FR2927072A1 - MANUFACTURING PROCESS OF NANOSTRUCTURES OF CHALCOGEN ELEMENTS, IN PARTICULAR NANOSTRUCTURES CALLED ONE DIMENSION OR 1 D - Google Patents

Abstract

The present invention relates to a method of manufacturing nanostructures of chalcogenic elements, including: - a step of forming a colloidal suspension of particles of amorphous chalcogenic elements and, - a step of nucleation and growth of said particles of chalcogenic elements amorphous to crystalline nanostructures of said chalcogen elements. According to the invention, said step of forming said colloidal suspension of particles of amorphous chalcogen elements includes a step of dissolving at least one material comprising at least one glassy chalcogenide phase in a solution containing hydroxyl ions (HO <->).

Description

The present invention relates to a method of manufacturing nanostructures of chalcogenic elements, in particular so-called one-dimensional or 1D nanostructures. In the present description, we call "nanostructures" structures of which at least one dimension has a value which is expressed in nanometers, that is to say of which at least one dimension is between 1 and a few thousand nanometers, for example. example 500 or even 700 nm. Among the nanostructures, mention may be made, on the one hand, of nanoparticles, that is to say particles whose main dimensions (three in number) are nanometric. A distinction is then made between 3D nanoparticles (for example particles in the form of an ellipsoid), 2D nanoparticles (for example platelets) and 1D nanoparticles, i.e. nanotubes, nanofibers, nanowires and nanobars whose main dimension is at least micrometric and the other dimensions of which are nanometric (in the sense given above). Among these latest nanostructures, nanobars are the shortest compared to nanowires, nanofibers and nanotubes.

One-dimensional nanostructures (also called 1 D) are today the subject of intensive research due to their interesting properties, for example piezoelectric properties used in particular in pressure sensors, semiconductors used in particular in photosensitive cells. Reference may be made, for examples of other applications, to the following publications: - Bin Zhang, Wei Dai, Xingchen Ye, Weiyi Hou, Yi Xie. Solution-phase synthesis and electrochemical hydrogen storage of ultra-long single-crystal selenium submicrotubes. J. Phys. Chem. B, 109: 22830-22835, 2005, publication relating to the use for hydrogen storage, - Peng Liu, Yurong Ma, Weiwei Cai, Zhenzhong Wang, Jian Wang, Limin Qi, Dongmin Chen Photoconductivity of single-crystalline selenium nanotubes. Nanotechnology, 18: 205704-205709, 2007, publication relating to the use for photovoltaic cells, - Sudip Nath, Sujit Kumar Ghosh, Sudipa Panigahi, Thomas Thundat, and Tarasankar Pal Synthesis of selenium nanoparticle and its photocatalytic application for decolorization of methylene blue under uv irradiation. Langmuir, 20: 7880--7883, 2004, for a particular use related to the discoloration of methylene blue. Known nanostructures of this type consist for example of cylindrical filaments with a diameter of the order of a few tens of nanometers and a length of the order of several microns.

The materials concerned by the present patent application are based on chalcogen atoms, that is to say atoms present in column 16 (formerly called column VIA) of the periodic table of the elements, and more particularly atoms. selenium and / or tellurium.

For example, selenium exists in various crystal structures, the main one, called trigonal, consists of helical chains of selenium atoms which are all parallel to the crystallographic c-axis. This trigonal structure has the property of being more stable from a thermodynamic point of view, which gives it its interest for many applications.

Different methods are known for synthesizing such 1D nanostructures. By way of example, mention may be made of the article entitled "A new / route controlled synthesis of selenium nanowires" in the name Yuan-tao Chen and Co and published in Materials Letters 58 (2004), pages 2761 to 2763, which therefore describes a process which consists in dissolving in a solution of ethylenediamine a powder of selenium used as a precursor of selenium, then the solution obtained in distilled water. According to the authors, the solution very quickly turns brick red, which is a sign of the presence of amorphous selenium nanoparticles. Then, this brick red color slowly evolves to a black gray. This development can be accelerated by subjecting the solution to ultrasound producing an acoustic cavitation effect. The black gray solution ultimately consists of trigonal selenium nanostructures. After some time, the solution is centrifuged, washed with distilled water and alcohol and then air dried. These authors thus obtained nanotubes with a diameter of approximately 50 nanometers and lengths of between 5 and 20 micrometers. In an article entitled "Single Crystalline Trigonal Selenium Nanotubes and Nanowires Synthesized by Sonochemical Process", published in Crystal Growth & Design vol.5 (2005) pages 911 to 916, Xuemei Li and Co describe a process consisting in the reduction of selenian acid (H2SeO3) in various solvents, including hydrazine hydrate (N2H4-H2O) and excitation of the mixture by means of ultrasound. Trigonal selenium nanotubes were thus obtained. They had diameters less than 200 nanometers. Trigonal selenium nanowires were also obtained. They had diameters between 20 and 50 nanometers. The two methods, which have been succinctly described above, are only two examples among others.

The aim of the present invention is to provide a new process for manufacturing nanostructures of chalcogenic elements which is simpler to implement and more in accordance with safety and environmental standards, in particular with regard to the use of organic solvents, toxic gases, etc.

Such a method includes in a continuous process: a step of forming a colloidal suspension of particles of amorphous chalcogenic elements and, a step of nucleation and growth of said particles of amorphous chalcogenic elements into crystalline nanostructures of said chalcogenic elements.

While the nucleation and growth step may be a conventional step such as those described in the documents mentioned above, according to the invention, the step of forming said colloidal suspension of particles of amorphous chalcogenic elements includes a step of dissolving at least one material comprising at least one glassy chalcogenide phase in a solution containing hydroxyl ions (HO-). Among the solutions which have exhibited interesting properties, in addition to water, there may be mentioned: an advantageously strong X-OH base such as sodium hydroxide Na-OH, an alcohol R-OH in solution or not in water, an acid X- H or carboxylic acid R-COOH dissolved in water.

For example, water and sodium hydroxide at pH = 12 as solutions containing at least hydroxyl ions (HO-) have given advantageous results, in particular in terms of the time of appearance of crystalline particles of chalcogen element. As starting material, said material comprising at least one vitreous phase is for example a glass or a glass ceramic. Said or one of said glassy chalcogenide phases is a glassy phase of selenide or telluride or selenide and telluride. In addition, said vitreous phase is based on at least one of the following elements: Ge, Si, Sn, Ga, As, In, Sb, S. The following glasses and vitroceramics, the vitreous phase of which corresponds to these glasses , gave interesting results: AsxSei_x; AsxTei_x; GaxSei_x; GaxTe] _x; SixSei_x; SixTei_x; GexSe1_x; GexTei_x; AsxSeySi_x_y; AsxTeySi_x_y; AsxSeySbl_x_ ,,; AsXTeySbl_x_y; AsxSeyTei_x_y; GexAsySe1_ x_y; GexAsyTe1_x_y; GexGaySel_x_y; GexGayTe1_x_y; GexSiySei_x_y; GexSiyTe] _x_y; GexSySel_x; GexSyTe1_x; GexSnySe1_x; GexSnyTei_x; GexPbySei_x; Ge ,, PbyTei_x; Ge ,, SbySei_x; Ge ,, SbyTei_x; SixSySei_x; SixSyTei_X; SixSnySel_x; SixSnyTei_x; SixPbySei_x; If, PbyTei_x SixSbySei_x SixSbyTei_x; GexSeyTei_x_y; SixSeyTei_x_y; GexGaySeZTei _x_y_z Afm to increase the reaction rate of the step of forming a colloidal suspension of particles of amorphous chalcogenic elements, said solution containing at least hydroxyl ions (HO-) is heated. For the same reasons, said solution can be subjected to the action of ultrasonic waves, creating an acoustic cavitation effect.

In order to increase the surface / volume ratio of the glass or of the material with a vitreous phase so as to increase the dissolution rate, said dissolving step is preceded by a step of grinding said or at least one of the glasses or vitreous phase materials. For example, grinding resulting in particles of a few tens of micrometers to a few hundred nanometers has given complete satisfaction. Advantageously, said method includes a step of recovering trigonal selenium particles carried out during the nucleation and growth step. If a block of glass or a block of a glass phase material is used, particles of trigonal selenium develop on the surface of the bulk sample, while others develop in solution and then fall back and grow to the bottom of the sample. container. In the case where the sample of glass or of a material with a vitreous phase is previously ground, particles float and grow at the air-liquid interface while others nucleate and grow at the bottom of the container. In the first case, mechanical scraping of the surface layer of trigonal selenium particles deposited on the block of glass makes it possible to free the surface of the material which otherwise is blocked by the layer formed by said particles. The particles located at the bottom of the beaker can be, for example by subjecting to ultrasonic waves, detached from the bottom of the beaker, put into solution in order to be removed and recovered after decantation and washing. We can first empty the reaction solution to replace it with a suitable solvent such as ethanol or acetone. For the case of supernatant particles? a Langmuir B Lodgett technique can be used to recover and / or deposit the supernatant particles on the surface of the liquid on a substrate, for example a microscope slide by implementing the laws of capillarity and surface tension of the liquid. The latter can be modified by adding surfactants. It is also possible to place a substrate, for example of glass and / or of a polymer, for example of HDPE (high density polyethylene) type, immersed in the starting solution. After reaction, its surface will be covered with a film of trigonal selenium particles. Finally, at any time, it is possible either to stop the reaction, or to withdraw and reserve all or part of the colloidal solution and to continue the process of nucleation and growth in order to obtain a better homogeneity of the size of the particles of synthesized crystalline chalcogenides. In the remainder of the description, the application of the process of the invention to the manufacture of selenium nanostructures from a chalcogenide glass of composition Ge, (Seioo_X where x is between 0 and 40. This type of glass has a structure formed of chains or rings made up of atoms of selenium Seä (generally n = 6 for x = 20) trapped in a network of tetravalent germanium atoms which are linked together by a divalent selenium atom Ge-Se bond is slightly polarized Solvation of chalcogenide glass is carried out in an aqueous solution, that is, a solution which contains HO- ions. HO- ions in the solution aqueous show a polarization which will allow hydrolysis of the Ge-Se bond. This hydrolysis reaction allows the release into the solution of rings and chains of selenium Seä present in the glass which, in turn, come together to form a colloidal suspension of nanosp hers of amorphous selenium. In the case of selenium, the presence of these amorphous spherical particles is shown by the tomato red or brick red color of the solution. The hydrolysis reaction is facilitated by the supply of energy in the form of heat. It will be noted that the same reactions are carried out when the starting material is no longer a full-fledged glass but is a glass-ceramic which therefore contains a glassy chalcogenide phase.

Measurements made on the amorphous colloidal particles present in the solution revealed an average diameter of about 250 nm. The statistical data of these measurements are as follows: number of particles measured 131, minimum diameters of 170 nm and maximum of 600 nm, width at mid-height of the distribution curve in diameter 70 nm.

These amorphous chalcogen nanospheres, due to their instability, in a second step of the process of the invention, crystallize in the form of 3D nanoparticles, such as metastable polycrystalline spheres which then transform into trigonal selenium nanoparticles at a dimension (also called 1D), such as nanowires, nanofibers, nanobars and nanometric tubes (nanotubes), even micrometric, diameters measured ranging from 10 nanometers to 7 micrometers. The process which is then carried out here is known as the Ostwald ripening process. Such a process is described in an article entitled "On the Critical Radius in Ostwald Ripening" Langmuir 2004, 20, 2975-2976.

In case the glass used in the first step is based on selenium, the nanoparticles are made of trigonal selenium. More precisely, the following end products of this reaction could be observed: - poly-crystalline trigonal selenium spheres with a characteristic red-brown color and an average diameter equal to approximately 270 nm, - monocrystalline trigonal selenium nanowires of average diameter of about 10 to 40 nm and a few micrometers long, - bars of hexagonal section 100 to 300 nm in diameter and length ranging from a few micrometers to several hundred micrometers, as well as - tubes of hexagonal section from 2 to 3, or even 7, micrometers in diameter and millimeter length, the internal diameter being of the order of 400 to 500 nm. Selenium nanostructures were made from a chalcogenide glass of composition Ge, (Seioo_x where x is between 0 and 40. Three examples of reactions, for which the reagents and the experimental conditions are different, were carried out. .

This was done. The aqueous solution is poured into a container which contains the chalcogenide glass. In order to increase the exposed glass area / glass volume ratio and thereby increase the reaction area between the glass and the aqueous solution and hence the reaction rate, the chalcogenide glass is advantageously pre-ground.

It may also be necessary to polish the exposed surfaces of the chalcogenide glass in order to remove any oxide layer from them. Still in order to increase the reaction rate, the glass / aqueous solution assembly is heated, for example in an oven or an autoclave or else in a water bath. 10 Reaction 1:

This reaction consists in reacting a bulk sample of Ge20Se8o selenium glass with deionized water maintained at a temperature of 90 ° C, and in the quantities and conditions described in the table below. Nature Quantity S / V * (cm- ') T (° C) Glass Ge20Se80 Disc with radius 5.9 mm 0.08 90 and thickness 1.45 mm Solvent deionized water 35 ml * SN: ratio between surface area of the material exposed and total volume of the solution. The products observed at the sample surface as a function of the reaction time are given in the table below: Instant State of the products Length / Diameter Remarks 2 hours Production of trigonal selenium Diameter: 145 nm Rod crystals, Length: 2 , 5 m hexagonal section 4 hours Production of trigonal selenium Diameter: 200 nm 1D crystals in the form of Length: 25-30 m bar of hexagonal section 768 Production of trigonal selenium Diameter bars Bars and tubes of section hours 2000-6000 nm hexagonal Tubes internal diameter: 500 nm, external diameter: 1000-4000 nm and millimeter length 7 After analysis of the reaction products according to the Raman spectroscopy and electron diffraction method, it is found that the reaction described above produces Monocrystalline trigonal selenium nanotubes of hexagonal section, the dimensions of which have been defined after observation by scanning electron microscopy, in transmission o u at atomic forces. This reaction makes it possible to obtain, after 32 days, bars with a diameter of 2 to 6 m and tubes with an internal diameter of 0.5 m and an external diameter of 1 to 41 μm, these two types of structure having a millimeter length.

Reaction 2: Similar results were obtained with a massive sample (disc of radius 5.9 mm and thickness 1.45 mm) of a selenium glass Ge5Se95 which was reacted in water of -ionized at a temperature of 65 ° C for 150 hours. Nanotubes of micrometric length and a diameter of a few hundred nanometers were thus obtained.

Reaction 3: This reaction consists in reacting a bulk sample of selenium glass Ge25Se75 with deionized water, in the quantities and conditions described in the table below. Nature Quantity S / V (cm ') T (° C) Glass Ge25Se75 Block of 15x5x3 mm3 0.068 - first reaction: 65 ° C for 26 hours - second reaction: 85 ° C for 144 hours Solvent deionized water 40 ml The products of the reaction as a function of time are given in the table below: Instant State of the products Length / Diameter Remarks The surface of 26 hours Production of A few 1D structures of the sample is coated with selenium various sizes, 10-30 m of a dense layer of trigonal long for a diameter of rods of average diameter a few hundred equal to 300 min and average length nanometers of the order of a micrometer Hexagonal section bars 144 hours Production of average diameter of 1 m covering totally selenium for sample surface lengths. trigonal greater than 200 m Length / diameter ratio greater than 200 After analysis of the reaction products according to the Raman spectroscopy and electron diffraction method, it is found that the reaction described above produces trigonal selenium nanotubes of hexagonal section the dimensions of which were defined after observation under a scanning electron microscope. There are bars and tubes with an average diameter of 1 m and a length greater than 200 m. From these experiments, it was observed that the elements which are in suspension in the solution and which give a pink to brick red color depending on their concentration, are spherical nanoparticles of amorphous nature, as the nanospheres which appear at the start of the step of crystallization and which are at the bottom of the beaker, are of polycrystalline nature and that finally, the ID structures are of monocrystalline nature of hexagonal type (also called trigonal). Generally, depending on the reaction conditions, it has also been possible to observe several sizes of 1 D structures: wires with a diameter of the order of 10 nm and micrometric length; bars with a diameter of about 50 nm and several times micrometric in length; bars with a diameter greater than 100 nm and several micrometers in length. It was possible to measure nanospheres with an average diameter of the order of 250 nm.

The presence of germanium hydroxide Ge (OH) 4 in the form of platelets was also demonstrated. We also carried out a set of experiments with different aqueous solutions. The experimental conditions are as follows: 0.5 gram of powder from a glass of chalcogenide Ge20Se8o is placed in 10 milliliters of an aqueous solution. Stirring was then carried out by the action of ultrasonic waves for about one minute and then baking for 24 hours at 80 ° C. The aqueous solutions which were thus used were as follows: distilled water, nitric acid of pH = 3.4 hydrochloric acid of pH = 3 sodium hydroxide of pH = 12 absolute ethanol.

All these experiments made it possible to obtain 1 D nano or micro particles of trigonal selenium. The size (length, diameter) of the particles produced, as well as their relative quantity (estimate), are reported in the table below. Only the solution containing Na-OH sodium hydroxide made it possible, in 24 hours, to obtain tubes in very large quantities compared to the other conditions tested.

Length Variance Nb Diameter Variance Nb Quantities (m) measures (m) measures of objects produced Na-OH 344.10 254.60 124 1.12 0.67 166 Significant H20 2.66 1.44 112 0.11 0, 09 212 Average HC1 2.58 1.60 106 0.18 0.09 137 Average HNO3 4.75 2.47 112 0.17 0.10 256 Average Ethanol 0.63 0.26 27 0.07 0.02 27 Very weak, Enfm, we also put a glass powder of Ge20Te8o telluride in a sodium hydroxide solution NaOH whose pH is equal to 12 and which was heated to a temperature of the order of 80 ° C. could observe the formation of trigonal tellurium bars about 5 micrometers in length as well as wires of micrometric length.

Claims (16)

1) Process for manufacturing nanostructures of chalcogenic elements, including: - a step of forming a colloidal suspension of particles of amorphous chalcogenic elements and, - a step of nucleation and growth of said particles of amorphous chalcogenic elements in nanostructures crystalline of said chalcogen elements, characterized in that said step of forming said colloidal suspension of particles of amorphous chalcogen elements includes a step of dissolving at least one material comprising at least one glassy chalcogenide phase in a solution containing hydroxyl ions (HO-). 2) A method of manufacturing nanostructures according to claim 1, characterized in that said solution containing hydroxyl ions comprises at least one of the following solutions: H20, R û COOH (carboxylic acids) Rû OH (Alcohol) X-OH (strong base ) XH (Strong acid). 3) A method of manufacturing nanostructures according to claim 2, characterized in that the pH of said solution is greater than or equal to 7. 4) A method of manufacturing nanostructures according to claims 2 to 3, characterized in that said solution is water. 5) A method of manufacturing nanostructures according to claims 2 to 3, characterized in that said aqueous solution is a base of X-OH type, advantageously NaOH, or KOH. 30 6) A method of manufacturing nanostructures according to one of the preceding claims, characterized in that the or one of said glassy phases of said material25 comprises a glassy phase of selenide or telluride or a glassy phase of selenide and telluride. 7) A method of manufacturing nanostructures according to claim 6, characterized in that said or one of said glassy phases is based on at least one of the following elements: Ge, Si, Sn, Ga, As, In, Sb, S. 8) A method of manufacturing nanostructures according to claim 7, characterized in that said or one of said vitreous phases comprises at least one glass of the following chemical formula: As Sei_x; As Tei_x; GaxSel_x; GaXTei_X; SixSel_x; SixTe ~ _x; GexSel_x; GeXTe1_x; AsxSeySI_X_y; AsXTeySI_, t_y; AsXSeySbl_X_y; AsxTeySbl_x_y; AsxSeyTel_x_y; GexAsySel_ x_y; GexAsyTel_x_y; GexGaySel_x_y; Ge, (GayTel_x_y; GexSiySel_x_y; GeXSiyTel_x_y; 15 GexSySel_x; GexSyTel_),; GexSnySel_x; Ge ,, SnyTel_x; Ge ,, PbySel_x GexPbyTel_x; GexSbySel_x GexSbyTel_x; SixSySel_x; SixSyTel_x SixSnySel_x; SixSnyTel_x SixPbySel_x SixPbyTel_x; SixSbySel_x SixSbyTel_x; GexSeyTel_x_y; SixSeyTel_x_y; GexGaySe1Te1_x_y_Z. 20 9) A method of manufacturing nanostructures according to one of the preceding claims, characterized in that it consists in heating above ambient temperature said solution of HO- ions. 10) A method of manufacturing nanostructures according to one of the preceding claims, characterized in that the heating temperature is advantageously greater than or equal to 65 ° C. 11) A method of manufacturing nanostructures according to one of the preceding claims, characterized in that it consists prior to said dissolution step 30 in grinding said or at least the material with a vitreous phase. 12) A method of manufacturing nanostructures according to one of the preceding claims, characterized in that the nucleation and growth reaction can be activated by ultrasonic stirring. 13) A method of manufacturing nanostructures according to one of the preceding claims, characterized in that the nucleation and growth reaction can be stopped at any time. 14) A method of manufacturing nanostructures according to one of the preceding claims, characterized in that the solution containing the colloidal suspension can be taken and reserved to obtain a more homogeneous distribution of the size of the particles of chalcogenic elements. 15) A method of manufacturing nanostructures according to one of the preceding claims, characterized in that it includes a step of recovering particles of chalcogenic elements implemented during the nucleation and growth step. 15 16) A method of manufacturing nanostructures according to one of the preceding claims, characterized in the possibility of placing a substrate in the solution during the nucleation and growth reaction so as to deposit thereon a layer of nanoparticles of chalcogenic elements. 10