- Nano Express
- Open Access
Controlled Structure of Electrochemically Deposited Pd Nanowires in Ion-Track Templates
© Duan et al. 2015
Received: 10 September 2015
Accepted: 2 December 2015
Published: 12 December 2015
Understanding and controlling structural properties of the materials are crucial in materials research. In this paper, we report that crystallinity and crystallographic orientation of Pd nanowires can be tailored by varying the fabrication conditions during electrochemical deposition in polycarbonate ion-track templates. By changing the deposition temperature during the fabrication process, the nanowires with both single- and poly-crystallinities were obtained. The wires with preferred crystallographic orientations along , , and  directions were achieved via adjusting the applied voltage and temperature during electrochemical deposition.
Nanowire-based devices have been highly pursued for decades stimulated by their rapid expanding impact in nanotechnology. Metallic nanowires are not only interesting for fundamental research due to their unique structural and physicochemical properties compared to their bulk counterparts but also offer a fascinating potential for the future technological applications . It is widely accepted that the performance of a given material is not only affected by its intrinsic properties but also influenced by the structural characteristics such as crystallinity and crystallographic orientation [2, 3]. For instance, the resistivity of a polycrystalline metal film can be enhanced dramatically due to electron scattering at the grain boundaries . The hardness and yield stress of nanocrystalline materials typically increase with decreasing grain size, a phenomenon known as the Hall–Petch effect [5, 6]. However, in the case of very small grain sizes, the nanocrystalline copper becomes soft because of the plastic deformation originating from a large number of small “sliding” events of atomic planes at the grain boundaries, understood as anti-Hall–Petch effect [3, 7]. Similarly, the crystallographic orientation has great influence on the nanowires’ physicochemical properties. For example, the structural transition and melting of gold nanowires , the compressive pseudoelastic behavior in Cu nanowires , the thermal expansion of Cu nanowires , etc. Therefore, understanding and controlling structural properties of the nanowires have become a focus of the efforts to manipulate their electrical, mechanical, magnetic, and optical properties .
Among various noble metals, nanostructured Pd plays a significant role in many functional applications, such as hydrogen gas detection , catalyst in fuel cell , biosensors , and surface-enhanced Raman scattering . In previous studies, Pd nanowires have been successfully fabricated by template-based strategies, like electrochemical deposition in anodic aluminum oxide (AAO) templates [15–22], chemical reaction in porous polycarbonate template , and soft template . Some chemical methods, such as chemical reaction , lithographically patterned nanowire electrodeposition (LPNE) , galvanic displacement deposition , chemical vapor infiltration , and electroless deposition  have been employed to prepare Pd nanowires. Additionally, electron-beam lithography  and pattern-selective epitaxial growth  are also effective methods to fabricate Pd nanowires. In these studies, single crystalline [16, 23, 24, 30] and polycrystalline [21, 25] nanowires have been obtained by different experimental techniques and under different conditions. In these studies, single crystalline [16, 23, 24, 30] and polycrystalline [21, 25] nanowires have been obtained by different experimental techniques and under different conditions. Nanowires with preferred crystallographic orientations along the  and  directions have been reported by different research groups, however; these nanowires along  direction are hardly reported so far. To date, the challenge of controlling and tailoring the crystallinity and crystallographic orientation of Pd nanowires is still open.
In this work, we have prepared Pd nanowires by electrochemical deposition in homemade polycarbonate ion-track templates. Our results demonstrate that the Pd nanowires’ crystallinity and crystallographic orientation can be controlled by appropriately adjusting the fabrication conditions during the electrochemical deposition of the nanowires.
In order to fabricate home-made ion-track templates, polycarbonate (PC) foils (Makrofol N, Bayer Leverkusen) with thickness of 30 μm were irradiated at the UNILAC linear accelerator of GSI (Darmstadt, Germany) with Pb ions (kinetic energy 11.4 MeV · u−1, fluence 5 × 108 ions · cm−2) at normal incidence and at the HIRFL-SSC accelerator of IMP (Lanzhou, China) with Bi ions (kinetic energy 9.5 MeV · u−1, fluence 5 × 108 ions · cm−2) at normal incidence. The damaged regions produced by the ions along their trajectories, called latent tracks, were selectively etched in 5 M NaOH at 50 °C leading to the formation of cylindrical nanopores in the foils. In this work, all PC foils were chemically etched for 3 min, corresponding to nanopores’ diameter of 75 nm. Prior to the etching, both sides of the foils were exposed to UV light for 2 h in order to enhance the selectivity of the etchant, and thus, to increase the track etching rate. This track sensitization is a necessary step to produce highly cylindrical nanopores. During the etching process, an ultrasonic field was employed to achieve a homogeneous etching.
The strategy to prepare Pd nanowires is based on ion-track template coupled with electrochemical deposition, which is described in detail elsewhere [31, 32]. First, a thin gold film was sputtered onto one side of the template that was further reinforced electrochemically by a Cu layer with a thickness of few microns. This back-layer (Au + Cu) served as cathode during the electrochemical deposition of the Pd nanowires. The electrolyte consisted of aqueous solution of 20 gl−1 K2PdCl4 and 20 gl−1 H2SO4. For fabrication of nanowires, direct current (DC) electrochemical deposition was employed with platinum rod used as the anode. The deposition process was monitored by recording current versus time curves. To make sure that the nanopores are completely filled, an overgrowth of nanowires was intentionally adopted, which resulted in the formation caps on the surface of the template.
After dissolving the polycarbonate templates in dichloromethane (CH2Cl2), the morphology, composition, and crystallinity of nanowires were investigated by means of scanning electron microscopy (SEM, JEOL JSM-6701F), transmission electron microscopy (TEM, JEOL JEM-3010), energy dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED). For TEM sample preparation, an ultrasonic field was used to detach the nanowires from the back-layer. The crystallographic orientations of the wire arrays were examined by X-ray diffraction (XRD, RIGAKU RINT 2400, Cu Kα, λ = 0.154056 nm). For XRD analysis, the wires were left embedded in the templates; however, both the caps and backing layer were removed from the nanowires.
Results and Discussion
for 3D growth, where b(B), s (Vm), ϵ (σ), z, and e are a constant (b = π for circular), the area (volume) occupied by one metallic atom on the surface of the nucleus, the edge (surface) energy, the effective electron number, and elementary charge (approximately 1.602176565(35) × 10−19 coulomb), respectively; η is the overpotential. From the formulae, it is obvious that lower η is favorable for the formation of single crystalline because N c is larger. Otherwise, polycrystalline nanowires have more possibility to grow. Additionally, according to the formulae, only the overpotential η can be experimentally changed during the electrochemical deposition. Actually, the overpotential η is affected by the parameters like effective applied voltage and equilibrium potential. The effective applied voltage is the real applied voltage subtracting the voltage exhausted by electrolyte inside template channel because the electrolyte acted as a resistance. And the voltage exhausted by electrolyte inside template channel is greatly influenced by the temperature. Namely, higher temperature is beneficial for ions diffusion and, in sequence, making the resistance of electrolyte lower. In this case, the voltage exhausted by the electrolyte is less. Therefore, the overpotential η is higher and consequently the formation of polycrystalline nanowires is favorable, and the situation at lower temperature is vice versa.
The electrochemical deposition of metallic nanowires is a complex process, which is influenced by the factors such as charge transfer, ions diffusion, and H ions or micelles absorption. However, from the energy point of view, the crystal plane with low surface energy has higher possibilities to grow and fulfill the principle of minimization of free energy. It has been reported that H ions absorption on the crystal planes could decrease the surface energies of the crystal planes and such absorption on different crystal planes can be affected by overpotential [3, 38]. In this work, our electrolyte consisted of H2SO4 which provided H ions during the wires growth. Additionally, a high overpotential may give rise to the surface adsorption of H ions or micelles in the electrolyte and thus considerably enhances the electrochemical reaction driving force, which increases the deposition rate of metallic ions during the deposition , as shown in Fig. 4b. At different overpotentials, the surface energies of the (111), (200), and (220) planes changed via H ions absorption. The surface energies of the (111), (200), and (220) planes reached their minimum values when appropriate voltages were applied. Therefore, the crystallographic orientations along , , and  directions are obtained by changing the applied voltage during deposition process. The application of high temperature promotes the surface diffusion of the atoms and reduces the minimum applied voltage required to grow Pd wires and consequently increases the growth rate of the nanowires (Fig. 4d). Therefore, temperature is another factor that influences the free energy of Pd nanowires during the electrochemical deposition process via changing H ions adsorption, resultantly influences the crystallographic orientation of Pd nanowires.
Pd nanowires have been successfully fabricated in home-made polycarbonate ion-track templates by electrochemical deposition. The Pd nanowires with single crystalline and polycrystalline structures have been obtained via changing electrochemical deposition temperature. The critical grain size model is adopted to explain the effect of temperature on Pd nanowires’ crystallinity. The crystallographic orientations of the Pd nanowires along , , and  directions have been achieved and can be controlled by the applied voltage and temperature during the electrochemical deposition. A possible mechanism based on H ions absorption has been proposed to understand the control over the nanowires crystallographic orientations.
We thank the members of the Materials Research Department at the GSI Helmholtzzentrum (Darmstadt, Germany) for the preparation and irradiation of the polycarbonate foils. The financial supports from the National Natural Science Foundation of China (Grant Nos.: 11175221, 11375241, 11179003, 11205215, and 11275237) are acknowledged.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Lieber CM, Wang ZL (2007) Functional Nanowires. MRS Bull 32:99View ArticleGoogle Scholar
- Liu J, Duan JL, Toimil-Molares ME, Karim S, Cornelius TW, Dobrev D, Yao HJ, Sun YM, Hou MD (2006) Electrochemical fabrication of single-crystalline and polycrystalline Au nanowires: the influence of deposition parameters. Nanotechnology 17:1922View ArticleGoogle Scholar
- Duan JL, Liu J, Mo D, Yao HJ, Maaz K, Chen YH, Sun YM, Hou MD, Qu XH, Zhang L, Chen YF (2010) Controlled crystallinity and crystallographic orientation of Cu nanowires fabricated in ion-track templates. Nanotechnology 21:365605View ArticleGoogle Scholar
- Mayadas AF, Shatzkes M (1970) Electrical-resistivity model for polycrystalline films: the case of arbitrary reflection at external surfaces. Phys Rev B 1:1382View ArticleGoogle Scholar
- Hall EO (1951) The deformation and ageing of mild steel: II characteristics of the lüders deformation. Proc Phys Soc Lond B 64:747View ArticleGoogle Scholar
- Petch NJ (1953) The cleavage strength of polycrystals. J Iron Steel Inst 174:25Google Scholar
- Schiotz J, Di Tolla FD, Jacobsen KW (1998) Softening of nanocrystalline metals at very small grain sizes. Nature 391:561View ArticleGoogle Scholar
- Wen Y-H, Zhang Y, Zheng J-C, Zhu Z-Z, Sun S-G (2009) Orientation-dependent structural transition and melting of Au nanowires. J Phys Chem C 113:20611View ArticleGoogle Scholar
- Lee S, Lee B, Cho M (2010) Compressive pseudoelastic behavior in copper nanowires. Phys Rev B 81:224103View ArticleGoogle Scholar
- Zhou WF, Fei GT, Li XF, Xu SH, Chen L, Wu B, Zhang LD (2009) In situ X-ray diffraction study on the orientation-dependent thermal expansion of Cu nanowires. J Phys Chem C 113:9568View ArticleGoogle Scholar
- Penner RM (2010) Electrodeposition of nanowires for the detection of hydrogen gas. MRS Bull 35:771View ArticleGoogle Scholar
- Bai Z, Yang L, Li L, Lv J, Wang K, Zhang J (2009) A facile preparation of hollow palladium nanosphere catalysts for direct formic acid fuel cell. J Phys Chem C 113:10568View ArticleGoogle Scholar
- Zhang L, Guo S, Dong S, Wang E (2012) Pd nanowires as new biosensing materials for magnified fluorescent detection of nucleic acid. Anal Chem 84:3568View ArticleGoogle Scholar
- Feng C, Zhang R, Yin P, Li L, Guo L, Shen Z (2008) Direct solution synthesis of Pd nanowire networks and their application in surface-enhanced Raman scattering. Nanotechnology 19:305601View ArticleGoogle Scholar
- Taşaltın N, Öztürk S, Kılınç N, Yüzer H, Öztürk Z (2010) Fabrication of vertically aligned Pd nanowire array in AAO template by electrodeposition using neutral electrolyte. Nanoscale Res Lett 5:1137View ArticleGoogle Scholar
- Cheng F, Wang H, Sun Z, Ning M, Cai Z, Zhang M (2008) Electrodeposited fabrication of highly ordered Pd nanowire arrays for alcohol electrooxidation. Electrochem Commun 10:798View ArticleGoogle Scholar
- Xu C, Wang H, Shen PK, Jiang SP (2007) Highly ordered Pd nanowire arrays as effective electrocatalysts for ethanol oxidation in direct alcohol fuel cells. Adv Mater 19:4256View ArticleGoogle Scholar
- Kartopu G, Habouti S, Es-Souni M (2008) Synthesis of palladium nanowire arrays with controlled diameter and length. Mater Chem Phys 107:226View ArticleGoogle Scholar
- Wang H, Xu C, Cheng F, Jiang S (2007) Pd nanowire arrays as electrocatalysts for ethanol electrooxidation. Electrochem Commun 9:1212View ArticleGoogle Scholar
- Cherevko S, Fu J, Kulyk N, Cho SM, Haam S, Chung C-H (2009) Electrodeposition mechanism of palladium nanotube and nanowire arrays. J Nanosci Nanotechnol 9:3154View ArticleGoogle Scholar
- Jeon KJ, Jeun M, Lee E, Lee JM, Lee K, Allmen PV, Lee W (2008) Finite size effect on hydrogen gas sensing performance in single Pd nanowires. Nanotechnology 19:495501View ArticleGoogle Scholar
- Kim K, Kim M, Cho SM (2006) Pulsed electrodeposition of palladium nanowire arrays using AAO template. Mater Chem Phys 96:278View ArticleGoogle Scholar
- Koenigsmann C, Santulli AC, Sutter E, Wong SS (2011) Ambient surfactantless synthesis, growth mechanism, and size-dependent electrocatalytic behavior of high-quality, single crystalline palladium nanowires. ACS Nano 9:7471View ArticleGoogle Scholar
- Siril PF, Lehoux A, Ramos L, Beaunier P, Remita H (2012) Facile synthesis of palladium nanowires by a soft templating method. New J Chem 36:2135View ArticleGoogle Scholar
- Menke EJ, Thompson MA, Xiang C, Yang LC, Penner RM (2006) Lithographically patterned nanowire electrodeposition. Nat Mater 5:914View ArticleGoogle Scholar
- Inguanta R, Piazza S, Sunseri C (2009) Synthesis of self-standing Pd nanowires via galvanic displacement deposition. Electrochem Commun 11:1385View ArticleGoogle Scholar
- Kang H, Jun Y, Park J, Lee K, Cheon J (2000) Synthesis of porous palladium superlattice nanoballs and nanowires. Chem Mater 12:3530View ArticleGoogle Scholar
- Shi Z, Wu S, Szpunar JA (2006) Self-assembled palladium nanowires by electroless deposition. Nanotechnology 17:2161View ArticleGoogle Scholar
- Jeon KJ, Lee JM, Lee E, Lee W (2009) Individual Pd nanowire hydrogen sensors fabricated by electron-beam lithography. Nanotechnology 20:135502View ArticleGoogle Scholar
- Yoo Y, Yoon I, Lee H, Ahn J, Ahn JP, Kim B (2010) Pattern-selective epitaxial growth of twin-free Pd nanowires from supported nanocrystal seeds. ACS Nano 4:2919View ArticleGoogle Scholar
- Yao H, Duan J, Mo D, Gunel HY, Chen Y, Liu J, Schapers T (2011) Optical and electrical properties of gold nanowires synthesized by electrochemical deposition. J Appl Phys 110:094301View ArticleGoogle Scholar
- Mo D, Liu J, Duan J, Yao H, Chen Y, Sun Y, Zhai P (2012) Plasmon resonance of copper nanowire arrays embedded in etched ion-track mica templates. Mater Lett 68:201View ArticleGoogle Scholar
- Duan J, Liu J, Yao H, Mo D, Hou M, Sun Y, Chen Y, Zhang L (2008) Controlled synthesis and diameterdependent optical properties of Cu nanowire arrays. Mater Sci Eng B 147:57View ArticleGoogle Scholar
- Tian M, Wang J, Kurtz J, Mallouk TE, Chan MHW (2003) Electrochemical growth of single-crystal metal nanowires via a two-dimensional nucleation and growth mechanism. Nano Lett 3:919View ArticleGoogle Scholar
- Pan H, Liu B, Yi J, Poh C, Lim S, Ding J, Feng Y, Huan CHA, Lin J (2005) Growth of single-crystalline Ni and Co nanowires via electrochemical deposition and their magnetic properties. J Phys Chem B 109:3094View ArticleGoogle Scholar
- Paunovic M, Schlesinger M (1998) Fundamentals of Electrochemical Deposition. Wiley, New York, pp 108–117Google Scholar
- Lyu S, Lei DY, Liu W, Yao H, Mo D, Chen H, Hu P, Sun Y, Liu J, Duan JL (2015) Cyanide-free preparation of gold nanowires: controlled crystallinity, crystallographic orientation and enhanced field emission. RSC Adv 5:32103View ArticleGoogle Scholar
- Sun H, Yu Y, Li X, Li W, Li F, Liu B, Zhang X (2007) Controllable growth of electrodeposited single-crystal nanowire arrays: The examples of metal Ni and semiconductor ZnS. J Cryst Growth 307:472View ArticleGoogle Scholar