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Colloidal synthesis of ZnSe nanoparticles at room temperature
Author’s Accepted Manuscript Colloidal synthesis of ZnSe nanoparticles at room temperature R. Hernández, E. Rosendo, R. Romano-Trujillo, A.I. Oliva, G. García, G. Nieto, T. Díaz, C. Morales, H. Juárez, M. Pacio, R. Galeazzi www.elsevier.com
PII: DOI: Reference:
S0167-577X(15)30159-2 http://dx.doi.org/10.1016/j.matlet.2015.06.092 MLBLUE19163
To appear in: Materials Letters Received date: 7 April 2015 Revised date: 25 June 2015 Accepted date: 26 June 2015 Cite this article as: R. Hernández, E. Rosendo, R. Romano-Trujillo, A.I. Oliva, G. García, G. Nieto, T. Díaz, C. Morales, H. Juárez, M. Pacio and R. Galeazzi, Colloidal synthesis of ZnSe nanoparticles at room temperature, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2015.06.092 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Colloidal synthesis of ZnSe nanoparticles at room temperature R. Hernández1, E. Rosendo1, R. Romano-Trujillo1, A. I. Oliva2, G. García1, G. Nieto3, T. Díaz1, C. Morales1, H. Juárez1, M. Pacio1 and R. Galeazzi1. 1
PDS, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, 14 Sur y Av. San Claudio, edificio 103C, C.U. 72570 Puebla, Pue.
2
Departamento de Física Aplicada, CINVESTAV-IPN, Unidad Mérida, A. P. 73 Cordemex, Mérida Yucatán 97310, México.
3
Facultad de Ciencias Químicas, Benemérita Universidad Autónoma de Puebla, Av. San Claudio, C. U. 72570 Puebla, Pue. México. E-mail: [email protected].
Keywords: ZnSe, nanoparticles, colloidal method, semiconductors. Abstract. Structural, morphological and compositional characterizations of zinc selenide nanoparticles (NPsZnSe) are discussed in this work. NPs-ZnSe were obtained by colloidal synthesis in aqueous solution at room temperature, atmospheric pressure and without inert atmosphere. The synthesis was carried out using zinc chloride (ZnCl2) and elemental selenium as precursors. A mix of Na5P3O10 and NaOH called Extran was used as surfactant. Molar concentration and pH of the aqueous solution were varied to study their effect on the crystalline properties of the nanoparticles. The XRD measurements show that the NPs-ZnSe exhibits a cubic phase structure. The size of the nanocrystals was between 3 nm and 4.7 nm. HRTEM analysis showed that NPs-ZnSe exhibit semi-spherical shape. The presence of zinc and selenium in the NPs-ZnSe was confirmed through EDS measurements.
1. Introduction In recent years, there exist great interest in the study of nanoparticles (NPs) in order to improve the performance of electronic and optoelectronic devices. NPs show interesting properties when their size becomes smaller than its exciton Bohr radius due to the quantum confinement effect. These properties can be controlled by means of the particle size [1]. NPs-ZnSe have attracted especial interest by their potential applications in light emitting diodes [2], photodetectors [3], and solar cells [4]. ZnSe is a wide bandgap semiconductor material with a bulk value of 2.7 eV at room temperature, emitting in the wavelength range
from blue to UV [5, 6]. NPs-ZnSe have been synthesized by different methods, such that colloidal synthesis either in organic solutions [7] or in aqueous solution [8], sonochemical method [9], vapor phase [10], solvothermal route [11]. Among these methods, colloidal synthesis by aqueous solution allows obtaining NPs at low cost and good quality. In the present investigation, NPs-ZnSe were obtained in aqueous solution by the colloidal method at room temperature, atmospheric pressure and without inert atmosphere. The surfactant used is a solution of sodium hydroxide (NaOH), penta sodium tripolyphosphate (Na5P3O10) and water (H2O), commercially called Extran. The synthesis method used is easy to implement and economically feasible by not requiring the use of control equipment very expensive.
The synthesized NPs were analyzed by x-ray diffraction (XRD), scanning
electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS).
2. Experimental For sample preparation, 1 mmol of ZnCl2 (Baker, 98.2%) was dissolved in deionized water at room temperature with constant stirring. After that, Extran was added. Additionally, 1 mmol of selenium powder (Aldrich, 99.5 %) and 2 mmol of sodium borohydride (NaBH4, Sigma 95%) were dissolved in deionized water under constant stirring and maintained for 13 min at 75 oC. Following, the two solutions were mixed during 30 min at room temperature. A cleaning process was performed to eliminate the generated by-products [12], adding 1 ml of HCl (Merck, 37%) in the solution and stirred during 15 min, after, the stirring was stopped and then precipitation of the NPs was produced. Finally, NPs were dried at 45 oC for 2.5 h. The pH of the solutions was varied from 8 to 11 and the Zn:Se molar concentrations were varied as: 3:1, 2:1, 1:1, 1:2, 1:3. XRD measurements were done with a Bruker Axs D8 discover diffractometer with a Cu Kα radiation (λ = 1.5428 Å). The diffractograms were obtained in the range of 20° to 80° with intervals of 0.02°, step time of 1 s, 40 kV and 40 mA as operation conditions. Morphology and compositional studies were done in a Philips XL30 SEM at 20,000X and 2 kV. A JEOL JEM-2010 HRTEM at 200 kV was used to confirm the presence of nanoparticles.
2
3. Results and discussion The chemical reaction of this solution is carried out at 75 oC because selenium has low solubility in water. The chemical reactions during the process can be formulated as follows: 2ZnCl2 + 6H2O → 2Zn2+ + 4HCl + 4H2O + O2↑
(1)
2Zn2+ + 4HCl + 4H2O + Na5P3O10 +3 NaOH + 5H2O → Zn2HP3O10 +4NaCl + 4NaOH + 8H2O + 2H2↑ 2Se + 4NaBH4 + 12H2O → 2NaHSe + Na2B4O7 + 5H2O + 14H2↑
(2) (3)
2NaHSe + Na2B4O7 + 5H2O → 2Na2Se + 4H3BO3
(4)
2Na2Se + 4H3BO3 → 2Se2− + Na2B4O7 + 2NaOH + 3H2O + 2H2↑
(5)
Zn2HP3O10 + 4NaCl + 6NaOH + 11H2O + 2Se2− + Na2B4O7 → 2ZnSe + Na5P3O10 4NaCl + Na2B4O7 + NaOH +14H2O + O2↑
(6)
The chemical reaction involving the use of HCl to eliminate by-products is, 2ZnSe + Na5P3O10 + 4NaCl + Na2B4O7 + NaOH + 14H2O + HCl → 2ZnSe + 5NaClO3 + Na2B4O7 + 15H2↑
(7)
Fig. 1 shows the diffractograms of ZnSe samples obtained with 1:1 molar concentration and pH values of 8, 9, 10 and 11. The XRD pattern show peaks at 2θ = 27.2o, 45.2o and 53.5o related to the NPs-ZnSe. According to the ICDD card number 01-071-5977, the peaks position corresponds to the (111), (220) and (311) orientations, respectively, these results correspond to a cubic phase structure. The ZnSe peaks do not exhibit important variations as the pH value is increased. However, can be observed the presence of peaks at 2θ = 23.5o and 29.7° related to selenium, indicating that a basic solution promotes the formation of ZnSe as well as selenium. The size of the crystallites was estimated by using the Debye-Scherrer equation: τ=Kλ/β cos(θ), where k is 0.9, θ is the diffraction angle, λ is the x-ray wavelength and β is the full width at half maximum. The calculated crystallite size was similar for the range of pH studied and it was about 3.2 nm. Inset in Fig. 1 shows the crystallite size vs pH plot.
3
Fig. 2 shows the XRD patterns of samples obtained with pH=8 and Zn:Se molar concentrations of 1:3, 1:2, 1:1, 2:1 and 3:1. In all the diffractograms can be observed the peaks of NPs-ZnSe and elemental selenium; and the value of the crystallite size decreases from 4.7 to 3 nm in the range studied as can be seen in the inset of the Fig. 2.
4
Micrographs show that NPs-ZnSe join to form micrometer-sized agglomerates. It is noted that the surface morphology of the agglomerates depends on the molar concentration. Fig. 3 presents micrographs of samples obtained with pH=8. Fig. 3(a) shows sample obtained with 1:1 as molar concentration. This sample presents roughness surface a high amount of agglomerates. In some cases, particles with irregular shape and some rodlike structures are attributed to the elimination of Zn during the cleaning process. The mechanism is related with the formation of ZnCl2 from the erosion of NPs-ZnSe by HCl [13], therefore a high amount of selenium concentration is obtained, and the morphology is like nanorods even elemental selenium is also formed as nanorods. The surface morphology for the Zn:Se samples with 1:2 (Fig. 3(b)) and 1:3 (Fig. 3(c)) as molar concentrations shows agglomerates of thorns which can be attributed to the increase of the concentration of selenium. When the zinc concentration is increased at 2:1 (Fig. 3(d)) a mix of semi-spherical and rod shapes agglomerates appear on the morphology. Fig. 3(e) shows the case when the zinc concentration is increased at 3:1; here, the micrograph shows a smoothed and homogeneous surface. Similar surface morphologies of NPsZnSe observed in the SEM images are also reported in the literature [14, 15]. Fig. 3(f) shows a typical spectrum of sample with 1:1 molar concentration and pH=8. The presence of zinc and selenium was of 26.9 % and 73.6 % at, respectively. The excess of selenium is due to traces of selenium with hexagonal structure of the powder samples, as was discussed in the XRD analysis. Presence of small traces of oxygen and chloride is mainly due to the residuals and surface oxides. Thus, can be affirmed that, the by-products are greatly reduced during the cleaning process with HCl.
5
Figs. 4(a) and 4(b) show TEM images of the NPs-ZnSe, micrographs show that the nanoparticles are uniformly distributed and present almost spherical shape. The average diameter of the nanocrystallites obtained is around 3 nm as shown in the histogram in Fig. 4(c). This value is consistent with the values estimated by x-ray diffraction. The selected area electron diffraction (SAED) pattern shown in Fig. 4(d), describe three concentric rings, which correspond to the (111), (220) and (311) orientations of the cubic ZnSe, respectively.
4. Conclusions Nanoparticles of ZnSe were obtained by colloidal synthesis by using Extran as surfactant. ZnSe free of byproducts was successfully obtained after various cycles of the cleaning process with HCl. The x-ray diffraction results demonstrated that the NPs-ZnSe exhibit a cubic phase structure. The crystallite size of the obtained nanoparticles was estimated between 3 nm and 4.7 nm, these values are in agreement with those found by HRTEM. X-ray diffraction shows that the molar concentration influences the crystal size; smaller crystals are obtained when the molar concentration of Zn is larger than Se. Furthermore, SEM measurements show that the molar concentration affects surface morphology of the agglomerates. Variations of the pH value do not affect the NPs-ZnSe size. The presence of zinc and selenium was confirmed by the elemental analysis by EDS technique.
Acknowledgements The authors wish to thank the VIEP-BUAP by project funding provided by ROAE-EXC15-G and also to CNyN-UNAM for using for using JEOL JEM-2010 HRTEM.
6
References [1] Pokutnyi S. Semiconductors. 2003;37:718-22. [2] Chen HS, Wang SJJ, Lo CJ, Chi JY. Applied Physics Letters. 2005;86:131905. [3] Lin T, Chang S-J, Su Y-K, Chiou Y-Z, Wang C, Chang C, et al. Electron Devices, IEEE Transactions on. 2005;52:121-3. [4] Kim DH, Lee YH, Lee DU, Kim TW, Kim S, Kim SW. Optics express. 2012;20:10476-83. [5] Chang Y, Chieng M, Tsai C, Liao MH, Chen Y. Journal of Electronic Materials. 2000;29:173-6. [6] Hines MA, Guyot-Sionnest P. The Journal of Physical Chemistry B. 1998;102:3655-7. [7] Murray CB, Sun S, Gaschler W, Doyle H, Betley TA, Kagan CR. IBM Journal of Research and Development. 2001;45:47-56. [8] Dey S, Nath S. Journal of luminescence. 2011;131:2707-10. [9] Zhu J, Koltypin Y, Gedanken A. Chemistry of Materials. 2000;12:73-8. [10] Xiang B, Zhang H, Li G, Yang F, Su F, Wang R, et al. Applied Physics Letters. 2003;82:3330-2. [11] Deng Z-X, Wang C, Sun X-M, Li Y-D. Inorganic chemistry. 2002;41:869-73. [12] Romano-Trujillo R, Rosendo E, Ortega M, Morales-Sánchez A, Gracia J, Diaz T, et al. Nanotechnology. 2012;23:185602. [13] Li H, Jie W. Journal of crystal growth. 2003;257:110-5. [14] Liu X, Ma J, Peng P, Zheng W. Langmuir. 2010;26:9968-73. [15] Zhang L, Yang H, Yu J, Shao F, Li L, Zhang F, et al. The Journal of Physical Chemistry C. 2009;113:5434-43.
Figure captions Fig. 1. XRD patterns of NPs-ZnSe samples with Zn:Se molar concentration (1:1). Inset shows the crystallite size vs molar pH plot. Fig. 2. XRD patterns of samples with pH=8 and different molar concentrations. Inset shows the crystallite size vs molar concentration plot. Fig. 3. (a), (b), (c), (d) and (e) SEM images of NPs-ZnSe synthesized with pH=8 and different Zn:Se molar concentrations, (f) EDS spectrum of the NPs-ZnSe.
7
Fig. 4. (a), (b) NPs-ZnSe TEM images of a sample obtained with Zn:Se (3:1) molar concentration and pH=8, (c) crystallite size histogram, and (d) SAED pattern.
Highlights
ZnSe nanoparticles were obtained by colloidal synthesis at room temperature.
XRD measurements showed that the nanoparticles exhibit a cubic phase structure.
The size of the nanocrystals was founded between 3 nm and 4.7 nm.
HRTEM analysis showed that ZnSe nanoparticles exhibit semi-spherical shapes.
8
PII: DOI: Reference:
S0167-577X(15)30159-2 http://dx.doi.org/10.1016/j.matlet.2015.06.092 MLBLUE19163
To appear in: Materials Letters Received date: 7 April 2015 Revised date: 25 June 2015 Accepted date: 26 June 2015 Cite this article as: R. Hernández, E. Rosendo, R. Romano-Trujillo, A.I. Oliva, G. García, G. Nieto, T. Díaz, C. Morales, H. Juárez, M. Pacio and R. Galeazzi, Colloidal synthesis of ZnSe nanoparticles at room temperature, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2015.06.092 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Colloidal synthesis of ZnSe nanoparticles at room temperature R. Hernández1, E. Rosendo1, R. Romano-Trujillo1, A. I. Oliva2, G. García1, G. Nieto3, T. Díaz1, C. Morales1, H. Juárez1, M. Pacio1 and R. Galeazzi1. 1
PDS, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, 14 Sur y Av. San Claudio, edificio 103C, C.U. 72570 Puebla, Pue.
2
Departamento de Física Aplicada, CINVESTAV-IPN, Unidad Mérida, A. P. 73 Cordemex, Mérida Yucatán 97310, México.
3
Facultad de Ciencias Químicas, Benemérita Universidad Autónoma de Puebla, Av. San Claudio, C. U. 72570 Puebla, Pue. México. E-mail: [email protected].
Keywords: ZnSe, nanoparticles, colloidal method, semiconductors. Abstract. Structural, morphological and compositional characterizations of zinc selenide nanoparticles (NPsZnSe) are discussed in this work. NPs-ZnSe were obtained by colloidal synthesis in aqueous solution at room temperature, atmospheric pressure and without inert atmosphere. The synthesis was carried out using zinc chloride (ZnCl2) and elemental selenium as precursors. A mix of Na5P3O10 and NaOH called Extran was used as surfactant. Molar concentration and pH of the aqueous solution were varied to study their effect on the crystalline properties of the nanoparticles. The XRD measurements show that the NPs-ZnSe exhibits a cubic phase structure. The size of the nanocrystals was between 3 nm and 4.7 nm. HRTEM analysis showed that NPs-ZnSe exhibit semi-spherical shape. The presence of zinc and selenium in the NPs-ZnSe was confirmed through EDS measurements.
1. Introduction In recent years, there exist great interest in the study of nanoparticles (NPs) in order to improve the performance of electronic and optoelectronic devices. NPs show interesting properties when their size becomes smaller than its exciton Bohr radius due to the quantum confinement effect. These properties can be controlled by means of the particle size [1]. NPs-ZnSe have attracted especial interest by their potential applications in light emitting diodes [2], photodetectors [3], and solar cells [4]. ZnSe is a wide bandgap semiconductor material with a bulk value of 2.7 eV at room temperature, emitting in the wavelength range
from blue to UV [5, 6]. NPs-ZnSe have been synthesized by different methods, such that colloidal synthesis either in organic solutions [7] or in aqueous solution [8], sonochemical method [9], vapor phase [10], solvothermal route [11]. Among these methods, colloidal synthesis by aqueous solution allows obtaining NPs at low cost and good quality. In the present investigation, NPs-ZnSe were obtained in aqueous solution by the colloidal method at room temperature, atmospheric pressure and without inert atmosphere. The surfactant used is a solution of sodium hydroxide (NaOH), penta sodium tripolyphosphate (Na5P3O10) and water (H2O), commercially called Extran. The synthesis method used is easy to implement and economically feasible by not requiring the use of control equipment very expensive.
The synthesized NPs were analyzed by x-ray diffraction (XRD), scanning
electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS).
2. Experimental For sample preparation, 1 mmol of ZnCl2 (Baker, 98.2%) was dissolved in deionized water at room temperature with constant stirring. After that, Extran was added. Additionally, 1 mmol of selenium powder (Aldrich, 99.5 %) and 2 mmol of sodium borohydride (NaBH4, Sigma 95%) were dissolved in deionized water under constant stirring and maintained for 13 min at 75 oC. Following, the two solutions were mixed during 30 min at room temperature. A cleaning process was performed to eliminate the generated by-products [12], adding 1 ml of HCl (Merck, 37%) in the solution and stirred during 15 min, after, the stirring was stopped and then precipitation of the NPs was produced. Finally, NPs were dried at 45 oC for 2.5 h. The pH of the solutions was varied from 8 to 11 and the Zn:Se molar concentrations were varied as: 3:1, 2:1, 1:1, 1:2, 1:3. XRD measurements were done with a Bruker Axs D8 discover diffractometer with a Cu Kα radiation (λ = 1.5428 Å). The diffractograms were obtained in the range of 20° to 80° with intervals of 0.02°, step time of 1 s, 40 kV and 40 mA as operation conditions. Morphology and compositional studies were done in a Philips XL30 SEM at 20,000X and 2 kV. A JEOL JEM-2010 HRTEM at 200 kV was used to confirm the presence of nanoparticles.
2
3. Results and discussion The chemical reaction of this solution is carried out at 75 oC because selenium has low solubility in water. The chemical reactions during the process can be formulated as follows: 2ZnCl2 + 6H2O → 2Zn2+ + 4HCl + 4H2O + O2↑
(1)
2Zn2+ + 4HCl + 4H2O + Na5P3O10 +3 NaOH + 5H2O → Zn2HP3O10 +4NaCl + 4NaOH + 8H2O + 2H2↑ 2Se + 4NaBH4 + 12H2O → 2NaHSe + Na2B4O7 + 5H2O + 14H2↑
(2) (3)
2NaHSe + Na2B4O7 + 5H2O → 2Na2Se + 4H3BO3
(4)
2Na2Se + 4H3BO3 → 2Se2− + Na2B4O7 + 2NaOH + 3H2O + 2H2↑
(5)
Zn2HP3O10 + 4NaCl + 6NaOH + 11H2O + 2Se2− + Na2B4O7 → 2ZnSe + Na5P3O10 4NaCl + Na2B4O7 + NaOH +14H2O + O2↑
(6)
The chemical reaction involving the use of HCl to eliminate by-products is, 2ZnSe + Na5P3O10 + 4NaCl + Na2B4O7 + NaOH + 14H2O + HCl → 2ZnSe + 5NaClO3 + Na2B4O7 + 15H2↑
(7)
Fig. 1 shows the diffractograms of ZnSe samples obtained with 1:1 molar concentration and pH values of 8, 9, 10 and 11. The XRD pattern show peaks at 2θ = 27.2o, 45.2o and 53.5o related to the NPs-ZnSe. According to the ICDD card number 01-071-5977, the peaks position corresponds to the (111), (220) and (311) orientations, respectively, these results correspond to a cubic phase structure. The ZnSe peaks do not exhibit important variations as the pH value is increased. However, can be observed the presence of peaks at 2θ = 23.5o and 29.7° related to selenium, indicating that a basic solution promotes the formation of ZnSe as well as selenium. The size of the crystallites was estimated by using the Debye-Scherrer equation: τ=Kλ/β cos(θ), where k is 0.9, θ is the diffraction angle, λ is the x-ray wavelength and β is the full width at half maximum. The calculated crystallite size was similar for the range of pH studied and it was about 3.2 nm. Inset in Fig. 1 shows the crystallite size vs pH plot.
3
Fig. 2 shows the XRD patterns of samples obtained with pH=8 and Zn:Se molar concentrations of 1:3, 1:2, 1:1, 2:1 and 3:1. In all the diffractograms can be observed the peaks of NPs-ZnSe and elemental selenium; and the value of the crystallite size decreases from 4.7 to 3 nm in the range studied as can be seen in the inset of the Fig. 2.
4
Micrographs show that NPs-ZnSe join to form micrometer-sized agglomerates. It is noted that the surface morphology of the agglomerates depends on the molar concentration. Fig. 3 presents micrographs of samples obtained with pH=8. Fig. 3(a) shows sample obtained with 1:1 as molar concentration. This sample presents roughness surface a high amount of agglomerates. In some cases, particles with irregular shape and some rodlike structures are attributed to the elimination of Zn during the cleaning process. The mechanism is related with the formation of ZnCl2 from the erosion of NPs-ZnSe by HCl [13], therefore a high amount of selenium concentration is obtained, and the morphology is like nanorods even elemental selenium is also formed as nanorods. The surface morphology for the Zn:Se samples with 1:2 (Fig. 3(b)) and 1:3 (Fig. 3(c)) as molar concentrations shows agglomerates of thorns which can be attributed to the increase of the concentration of selenium. When the zinc concentration is increased at 2:1 (Fig. 3(d)) a mix of semi-spherical and rod shapes agglomerates appear on the morphology. Fig. 3(e) shows the case when the zinc concentration is increased at 3:1; here, the micrograph shows a smoothed and homogeneous surface. Similar surface morphologies of NPsZnSe observed in the SEM images are also reported in the literature [14, 15]. Fig. 3(f) shows a typical spectrum of sample with 1:1 molar concentration and pH=8. The presence of zinc and selenium was of 26.9 % and 73.6 % at, respectively. The excess of selenium is due to traces of selenium with hexagonal structure of the powder samples, as was discussed in the XRD analysis. Presence of small traces of oxygen and chloride is mainly due to the residuals and surface oxides. Thus, can be affirmed that, the by-products are greatly reduced during the cleaning process with HCl.
5
Figs. 4(a) and 4(b) show TEM images of the NPs-ZnSe, micrographs show that the nanoparticles are uniformly distributed and present almost spherical shape. The average diameter of the nanocrystallites obtained is around 3 nm as shown in the histogram in Fig. 4(c). This value is consistent with the values estimated by x-ray diffraction. The selected area electron diffraction (SAED) pattern shown in Fig. 4(d), describe three concentric rings, which correspond to the (111), (220) and (311) orientations of the cubic ZnSe, respectively.
4. Conclusions Nanoparticles of ZnSe were obtained by colloidal synthesis by using Extran as surfactant. ZnSe free of byproducts was successfully obtained after various cycles of the cleaning process with HCl. The x-ray diffraction results demonstrated that the NPs-ZnSe exhibit a cubic phase structure. The crystallite size of the obtained nanoparticles was estimated between 3 nm and 4.7 nm, these values are in agreement with those found by HRTEM. X-ray diffraction shows that the molar concentration influences the crystal size; smaller crystals are obtained when the molar concentration of Zn is larger than Se. Furthermore, SEM measurements show that the molar concentration affects surface morphology of the agglomerates. Variations of the pH value do not affect the NPs-ZnSe size. The presence of zinc and selenium was confirmed by the elemental analysis by EDS technique.
Acknowledgements The authors wish to thank the VIEP-BUAP by project funding provided by ROAE-EXC15-G and also to CNyN-UNAM for using for using JEOL JEM-2010 HRTEM.
6
References [1] Pokutnyi S. Semiconductors. 2003;37:718-22. [2] Chen HS, Wang SJJ, Lo CJ, Chi JY. Applied Physics Letters. 2005;86:131905. [3] Lin T, Chang S-J, Su Y-K, Chiou Y-Z, Wang C, Chang C, et al. Electron Devices, IEEE Transactions on. 2005;52:121-3. [4] Kim DH, Lee YH, Lee DU, Kim TW, Kim S, Kim SW. Optics express. 2012;20:10476-83. [5] Chang Y, Chieng M, Tsai C, Liao MH, Chen Y. Journal of Electronic Materials. 2000;29:173-6. [6] Hines MA, Guyot-Sionnest P. The Journal of Physical Chemistry B. 1998;102:3655-7. [7] Murray CB, Sun S, Gaschler W, Doyle H, Betley TA, Kagan CR. IBM Journal of Research and Development. 2001;45:47-56. [8] Dey S, Nath S. Journal of luminescence. 2011;131:2707-10. [9] Zhu J, Koltypin Y, Gedanken A. Chemistry of Materials. 2000;12:73-8. [10] Xiang B, Zhang H, Li G, Yang F, Su F, Wang R, et al. Applied Physics Letters. 2003;82:3330-2. [11] Deng Z-X, Wang C, Sun X-M, Li Y-D. Inorganic chemistry. 2002;41:869-73. [12] Romano-Trujillo R, Rosendo E, Ortega M, Morales-Sánchez A, Gracia J, Diaz T, et al. Nanotechnology. 2012;23:185602. [13] Li H, Jie W. Journal of crystal growth. 2003;257:110-5. [14] Liu X, Ma J, Peng P, Zheng W. Langmuir. 2010;26:9968-73. [15] Zhang L, Yang H, Yu J, Shao F, Li L, Zhang F, et al. The Journal of Physical Chemistry C. 2009;113:5434-43.
Figure captions Fig. 1. XRD patterns of NPs-ZnSe samples with Zn:Se molar concentration (1:1). Inset shows the crystallite size vs molar pH plot. Fig. 2. XRD patterns of samples with pH=8 and different molar concentrations. Inset shows the crystallite size vs molar concentration plot. Fig. 3. (a), (b), (c), (d) and (e) SEM images of NPs-ZnSe synthesized with pH=8 and different Zn:Se molar concentrations, (f) EDS spectrum of the NPs-ZnSe.
7
Fig. 4. (a), (b) NPs-ZnSe TEM images of a sample obtained with Zn:Se (3:1) molar concentration and pH=8, (c) crystallite size histogram, and (d) SAED pattern.
Highlights
ZnSe nanoparticles were obtained by colloidal synthesis at room temperature.
XRD measurements showed that the nanoparticles exhibit a cubic phase structure.
The size of the nanocrystals was founded between 3 nm and 4.7 nm.
HRTEM analysis showed that ZnSe nanoparticles exhibit semi-spherical shapes.
8