- Email: [email protected]
solid interfacial reaction
Chemical Physics Letters 382 (2003) 1–5 www.elsevier.com/locate/cplett
Immiscible silver–nickel alloying nanorods growth upon pulsed-laser induced liquid/solid interfacial reaction Q.X. Liu, C.X. Wang, W. Zhang, G.W. Wang
*
State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics Science and Engineering, Zhongshan University, Guangzhou 510275, PR China Received 25 August 2003; in final form 26 September 2003 Published online: 4 November 2003
Abstract Nanorods of the immiscible alloying silver–nickel were synthesized by pulsed-laser induced liquid/solid interfacial reaction (PLIIR). Typical diameters of these nanorods were in the range of 30–50 nm, and lengths were in the range of 300–500 nm. Transmission electronic microscope (TEM) equipped with energy depressive X-ray spectrometer (EDS) and selected area diffraction (SAD) were employed to characterize these nanorods. The analysis results showed that the prepared Ag–Ni alloying nanorods were single crystals with fcc structure. Eventually, we proposed the growth mechanism of the immiscible alloying nanorods upon PLIIR, in which both liquid and solid were simultaneously involved. Ó 2003 Elsevier B.V. All rights reserved.
One-dimensional nanostructures such as wires, rods, belts, and tubes have become the focus of intensive research owing to their unique applications in mesoscopis physics and fabrication of nanoscale devices [1]. For instance, they not only provide a good system to study the electrical and thermal transport in one-dimensional confinement, but also are expected to play an important role in both interconnection and functional units in fabricating electronic, optoelectronic, and magnetic storage devices with nanoscale dimension [2]. Laser ablation in high-temperature envi-
*
Corresponding author. Fax: +862084113692. E-mail address: [email protected] (G.W. Wang).
ronment has been demonstrated to be a general route to synthesize elemental semiconductor and binary oxides nanowires such as Si, Ge, SiO2 , GeO, ZnO, etc. [3–5]. It is noted that laser ablation to fabricate nanostructures is usually conducted in vacuum or in dilute gases. Very recently, we developed a novel laser ablation to synthesize nanocrystals, which was named to be pulsed-laser induced liquid/solid interfacial reaction (PLIIR) [6]. By used PLIIR, a series of nanocrystals including diamond with cubic and hexagonal structure [7,8], cubic C3 N4 [9], and boron nitride with cubic and explosion phase [10,11] was prepared, respectively. Interestingly, two points can be abstracted from PLIIR investigations [12], one point is that PLIIR is likely to synthesize metastable
0009-2614/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2003.10.004
2
Q.X. Liu et al. / Chemical Physics Letters 382 (2003) 1–5
phase, and another one is that new phase formation involves in both liquid and solid. In this Letter, we reported on the synthesis of single crystalline alloying nanorods of immiscible silver– nickel by PLIIR. It is known that magnetic nanostructures play a key role in fabrication of magnetic storage devices in nanoscale, and nickel is an important magnetic material. To the best of our knowledge, the synthesis of immiscible silver– nickel alloying nanorods has not been reported yet [2]. The preparation system was described in [6]. The second harmonic is produced by a Q-switch Nd:YAG laser device with wavelength k ¼ 532 nm, pulse width s ¼ 10 ns, repeating frequency m ¼ 5 Hz, and power density p ¼ 1010 W/cm2 . In our experiment, saturation silver nitrate solution was used as reactive liquid with chemical purity (99.999%), and the solid target is single nickel bulk (99.99%). The nickel target was first fixed on the bottom of a reactive chamber. Then, the silver nitrate solution was poured slowly into the chamber until the target was covered by 1–2 mm. Finally, the pulsed-laser was focused onto the target surface. During the laser ablating, the target and solution were maintained at room temperature, meanwhile, the target rotated at a slow speed (20 rotations per min). After the pulsed-laser interacted with the target for more than 60 min, the powders were collected from the solution, which were the samples to be analyzed. Transmission electronic microscope (TEM) equipped with energy depressive X-ray spectrometer (EDS) (JEM2010, 200 kV) and selected area diffraction (SAD) were employed to determine the morphology, composition, and crystalline structure of the synthesized samples by PLIIR. The typical nanorods were as evidenced by the bright field image of TEM shown in Fig. 1, in which one can see clearly that the uniform nanorods were synthesized upon pulsed-laser induced reaction at interface between nickel bulk and silver nitrate solution. From Fig. 1, one can see that the diameters of these nanorods were in the range of 20–50 nm, and the lengths were in the range of 400–600 nm. The average composition of these nanorods was about of Ag80 Ni20 determined by EDS analysis attached to TEM. Interestingly, the
Fig. 1. TEM bright field image of immiscible silver–nickel alloying nanorods synthesized by pulsed-laser induced reaction at nickel–silver nitrate solution interface.
bright field image and the corresponding diffraction of a single nanorod were shown in Fig. 2. From the inset of Fig. 2, the real compositions of the nanorod were silver and nickel, which was very closed to the average composition (Ag80 Ni20 ) of those nanorods in Fig. 1. It well known, normally, that the crystalline structure of silver nickel is face center cubic (fcc) structure, and silver and nickel are immiscible from the point of the view of equilibrium thermodynamics. Accordingly, the crystalline phase of the single Ag–Ni nanorod was identified as a new metastable fcc phase, Ag-based solid solution, with a lattice constant a ¼ 5.94 , from the corresponding SAD pattern 0.01 A shown in Fig. 3a. The indexing results for the metastable fcc phase was shown in Fig. 3b. It is noticed that the lattice constant of the Ag-based solid solution was larger than that of pure Ag
Fig. 2. TEM bright field image of a single crystalline Ag–Ni alloying nanorod, EDS spectra (inset) confirms that the nanorod is composed of Ag and Ni.
Q.X. Liu et al. / Chemical Physics Letters 382 (2003) 1–5
Fig. 3. The corresponding SAD pattern (a) and its indexing (b) of Fig. 2, in which B ¼ [111].
). In other words, the lattice constant of (a ¼ 4.85 A the Ag-based solid solution has a positive deviation from VegardÕs law [13]. These results demonstrated that the single crystalline Ag–Ni alloying nanorods was synthesized upon PLIIR. Simple silver, nickel, and their oxides nanoparticles were also encountered in the samples. However, the percentages of these nanocrystals are less than 30% according to our TEM statistics. A majority of the nanostructures in the products are stable Ag–Ni alloying nanorods, that is, Ag80 Ni20 . These results indicated that both nanocrystals and nanorods are easy to be synthesized upon pulsedlaser induced reaction at interface between nickel bulk and silver nitrate solution. Then, the Ag–Ni nanorods formation seems preferable. However, these nanorods were difficultly separated from the synthesized mixture in our lab. Now, we turned into the position to discuss the growth mechanism of these alloying nanorods upon PLIIR. Nano-sized silver, nickel, and metastable silver–nickel alloy particles have been syn-
3
thesized by liquid–solid interaction techniques from nitrate and acetate precursors of silver and nickel [14]. Moreover, the synthesis of nanoparticles and metastable alloys was also proposed to occur primarily at the laser-liquid–solid interface by a nucleation and growth mechanism [6,12]. Generally, it is proposed that PLIIR would be a very fast and far from equilibrium process, so that all metastable and stable phases forming at the initial, intermediate and final stages of the conversion could be reserved in the final products, especially, for the metastable intermediate phase [12]. In other words, the quenching times of PLIIR are so short that the metastable phase forming at the intermediate stage of the conversion could be frozen in the synthesized final products. In our early studies about synthesis of diamonds [6,8], two structures, i.e., metastable hexagonal and stable cubic structure, of diamonds had been observed simultaneously in the same samples. Furthermore, the intermediate phase of the conversion from graphite to diamond was also obtained in our experiment [12]. For the fabrication of the Ag–Ni alloying nanorods upon pulsed-laser induced reaction at the Ni/AgNO3 interface, the growth mechanism was proposed in the study. According to Fabbro and co-workers [15], at the very initial stage of interaction of high energy laser with the interface between nickel and silver nitrate solution, species ejected from the nickel target surface have a large initial kinetic energy and form a dense region in the vicinity of the solid–liquid interface due to the covering effect of liquid. This stage is similar to that occurred in vacuum or diluted air, where laser ablating generated a plasma plume. Since the plasma is confined in the liquid, it expends adiabatically at a supersonic velocity creating a shock wave in front, and the shock wave will induce an extra-pressure, called laser-induced pressure, in the plasma. Further, the laser-induced pressure will result in the temperature increasing in the plasma [16]. Therefore, compared with plasma formed in pulsed laser ablation in air or vacuum, the plasma formed in the duration of pulsed laser ablation at liquid–solid interface is in higher temperature, higher pressure, and higher density (HTHPHD) state. Sequentially, nanocrystals are would be
4
Q.X. Liu et al. / Chemical Physics Letters 382 (2003) 1–5
formed during the plasma rapidly being quenched confined in the liquid, in our case. Based on the emission spectroscopic study of pulsed laser ablation at a liquid–solid interface [17], the chemical reactions can occur not only inside the plasma, but also at the plasma–liquid interface, i.e., some chemical reactions between the ablation species and the species originated from the confined liquid, and other chemical reactions between the ablation plasma and the liquid molecules at the plasma–liquid interface. For the first case, due to extremely high temperature and pressure at the plasma–liquid interface, the interfacial region is excited to form new plasma, called plasma-induced plasma, which quickly dissolves into the laser plasma, once generated, thus, those species involving in the chemical reactions occurring in the plasma are from laser ablation solid target and excited liquid molecules. For the later case, the extremely pressure in front of the laser-induced plasma can impinge the ablation species into the confined liquid, and the chemical reaction between the ablation and the liquid molecules can occur at the plasma–liquid interface, or in the liquid region most closely to the plasma–liquid interface. Silver and nickel have the same crystalline structure (fcc), then, they are immiscible from the point of the view of equilibrium thermodynamics. In other words, normally, silver could not form an alloy phase with nickel by conventional techniques. However, non-conventional techniques such as ion beam mixing allow the fabrication of alloys from immiscible [18,19]. According to the discussion of interaction of pulsed-laser with liquid–solid interface above, Ag–Ni alloying phase would form in the plasma and its quenching upon pulsed-laser ablation at the Ni/AgNO3 interface. The laser-induced plasma is first generated at the liquid–solid interface when pulsed-laser ablated the solid target, it contains some species, e.g., Ni, and its ions, from the laser ablated solid. Following, due to the laser-induced pressure, the laserinduced plasma is driven into a HTHPHD state. Moreover, the interfacial chemical reactions between those species can occur in the laser-induced plasma. At the HTHPHD state, silver and nickel could form the alloy phase. Due to sufficient particles and energy available around the Ag–Ni
alloying nuclei because of the confinement of liquid, Ag–Ni nuclei forming and growing would be enhanced. However, as the discussed above, the quenching of plasma is a very short, rapid, and complex process, which can be affected by the parameters of pulsed-laser and surrounding liquid. Therefore, the size of these nuclei growth would be limited in nanometer. Meanwhile, silver, nickel, and their oxide particles would also form simultaneously in the products. These results are very similar to those of our early studies about preparation of diamond nanocrystals [6,12], where cubic- and hexagonal-diamond nanocrystals have been synthesized simultaneously, as well as an intermediate phase, rhombohedral phase graphite. Additionally, Poondi et al. [14,20] prepared silver, nickel, nickel oxide and silver–nickel alloying nanoparticles. It is noticed that the formation of rod-shape crystals in our case has not been fully understood yet, and the relevant study have been doing in our lab. The immiscible silver–nickel alloying nanorods were synthesized upon pulsed-laser induced quenching at nickel–silver nitrate solution interface. These results demonstrated that pulsed-laser induced liquid/solid interfacial reaction is an effective and general route to generate metastable phase nanostructures such as nanorods and nanoparticles. Importantly, it may also allow researchers to choose and combine other interesting solid targets and liquid to fabricate nanostructures of new compounds for purpose of fundamental research and potential applications.
Acknowledgements The authors are grateful to the support of the National Natural Science Foundation of the PeopleÕs Republic of China (No. 50072022).
References [1] Y. Xia, P. Yang, Adv. Mater. 15 (2003) 351. [2] Y. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, H. Yan, Adv. Mater. 15 (2003) 353. [3] P. Yang, C.M. Lieber, Science 277 (1996) 1836.
Q.X. Liu et al. / Chemical Physics Letters 382 (2003) 1–5 [4] S.T. Lee, N. Wang, Y.F. Zhang, Y.H. Tang, MRS Bull. 24 (1999) 36. [5] C.C. Tang, G. Meng, Y. Lei, F. Phillip, L. Zhang, Adv. Mater. 13 (2001) 1330. [6] G.W. Yang, J.B. Wang, Q.X. Liu, J. Phys.: Condens. Matter 10 (1998) 7923. [7] J.B. Wang, G.W. Yang, J. Phys.: Condens. Matter 11 (1999) 7089. [8] J.B. Wang, C.Y. Zhang, X.L. Zhong, G.W. Yang, Chem. Phys. Lett. 261 (2002) 86. [9] G.W. Yang, J.B. Wang, Appl. Phys. A 71 (2000) 343. [10] J.B. Wang, G.W. Yang, C.Y. Zhang, Chem. Phys. Lett. 367 (2003) 10. [11] Q.X. Liu, G.W. Yang, J.X. Zhang, Chem. Phys. Lett. 373 (2003) 56.
5
[12] G.W. Yang, J.B. Wang, Appl. Phys. A 72 (2001) 475. [13] R.A. Swalin, Thermodyamics of Solids, Wiley, New York, 1966, p. 91. [14] D. Poondi, J. Singh, J. Mater. Sci. 35 (2000) 2467. [15] L. Barther, R. Fabbro, P. Peyre, L. Tollier, E. Bartinicki, J. Appl. Phys. 89 (1997) 2836. [16] S. Zhu, Y.F. Lu, L.M. Hong, X.Y. Chen, J. Appl. Phys. 89 (2001) 2400. [17] T. Sakka, S. Iwanaga, Y.H. Ogata, J. Chem. Phys. 112 (2000) 8645. [18] G.W. Yang, W.S. Lai, C. Lin, B.X. Liu, Appl. Phys. Lett. 74 (1998) 3305. [19] B.X. Liu, W.S. Lai, Z.J. Zhang, Adv. Phys. 50 (2001) 367. [20] D. Poondi, T. Dobbins, J. Singh, J. Mater. Sci. 35 (2000) 6237.
Immiscible silver–nickel alloying nanorods growth upon pulsed-laser induced liquid/solid interfacial reaction Q.X. Liu, C.X. Wang, W. Zhang, G.W. Wang
*
State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics Science and Engineering, Zhongshan University, Guangzhou 510275, PR China Received 25 August 2003; in final form 26 September 2003 Published online: 4 November 2003
Abstract Nanorods of the immiscible alloying silver–nickel were synthesized by pulsed-laser induced liquid/solid interfacial reaction (PLIIR). Typical diameters of these nanorods were in the range of 30–50 nm, and lengths were in the range of 300–500 nm. Transmission electronic microscope (TEM) equipped with energy depressive X-ray spectrometer (EDS) and selected area diffraction (SAD) were employed to characterize these nanorods. The analysis results showed that the prepared Ag–Ni alloying nanorods were single crystals with fcc structure. Eventually, we proposed the growth mechanism of the immiscible alloying nanorods upon PLIIR, in which both liquid and solid were simultaneously involved. Ó 2003 Elsevier B.V. All rights reserved.
One-dimensional nanostructures such as wires, rods, belts, and tubes have become the focus of intensive research owing to their unique applications in mesoscopis physics and fabrication of nanoscale devices [1]. For instance, they not only provide a good system to study the electrical and thermal transport in one-dimensional confinement, but also are expected to play an important role in both interconnection and functional units in fabricating electronic, optoelectronic, and magnetic storage devices with nanoscale dimension [2]. Laser ablation in high-temperature envi-
*
Corresponding author. Fax: +862084113692. E-mail address: [email protected] (G.W. Wang).
ronment has been demonstrated to be a general route to synthesize elemental semiconductor and binary oxides nanowires such as Si, Ge, SiO2 , GeO, ZnO, etc. [3–5]. It is noted that laser ablation to fabricate nanostructures is usually conducted in vacuum or in dilute gases. Very recently, we developed a novel laser ablation to synthesize nanocrystals, which was named to be pulsed-laser induced liquid/solid interfacial reaction (PLIIR) [6]. By used PLIIR, a series of nanocrystals including diamond with cubic and hexagonal structure [7,8], cubic C3 N4 [9], and boron nitride with cubic and explosion phase [10,11] was prepared, respectively. Interestingly, two points can be abstracted from PLIIR investigations [12], one point is that PLIIR is likely to synthesize metastable
0009-2614/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2003.10.004
2
Q.X. Liu et al. / Chemical Physics Letters 382 (2003) 1–5
phase, and another one is that new phase formation involves in both liquid and solid. In this Letter, we reported on the synthesis of single crystalline alloying nanorods of immiscible silver– nickel by PLIIR. It is known that magnetic nanostructures play a key role in fabrication of magnetic storage devices in nanoscale, and nickel is an important magnetic material. To the best of our knowledge, the synthesis of immiscible silver– nickel alloying nanorods has not been reported yet [2]. The preparation system was described in [6]. The second harmonic is produced by a Q-switch Nd:YAG laser device with wavelength k ¼ 532 nm, pulse width s ¼ 10 ns, repeating frequency m ¼ 5 Hz, and power density p ¼ 1010 W/cm2 . In our experiment, saturation silver nitrate solution was used as reactive liquid with chemical purity (99.999%), and the solid target is single nickel bulk (99.99%). The nickel target was first fixed on the bottom of a reactive chamber. Then, the silver nitrate solution was poured slowly into the chamber until the target was covered by 1–2 mm. Finally, the pulsed-laser was focused onto the target surface. During the laser ablating, the target and solution were maintained at room temperature, meanwhile, the target rotated at a slow speed (20 rotations per min). After the pulsed-laser interacted with the target for more than 60 min, the powders were collected from the solution, which were the samples to be analyzed. Transmission electronic microscope (TEM) equipped with energy depressive X-ray spectrometer (EDS) (JEM2010, 200 kV) and selected area diffraction (SAD) were employed to determine the morphology, composition, and crystalline structure of the synthesized samples by PLIIR. The typical nanorods were as evidenced by the bright field image of TEM shown in Fig. 1, in which one can see clearly that the uniform nanorods were synthesized upon pulsed-laser induced reaction at interface between nickel bulk and silver nitrate solution. From Fig. 1, one can see that the diameters of these nanorods were in the range of 20–50 nm, and the lengths were in the range of 400–600 nm. The average composition of these nanorods was about of Ag80 Ni20 determined by EDS analysis attached to TEM. Interestingly, the
Fig. 1. TEM bright field image of immiscible silver–nickel alloying nanorods synthesized by pulsed-laser induced reaction at nickel–silver nitrate solution interface.
bright field image and the corresponding diffraction of a single nanorod were shown in Fig. 2. From the inset of Fig. 2, the real compositions of the nanorod were silver and nickel, which was very closed to the average composition (Ag80 Ni20 ) of those nanorods in Fig. 1. It well known, normally, that the crystalline structure of silver nickel is face center cubic (fcc) structure, and silver and nickel are immiscible from the point of the view of equilibrium thermodynamics. Accordingly, the crystalline phase of the single Ag–Ni nanorod was identified as a new metastable fcc phase, Ag-based solid solution, with a lattice constant a ¼ 5.94 , from the corresponding SAD pattern 0.01 A shown in Fig. 3a. The indexing results for the metastable fcc phase was shown in Fig. 3b. It is noticed that the lattice constant of the Ag-based solid solution was larger than that of pure Ag
Fig. 2. TEM bright field image of a single crystalline Ag–Ni alloying nanorod, EDS spectra (inset) confirms that the nanorod is composed of Ag and Ni.
Q.X. Liu et al. / Chemical Physics Letters 382 (2003) 1–5
Fig. 3. The corresponding SAD pattern (a) and its indexing (b) of Fig. 2, in which B ¼ [111].
). In other words, the lattice constant of (a ¼ 4.85 A the Ag-based solid solution has a positive deviation from VegardÕs law [13]. These results demonstrated that the single crystalline Ag–Ni alloying nanorods was synthesized upon PLIIR. Simple silver, nickel, and their oxides nanoparticles were also encountered in the samples. However, the percentages of these nanocrystals are less than 30% according to our TEM statistics. A majority of the nanostructures in the products are stable Ag–Ni alloying nanorods, that is, Ag80 Ni20 . These results indicated that both nanocrystals and nanorods are easy to be synthesized upon pulsedlaser induced reaction at interface between nickel bulk and silver nitrate solution. Then, the Ag–Ni nanorods formation seems preferable. However, these nanorods were difficultly separated from the synthesized mixture in our lab. Now, we turned into the position to discuss the growth mechanism of these alloying nanorods upon PLIIR. Nano-sized silver, nickel, and metastable silver–nickel alloy particles have been syn-
3
thesized by liquid–solid interaction techniques from nitrate and acetate precursors of silver and nickel [14]. Moreover, the synthesis of nanoparticles and metastable alloys was also proposed to occur primarily at the laser-liquid–solid interface by a nucleation and growth mechanism [6,12]. Generally, it is proposed that PLIIR would be a very fast and far from equilibrium process, so that all metastable and stable phases forming at the initial, intermediate and final stages of the conversion could be reserved in the final products, especially, for the metastable intermediate phase [12]. In other words, the quenching times of PLIIR are so short that the metastable phase forming at the intermediate stage of the conversion could be frozen in the synthesized final products. In our early studies about synthesis of diamonds [6,8], two structures, i.e., metastable hexagonal and stable cubic structure, of diamonds had been observed simultaneously in the same samples. Furthermore, the intermediate phase of the conversion from graphite to diamond was also obtained in our experiment [12]. For the fabrication of the Ag–Ni alloying nanorods upon pulsed-laser induced reaction at the Ni/AgNO3 interface, the growth mechanism was proposed in the study. According to Fabbro and co-workers [15], at the very initial stage of interaction of high energy laser with the interface between nickel and silver nitrate solution, species ejected from the nickel target surface have a large initial kinetic energy and form a dense region in the vicinity of the solid–liquid interface due to the covering effect of liquid. This stage is similar to that occurred in vacuum or diluted air, where laser ablating generated a plasma plume. Since the plasma is confined in the liquid, it expends adiabatically at a supersonic velocity creating a shock wave in front, and the shock wave will induce an extra-pressure, called laser-induced pressure, in the plasma. Further, the laser-induced pressure will result in the temperature increasing in the plasma [16]. Therefore, compared with plasma formed in pulsed laser ablation in air or vacuum, the plasma formed in the duration of pulsed laser ablation at liquid–solid interface is in higher temperature, higher pressure, and higher density (HTHPHD) state. Sequentially, nanocrystals are would be
4
Q.X. Liu et al. / Chemical Physics Letters 382 (2003) 1–5
formed during the plasma rapidly being quenched confined in the liquid, in our case. Based on the emission spectroscopic study of pulsed laser ablation at a liquid–solid interface [17], the chemical reactions can occur not only inside the plasma, but also at the plasma–liquid interface, i.e., some chemical reactions between the ablation species and the species originated from the confined liquid, and other chemical reactions between the ablation plasma and the liquid molecules at the plasma–liquid interface. For the first case, due to extremely high temperature and pressure at the plasma–liquid interface, the interfacial region is excited to form new plasma, called plasma-induced plasma, which quickly dissolves into the laser plasma, once generated, thus, those species involving in the chemical reactions occurring in the plasma are from laser ablation solid target and excited liquid molecules. For the later case, the extremely pressure in front of the laser-induced plasma can impinge the ablation species into the confined liquid, and the chemical reaction between the ablation and the liquid molecules can occur at the plasma–liquid interface, or in the liquid region most closely to the plasma–liquid interface. Silver and nickel have the same crystalline structure (fcc), then, they are immiscible from the point of the view of equilibrium thermodynamics. In other words, normally, silver could not form an alloy phase with nickel by conventional techniques. However, non-conventional techniques such as ion beam mixing allow the fabrication of alloys from immiscible [18,19]. According to the discussion of interaction of pulsed-laser with liquid–solid interface above, Ag–Ni alloying phase would form in the plasma and its quenching upon pulsed-laser ablation at the Ni/AgNO3 interface. The laser-induced plasma is first generated at the liquid–solid interface when pulsed-laser ablated the solid target, it contains some species, e.g., Ni, and its ions, from the laser ablated solid. Following, due to the laser-induced pressure, the laserinduced plasma is driven into a HTHPHD state. Moreover, the interfacial chemical reactions between those species can occur in the laser-induced plasma. At the HTHPHD state, silver and nickel could form the alloy phase. Due to sufficient particles and energy available around the Ag–Ni
alloying nuclei because of the confinement of liquid, Ag–Ni nuclei forming and growing would be enhanced. However, as the discussed above, the quenching of plasma is a very short, rapid, and complex process, which can be affected by the parameters of pulsed-laser and surrounding liquid. Therefore, the size of these nuclei growth would be limited in nanometer. Meanwhile, silver, nickel, and their oxide particles would also form simultaneously in the products. These results are very similar to those of our early studies about preparation of diamond nanocrystals [6,12], where cubic- and hexagonal-diamond nanocrystals have been synthesized simultaneously, as well as an intermediate phase, rhombohedral phase graphite. Additionally, Poondi et al. [14,20] prepared silver, nickel, nickel oxide and silver–nickel alloying nanoparticles. It is noticed that the formation of rod-shape crystals in our case has not been fully understood yet, and the relevant study have been doing in our lab. The immiscible silver–nickel alloying nanorods were synthesized upon pulsed-laser induced quenching at nickel–silver nitrate solution interface. These results demonstrated that pulsed-laser induced liquid/solid interfacial reaction is an effective and general route to generate metastable phase nanostructures such as nanorods and nanoparticles. Importantly, it may also allow researchers to choose and combine other interesting solid targets and liquid to fabricate nanostructures of new compounds for purpose of fundamental research and potential applications.
Acknowledgements The authors are grateful to the support of the National Natural Science Foundation of the PeopleÕs Republic of China (No. 50072022).
References [1] Y. Xia, P. Yang, Adv. Mater. 15 (2003) 351. [2] Y. Xia, P. Yang, Y. Sun, Y. Wu, B. Mayers, B. Gates, Y. Yin, F. Kim, H. Yan, Adv. Mater. 15 (2003) 353. [3] P. Yang, C.M. Lieber, Science 277 (1996) 1836.
Q.X. Liu et al. / Chemical Physics Letters 382 (2003) 1–5 [4] S.T. Lee, N. Wang, Y.F. Zhang, Y.H. Tang, MRS Bull. 24 (1999) 36. [5] C.C. Tang, G. Meng, Y. Lei, F. Phillip, L. Zhang, Adv. Mater. 13 (2001) 1330. [6] G.W. Yang, J.B. Wang, Q.X. Liu, J. Phys.: Condens. Matter 10 (1998) 7923. [7] J.B. Wang, G.W. Yang, J. Phys.: Condens. Matter 11 (1999) 7089. [8] J.B. Wang, C.Y. Zhang, X.L. Zhong, G.W. Yang, Chem. Phys. Lett. 261 (2002) 86. [9] G.W. Yang, J.B. Wang, Appl. Phys. A 71 (2000) 343. [10] J.B. Wang, G.W. Yang, C.Y. Zhang, Chem. Phys. Lett. 367 (2003) 10. [11] Q.X. Liu, G.W. Yang, J.X. Zhang, Chem. Phys. Lett. 373 (2003) 56.
5
[12] G.W. Yang, J.B. Wang, Appl. Phys. A 72 (2001) 475. [13] R.A. Swalin, Thermodyamics of Solids, Wiley, New York, 1966, p. 91. [14] D. Poondi, J. Singh, J. Mater. Sci. 35 (2000) 2467. [15] L. Barther, R. Fabbro, P. Peyre, L. Tollier, E. Bartinicki, J. Appl. Phys. 89 (1997) 2836. [16] S. Zhu, Y.F. Lu, L.M. Hong, X.Y. Chen, J. Appl. Phys. 89 (2001) 2400. [17] T. Sakka, S. Iwanaga, Y.H. Ogata, J. Chem. Phys. 112 (2000) 8645. [18] G.W. Yang, W.S. Lai, C. Lin, B.X. Liu, Appl. Phys. Lett. 74 (1998) 3305. [19] B.X. Liu, W.S. Lai, Z.J. Zhang, Adv. Phys. 50 (2001) 367. [20] D. Poondi, T. Dobbins, J. Singh, J. Mater. Sci. 35 (2000) 6237.