Processes for synthesizing nanocrystals

Abstract

A process of synthesizing GaSe nanocrystals is provided, the process including: contacting a first precursor containing gallium with a second precursor containing selenium to obtain a GaSe single precursor; and reacting the GaSe single precursor in a solvent in the presence of a ligand compound, and optionally with a third precursor including an element (A) other than gallium and selenium, to prepare a GaSe nanocrystal represented by Chemical Formula 1:
GaSe.sub.xA.sub.y[Chemical Formula 1] wherein x is about 1.1 to 3, and y is about 0.1 to 4.

Claims

1. A nanoparticle including a nanocrystal of a compound represented by Chemical Formula 1:
GaSe.sub.xA.sub.y[Chemical Formula 1] wherein x is greater than or equal to about 1.1 and less than 1.5, y is about 0.1 to 4, and A is S, Te, N, P, As, Al, In, Zn, Cd, Mg, Mn, Ag, or Au.

2. The nanoparticle of claim 1, wherein x is greater than or equal to about 1.2.

3. The nanoparticle of claim 1, wherein the A is S, Te, N, P, As, Al, Zn, Cd, Mg, Mn, Ag, or Au.

4. The nanoparticle of claim 1, wherein the nanoparticle has a core shell structure comprising a first nanocrystal and the nanocrystal of the compound represented by Chemical Formula 1 is disposed on a surface of the first nanocrystal.

5. The nanoparticle of claim 4, wherein the first nanocrystal comprises a Group II-VI compound, a Group III-V compound, a Group IV-VI compound, or a combination thereof.

6. The nanoparticle of claim 5, wherein the Group III-V compound further includes a Group II metal.

7. The nanoparticle of claim 4, wherein the first nanocrystal comprises a Group III-V semiconductor nanocrystal core.

8. The nanoparticle of claim 4, wherein the first nanocrystal is a core-shell type semiconductor nanocrystal.

9. The nanoparticle of claim 4, wherein the first nanocrystal comprises ZnS, ZnSe, ZnTe, ZnO, MgSe, MgS, ZnSeS, ZnSeTe, ZnSTe, MgZnSe, MgZnS, GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InZnP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, SnS, SnSe, SnTe, SnSeS, SnSeTe, SnSTe, or a combination thereof.

10. The nanoparticle of claim 4, wherein the nanoparticle further comprises a Group II-VI semiconductor nanocrystal shell that is disposed on the nanocrystal of a compound represented by Chemical Formula 1.

11. The nanoparticle of claim 10, wherein the Group II-VI semiconductor nanocrystal shell comprises ZnS, ZnSe, ZnTe, ZnO, MgSe, MgS, ZnSeS, ZnSeTe, ZnSTe, MgZnSe, MgZnS, or a combination thereof.

12. The nanoparticle of claim 1, wherein the nanoparticle has a particle diameter ranging from about 1 nm to about 100 nm.

13. The nanoparticle of claim 1, wherein the nanoparticle has a particle diameter of less than or equal to about 20 nm.

14. The nanoparticle of claim 1, wherein the nanoparticle comprises a ligand compound coordinated to a surface thereof and the ligand compound comprises RCOOH, RNH.sub.2, R.sub.2NH, R.sub.3N, RSH, R.sub.3PO, R.sub.3P, ROH, RCOOR, RCOOCOR, or a combination thereof, wherein R and R are each independently a C1 to C24 alkyl group, a C2 to C24 alkenyl group, or a C5 to C24 aryl group.

15. A nanoparticle including a nanocrystal of the compound represented by Chemical Formula 1-1:
GaSe.sub.x[Chemical Formula 1-1] wherein x is greater than or equal to about 1.1 and less than or equal to about 1.36, and wherein the nanoparticle has a zinc blend crystal structure, when determined by X-ray diffraction.

16. The nanoparticle of claim 15, wherein the nanoparticle has a core shell structure comprising a first nanocrystal and the nanocrystal of the compound represented by Chemical Formula 1-1 is disposed on a surface of the first nanocrystal.

17. The nanoparticle of claim 15, wherein the nanoparticle has a particle diameter of less than or equal to about 20 nm.

18. The nanoparticle of claim 15, wherein the nanoparticle comprises a ligand compound coordinated to a surface thereof, and the ligand compound comprises RCOOH, RNH.sub.2, R.sub.2NH, R.sub.3N, RSH, R.sub.3PO, R.sub.3P, ROH, RCOOR, RCOOCOR, or a combination thereof, wherein R and R are each independently a C1 to C24 alkyl group, a C2 to C24 alkenyl group, or a C5 to C24 aryl group.

19. The nanoparticle of claim 16, wherein the nanoparticle further comprises a Group II-VI semiconductor nanocrystal shell that is disposed on the nanocrystal of a compound represented by Chemical Formula 1-1.

Description

DESCRIPTION OF DRAWINGS

(1) These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a view schematically illustrating a nanocrystal particle of a multishell structure in accordance with an embodiment;

(3) FIG. 2 shows an H NMR result of a GaSe single precursor obtained by mixing trimethyl gallium and Se/TBP.

(4) FIG. 3 shows a P NMR result of a GaSe single precursor obtained by mixing trimethyl gallium and Se/DPP.

(5) FIG. 4 shows an X-ray diffraction spectrum of the Ga.sub.2Se.sub.3 nanocrystal synthesized in Example 1.

(6) FIG. 5 shows X-ray diffraction spectrums of the Ga.sub.2Se.sub.3 nanocrystals synthesized in Example 2 and Example 3.

BEST MODE

(7) This disclosure will be described more fully hereinafter in the following detailed description, in which some but not all embodiments of this disclosure are described. This disclosure may be embodied in many different forms and is not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will fully convey the scope of the invention to those skilled in the art. Thus, in some exemplary embodiments, well known technologies are not specifically explained to avoid ambiguous understanding of the present invention. Unless otherwise defined, all terms used in the specification (including technical and scientific terms) may be used with meanings commonly understood by a person having ordinary knowledge in the art. Further, unless explicitly defined to the contrary, the terms defined in a generally-used dictionary are not ideally or excessively interpreted. In addition, unless explicitly described to the contrary, the word comprise and variations such as comprises or comprising will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

(8) Unless specifically described to the contrary, a singular form includes a plural form.

(9) As used herein, the term and/or includes any and all combinations of one or more of the associated listed items. Expressions such as at least one of, when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

(10) It will be understood that when an element is referred to as being on another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being directly on another element, there are no intervening elements present.

(11) It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the present embodiments.

(12) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms a, an, and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. Unless specified otherwise, the term or means and/or.

(13) A process of synthesizing nanocrystals according to an embodiment includes:

(14) contacting a first precursor containing gallium with a second precursor containing selenium to obtain a GaSe single precursor; and

(15) reacting the GaSe single precursor in a solvent in the presence of a ligand compound, and optionally with a third precursor including an element (A) other than gallium and selenium, to prepare a GaSe nanocrystal represented by Chemical Formula 1:
GaSe.sub.xA.sub.y[Chemical Formula 1]

(16) wherein x is about 1.1 to 3, for example about 1.2 to 2.5, and y is about 0.1 to 4.

(17) The element (A) other than gallium and selenium may be S, Te, N, P, As, Al, In, Zn, Cd, Mg, Mn, Cu, Ag, Au, or a combination thereof.

(18) In the aforementioned method, the first precursor containing gallium and the second precursor containing selenium may be mixed prior to being introduced into a reaction system to generate a weak interaction of a bond between the Ga atoms and the Se atoms, and the product therefrom is used as a single precursor, and thereby it becomes easier to control the ratio between the gallium atoms and the selenium atoms in the GaSe nanocrystal. The first precursor may be a trialkyl gallium such as trimethyl gallium and triethyl gallium; gallium acetylacetonates a gallium halide such as gallium chloride and gallium iodide; a gallium oxide; a gallium alkoxide such as gallium ethoxide and gallium isopropoxide; or a combination thereof. The second precursor may be a complex of selenium with a compound selected from a dialkylphosphine, a diarylphosphine, a trialkylphosphine, a trialkylphosphine oxide, and a combination thereof, a bis(trialkylsilyl)selenide, or a combination thereof. For example, the second precursor may be selenium-diphenylphosphine (DPP), selenium-trioctylphosphine (Se-TOP), selenium-tributylphosphine (Se-TBP), selenium-triphenylphosphine (Se-TPP), bis(trimethyl silyl)selenide, bis(triethyl silyl)selenide, or a combination thereof.

(19) When the gallium precursor and the selenium precursor do not form a single precursor but they are introduced separately into a reaction system to perform a reaction, it is very difficult for the resulting nanocrystal to have a desired ratio between the gallium atoms and the selenium atoms. In contrast, in the aforementioned method, the GaSe single crystal is first formed and then subjected to a reaction, and thereby it becomes possible to obtain a GaSe nanocrystal having a desired ratio between the gallium atoms and the selenium atoms by controlling reaction conditions such as the ligand, the solvent, the reaction temperature, and the like. Contacting the first precursor containing gallium with the second precursor containing selenium may be accomplished by mixing the two precursors. The contacting may be conducted under an inert atmosphere (e.g., in a glove box), for example, at room temperature.

(20) The GaSe single precursor may be subjected to a reaction in a solvent in the presence of a ligand compound and optionally with a third precursor including an element (A) other than gallium and selenium, to form a nanocrystal of a compound represented by Chemical Formula 1:
GaSe.sub.xA.sub.y[Chemical Formula 1]

(21) wherein x, y, and A are the same as defined above.

(22) In the GaSe nanocrystal, the ratio between Ga and Se may be adjusted by controlling the types and the amount of the gallium precursor and the selenium precursor used in the single precursor, the types of the ligand compound in the reaction system, the types of the solvent, and the like. In an embodiment, the nanocrystal of the compound represented by Chemical Formula 1 may be a compound represented by Chemical Formula 1-1:
GaSe.sub.x[Chemical Formula 1-1]

(23) wherein x is the same as defined above.

(24) In a non-limiting example, the GaSe nanocrystal thus prepared may be a Ga.sub.2Se.sub.3 nanocrystal. In a non-limiting example, the GaSe nanocrystal thus prepared may have a zinc blend structure, which may be identified by an X-ray diffraction spectrum of the nanocrystal thus prepared.

(25) The solvent may be an organic solvent. The solvent may include a C6 to C22 primary alkyl amine such as hexadecylamine, a C6 to C22 secondary alkyl amine such as dioctylamine, a C6 to C40 tertiary alkyl amine such as trioctylamine, a heterocyclic compound having a nitrogen atom such as pyridine, a C6 to C40 olefin such as octadecene, a C6 to C40 aliphatic hydrocarbon such as hexadecane, octadecane, and squalene, an aromatic hydrocarbon substituted with a C6 to C30 alkyl group such as phenyldodecane, phenyltetradecane, and phenyl hexadecane, a phosphine substituted with a C6 to C22 alkyl group such as trioctylphosphine, a phosphine oxide substituted with a C6 to C22 alkyl group such as trioctylphosphine oxide, a C12 to C22 aromatic ether such as phenyl ether and benzyl ether, or a combination thereof.

(26) The ligand compound is coordinated to the surface of the nanocrystals as prepared, playing a role of well-dispersing the nanocrystals in a solution, and may have an effect on the light-emitting and electrical characteristics of the nanocrystals. The ligand compound may be at least one selected from the group consisting of RCOOH, RNH.sub.2, R.sub.2NH, R.sub.3N, RSH, R.sub.3PO, R.sub.3P, ROH, RCOOR, and RCOOCOR, wherein R and R are each independently a C1 to C24 alkyl group, a C2 to C24 alkenyl group, or a C5 to C24 aryl group. The ligand compound may be used alone or in a mixture of at least two compounds. The ligand compound may be separately introduced in the reaction system. In an example, the phosphine compound of the Se precursor or a coordinating organic solvent may further act as a ligand compound in the reaction system.

(27) Examples of the organic ligand compound may include, but are not limited to, methanethiol, ethanethiol, propanethiol, butanethiol, pentanethiol, hexanethiol, octanethiol, dodecanethiol, hexadecanethiol, octadecanethiol, benzylthiol, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine, oleylamine, dimethylamine, diethylamine, dipropylamine, methanoic acid, ethanoic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, dodecanoic acid, hexadecanoic acid, octadecanoic acid, oleic acid, benzoic acid, palmitic acid, stearic acid, a phosphine such as methylphosphine, ethylphosphine, propylphosphine, butylphosphine, pentylphosphine, tributylphosphine, trioctylphosphine, and the like, a phosphine compound or an oxide compound thereof such as methylphosphine oxide, ethylphosphine oxide, propylphosphine oxide, butylphosphine oxide, trioctylphosphine oxide, and the like, a diphenylphosphine compound, a triphenylphosphine compound, or an oxide compound thereof, and the like, and a phosphonic acid. The organic ligand compound may be used alone or as a mixture of two or more compounds.

(28) The reaction conditions such as a reaction temperature and a reaction time are not particularly limited, but may be chosen appropriately. In a non-limiting to example, a solvent and optionally a ligand compound may be heated under vacuum to a predetermined temperature (e.g., about 100 C. or higher). After the atmosphere is changed into an inert gas atmosphere, they may be heated to a reaction temperature (e.g., 100 C. or higher). The GaSe single crystal prepared in the aforementioned method is added to the heated reaction system, and optionally an additional nanocrystal (e.g., a first nanocrystal) and/or a third precursor may be added thereto, and the reaction proceeds.

(29) According to the method set forth above, it is possible to obtain a GaSe nanocrystal of a predetermined composition (for example, a Ga.sub.2Se.sub.3 nanocrystal). As used herein, the term Ga.sub.2Se.sub.3 nanocrystal may refer to a nanocrystal having a ratio between Ga and Se (Ga:Se) of 1:1.1 or higher, for example, 1:1.2 or higher. In an embodiment, the GaSe nanocrystal may have a zinc blend crystalline structure. Using such a Ga.sub.2Se.sub.3 nanocrystal as an interlayer in a multishell structured nanocrystal makes it possible to achieve charge balance between a Group III-V semiconductor nanocrystal (e.g. a core) and a Group II-VI semiconductor nanocrystal (e.g., a shell).

(30) The types and structure of the first nanocrystal may be chosen appropriately. In an embodiment, the first nanocrystal may be a semiconductor core or a core-shell type of nanocrystal. The first nanocrystal may include at least one compound selected from the group consisting of Group II-VI compounds, Group III-V compounds, and Group IV-VI compounds. The Group III-V compounds may further include a Group II metal if desired.

(31) The Group II-VI compound may be selected from: a binary element compound selected from CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, and a combination thereof; a ternary element compound selected from CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, and a combination thereof; and a quaternary element compound selected from HgZnTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, and a combination thereof.

(32) The Group III-V compound semiconductor may be selected from: a binary element compound selected from GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and a combination thereof; a ternary element compound selected from GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, and a combination thereof; and a quaternary element compound selected from GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and a combination thereof.

(33) The Group IV-VI compound may be selected from: a binary element compound selected from SnS, SnSe, SnTe, PbS, PbSe, PbTe, and a combination thereof; a ternary element compound selected from SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and a combination thereof; and a quaternary element compound selected from SnPbSSe, SnPbSeTe, SnPbSTe, and a combination thereof.

(34) The semiconductor nanocrystal may include at least two kinds of compounds. The binary element compound, the ternary element compound, or the quaternary element compound may be present in a form of an alloy, or in a form of a structure wherein at least two different crystalline structures coexist as layers such as a core/shell or as compartments such as multi-pods. When the first nanocrystal has a core-shell structure, a nanocrystal having a core-multishell structure may be prepared.

(35) The third precursor may include a metal selected from a Group II metal, a Group III metal other than Ga, a Group 11 metal, and a Group IV metal. The third precursor may include a Group V non-metal element or a Group VI non-metal element other than Se. The types of the third precursor are not particularly limited but may be selected as necessary. In non-limiting examples, the third precursor containing a metal element may include a Group II metal, a Group III metal, or a Group IV metal, and may be a metal powder, an alkylated metal compound, a metal alkoxide, a metal carboxylate, a metal nitrate, a metal perchlorate, a metal sulfate, a metal acetylacetonate, a metal halide, a metal cyanide, a metal hydroxide, a metal oxide, a metal peroxide, or a combination thereof. Examples of the metal precursor may be at least one selected from dimethyl zinc, diethyl zinc, zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc chloride, zinc fluoride, zinc carbonate, zinc cyanide, zinc nitrate, a zinc oxide, zinc peroxide, zinc perchlorate, zinc sulfate, dimethyl cadmium, diethyl cadmium, cadmium acetate, cadmium acetylacetonate, cadmium iodide, cadmium bromide, cadmium chloride, cadmium fluoride, cadmium carbonate, cadmium nitrate, cadmium oxide, cadmium perchlorate, cadmium phosphide, cadmium sulfate, mercury acetate, mercury iodide, mercury bromide, mercury chloride, mercury fluoride, mercury cyanide, mercury nitrate, mercury oxide, mercury perchlorate, mercury sulfate, lead acetate, lead bromide, lead chloride, lead fluoride, lead oxide, lead perchlorate, lead nitrate, lead sulfate, lead carbonate, tin acetate, tin bis(acetylacetonate), tin bromide, tin chloride, tin fluoride, tin oxide, tin sulfate, germanium tetrachloride, germanium oxide, germanium ethoxide, trimethyl gallium, triethyl gallium, gallium acetylacetonate, gallium-3-chloride, gallium fluoride, gallium oxide, gallium nitrate, gallium sulfate, trimethyl indium, indium acetate, indium hydroxide, indium chloride, indium oxide, indium nitrate, indium sulfate, thallium acetate, thallium acetylacetonate, thallium chloride, thallium oxide, thallium ethoxide, thallium nitrate, thallium sulfate, thallium carbonate, dimethyl magnesium, dibutyl magnesium, magnesium ethoxide, magnesium acetylacetonate, magnesium carboxylate, and magnesium halide, but it is not limited thereto.

(36) The third precursor containing a non-metal element may be at least one selected from hexanethiol, octanethiol, decanethiol, dodecanethiol, hexadecanethiol, mercaptopropylsilane, sulfur-trioctylphosphine (S-TOP), sulfur-tributylphosphine (S-TBP), sulfur-triphenylphosphine (S-TPP), sulfur-trioctylamine (S-TOA), trimethylsilyl sulfur, ammonium sulfide, sodium sulfide, tellurium-tributylphosphine (Te-TBP), tellurium-triphenylphosphine (Te-TPP), tris(trimethylsilyl)phosphine, tris(dimethylamino)phosphine, triethylphosphine, tributylphosphine, trioctylphosphine, triphenylphosphine, tricyclohexylphosphine, arsenic oxide, arsenic chloride, arsenic sulfate, arsenic bromide, arsenic iodide, tris(trimethylsilyl)arsenic, nitric oxide, nitric acid, and ammonium nitrate.

(37) In another embodiment, a nanoparticle includes a nanocrystal of a compound represented by Chemical Formula 1:
GaSe.sub.xA.sub.y[Chemical Formula 1]

(38) wherein x is about 1.1 to 3, y is about 0.1 to 4, A is an element other than Ga and Se.

(39) The element (A) other than gallium and selenium may be at least one selected from S, Te, N, P, As, Al, In, Zn, Cd, Mg, Mn, Cu, Ag, and Au.

(40) The nanocrystal of the compound represented by Chemical Formula 1 may be Ga.sub.2Se.sub.3. GaSe, which is a type of the GaSe nanocrystal, may have an indirect bandgap of 2.11 eV and a four layer structure of SeGaGaSe (i.e., a layered to structure), which is unfavorable for shelling. Unlike GaSe, the Ga.sub.2Se.sub.3 nanocrystal may exhibit a bandgap of 1.92 eV and has a zinc blend structure as identified in its XRD spectrum. However, the bandgap value may vary with the measuring conditions, the material state (e.g., film, crystalline, and the like), and the like. The value of 1.92 eV is a value for a bulk single crystal. Accordingly the Ga.sub.2Se.sub.3 nanocrystal may be useful as an interlayer in the quantum dot multishell structure. When the nanoparticle has a multishell structure, the nanocrystal of the compound represented by Chemical Formula 1 may be present as an interlayer between a core of the Group III-V semiconductor nanocrystal having a zinc blend structure and a shell of the Group II-VI semiconductor nanocrystal. Such a structure has an advantage in that the nanocrystal interlayer of the compound represented by Chemical Formula 1 may play a role of balancing the charge difference between the Group III-V core and the Group II-VI shell.

(41) Examples of the Group III-V semiconductor nanocrystal may include the Group III-V compounds as set forth above.

(42) Examples of the Group II-VI semiconductor nanocrystal may include the Group II-VI compounds as set forth above.

(43) The GaSe nanocrystal may have a particle diameter (the longest diameter in case of a non-spherical particle) ranging from about 1 nm to about 100 nm, for example about 1 nm to about 20 nm.

(44) The GaSe nanocrystals may find their utility in various fields such as a light emitting diode (LED), a solar cell, and a biosensor.

(45) Hereinafter, the present invention is illustrated in more detail with reference to specific examples. However, they are exemplary embodiments of the present invention, and the present invention is not limited thereto.

MODE FOR INVENTION

Examples

Reference Example: Formation of Single Precursor

(46) 0.35 mmol of trimethyl gallium (TMG) is mixed with 0.3 mmol of 2 M Se/TBP, and the resulting mixture is subjected to H NMR analysis, the results of which are shown in FIG. 2. 0.35 mmol of trimethyl gallium is mixed with 0.3 mmol of 1.15 M Se/DPP, and the resulting mixture is subjected to P NMR analysis, the results of which are shown in FIG. 3. The results of the P NMR analysis show that Se/DPP has two peaks, one being assigned to DPP, the other being assigned to Se-DPP. After TMG is added, the peak for Se-DPP disappears. Such results confirm that GaSe bonding is generated and the Se-DPP bonding is broken. The H NMR results of the mixture of Se/TBP and TMG show that the methyl peak of TMG is shifted from 0.15 ppm to 0.09 ppm and the coupling pattern of tert-butyl moiety of TBP exhibits an upfield shift, confirming the formation of GaSe bonding.

Example 1: Synthesis of a Ga.SUB.2.Se.SUB.3 .Nanocrystal I

(47) 10 mL of trioctylphosphine (TOP) is put into a flask purged by N.sub.2 and is heated to 120 C. The atmosphere of the flask is changed by N.sub.2 and the flask is heated to 280 C. 0.7 mmol of trimethyl gallium (TMG) and 0.6 mmol of Se/diphenylphosphine (DPP) are mixed well in a glove box and the resulting mixture is quickly injected into the flask. Then the reaction proceeds for 30 minutes, and the reaction mixture is cooled to room temperature and chloroform and methanol are added thereto to precipitate nanocrystals which are then separated by centrifugation. The nanocrystals thus obtained are subjected to inductively coupled plasma analysis, and the results confirm that the ratio between Ga and Se is 1:1.23 (Ga:Se). The X-ray diffraction spectrum of the nanocrystals thus obtained is shown in FIG. 4.

Example 2: Synthesis of a Ga.SUB.2.Se.SUB.3 .Nanocrystal II

(48) 10 mL of trioctylphosphine oxide (TOPO) is put into a flask purged by N.sub.2 and is heated to 120 C. for 10 minutes. The atmosphere of the flask is changed by N.sub.2 and 10 mL of trioctylphosphine is added thereto and is heated to 280 C. under the N.sub.2 atmosphere. 0.7 mmol of trimethyl gallium (TMG) and 0.6 mmol of Se/diphenylphosphine (DPP) are mixed well in a glove box and the resulting mixture is quickly injected into the flask at 280 C. Then the reaction proceeds for 30 minutes, the reaction mixture is cooled to room temperature, and chloroform and methanol are added thereto to precipitate nanocrystals, which are then separated by centrifugation. The nanocrystals thus obtained are subjected to inductively coupled plasma analysis, and the results confirm that the ratio between Ga and Se is 1:1.36 (Ga:Se). The X-ray diffraction spectrum of the nanocrystals thus obtained is shown in FIG. 5.

Example 3

(49) Nanocrystals are prepared in the same manner as set forth in Example 2, except for using 0.35 mmol of trimethyl gallium (TMG) and 0.3 mmol of Se/diphenylphosphine (DPP). The nanocrystals thus obtained are subjected to inductively coupled plasma analysis, and the results confirm that the ratio between Ga and Se is 1:1.29 (Ga:Se). The X-ray diffraction spectrum of the nanocrystals thus obtained is shown in FIG. 5.

Example 4: Synthesis of an InZnP/Ga.SUB.2.Se.SUB.3./ZnSe/ZnS Nanocrystal

(50) 10 mL of octadecene (ODE) is put into a flask purged by N.sub.2 and is heated to 120 C. under vacuum. The atmosphere of the flask is changed by N.sub.2 and is heated again to 280 C. 0.35 mmol of trimethyl gallium (TMG) and 0.3 mmol of Se/diphenylphosphine (DPP) are mixed well in a glove box and the resulting mixture is quickly injected into the flask at 280 C. After 15 minutes, InZnP (optical density: 0.15) is injected quickly and the reaction proceeds for 75 minutes. Then, 0.15 mmol of Zn(OA).sub.2-TOP is added dropwise to the reaction mixture thus obtained, and 0.3 mmol of 0.4M S/TOP is added dropwise thereto. The reaction then proceeds for 3 hours and 15 minutes. The resulting reaction mixture is cooled to room temperature, and chloroform and methanol are added thereto to precipitate nanocrystals, which are then separated by centrifugation. The nanocrystals thus obtained are subjected to inductively coupled plasma analysis and the results are shown in Table 1.

(51) TABLE-US-00001 TABLE 1 Sample In P Ga Se Zn S Example 5 1.00 1.06 0.79 1.80 0.62 0.12

(52) The results of Table 1 confirm that a multishell structured nanocrystal is prepared with a Ge.sub.2Se.sub.3 nanocrystal as an interlayer.

Comparative Example

(53) 15 gram of trioctylphosphine oxide (TOPO) is put into a flask purged by N.sub.2 and is heated to 120 C. for 10 minutes. The atmosphere of the flask is changed by N.sub.2 and 5 mL of trioctylphosphine is added thereto and is heated to 120 C. under a N.sub.2 atmosphere. In a glove box, 20 mmol of 1.6 M Se/diphenylphosphine (DPP) is injected into the flask, and the temperature is raised to 278 C. 8 mmol of trimethyl gallium (GaMe.sub.3) and 7.5 mL of TOP are injected quickly into the flask and the reaction proceeds at 266 C. for 2 hours. The reaction mixture is cooled to room temperature, and chloroform and methanol are added thereto to precipitate nanocrystals, which are then separated by centrifugation. The nanocrystals thus obtained are subjected to inductively coupled plasma analysis, and the results confirm that the ratio between Ga and Se is 1:0.99 (Ga:Se). The electron diffraction pattern of the nanocrystals confirm that they have a two dimensional tetra-layered structure.

Example 5: Synthesis of a GaSeZn Nanocrystal II

(54) 10 mL of trioctylphosphine (TOP) is put into a flask purged by N.sub.2 and is heated to 120 C. The atmosphere of the flask is changed by N.sub.2 and the flask is heated again to 280 C. 0.7 mmol of trimethyl gallium (TMG) and 0.6 mmol of Se/diphenylphosphine (DPP) are mixed well in a glove box and the resulting mixture is quickly injected into the flask at 280 C. After 20 minutes, a mixture of 0.1 mmol of diethyl zinc and 1 mL of TOP is injected into the flask. Then the reaction proceeds for 30 minutes, and the reaction mixture is cooled to room temperature and chloroform and methanol are added thereto to precipitate nanocrystals represented by GaSe.sub.xZn.sub.y (wherein x is 1.1 to 3, and y is 0.1 to 4), which are then separated by centrifugation.

Example 6: Synthesis of a GaSeMg Nanocrystal II

(55) 10 mL of trioctylphosphine (TOP) is put into a flask purged by N.sub.2 and is heated to 120 C. The atmosphere of the flask is changed by N.sub.2 and the flask is heated again to 280 C. 0.7 mmol of trimethyl gallium (TMG) and 0.6 mmol of Se/diphenylphosphine (DPP) are mixed well in a glove box and the resulting mixture is quickly injected into the flask. After 20 minutes, a mixture of 0.1 mmol of dimethyl magnesium and 1 mL of TOP is injected to the flask. Then the reaction proceeds for 30 minutes, and the reaction mixture is cooled to room temperature and chloroform and methanol are added thereto to precipitate nanocrystals represented by GaSe.sub.xMg.sub.y (wherein x is 1.1 to 3, and y is 0.1 to 4), which are then separated by centrifugation.

(56) While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.