(12) Patent Application Publication (10) Pub. No.: US 2010/0283005 A1 Pickett Et Al
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US 2010O283 005A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2010/0283005 A1 Pickett et al. (43) Pub. Date: Nov. 11, 2010 (54) NANOPARTICLES AND THEIR Publication Classification MANUFACTURE (51) Int. Cl. (75) Inventors: Nigel Pickett, London (GB); C09K II/70 (2006.01) Steven Daniels, Manchester (GB); C09K II/62 (2006.01) Imrana Mushtaq, Manchester C09K II/56 (2006.01) (GB) s C09K II/54 (2006.01) HOIL 3.3/04 (2010.01) Correspondence Address: HOIL 2L/20 (2006.01) GOODWIN PROCTER LLP (52) U.S. Cl. ...... 252/301.6 S; 252/301.6 P; 252/301.4 P: PATENT ADMINISTRATOR 252/301.6 R; 257/13:438/104;977/773; 53 STATE STREET, EXCHANGE PLACE 977/774; 257/E33.005; 257/E21.09 BOSTON, MA 02109-2881 (US) (73) Assignee: NANOCOTECHNOLOGIES (57)57 ABSTRACT LIMITED, Manchester (GB) Nanoparticles include or consist essentially of (i) a core that itself includes or consists essentially of a first material, and (21) Appl. No.: 12/239,254 (ii) a layer including or consisting essentially of a second material. In various embodiments, one of the first and second (22) Filed: Sep. 26, 2008 materials is a semiconductor material incorporating ions from O O group 13 and group 15 of the periodic table, and the other of Related U.S. Application Data the first and second materials is a metal oxide material incor (60) Provisional application No. 60/980.946, filed on Oct. porating metal ions selected from any one of groups 1 to 12, 18, 2007. 14 and 15 of the periodic table. In other embodiments, one of s the first and second materials is a semiconductor material, and (30) Foreign Application Priority Data the other of the first and second materials is an oxide of a metal selected from any one of groups 3 to 10 of the periodic Sep. 28, 2007 (GB) ................................... O719073.9 table. Methods for preparing Such nanoparticles are also Sep. 28, 2007 (GB) ................................... O719075.4 described. Patent Application Publication Nov. 11, 2010 Sheet 1 of 5 US 2010/0283005 A1 HYDROCARBON CHAIN Patent Application Publication Nov. 11, 2010 Sheet 2 of 5 US 2010/0283005 A1 s - - y n -ZnO - N. n > - se f w f y w - ?. - / f as s Fe2O3 FIG. 4 Patent Application Publication Nov. 11, 2010 Sheet 3 of 5 US 2010/0283005 A1 700000 6OOOOO InPlln2O3 5 O O O OO 4OOOOO 3OOOOO 2OOOOO OOOOO O m 350 450 550 650 750 850 950 WAVELENGTH(nm) FIG. 5 Patent Application Publication Nov. 11, 2010 Sheet 4 of 5 US 2010/0283005 A1 400 450 500 550 600 650 700 WAVELENGTH(nm) FIG. 6 Patent Application Publication Nov. 11, 2010 Sheet 5 of 5 US 2010/0283005 A1 CdSely-Fe2O3 CdSe 20 30 40 50 60 70 2-theta (degrees) FIG. 7 US 2010/0283005 A1 Nov. 11, 2010 NANOPARTICLES AND THEIR responding macrocrystalline material and consequently the MANUFACTURE first excitonic transition (band-gap) increases in energy with decreasing particle diameter. CROSS-REFERENCE TO RELATED 0006 Single-core semiconductor nanoparticles, which APPLICATIONS involve a single semiconductor material along with an outer organic passivating layer, may have relatively low quantum 0001. This application claims priority to and the benefit of and incorporates herein by reference in their entireties, U.S. efficiencies due to electron-hole recombination occurring at Provisional Patent Application No. 60/980.946, filed on Oct. defects and dangling bonds situated on the nanoparticle Sur 18, 2007; U.K. Patent Application No. 0719073.9, filed on face (which lead to non-radiative electron-hole recombina Sep. 28, 2007; and U.K. Patent Application No. 0719075.4, tions). filed on Sep. 28, 2007. 0007. One method to eliminate defects and dangling bonds is to grow a second inorganic material, having a wider band-gap and Small lattice mismatch to that of the core mate FIELD OF THE INVENTION rial, epitaxially on the Surface of the core particle to produce 0002 The present invention relates to semiconductor a “core-shell' particle. Core-shell particles separate any car nanoparticles and techniques for their production. riers confined in the core from surface states that would otherwise act as non-radiative recombination centres. One example is ZnS grown on the surface of a CdSe core to BACKGROUND provide a CdSe/ZnS core/shell nanoparticle. 0003. There has been substantial interest in the prepara 0008 Another approach is to prepare a core/multi-shell tion and characterisation of compound semiconductors com structure where the “electron-hole' pair is completely con prising particles with dimensions, for example in the range fined to a single shell layer Such as the quantum dot-quantum 2-50 nm, often referred to as 'quantum dots or nanocrystals. well structure. Here, the core is of a wide bandgap material, These studies have occurred mainly due to the size-tuneable followed by a thin shell of narrower bandgap material, and electronic properties of these materials that may be exploited capped with a further wide bandgap layer, such as CdS/HgS/ in many commercial applications such as optical and elec CdS grown using a substitution of Hg for Cd on the surface of tronic devices and other applications that now range from the core nanocrystal to depositjust a few monolayers of HgS. biological labelling, Solar cells, catalysis, biological imaging, The resulting structures exhibited clear confinement of light-emitting diodes, general space lighting and both elec photo-excited carriers in the HgSlayer. troluminescence and photoluminescence displays amongst 0009. The coordination about the final inorganic surface many new and emerging applications. atoms in any core, core-shell or core-multi shell nanoparticle 0004. The most studied of semiconductor materials have is generally incomplete, with highly reactive atoms that are been the chalcogenide II-VI (i.e., group 12-group 16 of the not fully coordinated leaving "dangling bonds on the Surface periodic table) materials, such as ZnS, ZnSe, CdS, CdSe and of the particle, which may lead to particle agglomeration. CdTe. CdSe has been greatly studied due to its optical tune This problem is overcome bypassivating (capping) the "bare ability over the visible region of the spectrum. Although some Surface atoms with protecting organic groups. earlier examples appear in the literature, more recently, repro 0010. The outermost layer (capping agent) of organic ducible methods have been developed from “bottom up' material or sheath material helps to inhibit particle aggrega techniques, whereby particles are prepared atom-by-atom tion and also further protects the nanoparticle from its Sur using 'wet' chemical procedures. rounding chemical environment. It also provides chemical 0005. Two fundamental factors, both related to the size of linkage to other inorganic, organic or biological material. In the individual semiconductor nanoparticle, are responsible many cases, the capping agent is the solvent in which the for the unique properties of these particles. The first is the nanoparticle preparation is undertaken, and may be a Lewis large Surface-to-volume ratio: as a particle becomes Smaller, base compound, or a Lewis base compound diluted in an inert the ratio of the number of surface atoms to those in the interior Solvent, such as a hydrocarbon, whereby a lone pair of elec increases. This leads to the Surface properties playing an trons are capable of donor-type coordination to the Surface of important role in the overall properties of the material. The the nanoparticle. second factor is that, with semiconductor nanoparticles, there 0011 Important issues concerning the synthesis of high is a change in the electronic properties of the material with quality semiconductor nanoparticles include particle unifor size; for example, the band-gap gradually becomes larger mity, size distribution, quantum efficiencies, and, for com because of quantum confinement effects as the size of the mercial applications, long-term chemical and photostability. particles decreases. This effect gives rise to discrete energy Early routes applied conventional colloidal aqueous chemis levels similar to those observed in atoms and molecules, try, with more recent methods involving the kinetically con rather than a continuous band as in the corresponding bulk trolled precipitation of nanocrystallites, using organometallic semiconductor material. Thus, for a semiconductor nanopar compounds. Most of the more recent methods are based on ticle, because of the physical parameters, the “electron and the original “nucleation and growth' method described by hole', produced by the absorption of electromagnetic radia Murray et al., J. Am. Chem. Soc. 115:8706 (1993) (hereafter tion (a photon) with energy greater then the first excitonic “Murray et al.”), the entire disclosure of which is incorporated transition, are closer together than in the corresponding mac by reference herein, but use other precursors from that of the rocrystalline material, so that the Coulombic interaction can organometallic ones originally used, such as oxides (e.g., not be neglected. This leads to a narrow bandwidth emission, CdO), carbonates (e.g., MCO), acetates (e.g., M(CHCO)) which is dependent upon the particle size and composition. and acetylacetanates (e.g., MICHCOOCH=C(C )CH) Thus, quantum dots have higher kinetic energy than the cor in which, for example, M=Cd or Zn. US 2010/0283005 A1 Nov. 11, 2010 0012 Murray et al. originally used organometallic solu (0016 Strouse et al., Chem. Mater. 14:1576 (2002) (here tions of metal-alkyls (RM) where M-Cd, Zn, Te: R=Me, Et after “Strouse et al.”), the entire disclosure of which is incor and tri-n-octylphosphine sulfide/selenide (TOPS/Se) dis porated by reference herein, used a similar synthetic approach solved in tri-n-octylphosphine (TOP). These precursor solu using II-VI clusters to grow II-VI nanoparticles, but tions are injected into hot tri-n-octylphosphine oxide (TOPO) employed thermolysis (lyothermal) rather than a chemical in the temperature range 120-400° C.