral gas and oxygen.
6. Procédé selon la revendication 1, caractérisé en ce que la contre-électrode est une électrode constituée par le métal M. 6. Method according to claim 1, characterized in that the counter-electrode is an electrode constituted by the metal M.
7. Procédé selon la revendication 1, caractérisé en ce que l'électrolyte contient au moins un sel support dissocia¬ ble choisi parmi les sels organiques et les sels inorganiques de sodium, de potassium ou d'ammonium, dont l'anion ne provo¬ quera pas la précipitation d'un composé insoluble avec le cation métallique M.7. Method according to claim 1, characterized in that the electrolyte contains at least one dissociable carrier salt chosen from organic salts and inorganic sodium, potassium or ammonium salts, the anion of which is not provo¬ will not be the precipitation of an insoluble compound with the metal cation M.
8. Procédé selon la revendication 7, caractérisé en ce que le sel support est choisi parmi les halogenures, les sul- fates, les nitrates, les perchlorates, les acétates, les lac- tates, les formiates, les oxalates et les citrates.8. Method according to claim 7, characterized in that the support salt is chosen from halides, sul- fates, nitrates, perchlorates, acetates, lactates, formates, oxalates and citrates.
9. Procédé selon la revendication 1, pour la prépara¬ tion d'un film d'oxyde, caractérisé en ce que ce que l'on utilise un milieu aqueux contenant KCl dans lequel la concen¬ tration en Zn(II) est inférieure à 10-2 mole/1, la tempéra¬ ture est au moins égale à 50 °C, et la concentration en oxy¬ gène est inférieure à la concentration saturante dans la solution. 10. Procédé selon la revendication 9, caractérisé en ce que la concentration en Zn(II) est inférieure à 5.9. Method according to claim 1, for the preparation of an oxide film, characterized in that an aqueous medium containing KCl is used in which the concentration in Zn (II) is less than 10 -2 mole / 1, the temperature is at least equal to 50 ° C., and the oxygen concentration is lower than the saturating concentration in the solution. 10. Method according to claim 9, characterized in that the concentration of Zn (II) is less than 5.
10-3 mole/1.10 -3 mole / 1.
11. Procédé selon la revendication 1, pour la prépara¬ tion d'un film de Zn(OH)xAy, caractérisé en qu'on utilise un milieu aqueux contenant KCl dans lequel la concentration en Zn(II) est supérieure à 2.10-2 mole/1, la température est in¬ férieure à 50°C et la concentration en oxygène est inférieure ou égale à la concentration saturante.11. The method of claim 1, for the preparation of a film of Zn (OH) x A y , characterized in that an aqueous medium containing KCl is used in which the concentration of Zn (II) is greater than 2.10 -2 mole / 1, the temperature is below 50 ° C and the oxygen concentration is less than or equal to the saturating concentration.
12. Procédé selon la revendication 1, caractérisé en ce que l'électrolyte contient au moins un sel précurseur d'espèces métalliques M différentes.12. Method according to claim 1, characterized in that the electrolyte contains at least one precursor salt of different metallic species M.
13. Procédé selon la revendication 1, caractérisé en ce que l'électrode est constituée par un matériau métallique choisi parmi le fer, les aciers, le cuivre ou l'or, un oxyde métallique conducteur tel que par exemple l'oxyde d'étain Sn02, l'oxyde d'indium ln203, l'oxyde mixte d'indium et d'étain (ITO) ou l'oxyde de titane Ti02, un matériau semi¬ conducteur tel que le silicium, GaAs, InP, Cu(In,Ga) (S, Se) 2 ou CdTe. 13. Method according to claim 1, characterized in that the electrode consists of a metallic material chosen from iron, steels, copper or gold, a conductive metallic oxide such as for example tin oxide Sn0 2 , indium oxide ln 2 0 3 , mixed indium tin oxide (ITO) or titanium oxide Ti0 2 , a semiconductor material such as silicon, GaAs, InP , Cu (In, Ga) (S, Se) 2 or CdTe.
14. Procédé selon la revendication 13, caractérisé en ce que le matériau métallique ou le matériau semi-conducteur est sous forme de couche mince déposée sur un support iso¬ lant.14. Method according to claim 13, characterized in that the metallic material or the semiconductor material is in the form of a thin layer deposited on an insulating support.
15. Procédé selon la revendication 14, caractérisé en ce que le support isolant est transparent.15. The method of claim 14, characterized in that the insulating support is transparent.
16. Procédé selon la revendication 1, caractérisé en ce que l'électrolyte contient au moins deux seuls métalliques, M représentant plus d'une espèce métallique. 16. The method of claim 1, characterized in that the electrolyte contains at least two metallic, M representing more than one metallic species.
17. Procédé selon la revendication 1, caractérisé en ce que l'électrolyte contient, en plus ou à la place du deuxième sel, un composé complexant vis à vis du cation M.17. Method according to claim 1, characterized in that the electrolyte contains, in addition to or in place of the second salt, a compound complexing with respect to the cation M.
18. Procédé selon la revendication 17, caractérisé en ce que, pour les composés de gallium ou d'indium, le com¬ plexant est choisi parmi les oxalates, les citrates et les fluorures, les chlorures, les bromures et les iodures.18. Method according to claim 17, characterized in that, for the compounds of gallium or indium, the com¬ plexant is chosen from oxalates, citrates and fluorides, chlorides, bromides and iodides.
19. Structure multi-couche constituée par une couche support portant un film d'un oxyde métallique ou d'un hy- droxyde métallique de formule M(0H)xAy, M représentant au moins une espèce métallique au degré d'oxydation i choisie parmi les éléments des colonnes II ou III de la classifica¬ tion, A étant un anion dont le nombre de charges est n, 0<x<i et x+ny=i, la couche support étant une couche d'un matériau conducteur choisi parmi le fer, les aciers, le cuivre ou l'or, les oxydes métalliques conducteurs ou les matériaux semi-conducteurs.19. Multi-layer structure constituted by a support layer carrying a film of a metal oxide or a metal hydroxide of formula M (0H) x A y , M representing at least one metallic species with the degree of 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, the support layer being a layer of a conductive material chosen from iron, steels, copper or gold, conductive metal oxides or semiconductor materials.
20. Structure multi-couche selon la revendication 19, caractérisé en ce que la couche de matériau conducteur ou de matériau semi-conducteur est portée par une plaque isolante.20. Multi-layer structure according to claim 19, characterized in that the layer of conductive material or semiconductor material is carried by an insulating plate.
21. Structure multi-couche selon la revendication 19, caractérisé en ce que l'oxyde métallique conducteur est choi¬ si parmi l'oxyde d'étain Sn02, l'oxyde d'indium ln203, l'oxyde mixte d'indium et d'étain (ITO) ou l'oxyde de titane Ti02. 21. Multi-layer structure according to claim 19, characterized in that the conductive metal oxide is chosen if among the tin oxide Sn0 2 , the indium oxide ln 2 0 3 , the mixed oxide d indium and tin (ITO) or titanium oxide Ti0 2 .
22. Structure multi-couche selon la revendication 19, caractérisé en ce que le matériau semi-conducteur est choisi parmi le silicium, GaAs, InP, Cu(In,Ga) (S,Se)2 et CdTe.22. Multi-layer 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 pour photopile, constituée par une struc¬ ture multi-couche selon l'une des revendications 19 à 22. 23. Electrode for solar cell, constituted by a multi-layer structure according to one of claims 19 to 22.
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)

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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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