Process for the thickness growth of colloidal nanosheets and materials composed of said nanosheets

Abstract

A process of growth in the thickness of at least one facet of a colloidal inorganic sheet, by sheet is meant a structure having at least one dimension, the thickness, of nanometric size and lateral dimensions great compared to the thickness, typically more than 5 times the thickness. The process allows the deposition of at least one monolayer of atoms on at least one inorganic colloidal sheet, this monolayer being constituted of atoms of the type of those contained or not in the sheet. Homostructured and heterostructured materials resulting from such process as well as the applications of the materials are also described. By homostructured is meant a material of homogeneous composition in the thickness and by heterostructured is meant a material of heterogeneous composition in the thickness.

Claims

1. An inorganic colloidal nanoparticle comprising an initial inorganic nanosheet partially or totally covered with at least one monolayer of inorganic material, wherein the initial inorganic nanosheet is an inorganic colloidal nanosheet, wherein the inorganic colloidal nanoparticle has a thickness of 0.5 nm to 10 mm, wherein the initial inorganic nanosheet comprises a material MxEy, wherein: M is Zn, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or a mixture thereof, E is O, S, Se, Te, N, P, As, F, Cl, Br, I, or a mixture thereof, and x and y are independently a decimal number from 0 to 5, and wherein the initial inorganic nanosheet is partially or totally covered by a monolayer of a material M or E wherein: M is Zn, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or a mixture thereof, and E is O, S, Se, Te, N, P, As, F, Cl, Br, I, or a mixture thereof.

2. The inorganic collodial nanoparticle according to claim 1, whose lateral dimensions are at least 1.5 times its thickness.

3. The inorganic collodial nanoparticle according to claim 1, wherein the initial inorganic nanosheet is partially or totally covered by at least two monolayers, where the monolayers are alternatively composed of M then E or conversely, wherein M is Zn, Cd, Hg, Cu, Ag, Au, Ni, Pd, Pt, Co, Fe, Ru, Os, Mn, Tc, Re, Cr, Mo, W, V, Nd, Ta, Ti, Zr, Hf, Be, Mg, Ca, Sr, Ba, Al, Ga, In, Tl, Si, Ge, Sn, Pb, As, Sb, Bi, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or a mixture thereof, and E is O, S, Se, Te, N, P, As, F, Cl, Br, I, or a mixture thereof.

4. The inorganic colloidal nanoparticle according to claim 1, wherein the inorganic colloidal nanoparticle has a core/shell structure.

5. A product comprising at least one inorganic colloidal nanoparticle according to claim 1, wherein the product is a luminescent system, an electroluminescent system, an amplifying stage of a laser, a catalyst, a photovoltaic cell, or a transistor.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a functional block diagram of steps of a method of growth in thickness according to an embodiment of the invention.

(2) FIG. 2 shows the crystal structure of a CdSe sheet seen in sectional view according to one embodiment of the invention.

(3) FIG. 3 shows the schematic structure of a heterostructured nanosheet seen in sectional view according to one embodiment of the invention.

(4) FIG. 4 shows the schematic structure of a heterostructured nanosheet obtained by growth after immobilization on a substrate seen in sectional view according to one embodiment of the invention.

EXAMPLES

(5) The present invention will be better understood on reading the following examples illustrating non-exhaustively the invention.

(6) Initial Sheets:

(7) The initial nanosheets on which a process of growth in the thickness according to at least one embodiment of the invention is particularly efficient are the nanosheets having a surface charge. This surface charge can be positive or negative depending on the nature of the initial nanosheet considered. The semiconducting nanosheets such as described above (for example CdSe, CdS or CdTe) belong to this class of materials and will be taken as non-limitative examples of initial nanosheets. Such a sheet whose structure is schematized in FIG. 2 has a zinc-blende structure, a [0, 0, 1] zone axis and has a cationic surface stabilized by carboxylates on each facet of the sheet. These facets are perfectly polar (in this case cationic).

(8) CdSe nanosheets for example can be obtained by any method known, such as described for example in the following documents: Ithurria, S.; Dubertret, B. Journal of the American Chemical Society 2008, 130, 16504-5 and Ithurria, S.; Bousquet, G.; Dubertret, B. Journal of the American Chemical Society 2011, 133, 3070-7. 174 mg of Cd(myristate).sub.2 and 12 mg of selenium are introduced in a three-necked round-bottomed flask containing 16 ml, of 1-octadecene (ODE, 90%). The flask is degassed under reduced pressure and stirring at room temperature for 30 minutes. Argon is introduced in the flask which is then heated. When the temperature reaches 200 C., 40 mg of Cd(acetate).sub.2(H.sub.2O).sub.2 are rapidly introduced in the reaction medium inducing the growth of the nanosheets. The reaction mixture is heated at 240 C., temperature at which it is held for approximately 10 minutes in order to ensure the growth of the sheets. The solution is then cooled down and washed by successive precipitation/suspension. The first precipitation is done by addition of a non-solvent: ethanol (80 mL approximately) and centrifugation (5000 rpms for 10 minutes). The supernatant is discarded and the pellet is suspended in hexane (10 mL approximately). The sheets' solution still contains a lot of Cd(myristate).sub.2 in excess. Adding a few milliliters of octylamine (4 mL) allows its dissolution. The suspension of nanoplatelets is then precipitated a second time by addition of ethanol (80 mL) and centrifugation. The suspension/precipitation process is repeated twice more with octylamine and one last time simply by suspension in hexane and precipitation with ethanol. The final precipitate is suspended in 10 mL of chloroform (CHCl.sub.3). The as-obtained sheets have the structure schematized in FIG. 2 which shows the crystalline structure of a CdSe sheet seen in sectional view.

(9) Deposition of a Film of Chalcogenides on the Sheets

(10) The colloidal CdSe/CdS sheets, according to at least one embodiment of the invention, are prepared by a layer-by-layer deposition of CdS on initial CdSe sheets.

(11) The process steps used are summarized in the block diagram presented in FIG. 1.

(12) In a first embodiment of the invention the sulfur precursor comprises bis(trimethylsilyl) sulfide (TMS.sub.2S). 2 mL of the CdSe sheets solution in chloroform are placed under magnetic stirring in a glove box under inert atmosphere (E101). 100 L of bis(trimethylsilyl) sulfide (TMS.sub.2S) are then injected into the solution containing the sheets (E103), inducing a color change and a rapid aggregation. The mixture is allowed to react for one hour at room temperature (E104). The solution is then centrifuged, the supernatant removed and the pellet washed twice with ethanol. The sheets making up the precipitate (E105) are thicker than the initial sheets, they present an additional monolayer of sulfur on each side of the initial CdSe. The precipitate (E105) is then dispersed in a few milliliters of hexane to which 10 mg of Cd(Acetate).sub.2(H.sub.2O).sub.2 powder (E101) are added (E103). Under stirring, there is another color change, the reaction is allowed to proceed for one hour (E104). 200 L of oleic acid are then added, the solution becomes clear. The final sheets (E106) are then precipitated with ethanol and suspended in hexane. This process allows the deposition of a monolayer of CdS layers on each side of the CdSe sheets.

(13) In the second embodiment of the invention, the sulfur precursor comprises hydrogen sulfide H.sub.2S. 2 ml of the CdSe sheets solution in CHCl.sub.3 (E101) are placed under magnetic stirring in a glove box. 2 mmol of H.sub.2S (48 mL) (E102) are bubbled (E103) in the solution. It changes color and becomes turbid immediately (E104). Aggregated sheets are precipitated by centrifugation, the supernatant is discarded and the precipitate is dispersed in hexane (E105). 10 mg of Cd(Acetate).sub.2(H.sub.2O).sub.2 (E102) are added (E103), and cause a new change of color (E104). After one hour, 200 L of oleic acid are added and the solution becomes clear, sign of the disaggregation of the sheets. The final sheets (E106) are then precipitated in ethanol, centrifuged and suspended in hexane. This process allows the deposition of a CdS monolayer on each side of the CdSe sheets.

(14) In a third embodiment of the invention the sulfur precursor comprises ammonium sulfide. 2 mL of the CdSe sheets solution in CHCl.sub.3 (E101) and 2 mL of aqueous tetramethylammonium hydroxide solution (100 mg/mL) were introduced into a vial. 100 L of an aqueous solution of ammonium sulfide (20%, E102) are rapidly injected into the biphasic mixture (E103). The color of the organic phase containing the sheets changes immediately (E104). Under stirring, the sheets then transfer in a few minutes in the upper aqueous phase. The addition of 10 mL of ethanol breaks the biphasic mixture and induces aggregation of the sheets which are then precipitated by centrifugation. The supernatant is removed and the sheets suspended in distilled water (E105). 20 mg of Cd(Acetate).sub.2(H.sub.2O).sub.2 (E102) were added to the solution (E103), which causes an immediate change in color followed by the aggregation of sheets (E104). The final sheets (E106) are precipitated by centrifugation and dispersed in hexane using 200 L oleic acid. This process allows the deposition of a CdS monolayer on each side of the CdSe sheets.

(15) The iteration of the process described in any of the embodiments above allows the deposit of additional layers. The final structure of the sheets obtained is shown schematically in FIG. 3, where A0 is the CdSe and A1 is the CdS. Replacement of Cd(Acetate).sub.2(H.sub.2O).sub.2 by Zn(Acetate).sub.2(H.sub.2O).sub.2 allows the deposition of a ZnS monolayer on the CdSe sheets.

(16) Same processes can be used to deposit selenide or telluride instead of sulfide. In this case the precursor used may be the selenium or tellurium analog precursors than the one used above.

(17) Deposition of a Film of Oxides on the Sheets.

(18) One describes for example the deposition of a film of zinc oxide ZnO, according to one embodiment of the invention, on the initial CdSe sheets. 2 mL of the solution of CdSe sheets in CHCl.sub.3 (E101) are introduced in a vial. 100 L of a tetramethylammonium hydroxide solution (E102) in methanol are injected (E103). The color of the solution changes immediately from yellow to red and the sheets aggregate strongly (E104). The sheets (E105) are then precipitated by centrifugation and washed twice with ethanol. The sheets (E105) are then dispersed in chloroform and 10 mg of Zn(stearate).sub.2 (E101) are added. After 10 minutes of sonication (E104), the final sheets (E106) are precipitated with ethanol and dispersed in chloroform. The process allows the deposition of a ZnO monolayer on each side of the CdSe sheets. The final structure of the as-obtained sheets is schematized in FIG. 3, where A0 is CdSe, and A1 is ZnO.

(19) Deposition of a Metallic Film

(20) One describes for example the deposition of gold, according to one embodiment of the invention, on the initial CdSe nanosheets. These sheets have a positive surface charge and it is first of all necessary to invert it. This inversion is done by deposition of a monolayer of sulfur at the surface of the sheets.

(21) 2 mL of the solution of CdSe sheets in CHCl.sub.3 (E101) as well as 100 L of a solution of tetramethylammonium sulfide (1 M) in ethanol are introduced in a vial. Under stirring, the color of the solution containing the sheets changes immediately and the sheets aggregate. After 10 minutes of reaction, the sheets are precipitated by centrifugation. The supernatant is discarded and the sheets are washed twice with ethanol. The sheets are suspended in distilled water.

(22) One then adds dropwise (E103) in the solution of sheets a solution of HAuCl.sub.4 (E102) at 0.1 M. The color of the solution changes progressively due to the deposition of gold at the sheets' surface (E104). The final sheets (E106) are washed twice by precipitation with ethanol. The final structure of the as-obtained sheets is schematized in FIG. 3 where A0 is CdSe, and A1 is gold (Au).

(23) According to another embodiment of the invention, one describes for example the deposition of a gold layer on initial nanosheets.

(24) In a vial are successively added 2 mL of chloroform, 400 L of the solution of CdSe sheets, 20 mg of thioacetamide (TAA) as well as 200 L of octylamine. The solution is submitted to sonication for 5 minutes, which causes the complete dissolution of TAA as well as a color change from yellow to orange. The sheets are then aggregated by addition of a few drops of ethanol and the solution is centrifuged for 5 minutes at 5000 rpms. The supernatant containing the unreacted precursors is discarded and the pellet containing the sheets is dispersed in 2 mL of toluene. 2 mL of a solution of gold precursors and ligands prepared by dissolution in 10 mL of toluene of 10 mg of AuCl.sub.3, 80 mg of didodecyldimethylammonium bromide as well as 120 mg of dodecylamine are added. The mixture is left reacting for 15 minutes. The resulting core/shell objects are precipitated by centrifugation for 5 minutes at 5000 rpms, the supernatant is discarded and the pellet dispersed in 2 mL of toluene.

(25) Deposition of an Alloyed Film

(26) One describes for example the deposition, according to one embodiment of the invention, of an alloy of cadmium sulfide and zinc sulfide CdZnS on the initial CdSe nanosheet.

(27) 2 mL of a CdSe sheets solution in chloroform (E101) is placed under magnetic stirring in a glove box under inert atmosphere. 100 L of bis(trimethylsilyl) sulfide (TMS.sub.2S) (E102) are then injected (E103), inducing a color change and a rapid aggregation. The mixture is allowed to react for one hour at room temperature (E104). The solution is then centrifuged, the supernatant discarded and the precipitate washed twice with ethanol. It is then dispersed in few milliliters of hexane (E105). A 5 mg of Cd(Acetate).sub.2(H.sub.2O).sub.2 and 3.5 mg of Zn(Acetate).sub.2 solution (E102) dissolved in 1 mL of ethanol is added drop wise over 10 minutes (E103). A new color change is observed, the reaction is allows to proceed under stirring for one hour (E104). 200 L of oleic acid are then added, the solution becomes clear. The final sheets (E106) are then precipitated with ethanol and suspended in hexane. The process allows the deposit of a Cd.sub.0.5Zn.sub.0.5S monolayer on each side of CdSe sheets. The iteration of the process allows the deposition of additional layers. The final structure of the sheets obtained is shown schematically in FIG. 3, where A0 is the CdSe and A1 is the CdZnS.

(28) Deposition of a Doped Film

(29) One describes for example the deposition of a film of zinc sulfide doped with manganese on the initial CdSe sheets according to one embodiment of the invention.

(30) 2 mL of a CdS sheets solution in chloroform (E101) is placed in a vial under magnetic stirring in a glove box under inert atmosphere. 100 L of bis(trimethylsilyl) sulfide (TMS.sub.2S, E102) are then injected (E103), inducing a rapid aggregation. The mixture is allowed to react for one hour at room temperature (E104). The solution is then centrifuged, the supernatant discarded and the pellet washed twice with ethanol. It is then dispersed in few milliliters of hexane (E105). 1 mL of a Zn(Acetate).sub.2 and Mn(Acetate).sub.2 solution (1% molar in Mn) in ethanol (E102) is added drop wise over 10 minutes (E103). The reaction is allowed to proceed under stirring for one hour (E104). 200 L of oleic acid are then added, the solution becomes clear. The final sheets (E106) are then precipitated with ethanol and suspended in hexane. The process allows the deposit of a manganese-doped ZnS monolayer on each side of CdS sheets. The iteration of the process allows the deposition of additional layers.

(31) Successive Deposition of Several Films of Different Chemical Composition

(32) One describes for example the deposition of a film of cadmium sulfide then of zinc sulfide on the initial CdSe nanosheets according to one embodiment of the invention.

(33) 2 mL of a CdSe sheets solution in chloroform (E101) is placed under magnetic stirring in a glove box under inert atmosphere. 100 L of bis(trimethylsilyl) sulfide (TMS.sub.2S, E102) are then injected (E103), inducing a color change and a rapid aggregation. The mixture is allowed to react for one hour at room temperature (E104). The solution is then centrifuged, the supernatant discarded and the precipitate washed twice with ethanol. This (E105) is then dispersed in few milliliters of hexane to which 10 mg of Cd(Acetate).sub.2(H.sub.2O).sub.2 (E102) powder are added (E103). Under stirring, a new color change is observed, the reaction is allowed to proceed for one hour (E104). 200 L of oleic acid are then added, the solution becomes clear. The sheets are then precipitated with ethanol and suspended in 2 mL of chloroform. We now have sheets covered with a CdS monolayer (E105). This solution is placed again under magnetic stirring in a glove box under inert atmosphere. 100 L of bis(trimethylsilyl) sulfide (TMS.sub.2S, E102) are then injected (E103), inducing a color change and a rapid aggregation. The mixture is allowed to react for one hour at room temperature (E104). The solution is then centrifuged, the supernatant discarded and the pellet washed twice with ethanol. This (E105) is then dispersed in few milliliters of hexane to which 10 mg of Zn(Acetate).sub.2 (E102) powder are added (E103). Under stirring, a new color change is observed. The reaction is allowed to proceed for one hour (E104). 200 L of oleic acid are then added, the solution becomes clear. The final sheets (E106) are then precipitated with ethanol and suspended in hexane. The final structure of the sheets obtained is shown schematically in FIG. 3, where A0 is the CdSe, A1 is the CdS and A2 is the ZnS.

(34) Immobilization of Sheets on a Substrate then Growth:

(35) In one embodiment of the invention, a microscope glass slide (26 mm by 26 mm) is cleaned with an oxygen plasma. It is then functionalized with 3-mercaptopropyl-triethoxysilane by immersion for 10 minutes in a 1% in volume solution of 3-mercaptopropyl-triethoxysilane in ethanol. The glass slide is rinsed 3 times with ethanol then dried. It is then immersed for 1 h in a solution of CdSe sheets dispersed in chloroform. The sheets adsorb at the surface of the glass slide and form a monolayer of sheets. The slide is rinsed twice with chloroform in order to eliminate sheets that are not bound to the substrate.

(36) One then deposits a monolayer of sulfur on the surface of sheets absorbed on the glass plate. The slide covered with sheets (E101) is placed in a glove box under inert atmosphere and immersed in chloroform. 10 L bis(trimethylsilyl) sulfide (TMS.sub.2S, E102) are then injected (E103). After hour of reaction (E104), the slide is rinsed twice with chloroform, then twice with ethanol. It is then possible to deposit a monolayer of cadmium to form a film of CdS. For this, the glass side covered with thicker sheets (E105) is immersed (E103) in a 0.1 M solution of Cd(acetate).sub.2(H.sub.2O).sub.2 (E102) in ethanol and is allowed to react for one hours (E104). After two washes with ethanol, the glass slide is thus covered with a layer of CdSe/CdS sheets (E106). The final structure of sheets obtained on substrate is shown schematically in FIG. 4, where A0 is the CdSe and A1 is the CdS.

(37) As obvious and as already resulting from the foregoing, the invention is in no way limited to those modes of applications and achievements that have been especially considered, it encompasses all variants without departing from the scope of the invention as defined by the claims.

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