SEMICONDUCTOR NANO-PARTICLE COMPOSED OF AgAuS-BASED COMPOUND

Abstract

The present invention is a semiconductor nanoparticle composed of a semiconductor crystal of a compound containing Ag, Au and S as essential constitutional elements. A AgAuS-based compound constituting the semiconductor nanoparticle has a total content of Ag, Au and S of 95 mass % or more. In addition, the compound is preferably a AgAuS ternary compound represented by the general formula Ag.sub.(nx)Au.sub.(ny)S.sub.(nz). In the formula, n is any positive integer. x, y and z represent proportions of the number of atoms of the respective atoms of Ag, Au and S in the compound and are real numbers satisfying 0<x, y, z?1, and x/y is 1/7 or more and 7 or less.

Claims

1. A semiconductor nanoparticle comprising: a semiconductor crystal of a compound containing Ag, Au and S as essential constitutional elements, wherein the compound has a total content of Ag, Au and S of 95 mass % or more.

2. The semiconductor nanoparticle according to claim 1, wherein the compound is a AgAuS ternary compound represented by the general formula Ag(nx)Au(ny)S(nz), wherein n is any positive integer; x, y and z represent proportions of the number of atoms of the respective atoms of Ag, Au and S in the compound, and are real numbers satisfying 0<x, y, z?1; and x/y is 1/7 or more and 7 or less.

3. The semiconductor nanoparticle according to claim 2, wherein z is a real number satisfying z?(x+y)/2.

4. The semiconductor nanoparticle according to claim 2, wherein a value of x/(x+y) is a real number of 0.33 or more and 0.78 or less.

5. The semiconductor nanoparticle according claim 1, having an average particle diameter of 2 nm or more and 20 nm or less.

6. The semiconductor nanoparticle according claim 1, having at least any of an alkylamine having 4 to 20 carbon atoms in an alkyl chain, an alkenylamine having 4 to 20 carbon atoms in an alkenyl chain, an alkylcarboxylic acid having 3 to 20 carbon atoms in an alkyl chain, an alkenylcarboxylic acid having 3 to 20 carbon atoms in an alkenyl chain, an alkanethiol having 4 to 20 carbon atoms in an alkyl chain, a trialkylphosphine having 4 to 20 carbon atoms in an alkyl chain, a trialkylphosphine oxide having 4 to 20 carbon atoms in an alkyl chain, triphenylphosphine and triphenylphosphine oxide as a protective agent bonded to a surface thereof

7. The semiconductor nanoparticle according claim 1, wherein a long wavelength-side absorption edge wavelength of an absorption spectrum is 600 nm or higher.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is a view for describing the outline of steps for manufacturing AgAuS semiconductor nanoparticles of First and Second Embodiments;

[0037] FIG. 2 is TEM images of the AgAuS semiconductor nanoparticles manufactured in First Embodiment;

[0038] FIG. 3 is a view showing a relationship between the charged atomic ratio a:b of the AgAuS semiconductor nanoparticles manufactured in First Embodiment and the average particle diameter;

[0039] FIG. 4 is a view showing XRD diffraction patterns of the AgAuS semiconductor nanoparticles manufactured in First Embodiment;

[0040] FIG. 5a is a view showing an XRD diffraction pattern of the AgAuS semiconductor nanoparticle (charged atomic ratio a:b=1:0) manufactured in First Embodiment;

[0041] FIG. 5b is a view showing XRD diffraction patterns of the AgAuS semiconductor nanoparticles (charged atomic ratio a:b=0.60:0.40) manufactured in First Embodiment;

[0042] FIG. 5c is a view showing an XRD diffraction pattern of the AgAuS 5 semiconductor nanoparticle (charged atomic ratio a:b=0:1) manufactured in First Embodiment;

[0043] FIG. 6 is a view showing the measurement results of the absorption spectra of the AgAuS semiconductor nanoparticles manufactured in First Embodiment;

[0044] FIG. 7 is a view showing the measurement results of the emission spectra of the AgAuS semiconductor nanoparticles manufactured in First Embodiment;

[0045] FIG. 8 is a view showing the measurement results of the emission spectra of the AgAuS semiconductor nanoparticles (long wavelength region) manufactured in First Embodiment;

[0046] FIG. 9 is a view showing a relationship between the charged atomic ratio a:b of the AgAuS semiconductor nanoparticles manufactured in First Embodiment and the absorption edge wavelength;

[0047] FIG. 10 is a view showing a relationship between the charged atomic ratio a:b of the AgAuS semiconductor nanoparticles manufactured in First Embodiment and the emission quantum yield;

[0048] FIG. 11 is TEM images of the AgAuS semiconductor nanoparticles manufactured in Second Embodiment;

[0049] FIG. 12 is a view showing a relationship between the reaction temperature of the AgAuS semiconductor nanoparticles manufactured in Second Embodiment and the average particle diameter;

[0050] FIG. 13 is a view showing the measurement results of the absorption spectra of the AgAuS semiconductor nanoparticles manufactured in Second Embodiment;

[0051] FIG. 14 is a view showing a relationship between the reaction temperature of the AgAuS semiconductor nanoparticles manufactured in Second Embodiment and the absorption edge wavelength;

[0052] FIG. 15 is a view showing the measurement results of the emission spectra of the AgAuS semiconductor nanoparticles manufactured in Second Embodiment;

[0053] FIG. 16 is a view showing a relationship between the reaction temperature of the AgAuS semiconductor nanoparticles manufactured in Second Embodiment and the emission quantum yield; and

[0054] FIG. 17 is a view showing XRD diffraction patterns of the AgAuS semiconductor nanoparticles (reaction temperatures: 125? C., 150? C. and 165? C.) manufactured in Second Embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] First Embodiment: Hereinafter, an embodiment of the present invention will be described. In the present embodiment, semiconductor nanoparticles composed of AgAuS-based compounds (Ag.sub.(nx)Au.sub.(ny)S.sub.(nz)) having a variety of compositions were manufactured by adjusting the mixing ratio between a Ag precursor and a Au precursor. In addition, regarding the manufactured semiconductor nanoparticles, the average particle diameters and the crystal structures were confirmed by performing TEM observation and XRD analysis, and then absorption spectra and emission spectra were measured. The outline of the steps for manufacturing the Ag.sub.(nx)Au.sub.(ny)S.sub.(nz)semiconductor nanoparticles in the present embodiment is shown in FIG. 1.

[0056] As raw materials, silver acetate (Ag(OAc)) as the Ag precursor, Au resinate (C.sub.10H.sub.18Au.sub.2S.sub.2: refer to the following chemical formula) as the Au precursor and 0.2 mmol of thiourea as a S precursor were weighed and put into a test tube, and furthermore, 100 mm.sup.3 of 1-dodecanethiol (DDT) as a protecting agent and 2900 mm.sup.3 of oleylamine (OLA) as a solvent were added thereto.

##STR00001##

[0057] In the present embodiment, the metal atom charged atomic ratio (a:b) of Ag:Au was adjusted while the total amount of silver acetate and Au resinate was maintained at 0.4 mmol. In the present embodiment, seven Ag.sub.(nx)Au.sub.(ny)S.sub.(nz) compounds having charged atomic ratios (a:b) of 1.0:0, 0.78:0.22, 0.60:0.40, 0.45:0.55, 0.33:0.67, 0.14:0.86 and 0:1.0 were synthesized. In addition, each precursor, the protective agent, the solvent and a stirrer were put into the test tube, substituted with nitrogen three times, and then heated and stirred with a hot stirrer for 10 minutes at a reaction temperature set to 150? C. After the end of a reaction, the components were left to stand for 30 minutes until cool and then transferred to a small test tube, centrifugation was performed at 4000 rpm for five minutes, and a supernatant and a precipitate were separated.

[0058] Subsequently, 4000 mm.sup.3 of methanol was added to the supernatant as a nonsolvent to generate a precipitate, centrifugation was performed at 4000 rpm for five minutes, and the precipitate was collected. Furthermore, this precipitate was dispersed by adding 4000 mm.sup.3 of ethanol thereto, then, centrifugation was performed under the same conditions, and a by-product and the solvent were removed to purify the precipitate. The precipitate (semiconductor nanoparticle) thus obtained was dispersed in 4000 mm.sup.3 of chloroform, thereby obtaining a dispersion liquid of the semiconductor nanoparticle of the AgAuS-based compound (Ag.sub.(nx)Au.sub.(ny)S.sub.(nz)). This dispersion liquid was transferred to a sample bottle, substituted with nitrogen, shielded from light and stored in a refrigerator.

[TEM Observation and Average Particle Diameter Measurement]

[0059] On the manufactured semiconductor nanoparticles (a:b=1.0:0, 0.78:0.22, 0.60:0.40, 0.45:0.55, 0.33:0.67, 0.14:0.86 and 0:1.0), TEM observation was performed. FIG. 2 shows the TEM images of the semiconductor nanoparticles manufactured in the present embodiment (regarding magnifications, refer to a scale bar (10 nm) on each photograph). From each TEM image, it was confirmed that a substantially spherical semiconductor nanoparticle was synthesized.

[0060] Based on the TEM image, the average particle diameter of the semiconductor nanoparticle having each composition was measured and calculated. In the measurement of the particle diameters, particle diameters are obtained from all measurable semiconductor nanoparticles in the TEM image, and the average particle diameter and the standard deviation were calculated. The results are shown in FIG. 3. An error bar for each plot indicates the standard deviation. FIG. 3 shows that the average particle diameters of the semiconductor nanoparticles manufactured in the present embodiment are within a range of 2 nm to 5 nm. Regarding the proportions of Ag and Au, the particle with a:b=0:1 (Au.sub.2S) is liable to have small particle diameters, but there is no significant difference in other particles.

[Composition Analysis of Semiconductor Nanoparticle]

[0061] ICP analysis was performed together with the above-described TEM observation, thereby analyzing the compositions of semiconductor nanoparticle samples. The ICP analysis was performed using Agilent 5110 manufactured by Agilent Technologies International Japan, Ltd. as a measuring instrument by performing a pretreatment by a microwave acid digestion method and then performing measurement at a RF power of 1.2 kW, a plasma gas flow rate of 12 L/min. and an auxiliary gas flow rate of 1.0 L/min. The analysis results for the seven semiconductor nanoparticles for which the charged atomic ratios (a:b) between Ag and Au were set to 1.0:0, 0.78:0.22, 0.60:0.40, 0.45:0.55, 0.33:0.67, 0.14:0.86 and 0:1.0 are shown in Table 1. It was found from Table 1 that the atomic ratios (x:y:z) of the semiconductor nanoparticles manufactured in the present embodiment do not completely coincide with the charged atomic ratio (a:b) between the metal precursors but are close values. The cation/anion ratios ((x+y)/(2z)) showed values of 0.78 to 0.95, and the semiconductor particles were composed of a non-stoichiometric composition in which a cation was deficient. For the semiconductor nanoparticles synthesized in the present embodiment, the total concentration of Ag, Au and S in a AgAuS compound were 100 mass %.

TABLE-US-00001 TABLE 1 Compound composition (atomic ratio) Charged atomic ratio Ag Au S (a:b) x y z (x + y)/(2z) 1.0:0.sup. 1.0 0 0.64 0.78 0.78:0.22 0.78 0.22 0.61 0.82 0.60:0.40 0.68 0.32 0.60 0.83 0.45:0.55 0.54 0.46 0.63 0.79 0.33:0.67 0.46 0.54 0.61 0.82 0.14:0.86 0.27 0.73 0.53 0.95 .sup.0:1.0 0 1.0 0.61 0.82

[XRD Analysis]

[0062] XRD analysis was performed on each semiconductor nanoparticle. An XRD analyzer was Ultima IV manufactured by Rigaku Corporation, CuKa 10 rays were used as characteristic X rays, and 1?/m in. was set as an analysis condition. FIG. 4 shows the diffraction patterns of the seven nanoparticles manufactured in the present embodiment. Furthermore, among them, the diffraction patterns of the three nanoparticles for which the charged atomic ratios (a:b) between Ag and Au were 0:1.0, 0.60:0.40 and 0:1.0 are enlarged 15 and shown in FIG. 5a to FIG. 5c. FIG. 5c shows that, from the nanoparticle for which the charged atomic ratio was 0:1.0, a peak coinciding with the diffraction peak of Au.sub.2S is obtained. In addition, FIG. 5a shows that, from the semiconductor nanoparticle for which the charged atomic ratio was 1.0:0, while there is a mismatch in a part of the peak on the high angle side, a peak near 35? C. to 37? C. that is derived from the diffraction of Ag.sub.2 S is observed. On the other hand, when FIG. 5b is referred to, from the semiconductor nanoparticle for which the charged atomic ratio was 0.60:0.40, not only a peak derived from Ag3AuS2 but also a peak derived from Ag1.43Au0.66S were observed. From these facts, it is considered that, for these semiconductor nanoparticles, Table 1 shows that all of the compounds had compositions of Ag.sub.n(0.68)AU.sub.n(0.32)S.sub.n(0.6) (x=0.68, y=0.32, z=0.60) but were possibly composed of a mixed phase of Ag.sub.3AuS.sub.2 and Ag.sub.1.43Au.sub.0.66S.

[0063] In addition, when FIG. 4 is referred to, it is confirmed that, in the semiconductor nanoparticles for which the charged metal ratios (Ag:Au) were 0.78:0.22, 0.60:0.40, 0.45:0.55, 0.33:0.67 and 0.14:0.86, as the ratio of Ag increases and the ratio of Au decreases, the peak patterns gradually changed from Au.sub.2S to Ag.sub.2S. The XRD analysis of the present embodiment does not make it possible to determine the structure and composition of a solid solution of the particle synthesized with each charged atomic ratio or to determine the composition and abundance of a mixture in a case where the mixture coexist, but makes it possible to confirm that crystalline particles could be synthesized in all of the charged compositions.

[Measurement of Absorption Spectrum and Emission Spectrum]

[0064] Next, for each semiconductor nanoparticle, the absorption spectrum and the emission spectrum were measured. The absorption spectrum was measured using a UV-Visible spectrophotometer (manufactured by Agilent Technologies International Japan, Ltd., Agilent 8453) within a wavelength range of 400 nm to 1100 nm. The measurement results of the absorption spectra of the semiconductor nanoparticles of the present embodiment are shown in FIG. 6.

[0065] The emission spectrum was measured using a fluorescence spectrophotometer (manufactured by Hamamatsu Photonics K.K., PMA-12) at an excitation wavelength set to 365 nm. At this time, the sample was adjusted in a chloroform solution (n=1.4429) so that the absorbance at 365 nm reached 0.1, and the measurement was performed.

[0066] In addition, for the measurement of the emission quantum yield, an absolute PL quantum yield spectrometer (manufactured by Hamamatsu Photonics K.K., C9920-03) was used. In a case where emission was observed at a long wavelength of 1000 nm or longer, the emission spectrum was measured using a photonic multichannel analyzer (manufactured by Hamamatsu Photonics K.K., PMA-12 (model Nos.: C10027-02 (wavelength range: 350 to 1100 nm) and 10028-01 (wavelength range: 900 to 1650 nm)). At this time, the sample was adjusted in a chloroform solution (n=1.4429) so that the absorbance at 700 nm reached 0.1, and the measurement was performed. The excitation light wavelength was set to 700 nm in the measurement. For the calculation of the emission quantum yield, regarding the emission spectrum measured with the fluorescence spectrophotometer, the emission spectrum of an ethanol solution (n=1.3618) of indocyanine green (ICG: ?=13.2%), which is a near-infrared emitting organic fluorescent dye, was measured as a standard specimen, and the emission quantum yield of each sample was calculated from the following expression by the comparative method.

[00001]$\begin{array}{cc}{?}_x={?}_{st}?\left(\frac{F{A}_x}{F{A}_{st}}\right)?\left(\frac{A_{st}}{A_x}\right)?\left(\frac{I_{\mathrm{ex}},\mathrm{st}}{I_{\mathrm{ex}},x}\right)?\left(\frac{n_x^2}{n_{\mathrm{st}}^2}\right)& \left[\mathrm{Expression}1\right]\end{array}$ [0067] (A: Absorbance of specimen at excitation wavelength, [0068] lex: Intensity of excitation light at excitation wavelength, [0069] n: Refractive index of solvent)

[0070] The emission spectra of the semiconductor nanoparticles of the present embodiment measured and calculated as described above are shown in FIG. 7 and FIG. 8. In addition, the relationship between the charged atomic ratio a:b of the semiconductor nanoparticle obtained from FIG. 6 and the long wavelength-side absorption edge wavelength is shown in FIG. 9. In addition, the relationship between the charged atomic ratios a:b of the semiconductor nanoparticles of the present embodiment, which are obtained from FIG. 7 and FIG. 8, and the emission quantum yields is shown in FIG. 10.

[0071] FIG. 9 shows that, in the semiconductor nanoparticles for which a:b=1.0:0 (Ag.sub.2S) and 0.78:0.22, the absorption edge wavelengths reached up to a long wavelength range of 1100 nm or longer and accurate measurement was not possible. The absorption edge wavelength once shifted toward the short wavelength side from a:b=0.78:0.22 as the Ag proportion decreased and became the shortest wavelength (660 nm) when a:b was 0.45:0.55. When the Ag proportion further decreased from the above, the absorption edge wavelength shifted toward the long wavelength side again and was expected to reach 970 nm in the particle for which a:b=0:1.0 (Au.sub.2S). In the semiconductor nanoparticle composed of Ag.sub.(nx)Au.sub.(ny)S.sub.(nz) of the present invention, it was confirmed that the absorption edge wavelength is 600 nm or longer.

[0072] In addition, it is found from FIG. 10 that the emission quantum yield of the semiconductor nanoparticle of the present embodiment is maximized at a charged atomic ratio (a:b) of near 0.60:0.40. In the semiconductor nanoparticle composed of Ag.sub.(nx)Au.sub.(ny)S.sub.(nz) of the present invention, when a:b=1.0:0 or 0:1.0 is considered as a reference example (Ag.sub.2S or Au.sub.2S), it is 10 considered that the semiconductor nanoparticles synthesized at a:b=0.33:0.67 to 0.78:0.22 are particularly preferable. In addition, Table 1 shows that, in the semiconductor nanoparticles manufactured at the preferable charged atomic ratios, the atom proportions of Ag and Au (x, y) are 0.46 to 0.78 in terms of x/(x+y), that is, x/y is 0.85 to 3.5.

[0073] Second Embodiment: In the present embodiment, semiconductor nanoparticles composed of a Ag.sub.(nx)Au.sub.(ny)S.sub.(nz) compound were manufactured using silver acetate and gold resinate by changing the reaction temperature during synthesis while the charged atomic ratio (a:b) between the metal atoms is fixed to 0.60:0.40, the average particle diameters were measured, and the absorption spectra and the emission spectra were measured. The steps for manufacturing the Ag.sub.(nx)Au.sub.(ny)S.sub.(nz) semiconductor nanoparticles are basically the same as those in First Embodiment. In FIG. 1, the total amount of silver acetate and Au resinate was set to 0.4 mmol, and each metal charged atomic ratio a:b was set to 0.60:0.40, thereby forming a reaction system. In addition, the semiconductor nanoparticles were manufactured under five conditions where the reaction temperature was 100? C., 125? C., 150? C., 165? C. or 175? C.

[TEM Observation and Average Particle Diameter Measurement]

[0074] On the semiconductor nanoparticle manufactured at each reaction temperature, TEM observation was performed in the same manner as in First Embodiment. FIG. 11 shows a TEM image of each semiconductor nanoparticle. From FIG. 11, the generation of substantially spherical nanoparticles is confirmed even in the present embodiment. In addition, FIG. 12 shows the relationship between the reaction temperature and the average particle diameter measured regarding each semiconductor nanoparticle. The fact that the particle diameter of the semiconductor nanoparticle increases as the reaction temperature increases is revealed. This is considered to be attributed to the fact that an increase in the reaction temperature promotes crystal growth.

[Measurement of Absorption Spectrum and Emission Spectrum]

[0075] For each semiconductor nanoparticle, the absorption spectrum and the emission spectrum were measured. Methods for measuring these were the same as those in First Embodiment.

[0076] The measurement results of the absorption spectra of the semiconductor nanoparticles of the present embodiment are shown in FIG. 13. In addition, the relationship between the reaction temperature and the long wavelength-side absorption edge wavelength obtained from the measurement results of the absorption spectra is shown in FIG. 14. FIG. 14 shows that, even when the reaction temperatures changed, the absorption edge wavelengths of the semiconductor nanoparticles were not significantly affected and were almost constant at 650 to 750 nm. Even for the semiconductor nanoparticles manufactured in the present embodiment, it was confirmed that the absorption edge wavelengths were 600 nm or longer.

[0077] In addition, the emission spectra of the semiconductor nanoparticles of the present embodiment are shown in FIG. 15. It is found from FIG. 15 that, at the reaction temperatures of 100? C. to 165? C., the emission peak wavelengths of the semiconductor nanoparticles are 700 to 800 nm and almost do not change. At 175? C., no emission peak was detected. The relationship between the reaction temperatures of the semiconductor nanoparticles manufactured in the present embodiment and the emission quantum yields is shown in FIG. 16. FIG. 16 shows that, within a range of 100? C. to 150? C., the emission quantum yield of the obtained semiconductor nanoparticle increased as the reaction temperature increased. On the other hand, when the reaction temperatures were further increased to 165? C. and 175? C., the emission quantum yields of the obtained semiconductor nanoparticles conversely decreased.

[XRD Analysis]

[0078] Furthermore, XRD analysis was performed on the semiconductor nanoparticles obtained at the reaction temperatures set to 125? C., 150? C. and 165? C. The analysis condition is the same as that in First Embodiment. FIG. 17 shows the diffraction pattern of each semiconductor nanoparticle. It was found from FIG. 17 that the semiconductor nanoparticle manufactured at 165? C. was more highly crystalline since each diffraction peak became sharp. When the diffraction patterns are considered together with the measurement results of the average particle diameters, it is suggested that the promotion of crystal growth by an increase in the reaction temperature increases the particle diameter of the semiconductor nanoparticle and enhances crystallinity. Based on what has been described above, it is considered that the semiconductor nanoparticle of the present invention can be manufactured at reaction temperatures of 100? C. to 175? C., but more preferable reaction temperatures are 165? C. or lower from the viewpoint of the emission quantum yield.

Industrial Applicability

[0079] As described above, the semiconductor nanoparticle of the present invention that is composed of a AgAuS-based compound and has a novel composition is capable of exhibiting favorable light characteristics. In addition, the AgAuS-based compound is a low-toxic biocompatible compound. The semiconductor nanoparticle of the present invention is expected to be applied to light-emitting elements and fluorescent substances that are used for display devices, marker substances for detecting bio-related substances and the like or photoelectric conversion elements or light-receiving elements, which are mounted in solar cells, light sensors and the like.

[0080] In addition, it is also possible to obtain a semiconductor nanoparticle capable of exhibiting emission and extinction characteristics in the near-infrared range based on the present invention. As photoelectric conversion elements for which responsiveness in the near-infrared range has been emphasized recently, there are light-receiving elements that are applied to LIDAR (light detection and ranging) or short-wave infrared (SWIR) image sensors. The semiconductor nanoparticle of the present invention is expected to be applied to such photoelectric conversion elements that operate in the near-infrared range.