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Low-temperature synthesis and shape control of ZnO nanorods
Current Applied Physics 6 (2006) 796–800 www.elsevier.com/locate/cap www.kps.or.kr
Low-temperature synthesis and shape control of ZnO nanorods Xiao Li Zhang, Young Hwan Kim, Young Soo Kang
*
Department of Chemistry, Pukyong National University, 599-1 Daeyeon-3-dong, Nam-gu, Busan 608-737, Republic of Korea Received 17 June 2004; received in revised form 13 December 2004 Available online 31 May 2005
Abstract Semiconducting ZnO nanorods were synthesized by wet-chemical approach with an alcohol solution containing zinc ions at low temperature. A novel sonochemical method had been added into the process to study the mechanism of shape-control of 1D nanostructure assembly. The different solvent condition and the sonic-treating had shown clearly to have an effects on the shape control. The crystallinity and the character of the particles were described in the patterns of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS) and UV–visible absorption spectroscopy. Ó 2005 Elsevier B.V. All rights reserved. PACS: 81.16. c Keywords: Zinc oxide; Nanorods; Wet-chemical approach; Sonochemistry; Shape control
1. Introduction In recent years, research on one-dimensional (1D) nanostructure semiconductors has been increasingly popular due to their importance in basic scientific studies and potential technological applications [1,2]. For example, the novel optical, electrical, and mechanical properties of devices comprising nanocrystallite semiconductors and oxides have been demonstrated in photovoltaic solar cells, light-emitting diodes, varistors, and ceramics. Other than carbon nanotubes, 1D nanostructures such as nanowires (or nanorods) and quantum wires (or rods) are ideal systems for investigating the dependence of electrical transport, optical and mechanical properties on size and dimensionality [3]. Semiconductor ZnO has a wide bandgap of 3.37 eV at room temperature with a large exciton binding energy of 60 meV. The strong exciton binding energy, which is much larger than that of GaN (25 meV) and the thermal *
Corresponding author. E-mail address: [email protected] (Y.S. Kang).
1567-1739/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2005.04.042
energy at room temperature (26 meV), can ensure an efficient exciton emission at room temperature under low excitation energy [4,5]. On the other hand, zinc oxide is also recognized as a promising photonic material in the blue–UV region. Room temperature UV lasing properties have recently been reported in disordered particles, thin films, and nanoclusters [6,7]. The assembly of one-dimensional single-crystalline ZnO nanostructures has been of growing interest owing to their promising application in nanoscale optoelectronic devices. Single-crystalline ZnO nanorods have been synthesized successfully using high-temperature vapor–liquid–solid (VLS) growth methods and wet-chemical methods [8–11]. Currently, the sonochemical process has been proved to be a useful technique for generating nanodimensional materials, and various nanostructured materials, including metal colloids, and low aspect-ratio semiconductor nanorods [12–20]. During sonication, ultrasonic sound waves radiate through the solution causing alternating high and low pressures in the liquid medium. Millions of microscopic bubbles form and grow in the low
X.L. Zhang et al. / Current Applied Physics 6 (2006) 796–800
pressure stage, and subsequently collapse in the high pressure stage [17,18]. Hot spots that localized regions of extremely high temperatures as high as 5000 K, and pressures of up to 1800 atm can occur from the collapsing bubbles, and cooling rates can often exceed 1010 K s 1 [12]. The energy released from this process, known as cavitation, can lead to enhanced chemical reactivities and accelerated reaction rates. Here, the preparation of ZnO nanorods according to a method described earlier [10] was adapted to study the factors that influence the rate of particle growth and shape-control. The results enable a more controlled and more easyto-use sol–gel method of quantum-sized ZnO nanorods.
2. Experimental 2.1. Materials Zinc acetate dihydrate (Zn(C2H4O2)2 Æ 2H2O, 98%), sodium hydroxide (NaOH, 93%), methanol (CH3OH, 99.85%) and ethanol (CH3CH2OH, 99.9%) were purchased from Aldrich Chemical Co. All reagent-grade chemicals were used as received without any further purification. House-distilled water was passed through a four-cartridge Barnstead Nanopure II purification train consisting of Macropure pretreatment, organic free, and a 0.2 lm hollow-fiber final filter for removing particles. Its resistivity was determined as 18.4 MX and used throughout. 2.2. Preparation of ZnO nanorods ZnO nanorods were synthesized form zinc acetate dihydrate in alcohol solution. In a typical reaction, zinc acetate dihydrate was dissolved in methanol with intense stirring at room temperature. Subsequently, a methanol solution containing sodium hydroxide (1.5 stoichiometric ratio of zinc acetate) was added dropwise into at same temperature. The resulting mixture was refluxed at boiling point of the alcohol to obtain rod-shaped products. For studying the shape-control, a pretreatment of ultrasonic was used while the alkali solution was dropped. To learn more about the growth mechanism, we have performed the experiments in different ways. First, we prepared a sol of quasi-spherical particles at low concentration, in order to observe the effect of sonochemistry clearly. Then we increased the particle concentration in a second step by solvent evaporation, and finally refluxed these solutions for 2 h—3 days. We also used alcohols with different polarity to represent. 2.3. Apparatus ZnO nanoparticles were structurally characterized by transmission electron microscopy (TEM, JEOL, JEM-
797
2010), X-ray diffractometer (XRD, PHILIPS, XPertMPD system), and Energy dispersive X-ray spectrometer (EDS, HITACHI, S-2400). Optical absorption spectra were recorded on a Unicam UV2 spectrophotometer.
3. Results and discussion The particles of the low-concentration (0.33 M) starting sol in methanol solvent are described in Fig. 1. The 2 hours refluxing products with an average particle size of approximately 9 nm is shown in Fig. 1A. Fig. 1B shows a lot of shot-rod-shaped particles that were carried by an ultrasonic pretreatment. The main diameter of these rods is similar to the particles observed in Fig. 1A. The similar phenomenon appears in ethanol solvent also. The corresponding 3-day refluxed products are in Fig. 1C and D apart. The rod-shape, length and diameter are more uniform in image D. The results exhibit that ultrasonic pretreatment can increase ZnO growth speed on c axis. From image A to C, then to E, the length of the rods appears an observed improvement along the c axis. Except the ultrasonic pretreatment, the further growth of rod depends on the reaction time and the concentration of starting sol. And Fig. 1E and F record the 3-day refluxed products that were carried in methanol solvent (boiling point is 60 °C) and ethanol solvent (boiling point is 80 °C) at a high concentration (0.53 M) of starting sol. As we all know, the polarity of methanol is very close to ethanol. Here, the product came out from methanol solvent shows a main diameter around 10 nm and an aspect ratio to 5.5–7.9. And the product synthesized in ethanol has the general diameter about 19 nm and the aspect ratio 3.4–4.6. Regarding the growth process, it is believed that the reactive temperature is important to assemble 1D ZnO nanorods. Typical XRD pattern (Fig. 2) shows a high degree of crystallinity, and all of the peaks match well with the standard wurtzite structure (P63mc, JCPDS card no. 05-0664). Curve A, B and C corresponds to starting sol (Fig. 1A), ultrasonic pretreated starting sol (Fig. 1B) and ultrasonic pretreated 3-day refluxed product (Fig. 1D). All of them were synthesized in methanol solvent at 0.33 M concentration. In the diffraction patterns, curve B is smoother than curve A that confirms the effect of ultrasonic treatment. Ultrasonic pretreatment of the mixture solution may generate a suitable amount of ZnO crystal nuclei for the subsequent growth. In comparison with curve B, in curve C the 002 reflection has strongly sharpened up which is consistent with rod formation along the c axis. Under ultrasonic condition, the inner environment of the collapsing bubble which causes alcohol to vaporize and further to paralyzed into H and RO radicals [21– 23]. These radicals increase the ionization of OH ions
798
X.L. Zhang et al. / Current Applied Physics 6 (2006) 796–800
Fig. 1. Transmission electron microscopic images: A and B (with ultrasonic pretreatment) show a low concentration (0.33 M) ZnO starting sol that were carried in methanol solvent; the corresponding 3-day refluxed ZnO nanorods are in C and D (with ultrasonic pretreatment); E and F record the 3-day refluxed ZnO nanorods that were carried in methanol solvent (boiling point is 60 °C) and ethanol solvent (boiling point is 80 °C) at a high concentration (0.53 M) of starting sol.
from sodium hydroxide in alcohol solvent, especially on the c axis. The chemical stoichiometry of ZnO nanorods was investigated with EDX (Fig. 3), which affirmed an atomic ratio of Zn:O 1:1.
In UV/vis absorbance spectra (Fig. 4), kmax value shows a red shift that is coincident with the rodlength increasing from ultrasonic carried starting sol (Fig. 1B), 3-day refluxed product at 0.33 M (Fig. 1D) to
X.L. Zhang et al. / Current Applied Physics 6 (2006) 796–800 1.4
002 101
500
1.2
400
355.00
100
Absorbance
110
300
103
1.0
102
Intensity
799
C 200
B
0.8 0.6
B A
347.00 361.00
C
0.4
100 0.2
A 0 20
30
40
50
60
70
80
0.0 325
2o theta
350
375
400
425
Wavelength (nm)
Fig. 2. X-ray diffraction patterns: curve A corresponds to the 0.33 M ZnO starting sol in methanol solvent; curve B corresponds to the 0.33 M ZnO starting sol (with ultrasonic pretreatment) in methanol solvent; curve C corresponds to the 3-day refluxed ZnO nanorods (with ultrasonic pretreatment).
Fig. 4. UV–vis absorbance spectra: curve A and B corresponds to the 0.33 M ZnO starting sol and the 3-day refluxed ZnO nanorods (with ultrasonic pretreatment) in methanol solvent; curve C corresponds to the 3-day refluxed ZnO nanorods that were carried in methanol solvent 0.53 M of start sol.
Acknowledgement 9000
Zn
This work was supported by Functional Chemicals Development Program in 2003–2004.
Counts
Elmt Element % Atomic % O 18.29 47.78 Zn 81.71 52.22 Total 100.00 100.00 6000
References Zn 3000
O
Zn
0 0
5
10
Energy (KeV)
15
20
Fig. 3. EDX patterns of the 3-day refluxed ZnO nanorods (with ultrasonic pretreatment).
3-day-refluxed product at 0.55 M (Fig. 1E). Hence, UV/ vis absorbance spectra may provide a convenient way to investigate rod growth. The method had been used to determine the relative size of ZnO nanoparticle [14].
4. Conclusion The known method of preparation of ZnO nanorods in alcoholic solution has been modified and extended. The pretreatment was used in the experimental process by addition of application of sonochemistry. Recognizing the influence of ultrasonic pretreatment, temperature and reaction time improved the shape-control of the ZnO nanorods during the growing process.
[1] J. Hu, T.W. Odom, C.M. Lieber, Acc. Chem. Res. 32 (1999) 435. [2] Y. Wu, H. Yan, P. Yang, Chem. Eur. J. 8 (2002) 1260. [3] P. Yang, H. Yan, S. Mao, R. Russo, J. Johnson, R. Saykally, N. Morris, J. Pham, R. He, H. Choi, Adv. Funct. Mater. 12 (2002) 323. [4] Y. Chen, D.M. Bagnall, H. Koh, K. Park, K. Hiraga, Z. Zhu, T. Yao, J. Appl. Phys. 84 (1998) 3912. [5] A. Ohtomo, M. Kawasaki, Y. Sakurai, I. Ohkubo, R. Shiroki, Y. Yoshida, T. Yasuda, Y. Segawa, H. Koinuma, Mater. Sci. Eng. B 56 (1998) 263. [6] D.M. Bagnall, Y.F. Chen, Z. Zhu, T. Yao, S. Koyama, M.Y. Shen, T. Goto, Appl. Phys. Lett. 70 (1997) 2230. [7] H. Co, J.Y. Xu, E.W. Seelig, R.P.H. Chang, Appl. Phys. Lett. 76 (2000) 2997. [8] M.H. Huang, Y. Wu, H. Feick, N. Tran, E. Wever, P. Yang, Adv. Mater. 13 (2001) 113. [9] Y.C. Kong, D.P. Yu, B. Zhang, W. Fang, S.Q. Feng, Appl. Phys. Lett. 78 (2001) 407. [10] C. Pacholski, A. Kornowski, H. Weller, Angew. Chem. Int. Ed. 41 (2002) 1188. [11] B. Liu, H.C. Zeng, J. Am. Chem. Soc. 125 (2003) 4430. [12] K.S. Suslick, Science 247 (1990) 1439. [13] C.L. Bianchi, R. Carli, S. Lanzani, D. Lorenzetti, G. Vergani, V. Ragaini, Ultrason. Sonochem. 1 (1994) S47. [14] Y. Koltypin, G. Katabi, R. Prozorov, A. Gedanken, J. NonCryst. Solids 201 (1996) 159. [15] J.J. Zhu, Y. Koltypin, A. Gedanken, Chem. Mater. 12 (2000) 73. [16] S.V. Ley, C.M.R. Low, Ultrasound in Synthesis, Springer-Verlag, New York, 1989. [17] T.J. Mason, J.P. Lorimer, Sonochemistry: Theory, Applications and Uses of Ultrasound in Chemistry, John Wiley and Sons, New York, 1988.
800
X.L. Zhang et al. / Current Applied Physics 6 (2006) 796–800
[18] K.S. Suslick, Ultrasound: Its Chemical, Physical, and Biological Effects, VCH Publishers, New York, 1988. [19] H. Wang, J.J. Zhu, J.M. Zhu, H.Y. Chen, J. Phys. Chem. 106 (2002) 3848. [20] B. Gates, B. Mayers, A. Grossman, Y.N. Xia, Adv. Mater. 14 (2002) 1749.
[21] Y. Nagata, Y. Watanabe, S. Fujita, T. Dohmaru, S. Taniguchi, Chem. Commun. (1992) 1620. [22] E.B. Flint, K. Suslick, J. Phys. Chem. 95 (1991) 1484. [23] T. Fujimoto, S.-Y. Terauchi, H. Umehara, I. Kojima, W. Henderson, Chem. Mater. 13 (2001) 1057.
Low-temperature synthesis and shape control of ZnO nanorods Xiao Li Zhang, Young Hwan Kim, Young Soo Kang
*
Department of Chemistry, Pukyong National University, 599-1 Daeyeon-3-dong, Nam-gu, Busan 608-737, Republic of Korea Received 17 June 2004; received in revised form 13 December 2004 Available online 31 May 2005
Abstract Semiconducting ZnO nanorods were synthesized by wet-chemical approach with an alcohol solution containing zinc ions at low temperature. A novel sonochemical method had been added into the process to study the mechanism of shape-control of 1D nanostructure assembly. The different solvent condition and the sonic-treating had shown clearly to have an effects on the shape control. The crystallinity and the character of the particles were described in the patterns of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS) and UV–visible absorption spectroscopy. Ó 2005 Elsevier B.V. All rights reserved. PACS: 81.16. c Keywords: Zinc oxide; Nanorods; Wet-chemical approach; Sonochemistry; Shape control
1. Introduction In recent years, research on one-dimensional (1D) nanostructure semiconductors has been increasingly popular due to their importance in basic scientific studies and potential technological applications [1,2]. For example, the novel optical, electrical, and mechanical properties of devices comprising nanocrystallite semiconductors and oxides have been demonstrated in photovoltaic solar cells, light-emitting diodes, varistors, and ceramics. Other than carbon nanotubes, 1D nanostructures such as nanowires (or nanorods) and quantum wires (or rods) are ideal systems for investigating the dependence of electrical transport, optical and mechanical properties on size and dimensionality [3]. Semiconductor ZnO has a wide bandgap of 3.37 eV at room temperature with a large exciton binding energy of 60 meV. The strong exciton binding energy, which is much larger than that of GaN (25 meV) and the thermal *
Corresponding author. E-mail address: [email protected] (Y.S. Kang).
1567-1739/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cap.2005.04.042
energy at room temperature (26 meV), can ensure an efficient exciton emission at room temperature under low excitation energy [4,5]. On the other hand, zinc oxide is also recognized as a promising photonic material in the blue–UV region. Room temperature UV lasing properties have recently been reported in disordered particles, thin films, and nanoclusters [6,7]. The assembly of one-dimensional single-crystalline ZnO nanostructures has been of growing interest owing to their promising application in nanoscale optoelectronic devices. Single-crystalline ZnO nanorods have been synthesized successfully using high-temperature vapor–liquid–solid (VLS) growth methods and wet-chemical methods [8–11]. Currently, the sonochemical process has been proved to be a useful technique for generating nanodimensional materials, and various nanostructured materials, including metal colloids, and low aspect-ratio semiconductor nanorods [12–20]. During sonication, ultrasonic sound waves radiate through the solution causing alternating high and low pressures in the liquid medium. Millions of microscopic bubbles form and grow in the low
X.L. Zhang et al. / Current Applied Physics 6 (2006) 796–800
pressure stage, and subsequently collapse in the high pressure stage [17,18]. Hot spots that localized regions of extremely high temperatures as high as 5000 K, and pressures of up to 1800 atm can occur from the collapsing bubbles, and cooling rates can often exceed 1010 K s 1 [12]. The energy released from this process, known as cavitation, can lead to enhanced chemical reactivities and accelerated reaction rates. Here, the preparation of ZnO nanorods according to a method described earlier [10] was adapted to study the factors that influence the rate of particle growth and shape-control. The results enable a more controlled and more easyto-use sol–gel method of quantum-sized ZnO nanorods.
2. Experimental 2.1. Materials Zinc acetate dihydrate (Zn(C2H4O2)2 Æ 2H2O, 98%), sodium hydroxide (NaOH, 93%), methanol (CH3OH, 99.85%) and ethanol (CH3CH2OH, 99.9%) were purchased from Aldrich Chemical Co. All reagent-grade chemicals were used as received without any further purification. House-distilled water was passed through a four-cartridge Barnstead Nanopure II purification train consisting of Macropure pretreatment, organic free, and a 0.2 lm hollow-fiber final filter for removing particles. Its resistivity was determined as 18.4 MX and used throughout. 2.2. Preparation of ZnO nanorods ZnO nanorods were synthesized form zinc acetate dihydrate in alcohol solution. In a typical reaction, zinc acetate dihydrate was dissolved in methanol with intense stirring at room temperature. Subsequently, a methanol solution containing sodium hydroxide (1.5 stoichiometric ratio of zinc acetate) was added dropwise into at same temperature. The resulting mixture was refluxed at boiling point of the alcohol to obtain rod-shaped products. For studying the shape-control, a pretreatment of ultrasonic was used while the alkali solution was dropped. To learn more about the growth mechanism, we have performed the experiments in different ways. First, we prepared a sol of quasi-spherical particles at low concentration, in order to observe the effect of sonochemistry clearly. Then we increased the particle concentration in a second step by solvent evaporation, and finally refluxed these solutions for 2 h—3 days. We also used alcohols with different polarity to represent. 2.3. Apparatus ZnO nanoparticles were structurally characterized by transmission electron microscopy (TEM, JEOL, JEM-
797
2010), X-ray diffractometer (XRD, PHILIPS, XPertMPD system), and Energy dispersive X-ray spectrometer (EDS, HITACHI, S-2400). Optical absorption spectra were recorded on a Unicam UV2 spectrophotometer.
3. Results and discussion The particles of the low-concentration (0.33 M) starting sol in methanol solvent are described in Fig. 1. The 2 hours refluxing products with an average particle size of approximately 9 nm is shown in Fig. 1A. Fig. 1B shows a lot of shot-rod-shaped particles that were carried by an ultrasonic pretreatment. The main diameter of these rods is similar to the particles observed in Fig. 1A. The similar phenomenon appears in ethanol solvent also. The corresponding 3-day refluxed products are in Fig. 1C and D apart. The rod-shape, length and diameter are more uniform in image D. The results exhibit that ultrasonic pretreatment can increase ZnO growth speed on c axis. From image A to C, then to E, the length of the rods appears an observed improvement along the c axis. Except the ultrasonic pretreatment, the further growth of rod depends on the reaction time and the concentration of starting sol. And Fig. 1E and F record the 3-day refluxed products that were carried in methanol solvent (boiling point is 60 °C) and ethanol solvent (boiling point is 80 °C) at a high concentration (0.53 M) of starting sol. As we all know, the polarity of methanol is very close to ethanol. Here, the product came out from methanol solvent shows a main diameter around 10 nm and an aspect ratio to 5.5–7.9. And the product synthesized in ethanol has the general diameter about 19 nm and the aspect ratio 3.4–4.6. Regarding the growth process, it is believed that the reactive temperature is important to assemble 1D ZnO nanorods. Typical XRD pattern (Fig. 2) shows a high degree of crystallinity, and all of the peaks match well with the standard wurtzite structure (P63mc, JCPDS card no. 05-0664). Curve A, B and C corresponds to starting sol (Fig. 1A), ultrasonic pretreated starting sol (Fig. 1B) and ultrasonic pretreated 3-day refluxed product (Fig. 1D). All of them were synthesized in methanol solvent at 0.33 M concentration. In the diffraction patterns, curve B is smoother than curve A that confirms the effect of ultrasonic treatment. Ultrasonic pretreatment of the mixture solution may generate a suitable amount of ZnO crystal nuclei for the subsequent growth. In comparison with curve B, in curve C the 002 reflection has strongly sharpened up which is consistent with rod formation along the c axis. Under ultrasonic condition, the inner environment of the collapsing bubble which causes alcohol to vaporize and further to paralyzed into H and RO radicals [21– 23]. These radicals increase the ionization of OH ions
798
X.L. Zhang et al. / Current Applied Physics 6 (2006) 796–800
Fig. 1. Transmission electron microscopic images: A and B (with ultrasonic pretreatment) show a low concentration (0.33 M) ZnO starting sol that were carried in methanol solvent; the corresponding 3-day refluxed ZnO nanorods are in C and D (with ultrasonic pretreatment); E and F record the 3-day refluxed ZnO nanorods that were carried in methanol solvent (boiling point is 60 °C) and ethanol solvent (boiling point is 80 °C) at a high concentration (0.53 M) of starting sol.
from sodium hydroxide in alcohol solvent, especially on the c axis. The chemical stoichiometry of ZnO nanorods was investigated with EDX (Fig. 3), which affirmed an atomic ratio of Zn:O 1:1.
In UV/vis absorbance spectra (Fig. 4), kmax value shows a red shift that is coincident with the rodlength increasing from ultrasonic carried starting sol (Fig. 1B), 3-day refluxed product at 0.33 M (Fig. 1D) to
X.L. Zhang et al. / Current Applied Physics 6 (2006) 796–800 1.4
002 101
500
1.2
400
355.00
100
Absorbance
110
300
103
1.0
102
Intensity
799
C 200
B
0.8 0.6
B A
347.00 361.00
C
0.4
100 0.2
A 0 20
30
40
50
60
70
80
0.0 325
2o theta
350
375
400
425
Wavelength (nm)
Fig. 2. X-ray diffraction patterns: curve A corresponds to the 0.33 M ZnO starting sol in methanol solvent; curve B corresponds to the 0.33 M ZnO starting sol (with ultrasonic pretreatment) in methanol solvent; curve C corresponds to the 3-day refluxed ZnO nanorods (with ultrasonic pretreatment).
Fig. 4. UV–vis absorbance spectra: curve A and B corresponds to the 0.33 M ZnO starting sol and the 3-day refluxed ZnO nanorods (with ultrasonic pretreatment) in methanol solvent; curve C corresponds to the 3-day refluxed ZnO nanorods that were carried in methanol solvent 0.53 M of start sol.
Acknowledgement 9000
Zn
This work was supported by Functional Chemicals Development Program in 2003–2004.
Counts
Elmt Element % Atomic % O 18.29 47.78 Zn 81.71 52.22 Total 100.00 100.00 6000
References Zn 3000
O
Zn
0 0
5
10
Energy (KeV)
15
20
Fig. 3. EDX patterns of the 3-day refluxed ZnO nanorods (with ultrasonic pretreatment).
3-day-refluxed product at 0.55 M (Fig. 1E). Hence, UV/ vis absorbance spectra may provide a convenient way to investigate rod growth. The method had been used to determine the relative size of ZnO nanoparticle [14].
4. Conclusion The known method of preparation of ZnO nanorods in alcoholic solution has been modified and extended. The pretreatment was used in the experimental process by addition of application of sonochemistry. Recognizing the influence of ultrasonic pretreatment, temperature and reaction time improved the shape-control of the ZnO nanorods during the growing process.
[1] J. Hu, T.W. Odom, C.M. Lieber, Acc. Chem. Res. 32 (1999) 435. [2] Y. Wu, H. Yan, P. Yang, Chem. Eur. J. 8 (2002) 1260. [3] P. Yang, H. Yan, S. Mao, R. Russo, J. Johnson, R. Saykally, N. Morris, J. Pham, R. He, H. Choi, Adv. Funct. Mater. 12 (2002) 323. [4] Y. Chen, D.M. Bagnall, H. Koh, K. Park, K. Hiraga, Z. Zhu, T. Yao, J. Appl. Phys. 84 (1998) 3912. [5] A. Ohtomo, M. Kawasaki, Y. Sakurai, I. Ohkubo, R. Shiroki, Y. Yoshida, T. Yasuda, Y. Segawa, H. Koinuma, Mater. Sci. Eng. B 56 (1998) 263. [6] D.M. Bagnall, Y.F. Chen, Z. Zhu, T. Yao, S. Koyama, M.Y. Shen, T. Goto, Appl. Phys. Lett. 70 (1997) 2230. [7] H. Co, J.Y. Xu, E.W. Seelig, R.P.H. Chang, Appl. Phys. Lett. 76 (2000) 2997. [8] M.H. Huang, Y. Wu, H. Feick, N. Tran, E. Wever, P. Yang, Adv. Mater. 13 (2001) 113. [9] Y.C. Kong, D.P. Yu, B. Zhang, W. Fang, S.Q. Feng, Appl. Phys. Lett. 78 (2001) 407. [10] C. Pacholski, A. Kornowski, H. Weller, Angew. Chem. Int. Ed. 41 (2002) 1188. [11] B. Liu, H.C. Zeng, J. Am. Chem. Soc. 125 (2003) 4430. [12] K.S. Suslick, Science 247 (1990) 1439. [13] C.L. Bianchi, R. Carli, S. Lanzani, D. Lorenzetti, G. Vergani, V. Ragaini, Ultrason. Sonochem. 1 (1994) S47. [14] Y. Koltypin, G. Katabi, R. Prozorov, A. Gedanken, J. NonCryst. Solids 201 (1996) 159. [15] J.J. Zhu, Y. Koltypin, A. Gedanken, Chem. Mater. 12 (2000) 73. [16] S.V. Ley, C.M.R. Low, Ultrasound in Synthesis, Springer-Verlag, New York, 1989. [17] T.J. Mason, J.P. Lorimer, Sonochemistry: Theory, Applications and Uses of Ultrasound in Chemistry, John Wiley and Sons, New York, 1988.
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X.L. Zhang et al. / Current Applied Physics 6 (2006) 796–800
[18] K.S. Suslick, Ultrasound: Its Chemical, Physical, and Biological Effects, VCH Publishers, New York, 1988. [19] H. Wang, J.J. Zhu, J.M. Zhu, H.Y. Chen, J. Phys. Chem. 106 (2002) 3848. [20] B. Gates, B. Mayers, A. Grossman, Y.N. Xia, Adv. Mater. 14 (2002) 1749.
[21] Y. Nagata, Y. Watanabe, S. Fujita, T. Dohmaru, S. Taniguchi, Chem. Commun. (1992) 1620. [22] E.B. Flint, K. Suslick, J. Phys. Chem. 95 (1991) 1484. [23] T. Fujimoto, S.-Y. Terauchi, H. Umehara, I. Kojima, W. Henderson, Chem. Mater. 13 (2001) 1057.