GB2626009A

GB2626009A - Scalable synthesis of III-V nanocrystals

Info

Publication number: GB2626009A
Application number: GB2300166.2A
Authority: GB
Inventors: Mehta Joshua; Kishore Sagar Chiluka Laxmi
Original assignee: Quantum Science Ltd
Current assignee: Quantum Science Ltd
Priority date: 2023-01-05
Filing date: 2023-01-05
Publication date: 2024-07-10
Also published as: TW202432920A; WO2024147019A1

Abstract

A method for producing indium pnictogenide nanocrystals (InP, InAs, InSb) involving forming a mixture comprising an indium-containing compound; a phosphorus, arsenic or antimony containing precursor composition; a plurality of ligands and a non-polar solvent. The mixture is heated from a first temperature of 0 to 120 °C to a second temperature of 160 to 350 °C. The mixture is maintained at this second temperature for between 1 second to 180 minutes. The ligand may comprise an amino, thiol, hydroxyl or carboxylic acid functional group and may preferably be oleic acid, oleylamine or octanoic acid. The indium compound may be indium acetate. The arsenic, antimony or phosphorus containing precursor compositions may be tris(trimethylsilyl)arsine, tris(trimethylsilyl)antimony or tris(trimethylsilyl)phosphine respectively. The mixture may also comprise a reducing agent such as tris(dialkylamino)phosphine.

Description

SCALABLE SYNTHESIS OF III-V NANOCRYSTALS FIELD OF THE INVENTION

The present invention relates in general to nanocrystals. In particular, the present invention relates to a scalable method for producing indium pnictogenide nanocrystals comprising forming a mixture comprising an indium-containing compound, a pnictogen precursor composition, a plurality of ligands and a non-polar solvent; heating the mixture from a first temperature to a second temperature in the range of 160 °C to 350 °C; and maintaining the mixture at the second temperature for a first predetermined length of time in the range of 1 second to 180 minutes.

BACKGROUND

Nanocrystals are useful in a wide range of applications, for example because their optical properties can be finely tuned to provide the desired properties. The optical properties (for example light absorption and emission characteristics) of nanocrystals can be finely tuned by controlling their size. The largest nanocrystals produce the longest wavelengths (and lowest frequencies), while the smallest nanocrystals produce shorter wavelengths (and higher frequencies). The size of the nanocrystals may be controlled by means of the method by which they are produced. This ability to finely tune the optical properties of the nanocrystals, by controlling their size, makes nanocrystals suitable for use in a wide range of applications, including, for example, photodetectors, sensors, solar cells, bioimaging and bio-sensing, photovoltaics, displays, lighting, security and counterfeiting, batteries, wired high-speed communications, quantum dot (QD) lasers, photocatalysts, spectrometers, injectable compositions, field-effect transistors, light-emitting diodes, lasers, photonic or optical switching devices, hydrogen production and metamaterials.

In consumer electronics, the Restriction of Hazardous Substances Directive (RoHS) guidelines strongly advise developing heavy-metal free and less toxic materials. In the near infrared (NI R) and mid infrared (MIR) ranges, conventional epitaxially-grown materials or Pb-, Cd-and Hg-containing semiconductors have dominated until now. Even though these materials perform very well for targeted applications, heavy metal toxicity and high fabrication costs remain a long-term concern. Therefore, there is a strong need for green, less toxic infrared active materials.

In this context, colloidal III-V semiconductors such as InAs, InP, InSb, InGaAs, InAsSb have the potential to be heavy-metal free sensors active in the NIR and MIR ranges. Higher carrier mobilities and faster response times associated with these materials is an exciting prospect for optoelectronic devices. Furthermore, these materials have good solution processability and a tunable size-dependent bandgap, reducing the cost of producing indium pnictogenide sensor production compared to systems using conventional semiconductors.

However, these materials at present have significant drawbacks lack of scalability in the synthesis procedures. So far, indium pnictogenide nanocrystals have been produced using a hot-injection method. As described in the review by Tamang et al. (Chem. Rev. 2016, 116, 10731-10819), in the case of the hot injection method, the separation of nucleation and growth can be achieved by the rapid injection of the reagents into the hot solvent, which raises the concentration in the reaction flask above the nucleation threshold. The hot injection leads to a nucleation burst, which is quickly quenched by two factors: (i) the fast cooling of the reaction mixture, enhanced by the fact that the solution to be injected is at room temperature; (ii) the decreased supersaturation due to precursor/monomer consumption during nucleation.

However, the hot injection method is not scalable, and the hot injection is a potentially dangerous step due to the high temperature of the solution. There are also further disadvantages of the hot injection method. For example, the precursors used in the hot injection method may decompose at the high temperatures required, which leads to a drop in the synthesis yield and the formation of unnecessary side products, compromising the quality of nanocrystals.

The present inventors have also found that the method of Bawendi may lead to the formation of indium metal. The hot injection method may lead to a broad size distribution for III-V nanocrystals, and the nanocrystal size (and reaction kinetics) are difficult to control.

Despite growing interest and demands from industry, III-V QDs lack a systematic method to produce a single batch of indium pnictogenide nanocrystals on a large scale. There is therefore a need to provide a method for producing indium pnictogenide nanocrystals that is safer and more scalable, and avoids the abovementioned disadvantages of the hot injection method.

SUMMARY OF INVENTION

According to a first aspect, the present invention provides a method for producing indium pnictogenide nanocrystals comprising: a) forming a mixture comprising: (i) an indium-containing compound; (ii) a pnictogen precursor composition comprising at least one compound selected from the group consisting of a phosphorus-containing 15 compound, an arsenic-containing compound and an antimony-containing compound; (iii) a plurality of ligands, wherein the ligand is a C3-C24 organic compound comprising a functional group selected from the group consisting of amino, thiol, hydroxyl and carboxylic acid; and (iv) a non-polar solvent; b) heating the mixture from a first temperature to a second temperature in the range of 160 °C to 350 °C; and c) maintaining the mixture at the second temperature for a first predetermined length of time in the range of 1 second to 180 minutes.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 shows absorption spectra of InAs nanocrystals produced by the method of the invention, and using oleic acid as the ligand, showing how the absorption changes during the synthesis and the impressive tunability of the synthesis.

Figure 2 shows absorption spectra of I nAs nanocrystals produced by the method of the invention, and using octanoic acid as the ligand, showing how the absorption changes during the synthesis and the impressive tunability of the synthesis.

Figure 3 shows absorption spectra of I nAs nanocrystals produced by the method of the invention, and using oleylamine as the ligand and an indium chloride as the indium-containing compound, showing how the absorption changes during the synthesis and the impressive tunability of the synthesis.

DETAILED DESCRIPTION

When describing the aspects of the invention, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

As used in the specification and the appended claims, the singular forms "a", "an," and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a nanocrystal" means one nanocrystal or more than one nanocrystal. By way of example, "an indium-containing compound" means one indium-containing compound or more than one indium-containing compound. References to a number when used in conjunction with comprising language include compositions comprising said number or more than said number.

The terms "comprising", "comprises" and "comprised of' as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms "comprising", "comprises" and "comprised of' also include the term "consisting of'.

As used herein, the term "and/or," when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a list is described as comprising group A, B, and/or C, the list can comprise A alone; B alone; C alone; A and B in combination; A and C in combination, B and C in combination; or A, B, and C in combination.

As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts of percentages may be read as if prefaced by the word "about", even if the term does not expressly appear The term "about" as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, indicates that a value includes the standard deviation of error for the device or method being employed to determine the value. The term "about" is meant to encompass variations of +/- 10% or less, +/-5% or less, or +/-0.1 % or less of and from the specified value, insofar such variations are appropriate to perform in the disclosure. It is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

Unless otherwise defined, all terms used in the disclosure, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. By means of further guidance, definitions for the terms used in the description are included to better appreciate the teaching of the present disclosure. All publications referenced herein are incorporated by reference thereto.

As used herein, unless otherwise defined, the term "composition" may be open ended or closed. For example, "composition" comprises the specified material, i.e., the nanocrystals, and further unspecified material, or may consist of the specified material, i.e., to the substantial exclusion of non-specified materials.

According to a first aspect, the present invention provides a method for producing indium pnictogenide nanocrystals comprising: a) forming a mixture comprising: (i) an indium-containing compound; (ii) a pnictogen precursor composition comprising at least one compound selected from the group consisting of a phosphorus-containing compound, an arsenic-containing compound and an antimony-containing 10 compound; (iii) a plurality of ligands, wherein the ligand is a 03-024 organic compound comprising a functional group selected from the group consisting of amino, thiol, hydroxyl and carboxylic acid; and (iv) a non-polar solvent; b) heating the mixture from a first temperature to a second temperature in the range of 160 °C to 350 °C; and c) maintaining the mixture at the second temperature for a first predetermined length of time in the range of 1 second to 180 minutes.

The method of the present invention is safer than the hot injection technique as there is no step including the injection of cold reagents into a hot solution.

Furthermore, the method of the present invention is easier to scale and avoids the several other issues commonly associated with the hot injection technique for III-V nanocrystals. The present invention discloses a versatile route to synthesize III-V QDs on a large scale by simply mixing the components and crystallizing the nanocrystals at a suitable crystallization temperature. The indium pnictogenide nanocrystals are preferably indium pnictogenide semiconductor nanocrystals, and can be used in a variety of devices including IR sensors, photodetectors, sensors, solar cells, bio-imaging or bio-sensing compositions, photovoltaic systems, displays, batteries, lasers, photocatalysts, spectrometers, injectable compositions, field-effect transistors, light-emitting diodes, photonic or optical switching devices or metamaterials, fiber amplifiers, optical gain media, optical fibers, infrared LEDs, lasers, and electroluminescent devices.

A major benefit of the method of the present invention is that it allows for facile tunability of the nanocrystals over a wide range of sizes and wavelengths, particularly from 400 nm to 1000 nm. This may be achieved by simply adjusting the second temperature and/or the predetermined length of time. The results can be seen in Figures 1-3, wherein the absorption peaks are sharp and vary depending on the second temperature and/or the predetermined length of time. Thus, the inventors have discovered a much simpler, safer and more scalable way of producing group III-V nanocrystals.

Preferably, steps a), b) and c) take place under inert conditions. For example, the steps may take place under nitrogen atmosphere, or an argon atmosphere. In particular, it is preferable to carry out steps b) and c) under inert conditions.

Step c) comprises maintaining the mixture at the second temperature for a first predetermined length of time in the range of 1 second to 180 minutes. Maintaining the mixture at the second temperature may comprise maintaining the temperature of the mixture at a specific temperature. However, it is to be understood that the temperature may vary during the first predetermined length of time, and maintaining the mixture at the second temperature may comprise maintaining the temperature of the mixture within the range of suitable second temperatures, for example within the range of 160 °C to 350 °C.

In an embodiment, step c) further comprises continuously adding the pnictogen precursor composition to the mixture for the first predetermined length of time. This may be via injection or any other suitable method of adding the pnictogen precursor, as would be understood by the skilled person.

As used herein, the term "nanocrystal" is used to refer to a crystalline particle with at least one dimension measuring less than 100 nanometres (nm).

As used herein, the term "semiconductor nanocrystal" is used interchangeably with the term "quantum dot", and is used to refer to a semiconductor crystalline material exhibiting quantum confinement effects that allow it to mimic the properties of an atom. Quantum dots may also be known as zero-dimensional nanocrystals. As used herein, the term "semiconductor nanocrystal composition" is used to refer to a composition comprising at least one semiconductor nanocrystal.

As used herein, the term "indium pnictogenide semiconductor nanocrystal" is used to refer to a semiconductor nanocrystal comprising indium and a pnictogen.

As used herein, the term "pnictogen" is used to refer to an element in group 15 of the periodic table. For example, a pnictogen may be nitrogen, phosphorus, arsenic, antimony or bismuth.

As used herein, the term "ligand" is used to refer to a compound capable of forming a complex with the nanocrystal by coordinating to a surface of the nanocrystal. A nanocrystal generally comprises a crystalline core with dimensions in the order of tens of nanometres. They are typically stabilised as a colloidal solution by surface capping ligands, which may coordinate to the crystalline core as Lewis acidic (Z-type), Lewis basic (L-type) or anionic (X-type) species.

As used herein, the term "organic compound" is used to refer to a compound comprising carbon atoms covalently bound to other atoms. As used herein, the term "Cx-Cy" organic compound, wherein x and y are integers, is used to refer to 20 an organic compound containing at least x and no more than y carbon atoms.

Preferably, the first temperature is in the range of 0 °C to 120 °C, preferably in the range of 5 °C to 80°C, preferably in the range of 10 °C to 60°C, preferably in the range of 15 °C to 5000.

In a preferred embodiment, forming the mixture in step a) comprises: (i) forming a first mixture comprising the indium-containing compound, the plurality of ligands and a non-polar solvent; (ii) adding the pnictogen precursor composition to the first mixture.

In a preferred embodiment, wherein step (i) further comprises degassing the first mixture under vacuum (-0.1 mbar) for a degassing time in the range of 5 to 180 minutes at a degassing temperature in the range of 50 °C to 150 °C. Preferably, the degassing time is in the range of 20 minutes to 160 minutes, preferably in the range of 40 minutes to 140 minutes, preferably in the range of 60 minutes to 120 minutes, preferably in the range of 80 minutes to 100 minutes. Preferably, the degassing temperature is in the range of 70 °C to 150 °C, preferably in the range of 80 °C to 140 °C, preferably in the range of 90 °C to 130 °C, preferably in the range of 100 °C to 120 °C. The first temperature may be the degassing temperature, wherein the synthesis is carried out without cooling down the mixture before heating to the second temperature. Alternatively, the mixture may be cooled down after degassing to a first temperature in the range of 0 °C to 50 °C, more preferably in the range of 20 °C to 30 °C, before being heated to the second temperature. Both of these options have so far been found to yield the same results.

VVhere a gallium-containing compound is present in the mixture, the gallium-containing compound is also present in the first mixture for degassing.

Preferably, the second temperature is a temperature at which the indium pnictogenide nanocrystals form (a "crystallisation temperature"). In other words, the second temperature is preferably a crystallisation temperature of the indium pnictogenide nanocrystals. The crystallisation temperatures of these materials are generally known in the art, for example in J. R. Heath, Chem. Soc. Rev, 1998, 27, 65-71, and would be apparent to the skilled person. For example, the highest crystallisation temperature for InAs nanocrystals is reported by Bawendi et al (Journal of American Chemical Society, 2020,142, 9, 4088-4092) to be around 330 °C; the highest crystallisation temperature for InP nanocrystals is reported by Ji et al (Nano letters, 2022, 22, 10,4067-4073) to be around 29000 As far as the applicant is aware, the lowest crystallization temperatures of InAs nanocrystals are 175 °C (Banin et al, Chemical Communications, 2017, 53, 2326) and 190 °C (Hens et al, Journal of American Chemical Society, 2016, 138, 41, 13845-13848).

The lowest reported crystallization temperature of InP is around 170 °C (Banin et al, Chemical Communications, 2017, 53, 2326). Therefore, the second temperature is in the range of 160 °C to 350 °C. Any second temperature within this range is believed to be suitable for the formation of indium pnictogenide nanocrystals according to the method if the invention.

In general, the first predetermined length of time is preferably in the range of 1 second to 120 minutes, preferably in the range of 1 second to 60 minutes, preferably in the range of 1 second to 40 minutes, preferably in the range of 1 second to 20 minutes.

In a certain embodiment, the second temperature is in the range of 180 °C to 340 °C, preferably in the range of 200 °C to 330 °C, preferably in the range of 220 °C to 320 °C, preferably in the range of 240 °C to 310 °C, preferably in the range of 260 °C to 300 °C. Where the second temperature is higher (for example, above 250 °C), the first predetermined length of time is preferably longer. For example, the first predetermined length of time is in the range of 1 minute to 18 minutes, preferably in the range of 2 minutes to 16 minutes, preferably in the range of 3 minutes to 14 minutes, preferably in the range of 4 minutes to 12 minutes, preferably in the range of 5 minutes to 10 minutes.

In an alternative embodiment, the second temperature is in the range of 160 °C to 300 °C, preferably in the range of 16000 to 26000 preferably in the range of 170 °C to 250 °C, preferably in the range of 180 °C to 240 °C. Where the second temperature is lower (for example, below 250 °C), the first predetermined length of time is preferably shorter. For example, the first predetermined length of time is in the range of 1 second to 5 minutes, preferably in the range of 5 seconds to 3 minutes, preferably in the range of 10 seconds to 1 minute, preferably in the range of 15 seconds to 30 seconds.

The mixture may be formed in any suitable way. For example, the forming the mixture preferably comprises adding the components (i) to (iv) to a reaction vessel in any order Preferably, the indium-containing compound is selected from the group consisting of an indium acetate, indium triformate, dimethyl indium bromide, indium trifluoromethanesulfonate, indium trifluoro acetylacetonate, indium trifluoroacetate, indium perchloratehydrate, an indium nitrate, an indium carbonate, an indium carboxylate, an indium phosphate, an indium sulfonate, an indium sulphate, an indium thiolate, an indium halide, an indium amine, and an indium acetyl acetonate. More preferably, the indium-containing compound is selected from the group consisting of an indium acetate, an indium halide, an indium carboxylate, an indium thiolate and an indium arsenic acid. A particularly preferred indium-containing compound is indium acetate.

The pnictogen precursor composition may comprise any pnictogen-containing compound or any combination of pnictogen-containing compounds. The only pnictogen-containing compound in the pnictogen precursor composition may be an arsenic-containing compound. The only pnictogen-containing compound in the pnictogen precursor composition may be an antimony-containing compound. The only pnictogen-containing compound in the pnictogen precursor composition may be a phosphorus-containing compound. The pnictogen precursor composition may comprise two pnictogen-containing compounds, for example an arsenic-containing compound and an antimony-containing compounds.

In an embodiment, the pnictogen precursor composition comprises the arsenic-containing compound. In an embodiment, the pnictogen precursor composition comprises the antimony-containing compound. In an embodiment, the pnictogen precursor composition comprises the phosphorus-containing compound.

Preferably, the arsenic-containing compound is selected from the group consisting of an aminoarsine, tris(trimethylsilyl)arsine, tris(dimethylamino) arsine, triphenyl arsine and mixtures thereof. More preferably, the arsenic-containing compound is tris(trimethylsilyl)arsine.

Preferably, the antimony-containing compound is selected from the group consisting of tris(trialkylsilylantimony), wherein the alkyl is ethyl, propyl, butyl or substituted alkyl chains, tris(trimethylsilyl)antimony, tris(trimethylgermyl)antimony and aminoantimony (R2N)3Sb, wherein R is an alkyl or aryl group, antimony halides, antimony dialkaylamides, dialkylsilylamides, antimony hydrides, antimony aziridinides, antimony thiolates, antimony carbamates, antimony guanidinates and mixtures thereof. Preferably, the antimony-containing compound is tris(trimethylsilyl)antimony.

Preferably, the phosphorus-containing compound is selected from the group consisting of tris(trialkylsilylphosphine), wherein the alkyl is ethyl, propyl, butyl or substituted alkyl chains, tris(trimethylsilyl)phosphine, tris(trimethylgermyl) phosphine, tris(triphenylsilylphosphine) and aminophosphine (R2N)3P, wherein R is alkyl or aryl, phosphonic halides, and alkyl or aryl phosphorus acids.

The ligands of the present invention are compounds capable of forming a complex with the indium pnictogenide semiconductor nanocrystal by coordinating to a surface of the nanocrystal. The ligands on the surface of the nanocrystal may be all the same compound, or there may be mixtures of different compounds coordinated to the surface of the nanocrystal.

Preferably, the ligand is a compound selected from the group consisting of aminobenzoic acids, dicarboxylic acids, aminoalkylcarboxylic acids, mercaptopropionic acid, mercaptobenzoic acid, thioalkanes, dithioalkanes, thiocarboxylic acids, thioglycolic acid, poly(ethylene glycol), poly(ethylene glycol) bis(3-aminopropyl) terminated, didodecyldimethylammonium bromide, n-dodecylammonium bromide, dodecyltrimethylammonium bromide, dimercaptosuccinic acid, octanoic acid, oleic acid, oleylamine, bis(diphenylphosphino)methane and alkylamines.

Preferably, the ligand is an organic acid or organic amine. Preferably, the ligand is a compound selected from the group consisting of mercaptopropionic acid, mercaptobenzoic acid, octanoic acid, thioglycolic acid, dimercaptosuccinic acid, oleic acid and oleylamine. More preferably, the ligand is oleic acid, octanoic acid or oleylamine, preferably octanoic acid.

Preferably, the non-polar solvent has a relative permittivity at 20 °C of less than 3, preferably less than 2.5. As used herein, the term "relative permittivity" is used to refer to the ratio of the permittivity of a substance to the permittivity of a vacuum; it is a dimensionless number. As defined in Permittivity (Dielectric Constant) of Liquids, by Christian Wohlfarth, the permittivity of a substance (often called the dielectric constant) is the ratio of the electric displacement D to the electric field strength E when an external field is applied to the substance. The relative permittivity is measured with a BI-870 Dielectric Constant Meter available from Brookhaven Instruments, using the sensitivity range of 1 to 200. The instrument may be calibrated with a liquid of known relative permittivity.

Preferably, the non-polar solvent is selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, hexadecane, oleic acid, tertiary phosphines and secondary phosphines.

The heating of the mixture from the first temperature to the second temperature may be carried out at any suitable rate. Preferably, step b) comprises heating the mixture to the second temperature at a rate in the range of 1 °C min-1 to 30 °C min-1, preferably at a rate in the range of 5 °C min-1 to 26 °C preferably at a rate in the range of 8 °C min-1 to 22 °C min-1, preferably at a rate in the range of 10°C min-1 to 20 °C min-1, preferably at a rate in the range of 12 °C min-1 to 18 °C min-1.

The method of the present invention may also incorporate gallium into the nanocrystal to form a ternary or quaternary quantum dot. In an embodiment, the mixture further comprises a gallium-containing compound. In an embodiment, step a) comprises forming the mixture further comprising a gallium-containing compound. The advantage of introducing gallium into the nanocrystal is to tune the bandgap and the lattice parameter based on the composition of the ternary or quaternary alloy. In the bulk, InGaAs photodetectors are also generally found to be more sensitive and better photodetectors. Additionally, I nGaAs can be grown on III-V substrates.

Preferably, the gallium-containing compound is selected from the group consisting of gallium acetate, gallium nitrate, gallium sulfate, gallium hydroxide, galliumtrifluoromethane sulfonate, galliumtrifluoroacetyl acetonate, gallium acetylacetonate, galliumtrifluoroacetate, gallium phosphate, gallium perchlorate hydrate, gallium (III) trihalides, gallium (I) halides and gallium (II) halides.

Preferably, step a) comprises forming the mixture further comprising a reducing agent. Preferably, the reducing agent is selected from the group consisting of trisdialkylaminophosphine, tris(2-carboxyethyl)phosphine, sodium cyanoborohydride, sodium borohydride, diisobutylalumnium hydride, alane N,N-dimethylethylamine complex and lithium triethylborohydride, and mixtures thereof.

The inventors have further found that the method of the present invention allows for excellent control of the shape of the nanocrystals produced. In particular, the inventors have found that by introducing some additives such as metal halides or metal carboxylates in step a) (often along with the indium precursors), the shape of the nanocrystals (III-V ODs) can be controlled from cuboctahedron to tetrahedral. Metal halides (MX, MX2 or MX3) include, but are not limited to, where M is Cd, Zn, Mn, Cu, Sb, Na, Li, K etc, X= F, Cl, Br, I. Metal carboxylates include, but are not limited to, M(R-000)2 or M(R-000)3; where M = Cd, Zn, Mn, Cu, Sb, R= C6_22. In other words, step a) preferably comprises forming a mixture further comprising an additive, wherein the additive is a metal halide, a metal carboxylate or mixtures thereof. In a particularly preferred embodiment, the additive is a metal halide and the metal halide has formula MX, wherein M is selected from the group consisting of Cd, Zn, Mn, Cu, Sb, Na, Li, and K, X is selected from the group consisting of F, Cl, Br, and I, and n is 1, 2 or 3, preferably wherein the metal halide is ZnBr2. In an alternative particularly preferred embodiment, the additive is a metal carboxylate and the metal carboxylate has formula M(R-COO), wherein M is selected from the group consisting of Cd, Zn, Mn, Cu, or Sb, R is an alkyl group comprising at least 6 and no more than 22 carbon atoms, and n is 2 or 3.

EXAMPLES

Examples are described hereunder illustrating the methods according to the present disclosure.

Whereas particular examples of this invention have been described below for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Unless other indicated, all parts and all percentages in the following examples, as well as throughout the specification, are parts by weight or percentages by weight respectively.

Absorption spectra of colloidal quantum dots or quantum dots films were obtained on a JASCO V-770 UV-visible/NI R spectrometer which can provide measurements in the 400 to 3200nm wavelength.

Chemicals All glassware was dried in an oven overnight at 120 °C before use. All manipulations were performed using a standard Schlenk line or glove box techniques under nitrogen. All the solvents and reagents are used as it is unless stated otherwise.

Indium acetate ((ln(0Ac)3 99.99%), oleic acid, technical grade (OA, 90%), octanoic acid (98%), octadecene (ODE, 90%), n-heptadecane (0-17, 99%), n-hexadecane (0-16, 99%) and acetone (99.8%, HPLC grade) were purchased from fisher scientific. Oleylamine (98%), Indium (I) chloride {In(1)C1, 99.99%), trisdimethylaminoarsine (DMAAs,99%), dioctylamine (DOA, 97%), triphenylphosphine, anhydrous hexane (95%), propan-2-ol (1PA,99.5%) were purchased from Merck. Tris(trimethylsilyl)arsine (TMS03As was purchased from Gelest or DOCK Chemicals.

Solvents like heptadecane and oleylamine were dried under vacuum (-0.015 mbar) at 100 °C for 120 minutes to remove any oxygen, water, and other impurities. The temperature was cooled down to 20 °C and transferred into the glovebox for further use.

Example 1 -Preparation of InAs nanocrystals using tris(trimethylsily1) arsine, and oleic acid as the ligand In a 3-neck 100 mL flask with a magnetic stirring bar, 0.4 mmol of In(0Ac)3, 1.2 mmol of oleic acid and 6 mL heptadecane were taken and degassed under vacuum (-0.1 mbar) at 110 °C for 90 minutes. During this step, Indium oleate was formed and 1.2 mmol of acetic acid was collected in the cold trap.

In(0Ac)3 + R-COOH (R= 017H33) -> In-000R + CH3000H The flask was switched to nitrogen atmosphere and temperature was maintained at 100 °C. In the glovebox, 0.32 mmol of (TMS03As, 0.56 mmol of dioctyl amine and 1 mL of degassed heptadecane were loaded into a syringe. This solution is added to indium oleate solution at 100 °C. There was an immediate color change after the injection of arsenic precursor solution. The solution was simply heated up to 290 °C at a heating rate of approximately 15 °C /minute. CODs growth was monitored by taking aliquots at a regular time intervals, different temperatures and measuring the absorption spectra.

Figure 1 shows absorption spectra for the nanocrystals produced by the method of Example 1. The length of time at the second temperature and second temperatures were varied as shown in the legend of the Figures. As can be seen in Figure 1, the nanocrystals are size-tunable by varying the temperature, heating rate and length of time at the second temperature. The synthesis of the indium pnictogenide nanocrystals is therefore very versatile and scalable.

Example 2 -Preparation of InAs nanocrystals using tris(trimethylsily1) arsine, and octanoic acid as the ligand The method of preparing the nanocrystals was equivalent to the method of Example 1, using octanoic acid as the ligand in place of oleic acid.

Figure 2 shows absorption spectra for the nanocrystals produced by the method of Example 2. The length of time at the second temperature and second temperatures were varied as shown in the legend of the Figure. As can be seen in Figure 2, octanoic acid provides wider tunability of size. Furthermore, octanoic acid comprises a linear eight-carbon chain which is sterically unhindered at the nanocrystal surface, whereas oleic acid comprises an eighteen-carbon chain and a double bond which creates steric hindrance on the nanocrystal surface. As a result, octanoic acid binds more strongly to the surface of the nanocrystals when compared to oleic acid. This makes octanoic acid a particularly preferred ligand of the present invention.

Example 3-Preparation of InAs nanocrystals using tris(dimethylamino) arsine, and oleylamine as the ligand In a 3-neck 100 mL flask with a magnetic stirring bar, 0.5 mmol of In(1)C1 and 1.14 mmol of triphenylphosphine were added in a glovebox. The flask is removed from the glovebox and attached to a Schlenk line. The flask is evacuated under vacuum at room temperature for 10 minutes. The flask is switched to nitrogen atmosphere.

In the glovebox, oleylamine (1 mL) is combined with 0.4 mmol of trisdimethylaminoarsine (DMAAs) (75 pL) and stirred at 50 00 for 1 hour in a septum capped vial before cycling on to the Schlenk line. With the flask under N2, add oleylamine (7 mL). The temperature is increased 50 °C. When the reaction solution reaches 50 0C, 0.4 mL of the DMAAs/oleylamine solution is injected at once into the flask. The solution was simply heated up to 290 °C at a heating rate of approximately 15 °C /minute. CODs growth was monitored by taking aliquots at a regular time intervals, different temperatures and measuring the absorption spectra.

Figure 3 shows that the synthesis of the present invention is very versatile, and can use many different starting materials whilst still producing indium pnictogenide nanocrystals. The length of time at the second temperature and second temperatures were varied as shown in the legend of the Figure.

EMBODIMENTS

1. A method for producing indium pnictogenide nanocrystals comprising: a) forming a mixture comprising: (i) an indium-containing compound; (ii) a pnictogen precursor composition comprising at least one compound selected from the group consisting of a phosphorus-containing compound, an arsenic-containing compound and an antimony-containing compound; (iii) a plurality of ligands, wherein the ligand is a 03-024 organic compound comprising a functional group selected from the group consisting of amino, thiol, hydroxyl and carboxylic acid; and (iv) a non-polar solvent; b) heating the mixture from a first temperature to a second temperature in the range of 160°C to 350 °C; and c) maintaining the mixture at the second temperature for a first predetermined length of time in the range of 1 second to 180 minutes.

2. The method of embodiment 1, wherein the first temperature is in the range of 000 to 120 °C, preferably in the range of 5 °C to 80 °C, preferably in the range of 1000 to 60°C, preferably in the range of 15°C to 5000.

3 The method of embodiment 1 or embodiment 2, wherein the second temperature is a temperature at which the indium pnictogenide nanocrystals form.

4. The method of any one of the preceding embodiments, wherein the second temperature is a crystallisation temperature of the indium pnictogenide nanocrystals.

5. The method of any one of the preceding embodiments, wherein the first predetermined length of time is in the range of 1 second to 120 minutes, preferably in the range of 1 second to 60 minutes, preferably in the range of 1 second to 40 minutes, preferably in the range of 1 second to 20 minutes.

6. The method of any one of the preceding embodiments, wherein the second temperature is in the range of 180°C to 340 °C, preferably in the range of 200 °C to 330 °C, preferably in the range of 220 °C to 320 °C, preferably in the range of 240 °C to 310 °C, preferably in the range of 260 °C to 300 °C.

7. The method of embodiment 6, wherein the first predetermined length of time is in the range of 1 minute to 18 minutes, preferably in the range of 2 minutes to 16 minutes, preferably in the range of 3 minutes to 14 minutes, preferably in the range of 4 minutes to 12 minutes, preferably in the range of 5 minutes to 10 minutes.

8. The method of any one of embodiments 1 to 5, wherein the second temperature is in the range of 16000 to 300°C, preferably in the range of 160 °C to 260 °C, preferably in the range of 170 °C to 250 °C, preferably in the range of 18000 to 24000 9. The method of embodiment 8, wherein the first predetermined length of time is in the range of 1 second to 5 minutes, preferably in the range of 5 seconds to 3 minutes, preferably in the range of 10 seconds to 1 minute, preferably in the range of 15 seconds to 30 seconds.

10. The method of any one of the preceding embodiments, wherein step c) further comprises continuously adding the pnictogen precursor composition to the mixture for the first predetermined length of time.

11. The method of any one of the preceding embodiments, wherein forming the mixture comprises adding the components (i) to (iv) to a reaction vessel in any order.

12. The method of any one of embodiments 1 to 10, wherein forming the mixture comprises: (i) forming a first mixture comprising the indium-containing compound, the plurality of ligands and a non-polar solvent; (ii) adding the pnictogen precursor composition to the first mixture.

13. The method of embodiment 12, wherein step (i) further comprises degassing the first mixture under vacuum for a degassing time in the range of 5 to 180 minutes at a degassing temperature in the range of 50 °C to 150 °C.

14. The method of embodiment 13, wherein the degassing time is in the range of 20 minutes to 160 minutes, preferably in the range of 40 minutes to 140 minutes, preferably in the range of 60 minutes to 120 minutes, preferably in the range of 80 minutes to 100 minutes.

15. The method of embodiment 13 or embodiment 14, wherein the degassing temperature is in the range of 70 °C to 150 °C, preferably in the range of 80 °C to 140 °C, preferably in the range of 9000 to 130 °C, preferably in the range of 100 °C to 120 °C.

16. The method of any one of the preceding embodiments, wherein the indium-containing compound is selected from the group consisting of an indium acetate, indium triformate, dimethyl indium bromide, indium trifluoromethanesulfonate, indium trifluoro acetylacetonate, indium trifluoroacetate, indium perchloratehydrate, an indium nitrate, an indium carbonate, an indium carboxylate, an indium phosphate, an indium sulfonate, an indium sulphate, an indium thiolate, an indium halide, an indium amine, and an indium acetyl acetonate, preferably wherein the indium-containing compound is indium acetate.

17. The method of any one of the preceding embodiments, wherein the indium-containing compound is selected from the group consisting of an indium acetate, an indium halide, an indium carboxylate, an indium thiolate and an indium arsenic acid.

18. The method of any one of the preceding embodiments, wherein the pnictogen precursor composition comprises the arsenic-containing compound.

19. The method of embodiment 18, wherein the arsenic-containing compound is selected from the group consisting of an aminoarsine, tris(trimethylsilyl)arsine, tris(dimethylamino) arsine, triphenyl arsine and mixtures thereof.

20. The method of embodiment 18 or embodiment 19, wherein the arsenic-containing compound is tris(trimethylsilyl)arsine.

21. The method of any one of the preceding embodiments, wherein the pnictogen precursor composition comprises the antimony-containing compound.

22. The method of embodiment 21, wherein the antimony-containing compound is selected from the group consisting of tris(trialkylsilylantimony), wherein the alkyl is ethyl, propyl, butyl or substituted alkyl chains, tris(trimethylsilyl)antimony, tris(trimethylgermyl)antimony and aminoantimony (R2N)38b, wherein R is an alkyl or aryl group, antimony halides, antimony dialkaylamides, dialkylsilylamides, antimony hydrides, antimony aziridinides, antimony thiolates, antimony carbamates, antimony guanidinates and mixtures thereof.

23. The method of embodiment 21 or embodiment 22, wherein the antimony-containing compound is tris(trimethylsilyl)antimony.

24. The method of any one of the preceding embodiments, wherein the pnictogen precursor composition comprises the phosphorus-containing compound 25. The method of embodiment 24, wherein the phosphorus-containing compound is selected from the group consisting of tris(trialkylsilylphosphine), wherein the alkyl is ethyl, propyl, butyl or substituted alkyl chains, tris(trimethylsilyl)phosphine, tris(trimethylgermyl)phosphine, tris(triphenylsilylphosphine) and aminophosphine (R2N)3P, wherein R is alkyl or aryl, phosphonic halides, and alkyl or aryl phosphorus acids.

26. The method of any one of the preceding embodiments, wherein the ligand is a compound capable of forming a complex with the indium pnictogenide semiconductor nanocrystal by coordinating to a surface of the nanocrystal.

27. The method of any one of the preceding embodiments, wherein the ligand is a compound selected from the group consisting of aminobenzoic acids, dicarboxylic acids, aminoalkylcarboxylic acids, mercaptopropionic acid, mercaptobenzoic acid, thioalkanes, dithioalkanes, thiocarboxylic acids, thioglycolic acid, poly(ethylene glycol), poly(ethylene glycol) bis(3-aminopropyl) terminated, didodecyldimethylammonium bromide, n-dodecylammonium bromide, dodecyltrimethylammonium bromide, dimercaptosuccinic acid, octanoic acid, oleic acid, oleylamine, bis(diphenylphosphino)methane and alkylamines.

28. The method of any one of the preceding embodiments, wherein the ligand is an organic acid or organic amine.

29. The method of any one of the preceding embodiments, wherein the ligand is a compound selected from the group consisting of mercaptopropionic acid, mercaptobenzoic acid, octanoic acid, thioglycolic acid, dimercaptosuccinic acid, oleic acid and oleylamine.

30. The method of any one of the preceding embodiments, wherein the ligand is oleic acid, octanoic acid or oleylamine, preferably octanoic acid.

31. The method of any one of the preceding embodiments, wherein the non-polar solvent has a relative permittivity at 20 °C of less than 3, preferably less than 2.5.

32. The method of any one of the preceding embodiments, wherein the non-polar solvent is selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, hexadecane, oleic acid, tertiary phosphines and secondary phosphines.

33. The method of any one of the preceding embodiments, wherein step b) comprises heating the mixture to the second temperature at a rate in the range of 1 °C min-1 to 30 °C min-1, preferably at a rate in the range of 5 °C min-1 to 26 °C min-1, preferably at a rate in the range of 8 °C min-I to 22 °C preferably at a rate in the range of 10 °C min-1 to 20 °C min-1, preferably at a rate in the range of 12 °C min -I to 18 °C min-1.

34. The method of any one of the preceding embodiments, wherein the mixture further comprises: (v) a gallium-containing compound.

35. The method of any one of the preceding embodiments, wherein step a) comprises forming the mixture further comprising: (v) a gallium-containing compound.

36. The method of embodiment 24 or embodiment 35, wherein the gallium-containing compound is selected from the group consisting of gallium acetate, gallium nitrate, gallium sulfate, gallium hydroxide, galliumtrifluoromethane sulfonate, galliumtrifluoroacetyl acetonate, gallium acetylacetonate, galliumtrifluoroacetate, gallium phosphate, gallium perchlorate hydrate, gallium (III) trihalides, gallium (I) halides and gallium (II) halides.

37. The method of any one of the preceding embodiments, wherein step a) comprises forming the mixture further comprising: (vi) a reducing agent.

38. The method of embodiment 37, wherein the reducing agent is selected from the group consisting of trisdialkylaminophosphine, tris(2-carboxyethyl)phosphine, sodium cyanoborohydride, sodium borohydride, diisobutylalumnium hydride, alane N,N-dimethylethylamine complex and lithium triethylborohydride, and mixtures thereof 39. The method of any one of the preceding embodiments, wherein step a) comprises forming a mixture further comprising an additive, wherein the additive is a metal halide, a metal carboxylate or mixtures thereof 40. The method of embodiment 39, wherein the additive is a metal halide and the metal halide has formula MX, wherein M is selected from the group consisting of Cd, Zn, Mn, Cu, Sb, Na, Li, and K, X is selected from the group consisting of F, Cl, Br, and I, and n is 1, 2 or 3, preferably wherein the metal halide is ZnBr2.

41. The method of embodiment 39, wherein the additive is a metal carboxylate and the metal carboxylate has formula M(R-COO), wherein M is selected from the group consisting of Cd, Zn, Mn, Cu, or Sb, R is an alkyl group comprising at least 6 and no more than 22 carbon atoms, and n is 2 or 3.

1. REFERENCES 9, 4088-2. 3.

Tamang et al., Chem. Rev. 2016, 116,10731-10819. J. R. Heath, Chem. Soc. Rev, 1998, 27, 65-71.

Bawendi et al, Journal of American Chemical Society, 2020,142, 4092 4. Ji et al Nano letters, 2022, 22, 10, 4067-4073.

5. Banin et al, Chemical Communications, 2017, 53, 2326.

6. Hens et al, Journal of American Chemical Society, 2016, 138, 41, 13845-13848.

Claims

CLAIMS1. A method for producing indium pnictogenide nanocrystals comprising: a) forming a mixture comprising: an indium-containing compound; (ii) a pnictogen precursor composition comprising at least one compound selected from the group consisting of a phosphorus-containing compound, an arsenic-containing compound and an antimony-containing compound; (iii) a plurality of ligands, wherein the ligand is a 03-024 organic compound comprising a functional group selected from the group consisting of amino, thiol, hydroxyl and carboxylic acid; and (iv) a non-polar solvent; b) heating the mixture from a first temperature to a second temperature in the range of 160°C to 350 °C; and c) maintaining the mixture at the second temperature for a first predetermined length of time in the range of 1 second to 180 minutes.
2. The method of claim 1, wherein the first temperature is in the range of 0 °C to 120 °C, preferably in the range of 5 °C to 80 °C, preferably in the range of 10 °C to 60 °C, preferably in the range of 15 °C to 50 °C.
3. The method of claim 1 or claim 2, wherein the second temperature is a temperature at which the indium pnictogenide nanocrystals form, preferably wherein the second temperature is a crystallisation temperature of the indium pnictogenide nanocrystals.
4. The method of any one of the preceding claims, wherein the first predetermined length of time is in the range of 1 second to 120 minutes, preferably in the range of 1 second to 60 minutes, preferably in the range of 1 second to 40 minutes, preferably in the range of 1 second to 20 minutes.
5. The method of any one of the preceding claims, wherein the second temperature is in the range of 180 °C to 340 °C, preferably in the range of 200 °C to 330 °C, preferably in the range of 220 °C to 320 °C, preferably in the range of 240 °C to 310 °C, preferably in the range of 260 °C to 300 °C, and/or wherein the first predetermined length of time is in the range of 1 minute to 18 minutes, preferably in the range of 2 minutes to 16 minutes, preferably in the range of 3 minutes to 14 minutes, preferably in the range of 4 minutes to 12 minutes, preferably in the range of 5 minutes to 10 minutes.
6. The method of any one of claims 1 to 4, wherein the second temperature is in the range of 160 °C to 300 °C, preferably in the range of 160 °C to 260 °C, preferably in the range of 170 °C to 250 °C, preferably in the range of 180 °C to 240 °C, and/or wherein the first predetermined length of time is in the range of 1 second to 5 minutes, preferably in the range of 5 seconds to 3 minutes, preferably in the range of 10 seconds to 1 minute, preferably in the range of 15 seconds to 30 seconds.
7. The method of any one of the preceding claims, wherein step c) further comprises continuously adding the pnictogen precursor composition to the mixture for the first predetermined length of time.
8. The method of any one of the preceding claims, wherein forming the mixture comprises adding the components (i) to (iv) to a reaction vessel in any 20 order.
9. The method of any one of claims 1 to 7, wherein forming the mixture comprises: (i) forming a first mixture comprising the indium-containing compound, the plurality of ligands and a non-polar solvent; (ii) adding the pnictogen precursor composition to the first mixture.
10. The method of claim 9, wherein step (i) further comprises degassing the first mixture under vacuum for a degassing time in the range of 5 to 180 minutes at a degassing temperature in the range of 50 °C to 150 °C, preferably wherein the degassing time is in the range of 20 minutes to 160 minutes, preferably in the range of 40 minutes to 140 minutes, preferably in the range of 60 minutes to 120 minutes, preferably in the range of 80 minutes to 100 minutes, preferably wherein the degassing temperature is in the range of 70 °C to 150 °C, preferably in the range of 80 °C to 140 °C, preferably in the range of 90 °C to 130 °C, preferably in the range of 10000 to 120 °C.
11. The method of any one of the preceding claims, wherein the indium-containing compound is selected from the group consisting of an indium acetate, indium triformate, dimethyl indium bromide, indium trifluoromethanesulfonate, indium trifluoro acetylacetonate, indium trifluoroacetate, indium perchloratehydrate, an indium nitrate, an indium carbonate, an indium carboxylate, an indium phosphate, an indium sulfonate, an indium sulphate, an indium thiolate, an indium halide, an indium amine, and an indium acetyl acetonate, preferably wherein the indium-containing compound is selected from the group consisting of an indium acetate, an indium halide, an indium carboxylate, an indium thiolate and an indium arsenic acid, preferably wherein the indium-containing compound is indium acetate.
12. The method of any one of the preceding claims, wherein the pnictogen precursor composition comprises the arsenic-containing compound.
13. The method of claim 12, wherein the arsenic-containing compound is selected from the group consisting of an aminoarsine, tris(trimethylsilyl)arsine, tris(dimethylamino) arsine, triphenyl arsine and mixtures thereof, preferably wherein the arsenic-containing compound is tris(trimethylsilyl)arsine.
14. The method of any one of the preceding claims, wherein the pnictogen precursor composition comprises the antimony-containing compound.
15. The method of claim 14, wherein the antimony-containing compound is selected from the group consisting of tris(trialkylsilylantimony), wherein the alkyl is ethyl, propyl, butyl or substituted alkyl chains, tris(trimethylsilyl)antimony, tris(trimethylgermyhantimony and aminoantimony (R2N)3Sb, wherein R is an alkyl or aryl group, antimony halides, antimony dialkaylamides, dialkylsilylamides, antimony hydrides, antimony aziridinides, antimony thiolates, antimony carbamates, antimony guanidinates and mixtures thereof, preferably wherein the antimony-containing compound is tris(trimethylsilyl)antimony.
16. The method of any one of the preceding claims, wherein the pnictogen precursor composition comprises the phosphorus-containing compound.
17. The method of claim 16, wherein the phosphorus-containing compound is selected from the group consisting of tris(trialkylsilylphosphine), wherein the alkyl is ethyl, propyl, butyl or substituted alkyl chains, tris(trimethylsilyl)phosphine, tris(trimethylgermyl)phosphine, tris(triphenylsilylphosphine) and aminophosphine (R2N)3P, wherein R is alkyl or aryl, phosphonic halides, and alkyl or aryl phosphorus acids
18. The method of any one of the preceding claims, wherein the ligand is a compound capable of forming a complex with the indium pnictogenide semiconductor nanocrystal by coordinating to a surface of the nanocrystal, preferably wherein the ligand is a compound selected from the group consisting of aminobenzoic acids, dicarboxylic acids, aminoalkylcarboxylic acids, mercaptopropionic acid, mercaptobenzoic acid, thioalkanes, dithioalkanes, thiocarboxylic acids, thioglycolic acid, poly(ethylene glycol), poly(ethylene glycol) bis(3-aminopropyl) terminated, didodecyldimethylammonium bromide, n-dodecylammonium bromide, dodecyltrimethylammonium bromide, dimercaptosuccinic acid, octanoic acid, oleic acid, oleylamine, bis(diphenylphosphino)methane and alkylamines, preferably wherein the ligand is an organic acid or organic amine, preferably wherein the ligand is a compound selected from the group consisting of mercaptopropionic acid, mercaptobenzoic acid, octanoic acid, thioglycolic acid, dimercaptosuccinic acid, oleic acid and oleylamine, preferably wherein the ligand is oleic acid, octanoic acid or oleylamine, preferably octanoic acid.
19. The method of any one of the preceding claims, wherein the non-polar solvent has a relative permittivity at 20 °C of less than 3, preferably less than 2.5, preferably wherein the non-polar solvent is selected from the group consisting of octadecene, oleylamine, octylamine, butylamine, dioctylamine, heptadecane, hexadecane, oleic acid, tertiary phosphines and secondary phosphines.
20. The method of any one of the preceding claims, wherein step b) comprises heating the mixture to the second temperature at a rate in the range of 1 °C mind to 30 °C min-I, preferably at a rate in the range of 5 °C min-1 to 26 °C min-1, preferably at a rate in the range of 8 °C min-1 to 22 °C min-I, preferably at a rate in the range of 10 °C min-1 to 20 °C min-1, preferably at a rate in the range of 12 °C min -I to 18 °C min-I.
21. The method of any one of the preceding claims, wherein step a) comprises forming the mixture further comprising: (v) a gallium-containing compound, preferably wherein the gallium-containing compound is selected from the group consisting of gallium acetate, gallium nitrate, gallium sulfate, gallium hydroxide, galliumtrifluoromethane sulfonate, galliumtrifluoroacetyl acetonate, gallium acetylacetonate, galliumtrifluoroacetate, gallium phosphate, gallium perchlorate hydrate, gallium (Ill) trihalides, gallium (I) halides and gallium (II) halides.
22. The method of any one of the preceding claims, wherein step a) comprises forming the mixture further comprising: (vi) a reducing agent, preferably wherein the reducing agent is selected from the group consisting of trisdialkylaminophosphine, tris(2-carboxyethyl)phosphine, sodium cyanoborohydride, sodium borohydride, diisobutylalumnium hydride, alane N,Ndimethylethylamine complex and lithium triethylborohydride, and mixtures thereof.
23. The method of any one of the preceding claims, wherein step a) comprises forming a mixture further comprising an additive, wherein the additive is a metal halide, a metal carboxylate or mixtures thereof
24. The method of claim 23, wherein the additive is a metal halide and the metal halide has formula MX, wherein M is selected from the group consisting of Cd, Zn, Mn, Cu, Sb, Na, Li, and K, X is selected from the group consisting of F, Cl, Br, and I, and n is 1, 2 or 3, preferably wherein the metal halide is ZnBr2.
25. The method of claim 23, wherein the additive is a metal carboxylate and the metal carboxylate has formula M(R-COO), wherein M is selected from the group consisting of Cd, Zn, Mn, Cu, or Sb, R is an alkyl group comprising at least 6 and no more than 22 carbon atoms, and n is 2 or 3.