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Efficient preparation of NiSi nanowires by DC arc-discharge
ARTICLE IN PRESS Physica E 41 (2008) 185– 188
Contents lists available at ScienceDirect
Physica E journal homepage: www.elsevier.com/locate/physe
Efficient preparation of NiSi nanowires by DC arc-discharge Z.R. Geng a, Q.H. Lu a, P.X. Yan a,b,, D. Yan a, G.H. Yue a a b
Institute for Plasma and Metal Materials, Lanzhou University, Lanzhou 730000, PR China State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China
a r t i c l e in fo
abstract
Article history: Received 31 March 2008 Received in revised form 11 May 2008 Accepted 16 May 2008 Available online 4 June 2008
NiSi nanowires were synthesized by DC arc-discharge approach. As material sources, mixtures of Si and Ni powders (high purity chemicals) were put into a graphite crucible as the anode. The products were characterized by SEM, TEM, EDX and XRD. As-prepared NiSi nanowires have the diameter of 50–100 nm and length of several micrometers. From the obtained experimental results, we explain the growth mechanism of the nanowires based on the vapor–liquid–solid (VLS) growth model. Two important conditions, high temperature and enough Ni supply, are emphasized for the synthesis of the NiSi nanowires. Magnetic characterization was carried out and the results show that the NiSi nanowires exhibit ferromagnetic characteristics at room temperature. & 2008 Elsevier B.V. All rights reserved.
PACS: 61.46.Hk 75.75.+a Keywords: NiSi nanowires Vapor–liquid–solid Magnetic characterization
1. Introduction It is known that nanomaterials often exhibit outstanding physical and chemical properties that differ from their bulk counterparts greatly. Recently, considerable interest is focused on the understanding of basic concepts and potential applications of the nanomaterials [1], especially on the silicon [2,3] and silicide [4] nanomaterials, owing to their potential applications in optics and electronics. In particular, metallic silicide nanowires are promising candidates, because their growth can be easily integrated with silicon processing technology [4–6]. Indeed the synthesis of single-crystalline, transition metal silicide nanowires, such as TaSi2 [7], a-FeSi [8], and CoSi [9], have been recently reported using diverse methods. But they have some limitations, such as high resistivity, high Si consumption and high formation temperature [10]. Currently, Ni silicide nanowires are candidates as one-dimensional (1D) nanoscale building blocks having a potential to solve the problems of other silicide materials. Ni silicide has been intensively researched for use as a contact material of gate and source/drain in complementary metal oxide semiconductor (CMOS) devices [11]. Cheol-Joo Kim et al. [12] reported that the single-crystalline NiSi nanowires fabricated by chemical vapor process showed highly metallic properties.
Corresponding author at: School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, PR China. Tel.: +86 9318912719; fax: +86 9318913554. E-mail address: [email protected] (P.X. Yan).
1386-9477/$ - see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2008.05.013
Joondong Kim previously reported the NiSi NW growth by metal-induced growth [13]. Nevertheless, it still remains a challenge to develop simple and versatile approaches to synthesize 1D nanostructures of NiSi. But a more simple and effective method still needs to be developed to prepare NiSi nanowires. In this communication we report the synthesis of nanometer-sized NiSi wires for the first time, using the DC arc-discharge process. We used a mixture of Ni powder and Si powder as the anode in the DC arc-discharge process, developed in our lab to fabricate NiSi nanowires. The growth mechanism of NiSi nanowires is proposed according to the vapor–liquid–solid (VLS) growth mechanism method. Magnetic characterization has also been investigated.
2. Experiment NiSi nanowires were synthesized using a conventional DC arcdischarge method. The mixture of Si powder and Ni powder (high purity chemicals) was put into a small graphite crucible of the anode. A direct current of 40 A with a voltage of 40 V was applied between two electrodes under a total pressure of 1000 Torr of argon. The arcing time was typically 15 min. The chamber wall was kept cool by circulating water. Nanowires were deposited inside of the water-cooled collection cylinder and formed a weblike network. Silver gray powders were obtained. The structure of the sample was measured by X-ray diffraction (XRD) on a Rigaku D/Max-2400 diffractometer with monochromatized Cu Ka
ARTICLE IN PRESS 186
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radiation (l ¼ 1.54056 A˚) and y–2y scan. The chemical compositions were recorded by energy dispersive spectroscopy (EDS). Transmission electron microscope (TEM) examination was carried out by using a Hitachi H-600 transmission electron microscope operated at 100 kV with a nominal point-to-point resolution of 0.23 nm. The morphology observation was performed by a field emission scanning electron microscope (FE-SEM, Hitachi S-4800) operated at keV. The magnetic properties were measured by a Lake Shore 7300 vibrating sample magnetometer (VSM) at room temperature.
3. Results and discussion Fig. 1 shows a typical XRD diffraction pattern of the NiSi nanowires on different crystal planes synthesized by DC
Fig. 1. XRD diffraction pattern of the NiSi nanowires prepared by DC arc-discharge.
Spectrum: LD-B Cursor = 9.940KeV 14cnts
arc-discharge. As shown in Fig. 1, all of the diffraction peaks in the XRD pattern can be identified; they correspond to an orthorhombic-structure NiSi crystal with lattice constants of a ¼ 0.562 nm, b ¼ 0.518 nm and c ¼ 0.334 nm, consistent with the Joint Committee Powder Diffraction Standard (JCPDS) data file (Card No. 85-0901). Fig. 2 shows the corresponding EDX spectrum. It indicates that the nanowires are composed of Si and Ni. The molecular ratio of Si/Ni of the nanowires calculated from the EDX data is about 1:1, and this corresponds to the stoichiometric composition of NiSi within the experimental error. The SEM examination was conducted to investigate the morphology characteristics of the as-synthesized product. Fig. 3(a) is the low-magnification SEM image, which shows that many wire-like nanostructures with length up to several micrometers have been synthesized and the nanowires were gently curved, and most of these nanowires are smooth in appearance. Fig. 3(c) shows the TEM image of as-prepared NiSi nanowires containing well-developed single crystals with diameters of 50–100 nm. The SAED pattern of the nanowire (insetted in the upper left corner of Fig. 3(b)) indicates its single-crystal nature and its growth direction along c-axis. As shown by Fig. 3(b), NiSi nanowires terminated at one end in a nanoparticle with diameter 1–1.2 times that of the connected nanowire. The presence of a nanoparticle catalyst at the ends of the nanowires is the essential feature of VLS growth. Below, we consider two important conditions for the synthesis of NiSi nanowires: (1) enough Ni supply; (2) high temperatures. In our current experiments, when the content of the Ni powder is much less than that of the Si powder in the vapor source, with the molar ratio of Ni:Si ranging from 1:20 to 1:100, the product was only Si nanoparticles. It was reported that the product was only Si nanowires when the content of Ni was less than 15.52 wt% [14]. We increase the content of the Ni element in the vapor source to the molar ratio of Ni:Si ¼ 3:2 so that the Ni supply is sufficient. The temperature at the vapor source position is evaluated to be
Range:10 keV
Total Cnts = 95997 Linear VS = 5000
4000
Intensity (arb. units)
NiLa1
3000 SiKa1
NiKa1
2000
1000 AIKa1 0 Ka1 C Ka1
0.0
SiKb1 NiLa2 AIKb1
1.0
2.0
NiKb
3.0
4.0
5.0
6.0
7.0
Voltage (keV) Fig. 2. EDX spectrum of the NiSi nanowires prepared by DC arc-discharge.
8.0
0
9.0
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187
Fig. 3. (a) SEM image of the NiSi nanowires. (b) and (c) TEM image of the NiSi nanowires.
Fig. 4. Schematic illustration of the growth mechanism.
more than 5000 1C [15], which is sufficient for the vaporization of Si and Ni. Thus, at this temperature, Ni will react with Si to form NinSi (n41) supersaturated liquid alloy droplets. In the experiments, the NiSi nanowires have been synthesized in the central area instead of on the inner walls of the water-cooled collection cylinder. The position of synthesizing NiSi nanowires is at a distance of 3–8 cm near the core position of the cathode, where the temperature is kept rather high (500 1C). This indicates that the temperature is an important factor for the synthesis of different kinds of nanowire. From the binary Ni–Si diagram, it can be seen that the eutectic point of Si, Ni is 845 1C. With the temperature decreasing from 5000 1C, the NinSi (n41) supersaturated liquid alloy droplets start to separate out into the NiSi eutectic liquid alloy droplets and Ni2Si liquid droplets. From the SEM image of Fig. 3(b), we can see that there are Ni2Si heads attaching to nanowires, thus showing a typical VLS growth feature. According to the VLS growth mechanism [16–20], the growth of nanowires is governed by the presence of eutectic metal alloys at the end of nanowires. Transition metals adsorbed at the edge of nanowires play an important role during the growth of NiSi nanowires. Therefore, we can suggest a VLS growth process in Fig. 4: (1) The Si powder and Ni power were vaporized by DC arc-discharge. The NinSi(n41) are synthesized with excess Ni at high temperature, and then formed the NinSi(n41) supersaturated liquid alloy droplets. (2) The temperature decreases to below 845 1C; inside the NinSi(n41) supersaturated liquid alloy droplets the NinSi(n41) separate out into the NiSi eutectic liquid alloy droplets and, in the meantime, other sorts of nickel silicide liquid alloy droplets, such as Ni2Si, are formed. (3) According to the VLS growth mechanism, the nickel silicide forms the heads of NiSi nanowires on the surface of the NiSi eutectic liquid alloy droplets. Since there is enough Ni content,
Fig. 5. The ferromagnetic hysteresis loop at room temperature.
the nanowires containing Si and Ni compositions have grown from the heads of nickel silicide. Owing to the difficulty of controlling the conditions in the DC arc-discharge, the suggested growth mechanism is a matter for further discussion. Investigations for the synthesis of bulk amounts of the NiSi nanowires are underway. As-synthesized NiSi nanowires were investigated by VSM with applied field up to 10 kOe at 300 K. The hysteresis loop of the as-synthesized magnetic product is shown in Fig. 5. It can be seen from Fig. 5 that the NiSi nanowires show ferromagnetic behavior with a saturation magnetization (Ms) of 2.24 emu/g, a remanent magnetization (Mr) of 0.59 emu/g, and a coercivity (Hc) of 382.04 Oe.
4. Conclusion In summary, NiSi nanowires with high aspect ratios have been successfully prepared on a large scale via a simple convenient DC arc-discharge approach. The nanowires have diameters of 50–100 nm and lengths of several micrometers. The growth mechanism was discussed and a three-step growth process based on VLS mechanism was proposed. We have emphasized that two important conditions, high temperatures and enough Ni supply, are necessary for the synthesis of NiSi nanowires. Magnetic characterization was carried out and the results show that the
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NiSi nanowires exhibit ferromagnetic characteristics at room temperature. It is possible that these NiSi nanowires may offer more opportunities for both fundamental research and technological applications.
Acknowledgments This work was supported by the fund from the National Natural Science Foundation of China (Grant No. 60376039). The authors would like to thank the Laboratory of Field Emission Scanning Electron Microscope (FE-SEM, Hitachi S-4800) Platform of Information Material and Technology Innovation, Lanzhou University. References [1] A.P. Alivisatos, Science 27 (1996) 933. [2] J. Hu, T.W. Odom, C.M. Lieber, Acc. Chem. Res. 32 (1999) 435. [3] X. Peng, L. Manna, W. Yang, J. Wickham, E. Sher, A. Kadavanich, A.P. Alivisatos, Nature 404 (2000) 59.
[4] Y. Wu, J. Xiang, C. Yang, W. Lu, C.M. Lieber, Nature 430 (2004) 61. [5] C.A. Decker, R. Solanki, J.L. Freeouf, J.R. Carruthers, D.R. Evans, Appl. Phys. Lett. 84 (2004) 1389. [6] J.P. Gambino, E.G. Colgan, Mater. Chem. Phys. 52 (1998) 99. [7] Y.L. Chueh, M.T. Ko, L.J. Chou, L.J. Chen, C.S. Wu, C.D. Chen, Nano Lett. 6 (2006) 1637. [8] O.Y. Lian, E.S. Thrall, M.M. Deshmukh, H. Park, Adv. Mater. 18 (2006) 1437. [9] A.L. Schmitt, L. Zhu, D. Schmeisser, F.J. Himpsel, S. Jin, J. Phys. Chem. B 110 (2006) 18142. [10] G.B. Kim, D.-J. Yoo, H.K. Baik, J.-M. Myoung, S.M. Lee, S.H. Oh, C.G. Park, J. Vac. Sci. Technol. B 21 (2003) 319. [11] C. Lavoie, F.M. d’Heurle, C. Detavernier, C. Cabral, J. Microelectron. Eng. 70 (2003) 144. [12] Cheol-Joo Kim, Kibum Kang, Yun Sung Woo, Kyung-Guk Ryu, Heesung Moon, Jae-Myung Kim, Dong-Sik Zang, Moon-Ho Jo, Adv. Mater. 19 (2007) 3637. [13] Joondong Kim, Anderson Wayne, Thin Solid Films 483 (2005) 60. [14] Jung-Fu Hsua, Bohr-Ran Huang, Thin Solid Films 514 (2006) 20. [15] P. Kovitya, L.E. Cram, Weld. J. 65 (1986) 34. [16] R.S. Wagner, W.C. Ellis, Appl. Phys. Lett. 4 (1964) 89. [17] G.W. Zhou, Z. Zhang, Z.G. Bai, S.Q. Feng, D.P. Yu, Appl. Phys. Lett. 75 (1999) 2447. [18] E.I. Givargizov, Vac. J. Sci. Technol. B 11 (1993) 449. [19] A.M. Morales, C.M. Lieber, Science 279 (1998) 208. [20] X.T. Zhou, N. Wang, H.L. Lai, H.Y. Peng, I. Bello, N.B. Wong, C.S. Lee, S.T. Lee, Appl. Phys. Lett. 74 (1999) 3942.
Contents lists available at ScienceDirect
Physica E journal homepage: www.elsevier.com/locate/physe
Efficient preparation of NiSi nanowires by DC arc-discharge Z.R. Geng a, Q.H. Lu a, P.X. Yan a,b,, D. Yan a, G.H. Yue a a b
Institute for Plasma and Metal Materials, Lanzhou University, Lanzhou 730000, PR China State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China
a r t i c l e in fo
abstract
Article history: Received 31 March 2008 Received in revised form 11 May 2008 Accepted 16 May 2008 Available online 4 June 2008
NiSi nanowires were synthesized by DC arc-discharge approach. As material sources, mixtures of Si and Ni powders (high purity chemicals) were put into a graphite crucible as the anode. The products were characterized by SEM, TEM, EDX and XRD. As-prepared NiSi nanowires have the diameter of 50–100 nm and length of several micrometers. From the obtained experimental results, we explain the growth mechanism of the nanowires based on the vapor–liquid–solid (VLS) growth model. Two important conditions, high temperature and enough Ni supply, are emphasized for the synthesis of the NiSi nanowires. Magnetic characterization was carried out and the results show that the NiSi nanowires exhibit ferromagnetic characteristics at room temperature. & 2008 Elsevier B.V. All rights reserved.
PACS: 61.46.Hk 75.75.+a Keywords: NiSi nanowires Vapor–liquid–solid Magnetic characterization
1. Introduction It is known that nanomaterials often exhibit outstanding physical and chemical properties that differ from their bulk counterparts greatly. Recently, considerable interest is focused on the understanding of basic concepts and potential applications of the nanomaterials [1], especially on the silicon [2,3] and silicide [4] nanomaterials, owing to their potential applications in optics and electronics. In particular, metallic silicide nanowires are promising candidates, because their growth can be easily integrated with silicon processing technology [4–6]. Indeed the synthesis of single-crystalline, transition metal silicide nanowires, such as TaSi2 [7], a-FeSi [8], and CoSi [9], have been recently reported using diverse methods. But they have some limitations, such as high resistivity, high Si consumption and high formation temperature [10]. Currently, Ni silicide nanowires are candidates as one-dimensional (1D) nanoscale building blocks having a potential to solve the problems of other silicide materials. Ni silicide has been intensively researched for use as a contact material of gate and source/drain in complementary metal oxide semiconductor (CMOS) devices [11]. Cheol-Joo Kim et al. [12] reported that the single-crystalline NiSi nanowires fabricated by chemical vapor process showed highly metallic properties.
Corresponding author at: School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, PR China. Tel.: +86 9318912719; fax: +86 9318913554. E-mail address: [email protected] (P.X. Yan).
1386-9477/$ - see front matter & 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2008.05.013
Joondong Kim previously reported the NiSi NW growth by metal-induced growth [13]. Nevertheless, it still remains a challenge to develop simple and versatile approaches to synthesize 1D nanostructures of NiSi. But a more simple and effective method still needs to be developed to prepare NiSi nanowires. In this communication we report the synthesis of nanometer-sized NiSi wires for the first time, using the DC arc-discharge process. We used a mixture of Ni powder and Si powder as the anode in the DC arc-discharge process, developed in our lab to fabricate NiSi nanowires. The growth mechanism of NiSi nanowires is proposed according to the vapor–liquid–solid (VLS) growth mechanism method. Magnetic characterization has also been investigated.
2. Experiment NiSi nanowires were synthesized using a conventional DC arcdischarge method. The mixture of Si powder and Ni powder (high purity chemicals) was put into a small graphite crucible of the anode. A direct current of 40 A with a voltage of 40 V was applied between two electrodes under a total pressure of 1000 Torr of argon. The arcing time was typically 15 min. The chamber wall was kept cool by circulating water. Nanowires were deposited inside of the water-cooled collection cylinder and formed a weblike network. Silver gray powders were obtained. The structure of the sample was measured by X-ray diffraction (XRD) on a Rigaku D/Max-2400 diffractometer with monochromatized Cu Ka
ARTICLE IN PRESS 186
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radiation (l ¼ 1.54056 A˚) and y–2y scan. The chemical compositions were recorded by energy dispersive spectroscopy (EDS). Transmission electron microscope (TEM) examination was carried out by using a Hitachi H-600 transmission electron microscope operated at 100 kV with a nominal point-to-point resolution of 0.23 nm. The morphology observation was performed by a field emission scanning electron microscope (FE-SEM, Hitachi S-4800) operated at keV. The magnetic properties were measured by a Lake Shore 7300 vibrating sample magnetometer (VSM) at room temperature.
3. Results and discussion Fig. 1 shows a typical XRD diffraction pattern of the NiSi nanowires on different crystal planes synthesized by DC
Fig. 1. XRD diffraction pattern of the NiSi nanowires prepared by DC arc-discharge.
Spectrum: LD-B Cursor = 9.940KeV 14cnts
arc-discharge. As shown in Fig. 1, all of the diffraction peaks in the XRD pattern can be identified; they correspond to an orthorhombic-structure NiSi crystal with lattice constants of a ¼ 0.562 nm, b ¼ 0.518 nm and c ¼ 0.334 nm, consistent with the Joint Committee Powder Diffraction Standard (JCPDS) data file (Card No. 85-0901). Fig. 2 shows the corresponding EDX spectrum. It indicates that the nanowires are composed of Si and Ni. The molecular ratio of Si/Ni of the nanowires calculated from the EDX data is about 1:1, and this corresponds to the stoichiometric composition of NiSi within the experimental error. The SEM examination was conducted to investigate the morphology characteristics of the as-synthesized product. Fig. 3(a) is the low-magnification SEM image, which shows that many wire-like nanostructures with length up to several micrometers have been synthesized and the nanowires were gently curved, and most of these nanowires are smooth in appearance. Fig. 3(c) shows the TEM image of as-prepared NiSi nanowires containing well-developed single crystals with diameters of 50–100 nm. The SAED pattern of the nanowire (insetted in the upper left corner of Fig. 3(b)) indicates its single-crystal nature and its growth direction along c-axis. As shown by Fig. 3(b), NiSi nanowires terminated at one end in a nanoparticle with diameter 1–1.2 times that of the connected nanowire. The presence of a nanoparticle catalyst at the ends of the nanowires is the essential feature of VLS growth. Below, we consider two important conditions for the synthesis of NiSi nanowires: (1) enough Ni supply; (2) high temperatures. In our current experiments, when the content of the Ni powder is much less than that of the Si powder in the vapor source, with the molar ratio of Ni:Si ranging from 1:20 to 1:100, the product was only Si nanoparticles. It was reported that the product was only Si nanowires when the content of Ni was less than 15.52 wt% [14]. We increase the content of the Ni element in the vapor source to the molar ratio of Ni:Si ¼ 3:2 so that the Ni supply is sufficient. The temperature at the vapor source position is evaluated to be
Range:10 keV
Total Cnts = 95997 Linear VS = 5000
4000
Intensity (arb. units)
NiLa1
3000 SiKa1
NiKa1
2000
1000 AIKa1 0 Ka1 C Ka1
0.0
SiKb1 NiLa2 AIKb1
1.0
2.0
NiKb
3.0
4.0
5.0
6.0
7.0
Voltage (keV) Fig. 2. EDX spectrum of the NiSi nanowires prepared by DC arc-discharge.
8.0
0
9.0
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187
Fig. 3. (a) SEM image of the NiSi nanowires. (b) and (c) TEM image of the NiSi nanowires.
Fig. 4. Schematic illustration of the growth mechanism.
more than 5000 1C [15], which is sufficient for the vaporization of Si and Ni. Thus, at this temperature, Ni will react with Si to form NinSi (n41) supersaturated liquid alloy droplets. In the experiments, the NiSi nanowires have been synthesized in the central area instead of on the inner walls of the water-cooled collection cylinder. The position of synthesizing NiSi nanowires is at a distance of 3–8 cm near the core position of the cathode, where the temperature is kept rather high (500 1C). This indicates that the temperature is an important factor for the synthesis of different kinds of nanowire. From the binary Ni–Si diagram, it can be seen that the eutectic point of Si, Ni is 845 1C. With the temperature decreasing from 5000 1C, the NinSi (n41) supersaturated liquid alloy droplets start to separate out into the NiSi eutectic liquid alloy droplets and Ni2Si liquid droplets. From the SEM image of Fig. 3(b), we can see that there are Ni2Si heads attaching to nanowires, thus showing a typical VLS growth feature. According to the VLS growth mechanism [16–20], the growth of nanowires is governed by the presence of eutectic metal alloys at the end of nanowires. Transition metals adsorbed at the edge of nanowires play an important role during the growth of NiSi nanowires. Therefore, we can suggest a VLS growth process in Fig. 4: (1) The Si powder and Ni power were vaporized by DC arc-discharge. The NinSi(n41) are synthesized with excess Ni at high temperature, and then formed the NinSi(n41) supersaturated liquid alloy droplets. (2) The temperature decreases to below 845 1C; inside the NinSi(n41) supersaturated liquid alloy droplets the NinSi(n41) separate out into the NiSi eutectic liquid alloy droplets and, in the meantime, other sorts of nickel silicide liquid alloy droplets, such as Ni2Si, are formed. (3) According to the VLS growth mechanism, the nickel silicide forms the heads of NiSi nanowires on the surface of the NiSi eutectic liquid alloy droplets. Since there is enough Ni content,
Fig. 5. The ferromagnetic hysteresis loop at room temperature.
the nanowires containing Si and Ni compositions have grown from the heads of nickel silicide. Owing to the difficulty of controlling the conditions in the DC arc-discharge, the suggested growth mechanism is a matter for further discussion. Investigations for the synthesis of bulk amounts of the NiSi nanowires are underway. As-synthesized NiSi nanowires were investigated by VSM with applied field up to 10 kOe at 300 K. The hysteresis loop of the as-synthesized magnetic product is shown in Fig. 5. It can be seen from Fig. 5 that the NiSi nanowires show ferromagnetic behavior with a saturation magnetization (Ms) of 2.24 emu/g, a remanent magnetization (Mr) of 0.59 emu/g, and a coercivity (Hc) of 382.04 Oe.
4. Conclusion In summary, NiSi nanowires with high aspect ratios have been successfully prepared on a large scale via a simple convenient DC arc-discharge approach. The nanowires have diameters of 50–100 nm and lengths of several micrometers. The growth mechanism was discussed and a three-step growth process based on VLS mechanism was proposed. We have emphasized that two important conditions, high temperatures and enough Ni supply, are necessary for the synthesis of NiSi nanowires. Magnetic characterization was carried out and the results show that the
ARTICLE IN PRESS 188
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NiSi nanowires exhibit ferromagnetic characteristics at room temperature. It is possible that these NiSi nanowires may offer more opportunities for both fundamental research and technological applications.
Acknowledgments This work was supported by the fund from the National Natural Science Foundation of China (Grant No. 60376039). The authors would like to thank the Laboratory of Field Emission Scanning Electron Microscope (FE-SEM, Hitachi S-4800) Platform of Information Material and Technology Innovation, Lanzhou University. References [1] A.P. Alivisatos, Science 27 (1996) 933. [2] J. Hu, T.W. Odom, C.M. Lieber, Acc. Chem. Res. 32 (1999) 435. [3] X. Peng, L. Manna, W. Yang, J. Wickham, E. Sher, A. Kadavanich, A.P. Alivisatos, Nature 404 (2000) 59.
[4] Y. Wu, J. Xiang, C. Yang, W. Lu, C.M. Lieber, Nature 430 (2004) 61. [5] C.A. Decker, R. Solanki, J.L. Freeouf, J.R. Carruthers, D.R. Evans, Appl. Phys. Lett. 84 (2004) 1389. [6] J.P. Gambino, E.G. Colgan, Mater. Chem. Phys. 52 (1998) 99. [7] Y.L. Chueh, M.T. Ko, L.J. Chou, L.J. Chen, C.S. Wu, C.D. Chen, Nano Lett. 6 (2006) 1637. [8] O.Y. Lian, E.S. Thrall, M.M. Deshmukh, H. Park, Adv. Mater. 18 (2006) 1437. [9] A.L. Schmitt, L. Zhu, D. Schmeisser, F.J. Himpsel, S. Jin, J. Phys. Chem. B 110 (2006) 18142. [10] G.B. Kim, D.-J. Yoo, H.K. Baik, J.-M. Myoung, S.M. Lee, S.H. Oh, C.G. Park, J. Vac. Sci. Technol. B 21 (2003) 319. [11] C. Lavoie, F.M. d’Heurle, C. Detavernier, C. Cabral, J. Microelectron. Eng. 70 (2003) 144. [12] Cheol-Joo Kim, Kibum Kang, Yun Sung Woo, Kyung-Guk Ryu, Heesung Moon, Jae-Myung Kim, Dong-Sik Zang, Moon-Ho Jo, Adv. Mater. 19 (2007) 3637. [13] Joondong Kim, Anderson Wayne, Thin Solid Films 483 (2005) 60. [14] Jung-Fu Hsua, Bohr-Ran Huang, Thin Solid Films 514 (2006) 20. [15] P. Kovitya, L.E. Cram, Weld. J. 65 (1986) 34. [16] R.S. Wagner, W.C. Ellis, Appl. Phys. Lett. 4 (1964) 89. [17] G.W. Zhou, Z. Zhang, Z.G. Bai, S.Q. Feng, D.P. Yu, Appl. Phys. Lett. 75 (1999) 2447. [18] E.I. Givargizov, Vac. J. Sci. Technol. B 11 (1993) 449. [19] A.M. Morales, C.M. Lieber, Science 279 (1998) 208. [20] X.T. Zhou, N. Wang, H.L. Lai, H.Y. Peng, I. Bello, N.B. Wong, C.S. Lee, S.T. Lee, Appl. Phys. Lett. 74 (1999) 3942.