Case 2:20-cv-00038-JRG Document 1-2 Filed 02/14/20 Page 1 of 19 PageID #: 20
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`Exhibit 1
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`

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`Case 2:20-cv-00038-JRG Document 1-2 Filed 02/14/20 Page 2 of 19 PageID #: 21
`
`US007588828B2
`
`(12) United States Patent
`Mushtaq et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,588,828 B2
`Sep. 15, 2009
`
`(54) PREPARATION OF NANOPARTICLE
`MATERLALS
`
`(75) Inventors: Imrana Mushtaq, Manchester (GB);
`Steven Daniels, Manchester (GB); Nigel
`Pickett, East Croyden (GB)
`(73) Assignee: Nanoco Technologies Limited,
`Manchester (GB)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`(21) Appl. No.: 11/852,748
`(22) Filed:
`Sep. 10, 2007
`
`(*) Notice:
`
`(65)
`
`Prior Publication Data
`US 2008/O160306 A1
`Jul. 3, 2008
`
`Related U.S. Application Data
`(63) Continuation-in-part of application No. 1 1/579,050,
`filed on Oct. 27, 2006.
`Foreign Application Priority Data
`(30)
`Apr. 30, 2004
`(GB) ................................. O4O9877.8
`Apr. 27, 2005
`(GB) ............... PCT/GB2005/OO1611
`
`(51) Int. Cl.
`(2006.01)
`B32B5/66
`(52) U.S. Cl. ....................... 428/403; 428/404; 428/405:
`428/406; 427/212
`(58) Field of Classification Search ................. 428/403,
`428/404, 405, 406; 427/212
`See application file for complete search history.
`References Cited
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`(Continued)
`Primary Examiner Leszek Kiliman
`(74) Attorney, Agent, or Firm Goodwin Procter LLP
`(57)
`ABSTRACT
`
`Nanoparticles including a molecular cluster compound incor
`porating ions from groups 12 and 16 of the periodic table, as
`well as a core semiconductor material incorporating ions
`from groups 13 and 15 of the periodic table, are fabricated.
`The core semiconductor material is provided on the molecu
`lar cluster compound.
`
`14 Claims, 4 Drawing Sheets
`
`

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`US 7,588,828 B2
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`
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`1.
`PREPARATION OF NANOPARTICLE
`MATERALS
`
`RELATED APPLICATIONS
`
`The present application is a continuation-in-part of U.S.
`application Ser. No. 1 1/579,050, filedon Oct. 27, 2006, which
`is the U.S. national stage application of International (PCT)
`Patent Application Serial No. PCT/GB2005/001611, filed
`Apr. 27, 2005, which claims the benefit of GB Application
`No. 0409877.8, filed Apr. 30, 2004. The entire disclosure of
`each of these applications is hereby incorporated by refer
`CCC.
`
`BACKGROUND
`
`10
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`15
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`2
`Single-core semiconductor nanoparticles, which generally
`consist of a single semiconductor material along with an outer
`organic passivating layer, tend to have relatively low quantum
`efficiencies due to non-radiative electron-hole recombination
`occurring at defects and dangling bonds situated on the nano
`particle surface. FIG. 1A schematically depicts an indium
`phosphide (InP) single-core nanoparticle 100 with a core 110
`including InP and an organic passivation layer 120. The
`hydrocarbon chains of passivation layer 120 promote mono
`dispersity of a group of nanoparticles in Solution.
`One method to eliminate defects and dangling bonds is
`growth of a second inorganic material, having a wider band
`gap and Small lattice mismatch to that of the core material,
`epitaxially on the Surface of the core particle to produce a
`“core-shell' nanoparticle. Core-shell nanoparticles separate
`any carriers confined in the core from Surface states that
`would otherwise act as non-radiative recombination centers.
`Small lattice mismatch between the core and shell materials
`also minimizes non-radiative recombination. One example of
`a core-shell nanoparticle is ZnS grown on the surface of CdSe
`cores. FIG. 1B schematically depicts a core-shell nanopar
`ticle 140 with a core 150 including InP and a shell 160
`including ZnS.
`Another approach is the formation of a core-multi shell
`structure where the electron-hole pair is completely confined
`to a single shell layer. In these structures, the core is of a wide
`bandgap material, Surrounded by a thin shell of narrower
`bandgap material, and capped with a further wide bandgap
`layer, such as CdS/HgS/CdS. In such a structure, a few mono
`layers of mercury sulfide (HgS) are formed on the surface of
`the core CdS nanocrystal and then capped by additional CdS.
`The resulting structures exhibit clear confinement of photo
`excited carriers in the narrower bandgap HgSlayer. FIG. 1C
`schematically depicts a multi-shell nanoparticle 170 with a
`core 180 including InP, a shell 190 including ZnSe, and an
`outer shell 195 including ZnS. FIG. 2 schematically depicts a
`nanoparticle 200 coated with a capping layer 210 having a
`head group 220 (bonded to the nanoparticle) and hydrocarbon
`chains 230.
`The outermost layer of organic material (i.e., the capping
`agent) or sheath material helps to inhibit particle aggregation,
`and further protects the nanoparticle from the Surrounding
`chemical environment. It also may provide a means of chemi
`cal linkage to other inorganic, organic, or biological material.
`In many cases, the capping agent is the solvent in which the
`nanoparticle preparation is undertaken, and consists of a
`Lewis base compound or a Lewis base compound diluted in a
`inert solvent Such as a hydrocarbon. The capping agent
`includes alone pair of electrons that are capable of donor-type
`coordination to the Surface of the nanoparticle, and may
`include mono- or multi-dentate ligands of the types: phos
`phines (trioctylphosphine, triphenolphosphine, t-butylphos
`phine), phosphine oxides (trioctylphosphine oxide), alkyl
`phosphonic acids, alkyl-amine (hexadecylamine, octy
`lamine), aryl-amines, pyridines, long chain fatty acids, and
`thiophenes. Other types of materials may also be appropriate
`capping agents.
`The outermost layer (capping agent) of a quantum dot may
`also consist of a coordinated ligand that processes additional
`functional groups that can be used as chemical linkage to
`other inorganic, organic or biological material. In such a case,
`the functional group may point away from the quantum dot
`surface and is available to bond/react with other available
`molecules, such as primary, secondary amines, alcohols, car
`boxylic acids, azides, or hydroxyl groups. The outermost
`layer (capping agent) of a quantum dot may also consist of a
`
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`45
`
`There has been substantial interest in the preparation and
`characterization of compound semiconductors in the form of
`particles with dimensions in the order of 2-50 nanometers
`(nm), often referred to as quantum dots, nanoparticles, or
`nanocrystals. Interest has arisen mainly due to the size-related
`electronic properties of these materials that can be exploited
`in many commercial applications such as optical and elec
`tronic devices, biological labeling, Solar cells, catalysis, bio
`logical imaging, light-emitting diodes, general space light
`ing, and electroluminescent and photoluminescent displays.
`Two fundamental factors, both related to the size of the
`individual semiconductor nanoparticle, are responsible for
`their unique properties. The first is the large Surface-to-Vol
`ume ratio: as a particle becomes Smaller, the ratio of the
`number of surface atoms to that in the interior increases. This
`leads to the Surface properties playing an important role in the
`overall properties of the material. The second factor is the
`change in the electronic properties of the material with size,
`e.g., the band gap gradually becomes larger because of quan
`tum confinement effects as the size of the particle decreases.
`This effect is a consequence of increased carrier confinement
`giving rise to discrete energy levels similar to those observed
`in atoms and molecules, rather than the continuous band of
`40
`the corresponding bulk semiconductor material. Thus, for a
`semiconductor nanoparticle, because of the physical param
`eters, the carriers (i.e., electrons and holes) produced by the
`absorption of electromagnetic radiation (i.e., a photon) with
`energy greater then the first excitonic transition, are closer
`together than in the corresponding bulk (or macrocrystalline)
`material. So that the coulombic interaction cannot be
`neglected. This leads to a narrow bandwidth emission, which
`is dependent upon the particle size and composition. Thus,
`quantum dots have higher kinetic energy than the correspond
`ing macrocrystalline material and, consequently, the first
`excitonic transition (i.e., the bandgap) increases in energy
`with decreasing particle diameter.
`Among the most studied semiconductor quantum dot
`materials have been the chalcogenide II-VI materials, namely
`Zinc sulfide (ZnS), zinc selenide (ZnSe), cadmium sulfide
`(CdS), cadmium selenide (CdSe), cadmium telluride (CdTe).
`Reproducible quantum dot production methods have been
`developed from “bottom-up' techniques, whereby particles
`are prepared atom-by-atom, i.e. from molecules to clusters to
`particles, using wet chemical procedures. The coordination
`about the final inorganic Surface atoms in any nanoparticle
`may be incomplete, with highly reactive non-fully coordi
`nated atomic “dangling bonds on the Surface of the particle,
`which can lead to particle agglomeration. This problem may
`be overcome by passivating (e.g., capping) the bare surface
`atoms with protective organic groups.
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`3
`coordinated ligand, processing a functional group that is
`polymerizable, which may be used to form a polymer around
`the particle.
`The outermost layer (capping agent) may also consist of
`organic units that are directly bonded to the outermost inor
`ganic layer, and may also process a functional group, not
`bonded to the surface of the particle, that may be used to form
`a polymer around the particle.
`Important issues related to the synthesis of high-quality
`semiconductor nanoparticles are particle uniformity, size dis
`tribution, quantum efficiencies, long-term chemical stability,
`and long-term photostability. Early routes applied conven
`tional colloidal aqueous chemistry, with more recent methods
`involving the kinetically controlled precipitation of nanocrys
`tallites, using organometallic compounds.
`
`5
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`4
`In an embodiment, the nanoparticle includes a first layer
`including a first semiconductor material provided on the
`nanoparticle core. The first semiconductor material may
`incorporate ions from group 12 of the periodic table, e.g., Zinc
`ions, and/or from group 16, e.g., at least one member of the
`group consisting of oxide ions, Sulfide ions, selenide ions, and
`telluride ions. A second layer including a second semicon
`ductor material may be provided on the first layer.
`In a second aspect, the invention features a method for
`producing nanoparticles including the steps of providing a
`nanoparticle precursor composition including group 13 ions
`and group 15 ions, and effecting conversion of the nanopar
`ticle precursor into nanoparticles. The conversion is effected
`in the presence of a molecular cluster compound incorporat
`ing group 12 ions and group 16 ions under conditions permit
`ting nanoparticle seeding and growth.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the drawings, like reference characters generally refer to
`the same parts throughout the different views. Also, the draw
`ings are not necessarily to scale, emphasis instead generally
`being placed upon illustrating the principles of the invention.
`In the following description, various embodiments of the
`present invention are described with reference to the follow
`ing drawings, in which:
`FIGS. 1A-1C schematically depict exemplary single-core,
`core-shell, and multi-shell nanoparticles;
`FIG. 2 schematically depicts a nanoparticle coated with a
`capping layer;
`FIG. 3 schematically depicts the formation of a nanopar
`ticle using a molecular seed, capping agent, and precursors;
`and
`FIGS. 4A-4E schematically depict various exemplary
`molecular clusters that may be utilized as seeding templates
`for nanoparticle formation.
`
`DETAILED DESCRIPTION
`
`Embodiments of the invention involve the large-scale syn
`thesis of III-V quantum dots (nanoparticles) whereby a seed
`ing molecular cluster is placed in a solvent (coordinating or
`otherwise) in the presence of other precursors to initiate par
`ticle growth. Moreover, the seeding molecular cluster is
`employed as a template to initiate particle growth from other
`precursors present within the reaction solution. The molecu
`lar cluster used as a seed can either consist of the same
`elements as those required in the Subsequent quantum dot or
`different elements that are not required in the final quantum
`dots but facilitate the seeding process. In accordance with
`embodiments of the current invention, the molecular cluster
`to be used as the seeding agent is either prefabricated or
`produced in situ prior to acting as a seeding agent. In accor
`dance with embodiments of the invention, Some precursors
`may not be present at the beginning of the reaction process
`along with the molecular cluster; however, as the reaction
`proceeds and the temperature is increased, additional
`amounts of precursors are periodically added to the reaction
`either drop-wise as a solution or as a Solid.
`In various embodiments of the invention, the formation of
`nanoparticles from the precursor(s) is carried out under con
`ditions to ensure that, either there is direct reaction and
`growth between the precursor composition and the molecular
`cluster, or some clusters grow at the expense of others (due to
`Ostwald ripening) until reaching a certain size at which there
`is direct growth of the nanoparticle from the precursor(s).
`
`SUMMARY OF THE INVENTION
`
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`In accordance with embodiments of the invention, conver
`sion of a precursor composition to nanoparticles is effected in
`the presence of a molecular cluster compound. Molecules of
`the cluster compound act as a seed or nucleation point upon
`which nanoparticle growth may be initiated. In this way, a
`high-temperature nucleation step is not required to initiate
`nanoparticle growth because Suitable nucleation sites are
`already provided in the system by the molecular clusters. The
`molecules of the cluster compound act as a template to direct
`nanoparticle growth. “Molecular cluster' is a term which is
`widely understood in the relevant technical field, but for the
`sake of clarity should be understood herein to relate to clus
`ters of three or more metal atoms and their associated ligands
`of sufficiently well-defined chemical structure such that all
`molecules of the cluster compound possess approximately
`the same relative molecular formula. (When the molecules
`possess the same relative molecular formula, the molecular
`clusters are identical to one another in the same way that one
`HO molecule is identical to another HO molecule.) The
`molecular clusters act as nucleation sites and are much better
`defined than the nucleation sites employed in other methods.
`The use of a molecular cluster compound may provide a
`population of nanoparticles that are essentially monodis
`perse. A significant advantage of this method is that it can be
`more easily scaled-up to production Volumes when compared
`to other methods of nanoparticle generation. Methods of pro
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`ducing Suitable molecular cluster compounds are known
`within the art, examples of which can be found at the Cam
`bridge Crystallographic Data Centre (www.cccdc.ca.ac.uk).
`Accordingly, in a first aspect, the invention features a nano
`particle including a molecular cluster compound incorporat
`ing ions from groups 12 and 16 of the periodic table, as well
`as a core semiconductor material incorporating ions from
`groups 13 and 15 of the periodic table provided on the
`molecular cluster compound. The molecular cluster com
`pound and the core semiconductor material may have com
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`patible crystal phases, and the molecular cluster compound
`may incorporate Zinc ions.
`Various embodiments of the invention incorporate one or
`more of the following features. The group 16 ions may
`include at least one member of the group consisting of oxide
`ions, sulfide ions, selenide ions, and telluride ions. The group
`13 ions may include at least one member of the group con
`sisting of aluminum ions, gallium ions, and indium ions. The
`group 15 ions may include at least one member of the group
`consisting of nitride ions, arsenide ions, and antimonide ions.
`The nanoparticle may exhibit a quantum efficiency ranging
`from about 20% to about 60%.
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`US 7,588,828 B2
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`ticle growth but not so high as to damage the integrity of the
`cluster compound molecules. For example, the growth initia
`tion temperature may be within the range of approximately
`100° C. to approximately 350° C. As the temperature is
`increased, further quantities of the precursor may be added to
`the reaction in a drop-wise manner (i.e., in liquid form) or as
`a solid. The temperature of the solution may then be main
`tained at the formation temperature (or within the formation
`temperature range) for as long as required to form nanopar
`ticles possessing the desired properties.
`A wide range of appropriate solvents is available. The
`choice of Solvent used may depend upon the nature of the
`reacting species, i.e. the nanoparticle precursor and/or cluster
`compound, and/or the type of nanoparticles which are to be
`formed. Typical Solvents include Lewis base-type coordinat
`ing solvents, such as a phosphine (e.g., tri-n-octylphosphine
`(TOP)), a phosphine oxide (e.g., tri-n-octylphosphine oxide
`(TOPO)), an amine (e.g., hexadecylamine (HDA)), a thiol
`Such as octanethiol, or a non-coordinating organic solvent,
`e.g. an alkane or an alkene. If a non-coordinating solvent is
`used, it will usually be in the presence of an additional coor
`dinating agent to act as a capping agent. The reason is that
`capping of nanoparticle Surface atoms which are not fully
`coordinated, i.e., have dangling bonds, serves to minimize
`non-radiative electron-hole recombination and inhibit par
`ticle agglomeration (which can lower quantum efficiencies).
`A number of different coordinating solvents may also act as
`capping or passivating agents, e.g. TOP TOPO, organo-thi
`ols, long-chain organic acids Such as myristic acid, long chain
`amines, or functionalized PEG chains. If a solvent is used
`which does not act as a capping agent, then any desirable
`capping agent may be added to the reaction mixture during
`nanoparticle growth. Such capping agents are typically Lewis
`bases, but a wide range of other agents is available. Such as
`oleic acid or organic polymers which form protective sheaths
`around the nanoparticles.
`In accordance with embodiments of the invention, III-V
`nanoparticles are produced using molecular clusters, which
`may be collections of identical molecules (rather than
`ensembles of Small nanoparticles which may lack the anony
`mous nature of molecular clusters). Molecular clusters can
`either have the same elements as required in the nanoparticles
`to be formed, or other elements, as long as they can facilitate
`a seeding reaction. For example, III-V molecular clusters are
`notoriously difficult to produce, but many types of II-VI
`molecular clusters may be produced relatively easily. More
`over, it is possible to use a II-VI molecular cluster, such as
`HNEtaZnS,(SPh), to seed the growth of III-V mate
`rials, such as InP and gallium phosphide (GaP) and their
`alloys, in nanoparticle form. Other molecular compounds,
`herein referred to as "molecular feedstocks.” may be added
`and consumed to facilitate particle growth. These molecular
`Sources may be periodically added to the reaction solution to
`keep the concentration of free ions to a minimum but also
`maintain a concentration of free ions to inhibit Ostwald rip
`ening and defocusing of nanoparticle size range.
`Nanoparticle growth may be initiated by heating (ther
`molysis), or by Solvothermal methods. (AS used herein, Sol
`Vothermal refers to heating in a reaction solution so as to
`initiate and Sustain particle growth, and may also be referred
`to as thermolsolvol. Solution-pyrolysis, or lyothermal meth
`ods.) Particle preparation may also include changing of the
`reaction conditions such as adding a base or an acid (i.e.,
`changing the pH of the mixture), pressure change (e.g., using
`pressures much greater than atmospheric pressure), or utiliz
`ing microwave or other electromagnetic radiation.
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`Such conditions ensure that the monodispersity of the cluster
`compound is maintained throughout nanoparticle growth,
`which in turn ensures that a monodisperse population of
`nanoparticles is obtained.
`Any suitable molar ratio of the molecular cluster com
`pound to, e.g., first and second nanoparticle precursors may
`be used, and may depend upon the structure, size and com
`position of the nanoparticles being formed. The desired ratio
`may also depend upon the nature and concentration of the
`other reagents, such as the nanoparticle precursor(s), the cap
`ping agent, size-directing compounds, and/or solvents. In
`embodiments utilizing first and second precursors, ratios of
`the number of moles of the molecular cluster compound to the
`total number of moles of the first and second precursor spe
`cies may be in the range 0.0001-0.1 (no. moles of cluster
`compound): 1 (total no. moles of first and second precursor
`species), 0.001-0.1:1, or 0.001-0.060:1. The ratios of the
`number of moles of the molecular cluster compound to the
`total number of moles of the first and second precursor spe
`cies may lie in the range 0.002-0.030:1, or 0.003-0.020:1. In
`preferred embodiments, the ratio of the number of moles of
`the molecular cluster compound to the total number of moles
`of the first and second precursor species may lie in the range
`O.OO35-OOO45:1.
`Any Suitable molar ratio of a first precursor species to a
`second precursor species may be used. For example, the
`molar ratio of the first precursor species to the second precur
`Sor species may lie in the range 100-1 (first precursor spe
`cies): 1 (second precursor species), or 50-1:1. The molar ratio
`of the first precursor species to the second precursor species
`may even lie in the range 40-5:1, or 30-10:1. In various
`embodiments, approximately equal molar amounts of the first
`and second precursor species are used. The molar ratio of the
`first precursor species to the second precursor species may lie
`in the range 0.1-1.2:1, 0.9-1.1:1, or 1:1. In some embodi
`35
`ments, it is appropriate to use approximately twice the num
`ber of moles of one precursor species than that of the other
`precursor species. Thus, the molar ratio of the first precursor
`species compared to the second precursor species may lie in
`the range 0.4–0.6:1, or, in a preferred embodiment, 0.5:1.
`Various embodiments of the invention concern the conver
`sion of a nanoparticle precursor composition to a desired
`nanoparticle. Suitable precursors include single-source pre
`cursors which comprise the two or more ions to be incorpo
`rated into the growing nanoparticle, or multi-source precur
`sors in which two or more separate precursors each cont