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Tl multilayer nanowires
Superlattices and Microstructures 85 (2015) 768–775
Contents lists available at ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
Electrodeposition and characterization of Bi/Tl multilayer nanowires Babak Jaleh a,⇑, Atefeh Nasri a, Omidreza Kakuee b a b
Physics Department, Bu-Ali Sina University, 65174 Hamedan, Iran Physics & Accelerators Research School, NSTRI, P.O. Box 14395-836, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 26 June 2015 Accepted 27 June 2015 Available online 29 June 2015 Keywords: Electrodeposition Polycarbonate Nanowires Bi/Tl Nanotubes
a b s t r a c t Bi/Tl multilayer nanowires have been successfully fabricated using template-based electordeposition by polycarbonate nanoporous template with 100 nm diameter. The growth Bi/Tl multilayer nanowires was performed using dual-bath system containing Bi and Tl salt, respectively. The electrochemical reduction of ions was explored by cyclic voltammetry (CV). The deposition process was controlled with current–time profiles. X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed for characterization of crystalline structure and morphology of nanowires. The XRD spectra showed that the lattice structure of Bi segment is rhombohedral and thallium segment has hexagonal lattice structure. The average nanowires diameter was determined from TEM images. Elemental analysis of nanowires was carried out using energy dispersive X-ray (EDX), Rutherford backscattering spectrometry (RBS), and proton induced X-ray emission (PIXE). The length of nanowires was determined by RBS technique. Elemental concentration and weight percent of sample were measured by PIXE analysis. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Recently, many kinds of nanostructured materials in different dimensions are studied [1–5]. Nanowires and nanotubes are one-dimension nanomaterials which have attracted considerable attention and can be formed by limitation in two dimensions and possess a one dimensioned periodic structure. Their large aspect ratio (length/diameter) effects on physical properties such as structural, optical, and electrical properties [6,7] and makes them suitable for using in physics, chemistry and material science such as electronic circuits, biological and chemical sensing, optoelectronics, nanophotonics and thermoelectric applications [8–12]. Nanowires have been fabricated using atomic deposition and lithographic methods [7,12]. The most used method is atomic deposition which involves electrodepostion, thermal evaporation, thermal decomposition, physical vapor deposition (PVD), chemical vapor deposition (CVD), and metalorganic vapor-phase epitaxy [7,13–17]. Among these techniques, electrodeposition is well suited for fabrication of nanowires [12,18]. The synthesis of nanowires using template-based electrodeposition involves the reduction of a metal salt. It is a wet chemical synthesis and can be performed at the room temperature and ambient pressure [12]. Templates which were used in electrodeposition method have parallel cylindrical small pores. The metal ions were deposited within the pores of templates and filled them to form the nanowires [12,19]. ⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (B. Jaleh). http://dx.doi.org/10.1016/j.spmi.2015.06.037 0749-6036/Ó 2015 Elsevier Ltd. All rights reserved.
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Fig. 1. Cyclic voltammogramsof (a) Bi3+ ions and (b) Tl+ ions on polycarbonate template.
Fig. 2. The current transient during the electrodeposition of the Bi/Tl nanowires in the polycarbonate template.
Polycarbonate template is one of the templates which wildly used to formation nanowires. This produced by ion bombardment and chemically etching of the ion tracks. Pore size of templates can be changed by varying the ion-bombardment conditions [20]. The electrodeposition is a simple and low cost technique and requires much less complex equipment than the other methods. The length, diameter, and density of the nanowires can be controlled by varying the deposition conditions such as template, pH value of the electrolyte, deposition potential and electrolyte composition. These features makes electrodeposition an attractive and ideal method for nanowires fabrication [18,21]. The materials which can be useful for thermoelectric applications have a high figure of merit (ZT) value. The figure of merit determines the thermoelectric conversion efficiency of a material [22]. Thermoelectric devices can convert electrical energy into thermal energy without moving parts or refrigerants. These devices can also convert an existing temperature difference into electricity. Thermoelectric devices are used in IR detectors, diode laser, cooling systems, etc. [23]. In recent years, formation of multilayer nanowires has produced much interesting research [19,24–26]. Multilayer nanowires can be useful for thermoelectric applications and better than conventional nanowires for this. Because of interfaces between the two layers which can reducing phonon transport and keeping high electron mobility. It causes a reduction in thermal conductivity [9,24]. III–V semiconductors such as bismuth and thallium have good thermoelectric properties.
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B. Jaleh et al. / Superlattices and Microstructures 85 (2015) 768–775
Fig. 3. XRD patterns of (a) Bi, (b) Tl and (c) Bi/Tl multilayer nanowires.
Single-crystalline Bi nanowires and Bi-based alloy or multilayer nanowires are expected suitable for thermoelectric applications with high ZT values. Thallium nanowires have high electron mobilities and can be used for IR detectors, laser and field effect transistors [27,28]. Tl doping helps enhancing the ZT value [29]. Compounds containing Bi and Tl also have good thermoelectric properties [30]. Many kinds of multilayer nanowire systems have been reported such as Bi/Sn [7], Bi/Si [8], Bi/Sb [9], Bi2Si3/Bi [24], Bi2Te2Se/Te [25], Si/SiGe [26] and Bi2Te3/Te [31]. In this work, Bi/Tl multilayer nanowires have been prepared by electrodeposition filling the pores of the PC template. Crystalline structure and morphology of nanostructures have been characterized using XRD, SEM, and TEM techniques. Elemental analysis of nanowires was performed by EDX, PIXE, and RBS. 2. Experimental The growth of Bi/Tl multilayer nanowires was carried out by potentiostatic electrodeposition method using the dual-bath technique and three-electrodes cell. Nanowires have been electrodeposited into commercially available ion track-etched polycarbonate membrane with 100 nm pore-diameter (Millipore USA). The one side of polycarbonate membrane was coated by nearly 100 nm gold layer was employed as a working electrode. Polycarbonate membrane was chosen for their biocompatibility and lower thermal conductivity in compared with alumina templates [4]. The reference and counter electrodes were Ag/AgCl in 3 M KCl and platinum mesh, respectively. The electrodeposition process was performed using two
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Fig. 4. SEM image of released Bi/Tl multilayer nanowires from PC membrane.
Fig. 5. SEM image of released Bi/Tl multilayer nanotubes from PC membrane.
electrolyte baths. The electrolytic solution for bismuth deposition had a concentration of 0.03 M Bi(NO3)35H2O in 2 M HNO3 at pH 1.3. The electrolytic solution for thallium deposition had a concentration of 0.03 M Tl2SO4 in 2 M Na2SO4 at pH 1.1. The similar electrolytes composition were used for the bismuth and thallium deposition at the lower pH value about 0.7. Cyclic voltammogram (CV) measurements of the bismuth and thallium electrolytic solutions were performed to determine the deposition potentials of Bi3+ and Tl+ ions in polycarbonate membrane. The potentials for deposition of Bi3+ and Tl+ ions are 0.26 V and 1 V, respectively (Fig. 1) but we applied overvoltage due to accelerate precipitation rate of Bi3+ and Tl+ ions and worked at 0.1 V for Bi3+ ions and 0.8 for Tl+ ions. The deposition process was accomplished while monitoring the current–time profiles to derive information related to growth mechanism. Structure of Bi/Tl nanowires was studied using X-ray diffraction (Philips power diffractometer type PW 1373 gonimeter). The XRD was equipped with a graphite monochromator crystal. The X-ray wavelength was 1.5405 Å and diffraction patterns were recorded in a 2h range (20–90°) with a scanning speed of 2°/min. The nanowires were released by dissolving the polycarbonate membrane in dichloromethane and then scanning electron microscopy (SEM) of nanowires was performed using a TSCAN SEM, for study of samples morphology. The composition of the Bi/Tl multilayer nanowires was analyzed by energy dispersive X-ray (EDX) performed in the SEM. The diameter of nanowires were determined by TEM (Ziess, EM10C, 80 kV). For TEM studies, the
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Fig. 6. EDX of the Bi/Tl multilayer nanowires deposited in polycarbonate template.
Table 1 Weight percent and atomic percent of elements. Elements
wt%
at%
O Bi Tl Total
7.46 78.09 14.45 100
51.21 41.03 7.76 100
Fig. 7. TEM image of Bi/Tl multilayer nanowires.
sample was dispersed in the dichloromethane to dissolving the polycarbonate membrane and nanowires were liberated from the membrane. After evaporation of dichloromethane, the nanowires were recovered on a formvar carbon grid. Proton induced X-ray emission (PIXE) and Rutherford backscattering spectrometry (RBS) experiments were carried out using a 3 MV Van de Graff accelerator. Sample was bombareded by 2 MeV proton beams. The X-ray spectra were collected using a Si(li) X-ray detector placed at an angle of 135° and the backscattered protons were detected using a surface barrier detector placed at the backscattering angle of 165°.
3. Results and discussion The steps of Bi/Tl multilayer nanowires deposition into the pores of polycarbonate membrane were shown in current– time diagram (Fig. 2). Electrodeposition of Bi3+ and Tl+ ions was carried out for the same time. In the first step Bi3+ ions electrodeposited into the pores at 0.1 V using electrolyte at pH 1.3 for 60 s and then Tl+ ions electrodeposited at 0.8 V using electrolyte at pH 1.1 for 60 s and then this process repeated to filling the pores. It is clearly that the precipitation rate of Bi3+ ions is more than Tl+ ions.
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Fig. 8. RBS spectrum of Bi/Tl multilayer nanowires.
Fig. 9. PIXE spectrum of Bi/Tl multilayer nanowires deposited on polycarbonate template.
The XRD patterns of the Bi/Tl multilayer nanowires deposited using a 100 nm pore diameter polycarbonate membrane are presented in Fig. 3. The corresponding XRD patterns of Bi, Tl and Bi/Tl multilayer nanowires and ICDD Card, Binanostructures have a rhombohedral lattice structure with space group R-3m (1 6 6) and Tl nanostructure have a hexagonal lattice structure with space group P63/mmc (1 9 4). The typical SEM microghraph of Bi/Tl multilayer nanowires released from PC template is shown in Fig. 4. It can be clearly seen that the nanowires are cylindrical shape and the pores of template are completely filled. Fig. 5 shows the SEM of nanostructures which was electrodeposited under the same condition but the electrolyte solutions of Bi3+ and Tl+ have pH 0.7. A mixture of nanowires and nanotubes have been observed in SEM image. It was found that decreasing pH value of the electrolyte solution caused formation of tubular nanostructures. Hydrogen generation and side reaction have an important role in formation of nanotubes. Hydrogen gas formation increase at lower electrolyte pH and hydrogen gas bubbles inside the pores cause incomplete filling of the pores and nanotube formation [32–34]. Fig. 6 shows the EDX spectra of Bi/Tl nanowires. In EDX spectra bismuth, thallium and oxygen peaks are present. The peak of oxygen is relevant to polycarbonate membrane which has not been dissolved completely. This analysis gives the weight percent (wt%) and atomic percent (at%) of each element identified which is given in Table 1. It indicate that contribution of Bi segment is more than Tl segment, suggesting that it is dependent on the electrodepostion potential and precipitation rate.
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Table 2 Elemental concentration (ppm) was obtained from PIXE analysis. Elements
Cu
Zn
Au
Tl
Bi
Concentration
813
460
174,782
34,247
214,060
Fig. 7 shows the typical TEM image of Bi/Tl multilayer nanowires. TEM images revealed that the average diameter of the nanowires is approximately 93 nm. The control of nanopore filling is performed by RBS analysis. The length of Bi/Tl multilayer nanowires was 4.92 lm that determined by RBS technique (Fig. 8). This technique is not be able to determine the thickness of each layer of Bi/Tl multilayer nanowires because of the atomic number of bismuth and thallium elements are very close together. Elemental concentration of sample was measured by PIXE analysis. PIXE analysis showed that Bi, Tl, Au, Cu, and Zn are present in the sample. Fig. 9 shows PIXE spectra of sample. Al peak in PIXE spectrum is due to proton interaction with chamber. The weight percent of elements can be calculated from elemental concentration (ppm) which obtained from PIXE analysis. The PIXE results and weight percent are summarized in Table 2. Element of Au is due to gold-sputtered layer at the backside of polycarbonate membrane. Elements of Zn and Cu are present due to impurities of gold-sputtered layer. 4. Conclusion Bi/Tl multilayer nanowire and nanotubes were prepared using electrodeposition filling the pores of the PC template with 100 nm diameter. Structural characterization of these nanowires was studied using X-ray diffraction. XRD patterns of nanowires indicated that lattice structure of Bi and Tl segments are rhombohedral and hexagonal respectively. Morphology of nanowires was investigated by SEM images and it was found that changing pH value can be caused transformation nanowire structures to nanotube structures and vice versa. Decreasing pH value of the electrolyte solution caused formation of nanotube structure. Bi3+ ions has higher precipitation rate. So contribution of Bi segment is more than Tl segment and EDX spectra showed it. Average diameter of nanowires which was measured from TEM images is approximately 93 nm. Length of nanowires was obtained 4.92 lm using RBS technique. Also weight percent of elements in template which filled by Bi and Tl segments was measured by PIXE analysis. The fabricated nanowires will have promising thermoelectric applications. References [1] M.A. Ghanem, P.N. Bartlett, P. Groot, A. Zhokov, A double templated electrodeposition method for the fabrication of arrays of metal nanodots, Electrochem. Commun. 6 (2004) 447–453. [2] G.Y. Teo, M.P. Ryan, D.J. Riley, A mechanistic study on templated electrodeposition of one dimensional TiO2 nanorods and nanotubes using TiOSO4 as a precursor, Electrochem. Commun. 47 (2014) 13–16. [3] K. Hnida, J. Mech, G.D. Sulka, Template-assisted electrodeposition of indium–antimony nanowires-comparison of electrochemical methods, Appl. Surf. Sci. 287 (2013) 252–256. [4] D. Pinisetty, D. Davis, E.J. Podlaha-Murphy, M.C. Murphy, A.B. Karki, D.P. Young, R.V. 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Contents lists available at ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
Electrodeposition and characterization of Bi/Tl multilayer nanowires Babak Jaleh a,⇑, Atefeh Nasri a, Omidreza Kakuee b a b
Physics Department, Bu-Ali Sina University, 65174 Hamedan, Iran Physics & Accelerators Research School, NSTRI, P.O. Box 14395-836, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 26 June 2015 Accepted 27 June 2015 Available online 29 June 2015 Keywords: Electrodeposition Polycarbonate Nanowires Bi/Tl Nanotubes
a b s t r a c t Bi/Tl multilayer nanowires have been successfully fabricated using template-based electordeposition by polycarbonate nanoporous template with 100 nm diameter. The growth Bi/Tl multilayer nanowires was performed using dual-bath system containing Bi and Tl salt, respectively. The electrochemical reduction of ions was explored by cyclic voltammetry (CV). The deposition process was controlled with current–time profiles. X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed for characterization of crystalline structure and morphology of nanowires. The XRD spectra showed that the lattice structure of Bi segment is rhombohedral and thallium segment has hexagonal lattice structure. The average nanowires diameter was determined from TEM images. Elemental analysis of nanowires was carried out using energy dispersive X-ray (EDX), Rutherford backscattering spectrometry (RBS), and proton induced X-ray emission (PIXE). The length of nanowires was determined by RBS technique. Elemental concentration and weight percent of sample were measured by PIXE analysis. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Recently, many kinds of nanostructured materials in different dimensions are studied [1–5]. Nanowires and nanotubes are one-dimension nanomaterials which have attracted considerable attention and can be formed by limitation in two dimensions and possess a one dimensioned periodic structure. Their large aspect ratio (length/diameter) effects on physical properties such as structural, optical, and electrical properties [6,7] and makes them suitable for using in physics, chemistry and material science such as electronic circuits, biological and chemical sensing, optoelectronics, nanophotonics and thermoelectric applications [8–12]. Nanowires have been fabricated using atomic deposition and lithographic methods [7,12]. The most used method is atomic deposition which involves electrodepostion, thermal evaporation, thermal decomposition, physical vapor deposition (PVD), chemical vapor deposition (CVD), and metalorganic vapor-phase epitaxy [7,13–17]. Among these techniques, electrodeposition is well suited for fabrication of nanowires [12,18]. The synthesis of nanowires using template-based electrodeposition involves the reduction of a metal salt. It is a wet chemical synthesis and can be performed at the room temperature and ambient pressure [12]. Templates which were used in electrodeposition method have parallel cylindrical small pores. The metal ions were deposited within the pores of templates and filled them to form the nanowires [12,19]. ⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (B. Jaleh). http://dx.doi.org/10.1016/j.spmi.2015.06.037 0749-6036/Ó 2015 Elsevier Ltd. All rights reserved.
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Fig. 1. Cyclic voltammogramsof (a) Bi3+ ions and (b) Tl+ ions on polycarbonate template.
Fig. 2. The current transient during the electrodeposition of the Bi/Tl nanowires in the polycarbonate template.
Polycarbonate template is one of the templates which wildly used to formation nanowires. This produced by ion bombardment and chemically etching of the ion tracks. Pore size of templates can be changed by varying the ion-bombardment conditions [20]. The electrodeposition is a simple and low cost technique and requires much less complex equipment than the other methods. The length, diameter, and density of the nanowires can be controlled by varying the deposition conditions such as template, pH value of the electrolyte, deposition potential and electrolyte composition. These features makes electrodeposition an attractive and ideal method for nanowires fabrication [18,21]. The materials which can be useful for thermoelectric applications have a high figure of merit (ZT) value. The figure of merit determines the thermoelectric conversion efficiency of a material [22]. Thermoelectric devices can convert electrical energy into thermal energy without moving parts or refrigerants. These devices can also convert an existing temperature difference into electricity. Thermoelectric devices are used in IR detectors, diode laser, cooling systems, etc. [23]. In recent years, formation of multilayer nanowires has produced much interesting research [19,24–26]. Multilayer nanowires can be useful for thermoelectric applications and better than conventional nanowires for this. Because of interfaces between the two layers which can reducing phonon transport and keeping high electron mobility. It causes a reduction in thermal conductivity [9,24]. III–V semiconductors such as bismuth and thallium have good thermoelectric properties.
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Fig. 3. XRD patterns of (a) Bi, (b) Tl and (c) Bi/Tl multilayer nanowires.
Single-crystalline Bi nanowires and Bi-based alloy or multilayer nanowires are expected suitable for thermoelectric applications with high ZT values. Thallium nanowires have high electron mobilities and can be used for IR detectors, laser and field effect transistors [27,28]. Tl doping helps enhancing the ZT value [29]. Compounds containing Bi and Tl also have good thermoelectric properties [30]. Many kinds of multilayer nanowire systems have been reported such as Bi/Sn [7], Bi/Si [8], Bi/Sb [9], Bi2Si3/Bi [24], Bi2Te2Se/Te [25], Si/SiGe [26] and Bi2Te3/Te [31]. In this work, Bi/Tl multilayer nanowires have been prepared by electrodeposition filling the pores of the PC template. Crystalline structure and morphology of nanostructures have been characterized using XRD, SEM, and TEM techniques. Elemental analysis of nanowires was performed by EDX, PIXE, and RBS. 2. Experimental The growth of Bi/Tl multilayer nanowires was carried out by potentiostatic electrodeposition method using the dual-bath technique and three-electrodes cell. Nanowires have been electrodeposited into commercially available ion track-etched polycarbonate membrane with 100 nm pore-diameter (Millipore USA). The one side of polycarbonate membrane was coated by nearly 100 nm gold layer was employed as a working electrode. Polycarbonate membrane was chosen for their biocompatibility and lower thermal conductivity in compared with alumina templates [4]. The reference and counter electrodes were Ag/AgCl in 3 M KCl and platinum mesh, respectively. The electrodeposition process was performed using two
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Fig. 4. SEM image of released Bi/Tl multilayer nanowires from PC membrane.
Fig. 5. SEM image of released Bi/Tl multilayer nanotubes from PC membrane.
electrolyte baths. The electrolytic solution for bismuth deposition had a concentration of 0.03 M Bi(NO3)35H2O in 2 M HNO3 at pH 1.3. The electrolytic solution for thallium deposition had a concentration of 0.03 M Tl2SO4 in 2 M Na2SO4 at pH 1.1. The similar electrolytes composition were used for the bismuth and thallium deposition at the lower pH value about 0.7. Cyclic voltammogram (CV) measurements of the bismuth and thallium electrolytic solutions were performed to determine the deposition potentials of Bi3+ and Tl+ ions in polycarbonate membrane. The potentials for deposition of Bi3+ and Tl+ ions are 0.26 V and 1 V, respectively (Fig. 1) but we applied overvoltage due to accelerate precipitation rate of Bi3+ and Tl+ ions and worked at 0.1 V for Bi3+ ions and 0.8 for Tl+ ions. The deposition process was accomplished while monitoring the current–time profiles to derive information related to growth mechanism. Structure of Bi/Tl nanowires was studied using X-ray diffraction (Philips power diffractometer type PW 1373 gonimeter). The XRD was equipped with a graphite monochromator crystal. The X-ray wavelength was 1.5405 Å and diffraction patterns were recorded in a 2h range (20–90°) with a scanning speed of 2°/min. The nanowires were released by dissolving the polycarbonate membrane in dichloromethane and then scanning electron microscopy (SEM) of nanowires was performed using a TSCAN SEM, for study of samples morphology. The composition of the Bi/Tl multilayer nanowires was analyzed by energy dispersive X-ray (EDX) performed in the SEM. The diameter of nanowires were determined by TEM (Ziess, EM10C, 80 kV). For TEM studies, the
772
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Fig. 6. EDX of the Bi/Tl multilayer nanowires deposited in polycarbonate template.
Table 1 Weight percent and atomic percent of elements. Elements
wt%
at%
O Bi Tl Total
7.46 78.09 14.45 100
51.21 41.03 7.76 100
Fig. 7. TEM image of Bi/Tl multilayer nanowires.
sample was dispersed in the dichloromethane to dissolving the polycarbonate membrane and nanowires were liberated from the membrane. After evaporation of dichloromethane, the nanowires were recovered on a formvar carbon grid. Proton induced X-ray emission (PIXE) and Rutherford backscattering spectrometry (RBS) experiments were carried out using a 3 MV Van de Graff accelerator. Sample was bombareded by 2 MeV proton beams. The X-ray spectra were collected using a Si(li) X-ray detector placed at an angle of 135° and the backscattered protons were detected using a surface barrier detector placed at the backscattering angle of 165°.
3. Results and discussion The steps of Bi/Tl multilayer nanowires deposition into the pores of polycarbonate membrane were shown in current– time diagram (Fig. 2). Electrodeposition of Bi3+ and Tl+ ions was carried out for the same time. In the first step Bi3+ ions electrodeposited into the pores at 0.1 V using electrolyte at pH 1.3 for 60 s and then Tl+ ions electrodeposited at 0.8 V using electrolyte at pH 1.1 for 60 s and then this process repeated to filling the pores. It is clearly that the precipitation rate of Bi3+ ions is more than Tl+ ions.
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Fig. 8. RBS spectrum of Bi/Tl multilayer nanowires.
Fig. 9. PIXE spectrum of Bi/Tl multilayer nanowires deposited on polycarbonate template.
The XRD patterns of the Bi/Tl multilayer nanowires deposited using a 100 nm pore diameter polycarbonate membrane are presented in Fig. 3. The corresponding XRD patterns of Bi, Tl and Bi/Tl multilayer nanowires and ICDD Card, Binanostructures have a rhombohedral lattice structure with space group R-3m (1 6 6) and Tl nanostructure have a hexagonal lattice structure with space group P63/mmc (1 9 4). The typical SEM microghraph of Bi/Tl multilayer nanowires released from PC template is shown in Fig. 4. It can be clearly seen that the nanowires are cylindrical shape and the pores of template are completely filled. Fig. 5 shows the SEM of nanostructures which was electrodeposited under the same condition but the electrolyte solutions of Bi3+ and Tl+ have pH 0.7. A mixture of nanowires and nanotubes have been observed in SEM image. It was found that decreasing pH value of the electrolyte solution caused formation of tubular nanostructures. Hydrogen generation and side reaction have an important role in formation of nanotubes. Hydrogen gas formation increase at lower electrolyte pH and hydrogen gas bubbles inside the pores cause incomplete filling of the pores and nanotube formation [32–34]. Fig. 6 shows the EDX spectra of Bi/Tl nanowires. In EDX spectra bismuth, thallium and oxygen peaks are present. The peak of oxygen is relevant to polycarbonate membrane which has not been dissolved completely. This analysis gives the weight percent (wt%) and atomic percent (at%) of each element identified which is given in Table 1. It indicate that contribution of Bi segment is more than Tl segment, suggesting that it is dependent on the electrodepostion potential and precipitation rate.
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Table 2 Elemental concentration (ppm) was obtained from PIXE analysis. Elements
Cu
Zn
Au
Tl
Bi
Concentration
813
460
174,782
34,247
214,060
Fig. 7 shows the typical TEM image of Bi/Tl multilayer nanowires. TEM images revealed that the average diameter of the nanowires is approximately 93 nm. The control of nanopore filling is performed by RBS analysis. The length of Bi/Tl multilayer nanowires was 4.92 lm that determined by RBS technique (Fig. 8). This technique is not be able to determine the thickness of each layer of Bi/Tl multilayer nanowires because of the atomic number of bismuth and thallium elements are very close together. Elemental concentration of sample was measured by PIXE analysis. PIXE analysis showed that Bi, Tl, Au, Cu, and Zn are present in the sample. Fig. 9 shows PIXE spectra of sample. Al peak in PIXE spectrum is due to proton interaction with chamber. The weight percent of elements can be calculated from elemental concentration (ppm) which obtained from PIXE analysis. The PIXE results and weight percent are summarized in Table 2. Element of Au is due to gold-sputtered layer at the backside of polycarbonate membrane. Elements of Zn and Cu are present due to impurities of gold-sputtered layer. 4. Conclusion Bi/Tl multilayer nanowire and nanotubes were prepared using electrodeposition filling the pores of the PC template with 100 nm diameter. Structural characterization of these nanowires was studied using X-ray diffraction. XRD patterns of nanowires indicated that lattice structure of Bi and Tl segments are rhombohedral and hexagonal respectively. Morphology of nanowires was investigated by SEM images and it was found that changing pH value can be caused transformation nanowire structures to nanotube structures and vice versa. Decreasing pH value of the electrolyte solution caused formation of nanotube structure. Bi3+ ions has higher precipitation rate. So contribution of Bi segment is more than Tl segment and EDX spectra showed it. 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